jurnal spe ms

8/10/2019 Jurnal SPE MS

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SPE 132214

Coalbed Methane Cementing Best Practices - Indian Case HistoryHaidher Syed Gaus Mohammad and Shahnawaz Shaikh, SPE, BJ Services Company

Copyright 2010, Society of Petroleum Engineers

This paper was prepared for presentation at the CPS/SPE International Oil & Gas Conference and Exhibition in China held in Beijing, China, 810 June 2010.

This paper was selected for presentation by a CPS/SPE program committee following review of information contained in an abstract submitted by the author(s). Contents of the paper have not beenreviewed by the Society of Petroleum Engineers and are subject to correction by the author(s). The material does not necessarily reflect any position of the Society of Petroleum Engineers, its officers, ormembers. Electronic reproduction, distribution, or storage of any part of this paper without the written consent of the Society of Petroleum Engineers is prohibited. Permission to reproduce in print isrestricted to an abstract of not more than 300 words; illustrations may not be copied. The abstract must contain conspicuous acknowledgment of SPE copyright.

Abst ractCement is placed as a sheath across coal seams in coalbed methane wells primarily for hydraulic isolation and to support the

casing. Designing a cement job for coal seam wells requires contemplating factors beyond those considered in cementingconventional oil & gas wells.

Cement invasion into coal seams, losses during jobs, annulus pack off and low fracture gradient are the challenges generally

encountered during cementing these wells. The low formation temperature also exacerbates the challenges as the cement must set

within drilling schedule time constraints. Predicting the bottom hole circulating temperature during cementation is also a challenge

because many such wells are drilled with air. Finally, most coal wells will be fractured and proppant placed for productionenhancement. Cement invasion or improper cement sheath will hinder fracture performance.

Based on a seven-year study, pumping lower-density slurries does not completely prevent cement invasion but does affect the

cement quality behind the casing. Achieving successful cement jobs in these wells requires special designs and techniques. The

requirements include not only extensive testing in the lab, but also special placement techniques and cement systems designed toaccommodate a low fracture gradient and to avoid cement invasion into these soft seams.

This paper will share case histories and best practices developed from seven years of experience in designing and placing

cement successfully in coalbed methane wells in India. These case histories will include cement design considerations, lab testingprocedures, special placement techniques and cement system choices.

IntroductionCement is used during construction of coalbed methane (CBM) wells from surface casing to the production casing, as is the

practice for conventional oil & gas wells. In case of CBM wells, successful cementation is a challenge due to the nature of the

formations. In these wells, several layers of coals exist along the wellbore. The challenges exacerbate when the wells are deviated

or approach horizontal or have a low temperature at the bottom. The coal seams that exist along the wellbore are naturally

fractured, and the networks of the fractured paths in coal strata are called cleats (Figures 3 & 4). The details of the cleats aredescribed in the later sections. As the coal seams have low strength compared to the adjacent rocks and have natural fractures,

proper cement system design is necessary and vital to achieve a successful cement job and enhance the economy of the well for

subsequent operations.The coal fields in India are shown in Figure 1. In general, the fracture gradient is in between 0.6 and 0.8 psi/ft. The average

fracture gradients in our cases were around 0.6 to 0.7 psi/ft. As seen from the perspective of frac gradient, conventional oilfield

cement would fracture the formation and be lost inside the coal. In addition to potentially affecting the cement operation, this

cement invasion inside the coal cleats is detrimental for hydraulic fracturing and proppant placement operations afterwards.Various papers describe the undesired effects of losing cement: reduced cement sheath height, leaving some formation open,

etc.3,4Case studies were made to investigate the effects of using various cement systems for CBM wells in the campaigns and

described in details in the later sections.

Existence of big void fracture around the coal seams near faults also observed and cement found lost. These kinds of fractures

impose greater challenges and require special techniques to overcome. Due to the economic operations of the drilling andcompleting these CBM wells, it is often remain unnoticed during cementation and could be noticed after the cement started

loosing. Details precautions and planning beforehand may overcome this kind of difficulties.

