A REVIEW OF THE WORLDWIDESTATUS OF COALBED METHANEEXTRACTION AND UTILISATION

Report No. COAL R210DTI/Pub URN 01/1040

by

D P Creedy and K GarnerS Holloway*T X Ren**

Wardell ArmstrongBritish Geological Survey*University of Nottingham**

The work described in this report was carried out under contract as part of theDepartment of Trade and Industry’s Cleaner Coal Technology Transfer Programme.The Programme is managed by ETSU. The views and judgements expressed in thisreport are those of the authors and do not necessarily reflect those of ETSU or theDepartment of Trade and Industry.

Crown Copyright 2001First published July 2001

A REVIEW OF THE WORLDWIDE STATUS OF COALBED METHANEEXTRACTION AND UTILISATION

by

D P Creedy, K Garner,S Holloway and T X Ren

SUMMARY

Coalbed methane (CBM) is a natural gas formed by geological, or biological, processesin coal seams. CBM consists predominantly of methane. Lower concentrations ofhigher alkanes and non-combustible gases are also often present.

Most of the world’s CBM resource of around 1x1014m3 lies in seams that have not beenmined or are unlikely to be mined except in the distant future. Although considerableeffort has been expended in exploring and testing virgin CBM (VCBM) wells, nocommercial schemes have yet been developed outside of the USA and Australia.Remoteness or lack of markets and low coal seam permeability are the majorconstraints. The latter appears to be a particular limitation in European prospects,including those of the UK and widespread development is unlikely to occur in the shortand medium term.

Methane rich gases captured in operational mines have been exploited for many years.Uses of this coal mine methane (CMM) have included space heating, industrialprocesses and power generation. At present, 80% of UK coal mines rely on methanedrainage to capture gas before it enters the mine ventilation system, thus enabling gassycoal seams to be worked safely. About 40% of the gas drained in UK mines is usedand could increase to 70% if proposed new schemes are introduced.

An important CBM development is the exploitation of methane from abandoned mines.Six schemes producing an equivalent of 42.5MWe are operational in the UK (June2001) and more are planned. Abandoned mine methane (AMM) reservoirs consist ofgroups of coal seams that have been de-stressed, and therefore of enhancedpermeability, but only partially degassed by longwall working. There is strongcommercial interest in this field in the UK, Germany and USA. The UK has alsoinitiated transfer of this technology to China. Abandoned mine gas utilisation schemesbenefit the community by providing clean energy from a waste product and reducingsurface emission hazards associated with old workings. They also contribute to areduction in greenhouse gas emissions.

CBM exploitation in the UK currently amounts to about 55MWe equivalent in total butthis could be more than trebled in the next five years.

Exploitation of CBM from working and abandoned coal mines directly benefits theenvironment by reducing greenhouse gas emissions to the atmosphere. The benefit ofCBM from all sources is that a high quality, clean fuel is produced that can displacecoal burning thus reducing emissions of oxides of sulphur and nitrogen to theatmosphere. As coal mining releases methane, any reduction in coal production is

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accompanied by a reduction in greenhouse gas emissions. There are opportunities anda need to increase the utilisation of drained gas at working mines. However, even if amine has a scheme for using drained gas, a substantial proportion will continue to beemitted with the ventilation air. Technologies for removing this gas are available butthey have not been demonstrated at full scale and the financial viability could bemarginal.

Recent discoveries indicate that commercial quantities of gas may be recoverable froma greater range of geological environments than previously thought. Biologicalprocesses may be important gas generators in low rank, high permeability coal seamaquifers.

Recent technological developments include the use of guided in-seam drilling from thesurface for production of VCBM, and innovative micro-turbines and fuel cells forgenerating on site electricity using coal mine or abandoned mine methane.

There is a substantial repository of knowledge on CBM in the UK, particularly in respectof producing gas from abandoned mines that could be used to promote commercialactivities overseas. Climate change concerns are driving interest in mine gas utilisationschemes creating possible opportunities for UK investors and equipment suppliers inChina and the former Soviet Union. There is an estimated potential for plant andequipment sales of £260 million for CMM projects in the latter countries, and possibly inexcess of £100 million for AMM projects, assuming a 20% market share.

CONTENTS Page No.

GLOSSARY OF TERMS 1FOREWORD 21. INTRODUCTION 3

1.1 Sources of CBM 31.2 CBM and its Nomenclature 41.3 Occurrence of Methane in Coal Seams 41.4 Gas Storage in Coals 51.5 Coal Seam Permeability 51.6 Environmental Benefits of CBM 6

2. CBM RESOURCES AND RESERVES IN THE UK 72.1 Introduction 72.2 VCBM Resources and Reserves 72.3 CMM Resources and Reserves in Working Mines 82.4 AMM Resources and Reserves 82.5 UK Resources and ‘Reserves’ 11

3. VCBM PRODUCTION 113.1 Introduction 113.2 Site Selection 123.3 Reservoir Characterisation 133.4 Modelling Techniques and Simulation Tools 133.5 VCBM Well Design, Testing and Completion 133.6 Gas Production 143.7 Water Treatment 143.8 Improving Well Completion and Performance 143.9 New Geological Potential 153.10 VCBM Production from Surface to In-Seam Guided Boreholes 153.11 Enhanced CBM Recovery (ECBM) 193.12 Increasing Seam Permeability 203.13 General Status of VCBM Development 21

4. CMM FROM WORKING COAL MINES 214.1 Introduction 214.2 Gas Release in Coal Mines 224.3 Capture Efficiency 234.4 CMM Availability 234.5 CMM Drainage Techniques 244.6 Recent Developments 274.7 The General CMM Situation 27

5. EXTRACTION OF AMM 285.1 Introduction 285.2 AMM Reservoirs 305.3 Effect of Water Ingress 315.4 Environmental Benefits 325.5 Production Equipment 325.6 Safety 335.7 Estimating AMM Resources and Reserves 335.8 Enhancement of Gas Recovery 34

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5.9 Development of New Projects 34

6. CBM UTILISATION 356.1 Introduction 356.2 Markets 356.3 CBM Use 376.4 USA Government R&D 436.5 Relevance of New Utilisation Technologies to the UK 43

7. CBM ACTIVITIES IN THE UK 447.1 Introduction 447.2 VCBM Exploration and Potential 447.3 Exploitation of CMM 457.4 AMM Extraction 467.5 CBM Utilisation 467.6 Future CBM Development 487.7 Regulation of CBM 487.8 Barriers to Development 507.9 Status Summary 51

8. WORLDWIDE REVIEW OF CBM ACTIVITIES 518.1 Introduction 518.2 Australia 518.3 Canada 558.4 China 578.5 Europe (Geographical) 618.6 Former Soviet Union 618.7 India 648.8 Southern Africa 668.9 United States 668.10 Comparisons of CBM Production and Use Worldwide 71

9. FUTURE R&D NEEDS FOR THE UK 71

10. MARKET OPPORTUNITIES 7210.1 Introduction 7210.2 China and the Former Soviet Union 7310.3 India 7310.4 General 74

11. CONCLUSIONS 74

12. ACKNOWLEDGEMENTS 75

13. REFERENCES 75

TABLES 1-21

FIGURES 1-3

APPENDIX 1: NOTES ON THE 2ND ANNUAL CBM AND CMM CONFERENCE,APPENDIX 1:DENVER, COLORADO, USA, 27 – 28 MARCH2001.

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APPENDIX 2: WORKSHOP ON TECHNOLOGY OF THE EXTRACTION ANDAPPENDIX 1:USE OF CBM, LONDON, 27 JUNE 2001, BULLETPOINT SLIDES USED IN THE PRESENTATION.

APPENDIX 3: GREENHOUSE GAS EMISSIONS TRADING.

APPENDIX 4: GENERAL APPRAISAL OF AMM PROSPECTS IN THE UKCOALFIELDS.

APPENDIX 5: COMPUTERISED CBM MODELLING TECHNIQUES ANDSIMULATION TOOLS.

APPENDIX 6: ENGINEERING FOR AMM PRODUCTION: UK CASE STUDIES.

GLOSSARY OF TERMS

Abandoned mine methane (AMM) – gas produced from abandoned coal mineworkings through abandoned mine entries and from boreholes drilled into undergroundroadways or former workings. The usable gas is that remaining in coal seams and thestrata on cessation of underground coal mining operations. Gas from this source issometimes included in the definition of CMM.

AMM goaf borehole – a surface borehole drilled into strata disturbed by past miningto exploit any enhanced permeability. May be completed using standard VCBMtechniques.

Abandoned mine methane reservoir – coal seams disturbed by past mining which arecapable of releasing gas into a particular abandoned mine or interconnected group ofmines. The extent of workings marks the boundary of the reservoir, which may extendbeyond the Petroleum Exploration and Development Licence area.

Blackdamp – a mixture of carbon dioxide and nitrogen usually formed by theoxidation of air.

Coalbed methane (CBM) - a generic term, originating in the USA, for the methane-rich gas originating in coal seams. It is also often applied to gas from virgin coalseams. Approximately equivalent terms are firedamp [UK] and coal seam gas[Australia].

Desorbable gas - the quantity of gas (m3 per tonne (m3 t-1)) that can be produced fromthe primary coal seam sources in a gaseous environment at a particular pressure.

Goaf, waste [UK] or gob [USA] – broken, permeable ground where coal has beenextracted and the roof allowed to collapse thus fracturing and de-stressing strata aboveand, to a lesser extent, below.

Coal mine methane (CMM) – gas captured in a working mine by methane drainagetechniques. Sometimes known as mine gas [UK], coal gas [North America].

Natural gas – gas derived from geological strata other than coal seams.

Potentially recoverable gas – the estimated volume of gas that could probably berecovered using available technology.

Potentially recoverable AMM (AMM reserves) - the estimated volume of gasdesorbable to an absolute gas pressure of around 50kPa together with gas in void space.Contributions from any workings likely to be totally waterlogged are excluded.

Virgin CBM (VCBM) – methane rich gas recovered from coal seams that have notbeen disturbed by mining.

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FOREWORD

The principal aim of this study is to critically review the current UK and world-widestatus of CBM extraction and utilisation technologies. Thus, the R&D and technologytransfer activities needed to enhance the commercial potential of CBM technologiesoriginating or applied in the UK can be identified.

The contract was initiated on 15 November 2000 and the work completed in July 2001.During the course of the study the Second Annual Coalbed and Coal Mine Methaneconference in Denver (27&28 March 2001) was attended (Appendix 1) and also aconference on International Investment Opportunities in Coalbed and Coal MineMethane in London (28&29 March 2001).

The study was undertaken by Wardell Armstrong with the assistance of the BritishGeological Survey (BGS) and contributions from the University of Nottingham. Theproject was supervised by Mrs Heather Tilley of ETSU on behalf of the UKDepartment of Trade and Industry, Cleaner Coal Technology Transfer Programme.

The following tasks were undertaken as part of the study:

• Worldwide literature review and Internet search

• Consultations with the CBM operators, developers and users together with selectedcompanies, organisations and research institutes with specific CBM production andutilisation interests throughout the world.

• A review of CBM resources and reserves in respect of working mines, abandonedmines and virgin seams.

• Assessment of the environmental benefits and impacts of the various CBMproduction methods together with regulatory drivers and hurdles.

• Analysis of the CBM market potential for UK companies and institutions both inthe UK and overseas:

• Identify any barriers or inhibitors currently deterring CBM development in the UK.

• Identify future R&D needs to further develop CBM technologies and hence increasemarket potential.

Details of meetings, consultations and a survey have been filed in a separateconfidential document and the general findings incorporated in this report.

A Workshop was held on 27 June 2001 at the Department of Trade and Industry (DTI)Conference Centre, London, to discuss the findings of the project with industryrepresentatives. The bullet point slides used in the presentation are included asAppendix 2.

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1. INTRODUCTION

CBM is a potentially important energy resource in many of the major coal miningcountries of the world. Significant volumes of CBM are exploited worldwide. VCBMpredominates in the USA but elsewhere most of the gas originates from operationaldeep coal mines with lesser quantities recovered from abandoned mine workings.Many coal-producing countries are now looking at the potential for wider applicationof CBM technologies to maximise the exploitation of gas from coal seams.

CBM is a potentially significant energy resource in the major coal mining countries ofthe world especially China, Russia, the United States, Canada and Australia. Most ofthe CBM exploited in the world, other than in the USA, is produced from operationalunderground coal mines, and a lesser amount from abandoned coal mines.

The principal driver for increasing exploitation of gas from working and abandonedmines is the global desire to reduce atmospheric emissions of greenhouse gases. CBM,irrespective of the source, is a cleaner fuel than coal with lower emissions of sulphur,nitrogen and particulates when burned.

1.1 Sources of CBM

CBM is a clean fuel with similar properties to natural gas when not diluted by air orother non-combustible mine gases.

CBM can be recovered from coal seams by:

• Draining gas (CMM) from working coal mines

• Extracting (AMM) from abandoned coal mines

• Producing gas (VCBM) from unmined coal using surface boreholes.

Gas may also be recovered from surface boreholes drilled into coal seams in disturbedstrata around abandoned workings (AMM goaf boreholes). If necessary, theseboreholes can be completed using conventional VCBM hydrofraccing techniques toensure gas production rates are not limited by wellbore damage to permeability causedduring drilling.

The characteristics of the above CBM sources differ in terms of reservoir definition,production technology and gas composition. Gas schemes at working and abandonedcoal mines can generally be implemented at lower cost, and are less dependent onnatural coal permeability conditions, than virgin CBM projects.

The advantages and disadvantages to producers and users of the various CBM sourcesare compared in Table 1.

1.2 CBM and its Nomenclature

The gas found naturally occurring in coal seams is known generically as firedamp in theUK or as CBM. The principal constituent of firedamp is methane (typically 80-95%) withlower proportions of ethane, propane, nitrogen and carbon dioxide. As methane is thepredominant constituent of firedamp, the two terms are often used interchangeably.

The mixtures of firedamp, water vapour, air and associated oxidation products which arefound in coal mines are usually collectively termed ‘mine gas’. However, the USA term‘coal mine methane’ (CMM) is being increasingly used. In this report CMM refers to gasdrained form working coal mines.

Confusion is sometimes caused by also applying CMM to abandoned mines gas. Thequantity and composition of gas extracted from abandoned mines is influenced bydifferent factors than those in working mines. The reservoir characteristics are alsodifferent. Gas from abandoned mines therefore merits distinguishing with a different titleand AMM (abandoned mine methane) is used in this report. The high purity methaneobtained from unmined seams is termed ‘virgin CBM’ (VCBM) to differentiate it fromother CBM sources.

Some representatives of the CBM industry believe there are benefits in classifying bothmine gas and gas from abandoned mines as CMM because CMM is a widely acceptedterm and introduction of a new term could confuse emissions traders and regulators bothin the UK and the USA. However, it is the authors view that a clearer classification wouldhelp to reduce misunderstandings generally, especially in non-English speaking countrieswhere the subtleties of meaning are not always recognised.

It is also important to distinguish between CBM resources and CBM reserves. Theformer comprises gas-in-place whereas reserves represent the proportion of theresource that can be demonstrated as economically recoverable. Only proven reserveshave a commercial value. Many of the worlds’ proven reserves of CBM, outside theUSA, are associated with coal mining operations and would be described as CMM incurrent parlance. These reserves are relatively small compared with the estimated totalglobal VCBM resource of 84-281x 1012m3 (World Coal Institute, 1998).

1.3 Occurrence of Methane in Coal Seams

The compositions of coals change with increase in burial depth and time spent at theelevated temperatures encountered during burial. The heat-driven chemical reactionsaccompanying burial, generate various hydrocarbons and other gases which compriseCBM. The greater the temperature and duration of burial, the higher the coal maturity(rank) and hence the greater the amount of gas produced. Much more gas was producedduring the ‘coalification’ process than is now found in the seams. The lost gas has beenemitted at ancient land surfaces, dissipated into the pores of surrounding rocks, removedin solution, and some will have migrated into geological reservoir structures. Original gascontent patterns tend to be preserved following similar trends to coal rank but themagnitudes depend on the geological erosion history.

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1.4 Gas Storage in Coals

CBM can be detected in many sedimentary rocks but generally only in lowconcentrations. It occurs in much higher concentrations in coal rather than in any otherrock type because of the ‘adsorption’ process which enables methane molecules to bedensely packed into the coal substance, almost as if a liquid.

The quantity of gas that can be adsorbed increases with pressure, up to a limiting value.Conversely, it decreases as the temperature increases. At the elevated temperaturesprevailing during gas generation, the coal is able to adsorb less gas than in itssubsequent cooler conditions. In the absence of gas migration from other sources, theseams will tend to become progressively under-saturated as they are brought closer tothe surface as erosion continues.

The quantity of gas held in the coal substance, at a fixed temperature, varies withpressure. As pressure is reduced, gas desorbs until equilibrium is established betweenthe free gas and the adsorbed gas. The relationship between gas pressure and gascontent, known as an ‘adsorption’ isotherm, can be measured in the laboratory. Whenaccount is taken of free gas in porosity and micro-fracture spaces within the coal, inaddition to adsorbed gas, the term sorption is used. Adsorption or sorption test resultsare usually measured under conditions representative of the in situ moisture andtemperature of the coal seam. Such measurements of gas content are usually correctedto a clean coal or ash-free basis. The derived curve is termed a ‘sorption’ isotherm.The sorption isotherm is used to predict the quantity of gas available for production asthe strata fluid pressure is reduced. In addition to temperature, the sorption propertiesof coals depend on moisture content, rank and petrographic composition.

Gas that cannot be accommodated in the coal substance during burial is compressedinto pores or fracture spaces within coal seams and neighbouring strata. Alternatively,it may become trapped in adjoining strata to form natural gas reservoirs or seep to thesurface to be emitted to the atmosphere. Significant volumes of methane and othergases can also dissolve in strata water. For example, water pumped from a CBM wellat about 700m depth could, depending on salinity and temperature, contain dissolvedmethane up to 1.5 times the volume of water. The release of dissolved methane fromwells with high water production is not necessarily an indicator of good future CBMproducibility.

1.5 Coal Seam Permeability

Permeability is not a property of the coal but a condition that depends on the stressregime. Under normal virgin conditions the permeability of solid coal to gases is verylow, and significant gas flow rates will only occur in seams which have an open cleat orfracture network.

Permeable coal seam fracture systems are often water-filled. Removal of the waterfrom the fracture (or cleat) system reduces the fluid pressure, allowing methane andother gases to desorb from the coal once the fluid pressure is less than the sorptionpressure. Continuous de-watering of a CBM well can yield a rising gas productionrate, as the relative gas permeability of the fracture network is enhanced. Continuousdesorbtion of gas from the coal recharges the fractures, allowing gas production over

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long periods of time. Coal seams that behave as aquifers, even if gas contents are notparticularly high, have a high gas production potential due to their high permeability.

The cleat system is not always a network of open fractures because it may be partly orcompletely mineralised or closed by natural stresses. Mineralised cleat systems containminerals such as ankerite deposited by fluids circulating through the connected openspace within the coal seam during or after burial. No significant gas (or water) flowscan usually be produced from seams with heavily mineralised cleat.

The principal factors controlling the ability of coal seams to transmit methane are the cleator fracture density, cleat transmissivity, the degree of water saturation and the fluidpressures in the cleat. The preservation of fracture permeability depends on the structuralhistory of the coal basin.

1.6 Environmental Benefits of CBM

CBM will remain in a coal seam until extracted at a surface well or disturbed byunderground mining. Methane liberated by active mining or released from abandonedmineworkings, if not used, enters the atmosphere contributing to anthropogenicgreenhouse gas emissions. Estimated emissions from the various CBM sources in theUK are shown in Table 2. There is a large uncertainty attached to the AMM estimatedue to differences in methodology and assumptions that have yet to be resolved.

CMM and AMM utilisation schemes significantly benefit the environment by:

• reducing greenhouse gas emissions, as the carbon dioxide produced by combustionis some 21 times less harmful to the atmosphere than methane

• producing useful energy from a waste product of mining

• displacing coal use in environmentally sensitive areas.

CMM is a major greenhouse gas and the United States Environmental ProtectionAgency (USEPA) has set up a Coalbed Methane Outreach Programme to encouragecoal mines to capture and exploit mine gas. The importance of abandoned mines assources of greenhouse emissions have not yet been determined. There are indicationsthat emissions might be greater than first suspected but still considerably lower thanemissions from working coal mines.

VCBM production schemes, which are independent of mining, contribute indirectly toa reduction in greenhouse emissions by replacing coal burning. However, in somecircumstances they can provide high purity gas for enriching mine gas thus increasingthe total quantity available for utilisation and further contributing to a reduction ingreenhouse gas emissions.

In addition to similar benefits to mine gas schemes the extraction and use of gas fromabandoned mine workings provides the opportunity to minimise odour emissions andprevent surface hazards arising form the uncontrolled migration of gas to the surface.

A climate change levy has been introduced by the UK Government to promote the useof environmentally friendly fuels. HM Customs and Excise has informed AlkaneEnergy that mine gas used for burner tip fuel will be exempt but that used for electricity

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will not be. The levy for electricity is 0.43p kWh-1 (1). This levy will impact on mostmine gas and abandoned mine gas schemes and could discourage development ofmarginal projects, thus being environmentally counterproductive.

The Kyoto Protocol envisages the introduction of international trading of greenhousegas emission credits (carbon credits) in 2008. These will enable operations, whichachieve net reductions in emissions to sell their credits to companies who are netemitters to enable them to comply with their industry target. Some companies havealready started buying verified credits anticipating rapid increases in price as possiblecompulsory compliance with pre-set emission targets approaches. At current prices(first quarter 2001), revenue from a UK mine gas scheme could be increased by around10% by the sale of emission credits. Further details are provided in Appendix 3.

CMM projects are considered ‘good buys’ by emissions credits traders as they arereadily verifiable, the technology of emission reduction is well proven and theyrepresent a major greenhouse gas source (Fernandez, 2000). Nevertheless, there aresome complexities. For instance, if pre-drainage is practised a credit could not beclaimed until the mining has taken place that would have released the gas.

AMM utilisation schemes may be more difficult to verify for emissions reductions thandrained mine gas as all the gas extracted may not necessarily have been emitted to theatmosphere in the absence of an extraction scheme and the effects of rising water. Anyverification process should, however, take account of the long-term ameliorationbenefit of AMM production.

An emissions reduction registration scheme is being introduced in the UK inpreparation for formal trading against the national inventory. A scientifically based,rational emissions model is needed before AMM schemes can qualify for inclusion.

2. CBM RESOURCES AND RESERVES IN THE UK

2.1 Introduction

For the first time, preliminary estimates have been made of the potentially recoverablequantities of CBM on a source by source basis.

2.2 VCBM Resources and Reserves

Estimates have been made of the VCBM resources by BGS and presented in a previousreport (Creedy, 1999). Due to low seam permeability and surface access limitations,the total resource of 2.45x1012m3 was heavily discounted to arrive at a tentative, butfairly arbitrary, estimate of potentially recoverable reserves. As commercialproduction has still not been demonstrated, and also because no operator has yetattempted to obtain planning consent for a multi-well production field, no provenreserves can presently be identified. To date, planning consents have been limited tofour and five well groupings. The five-well trial of Evergreen Resources (UK) Ltd mayhelp to establish a technical basis for defining VCBM reserves in the UK.