In most cases, the wells in CBM fields are drilled by air and removing the cuttings before or during the cement jobs posedchallenges. After landing the casing at TD, the cement job starts by circulating water/spacer. The primary job of this spacer is to


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bring the cuttings up. Some cases, presence of excessive cuttings tend to pack off at some restricted areas along the openhole

annulus and block the flow path and eventually results in failure of the job.

The other aspect of the challenge is the economy of the CBM operations. The profit from these fields seems to be marginaland hence require low cost treatments and solutions. In conventional oil & gas wells, where the economy supports the expensive

remedy of the aforesaid difficulties, could be resolved by applying various innovative light weight high strength cement system.

But in the cases of CBM wells, choices are limited, but the successes are expected. The authors enumerated and shared such

practices to economically resolve the issues later in this paper.

The field blending procedures and job execution procedures including specific placement techniques and methods, werecarefully monitored, those helped in a successful application of the cement system for these CBM wells. The following sections

will describe step-by-step procedures, considerations, techniques, equipment & tools for such critical and crucial jobs frompreliminary designs to the post job evaluations.

Cleat SystemThe major difference between a conventional and a coalbed reservoir is the cleat system 3,4. Cleats are natural fractures in

coalbed reservoirs, providing the majority of permeability and porosity from these reservoirs. Cleats are of two types: face cleatsand butt cleats (see Figures 3 and 4). Face cleats are those fractures providing openings nearly parallel to the surface tangent. Butt

cleats are fracture openings perpendicular to the face. Face cleats are continuous and create pathways of higher permeability, while

butt cleats are non-continuous and finish at face cleats.

The cleat system forms a drainage mechanism for methane gas, which is helpful while producing but challenging whiledrilling or cementing through these systems. In the latter cases, they are a good medium for filtrate and slurry invasion into the

coalbed reservoir, which in turn creates excessive resistance during perforating and hydraulic fracturing operations afterward. Thissituation must be addressed by carefully engineered slurry design and placement techniques.

Cement System DesignIn addition to the major challenges described above, designing cement system for these cases found to be uniquely

engineered to address the economy of the operations. The design is based on three types of well situations/categories: 1) fracture

gradients of more than 0.7 psi/ft, 2) fracture gradient of 0.65 to 0.7 psi/ft and 3) fracture gradient of 0.6 to 0.65 psi/ft.Cement designs for wells in the first category are the least challenging, and objectives can be achieved economically. In these

cases, a 14.5-ppg cement system with loss control materials was successful3. The design of this 14.5-ppg cement system does not

require any expensive lightweight additives or chemicals and therefore is the most economical.For wells in the second category, designing a suitable cement becomes challenging. If the frac gradient is near 0.65 psi/ft, the

conentional 14.5-ppg cement induces fractures and results in cement invasion in the cleat matrix with lost circulation even when

lost-circulation material is used. To overcome these challenges, lightweight cement systems and mechanical aids were used. Thelightweight cement systems included hollow ceramic spheres, which both reduced the density of the slurry and also helped to

bridge off the entrance of the cleats due to their particle size distribution.When the wells fracture gradient approches 0.68 psi/ft, 11.5-ppg cement could be used successfully, but 12.5-ppg cement

invaded the cleats. However, the 11.5-ppg cement was found in most cases to have inadequate compressive strength and poor bond

with the casing (Figure 10). The 12.5-ppg cement had good bonding but entered the cleat faces, and unexpected pressure rise wasobserved, indicated fracturing was occurring by the cement system.

The third category, i.e., where the frac gradient is between 0.60 and 0.65 psi/ft, requires a 10.5- to 11.0-ppg cement system.

These systems require almost 50% (by weight of cement) lightweight materials and hence impact the CBM economicssubstantially. These systems tend to have lesser compressive strength, and the bond between the cement and casing may not be as

good as the other cases. These cement systems also do not exhibit good tensile strength, which may adversely affect

hydrofracturing operations.

All the above cement systems also require good fluid loss control to minimize the cement filtrate loss into the cleat matrix,and zero free water. To economize the cement system, thorough study is essential to determine the nature of the cleat matrix,

existence of any large voids or fractures, the behaviour around faults, mineralogy of the other formations, etc. After careful

observation and study the required information, effort needs to be exercised to optimize the design and develop the strategy fortreating such wells.

Due to the varied nature of the formal lightweight systems as observed, other cement systems may be appropriate in CBMwells. Two of such examples are enumerated bellow:

Thixotropic Cement System:

Thixotropic cement systems are effective in CBM wells because they stay in a thin state while pumping and become stiff

when pumping is stopped, i.e., the cement becomes static, but will again become thin when stirred/moving. These cements have

self-weight-bearing ability when they become static. So, while in stiff form, these will transfer their weight to the walls of thecasing and formation rather than the bottom of the well. Other useful benefits include:


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a. Prevention of cement invasion into the soft coal seams/cleats matrix due to thick nature and higher viscosity of the slurry.b. Stage cementing can be avoided because the weight-bearing characteristic minimizes hydrostatic issues that usually require

staged operations.c. Cement baskets may not be needed, depending on the length of the cement column and frac gradient.d. Better cement bonding with casing and formation because the cement expands while setting, which results in better CBL/VDL.e. Useful to stop lost circulation in coal seams.

Foamed Cement System:CBM wells have low fracture gradients and require low-density system for cementing. As an alternative to conventional

lightweight cement systems, higher-density cement systems can be foamed. This technology was introduced when a low-densitycement system was needed with some crucial requirement that conventional lightweight slurries were unable to provide. When the

foam cement system (cement slurry, foam agent, foaming stabilizer plus nitrogen gas) is properly mixed and fleeced, it generally

contains microscopic bubbles that do not mix, i.e., the cement becomes foam. This unique process creates a lower-density cement

system with higher compressive strength, which are two major requirements for a CBM wells. Lower densities can prevent cement

invasion into the cleat system, and higher compressive strength will give better results while perforating and stimulating the well.Some of the other advantages are

a) Can be designed for low fluid loss.

b) Can be designed to prevent gas migration.

The major disadvantage of foamed cement systems is that they are more operationally complicated.

Spacer System DesignAs the CBM wells are drilled using air, there is no drilling mud used, and hence the cement spacer system does not have to

remove mud filter cake from the annulus or inside the casing. The disadvantages is that formation cuttings and debris created

during running of the casing remain at the bottom of the well. When the spacer is pumped, these materials start to float together

and tend to bridge off the annulus at any restricted area.

A simple spacer can be designed for these wells using water with or without surfactants. However, any cuttings or debris that

are not lifted by the spacer may be entrained in the cement and pack off the annulus at restricted areas. Instead, a weighted spacerwill lit the cuttings, and the weight of the spacer can be designed so that the cuttings are dispersed in the system during lifting,

minimizing risks of bridging or packing off the flow path.

The volume of the spacer should be adequate to reach the float equipment before cement pumping begins; this will ensure thatthe float equipment is not plugged off by debris/cuttings. This volume could be the total of water and weighted spacer plus some

extra 5 bbl to ensure that the spacer passes the float equipment before the cement is pumped.

If the openings of the cleat faces are particularly large, lightweight additives in the cement cannot bridge them by particlepacking. In this case, reactive spacers can be effective to cover large voids and fractures. A detailed case history of using a reactive

spacer is described later in this paper.

Cement System TestingEstimating the circulating temperature for the cement system design is crucial to ensure that the cement will set in a stipulated

time frame. In this case, the air drilling practices in the CBM fields require a change in standard procedures for estimating

temperatures. In conventionally drilled oil & gas wells, mud acts as a coolant system, circulating heat out of the bottom of the well.