1 See http://www.hmce.gov.uk/notices/cc11-pt3.htm.

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In the absence of new information the best, albeit crude estimate of potentiallyrecoverable VCBM onshore UK, remains at 3x1010m3.

Offshore CBM development would be prohibitively costly. At best, natural gas wellsdrilled from existing platforms in certain parts of the North Sea could be deepened tointersect underlying coals. Any benefits would be marginal and the operation wouldnot necessarily be cost effective. Until technologies are available which will facilitate aquantum leap in the production of VCBM from low permeability seams, offshore UKCBM resources are not likely to attract commercial exploitation in their own right.

2.3 CMM Resources and Reserves in Working Mines

CMM reserves in working mines are represented by the volumes of gas in coal seamsthat will be released by planned longwall extraction over the life of the mines. Therecoverable reserves are the volumes of gas that can be captured by methane drainagesystems and delivered to an utilisation plant. When mining ceases and a mine isabandoned, the residual gas in the mining-disturbed seams contributes to the reserves inthe abandoned mine gas reservoir.

The estimated reserve of CMM in UK mines are 1,620x106m3, assuming that utilisationis feasible at all deep mines with methane drainage. In arriving at the above volume, itwas assumed that the average life of the remaining gassy deep mines is 10 years, withan average of 15 faces each producing 1x106tonnes per annum; 6m disturbed roof coal;a coverage of gas content of 6m3 t-1; worked seam thickness of 2m and 60% of roof gasavailable for emission or capture.

Assuming a 50% capture efficiency (and no use of methane in ventilation air) theamount of usable reserves would be 810x106m3.

The additional AMM reserves created by the closure of these mines, based on theabove assumptions = 40% x 18x106m3 = 7.2x106m3. This figure is much lower than theactual AMM reserves associated with these mines as all the workings, not just therecently worked faces, will contribute to the abandoned mine gas reservoir.

2.4 AMM Resources and Reserves

AMM resources consist of the volumes of gas remaining in coal seams that have been de-stressed by mining and that could potentially be extracted from abandoned mineworkings.Reserves are the volumes of gas expected to be recoverable having taken account ofgroundwater recovery.

Methods for estimating AMM resources and reserves differ in detail but all involvecalculating the quantity of gas remaining in un-mined coal that has been disturbed bymining activity and which could be extracted by applying a suction pressure to theabandoned workings.

The key factors are:

• the volume of coal in which the permeability has been enhanced by mining andwhich is connected to the extraction site (vent)

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• the remaining seam gas content of the coal

• the volume of this gas that can be desorbed from the coal at a given suction pressure.

The method developed by Wardell Armstrong assumes that the recoverable gas in amining disturbed seam is the calculated residual gas minus the gas adsorbed at a finalabsolute pressure of 50kPa. Further details of AMM reservoir characterisation areincluded in Section 5.

This section aims to provide a first broad estimate of the total AMM resource. Coalfieldedges have been omitted where shallow workings may have intimate surface connectionsand where opencasting activity is likely to have taken place. It is assumed that de-watering of a flooded mine is not financially viable and therefore mining areas in whichgroundwater is considered to have fully recovered were excluded from reserves.

The AMM potential of the various UK coalfield areas (Figure 1) have been assessed, ingeneral terms, on the basis of coal occurrence, mining history, gas content andgroundwater status (Appendix 4). It should be noted that individual mines may havebetter prospects than indicated in the overall area comments.

The locations of the more than 1500 coal mines that existed at the time ofnationalisation in 1947 has been used to delimit the maximum area of AMMprospectivity in the UK, as the most extensive longwall mining took place after thisdate. There were several coal mines outside these areas, principally in the Pennines,where Namurian and older coals, such as the Little Limestone Coal, occur. However,these mines are mostly small and are not considered to be significant AMM resources.In most of the coalfields, the distribution of post-war mines is influenced by the factthat the shallower, more accessible parts of the coalfields were mined out in earliertimes. In any event, the shallower parts of the coalfields would be unlikely AMMprospects due to the probability of air ingress occurring if gas extraction was attempted.

The ‘major mined areas’ of the UK post-1947, excluding the currently working deepmines are delineated in Figure 2. These areas form the basis for a UK resourceestimate. It should be emphasised that these ‘major mined areas’ are very poorlyconstrained at present. It is likely that they overestimate the true size of the areas withAMM resources, because a variable proportion of these areas will not be affected bylongwall mining. However, determination of the true limits of the areas affected bylongwall mining is beyond the scope of this report.

From the above, it is clear that a detailed assessment would require a study of localgeology, mine plans (eg to determine thickness and gas content of extracted seams andremaining coal, vertical distance between remaining coal and extracted seams) andminewater rebound.

An estimate of AMM resources for the entire country requires some broadgeneralisations to be made to estimate reservoir volume and gas availability.

Estimation of Coal Reservoir Volume

The AMM reservoir comprises the volume of coal in which the permeability has beenenhanced by mining. Overall, this is approximated by the mined area of the major

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coalfields of the UK shown in Figure 2. The total thickness of coal affected by miningin each mined area was estimated from boreholes or shaft sections in each coalfield.Where possible shaft sections were used, as these were considered to provide a betterestimate of the part of the Coal Measures section that has been mined. However, noaccount is taken of mining below the level of the base of the shaft examined and onesection was used to represent each ‘mined area.’

The following method was used to calculate the coal reservoir volume: The totalthickness of coal in the shaft or borehole was determined. The combined thickness ofthe seams known, or presumed, to have been extracted was subtracted from the total.The position of the extracted seams in the shaft or borehole was noted. Any unminedseams outside the combined 190m zone of disturbance surrounding a mined seam weresubtracted from the total.

Estimation of Potentially Producible AMM

This stage involves calculation of the remnant seam gas contents of the coal affected bymining and the volume of this gas that can be desorbed from the coal at a givenproduction pressure. Measurements of virgin seam gas content are available for manycoalfields and can be estimated for others. Using an empirical relationship establishedby Wardell Armstrong, the residual gas-in-place in worked areas of coal can beapproximated as:

• 0.4 x virgin gas content = gas potentially available for production at a pressure of50kPa in m3 of methane per m3 of disturbed coal.

For the purposes of national resource calculations, the above expression was used. Theresults are summarised in Table 3. Reserves were estimated from resources byapplying a correction to account for the proportion of AMM considered to beinaccessible due to flooding. The level of uncertainty is relatively high due to the grossassumptions and a detailed assessment is needed to confirm the result. Arguably, thelargest uncertainty is the volume of coal likely to have been isolated by groundwaterrecovery.

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An Alternative Resource Estimation Method

An alternative approach would be to estimate the resource per unit area, eg

Calculation for Selby (hypothetical as this is an area of active mining):

One seam extracted (Barnsley seam)Gas content 5.3m3 per tonne (Stillingfleet, Barnsley seam)Approximate thickness of coalwithin zone 150m above and 40mbelow Barnsley seam

6.28m (measured from an NCB borehole)

Assume 40% of virgin gas contentgas in surrounding seams potentiallyavailable for production to apressure of 50kPa.

= 0.4 × 5.3 × 6.28 per m2 of mine area

= 13.3m3 per m2 of mine area

= 13.3 million m3 per km2

2.5 UK Resources and ‘Reserves’

First order estimations of onshore UK CBM resources and potentially recoverable gasare summarised in Table 4. This study indicates that AMM ‘reserves’ could be moreimportant than other sources. However, these figures should be treated as preliminarypending a more detailed assessment.

3. VCBM PRODUCTION

3.1 Introduction

A detailed review of virgin CBM technology and its application in the UK andworldwide was prepared for the DTI in 1998 (Creedy, 1999). The results of this formerstudy are summarised and updated in this document.

VCBM recovery is achieved by means of reservoir pressure depletion and accounts forapproximately 28x109m3 per year of VCBM production in the USA. The formationpressure is allowed to decline as gas is produced under its own energy or as water ispumped from the coal seam to reduce the hydrostatic pressure. Primary VCBMproduction often leaves 50% or more of the methane remaining in the coalbed. VCBMrecovery and recovery rates ultimately depend on the properties of the reservoir. Theseinclude: coal type, coal seam thickness, desorption rate, absolute, relative, anddirectional permeability, porosity, pore compressibility, diffusion coefficients andwater saturation.

Despite global interest in VCBM technology no major commercial schemes involvinggas from virgin seams have evolved outside the USA and Australia. Resourceevaluations have not been matched by subsequent commercial development of reserves.The lack of VCBM development worldwide is due to institutional, regulatory, cultural,infrastructure, market, gas price and project financing issues rather than solely togeological factors. The VCBM industry in the USA recognises that, initially, projecteconomics were aided by a combination of factors. In particular, tax incentives largely

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offset the costs of establishing pipeline infrastructure without which the industry wouldnot have become firmly established.

The performance of a VCBM well will vary with geological and hydrogeologicalconditions, drilling techniques, stimulation method, maintenance and operationalprocedures. Maximum gas production rates of CBM wells in the USA average from1,400m3 day-1 (m3 d-1) (50,000ft3 d-1) to 8,400m3 d-1 (300,000ft3 d-1). Gas flowsachieved from productive wells in various countries are compared in Table 5.

CBM operators gain the knowledge that enables them to best exploit the naturalcharacteristics of the coal seam reservoirs in a particular area by trial and error. Thisskill and experience is location-specific. Transfer of the technology to coal basinselsewhere involves a learning process in which the technology is adapted to suit theprevailing geological conditions. The ultimate limitations are the natural fracturepermeability, thicknesses and gas contents of the coal seams.

A virgin CBM operation involves:

• desk study and exploration

• site selection

• reservoir characterisation

• gas well design, testing and completion

• production, gas treatment and water disposal.

3.2 Site Selection

Factors that influence the selection of well sites include geology, gas content,environmental impact, water disposal options, access and market opportunities.

The most technically attractive virgin CBM prospects comprise a succession of thick,continuous seams at moderately shallow depths with gas contents in excess of 7-8m3 t-1.Commercial success in producing from low gas content Powder River coals in the USAshows that high gas content is not essential provided the coal seam permeability is veryhigh. The gas production potential depends on its transmissibility within the seams andthe formation fluid pressure. Drilling and in situ testing are, therefore, essential.Definitive results may not even be obtained at this stage. Formation damage caused bydrilling fluids can result in an under-estimate of effective permeability. Production ofwater from a coal seam may indicate high permeability but unless pumping can reduce thehydrostatic head, no significant gas production will be achieved.

The features of a high-grade CBM site are summarised in Table 6 and the factorsindicative of gas production potential are listed in Table 7 (Creedy,1999).

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3.3 Reservoir Characterisation

Reservoir characterisation involves geological mapping, interpretation of geophysicalor cored borehole logs to determine the quantity of coal in place, and determination ofcoal seam properties from both measurements on samples and in situ testing.Simulation and modelling techniques are then used to predict the reservoir behaviourand likely production well performance. The methods described in the previous report(Creedy, 1999) continue to be used and no major changes are evident. Althoughmodern seismic techniques could assist exploration they are generally considered toocostly for the CBM industry to routinely use.

The tests can be undertaken by oilfield service companies and increasingly sophisticatedmeasuring and interpretation tools are becoming available. The parameters measuredgenerally relate to water rather than gas and need adjusting accordingly. In coal seams oflow permeability, response times to the various tests are likely to be long and the resultsmay be inconclusive.

3.4 Modelling Techniques and Simulation Tools

Mathematical models have been developed to predict the likely gas production capabilityof a reservoir and to aid the design of well spacing. The models are invariably applied inthe form of simulators to enable the sensitivity of parameter variability to be assessed.Some engineers are sceptical of these simulators because values for the criticalparameters are rarely known with any degree of confidence and are usually estimated byhistory matching (adjusting parameters until results match measured production results).Incorrect balances of values can yield a close match but yield erroneous predictions ofunknown parameters such as effective permeability. The limitation is not the quality ofmodels but a lack of measured data and inappropriate use of simulators.

Nevertheless, computer models can be helpful in gaining an understanding of reservoirperformance. Details of the available modelling and simulation techniques areprovided in Appendix 5 together with contact addresses.

3.5 VCBM Well Design, Testing and Completion

The most widely used system of stimulation is hydraulic fracturing, often calledhydrofraccing. This method involves inducing a fracture in the strata by the injectionof liquid under pressure, typically water, foam or gel. Sand, or some other material(proppant), is used to keep the fractures open to allow free passage of gas and wateronce the injection pressure is released.

A vertical hydraulic fracture can be propagated in the coal seam over distances of up to300m on either side of the borehole. The fracture forms a path of high conductivityalong which gas can flow into the borehole. Fractures may be created from the sameborehole in a whole series of seams either by isolating each seam with a packer andtreating it individually or by propagating a fracture through a series of closely spacedseams. Hydraulic fracturing usually produces a single elongate fracture propagatedalong the line of least resistance in the formation.

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Openhole dynamic cavity completion (sometimes known as natural cavitation) methodsare used in parts of the San Juan basin in the USA. This process, originally devised inCanada in the late 1970s, involves repeatedly pressurising and depressurising theexposed coal using compressed air and then removing the broken material on eachcycle by drilling. Cavity completions have been successful where reservoirpermeability is at least 5md and the reservoir is overpressured. The technique isgenerally more expensive to use than hydraulic fracturing and has not beendemonstrated to any extent outside the San Juan basin.

3.6 Gas Production

Where water is pumped to allow gas to desorb from the coal, the sooner the pressure islowered, the sooner the gas flows. De-watering a relatively small hydrogeologicallybounded block of coal (a fault-bounded block for example) using a single well mayallow early gas production in comparison with attempting to de-water a large unfaultedarea. Where natural permeability barriers such as faults do not exist, artificial barrierscan be created by using additional wells. For example, in a five well pattern, four wellssurrounding a central well could provide artificial boundaries to the area of influence ofthe central fifth well and allow full de-watering of the coal seams around it. Optimalborehole spacing depends on the radius of influence of the well on the coal seams. Thiswill depend mainly on coal seam permeability. It may be difficult to design optimalwell spacing in built-up areas where access for drilling is restricted.

3.7 Water Treatment

Treatment and disposal of water produced from CBM wells can be costly. Thecommon disposal methods used in the USA are deep injection wells and evaporationponds. Not all CBM wells produce large quantities of water. Some gas productive coalseams are dry. When coal seam permeability is low, water production is minimalunless an aquifer is inadvertently connected to the production well. Inadequatelycemented borehole casing can sometimes lead abnormal water inflows. Most UKVCBM wells are not expected to produce large volumes of water from coal seams.

3.8 Improving Well Completion and Performance

Improvements in individual well performance, mainly in the USA, have been obtainedby the continual refinement of techniques aimed at:

• identifying sites with favourable permeability

• minimising flow restrictions between the coal formation and production wells

• optimising borehole spacing and de-watering strategies

• identifying and remedying degraded well performance.

The effectiveness of a well completion is dependent on many different factors most ofwhich are not easily measured or controlled. In addition, the geology at each site isunique. There is always the uncertainty that a badly performing well may not beyielding expected fluid flows because of inadvertent damage to the coal seam, or poorconnectivity between the well and the natural fracture structure in the coal. Insufficientor overly enthusiastic stimulation can both create problems. Fluids and additives

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introduced during drilling and completion can reduce permeability of the coal aroundthe wellbore, and in the worst case also around a hydraulically induced fracture. Thisresults in under estimation of the production capability of the coal and could lead toabandonment of a potentially commercial prospect. Some producers seek to minimiseformation permeability damage during drilling and fraccing by using clean fluids,under-balance drilling and, where practicable, by avoiding coring mini-fraccing anddownhole testing prior to completion of production wells. VCBM production is stillvery much an art.

3.9 New Geological Potential

In the USA, persistence has paid off in some coalfield areas that were initially consideredpoor CBM prospects. For example, the low gas content (1.8m3 t-1) sub-bituminous coalsof the Powder River Basin in Wyoming, USA, have proved to be good producers. Acombination of thick seams and high permeability (10-1000mD) compensates for the lowgas content. The penalty for high permeability is a high water make and water disposalproblems.

Anthracite coals have a reputation as poor producers in the USA but studies in China haveshown that in some geological circumstances, such as those exhibited in the Qinshuicoalfield, anthracites can retain a fracture network capable of producing commercial gasflows.

There is some evidence that, in the San Juan basin, USA, a proportion of the methaneproduced from the most prolific wells (located in the so-called ‘fairway’) may be ofrelatively recent biogenic origin. Methanogens are thought to have been introduced ingroundwater. Methanogens may also be responsible for the highly productive PowderRiver coal seam gas occurrences. This opens the possibility of significant gas occurrencesin a wide range of shallow permeable coals (ie coal seam aquifers), irrespective of coalrank (Scott, 2001).

3.10 VCBM Production from Surface to In-Seam Guided Boreholes

In-seam boreholes can be installed from a surface borehole using specialist guideddrilling techniques.

The benefits for VCBM production are:

• a borehole can be steered to intersect the dominant fracture system of the coal, thuscommercial production may be achievable from marginal permeability coals ifsufficient fractures are intercepted

• increased contact with coal production zone and clean drilling obviates need forfraccing

• multiple branched holes can be drilled from a single, convenient surface location

• multiple wells can be drilled from a single pad, thus reducing the costs of access,drilling and gas gathering

• improved mine safety when used for pre-drainage of coal seams ahead of mining.

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Guided drilling technologies have been used successfully for many years within the oiland gas industry. Advancements in down-hole measurement and communicationstechnology coupled with ability to locate guidance sensors directly behind the drill bit,has resulted in the development of a new generation of guided drill equipment capableof providing greater accuracy, increased drilling speeds and cleaner hole completions.

The measurement of position co-ordinates and formation characteristics close to the bit,together with the ability to transmit the information to the surface, allows the engineerto steer the borehole accurately, particularly when combined with rotary steerabledrilling systems that can be operated remotely from the surface.

Guided Drilling Technology

There are two main types of guided drilling systems:

• down hole motors (DHM) with bent-sub assemblies, and

• advanced rotary steerable systems.

Both systems incorporate down-hole monitoring sensors to capture and relay informationto the surface, and in some instances, also to transmit commands to the steering unit.

DHM are turbines which use the hydraulic force of the drilling fluid to rotate thecutting bit. Sensors are located behind the motor. The accuracy of steering depends onthe proximity of the sensors to the drill head. Older systems in which the sensors are10m or more behind the drilling tool can be difficult to keep in-seam.

For guided drilling a bent-sub assembly with a fixed angle is used with a DHM. Theangle cannot be adjusted during drilling, any changes require the drill assembly to bewithdrawn from the hole. Control is achieved by rotating the bent-sub to follow therequired trajectory using a combination of pushing and rotating of the drill string. Theangle of the bent sub assembly is selected to match the required deviation of the hole.

Greater control of the borehole along the planned trajectory can be achieved usingrotary steerable technology. These systems incorporate guidance sensors directlybehind the drill bit providing data at the point of drilling. Communications between thedown-hole drill assembly and surface allows the direction of the drill bit to be adjustedremotely without the need to withdraw the rods. Changing the drill bit direction can beachieved by the use of ribs or eccentric cams that push against the wall of the borehole.Alternatively, the drill assembly can be deflected using an eccentric cam.

Rotary steerable techniques produce a smoother borehole than DHM systems as thedegree of correction is more easily adjusted. The other main advantage is faster drillingrates due to better cuttings removal. As with many technologies inappropriate use ormanagement of the equipment will result in poor performance.

Control of surface to in-seam guided drilling is aided by the use of 3-dimesional (3D)modelling software to represent and characterise the geological conditions. Advancesin technology have resulted in the option to incorporate sensors that measure bothdrilling parameters (co-ordinates) and petrophysical properties of the surrounding

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strata. The quantity and quality of down-hole data will vary for each applicationdepending on the characteristics of the target horizon and immediate strata.

Various specialist tools and methods are available for initiating a branched boreholefrom the primary casing. All involve the following elements:

• Access through casing – this can be achieved by physically cutting a slot (accesswindow) in an existing set casing or by the use of preformed opening in the casingstring. The position is predetermined prior to installing the casing. An opening isformed in the casing and covered with a composite material, which is easily drilled,to maintain the integrity of the casing.

• A deflection tool – this is installed below the access window that guides the drill bitthrough the composite material allowing drilling of the lateral. This tool isretrieved once the lateral borehole is completed.

• Casing – options are available to install permanent or temporary casing in thelateral borehole. Specialist tools can be used to ensure that lateral casing does notobstruct the primary vertical casing so allowing access to all parts of the borehole.

Experience of Surface to In-seam Guided Drilling

CDX Gas (USA) have developed a guided system using under-balanced drillingtechniques together with rotary steerable drilling to install surface to in-seam horizontalboreholes. The technique allows a large area of coal reserves to be accessed from asingle surface location resulting in benefits relating to planning, access, environmentalissues, visual impact and restoration. It is reported that from a single surface location a1000acre area of coal can be accessed.

Holditch Associates have compared this technique with conventional vertical fraccedwells. Initial results indicate that a vertical well at 1000ft in a 45ft thick coal seam willyield about 11% gas over 20 plus years whereas horizontal guided drilling can enable agas capture of 90% to be achieved in less than 30 months. An additional benefit of thistechnology is that an area of coal can be quickly de-watered.

CDX claim that boreholes can be controlled using their rotary steerable system in a0.5m coal seam. Drilling rates of over 300m d-1 can be achieved with boreholesextending to 6000m. This technology is presently been employed by US Steel to pre-drain coal in advance of mining. The method of drilling has the advantage that nometal casing is used and so mining is unrestricted in the panel.

Consol (USA) is planning a number of guided in-seam test holes in 2001. It isunderstood that Halliburton’s drilling subsidiary Sperry Sun will be using their rotarysteerable system.

Surface to in-seam guided drilling technology has been developed by Sigra Pty Ltd(Australia). The system uses a DHM and bent sub assembly to control the trajectory ofthe borehole. The have developed a sophisticated high frequency rock recognitionsystem to provide detailed information of the geological conditions. Unlikeconventional oil and gas communications systems, the Sigra guided drilling systemuses a helical connection on the inside of the drill rods to transfer data from down-holeto the surface. This method offers the advantage of faster data transfer than

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conventional mud pulse systems. Interception of guided boreholes is achieved byplacing a radio source down one borehole, accuracy increasing within a 50m radius.Research is continuing on the incorporation of formation logging sensors to supplementlocation sensors for underground guided drilling.

Tight-radius Drilling Technology

The Australian Centre for Mining Technology and Equipment (CMTE), incollaboration with BHP Mitsui Coal Pty Ltd, has developed a tight-radius drillingsystem (TRD) shown in Figure 3. The system is lowered into a conventional boreholewhere a water-jetting device is directed within the borehole to cut lateral boreholes.Field trials have been undertaken and Anglo Coal Pty Ltd envisage using the system topre-drain methane in advance of mining. The system could also have a role in VCBMwell completion as an alternative to hydrofraccing.