Because air has very low heat capacity, it will circulate out very little formation heat. As a result, API tables or other conventionalmethods for estimating the circulating temperature may not be applicable in CBM fields where air is used for drilling. Instead, a

field-proven temperature simulator1can be used to determine the circulating temperature profile along the wellbore, as shown in

figure 11. It can be seen that the highest temperature is not at the bottom of the well but some way up the annulus. This type of

profile is essential for proper cement design and for successfully executing cement operations.After determining the circulating temperature, extensive testing is performed to ensure that a cement design achieves critical

properties. The system is tested at the maximum temperature and at the temperature where the cement top will be. The goal is to

eliminate the prolonged setting process at the lower temperature at any point.

Special Placement TechniquesAfter designing the slurry, a proper placement technique must be developed to support the slurry and accomplish a successful

cement job.

Centralizers should be of proper size. Positive standoff is desired, and centralizers should be placed on the basis of caliperlogs and at zones of interest. Centralizers are recommended with 40-ft spacing at the shoe and thereafter 120-ft spacing to the top

of cement if the well is vertical. A spirolizer is recommended between zones to improve flow. Placement and number of

centralizers can be decided by API practices or an equivalent method.The rate of circulation prior to cementing should be designed to clean the hole of cuttings and debris without fracturing the

formation. In most cases, because no mud is used in drilling, pipe movement merelyt improve the cement bonds with casing.


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Throughout cementing, returns should be measured through the trip tank or a meter tank to monitor circulation (if a full

circulation is planned) and thereby avoid lost circulation by keeping the pumping rate bellow the fracture pressure. Note that free-

fall phenomenon of the cement in the casing can be misleading when measuring returns. If the well is under vacuum (free fall), themud return rate will exceed the displacement rate. When the vacuum drops, the mud return rate decreases below the displacement

rate.

Some important casing accessories are being used to achieve successful CBM well cement operations:

1) Bow Spring Centralizers: Used to achieve maximum centralization when placed properly, helping to distribute the cement

evenly around the casing-to-openhole annulus. Figure 5 illustrates such a centralizer.2) Cement Baskets are simple and economical devices for supporting cement. They are placed outside the casing to support

the cement column, spaced 40 m apart or between zones where weak formations are encountered. They are designed sothat cement can flow up through it but cant fall down. The cement also should be designed to develop gel strength

quickly to support itself. Figure 6 illustrates such baskets.

3) A Stage Collar is used in stage cementation when long cement sheaths are needed in front of soft coal seams. The collarprevent casing collapse due to the hydrostatic pressure of the long cement column and permits circulating cement above

lost-circulation zones. With such collars, different economical slurry designs can be pumped for wells with significanttemperature differences. Figure 7 illustrates such stage collar.

Operational AspectsIn addition to proper cement system design, proper operations at the field ensure the overall success of a cement job. As the

economy of the CBM operations are very tight, pre planning may reduce a lot of extra costs like rig waiting time, unutilized

equipment, repetitive movement of equipment, and personnel. In many places, batch cementing is used, so that in one day multiplecement jobs are pumped to reduce the various costs. To cope up with these demands, adequate operational planning and resources

are essential.

As it is very important to pump the right weight of the cement due to less tolerance of additional ECD at the cleat faces, batch

mixers are often preferred by the operators. If a batch mixer is being deployed to mix and prepare the cement, the lab test for the

cement should simulate the batch mixing process. When using lightweight cement, the blend must be homogeneous since slurry

volume is typically small, otherwise it raise the chance to have a nonuniform cement mix that contributes to poor results.