Current limitations of the technology are:

• maximum length of laterals about 200m

• inability to control the trajectory of the laterals

• unable to line the lateral holes against collapse

• operating depth limited to some 500m.

The main components of the TRD system are:

• Waterjet drilling assembly - a self-advancing, high-pressure waterjet drill,connected to a high-pressure supply proving both cutting and trust force.

• Whipstock - a device which guides the drilling assembly from a vertical tohorizontal orientation by means of an erectable arm providing a smooth curved pathfor flexible service pipes and monitoring instrumentation.

• Surface rig - capable of moving the waterjet drilling assembly to the desired depthof operation within the borehole, and control the drilling system during lateraldrilling. The rig will incorporate a number of powered drums to feed or retract thehigh pressure hose and control bundle, as well as a computer unit to analyse anddisplay the information coming from the whipstock via the control bundle.

A vertical well is drilled with a cavity created at each target horizon to allow access forthe TDR equipment. The whipstock is lowered down the well and positioned relativeto the cavity allowing the drilling assembly to be lowered down the inside of thetubing. The drilling assembly passes through the top section of the whipstock andlands in the erectable arm. The arm is then pushed into position to align the drillingtool at the coal seam target. High-pressure water is then supplied from a surface pump,down the high-pressure conduit to the drilling tool. The water is used to both cut theborehole and provide sufficient thrust force to advance the drill. This procedure isrepeated for each lateral.

Over the past five years more than A$7.5 million has been spent on research anddevelopment of the TRD technology. In addition to laboratory based work two majorfield trials have been conducted.

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Hillview 14 Trial - Moura 1997: This trial was held at BHP-Mitsui Coal’s Moura MineSite, located within the Bowen Basin, Queensland. It used an early proof-of-conceptprototype TRD system. A total of just under 1000m of lateral in-seam holes weredrilled most at a depth of 230m with some relatively short holes drilled at a depth of300m. After drilling the hole was de-watered and gas production quickly reached apeak of just over 1 TeraJoule (TJ) of methane per day, with cumulative production ofover 250TJ measured over the next 2 years.

Grasstree Trial - German Creek June 2000: This trial took place at Anglo Coal’sGrasstree Mine. In excess of 1100m of horizontal laterals were drilled at a depth of250m. Lateral hole lengths of up to 170m were achieved, with the average length ofthe seven longest holes being 140m. The average drilling rate was approximately 1mper minute. A prototype survey system showed encouraging performance althoughimprovement in precision will be necessary for commercial application.

Gas production could not be properly assessed due to reliability problems with the de-watering pump. Indications were that peak gas flows in excess of 1TJ per day could bereached if continuous pumping is sustained for at least one month.

Subsequent technical improvements are expected to result in an increase of the averagelateral drilling distance to 200m, an improved survey system and an averagepenetration rate in excess of 1m per minute. This performance probably represents thelimit of the capability of the current TRD equipment.

Applicability of Surface to In-seam Drilling in the UK

Despite the availability of sophisticated guided drilling technology, there is limitedexperience of its application in-seam drilling in UK Coal Measures Strata.

Specialist drilling operators report significant benefits of surface to in-seam guideddrilling techniques although the precise details of the technology are not available forreview due to commercial sensitivity.

3.11 Enhanced CBM Recovery (ECBM)

ECBM is a process which involves the injection of a gas into the coal seams to increasethe quantity of methane recovered. Nitrogen or carbon dioxide is used to sweepmethane from the fracture network in the coal, reducing the partial pressure of methaneand thus enhancing desorption from the matrix. Carbon dioxide has an additionaleffect because it is preferentially adsorbed onto coal surfaces, displacing methane fromadsorption sites. Field tests have confirmed higher production of methane wheninjecting carbon dioxide and the retention of two to three times more carbon dioxidethan the volume of methane produced. However, the use of nitrogen proved financiallymore attractive than carbon dioxide injection in the USA as the nitrogen could berecovered and recycled whereas the carbon dioxide was retained by the coal.

Carbon dioxide retention in coal seams is now being considered by some countries as apotentially important sequestration process with enhanced CBM recovery as a by-product and a means of subsidising the operation. This topic is currently beinginvestigated in European Union research projects involving the UK, Netherlands,

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France, Germany and Poland. The Dutch government in particular is anxious to find acost-effective means of disposing of carbon dioxide to enable it to meet its emissionreduction targets.

In order for injected gases to penetrate the coal substance at a reasonable rate, theseams must have a moderate to high permeability (perhaps 1-5mD). This could be abarrier to the commercial application of ECBM injection techniques in many coalfieldareas of the world, unless a means of artificially enhancing coal seam permeability canbe found.

3.12 Increasing Seam Permeability

Various artificial methods for increasing seam permeability have been suggested. Allthose involving injecting fluids, however, require a sufficiently high permeability toallow fluid penetration in the first instance. No practical cost-effective method forenhancing the natural fracture permeability of tight coal seams has yet beendemonstrated other than by undermining with a longwall.

Chemical Removal of Mineralisation from the Cleat System

Injecting acid into reservoirs to remove carbonate cement and improve wellproductivity is practised in the oil industry. However, injecting acid into coal seams todissolve cleat mineralisation is unlikely to be commercially feasible or environmentallyacceptable, as vast amounts of acid and long injection periods would be needed toenhance permeability over a significant area.

Biotechnological Enhancement of Gas Content and Permeability

Scott (2001) suggests biotechnology might be used to improve the gas bearing and flowcharacteristics of selected CBM reservoirs. Coal bioconversion is a natural process andhas been observed in samples of well cuttings leading to the recording of erroneously highseam gas contents. This process has also been proposed as an explanation for theexceptional methane producibility in parts of the San Juan basin.

Methanogens artificially introduced into a coal deposit could microbially increase theCBM content as well as enhancing the permeability by removing pore-plugging waxes.However, reaction rates may be limited by formation temperatures, accumulation of toxicwaste products and the small cleat areas accessible to the microbes. Any biomassformation could detract from permeability gain arising from coal degradation.

This novel concept warrants further research.

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De-stressing by Previous Longwall Mining

An opportunistic approach to permeability enhancement is to take advantage of stratadisturbances caused by past longwall mining. The permeability of unmined coalseams, and surrounding strata, is greatly enhanced when underlying seams are mined,as the coal-bearing strata collapse to fill the void left by mining, reducing in situ stressand enhancing natural fractures within the strata. Favourable targets for CBM arelikely to be seams in the range 75-100m above a longwall goaf in an area of high gascontent coals. However, where weak strata are being mined, compaction followingmining and subsidence could result in little improvement in transmissibility in someinstances. In the UK coal seams are generally under-pressured. Aquifers disturbed bymining could saturate the fracture network, the increased fluid pressures inhibiting gasrelease until removed by de-watering.

Standing water in some boreholes drilled through old, shallow goaf in the UK indicatesenhanced permeability may not necessarily be conserved. In contrast, flows of gasfrom long abandoned surface goaf boreholes (originally drilled above active longwalls)in the USA demonstrates that in some instances enhanced fracture can be preserved.Strong roof beds may be a necessary requisite for the preservation of a productivereservoir. Further geotechnical research is needed in this area.

Geologically Enhanced Permeability

The permeability of coal seams can be influenced by geological structural variations.Coal seam permeability is sometimes enhanced in the vicinity of a fault, dyke or fold.However, structurally complex areas tend to have damaged cleat systems and lowpermeability especially where severe structural compression has occurred. The westernpart of the South Wales coalfield would fit this category. In general, productive CBMareas are likely to have a relatively simple geological structure to ensure the continuityof reservoirs.

3.13 General Status of VCBM Development

Advancement continues to be made in abilities to identify geologically favourable sites,minimising formation damage during the drilling and treatment of wells and increasingthe effectiveness of completions. Advanced drilling techniques used in theconventional oil and gas industry, such as deviated drilling and coiled tubingtechnologies are now also being used for VCBM applications. The geologicalunderstanding of CBM occurrences has also been challenged and new ideas introduced.

4. CMM FROM WORKING COAL MINES

4.1 Introduction

Methane is released from coal seams that are disturbed by mining activities. As coalproduction increases, more gas is released. There is a limiting coal production at whichthe gas emitted into the mine roadways can no longer be diluted to a safe and legallyacceptable concentration. In order to achieve higher coal production, some of the gas

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must be intercepted before it can enter the mine airways. This is achieved usingmethane drainage techniques. 13 out of 16 of the major collieries in the UK rely onmethane drainage to attain their planned coal output.

Methane drainage in UK mines involves capturing methane released from unminedcoal seams within the strata above and below a longwall face. Boreholes are drilledinto the strata which has been de-stressed by mining and connected to pipelines towhich suction is applied to draw out the gas.

Gas Drainage Infrastructure

Methane exhausters are generally installed on the surface although undergroundinstallations which vent the collected gas into return airways, are used in some mineswhere drained quantities of firedamp are relatively low.

The feasibility of colliery gas (CMM) utilisation schemes depends on both mine gasavailability and market conditions. The gas availability and its likely variability in flowand quality can be assessed from a study of the mine development plan, the miningmethod, geological conditions, seam gas content data, historical gas emission data and aknowledge of methane drainage practices and the methane drainage infrastructure at themine. Account must be taken of degassing effects of previous workings in a collierywhere more than one seam has been worked, uncertainty in the mining programme andthe expected life of the colliery.

4.2 Gas Release in Coal Mines

Longwall caving may de-stress strata from 160-200m above and from 40-70m below theworked seam. Any gas sources within the disturbed zone will release gas which will flowinto the workings unless it is captured in methane drainage boreholes.

The extent of the zone disturbed by longwall mining, at a particular location, depends onthe length of the coalface, the height of the coalface, the strata strength, the depth ofworking and effects of previous workings.

In virgin strata, where longwall coal faces are less than 250m in length, the de-stressedzone in the roof may not extend as high as 200m. Progressively shorter coalfaces willproduce correspondingly smaller heights of de-stressed strata in the roof. The volume ofgas released when the coal is worked will, therefore tend to decrease per tonne of coalmined due to the smaller number of coal seams disturbed. This effect is likely to be mostnoticeable where there are strong beds in the roof.

The rate of gas flow into a particular longwall mining district depends on the gas contents,number and thicknesses of seams in the disturbed zone, the proximity of the seams to theworked seam, the age of the district and, most importantly, the rate of advance or retreat.

The gas flow on the coalface correlates closely with the coal cutting activities but theemissions from seams above and below the workings depend not only on the current day’sretreat rate but also on that of previous days. This occurs due to the cumulative effect ofprogressive disturbance on gas emission.

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4.3 Capture Efficiency

The performance of a methane drainage system is usually assessed in terms of methanecapture efficiency. The methane capture efficiency of a gas drainage system in alongwall district, as a percentage, is calculated as:

(100×F) / T

where F is the flow of methane in the drainage pipework (on a pure gas basis) and T isthe total methane flow in the airway plus the drained methane (on a pure gas basis).Allowance is made for any pollution of the ventilation air entering the mining districtand for any unmeasured gas leaving the district through inaccessible bleeder roads,sewer gate systems or service boreholes.

The gas released from the coalface, from uncut coal left in situ and from coal cut by thecoalface machine is uncapturable. The capture efficiency is, therefore, always less than100%. Due to mining, geotechnical and engineering limitations, a gas drainage systemwould also be unlikely to capture all of the gas released from adjacent coal seams.

Depending on mining conditions, geology, coal permeability and method of methanedrainage employed capture efficiencies can range from 30% to in excess of 90%.Capture efficiencies achieved in the UK where a cross-measures drainage method isused range from 30-80%. Capture performance is site specific and even on a particularlongwall can vary over its length depending on geological and mining conditions.

4.4 CMM Availability

Ventilation and methane drainage planning are based on previous experience of working aparticular seam or on a gas prediction method. At UK collieries, the likely gas emissioninto a longwall district, and its dependence on coal production rate, is usually predicted.

The likely availability of CMM in terms of flow and quality can be determined from astudy of the mine development plan, projected coal production, the geological conditions,seam gas content data and historical gas emission data. Significant reductions in gasavailability can occur when previous workings in an overlying seam are underworkedprovided the interval is less than say 100m. This reduction occurs due to the degassingeffect of the earlier workings.

Methane prediction models (eg the MRDE firedamp prediction method developed by theformer British Coal Corporation) can be used to provide an estimate of the total flow ofgas expected. The models were designed to assist ventilation planning but with cautionthey can also be used for assessing gas availability for utilisation.

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However, not all of the predicted gas flow may be usable for several reasons:

• the captured gas flow could at times exceed the capacity of the utilisation plant, andtherefore some gas will be vented to the atmosphere

• an excess supply is needed to ensure the plant is able to run at capacity

• methane flows are highly variable and a scheme with sufficient utilisation capacity toconsume peak gas flows may not be financially viable

• equipment cannot run continuously and efficiently without regular attentionnecessitating planned maintenance stoppages. Plant breakdowns can also occur

• due to ground movement and practical underground engineering limitations excessiveair may occasionally be drawn into the gas collection system leading to loss of purity.At times, therefore, the concentration of gas arriving at the surface will be less than thepermitted minimum concentration to use. The unusable gas must either be vented orenriched with higher purity gas from another source eg natural gas or liquifiedpetroleum gas (LPG).

4.5 CMM Drainage Techniques

Various methane drainage techniques have been developed. They can be divided intotwo categories, either pre-drainage or post-drainage. Pre-drainage involves removingfiredamp from coal seams in advance of mining. Post-drainage involves capturingmethane released after the strata has been disturbed by extracting coal and allowing theroof to cave. The applicability of the fundamentally different approaches dependschiefly on the natural fracture permeability of the coal seams. Pre-drainage is onlyfeasible where seams have a sufficiently high permeability to allow significant gas flowin virgin conditions ie before being disturbed by mining.

Pre-drainage using horizontal boreholes drilled in the worked seam from undergroundroadways or shafts can be effective in reducing the gas contents of coal seams inadvance of mining. Attempts to apply it in the UK have not been successful due to lowseam permeability. Pre-drainage is used in many mines in the USA where seams aregenerally shallower and of higher permeability than those worked in UK mines.

Surface VCBM production techniques have been used in the USA to drain gas ahead ofworking. The depth of most underground workings, low seam permeability, highdrilling costs and surface environmental and access constraints precludes theapplication of surface pre-drainage technology to deep mining in the UK.

All post-drainage methods involve obtaining access, by some means or other, to thezone of disturbance above, and also sometimes below, the worked seam.

Access is gained by drilling from the underground roadways, drilling from the surface,driving roadways into the disturbed zone or exploiting old workings which lie withinthe disturbed zone. Irrespective of the method of access, the aim is to consistentlycapture sufficient gas to ensure that the mine ventilation can satisfactorily dilute anyremaining emissions at the planned rate of coal production. The choice of method isdetermined by practicality, safety and cost.

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Underground Cross-measures Methane Drainage

The most effective post-drainage method in common use in modern, deep gassy longwallcoal mines is cross-measures methane drainage. This method was initiated in Germanymore than 40 years ago but has been considerably refined since. It is in common usethroughout Europe but few if any mines in the USA use the method as shallowerconditions enable alternative approaches to be used.

Boreholes are drilled at an angle above, and also in some instances below, the goaf. Theboreholes are drilled close to the coalface and linked to a common pipe range. Suction isapplied to the pipe range from either surface or underground pumps to draw the gas to adischarge point or methane utilisation plant. Sufficient air is passed around the minedistrict to dilute gas, which is not captured by the firedamp drainage system, to a safe leveltogether with the gas emitted from the worked seam itself.

The suction applied to methane drainage boreholes to encourage gas flow also tends todraw ventilation air through fractures in the surrounding strata. Standpipes are insertedinto the initial section of borehole to minimise this air ingress. No gas can be capturedfrom any seams (or gas-bearing sandstones) within the standpipe length of 10m or soabove the worked seam. Any leaks in the pipework system within the mine will alsoresult in additional dilution of the captured methane.

Methane concentrations (purities) in drained gas can range from a few per cent to morethan 90% in exceptional circumstances. Some control on purity is achievable. Increasingsuction in an effort to increase gas flow will introduce more air and hence reduce the gaspurity. Conversely, reducing suction (eg by stopping a methane pump) will reduce thetotal mixture flow but improve gas purity. The balance between gas flow and purity isachieved either by manual adjustment or by an automatic control system at the methanedrainage plant. Gas purity is controlled by adjusting a by-pass valve, switching pumps offor on, and by regulating flows from sealed off waste areas underground.

The methane drainage system can only capture gas from seams above or below theworked seam. The gas released from the worked seam, uncut coal left in the seam andcoal cut by the coalface machine is uncapturable. Furthermore, due to mining,geotechnical and engineering constraints, a methane drainage system would be unable tocapture all of the gas released from the adjacent seams. The theoretical maximum captureefficiency is therefore always less than 100%.

Almost all modern high-production coalfaces use a retreat longwall method of mining.On a retreating coalface, boreholes are usually drilled behind the face line where specialsupport and ventilation arrangements are needed to enable the methane drainage boreholesto be drilled safely. Poor roof conditions, or floor lift behind the face can create accessdifficulties and seriously delay borehole installation. The difficulties of space limitationsare sometimes exacerbated by high temperatures and the occurrence of gas layering. Toreduce the access problem and ensure a safe drilling environment, boreholes aresometimes drilled from the return roadway before the face passes. Limited success hasbeen achieved with pre-drilling but consistency of capture and high capture efficienciesare rarely achieved due to the effects on the boreholes of high stresses around the facearea.

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Drainage to the Surface using Vertical Goaf Wells

This approach, used in Australia, China, South Africa and the USA, involves drillingvertical boreholes from the surface above longwall panels to capture gas from coalseams in the roof strata disturbed by coal extraction.

The method is applicable to relatively shallow longwall coal mines where there are fewrestrictions on surface drilling and the construction of surface venting sites. Due tosurface environmental and depth constraints the method is not likely to see futureapplication in the UK.

Goaf Drainage from Underlying or Overlying Roadways

In the late 1940s a method of gas drainage sometimes termed the ‘superjacent heading’or ‘Hirschbach’ method was developed in the Saar coalfield which involved driving aheading above the worked seam prior to its extraction by a longwall method. Wherepracticable the roadway was driven in coal to reduce the cost. Sometimes boreholeswere drilled from the roadway to extend its zone of influence. The roadway was thenstopped-off, a methane drainage pipe being installed in the stopping to draw the gasaway. Typically a drainage roadway would be situated from 20-25m above the workedseam or less than 20m below. Due to the high cost this method is not commerciallyviable in mines other than where an existing roadway can be exploited.

Goaf Drainage using Long, Horizontal Boreholes Above or Below the WorkedSeam

Modern guided longhole drilling techniques have the potential to achieve a similarresult to the above method without incurring the additional cost of driving an accessdrift and a gas drainage roadway. A borehole started from the worked seam can beguided through an arc to run parallel to the workings at a selected horizon above orbelow. To achieve a reasonable gas capture, and also to make due allowance forborehole damage as the longwall face retreats, three or more boreholes are required.An attempt to demonstrate the method in the UK failed due to drilling difficulties(Bennett, 1994) resulting from swelling of mudstones and borehole instability.Successful applications have been demonstrated in Australia, China and the USA.

A project, Improved drainage of methane gas, funded by British Coal, the ECSC andthe DTI investigated means for improving methane drainage in mines (IMCGeophysics Ltd, Dec 1997) using horizontal drilling techniques. However, attempts toinstall long boreholes at Harworth, Silverdale and Point of Ayr collieries all failed dueto geological difficulties.

No gas drainage was achieved during the project and it was concluded that presenttechnology for drilling steered and near-horizontal wells from within UK mines isgenerally not capable of producing reliable and repeatable progress.

There have been further developments in guided drilling technology since this workwas completed and so the above conclusion should be re-tested.

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Goaf Drainage from the Worked Horizon

Direct drainage of gas from the goaf can be achieved from pipes laid in the returnroadway of a retreat face and left open at the face start line, from pipes inserted throughstoppings erected at the return end of the face or in crosscuts driven from a parallelroadway. These methods are not usually particularly efficient, high drainage capacitiesare required and the captured gas can be of too low a purity for utilisation. The methodmay be adequate where gas emissions are relatively low. High flows and purities areobtained using this method of capture in some mines in China where thick seams areworked.

4.6 Recent Developments

Guided drilling technology has been developed and applied successfully in the USAand Australia for drilling underground horizontal in-seam boreholes. The systems arerelatively simple and robust. The trajectory of the borehole is estimated in advance ofdrilling and down-hole measurements of the bit location are taken to confirm itslocation. In most applications detailed information on the seam thickness and dip willbe known. There are a small number of companies in Australia and the USA whospecialise in the underground drilling of guided longholes and they appear keen toevaluate their technology in other countries.

In Australia about 500,000m of underground horizontal in-seam boreholes have beendrilled using the AMT DDM MECCA steering tool. However, others options areavailable for surface to in-seam boreholes. Lucas Drilling is in the process ofestablishing capabilities to drill boreholes up to 2km in coal.

Surface to in-seam guided drilling has apparently achieved some success in the USAfor pre-drainage ahead of mining. As the gas is produced from virgin seams, it isconsidered a VCBM operation (see Section 3).

Included in the Australian Coal Association Research Programme (ACARP) has been aproject at German Creek Mine, Central Colliery in Queensland to apply hydraulicfracturing techniques to small-diameter in-seam gas drainage boreholes in coal mines.The first trial was unsuccessful and no further funding has been allocated2.

4.7 The General CMM Situation

Collieries in many countries are draining methane for safety reasons and variousinternational assistance programmes are encouraging greater use of the methane toreduce greenhouse gas emissions. Most of the CMM projects concentrate effort onsurface utilisation installations and sometimes neglect to invest in underground drillingand gas monitoring equipment, training and management. High standards of design,planning, installation, operation and maintenance together with management commitment,experience and workforce training are essential elements of any successful mine gasdrainage scheme. The UK Health and Safety Executive have recently published guidanceto promote effective methane drainage management (Creedy, 2001).

2 http://www.dpr.csiro.au/people/rob/robs.html

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The key features of a successful CMM utilisation scheme are:

• an existing, well-managed gas drainage system

• sustainability of coal production and gas capture

• availability of gas from production and non production sources

• suitable infrastructure to enable on site use of gas or electrical power

• commitment of management to CBM extraction and use.

The UK has developed gas drainage techniques and technologies which are applicablein many of the deep mining countries of the world and new CMM projects will createopportunities for equipment manufacturers and suppliers.

A fundamental problem of CMM projects is financing. Many projects are too small toattract international investors and many coal-mining companies have limited funds attheir disposal. However, successful CMM schemes have been developed and operatedby third party energy supply companies.

Gas use options are constrained by variability of CMM flow and purity and theproximity of suitable customers. On-site power generation for mine use may befeasible at many remote locations.

Collieries should consider themselves as energy producers and include CMMutilisation in their general production strategy.

5. EXTRACTION OF AMM

5.1 Introduction

AMM schemes aim to recover the gas left behind in unmined coal which has beendisturbed by total extraction methods of mining such as longwall.

Methane and other gases are often vented from abandoned mines in the UK to preventthe build-up of underground pressures which could lead to uncontrolled seepages ofhazardous gas into the ground and surface structures. The vents, usually installed inshaft or drift seals, provide access for gas extraction. Where no suitable vents areavailable boreholes can be drilled into mine galleries to access the gas. Not all closedmines contain significant quantities of methane. Some mines which have worked coalswith low gas contents (eg less than 1m3 t-1) emit mixtures of de-oxygenated air andcarbon dioxide (blackdamp).

AMM extraction schemes are environmentally beneficial in that use is made of energythat would otherwise be wasted, the risk of uncontrolled emissions at the surface isreduced and greenhouse gas emissions to the atmosphere are lowered. Planning andregulatory authorities, therefore, tend to view schemes favourably.

AMM is suitable either for direct use in engines for power generation or fortransmission by a dedicated pipeline to a consumer for combustion in boilers. AMMprojects in the UK involve schemes ranging from 3MWe to 10MWe equivalent with

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average project lives varying from 10 to in excess of 20 years based on a conservativegas reserve estimation methodology.

The exploitation AMM is not a new concept. In the past, gas from closed mines hasbeen used to supply a single industrial customer or fed into a mine gas grid.Conventional mine gas drainage equipment was employed rather than the costeffective, purposed designed systems developed by present day operators of AMMschemes.

In Belgium, gas extraction was sometimes continued after mine closure until equipmentfell into disrepair and interest was lost. The final gas drainage scheme closed around1993 when the last mining engineer left to operate the pumps retired, 25 years after theclosure of the colliery in 1968 (Dusar, 2001). Other extraction schemes were closeddue to flooding of the workings, partial collapse of a shaft and damage to pipes, loss ofcustomers for the gas and sale of gas storage facilities. A press article on the release ofexplosive gases prompted the state mining authority to have the remaining pipescemented.

In the Pas-de-Calais region of northern France mine gas has been injected into theArtois high-pressure natural gas pipeline since May 1990. A 20-year contract providesfor the extraction of at least 440x106kWh of gas a year. Gas recovery has apparentlyexceeded expectations, with gas being drawn from extensive abandoned workings evenwhere separated by unmined coal pillars.

Gas has been produced from abandoned mine shafts in the Saar for many years.Hangard (closed 1959), Kohlwald and Sinnerthal produce about 51x106m3 per year ofwhich 92% is used by industry. The gas is distributed by a local pipeline networklinking working and closed mines.

A guaranteed price of 0.15DM kWh-1 to SME’s arising from the recently acquired‘renewable’ status of AMM in Germany has prompted considerable interest in theexploitation of the gas for use in CHP schemes. About 80 proposals have beensubmitted to mining authorities in Northrhine-Westfalia (Gerling, 2001). Apparentlymobile heat and power generators are to be used.

The effect of minewater recovery is critical. Gas cannot be extracted in commercialquantities from waterlogged workings. To pump out a mine solely to facilitate testingwith no certainty of commercial gas production would be considered high risk and toocostly an option to pursue at most sites. Account must, therefore, be taken ofminewater flows in estimating potentially recoverable gas. Preferred sites are thosewhere minewater recovery rates are low. However, de-watering may be continued atrecently closed mines to prevent the abandoned mine gas reservoir flooding in the firstinstance.

The limitation on gas extraction rate, in most instances, is determined by the resistanceof the access to the mine workings (unfilled shaft, filled shaft, adit or borehole), and thequality of gas depends strongly on the sealing of the surface access to prevent airingress.

The key features of a successful AMM scheme are:

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• An extensive area of interconnected abandoned workings

• A large coal volume in unmined seams de-stressed by under and overworkings

• Significant residual methane in the unmined coal seams

• Minimal water ingress with little or no ‘ponding’ in main roadways

• Unfilled shaft or drift from which gas can be extracted

• No connections to shallow outcrop workings so no air in-leakage

• Local market for gas

AMM schemes can be commercially attractive due to their rapid payback and highreturn potential compared with other types of CBM projects. A competitive pricingpolicy can persuade initially hesitant customers to enter into a commitment to useAMM.

5.2 AMM Reservoirs

Coal is the primary source of methane in an abandoned mine. The methane found inold goaf areas (worked-out longwall panels), roadways and shafts will also haveoriginated from primary coal seam sources. The precise origin of any produced AMMwill be indeterminate and therefore the whole mine complex and its associated fracturesystems can be considered to form a boundary to the reservoir. The gas reservoircomprises all the coal in strata disturbed by mining which is likely to emit significantquantities of gas into the workings. British Coal Corporation research indicates thatcoal seams up to 150m to 200m above a longwall coalface and 50m to 70m below arede-stressed. The reduction in stress results in the creation and relaxation of fractures,and thus greatly increases the permeability of the Coal Measures (including the coalseams) surrounding the extracted seam.

Underground roadways provide the means of transmitting suction pressure from thesurface pumps to the primary gas reservoirs. Suction is needed to generate pressuregradients and maintain flows of gas from the coal. The gas production process willtherefore largely rely on gas desorbing from primary coal seam sources entering goafareas and gas extraction pumps drawing leakage gas through a multiplicity ofstoppings; only small leakages from a large number of stoppings may be needed tomaintain a production flow. At the low flow rates required, pressure losses acrossstoppings are insignificant. In some instances, the effectiveness of gas extraction couldbe compromised where there are fresh air leakages into the mine workings throughimperfectly sealed surface entries. These problems would normally be identified andremedied at an early stage of the project.

The worst case effect of an air leakage is dilution of the produced gas to anunacceptably low calorific value. An important part of site preparation is to identifyand treat air leakages between ostensibly sealed mine entries and the surface

In mines that have been abandoned for some years prior to installation of a gasextraction system, minewater may have accumulated in some goaf areas and displacedmethane into roadways and shallower seam workings. The displaced gas may beaccessible for production and, if pressurised may initially enable high flow rates to beobtained.

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Once a goaf area has been flooded, the associated primary gas sources can no longerrelease gas into the workings. The resource is not lost but de-watering will be requiredbefore desorption processes can be re-established. However, any gas that hasaccumulated prior to flooding will be displaced and hence could be recoverable. Insome instances, gas in fracture space within the strata may also be compressed andforced into voids at a higher level.

The most important feature of a productive reservoir is probably the extent ofinterconnected, dry workings, and hence the physical volume of the reservoir, ratherthan gas content. Initial testing at some low gas content but extensive mines indicateshigh gas flows can be achieved. The situation is analogous to the high VCBMproduction potential of the highly permeable but low gas content coals of the PowderRiver Basin in the USA.

Reservoir characteristics are determined from monitoring and pumping tests undertakenat the exploration stage.

An indication of the underground volume of mine workings with mine gas vents can beobtained from passive tests by:

• monitoring the quantity of air that passes in through the vent during times of lowbarometric pressure and of mine gas that passes out through the vent at times ofhigh barometric pressure, or

• by a calculation based on the outflow under constant barometric pressure (cf.Massen, Dusar, Loy & Vandenberghe, 1998).

Active testing involves connecting a portable pump, vent stack and flare to anabandoned mine vent. Gas composition and system pressure are measured for a rangeof flow rates. An increase of oxygen as flow rate increases indicates fresh air is beingdrawn into the system and a need for surface remedial measures. A rapid decrease inpressure may indicate a ‘tight’ connection to the reservoir or a depleted reservoir.

5.3 Effect of Water Ingress

Coal mines may suffer from water ingress for a variety of reasons. Surface water, orwater contained in overlying strata or adjacent abandoned mines, leaks in to the mineand is pumped out. After abandonment, if water pumping operations in the mine cease,there will be a gradual flooding of the abandoned mine workings up to some surfaceoutflow level (not necessarily the top of the mine workings) or the level of an outflowinto another adjacent mine. This is known as minewater rebound or recovery. In theUK, this is commonly the result of water entering from the surface or other minesrather than water rising through porous and permeable rocks in the Measuresthemselves. The rate of minewater rebound may be highly variable. It depends on therate of recharge and the underground volume of the workings.

Whilst it is technically possible both to de-water mines and to extract dissolvedmethane from water by pumping it to the surface, this is likely to be uneconomic. Thusthe level of water in an abandoned mine is likely to be a very important constraint on

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mine methane prospectivity. This may also mean that there is a limited ‘window ofopportunity’ to exploit CMM from many UK mines, before they become flooded.

In some of the smaller UK coalfields, for example the Forest of Dean coalfield, the bestseams are completely exhausted. Minewater drainage studies (Aldous, Smart & Black,1986) have shown that there is relatively good underground connection between themajor workings throughout the entire coalfield. Furthermore it is known that water isemerging from free drainage levels installed from the mines to the ground surface. Insuch areas it can be said with a high degree of confidence that all the workings belowthe free drainage level are flooded. However, in the larger coalfields the situation ismuch more variable. Company mergers and the integration of previously separatedcolliery ‘takes’ since nationalisation in 1947, have resulted in the establishment oflarge, pervasively connected units of underground workings in many coalfields (Burke& Younger, 2000). In mining hydrogeology, these are commonly known as ‘ponds’.

As minewater levels recover, the water level in each block will be controlled bygravity, but the filling of different parts of the workings will be determined by thelevels of the connections between them. Within each pond there is sometimes someinformation on water inflow, provided by known pumping rates when the mines wereoperative. Individual ponds may be connected to other ponds, by one or more knownor unknown connections such as a drift or roadway. The water levels in the wholesystem or, more commonly, systems, are ultimately determined by the levels of theconnections between the individual ponds and between the ponds and the groundsurface.

5.4 Environmental Benefits

Gas is vented from some abandoned mines to prevent the build-up of undergroundpressures which could lead to uncontrolled emissions at the surface. Mine gasutilisation schemes are viewed as environmentally beneficial because they reduce therisk of uncontrolled gas leakage and surface emissions and also due to theircontribution to reduction of greenhouse gas emissions (methane is substantially morepotent than carbon dioxide as a greenhouse gas).

Judicious choice of sites, detailed consultation with local authorities, attention to localnoise sensitivity and the relatively small scale of operations tend to remove most, if notall, concerns raised by local authorities. Condensate water recovered from the gas canbe piped back into the mineworkings.

The conditions of AMM sites have usually to be substantially improved toaccommodate the production equipment and to raise the quality of mine entry seals.The landowner benefits from these environmental improvements and is thereforeunlikely to present any obstacles on termination of gas extraction.

5.5 Production Equipment

Equipment used at operating sites generally involves well-proven standard technology,similar to that used in landfill gas utilisation schemes or natural gas distribution.Remote monitoring and control systems allow efficient operation with the minimum ofattention. A modularised site layout allows major capital items to be re-located when a

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site becomes exhausted or when production capacity is reduced as a gas reservoirbecomes depleted.

5.6 Safety

AMM is flammable when allowed to mix with air. However, the risk of a fire or anexplosion occurring at an extraction site is very low. The extracted gas is non-flammable due to its low oxygen content when contained within a pipe. The risk offlammable gas accumulation is controlled by monitoring the oxygen content of theextracted gas, use of high quality pipework and incorporation of non-return, isolationand slam-shut valves in the gas plant. Buildings and enclosures are adequatelyventilated and also monitored with flammable gas detectors. Ignition risks on the plantare controlled by use of suitably protected electrical equipment. Flame traps would haltthe propagation of a flame in the unlikely event of an ignition within pipework. Safetyon the delivery side can be assured by the use of dedicated pipelines installed to currentbest practice standards. An odorant added to pipeline gas will enable leaks to bedetected readily.

5.7 Estimating AMM Resources and Reserves

The procedure generally involves identifying unmined coal which has been disturbed byunderworking, empirically estimating residual gas contents and calculating the volume ofgas associated with the remnant coal. The process is fairly mechanical but somejudgement is required to accommodate geological detail. The void volume in theworked-out seams is estimated as a proportion of the extraction height and an allowancemade for the degree of extraction. As the gas originates in the coal, the magnitude of thevoid volume is not relevant to the quantification of the gas resource. However, the voidspace is important as a conduit for collecting gas, for transmission of suction pressure andalso as a receptor for water inflow which will progressively reduce the magnitude of theaccessible reservoir.

The effect of minewater recovery is critical. One approach to recoverable reserveestimation is to take account of this effect by reducing recoverable gas in proportion tothe volume of void filled by water.

Mine water pumping records prior to closure provide an indication of likely waterinflow but the sealing of mine entries and removal of surface water connections mayattenuate this value. Groundwater studies can arrive at an apparently correct waterlevel scenario by a fortuitous combination of void volume and water inflow ratealthough the magnitudes of both values could be too high.

Due to the extensive nature of the mineworkings, additional links to other collieriesmay exist which could extend the reserve life. However, reserve estimates for a projectshould only consider gas within the area of the Petroleum Exploration andDevelopment Licence (PEDL), whereas in practice gas could be drawn from workingsthat continue beyond this artificial boundary. If there are no operators in the adjoiningblocks, an operator could benefit from this bonus gas through ‘right of capture’.Otherwise, a unitisation approach may be needed. Appropriate protocols areunderstood to have been established by the oil and gas industry.

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Project duration is estimated by dividing the predicted gas volume by the combinedsum of the gas quantity produced per year plus the estimated volume of gas trapped byflooding per year. The volume of gas that cannot be recovered due to rising water isobtained by reducing the volume of available methane in proportion to the inflow ofwater. The technology is too young for a record of project lives to be established butexpectations are for durations from 10 to 20 years or more.

5.8 Enhancement of Gas Recovery

There may be opportunities to advance the current technology and enhance gasrecovery from abandoned mine gas reservoirs. The possibilities include:

• Hydraulic stimulation of unworked seams above goafs to increase the release rateof residual gas

• Stimulation and carbon dioxide injection (carbon dioxide is preferentially adsorbedon coal displacing methane)

• Mine de-watering to access previously flooded, deep, gassy workings.

Drilling techniques could be used to:

• Connect workings to aid minewater drainage away from prime production zones

• Link adjoining mines where workings interleave but do not directly connect

• Improve underground cross-measures connectivity (and hence transmission ofsuction pressure) within a particular mine complex.

5.9 Development of New Projects

The critical path elements in starting new sites are identification of a customer andcompletion of either the utilisation facility or the delivery pipeline. Investment costscan be minimised by modularising equipment to allow just-in-time installation and easytransfer of existing equipment from exhausted sites to new sites. The major capitalcosts could include improving surface sealing of shafts and drifts, gas extraction andcleaning equipment, preparation of access to the mine and gas transport to remoteconsumers or grid connections.

Over time, as gas is produced, reservoir pressure will decline necessitating morepumping effort to maintain flow. Eventually, the pumps will no longer be able tomaintain the required gas flow rate and a lower steady production flow will have to beaccepted. A further step reduction may be required again at a later date and so on untilthe operation becomes financially unattractive.

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6. CBM UTILISATION

6.1 Introduction

The various options available for CBM use include electrical power generation, on-siteuse in boilers and space heating, local low pressure pipeline supply to industry or domesticconsumers and injection into high pressure national distribution pipelines.

Techniques for enriching CBM are available but these may have limited application in theUK due to plentiful natural gas supplies. The principal use of CBM (AMM, CMM, orVCBM) in the UK is as a competitive low cost fuel for industrial burners or small-scalepower generation.

A commercially feasible CBM utilisation project must have a gas supply and customer forgas use or for electrical power generation. A long-term supply contract is desirable. Thecost of supplying CBM needs to be competitive with other fuels in the energy market, inparticular it should be competitive with clean fuels such as natural gas and renewables.Factors such as local and national energy prices, gas and electrical supply arrangementsand grid connections, existing infrastructure, regulation, planning, environmental andaccess will determine whether a CBM scheme is practicable.

A CBM utilisation scheme can involve the extraction and use of gas from either a singlesource (working mines, abandoned mines and virgin seams) or a mixture from differentsources. Multiple sources offer benefits in terms of improved security of gas supply andopportunities for controlling and maintaining desired gas purity.

Irrespective of the end use, most CBM schemes will require gas to be delivered withinspecified flow rates and purities. Management of a scheme will require a real timeunderstanding of changes to gas composition and flow. Such changes may affect theend-use options and ultimately gas sales and revenue. There must be a reliable methodof measuring energy supplied. Heating value (adjusted to moisture free, standardtemperature and pressure conditions) is the internationally preferred measurementbasis.

6.2 Markets

Conventional natural gas prices include transmission costs which depend on thedistance, and type of terrain, between the producing well and consumers. A CBMoperator seeks to obtain the most advantageous price for the gas at the lowest cost. Thecost of conveying the gas to the consumer is therefore a critical issue. The options fordisposing of the gas are:

• inject into an existing pipeline;

• construct a pipeline to a nearby consumer;

• generate and sell electricity.

An option may be to connect to an existing natural gas pipeline where a pipeline passesclose to the CBM field and where there are no potential consumers in the immediateneighbourhood. The equipment and software necessary to control the quality, pressure

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and quantity of gas input can be costly but this disadvantage may be partially offset ifgas sales can be initiated earlier in a project than would otherwise be possible.

Site selection and development of a CBM scheme depends on several factors withmarket conditions and end use options influenced by:

• rates of gas production

• gas reserves

• direct or indirect market for gas

• contract conditions; length of supply, gas availability, back up fuel source

• capital and operating costs

• availability and cost of alternative fuels

• existing energy distribution infrastructure

• government support

• environmental, planning and regulations.

Pipeline Transport for Direct Use of CBM

Market factors influencing the selection and design of a scheme are:

• gas compression costs for direct injection into a high-pressure distribution pipenetwork and permissible gas compositions

• proximity of existing pipelines and the need to construct a pipe network

• maintaining minimum gas specification over the supply period

• access to alternative fuel source for gas enrichment or back-up supply

• access, control and regulation of gas supply to gas grid

• availability and need for on-site or down stream gas storage facilities

• presence of local industry

• land access for pipe network or storage.

Electrical Power Generation

The gas may be usable at, or near, the production site to generate electricity. Optionsfor the use of CBM to generate electrical power typically include reciprocating enginesand gas turbines. Market factors will influence the ability to generate, use and exportelectricity, namely:

• the location, capacity and rating of existing electrical distribution infrastructure

• access and connection charges from the point of generation to the supply grid

• costs associated with metering and control to export generated power

• power requirements of on-site user

• capacity of on-site infrastructure

• land and access requirements

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• on-site or local use for waste heat generated.

Fundamental to the commercial success of a CBM utilisation scheme is the ability toidentify a reliable, long-term customer. Once a potential customer is identified,consideration is needed of the infrastructure requirements and costs to transport anddeliver the energy. The need to maintain gas purity and flow may incur additionalcapital and operational expense in the form of enrichment and storage requirements.

Ultimately the success of a CBM utilisation scheme will depend on the ability tocompete with other fuel sources within the market place. Local and regional variationsare likely to exist which may be influenced by government support. The success ofCBM will depend on:

• availability, quality and rates of gas production

• end user markets and specification

• cost and availability of alternative fuels

• capital and operational costs.

6.3 CBM Use

The principal mine gas utilisation driver is global environment concern. Prior torecognition of the implications of increasing greenhouse gas emissions into theatmosphere, there were relatively few commercial mine gas schemes in operation. Minegas utilisation schemes are now being encouraged and assisted in developing countries bygovernments and international aid agencies including Japanese ‘green’ aid, World BankGlobal Environment Fund and the USEPA.

The typical characteristics of CBM from unmined coal, working mines (drained gasand ventilation air) and abandoned mines are shown in Table 8 and the principal usesare shown in Table 9.

CMM is either used on-site (Table 10) or transported by a local distributed pipeline toan industrial consumer. The CBM is either directly used (Table 11) or it may beupgraded (Table 12) depending on the application. AMM could be exploited similarly.

Technologies for removing and using low concentrations of methane in ventilation air(Table 13) are being developed in some of the advanced countries to reduce a furthermajor source of greenhouse gas emissions. For widespread commercial application ofthe technologies, revenue from gas or energy sales, perhaps supplemented by a carboncredit, must provide a respectable return on investment, Governments can assist byreducing tax burdens, or by providing soft loans or some other form of environmentallylinked incentives.

The USEPA technical options series of internet publications describes a range ofproven and emerging technologies for using coal mine methane, applicable to bothgases from working and abandoned mines3.

3 Further details can be found at http://yosemite.epa.gov/methane

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The technologies are classified according to applications:

• Electricity production

• On-site heat production

• Pipeline gas

• Product feed stock

• Boilers.

Some applications are not particularly relevant to the UK, such as the use of CMM tofuel a desalination plant, as at Morcinek mine, Poland. Others simply consider CMMas a substitute for natural gas or coke oven gas eg for injecting a supplemental fuel intoblast furnaces. Many of the applications are likely to be financially marginal, orpossibly even uneconomic, without emissions reduction credits. CMM has been usedin industrial boilers in the UK for many years although many of the schemes no longerexist due to the demise of the associated collieries. However, at least one AMMscheme in the UK is supplying fuel for boilers, the benefit to the consumer being alower fuel cost than distributed natural gas. CMM can be co-fired with other fuels andthe UK company Hamworthy Combustion produces burners and control systemssuitable for such applications.

Electricity Generation Using Reciprocating Engines

Modern spark ignition engines with electronic engine and fuel management systemshave proved eminently suitable for generating electricity using CMM or AMM as afuel. Suitable engines are manufactured by Caterpillar, Deutz, Wartsila and Jenbacher.Experience of all the makes of engines has been gained in the UK in both landfill gasand CBM power generation schemes. Gas turbines appear to be currently out offavour. The world’s largest CMM power generation schemes using reciprocatingengines are located at Appin and Tower collieries in Australia, where there are a totalof 94 generator sets. About half of the total mines emissions are used. A peak capacityof 94MWe can be achieved of which 4-10MWe is used by the mine, the rest is suppliedto the local distribution company. To ensure consistent quality and quantity, naturalgas is added when necessary implying shortfalls of mine gas may arise.

Electricity Generation Using Gas Turbines

CMM and AMM can be used for electricity generation in either reciprocating enginesor gas turbines. The former is preferred in the UK due to their higher efficiency andlower cost of ownership. However, developments in gas turbine technology areresulting in improved efficiencies, longer service life and lower maintenance costs.Turbines from 500kW to 25MW are available capable of using gas of 35-75% methaneconcentration. Installed costs range from US$650-1000 kWh-1. It should be noted thatthe USEPA CBM Outreach Program information on the web pages seriouslyunderstates the efficiencies of internal combustion engines in making comparisons.Gas turbine manufacturers, specifications and prices can be found on the internet site4.

4 www.gasturbine.com.

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Research is currently being undertaken by a private company to develop a turbinecapable of operating on ultra lean methane mixtures, possibly as low as 1%. The aimwould be to use ventilation air enriched with drained methane.

Electricity Generation Using Micro-turbines

The micro turbine is a new technology developed from the aerospace industry consistingof an air-cooled turbine, generator and compressor on a single shaft with floating airbearings eliminating the need for lubricants. Generating capacity can be sized from30kW to 2MW by integrating multiple units. Efficiencies are low at 22-30% comparedwith reciprocating engines, but the rating could be improved by using waste exhaust heat.Natural gas, diesel, petrol or fuel oil can be used as a backup fuel. Installed costs areexpected to range from US$350-700 kW-1. The envisaged application would begeneration of on-site or localised power needs in remote areas.

Combined Heat and Power

Combined heat and power (CHP) plants have traditionally been used in Europe toproduce heat and power for adjoining residential and commercial complexes. TheZofiowka mine in Poland used CMM to fuel a CHP plant which supplies heat andpower both to the mine and to the nearby town of Jastrzebie. AMM power generationschemes in the UK produce useful electricity but almost half of the energy producedfrom the gas is rejected as heat for which no application can be found. There needs tobe a customer near to the plant to facilitate use of the thermal energy. Possibilities suchas supplying greenhouses have been considered but no customers were forthcoming.

Fuel Cells

Commercially available phosphoric-acid fuel cells (PAFC’s) can operate on natural gasor CMM. Installations are available that could produce from 200kW to 11MW at 40%efficiency. Molten-carbonate fuel cells (MCFC’s) are smaller than PAFC’s andpotentially more efficient. The US Department of Energy (USDOE) plan to testMCFC’s using coal mine gas. The advantages of fuel cells are higher efficiencies andlower emissions than turbines. Typical approximate capital costs are US$2000-000kW-1 for PAFC’s and half that for MCFC’s with operating costs at US$0.0017 kWh-1.The technology is evolving rapidly and costs are expected to decrease. This technologyhas not yet been considered for CBM applications in the UK.

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Production of Liquefied Natural Gas

Small scale, portable plant is now available which is capable of using CMM and AMMto produce liquefied natural gas (LNG). These units use acoustic power to compressand expand helium, dissipating heat through exchangers. Outputs range from less than10 (45 litres) to several 100 gallons (455 litres) per day. A larger unit using a differentacoustic drive technology is planned that will produce 10,000-12,000 gallons (4,500litres) of LNG per day at around 80% efficiency. The largest market for LNG iselectricity power plants but it is becoming increasingly popular as a clean fuel for roadvehicles. In North America LNG is also used for seasonal gas storage.

Methanol Production

Methanol is a key chemical product used in the manufacture of formaldehyde resins,acetic acid and vehicle fuels. CMM or AMM could be used to fuel methanol plantsprovided the gas can be delivered at a price below that of natural gas. Methane of atleast 89% purity is required so CMM enrichment may be necessary, although somehigh quality AMM sources could be suitable without treatment. The manufacture ofmethanol involves a three-stage process. The first stage technology for convertingmethane to syngas can be costly although new technologies which may be more costeffective are being developed. A catalytic process converts syngas to crude methanol(Stage 2) which is then purified by distillation (Stage 3).

Production of Synthetic Fuels

Synthetic fuels are more easily transported than gas which requires a pipeline andhence offer attractions for remote CMM or AMM sites. Mine gas of less than 80%purity can be used. Synthetic fuels are environmentally superior to conventionalpetroleum products but the cost of manufacture is relatively high. However, newcatalyst developments have reduced the technology costs and methane conversionplants using the Fishcher-Tropsch process of less than 5,000 barrels per day (955,000litres) may be commercially viable with a low cost feedstock gas. The USDOE isworking with Air Products and Chemicals Inc to develop a ceramic membrane thatcould reduce gas conversion costs by 50%. Currently, Syntroleum Corporation uses aproprietary catalyst that allows up to 30% nitrogen and carbon dioxide in the feedstockgas. The product is suitable for upgrading diesel fuels to meet stringent environmentalemission standards and demand is likely to grow world-wide.

Gas Enrichment

Various enrichment processes for medium quality mine gases have been examined.BOC have demonstrated a pressure swing adsorption (PSA) process applied to goaf gasbut in order to achieve the desired quality it was necessary to use feed rates lower thanthe normal rating of the plant. NorthWest Fuel Development Inc have successfullydemonstrated PSA and continuous PSA nitrogen rejection units at the abandonedNelms mine, Ohio, USA. Typical feed flows range from 1-6000cfd (28-170m3 d-1).

Medium quality CMM and AMM can be upgraded by mixing with LPG, VCBM ornatural gas to satisfy a particular consumers specification. The gas may also have to be

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dried if it is to meet a pipeline standard, and also have oxygen removed.Deoxygenation is relatively costly with a capital requirement of less than US$450,000to treat a mine gas flow of about 1000l s-1.

Enrichment only becomes commercially feasible if the product can be supplied to aconsumer at a lower price than an alternative fuel. Possible applications would beenriching CMM or AMM to allow injection into a natural gas pipeline or to producehigh purity gas as a chemical feedstock.

Coal Drying

CMM is used for coal drying in coal preparation plants in many parts of the worldincluding Poland, Russia and the USA. Existing coal-fired thermal dryers can bemodified to accommodate gas burners. The benefit of coal drying is enhanced value ofthe coal – higher heat value, reduced transportation costs and easier handling.

The drying of 380 short tons per hour of coal at 3% moisture would require about 1200ls-1 of methane.

Shaft and Ventilation Heating

Another direct on-site use for CMM is for heating ventilation air to increase workercomfort and prevent hazardous ice accumulations in shafts in cold climates. Thebenefit is a saving on imported fuel costs or, if previously coal fired, increasedavailability of coal for sale.

Use of Mine Ventilation Air

Mine ventilation air can be used as combustion air in reciprocating engines to increasefuel availability as has been successfully demonstrated at Appin colliery in Australia.Electrically powered vacuum pumps draw up to 65m3 s-1 of air containing 0.5-1%methane from the upcast shaft, through a filtration unit to remove particulates and pipesthe gas to the engine intake manifolds.

Ventilation air could be used similarly in gas turbines. Depending on conditions, aircontaining 0.5% methane could supply 4-12% of a turbine’s energy requirements.

The above process will only use a proportion of the mine ventilation air. An approachto total removal of methane from the exhausted ventilation air could be made usingoxidation technologies, thus achieving the ultimate goal of zero greenhouse gasemissions from underground mining operations.

The principal of removal of volatile organic compounds from industrial emissions byuse of oxidation devices is well proven. Useful thermal energy can be recovered.There are two basic processes for oxidising methane; thermal and catalytic.

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The two most promising technologies are the:

• Regenerative thermal oxidiser

• Reverse-flow catalytic oxidiser

The regenerative thermal oxidiser (or thermal flow reversal reactor) consists of porousbed of high heat capacity material through which ventilation air is passed. The flowdirection is reversed at intervals to allow pre-heating of the incoming air and tomaintain the high temperature zone in the centre of the bed at a temperature greaterthan 1000ºC. Useful heat can be recovered through a heat transfer system. Thesesystems are self-sustaining with air feeds containing as little as 0.1% methane.MEGTEC Systems (Sweden) have designed modular units that could be used at a minesite but no full-scale trial has been undertaken.

Catalytic devices operate at lower temperatures than thermal systems (500-800ºC) andinvolve a burner and a catalyst bed. A reverse flow facility allows heat to be storedeither side of the catalyst ensuring full methane conversion and high heat recovery. Adevice has been demonstrated at pilot plant scale in Canada where development istaking place but proposals for a mine site trial were abandoned when the mine closedprematurely. The concept was promoted by CANMET and developed by NationalResources, Canada.

The commercial viability of whole mine air treatment is likely to be marginal even withefficient energy recovery. However, emission credits, or the threat of environmentalpenalties, could drive this technology to the operational stage.

Flaring CMM

Flaring is not strictly a commercial use of CMM but supported by emission credits itcould represent a net zero cost environmental solution.

Shell Coal have installed a methane flaring facility at Central Colliery (German CreekMine) in Queensland’s Bowen Basin (Greenwood, 1999). The aim was to provide animmediate reduction in emissions and a facility to burn excess gas in the event of anysubsequent utilisation development. The flare capacity of 4,200m3 per hour is similarto that of the drainage plant. The system is remotely monitored and is protected byflame traps, extinguishers and also cut-outs in the event of high oxygen, excess flow,low water in the separator seal or unusually high or low pressures. The 20m tall flarehas a continuous pilot flame to ensure combustion of all gases and is shrouded againstthe effects of high surface winds. In the event of a blockage or failure, the gas isdiverted to the original free venting stacks. Similar technology is being promoted bythe USEPA. Widespread adoption of this technology could result in rapid reductions ingreenhouse gas emissions being achieved. Suitable incentives are now needed toencourage mining companies to install flares where utilisation is not financially feasibledue to capital costs and inadequate markets.

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6.4 USA Government R&D

Various programmes have been implemented in the USA to introduce and demonstratealternative methods for capturing and using methane from underground coal mines withthe aim of reducing greenhouse gas emissions.

The USDOE’s Coal Mine Methane Recovery and Utilisation Program (Byrer et al,2000) aims to encourage better use of a valuable energy source that would otherwise bewasted by venting to the atmosphere.

Technologies for CMM enrichment, using mine ventilation air in engines and boilersand for co-firing were included in the CMM R&D programme initiated in 1992.

As part of the October 1993 Climate Change Action Plan and its goal of reducinggreenhouse gas emissions, the USDOE and the USEPA are supporting:

• a Coalbed Methane Outreach Program

• cost shared demonstrations of innovative technologies

• projects to evaluate and apply innovative and existing technologies for capturingand using CMM.

The USDOE can provide will provide up to 50% of the R&D funds for these projects,the remainder coming from the private sector. Targets for the fiscal years 2001–2003(Byrer et al, 2000) include:

• Demonstration and evaluation of pilot scale technologies at a selected mine site.

• Demonstration CMM utilisation with fuel cells, gas turbine, internal combustionengine or other technologies.

• Commercialisation of CMM recovery and utilisation technologies.

6.5 Relevance of New Utilisation Technologies to the UK

New utilisation technologies are only of commercial interest if the use of CMM orAMM results in a distinct market advantage. Such advantages may be rare andtherefore the most common scenario is for the gas to be sold to existing industrialplants that happen to be close to the source, or for the gas to be used on-site to produceelectricity that can easily be distributed. Once emissions trading becomes established,a greater range of utilisation options may become financially attractive.

AMM production technology in the UK has the potential to supply individual smallcustomers with gas from a borehole located on their premises. While most applicationsmay involve boilers, there could be interest in the use of fuel cells and micro turbinesfor power generation.

Expansion of CMM use in the UK is likely to mainly feature power generationsatisfying mines power requirements as a first priority. Any sales of gas off site will beopportunistic. Blending of CMM and AMM sources may be feasible in some instanceswhere high fuel demands need to be satisfied and security of supply needs to beassured.

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7. CBM ACTIVITIES IN THE UK

7.1 Introduction

The UK has a long history of CMM exploitation and has seen a rapid growth in theextraction and use of AMM in the past few years. VCBM exploration started in 1992.Delays caused by CBM ownership wrangles were overcome when the gas was vestedin the Crown and incorporated in the petroleum licensing regime. Deregulation of theelectricity supply industry provided openings for small-scale power generation whichserves as the main customer for AMM.

Interest in CBM in the UK continues to grow as demonstrated by the take up of PEDLareas under the latest 9th round submissions. Interest from organisations previously notinvolved in CBM in the UK together with the successful flotation’s of Alkane Energyand StrataGas, and funding support for Octagon Energy, indicate a growing confidencefrom investors, especially in AMM projects. There is also evidence of a ready marketfor embedded electrical power generation. However, costs of connection to thenational distribution grid remain high, affecting the financial viability of smallerschemes.

The success of CMM and AMM projects in a highly competitive energy market hasdemonstrated to the energy industry and financial markets, the potential of small-scaleCBM schemes. A number of UK operators have been successful in raising funds todevelop projects. Partnerships between CBM operators and energy suppliers continueto be developed strengthening the market for the extraction and use of CBM.

Increasing importance is given by government, industry and the public into measures toreduce greenhouse gas emissions. CMM and AMM schemes can be shown to have asignificant environmental benefit in reducing greenhouse gas emissions but thesebenefits have yet to be recognised in terms of incentives.

7.2 VCBM Exploration and Potential

A theoretical analysis of UK market conditions indicated that for a 30 well fieldaverage well flows of 5,600-7000m3 d-1 may be needed for commercial viability(Creedy, 1999). To date there is no evidence that such flows can be produced from UKcoal seams due to their apparently low permeability. Strong gas and electricity pricescombined with greatly reduced drilling and completion costs could enable lower gasflows to be exploited. Economies of scale associated with the drilling of large numbersof wells could be important but the fact that average well flows in the prolific Alabamacoalfields are around 3000m3 d-1 does not bode well.

Nevertheless, Evergreen Resources (UK) are applying their considerable experiencegained in the Raton basin in the USA combined with state-of-the-art drilling andcompletion methods to evaluating the potential. Evergreen also imported its ownpurpose-built drilling rig, fracture stimulation equipment and key personnel. Thecompany views the UK as an excellent opportunity for a long-term developmentproject, recognising the time and effort needed for experimentation. Evergreen have

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completed a five-well pilot scheme near Chester and the results of testing are awaitedwith interest.

Geomet, another USA based company, are now examining the potential for VCBM inthe UK.

7.3 Exploitation of CMM

Coal mines are major emitters of greenhouse gases to the atmosphere. Methane mixedwith ventilation air is emitted from all underground mines. Currently, there are majorgas utilisation schemes at only two mines, Harworth (commissioned circa 1993) andTower (commissioned October 1999). In addition, there are boilers at three mines thatcan burn methane. Eight other collieries bring captured methane to the surface but ventmost of the gas to the atmosphere, a small proportion being consumed in boilers atthree of the mines. Three collieries vent drained gas underground.

The gas contents of the seams being worked range from 0.01-15m3 t-1. The highestspecific emission is around 75m3 t-1 but this value arises at a mine with unusual gascapture conditions.

The feasibility of new CMM projects has been studied by UK Coal Mining (formerlyRJB Mining). Four projects ranging from 2-3MWe have been proposed andconstruction of the first scheme, 3MWe has commenced. Low firedamp drainagecaptures and marginal purities for utilisation may need to be improved at some minesbefore schemes are introduced. Any improvements would, however, be beneficial tomining operations.

Estimations of current and projected mine gas use and availability can be made but theresults should be considered as indicative. In calculating gas requirements accountmust be taken of drained gas that will be vented when utilisation equipment isunavailable due to maintenance, and also because of variability in gas quality due tounderground operational activities.

The generation of 1MW electricity would require a flow of 69l s-1 methane (pure basis)assuming a net conversion efficiency of 41% at a lower heating value for methaneenriched with ethane of 35.3MJ m-3. It is important to note that to achieve an overallaverage of 1MWe output a higher gas flow would be required, the excess being ventedduring planned and unplanned plant stoppages.

Gas drained at Harworth is typically of low purity due to the drainage methods beingused and therefore probably only about 30% of the net electricity generation, say4.5MWe, is attributable to mine gas. Added to the Tower colliery scheme, the totalgeneration from mine gas in the UK is about 11MWe. Provided that the UK CoalMining schemes proceed, this capacity could be doubled in a few years time.

Total methane emissions from UK mines for the year 2000 are estimated by WardellArmstrong at 300x106m3, equivalent to about 0.2x106 tonnes methane for the year2001, assuming a coal production of 20x106 tonnes and an average specific emission of12.5m3 t-1 (ETSU, 1995). This specific emission value excludes emissions from coal intransit. Of the total gas about 35% overall in the 81% of mines with drainage may be

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capturable, ie 71x106m3. The gas used is some 3x106m3 in boilers and 24x106m3 inpower generation, leaving 44x106m3 of unused drained or potentially drainable gas.The new UK Coal projects amounting to a total of about 10MWe should consume22x106m3 leaving 22x106m3 as a target for future projects. The above estimatessuggest that currently 38% of the potentially capturable gas is used. Once theadditional UK Coal schemes are completed this could increase to 69%.

If sufficient high quality gas could be captured at Harworth colliery to meet the needsof the utilisation plant a further 21x106m3 of methane could be consumed implyingclose to 100% utilisation of potentially capturable gas. While these figures may havelarge uncertainties it is clear that the proposals of UK Coal Mining, complemented byan effort to maximise gas use at Harworth, could significantly reduce greenhouse gasemissions using established technology.

Any improvements in methane drainage performance at mines can benefit utilisation.A recently completed Health and Safety Executive (HSE) research project on EffectiveDesign and Management of Firedamp Drainage (Creedy, 2001) made recommendationswhich, if implemented, may lead to more consistent drainage captures being achievedin UK mines.

7.4 AMM Extraction

AMM schemes have to date been constructed on disused mine sites and reclamationsites using the former mine entries as the access point to extract gas from theunderground workings. The access locations have been chosen as they provide a lowresistance connection at reasonable cost. As part of the site assessment process gaspumping trials are undertaken at mine vent sites to determine the likely compositionand flow of gas that could be sustained and also to assess the degree of air leakage andhence the need for remedial sealing work.

Case studies (see Appendix 6) have been gathered from some UK sites at which AMMschemes have been developed to assist future operators avoid the engineering pitfallsand to encourage the detailed consideration of possible AMM exploitationrequirements at mine closure.

AMM is used predominantly for electrical power generation although some is suppliedfor burner tip use. Limited investigation involving drilling into abandoned workingsand old goaf areas has been carried out.

7.5 CBM Utilisation

Historically in the UK, local gas distribution grids linked to operational mines havebeen operated successfully for many years, with gas supplied to local industry. Recentschemes have focused on the generation of electrical power using gas turbines as partof a CHP scheme, and spark ignition engines. Power generated is used for on-siteconsumption and export to the grid. Gas continues to be used at mines in collieryboilers.

CBM in the UK is predominantly used in spark ignition engines for electrical powergeneration. Significant advancements in the design, management and fuel control of

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spark ignition gas engines have resulted in improved reliability and efficiency. Engineavailability of over 90% is guaranteed by manufacturers with a number of schemesoperating above this figure. All current CMM and AMM schemes using spark ignitionengines generate electrical power only and are not CHP schemes. Further use could bemade of thermal energy derived from waste heat from the generation units typicallyequating to a similar value as that generated.

All the current electrical power generation schemes have the provision of a back-upfuel supply to ensure power stations can be run continuously to minimise the paybackperiods. As more confidence develops in the long-term viability of projects otheroptions to maximise revenue for the gas used may be considered. This could involveusing the gas only during peak demand periods, peak lopping, thus generating a highrate of return for the same amount of gas used. The options to supply and use gasshould be addressed as part of any contractual arrangements.

Current CBM utilisation schemes in the UK are summarised in Table 14.

The design, management and contractual arrangements of CBM utilisation schemesgenerally involve CBM operators either supplying and selling gas to a third party user,or using the gas to generate electrical power and selling the electricity to second tiersuppliers.

Capital and maintenance costs to extract the gas and supply to a fixed flange point arethe responsibility of the CBM operator. Costs associated with its use, either direct orfor electrical power generation, are the responsibility of the user.

This difference in how CBM schemes are managed is demonstrated by examining thebusiness development strategies of two of the major PEDL holders; Alkane Energy andOctagon Energy. Alkane Energy extract and sell the gas to a third party for eitherdirect use or electrical power generation. They presently have three abandoned minegas schemes operating with three different customers. De-regulation in the energymarket has seen a number of organisations, both small independent and larger energysupply companies, become interested in local embedded generation schemes.

Octagon Energy have an exclusive agreement to sell electricity generated from theirabandoned mine gas schemes to Enron. This will involve the current Hickleton sitetogether with further sites to be developed by Octagon over the next 15 years. Enronare prepared to invest £11.5 million in Octagon’s CBM activities. Octagon also havean agreement with Deutz Energy who will supply up to 22 containerised generatingsets, each rated at 1.36MWe over a three year period starting in September 2000. Deutzwill be responsible for the complete operation and maintenance of the units for a periodof ten years. The cost for the supply of engines and maintenance is reported to be inexcess of £7.5 million.

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7.6 Future CBM Development

VCBM

There has been insufficient exploration and testing completed in the UK to determinewhether favourable VCBM reservoir conditions exist which could support commercialproduction. The outcome of current and proposed further testing by Evergreen is awaited.

CMM

UK Coal, the largest deep mine operator in the UK, is examining the possibility ofexpanding CMM utilisation at its collieries. Feasibility studies have been undertaken toimprove the use of gas captured from its working mines. Use of gas is likely to involveon-site power generation using spark ignition engines.

AMM

A number of deep mines could close within the next few years. It is anticipated that thecommercial and environmental benefits of using AMM following abandonment will berecognised and engineering measures taken on closure to maximise gas availability.Measures could involve simple water control systems to prevent parts of the minebecoming isolated and installation of pipework through well-constructed surface shaftcaps and stoppings.

The number of open mine shafts suitable for gas extraction is limited. One scheme issuccessfully recovering gas from a filled shaft but tests on filled shafts elsewhere haverevealed very low fill permeability and problems of air in-leakage at shaft seals. FutureAMM projects will involve the use of drilling techniques, including deviated boreholesfrom the surface, to access the workings. The use of such techniques will provideflexibility in terms of access to the underground workings, surface location and also gasavailability at the point of end use. Schemes will be able to be located adjacent to thecustomer. The success of large diameter boreholes connecting into workings has yet tobe demonstrated. Technology for accurately intersecting abandoned roadways withoutcausing major damage holds the key to the long-term expansion of abandoned mine gasschemes.

Details of projected CBM developments are summarised in Table 15.

Consultations with PEDL holders with CBM interests indicate that increased practicalgovernment support to the CBM industry is needed in a number of specific areas,notably planning, regulation of drilling activities and guidance where PEDL interests inadjacent areas overlap. The development and implementation of guidance, usingaccepted oil and gas industry practices of field development plans may be a wayforward on this latter point.

7.7 Regulation of CBM

The development of CBM is not solely dependent on the geology, engineering and marketconditions. In the UK CBM exploration and exploitation is permitted within a framework

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of health and safety, environmental, licensing and planning legislation. The capture ofCBM in operational mines is undertaken for safety reasons and is permitted through amethane drainage licence. The safety of gas drainage is regulated as part of theunderground mining operation in accordance with mining legislation.

The status of a methane drainage licence at mine closure is not clear especially when heldby a different party to the PEDL. Clarification is required to pre-empt any litigationwhich could be costly and also damaging to the AMM industry.

Petroleum Licensing

CBM is owned by the Crown and its exploitation is regulated by the oil and gas licensingdivision of the DTI. PEDL’s are required by operators to facilitate exploration, appraisaland development from either virgin seams or abandoned mines. Most of the majorcoalfield areas where there is a potential for CBM extraction and utilisation have beenlicensed to commercial companies. Where progress is not attempted a PEDL may bewithdrawn and released to an alternative operator.

Access to Coal Seams

The Coal Authority is the owner of the coal seams in which CBM is stored. It is alsoresponsible for the management of historic mining liabilities including abandoned mineworkings. Permission must be obtained by any enterprise wishing to drill into virginseams or abandoned mine workings. The Coal Authority also manage applications for gaspumping trials at their venting sites.

The Coal Authority has a statutory duty to encourage CBM development where it iseconomically feasible and it adopts a flexible approach to the granting of access rightsprovided arrangements can be made to protect any coal mining interests through anInteraction Agreement. Access for CBM activities will not be granted unless a PEDL hasfirst been awarded to the applicant.

Planning Consent

CBM operators require planning consent from the local authority for exploration andextraction activities. The response by local authorities to CBM planning applicationsvaries from area to area. Where permission is denied the operator can appeal but theappeal process is invariably time consuming and costly, and the outcome uncertain.Problems can often be avoided by involving the local authority and community at an earlystage of a project and ensuring that they understand the basics of the technology andworking practices proposed.

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Environmental Protection

A number of environmental issues are associated with CBM development including thedisposal of any water produced. There is an automatic assumption based on USAexperience that virgin CBM production will involve the production and disposal of largevolumes of water. Currently, there is no evidence to suggest that this will be the case inthe UK.

Options for dealing with water are obtaining a discharge consent from the EnvironmentAgency (EA), on-site treatment or disposal is not available and the option for off-sitedisposal will need to be considered. Abandoned mine workings may need to be de-watered as part of a CBM scheme. Such activity will require consultation and agreementwith the EA and the Coal Authority. Environmental considerations such as noise, visualimpact and traffic management also need to be addressed for any surface operation.

Health and Safety Regulations

The detail of health and safety regulations applied by the HSE to CBM schemes variesdepending on whether they are associated with a VCBM, CMM or AMM project. Thepresent on-shore drilling regulations applied to CBM boreholes are onerous particularlywhen compared with similar drilling operations carried out by the Coal Authority.

7.8 Barriers to Development

Commercial CBM development could be accelerated if some of the regulatory hurdleswere removed or lessened. Government recognises the difficulties and some of theissues are already being tackled. Problem areas include:

• The high cost of electrical connection of small-scale power generation to the grid isa discouragement to all forms of CBM exploitation.

• The capacity of the UK electricity distribution grid may be a limitation to small-scale power generation in some areas.

• Incentives are warranted for CMM and AMM schemes which reduce greenhousegas emissions.

• Development relies generally on relatively small operators and therefore growth isdifficult to finance.

• The climate change levy imposed on power generated by CBM schemes, but not ongas supply schemes, could inhibit exploitation of some marginal sites which wouldbe counter productive.

• The present on-shore drilling regulations designed for deep oil and gas explorationare unnecessarily onerous for CBM and could discourage VCBM exploration andalso installation of AMM boreholes. CBM wells and boreholes must comply withthe onerous requirements of HSE’s offshore drilling regulations. These regulationsare designed for deep oil and gas wells and are not appropriate for typicalunderpressured moderate depth CBM drilling. Compliance carries a high costpenalty which could result in the cessation of further virgin CBM activity anddiscourage development of AMM schemes where borehole access is required. TheCBM operators feel particularly aggrieved, as the Coal Authority is able to drill

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mine water monitoring holes under similar conditions but under a less onerousregulatory regime. Some operators are understood to be pursuing these issues withHSE.

• The pursuit of planning consents for AMM activities could be aided if officialplanning guidance recognised the environmental benefits. Draft guidance onplanning issues is available but it could benefit from updating and widerdissemination to ensure it reaches all PEDL holders and local authorities.

• The status of a methane drainage licence at mine closure is not clear especially whenheld by a different party to the PEDL. Clarification is required to pre-empt anylitigation that could be costly and also damaging to the AMM industry.

7.9 Status Summary

CBM is currently being produced from working and abandoned mines in the UK andtesting of the VCBM potential of UK coal seams is continuing. Developers of AMMschemes are particularly bullish and early signs are promising. The Association ofCoal Mine Methane Operators believe that ‘given encouragement’, the industry couldinstall as many as 20 projects a year (World Coal, 2001).

At present, most of the investment in CBM in the UK is directed at AMM schemes.Once the relatively small companies involved in this activity have established a mature,profitable business they may turn their attention to alternative CBM sources. However,for at least the next five years the development of VCBM may be sluggish unlessgovernment incentives are introduced to stimulate activity.

8. WORLDWIDE REVIEW OF CBM ACTIVITIES

8.1 Introduction

The countries or geographical areas with the largest CBM resources are the formerSoviet Union (Kazakhstan, Russia and Ukraine), China, Canada, Australia, the USA,Europe and India in order of decreasing importance.

8.2 Australia

The domestic and industrial market for gas in Australia is growing at a rate of about 3%per annum thus encouraging the exploration and extraction of CBM. VCBM isgenerally transported in natural gas distribution pipelines and CMM used for electricalpower generation.

VCBM exploration continues but the commercial viability of production schemes issometimes difficult to judge.

VCBM

VCBM development has been carried out in both New South Wales (NSW) andQueensland with relatively small commercial schemes reported in Queensland.

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Difficulties in establishing the legalities of gas ownership and access have beenaddressed at State level to ensure that CBM development is encouraged whileprotecting the safety of underground mine workers. Experiences in the USA in thePowder River basin where CBM has been produced from low gas content, highlypermeable, low rank coals has led to a re-assessment of Australian VCBM prospects.

NSW

To encourage oil and gas exploration in NSW the State government introduced‘Discovery 2000’ which has resulted in unprecedented levels of exploration.

Sydney Gas Company (SGC) commenced a 25 test well drilling program at Johndilo,near Camden, south west of Sydney, in February 1999 aided by a Federal Governmentresearch grant of up to AUS$4.13 million. On the basis of initial test results from thefirst five wells a sales agreement was reached including the provision of connection toan existing national gas distribution pipeline. Full development of the area will involvedrilling about 100 wells per year. The company is presently looking to raiseapproximately AUS$90 million to fund development of the resource to drill a total of300 wells.

Substantial work has been undertaken by the SGC on the construction of collectionpipework to deliver the gas to the distribution point. The pipeline and infrastructureconsists of three main parts; a low pressure (70-200kPa) 200mm polyethylene pipelinelinking the wells to a compressor station, a compressor station to boost outlet pressureto 1050kPa, and a 5km 200mm steel pipeline from the compressor station to thedistribution point.

15 wells have been drilled to date to varying depths with different well completiontechniques and target seams selected for stimulation. The company is researching thegas production mechanisms of the coal and geology of the area with the aim of findingareas with higher permeability and gas contents.

CBM exploration has been undertaken in the Gunnedah basin north west of Sydney.First Sourcenergy (FSG) drilled 15 wells over a 12-month period from February 1998with wells stimulated using different techniques. Wells are presently under test. CBMactivities elsewhere in the basin are ongoing. Earth Resources Australia Pty Ltd,project managers for a CBM joint venture between Australian Coalbed and PacificPower, report recent investigation drilling in the Bando Trough region to haveintersected potentially commercial gas bearing seams with gas contents of 9-12m3 t-1

and permeabilities of 34-41mD.

Other CBM exploration drilling include Pacific Power who have completed four wellsin the Gloucester Basin and the Oil Company of Australia have completed four wells inthe Clarence-Moreton Basin. Suncore also have exploration interests in the northernpart of the Basin

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Queensland

Commercial VCBM production started in the mid 1990swith sale of gas into thenational distribution pipeline reported in the south-eastern part of the Bowen Basin byboth Conoco and BHP (QGMJ, April 1997). Conoco’s VCBM operation linked some31 production wells to its Moura (15 wells) and Dawson River (16 wells) compressorstations, supplying a total of about 110,000m3 d-1. Conoco sold its VCBM interests in1998.

The BHP operation differed in that gas production came from both conventionalvertical production wells and horizontal borehole drilled in-seam (approximately1500m) from the openpit highwall with total daily production similar to the ConocoCBM scheme.

In the northern Bowen basin, CH4 Pty Ltd, a subsidiary of BHP, is evaluating guideddrilling with a three-hole test currently producing gas.

Queensland Gas Company are carrying out CBM exploration in the Walloon coalmeasures in the Surat basin. Initial results indicate that this geological formation maycontain significant coal seam gas resources. Gas flow from the Argyle No.1 well is28,320m3 d-1 with most of their other wells having significant flows. The developmentof these coals is in direct response to the success of the Powder River basin. Targetareas have been identified on basis of the following criteria:

• total coal thickness greater than 10m

• in close proximity to reported gas blowouts

• main coal seam less than 500m depth

• close to existing or planned gas pipelines

• area covered by freehold land tenure.

Exploitation of the Surat basin is proposed using techniques similar to those developedin the Powder River basin involving low cost drilling and completion techniques atshallow depth. It is anticipated that CBM development of the Walloon coal usinginexpensive drilling and completion methods together with the presence of the existingnational pipeline infrastructure in the basin will allow commercial CBM operations tobe developed within three years.

Oil Company of Australia Ltd has a joint venture partnership with Sunoco Inc ofAustralia to undertake a major exploration program to test the viability of the JurassicWalloon Coal Measures and the Permian Baralaba Coal Measures. A number of othersmaller exploration companies including Arrow Energy NL, BNG Pty Ltd andSEQOIL Pty Ltd are undertaking test drilling.

CBM exploration elsewhere in Queensland includes Santos Ltd who are undertaking anactive exploration program to the north of their Scotia field with the aim of finding asimilar geological target. Galilee Energy Ltd is undertaking a major testing program atRodney Creek in central Queensland. Additional pumping equipment is to be installedto accelerate de-watering.

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Gas production from TriStar Petroleum Company Fairview Field near Injune is sold into the Duke Energy Wallumbilla – Gladstone pipeline. Oil Company of Australia ispresently developing the Dawson Valley coal seam gas fields near Moura. Thisproduction is connected to the Wallumbilla – Gladstone pipeline. Gas from these fieldsis supplied to the Queensland Nitrate’s ammonium nitrate plant at Moura in centralQueensland.

Oil Company of Australia Limited also operates in the Woodroyd coalfield nearWandoan where pipeline and compressor station infrastructure was constructed in 2000to connect into the Wallumbilla – Brisbane pipeline supplying gas to the BP oil refineryin Brisbane.

Present VCBM production comes mainly from the Bowen Basin. In 1999 to 2000, it isestimated that gas production amounted to 160x106m3, approximately 4% of the totalgas produced in the State. About half of this gas was flared although the constructionof lateral pipelines and the expansion of the in-field gathering systems has reduced thisamount.

Rights to CBM can be awarded under either the Petroleum Act 1923 or the MineralResources Act 1989. New legislation is being developed to addresses this potentialconflict.

Gas Transport

Patterns of natural gas and VCBM supply and demand are affected by the availabilityof gas transmission lines. During the 1990sthe length of high-pressure pipeline wasdoubled to about 16,000km. Pipeline construction costs have declined with the use ofhigher-grade steels allowing use of thinner pipe walls, improved welding techniquesand better trenching methods. Some states, like NSW, have open access. Any thirdparty can transport gas at tariffs set by the regulators through a public process ofdisclosure and debate (Minfo 66, Competitive reform and new pipelines reshape gasmarket, 2000, p8).

CMM

CMM exploitation is concentrated on three mines; Appin, Tower and West Clifflocated to the south of Sydney, NSW. The first scheme was installed at West Cliff andcomprised a 12.5MWe gas turbine electrical generating set. During its first five yearsof operation the gas turbine operated at 99.6% reliability and 96.4% availability. BHPwho owned mines nearby followed up a detailed investigation in the early 1980son theoptions for using methane gas resulting in a 15MWe gas turbine installed at Appincolliery. After a breakdown of the gas turbine, tests were carried out at Appin andTower using spark ignition engines. The tests indicated that methane emissions couldbe reduced by 50% with the introduction of new utilisation technology. Power stationswere completed in 1996 at both collieries with a total capacity of 94MWe. The designincluded for the feeding of a proportion of the low methane concentration bearing mineventilation air to the engine intakes.

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Power generation at Appin is 54MWe and Tower 40MWe. In 1997 typical electricalpower generated from CMM at Appin was between 35MWe and 45MWe and between25MWe and 35MWe at Tower colliery (Garner 2000). Full generating capacity wasachieved during peak demand to meet contractual obligations using natural gas tosupplement mine gas ensuring maximum use of mine gas available.

Following a change in ownership, the nearby West Cliff colliery was linked to theAppin colliery power generation station via an overland pipe providing approximately1600l s-1 methane on average during normal longwall production. A pipelineconnection between Appin and Tower allows for surplus gas to be diverted to Tower ifrequired (Hockey 2001)

The electrical power generation schemes at BHP’s Appin and Tower colliery in NSWare often cited as prime examples of technology for maximising CMM use andminimising greenhouse gas emissions. However, future commercial ventureselsewhere are likely to be smaller to ensure optimum use of capital equipment.

Gas drainage at Central Colliery, located in Queensland’s Bowen basin, has beenpracticed since 1989 involving both pre-drainage and goaf post-drainage techniques.While options to use the gas captured by pre-drainage are under consideration, a gasflaring scheme has been introduced to reduce greenhouse gas emissions. Once autilisation scheme has been commissioned, the flare will be used to burn surplus gas.Flow rates through the flare of 1000l s-1 methane are reported with an annual flow ofsome 20x106m3 anticipated (Greenwood, Oct 1999)

Further opportunities to utilise CMM are limited to some possible small schemesmainly in NSW.

AMM

The extraction and utilisation of gas from abandoned mines is presently not undertakenin Australia. Opportunities may arise in coalfields where gassy coals such as the Bulliseam in NSW have been mined.

8.3 Canada

VCBM

Exploration is currently being pursued by more than ten Canadian companies and asimilar number of USA-based gas producers (Sinclair, 2001). Estimates of gas-in-placerange from 17x1012m3 (Canadian Potential Gas Committee) to 85x1012m3 (AlbertaResearch Council). Most of the resource lies in the west with less than 0.3x1012m3 onthe east coast.

Interest in VCBM is increasing due to:

• rising demand for natural gas and a perceived shortfall by 2012

• strong price for natural gas

• low funding and development costs generally lower than conventional natural gas

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• large resources

• success achieved in the USA.

The use of coal seams for sequestration of carbon dioxide is currently beingexperimentally investigated in Canada.

VCBM investigations in western Canada started in the mid-1970s but to dateproduction testing only appears to have been conducted in about 20 wells. Flows of20m3 d-1 were obtained from shallow, low gas content coals which has sufferedformation damage from drilling additives (Pembina area, Alberta). Two coal seams ofabout 7m net thickness were completed at a depth of 1,536m yielding 1,130m3 d-1.Current activity is commercially sensitive but no significant production has beenreported.

VCBM resources have been identified in the east, mainly in Nova Scotia. The gas-in-place according to the Geological Survey of Canada is thought to be around 56x109m3

although one operator has proposed a volume three times higher. Despite drilling in thelate 1970’s, and more recently in 1994, no commercial production has been established.

VCBM exploration and development in Alberta and British Columbia is regulated inthe same manner as natural gas. The Nova Scotia provincial government has activelypromoted CBM development by making coal seam data available, sponsoring researchand by issuing calls for Exploration and Production agreements.

A Canadian Coalbed Methane Forum was established in 1991 to collate all theavailable CBM data. Presently, there are over 50 members.

CMM

Canada produced 61.5x106 tonnes of bituminous coal and 12x106 tonnes of lignite in1999 largely from opencast mines. Underground mines in Nova Scotia drained gas inthe past but no major CMM utilisation schemes were successfully initiated. Fewunderground mines remain so the scope for mine gas utilisation is negligible. A seriesof studies were, however, undertaken to develop a catalytic oxidation device to removemethane from ventilation air. Plans for a trial at Phalen colliery in Nova Scotia wereterminated when the colliery was closed prematurely in September 1999. Nevertheless,the technology has potential world-wide application if it can be demonstratedsuccessfully at commercial scale.

AMM

Gas emission rates are reported associated with Nanaimo abandoned undergroundmines on Vancouver Island but the quoted values of 9-24m3 t-1 at 984m are probablygas contents (Sinclair, 2001). Specific emission of 250m3 t-1 from the Crowsnest fieldmines in the 1920s indicates high gas contents but occurrences of outbursts suggestspermeability may be low. The potential for recovering gas from abandoned mines,assuming they are not all flooded, does not appear to have been recognised.

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Prospects for CBM Development

Any CBM development will predominantly involve VCBM. The future of VCBMdevelopment in Canada depends on the results of current pilot trials and governmentincentives as does the viability of the process to dispose of waste carbon dioxide fromflue gas in deep coal seams and exploit the displaced methane (ECBM).

8.4 China

China is heavily dependent on coal for primary energy. Some 988Mt was mined in theyear 2000. The vast coal burn, much of which takes place within densely populatedcities, is responsible for serious air pollution levels which are no longer consideredacceptable by the Chinese government. Various international aid programmes havebeen implemented to assist China develop and implement strategies to reduce pollutionwithin cities. The European Union and China are currently undertaking a major suiteof such projects under the Liaoning Integrated Environmental Programme including aCBM project involving CMM and VCBM exploitation.

Clean fuels which can substitute for coal are currently in short supply. In the long-termthere are plans to pipe natural gas from Eastern Siberia to north-east China.Meanwhile, there is an immediate need for gas, creating opportunities for CBMexploitation.

VCBM

The estimated CBM resource in China within explored coal areas to a depth of 2000m,amounts to an estimated 30x1012m3.

CBM drilling started in the early 1980s. Little success was achieved until 1996 when apilot well field was developed by the North China Bureau of Petroleum (NCBP), withtechnical assistance from the USA, in Shanxi Province as part of a UNDP supportedproject Exploration for Deep Coalbed Methane.

The target for the development of the CBM industry in China is to produce annually 3-4x109m3 by 2005, increasing to 10x109m3 by 2010 and attaining 20x109m3 by 2015.Although over-ambitious, these projections indicate the strong commitment by China tothe large-scale development of CBM throughout the country. At present there are nocommercial virgin CBM schemes in China although there are very small-scale powergeneration plants at some demonstration sites.

By the end of 1999, 201 virgin CBM wells had been drilled in China, mostly in existingcoal-mining areas. A test well at Jincheng produced a peak flow of 16,000m3 d-1.Typical gas flows in ‘successful’ wells have ranged from 2000m3 d-1 to 5000m3 d-1.

There are currently no commercial VCBM schemes in China. Commercial exploitationof VCBM is constrained by the lack of a pipeline infrastructure in China. Majornatural gas pipeline construction projects have been initiated and there is a policy todivert them through coalfield areas where VCBM potential has been identified.

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The need for overseas assistance to accelerate VCBM development was recognised bythe government of China, and the China United Coalbed Methane Company (CUCBM)company was formed to assist foreign co-operative ventures. CUCBM is currentlyseeking to extend its exploration base and initiate agreements with foreign companiesin new areas.

CUCBM signed 11 Production Sharing contracts (PSC’s) with six foreign companiesincluding Texaco, Phillips, Arco (now BP), Lowell, Greka and Virgin between January1998 and January 2001. By the end of 2000 over US$76 million had been invested ininternational projects, 47 wells were drilled and 29 fracced. De-watering of pilot wells isprogressing at development sites with exploration drilling at others. The highest reportedflow is 700m3 d-1 (Fan, 2001) but higher flows are expected as de-watering proceeds.

Greka (USA) are planning to import equipment into China for surface to in-seamdrilling trials. CUCBM is a partner. Four project sites have been identified. The aimis to obtain commercial gas flows without the need for costly fraccing.

CMM

More than 95% of the coal mined in China comes from underground workings, some ofwhich are very gassy. Chinese mines liberate about 9x109m3 of methane annually(more than 127x106 tonnes carbon dioxide equivalent) using only about 0.5x109m3.The growth potential for CMM utilisation schemes is therefore large. Coal mines arelikely to be required to increase use of gas drainage techniques in a drive to improvesafety and to increase CMM utilisation to avoid environmental fines.

Commercial exploitation of CBM in China is currently limited to CMM drained in coalmines primarily for safety reasons. The purity of the gas typically lies in the 35-90%range depending on geology, the mining method, the drainage methods in use, gasextraction rates, practises at the mine and the prevailing meteorological conditions.The methane is invariably diluted with various proportions of air, nitrogen (de-oxygenated air) and carbon dioxide and hence the quality of CMM supplied by mines isusually much less than that of natural gas.

CMM is used in a number of cities, in which it is distributed in local pipelines, andthere is potential to expand the exploitation of this resource. Some 400x106m3 of CBMwas recorded as used in 1999. The principal use is cooking. The gas rings used arefairly tolerant of fluctuations in gas composition and pressure, as are the customers.There would be environmental advantages in also considering the use of CMM fordistrict heating in cities and as a clean fuel for industry. CHP is another possibleapplication.

Drainage of gas in underground coal mines has been practised in China since the 1950s.By 1996 there were some 120 coal mines with established gas drainage systems, and in1995 about 600x106m3 of gas was drained in state-run mines. Some 20 mines wereoperating in 1992 with absolute methane emission rates of 50m3 min-1 or higher, themost gassy being Laohutai mine at Fushun with an emission rate of almost 223m3 min-

1.

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In 1982, utilisation of underground gas was included in the state investment programmefor capital construction of energy conservation projects. By the end of 1993, more than50 gas utilisation schemes had been introduced. Projects have involved supplying minegas to household consumers, industrial concerns and gas-fired power generationschemes. These utilisation schemes included a mine gas distribution system in Fushuncity which is still operating successfully. However, not all the schemes have beensustained. For example, a mine gas-fired 1.5MWe power generation plant was installedat the Laohutai mine in Fushun. It operated for about six years, burning gas in summerwhen there was a surplus, until a gear broke and attempts to machine a replacementfailed.

Attempts have been made to introduce advanced underground drilling equipment fromAustralia and the USA, to enhance methane drainage but it has either been unsuited togeological conditions in China, or too costly to maintain. Hence the expected benefitsof introducing new CBM technologies have not always been realised. Pipelinetransmission schemes seem to be currently preferred in China rather than on-site powergeneration at coal mines.

Future CMM developments

Should the World Bank prototype carbon fund prove successful, this proposed mutualfund for greenhouse gas reductions could mobilise capital in favour of CMM schemes,or dual CMM-VCBM schemes.

There is considerable scope for increasing gas availability and quality from coal mines.Few mines are connected to pipeline networks, monitoring and control of surface minegas distribution is generally fairly primitive and gas capture could probably beenhanced at most mines. A few mines have modern underground drilling equipmentbut investment in similar equipment is needed at other mines. Computerisedmonitoring and control systems are needed to regulate CMM extraction, collection,storage and delivery.

AMM

Financial constraints and a need to reduce explosion risk has focused the attention ofmining enterprises on safety benefits of gas capture in working mines so abandonedmines have received little attention as a gas resource. A UK-China CBM technologytransfer project, supported by the UK DTI, drew the attention of China to thecommercial potential of gas from abandoned mines. Subsequently, a further UK-Chinacollaborative project was initiated to concentrate on this issue.

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Current Status of CBM Development

Commercial co-operation arrangements

The following means of co-operation are available for CBM projects:

• Production sharing contracts as used by CUCBM Co.Ltd and foreign partiesinvolved with VCBM exploration and development. The Chinese contributionsamount to 30-51% of the development costs.

• Joint venture can involve two or more beneficiaries jointly financing a project.

• China-foreign joint ventures are fairly rare for CBM related projects.

• Equipment lease is a new approach whereby the supplier leases the equipment tothe customer and then recovers their investment from the project proceeds.Jincheng and Huainan CMM power generation projects are attempting this route.

Overseas assistance to CBM development

The Asian Development Bank, United Nations (UN), UN-Global Environment Facility(GEF), Asia-Pacific Economic Cooperation (APEC) and the Japanese ‘Green Fund’ havesponsored a range of CBM projects, mostly CMM. Technical assistance, training andequipment for VCBM and CMM projects have been supplied to China, mainly from theUSA, through various United Nations Development Programme (UNDP) projectsstarting in 1992.

VCBM and CMM demonstration projects have not been widely replicated, even whentechnically successful, because remoteness of markets has precluded commercialdevelopment.

A project to encourage coal mine methane market development started in October 1999aided by the USEPA. Eight coal mine areas were identified for market study.

Incentives and barriers to CBM development

Coal mining enterprises are encouraged to develop CBM resources. Foreign co-operative projects are favoured by preferential policies and tax incentives. Despitethese, VCBM is still not advancing at a rate which will enable the proposed productiontargets to be met. The principal barriers are:

• Lack of infrastructure to transport the gas to market.

• Lack of mature gas markets.

• Potentially long delays between obtaining exploration rights and production rights.

• Many schemes too small to attract international investors.

• High development costs and long, uncertain lead times.

• Uncertainties in licensing and permitting CBM activities especially outside existingmining areas.

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It is possible that any CBM developments in the western parts of China may attractadditional benefits under the ‘go west’ policy.

8.5 Europe (Geographical)

Czech Republic

The Czech Republic has a long history of coal mining. The company OKD DPBPASKOV Inc., a coalfield service company, is involved in AMM production, gasdrainage of CBM from strata reservoirs and CMM production in working mines. Gasis distributed to consumers through a 200km-pipeline network. Almost all drainedCMM and AMM is used. There are, however, problems of uncontrolled emissions ofAMM into the ground and surface structures in the Ostrava region.

France and Germany

Attempts have been made to produce commercial gas flows from VCBM wells in thesecountries. Testing in the Saar was terminated in 1999 due to low gas flows andindicated seam permeabilities of 0.01-0.001mD.

Several CMM schemes are operational at remaining working mines. Both thesecountries are exploiting AMM with the largest growth expected in Germany due to theinclusion of AMM as a ‘renewable’.

Netherlands

The Netherlands are underlain by Carboniferous measures with thin coals containing anestimated 0.8x1012m3 of VCBM to a depth of 2000m. All coal mining has ceased. TheDutch government are keen to find cost-effective means of reducing industrialemissions of carbon dioxide. The feasibility of combining carbon dioxide sequestrationwith VCBM production is therefore being investigated. Much of this work is beingundertaken through EU R&D programmes.

Poland

VCBM exploration has been undertaken but limited results indicate that developmentcould be constrained by the apparently low permeability coals.

CMM is used for mine site power generation, for powering mine cooling and at ademonstration desalination plant. The coal industry is being re-structured and theremay be opportunities for AMM developments especially where there are concernsabout uncontrolled surface emissions from closed mines.

8.6 Former Soviet Union

While it is likely that some of the major coalfields of the Former Soviet Union mayhave technical potential for VCBM, the principal interest appears to be in the captureand use of CMM. Resource statistics sometimes differ from reference to reference andeven within the same reference. Information is often patchy and its reliabilitydependent on the quality of translations.

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Kazakhstan

Existing energy supply and infrastructure is unable to meet industrial demands,providing an opportunity for CBM projects located close to users. No commercialVCBM production has been achieved.

The bulk of the CBM resources are concentrated in three coal basins lying withindensely populated areas.

Current areas of VCBM exploration include the Karaganda, Tentek, Saranskiy,Sherubaynurinskiy and Ekibastuz coal basins.

Exploration and research was carried out on blocks within the Karaganda basin that hadthe best CBM potential. This included a geophysical survey, 14 test wells andevaluation of gas reservoir assessment techniques. The exploration work (Stoupak,2001) identified the following key factors:

• Coal permeability increases in the vicinity of geological faults.

• Anticline structures with amplitudes greater than 6m form gas traps.

• Low permeability seals are formed by natural clays and mudstones greater than 1mthick.

• Seismic data can be used to detect favourable CBM areas.

• Gas content below 10m3 t-1 were not considered in the resources estimate.

• Target coal seams lie at depths between 700-1500m.

Russia

CMM from working mines is the CBM source of current interest.

Historically there has been little incentive to use CBM. However, political andenvironmental changes over the past 10 or so years have seen a change in attitudewhere by the use of CMM is seen as a method of improving mine profitability withimproved methane capture benefiting mine safety and providing an alternative cleanfuel. Inadequate drilling and utilisation equipment are now hampering development(Ruban, 2000; Burrell and Kershaw, 2000).

One of the main coal mining regions in Russia is the Kuzbass area where, in 1994,there were 76 mines producing some 58x106 tonnes of coal. These mines releasedmore than 1x109m3 of gas with some 860x106m3 vented with the mine ventilation air.196x106m3 of gas was captured but only a small amount was utilised. The number ofmines using methane drainage has reduced from 26 in 1995 to 17 in 1998. Thisreduction is mirrored elsewhere in Russia where only 30 mines are reported to drainmethane although a larger percentage of captured gas is used. Uses of CMM includeheating mines facilities, metallurgical processing and electrical power generation.

CMM is pre- and post-drained using various surface boreholes and undergroundhorizontal and cross measures boreholes.

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A pilot AMM utilisation scheme is presently been undertaken. The experiment at theChertinskaya mine in the Kuzbass uses gas drained from 16 surface boreholes (30mspacing) connected to a 420mm diameter, 3km pipeline. Gas flow from the regulatedboreholes is typically 200l s-1 at a purity of 60%. It is reported that two generatingengines are operating on mines gas producing 1.2MWe (Burrell and Kershaw, 2000). Itis interesting to note the contrasting performance of the two generating sets. The1MWe Caterpillar unit used 80l s-1 while the 200kWe Russia unit used 50l s-1.

Ukraine

The Ukrainian government has established the Alternative Fuels Centre (AFC) to assistthe exploitation and utilisation of CBM. Government re-organisation has seen themerger of three former Ministries; coal, oil and gas and electricity to form the Ministryof Fuel and Energy. It is hoped this will provide a cohesive approach to future energypolicy, including CBM.

The Ukraine has significant VCBM, CMM and AMM potential. Some of the mostgassy coal mines in the world are found in Ukraine, particularly in the Donetsk basin.

Development of VCBM in the Ukraine is at present restricted by the lack of suitabledemonstration of commercial viability.

EuroGas in partnership with the Ukrainian state-owned company ZahidUkrGeologiacompleted drilling the first VCBM well in January 2000 to a total depth of 830m in theVolyn coalfield (a 150 km2 concession) in western Ukraine adjacent to the Polishborder. Gas flows from both coal seams and sandstones were indicated. Depending onthe outcome, two further wells were planned.

Two CBM schemes, presumably CMM, are under development designed to usetechnology from BCCK Engineering in the USA to clean up the gas. Each methanetreatment plant will have a capacity of up to 100x106m3 per annum.

There are two main coal basins the Donetsk and L’vov-Volyn basin. In 2000 the totalmethane emissions from Ukrainian coalmines exceeded 1.8x109m3 with only260x106m3 drained, of which some 62x106m3 was used, ie 4% of total gas emissions(Kasianov, 2001). CMM is currently drained at 42 mines. Gas drainage uses both preand post methods involving surface and underground boreholes.

Gas reservoir characteristics in the Donetsk basin differ from elsewhere in thatsignificant gas is contained within the surrounding porous sandstones that are inter-bedded with the coal seams combining the characteristic of both a coal reservoir and anatural gas reservoir. It is estimated that the gas retained within the coal accounts foronly 15% of the total gas in the surrounding strata.

More than 120 boreholes have been drilled to depths of 260-1200m into different coalseams with 52 holes stimulated to increase gas flow. The maximum daily flowreported is 2600m3 prior to mining (virgin conditions) although daily gas flows of10,000m3 have been recorded when the borehole intersects gassy sandstone horizons.Undermining of surface gas drainage boreholes can increase the daily flow to

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48,000m3. The best holes can produce between 5-8x106m3 of gas and in someinstances, eg, at the Yuzhnodonbasskaya mine over 16x106m3 of gas in five years(Konarev, 2000). These results indicate that flows of up to 15,000m3 d-1 may beattainable from VCBM wells in the Donbas region.

Drained gas is used in mine boilers, as an alternative fuel for vehicles. Research is ongoing into the use of CBM for gas turbines and metallurgical processes. The primaryuses for CBM are likely to be gas distribution and electrical power generation.

8.7 India

Compared with the major coal mining countries, India has relatively modest CBMresources. Nevertheless, the government of India considers VCBM and CMM as apotentially important clean energy source. As within many countries ownership,exploration and extraction of CBM in India does not fall under one regulatory body.While the responsibility for future energy needs, including CBM, falls under theMinistry of Petroleum and Natural Gas CBM where coal mining activities are takingplace responsibility falls under Coal India Ltd (CIL) and the Ministry of Coal.

VCBM

Geological appraisal has identified about 20,000km2 of coalfield areas with a VCBMpotential in which recoverable gas reserves are estimated at 800x109m3 . Thebituminous coal basins with VCBM potential are: Damodar-Rajmahal in West Bengaland Bihar, Sone-Mahanadi, and Narmanda-Pranhita-Godavari in Madhya Pradesh,Orissa, Andhra Pradesh, and Maharashtra. Tertiary lignite-bituminous coal basins withCBM potential include Cambay in Gujarat, Barmer in Rajasthan and Cauvery in TamilNadu.

In 1999 the Oil and Natural Gas Corporation (ONGC) drilled a test well at Jharia inBihar and two wells in the Durgapur-Ranigunj area. Coal India Ltd (CIL) has alsoshown interest in CBM exploration and discussion have taken place with ONGC aboutpossible co-operation in CBM exploration. Interest has also been shown by theMinistry of Petroleum and Natural gas who has sought assistance from CIL inidentifying coal blocks for CBM exploration.

The Central Mining Research Institute (CMRI) has investigated virgin blocks in theJharia, Raniganj and East Bokaro coalfields (Sharma and Singh, 2000). Seam gascontents measured in the Jharia coalfield blocks ranged from 8-15m3 t-1, from 6-7.6m3 t-1 in Raniganj and 5-8m3 t-1 in parts of the East Bokaro coalfield. Great Eastern EnergyCorporation Ltd drilled two cored exploration holes at Surajnagar and Poradiha in theRaniganj coalfield and found gas contents of less than 3m3 t-1 to about 500m andincreases up to 8.3m3 t-1 at greater depths in the former well. Gas flows were reportedinto the wells indicating the possibility of high permeability at some horizons.

The Indian government proposes to allow bids including those from foreign companiesfor the exploration and exploitation of VCBM. Some companies from India and theUSA, Amoco (BP), Wayburn and Cardinal Resources, have already carried outexploration.

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The Directorate general of Hydrocarbons, Ministry of Petroleum and Natural Gas isresponsible for establishing the policy framework for VCBM development in India andhas evolved a model contract to facilitate global bidding. Exploration will be licensedunder a concession agreement, different from the production sharing contract approachused in China. The government offers tax breaks, freedom to sell the gas andprovisions for 100% cost recovery. A royalty will be paid on produced gas.

Notices inviting offers for CBM exploration and production for seven blocks have beenannounced by the government of India: two in Jharkhand, three in Madhya Pradesh,one in Rajasthan and one in West Bengal. Coal ranks from lignite to medium volatileare included, with gas contents ranging from 1.5-10.5m3 t-1 in the various prospects.Unfortunately, there is no indication of what proportion of the gas consists of methaneat the various localities.

CMM

Most underground coal mines (90%) use room-and-pillar methods of extraction. Gasdrainage will therefore mainly involve pre-drainage of the worked seam although theremay be a possibility of establishing post drainage where pillar recovery is practised.

CIL through the Central Mine Planning and Design Institute (CMPDI) in associationwith the UNDP and GEF are involved in a US$15 million demonstration project onCMM recovery and utilisation. The aim of the project is to demonstrate thecommercial feasibility of using CMM extracted during coal mining for powergeneration and as an alternative fuel for vehicles. Lack of technical know-how in Indiais considered a barrier to effective use of CMM.

It is anticipated that the project will encourage the adoption of drilling technology andworking practices to drain and use methane more effectively. Two mines, Moonidihand Sudamdih in the Jharia coalfield will be involved.

The project will include training and education of all levels within the Industry fromgovernment to research organisations and the founding of a CBM clearing house tofacilitate interaction with potential foreign investors.

Preliminary Assessment of CBM Potential

It is likely that forthcoming exploration will identify some technically promisingVCBM sites. However, the market position will require careful examination. CMMdevelopment under UNIDO involves the introduction of USA technology some ofwhich may prove to be inappropriate for Indian mining conditions and culture. Thepotential for AMM has yet to be assessed.

India has a shortfall in energy supply but CBM is only likely to be able to make amodest contribution at best. India can be a difficult market for foreign investors. Thepower sector suffers from electricity theft and payment from revenue to a project canbe fraught, as Enron have learnt to their cost.

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8.8 Southern Africa

South Africa has extensive coal resources but gas contents are generally low. Otherthan in fault zones and near igneous intrusions, coal seam permeability appears to below. No significant VCBM prospects have been reported. Shallow, mostly room-and-pillar workings offer little prospect of CMM or AMM development.

Geological conditions in Zimbabwe may be more favourable for VCBM and sometesting has been undertaken. Development is hindered by poor market and economicconditions.

8.9 United States

CBM in the US accounts for about 7% of the domestic natural gas production. A risein natural gas consumption in excess of 50% is forecasted over the next 15 years. CBMis expected to contribute to meeting this increase in demand. VCBM is seen as asignificant resource with its wide geographic dispersion and relatively lowdevelopment costs compared with natural gas.

The Potential Gas Committee (1999) estimated the total recoverable CBM resources ofthe USA as 141.422 trillion ft3, about 16% of the total natural gas resource. The CBMresource was subdivided thus:

• Probable 14,369 billion ft3

• Possible 43,467 billion ft3

• Speculative 83,586 billion ft3

Gas prices are strong, rising from US$1.5 per million cubic feet (Mcf-1) (aboutUS$0.05 per m3) in April 1999 to a peak of over US$10 in January 2001 falling back toUS$5 Mcf-1 (US$0.18 per m3) in April 2001. The present figure of US$5 is consideredby the industry to be sustainable in the short and medium term.

VCBM

CBM production has risen from 5660x106m3 in 1990 to over 34,000x106m3 in 1998(World Coal, March 2000) as the number of producing basins has expanded from theSan Juan and Black Warrior basins to a total of eight major areas (Table 16). Over8000 CBM wells are now in production. The contrasting properties of these areas canbe compared in Table 17.

Independent producers have played a key role in the expansion of VCBM into newareas, some of which were originally considered non viable on the basis of San Juanand Black Warrior experience. The support of Section 29 tax credits was not alwaysavailable necessitating the introduction of new techniques to reduce costs and improveperformance including coil tube fraccing completion techniques and guided in seamdrilling from the surface.

Alternative drilling techniques using guided boreholes to drill in-seam has beenidentified as having significant potential in the US for both VCBM wells and CMMdrainage needed for safe coal production. Guided drilling may allow coals to be

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exploited where surface access is restricted and also at depths where existing coalstimulation techniques may not be appropriate. CONSOL, one of the leading CBM andCMM operators is planning a number of test holes in 2001.

Water disposal

Water disposal from VCBM extraction in the USA is becoming increasingly difficult insome areas forcing CBM operators to look at a range of disposal options including:

• disposal to land

• injection wells

• off-site disposal

• evaporation

• specialist disposal.

Water disposal to land is the lowest cost and hence the preferred option. This ispractised where water quality is of a drinking water standard. For more difficultsituations a new generation of down-well injection pump has been devised which caninject water produced at the coal horizon into a selected disposal horizon in the samewell without bringing the water to the surface. Saline water can be used for dustcontrol on unpaved roads and for construction purposes (concrete additive) andhighway construction. This is particularly attractive to VCBM sites in remote miningareas where there is little infrastructure.

Powder River basin

The development of VCBM in the Powder River basin (Wyoming and Montana) hasbeen remarkable for its rapidity and also due to the fact that the basin had previouslybeen discounted because of low seam gas contents and low coal rank. Successfulexploitation has led to a re-evaluation of other coal basins previously consideredunsuitable.

The Powder River basin has a relatively simple geological structure. Coal seams, somein excess of 10m thick, are found at depths from 50m to 760m. As in parts of the SanJuan basin, a substantial proportion of the gas may be biogenic in origin.

The shallow depth of the coal enables small rigs to be employed. Simple open holecompletion methods are used. Depending on depth, typical well costs range fromUS$60,000 to US$120,000. Well completion involves setting the casing above thetarget coal seam and then under reaming the coal to increase surface contact area. Atpresent only one seam is targeted at a time due to concerns about controlling watermigration between different horizons.

The coal has a relatively low gas content but permeability can be as high as one Darcy.This high permeability means the coal has a high water content but once de-wateredgas recovery of up to 80% is anticipated. A high porosity also means that conventionalgas content measurement methods are not appropriate.

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After the initial de-watering, production wells produce on average some 4500m3 d-1 ofgas and 75m3 d-1 of water.

In April 2000 monthly production from 1657 wells was 300x106m3 with some 1000shut in wells awaiting pipeline connection. Production for the whole of 2000 wasprojected at 3800x106m3. Production in the first quarter of 2000 has increased by some50% with the number of production wells increasing by 60%. At present there are 72drilling rigs working in this area.

VCBM development of the Powder River basin has involved dealing with thefollowing issues:

• the need to develop pipeline infrastructure with sufficient capacity

• the environmental and practical logistics of drilling 5000 plus VCBM wells perannum

• disposal of large volumes of produced water

• access rights.

Most water discharged from CBM wells meets drinking water standards and iscurrently discharged at the surface into surface drains or into ponds where it can seepback into the ground or evaporate. Where water quality is poor an alternative disposaloption is needed. Water management is a critical element and co-operation andconsultation is encouraged between the VCBM operator and landowner to minimiseany problems.

In much of Wyoming the surface owner does not own the mineral rights. In 1999 theUS Supreme Court ruled that the oil and gas estates rather than the coal estate ownedthe CBM rights with the mineral owner having the rights of access to the mineralsubject to paying the surface owner compensation.

Raton basin

Evergreen Resources Inc have been at the fore of VCBM extraction in the Raton basin.Some 575 wells are in production at depths from 180m to 400m. Interchange ofexperience between their Raton basin and UK developments has led to the introductionof technologies appropriate to specific site conditions and recognising the need tocontrol costs and quality.

The use of coil tubing allows selective coal horizons to be targeted. For instance, a0.5m thick coal seam may be a good producer if the surrounding strata is suitable andgas content favourable.

The Raton basin is fairly remote and therefore the pipeline compressors consume about7.5% of the gas production.

Water disposal has been an issue in the Raton basin as elsewhere with 90% of the waterof drinking water standard and can be disposed of to land. The remaining 10% isdiluted with cleaned water. Typically wells produce 12 times less water than those ofthe Powder River basin.

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Future VCBM Prospects

Nelson and Pratt (2001), reflecting on recent experiences in the USA, state that lowrank, low gas content and depths greater than 4,500ft (1,372m) should no longer beconsidered inherently limiting factors. Bulk permeability is the inherent limitation tocommercial production. They conclude with the following: “Operators face numerousdata acquisition and analysis challenges when evaluating the resource, production andreserve potential of coalbed reservoirs. …….. Many commonly used coalbed reservoirproperty measurement and rule-of-thumb analysis practices are now known to havesignificant shortcomings. An important lesson learned from past experience is thatthere may be significant reserve growth in many producing coalbed reservoirs, andthat numerous coalbed reservoir prospects previously considered uneconomic mayactually hold significant commercial development potential.”

CMM

Methane drainage methods in the US typically involve a combination of pre-drainageof coal in advance of mining (from surface or underground in-seam boreholes) and postdrainage using goaf boreholes drilled from the surface above longwall coal productionpanels. Relatively shallow working and few surface access limitations allow thesemethods to be used.

Pre-drainage from the surface is achieved either from conventionally fracced VCBMwells or from in-seam drilling deviated from vertical wells. The latter methodincorporates guided drilling techniques from the oil and gas industry to allow theborehole to intersect and then follow the seam thus providing a larger surface area ofcontact with the coal over an extended area. No fraccing is necessary.

A combination of surface and underground drilling techniques have been used at thefour gassy Jim Walters Resources mines in the Black Warrior basin. The strategyinvolves using a combination of both pre and post drainage techniques including, predrainage surface wells, in seam boreholes drilled across the coal panel. The boreholesare drilled from the return roadway at intervals of about 75m to within 30m of theintake roadway. A slotted plastic is inserted within the borehole to minimise the risk ofborehole collapse. A typical hole can produce 35l s-1 when first drilled (Moloney,March 2001). Surface gob wells are drilled to about 5-10m above the coal seam, as thelongwall passes gas is released and captured by the gob well.

Target Drilling, formerly AMT Drilling International, are one of the leading exponentsof guided underground drilling. Using state of the art DDM MECCA (downhole drillmonitor utilising modular electronically connected cable assembly) equipmentproviding real time positional data they have drilled nearly 250,000m (Table 18) ofdrainage boreholes. Target have drilled 33 guided boreholes greater than 1219m, thelongest being 1537m.

The guided drilling technology provides borehole navigational data, including azimuth,pitch, elevation and orientation from the collar. Typically, information is relayed to thecontrol box in less than five seconds. The information is used to steer the downholemotor assembly by adjusting the trajectory of the bent sub drill bit. Borehole position

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is usually checked and refined ever drill rod or 3m interval. This system of guidedinseam drilling has successfully been demonstrated throughout the USA.

AMM

Initial reports of gas availability from abandoned mines indicate that the potential forgas capture and use is low with generating capacity lying in the range of 1–3MW fromthe gassiest abandoned mine (World Coal, June 2000).

Gas Utilisation

Coal companies are starting to look at revenue from gas sales as part of their businessplan, eg, as an energy company rather than a coal producer. Technology has beendeveloped to raise the quality of CMM to pipeline quality by removing nitrogen,carbon dioxide, oxygen and other gases. This allows advantage to be taken of the well-developed pipeline infrastructure.

Gas emissions from operational mines are a significant contributor to greenhouse gasemissions. CMM utilisation schemes are viewed as the primary means of reducingemissions. The USEPA is encouraging the development and introduction oftechnologies to further reduce emissions by removing methane from ventilation air andalso by flaring drained CMM where the use of the gas is impracticable. There are anumber of barriers to such a move with safety being the priority.

Technology is being developed for improving the quality of natural gas by reducing thenitrogen content that may also have applications for VCBM and CMM. A new‘Molecular Gate’ technology separates gases at the molecular scale using a titaniumsilicate sieve. The system is incorporated in an adsorbent bed as part of a PSA unit thatoperates at a lower pressure than conventional systems. The system removes carbondioxide and oxygen when present in the feed gas, as well as nitrogen.

Another technology to improve gas quality involves cryogenics. Cryogenic plantstypically require feed rates of over 3000l s-1 to be economically competitive. Even atthese high flow rates treatment costs are $0.035 m-3.

Small power generation sets, as low as 75kW, have been developed to exploit CMM atsites producing small quantities of gas especially when remote from pipelines.Alternative options include using the gas as a supplementary fuel for industrial andutility boilers. CMM can be co-fired with conventional fuel sources (coal, oil, gas) inexisting combustion units offering benefits not only in the quantity of base fuel usedbut also in reducing emissions of oxides of nitrogen and sulphur. It is not clear howmuch use is made of this technology which is being developed mainly under variousUS government R&D programmes.

CONSOL Energy and Allegheny Energy have formed a joint venture to install two44MW General Electric gas turbine powered generators at CONSOL’s Buchanon minein Virginia. This will be the largest CMM power project in the USA.

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8.10 Comparisons of CBM Production and Use Worldwide

The source of CBM production varies significantly from country to country. In theUSA 96% of the production is from virgin seams, about 3.5% from CMM and thebalance from AMM. The proportion attributable to VCBM production in Australia isuncertain, a value of 50% is suggested pending further investigation, the remainderbeing CMM. In China 100% of the CBM used comes from working mines. CBMproduction in the UK is shared between CMM (23%) and AMM (77%).

The types of CBM in commercial use in the various countries are shown in Table 19.

9. FUTURE R&D NEEDS FOR THE UK

Research in selected areas could enable more and better use to be made of the UK’sCBM resources.

VCBM Drilling Technology

Surface to in-seam drilling offers an alternative to conventional VCBM productionfrom a vertical well with fracced completion. Proponents of this technology suggest itcould facilitate commercial gas production from ‘tight’ coal seams as well as reducingsurface drilling location constraints. The applicability of this technology to UKconditions should be evaluated. A demonstration by a specialist contractor is required.

CMM Drilling Technology

The potential application of surface to in-seam drilling to CMM drainage should beexamined in conjunction with the above VCBM appraisal.

Guided drilling technology could enable gains to be made in underground CMMcapture. Research in this area should be concentrated on improving the design andsupport of guided longholes to facilitate drilling in soft material and disturbed ground.

AMM Exploitation

Any research programme should reflect the current interest in AMM and be aimed atensuring accurate quantification and maximum exploitation of this resource.

There is a large body of data relating to abandoned mines including geology, plans andminewater recovery which if processed in detail could provide an indication of themagnitude, distribution and accessibility of the UK’s AMM resources.

Prime sites for AMM are being targeted first by developers. Later developments maybecome more difficult. An understanding of the characteristics of abandoned mine gasreservoirs and methods for enhancing gas production need to be developed to ensureoptimum exploitation of this finite energy resource.

Abandoned coal mines with no surface connections other than the access shafts anddrifts could be candidates for sequestration of carbon dioxide. The feasibility should be

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examined of using this process to enhance methane recovery as the carbon dioxide willdisplace adsorbed gas from the coal.

Enhancing VCBM and AMM Production

The feasibility of developing biotechnological methods for enhancing CBMproducibility and content in both virgin seams and abandoned mines should beexamined.

Improving Energy Recovery

About half of the energy produced in most small-scale CMM and AMM powergeneration schemes is dissipated as waste heat. Research is needed to identifytechnologies for harnessing this thermal energy.

10. MARKET OPPORTUNITIES

10.1 Introduction

There is a substantial repository of knowledge on CBM in the UK that could be used topromote commercial activities worldwide. In particular, there are opportunities forinvestment in customer-focused AMM projects in the UK and also for transfer of thetechnology overseas. Future UK developments have been considered in Section 7.This Section examines overseas prospects.

Although overseas operators have sought involvement in CBM developments in theUK, there is little evidence of UK operators pursuing projects in other developedcountries. However, this is probably because of the small size of these companies andthe need to concentrate growth in the UK to establish a sustainable business.

CBM projects in developing countries require financial services, project management,design, construction and equipment supply. VCBM exploration and development tendsto be the preserve of major international oil and gas companies. CMM and AMMschemes are lower risk ventures which are beginning to attract some interest fromSME’s. Possible reasons for seeking involvement in CBM projects in these countriesare:

• To take advantage of incentives for foreign investors.

• To establish a presence in the development of domestic and industrial gas markets.

• A relatively low cost means of entering and studying the potential CBM and naturalgas markets.

• Possible future opportunities to benefit from carbon emissions trading.

• Exploit opportunities to improve performances of existing schemes with modestinvestments.

• Promote equipment sales (eg underground drilling, monitoring and control systems,power generation plant).

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Initial involvement could be considered as a ‘foot-in-the-door’ of an economy in whichconsumer demand is expected to grow. Rewards could be higher in the long-term if asuitable and progressive joint venture partner can be identified.

10.2 China and the Former Soviet Union

Table 20 shows the magnitude of worldwide CBM resources, indicating the importanceof the former Soviet Union and China as markets for VCBM, CMM and AMMproduction and utilisation technologies.

Table 21 shows the large coal mine methane emissions in China, Russia and theUkraine of which only a small proportion is currently utilised.

In terms of production technologies, CMM projects involve substantially higher capitalexpenditure than VCBM and AMM schemes due to the underground element additionalto surface installations (eg drilling machines, power packs, monitoring and controlsystems). Preliminary estimates suggest a market for CMM plant and equipment of£200 million in China and £60 million in the Former Soviet Union, assuming a 20%market share. Maintenance, spares, design, financial and consultancy services couldsubstantially increase these figures. Technological advancements enabling increasedgas capture and use could further increase these figures.

There are too few data currently available to assess possible AMM related exportbusiness with any degree of certainty but a first order estimate would perhaps be £100million in China and £30 million in the Former Soviet Union. A current DTI sponsoredtechnology transfer project should assist in quantifying AMM potential in China.

There are opportunities for joint venture partners to become involved in VCBM, CMMand hybrid (CMM, VCBM) schemes in China. Where the cost of constructing longpipelines has been included in projects, returns on investment are not particularlyattractive. However, where gas transport facilities are already in place, CBMproduction schemes could be promising.

10.3 India

The government of India is seeking to establish a CBM industry involving both VCBMand CMM activities. World Bank funds are in place to initiate this process but with astrong USA influence. Nevertheless, it is likely that there will be plant and equipmentrequirements that could be met by UK suppliers already established in India. Moreresearch on the market for CBM and its likely availability is needed before the fullbusiness potential can be evaluated.

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10.4 General

CBM projects can be relatively small and there could be many coalfields in differentparts of the world, not necessarily restricted to the major coal mining countries, with acombination of market and technical factors favourable to modest VCBM, CMM orAMM projects. Identification of these will probably be largely opportunistic.

11. CONCLUSIONS

The production of VCBM is proving difficult in the UK but the results of applyingstate-of-the-art conventional technology are still being assessed.

The importance of pipeline infrastructure, and the cost of establishing it, is generallyunderstated when assessing VCBM potential in developing countries. For this reason,VCBM development invariably fails to match expectations.

Many countries have found that VCBM approaches developed in the USA are notalways appropriate. It is now widely recognised that CBM development needs to becountry and coalfield specific. The relative importance of VCBM, CMM and AMMvaries from country to country.

Gas content and coal rank are not always reliable indicators of VCBM potential. Gasin substantial quantities has been produced from coal of rank from sub-bituminous toanthracite and from seams containing from 1m3 t-1 to more than 20m3 t-1. Highpermeability can compensate for low gas content. Preserved fracture permeability isthe key for producing CBM from bituminous and anthracite coals and this depends onthe structural history of a coalfield.

CMM schemes are being encouraged in the developing countries to reduce greenhousegas emissions from coal mining. Substantial investment in underground and surfaceequipment will be required presenting export opportunities for UK manufacturers andsuppliers.

In the UK, AMM may be the most important CBM energy source but CMM could be apotentially more serious emitter of greenhouse gases. Detailed, independent AMM andCMM emission, resource and reserve assessments would provide a basis fordetermining the optimum environmental and energy strategy.

Europe, and the UK in particular, leads the world in AMM production closely followedby the USA. There may be opportunities for introducing AMM technology intodeveloping countries with large coal mining industries such as China and the formerSoviet Union

CBM technologies are being developed in Australia and North America with emphasison new drilling technologies and utilisation options. Technologies for using methane inventilation air are receiving attention in the USA and developments are being pursuedin Australia, Canada and Sweden. Activities in the UK have been mainly aimed atoptimising VCBM drilling and completion techniques, and AMM exploitation.

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Recent innovations include:

• Optimising recovery of VCBM using clean drilling techniques.

• Application of surface to in-seam drilling techniques to VCBM production.

• Use of coiled tubing techniques for hydrofraccing.

• Reduction of greenhouse gas emissions from working mines by flaring CMM.

• Development of practical units for removing and using low concentrations ofmethane in mine ventilation air.

• Modularised AMM production systems.

• Casing while drilling through old workings to install AMM exploration andproduction boreholes.

• On-site power generation using CBM in micro-turbines and fuel cells.

12. ACKNOWLEDGEMENTS

The authors acknowledge the UK Department of Trade and Industry for its financialsupport of this review. The authors are also grateful to the many companies andindividuals who contributed to the technology survey and provided information on theirCBM activities.

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Table 1: Comparisons of CBM sources

Source Advantages Disadvantages

Virgin CBMsurface wells(VCBM)

• Consistently high gas purityobtainable.

• Operations independent of coalmining activities.

• Gas captured prior to miningcould improve mine safety.

• High turndown capability withno environmental emission risk.

• Initial drilling and completioncosts high.

• Land access agreements neededfor drilling and production sites.

• A large number of boreholesneeded together with surfacecollection pipework.

Working coal mines(CMM)

• Mine gas is delivered to thesurface at a fixed location usingexisting infrastructure installedfor safety reasons.

• The gas is produced as a wasteproduct, the primary reason forcapture being mine safety.

• Utilisation reduces greenhousegas emissions by convertingmethane to less harmful carbondioxide.

• High flow rates may beachievable.

• Gas purity can be variable(medium to low).

• Potential interruptions in supply aslinked to the mining operation butcan be buffered to a limited extentusing gas holders.

• No turndown capability.• An external fuel supply may be

necessary to sustain a utilisationprocess.

Abandoned coalmines(AMM)

• Access to gas reservoir usingformer mine entries or boreholes.

• Can, in some instances, installaccess borehole on customer’ssite.

• Reduction in greenhouse gasemissions from closed mines.

• High gas flow rates can beproduced with generally stablepurity (high to low).

• Can adjust supply to matchdemand within specified limits.

• Remedial work may be needed toadequately seal surface entries.

• The accessible gas reservoir maybe progressively reduced in sizeby rising mine water levels.

• May be necessary to continuemine water pumping.

Table 2: Estimated UK atmospheric emissions of CBM (year 2000)

CBM Source Methane emission (tonnes) Data source

VCBM negligible Wardell Armstrong

CMM 200,000 Wardell Armstrong estimate

AMM20,000300,000

Coal Authority dataACMMO

Table 3: Preliminary estimates of AMM resources and reserves in the UK

Area(excludesworkingmines)

Thicknessof coal

affected bymining

Averageinitial gascontent of

coal

EstimatedAMM

resource

EstimatedAMM

reserves

(km2) (m) (m3 t-1) (106m3) (106m3)Kent 40 2.1 2.3 77 0

Forest of Dean 87 1 0.1 3 0

Somerset 120 2 0.1 10 0

Yorks/Notts/Derbys 2550 10 5 51,000 30,600

Asfordby 5 5 0.6 6 6

Leics 44 17 0.5 150 15

S Derbys 60 6 0.5 72 36

Cannock 120 12 3.7 2131 1066

S Staffs 45 2 0.1 4 2

Coalbrookdale 30 13.5 0.1 16 8

Warwickshire 200 2 1.7 272 54

S Wales 1200 11 13.7 72,336 36,168

Pembs 1 1 10 4 0

Denbigh 90 10 8.4 3024 302

Flint 10 6 8.4 202 20

N Staffs 310 23 8 22,816 11,408

S Lancs 530 14.5 9.5 29,203 14,602

Burnley 125 4.8 5 1200 120

Northu'land/Durham 1850 10 1.4 10,360 5180

Cumbria 140 5 7.5 2100 210

Sanquhar 10 3 1 12 6

Douglas 40 20 1 320 160

Ayrshire 350 10 2.4 3360 672

Central/Clackmannan 1150 5.5 5 12,650 6325

Fife 200 5 0.9 360 36

Lothian 220 10 1 880 176

Totals 9527 212,568 107,172

Table 4: Estimates of UK CBM resources and potentially recoverable gas

CBM source Resource(109m3)

Potentially recoverable(109m3)

VCBM

AMM

CMM

2450

213

1.6

30

107

0.8

Table 5: Typical gas production rates in productive VCBM wells

Country Ranges of values m3 d-1

Australia 2,500 to 57,000

Canada 2,000 to 3,700

China 2,000 to 16,000

Europe 2,000 to 3,800

USA 1,400 to 28,000

Table 6: Features of a high-grade VCBM site

1. High methane content coal, ideally greater than 7m3/t

2. Substantial total coal thickness

3. Possible permeability enhancement eg by previous longwall mining

4. An anticlinal or other geological hydrocarbon trap structure

5. Well-jointed, fractured or permeable strata with hydrocarbon reservoir potential

6. A local customer for modest quantities of high quality gas

7. No environmentally sensitive features

8. Good access for drilling.

9. Low cost water disposal facilities..

Table 7: VCBM producibility indicators

Positive indicators Negative indicators• Elevated gas flows in virgin in-seam

driveages in mines and in boreholes

• High seam gas contents

• Seam fluids at normal pressure

• Pronounced cleat structure

• Absence of cleat mineralisation

• Limited mining activity

• Water produced from coal seams

• Coals gas-saturated

• Additional gas in anticlinal structures

• Negligible gas flows in virgin in-seamdriveages and in boreholes

• Low seam gas contents

• Seams under-pressured

• Poorly developed cleat

• Intense cleat mineralisation

• High proportion of seams mined

• No water production from coal seams

• Coals undersaturated with gas

• No significant geological trap features

Table 8: Typical characteristics from various sources

Characteristics VCBM CMM Ventilation air AMMMethaneconcentrations(%)

> 95 35 - 75 0.05 - 0.8 35 - 90

Mixture flow 1400 -8400m3 d-1

200 - 3000l s-1 100 - 200m3 s-2 30,000 -95,000m3 d-1

Pure flow(m3 d-1)

1400 - 8400 6,000 - 194,400 4320 - 138,240 11,000 - 86,000

Table 9: Principal uses of CBM from different sources

VCBM CMM AMMNatural gas substitute • Mine heating and

power generation• On site power generation

Local power generation • Dedicated localpipeline to industrialconsumers

• Pipeline to local industrialconsumers

• Dedicated pipeline todomestic distributionsystem (China)

Table 10: On-site uses of CMM

Uses ExamplesFiring or co-firing (with oil or coal)boilers for hot water and spaceheating.

• Examples in many mines world-wide.Generally only uses a small proportion ofthe drained gas.

Coal drying • Commonly used in coal preparation plants.

Shaft heating • Prevents dangerous ice forming andimproves workers comfort

Water treatment • Used to fuel a desalination plant atMorcinek mine in Poland.

Power generation • Reciprocating engines, gas turbines andcombined cycle plant have been used. Dueto capital cost some schemes have a naturalgas supply to ensure continuity of poweroutput. Surplus electricity can be sold to thegrid.

Combined heat and power (CHP) • Used in Poland to supply heat and power toa mine and a nearby town.

Table 11: Industrial uses of CBM

Application DetailBurner Process ovens, boilers

Vehicles Historically used but little if any current use

Fuel cells For production of hydrogen for both stationary and mobileunits

Chemical feedstock Manufacture of carbon block, formaldehyde, syntheticfuels and dimethyl ether (DME). DME is used as apropellant in spray cans and is a possible diesel enginefuel substitute. NKK Corporation, Taiheyo Coal MiningCompany and Sumitomo Metal Industries Ltd havedemonstrated DME manufacture using mine gas atKushiro colliery, Japan

Table 12: Upgrading CBM for pipeline or chemical use

Technology ProcessNitrogen rejection • Cryogenic distillation

• Pressure swing adsorption

• Selective absorption

Enrichment • Spiking with LPG to raise heat value

Blending • Mixing with natural gas, or higher purity CBM fromother sources

Table 13: Technology for using mine ventilation air

Technology Current StatusLean burn gas turbine Under development by EDL and Solar. The ventilation

air feed may require some enrichment with drained gas.No details of field experience currently available.

Fuel combustion air toraise fuel availability forreciprocating engines

Demonstrated at Appin colliery in Australia where about20% of the ventilation air is ducted to on-site caterpillargas engines. The methane in the ventilation air providesabout 10% of the fuel requirements of the engines.

Thermal flow reversalreactor (TFRR)

MEGTEC Systems have developed a thermal oxidationdevice called the VOCSIDZER capable of removing allthe methane from a ventilation stream. A small-scale unit(3m3 s-1) was operated at Thoresby colliery, UK. Modularuits have been designed for mine use but a full-scaledemonstration has not been made. Carbon credits may beneeded to make the process financially viable.

Catalytic flow reversalreactor (CFRR)

Developed by Natural Resources, Canada anddemonstrated as technically viable at pilot plant scale.Private partners are now needed to develop and prove thetechnology at full-scale.

Table 14: CBM use in the UK

Operator Site CBMsource

Use Output (1)

(MWe)Access for production

Alkane Energy Markham AMM Delivered by dedicated pipeline (500m) toboilers

6 Unfilled shaft

Alkane Energy Steetley AMM Electrical generation using 1x3MWe sparkignition engine

3 Unfilled shaft

Alkane Energy Shirebrook AMM Electrical generation using 5x1.8MWe sparkignition engines

9 Drift

Octagon Silverdale AMM Burner tip use and electrical generation (sparkignition engines). Gas supplied using localgas distribution grid

9 Drift

Octagon Hickleton AMM Electrical generation using 4x1.35MWe sparkignition engines.

5.5 Filled shaft

StrataGas Bentinck AMM Electrical generation using 3x3.5MWe sparkignition engines

10 Drift

Hyder Towercolliery

CMM Electrical generation for on-site use with6x1.35MWe spark ignition engines

8 Gas delivered from methanedrainage plant

UK CoalMining

Harworthcolliery

CMM Electrical generation using combined cycle,2x4MWe gas turbines, waste heat boiler and10MWe condensing steam turbine.

14 Gas delivered to on site powerstation from methane drainageplant and natural gas pipeline.

Note (1) equivalent electrical generation

Table 15: Projected CBM activities in the UK

Operator Scheme Description Output (1) (MWe)AlkaneEnergy

Wheldale Gas from an abandoned mine for on-site electrical power generation using spark ignitionengines.

9

AlkaneEnergy

Various Gas from abandoned mines involving electrical power generation and direct supply tolocal end user. Access may involve drilling large diameter surface boreholes.

400 by 2004

Evergreen Various Fove virgin CBM wells drilled in the Cheshire area are presently under test. Fourboreholes (three in de-stressed seams above mineworkings) drilled. Additional boreholesplanned for 2001.

-

Geomet Exploration for virgin CBM planned.StrataGas Various Four virgin CBM wells planned in the North Staffordshire area. -Octagon Various A number of proposed schemes using gas from abandoned mines likely to be for on-site

power generation. Access will include large diameter surface boreholes. A drillingprogramme has been developed with the aim of drilling from 20-40 goaf and VCBMwells over the next two years, subject to planning constraints

50 by 2002

UK Gas Ltd Various A number of proposed schemes using gas from abandoned mines, involving largediameter surface boreholes.

-

EdinburghOil and Gas

HemHeath

Gas from an abandoned mine to be used for electrical power generation. Furtherevaluation of the extraction and use of gas from the nearby former Florence colliery

Up to 9

CoalbedMethane Ltd

HillheadFarm

Additional virgin CBM well planned together with further de-watering tests at existingCBM wells

1

Hyder Towercolliery

Future generating capacity under review -

UK CoalMining

Variouscollieries

Feasibility studies into the on-site use of drained methane, possibly including powerelectrical power generation

10

(1) Electricity or equivalent

Table 16: Principal VCBM production basins in the USA

Basin State Major producing coalformation

Estimated VCBMresource

(109m3)

Estimatedrecoverable

VCBM resource(109m3)

Total VCBMproduction

1981-99(109m3)

San Juan Co,N.M Fruitlands 1415 328 188

Black Warrior Al Pottsville 566 122 30

Central Appalachian Va, V.W Pocohontas

New River

Lee

141 68 7

Uinta Ut Black Hawk

Ferron ss

282 85 3

Powder River Wy Fort Union 1104 263 3

Raton Co,N.M Raton

Vermejo

282 99 2

Piceance Co Williams Fork 2802 71 1

Arkoma Ok Hartshorne 113 48 1

Table 17: Comparisons of VCBM production methods in the principal basins

Properties Units Powder River Raton Uinta Arkoma CentralApplachian

Drilling Air - water Air - precussion Air - precussion Air - water Air - waterCompletion Open hole under

reamed water fracCased holeperforatedmultistage N2

foam/sand frac

Cased holeperforatedmultistage crosslinked/sand frac

Cased holeperforatedmultistageacid/water frac

Cased holeperforatedmultistage N2 foamor water/sand frac

Water extraction Electricalsubmersible

Progressive cavitypump, conventionalrod pump

Conventional rodpump

Conventional rodpump

Conventional rodpump

Water disposal Surface discharge Surface discharge,evaporation , deepinjection

Evaporation, deepinjection

Deep injection Deep injection

Coal rank Sub-bituminous High volatilebituminous

High volatilebituminous

Low volatilebituminous

Medium volatilebituminous

Net coal thickness m 23 9 7 2 3Gas content m3 t-1 1 10 11 16 9Well spacing) Acres 80 160 160 80 60Well costs US$ 65,000 330,000 375,000 50,000 130,000Well reserves 106

m3 11 51 42 5 11Reservoirpermeability

mD 1 - 1000 NA 5 - 15 1 - 10 1.5

Daily waterproduction per well

M3 60 10 - 20 45 2 2 - 5

Daily gas productionper well

m3 5560 7075 17,685 2264 2264

Table 18: Guided drilling distances

Borehole profile (m) Meters drilled (m)244 - 762 170,688

762 - 1006 15,240

1006 - 1219 6096

>1219 48,640

Table 19: Sources of commercial CBM production in different countries

CBM type Commercial productionVCBM USA, Australia

CMM USA, Australia, France, China, UK,Poland, Czech Republic, Germany,former Soviet Union

AMM UK, Germany, USA, Czech Republic

Table 20: Estimated worldwide VCBM resources (adapted from World CoalInstitute, 1998)

Country CBM Resource (1012m3)Former Soviet Union 20-116

China 30-55

Canada 6-76

Australia 8-14

USA 11

Germany 3

Poland 3

UK 2.5

India 1

South Africa 1

Indonesia <1

Approximate Total 86-283

Table 21: CMM opportunities

Country CMM emissions (106m3) CMM used (%)China 9000 5.6

Russia 1000 1 (1)

Ukraine 1800 3.4(1) Estimated value