Case HistoriesIndia is one of the largest coal producers (Table 1) in the world and has a substantial coal reserves. In the last decade due

to the growing demand of methane gas and its environmental benefits when produced from coalbed methane reservoirs, the Indian

government has taken deep interest in coalbed methane projects. With increasing numbers of coalbed methane wells drilled across

the country, it became necessary to collect best practices encountered for a successful primary cement job. Here the authors havedescribed mostly the wells from the Raniganj blocks of East India, some challenges encountered in the Sohagpur blocks of central

India and some from the Barmer blocks of West India (Table 2).CBM fields at Raniganj are divided into three major blocks called North, South and East, ranging up to an area of 1060

square kilometres. Figure 8 illustrates these blocks. These blocks contain 10 regional coal seams (e.g., RN-1, RN-2, RN-3, etc.)

with seam thicknesses ranging from 4 to 46 m. In these blocks, the most common targets were RN-2 and RN-3.Here 15 wells were drilled with two- and three-casing policies. Prior to drilling, conductor pipes were driven in the ground up

to 12 to 15 ft. Then surface holes were drilled using water to 404 to 663 ft, followed by 13 3/8-inch surface casing. The

intermediate holes were drilled with 1.08-sg bentonite mud to 1152 to 1595 ft, followed by 9 5/8-inch intermediate casing. Surfaceand intermediate holes were cemented to surface with two-slurry systems. Production holes were mostly drilled with air (water &

foam mixture), then wiper-tripped and logged and the 5 1/2-inch production casings run to 2297 to 3363 ft. Most production

casing cement jobs were pumped using a single slurry to cover up to 50 m inside the previous shoe. The rest were cemented withtwo-slurry systems, so cement came up to surface. The maximum bottom hole static temperature encountered was 143 Deg F.

Case History No. 1:

The wells are located in the Raniganj block of West Bengal, East India, where a 15-well drilling campaign was planned. Fiveproduction casing cement jobs were pumped using a 11.5-ppg lightweight slurry design. Static temperatures ranged from 130 to

143 deg F at depths from 2297 to 3363 ft. Holes were vertically drilled with air (water & foam mixture). Since lightweight, high-strength slurries were used rather then conventional cement, the CBL/VDL were expected to be good, but they did not meet

expectations (Figure 10). To improve the CBL/VDL, a slurry designed at 12.5-ppg with the same lightweight additive was pumped

in two wells, achieving better CBL/VDL results (Figure 9).Based on these results, the 12.5-ppg slurry was pumped in six more wells. Meanwhile, the operating company started the well

completion campaign and started fracturing the wells where the 12.5-ppg cement system was pumped. Stimulation was hindered

difficulty with perforating and then fracturing the wells, as the fracture initiation pressures were abnormally high. The operatorconcluded that the cement had invaded the cleat matrix.


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As a result, the last two wells of the campaign were cemented with the previously pumped 11.5-ppg slurry design. High fracture

pressures were also seen in some of wells where 11.5-ppg slurries were pumped. A subsequent study concluded that 10.5-ppg

cement would be better for these wells. Details and methodes of this study is a subject of another paper, which may be releasedsoon.

Discussion:

Experience has shown that pumping lower-density slurries will not completely avoid cement invasion problems and may affect the

cement quality behind the casing. Before selecting a cement weight for a particular coal seam, its important to evaluate all therelevant factors, including exact fracture gradient, openhole excess as per calliper logs, depth of zone of interest, length of fluid

plus slurry columns, proper centralization plan as per logs plus cement basket placement, etc.

Case History No. 2:

A four-well campaign was about to start in the Barmer Sanchor basin of Rajasthan, West India. The operating company was

concerned about the cement job because of the very soft formations, which could lead to large openhole washouts. Engineers

recommended pumping a special type of a pre-flush called reactive pre-flush, which could clean the washout sections better &prepare both casing and formation for better cement bonding. The reactive pre-flush consisted of sodium silicate and was pumped

in the following order: 2 % KCl solution > 2 % CaCl2> 2 % KCl solution > Na2SiO3solution > 2 % KCl solution. The 2 %

KCl solution was included to prevent contact between CaCl2and Na2SiO3as they can react to form solids if they mix.

The pre-flush and subsequent cementing operations were executed successfully.

Case History No. 3:A total of 31 CBM wells were drilled in the Sohagpur coalfield in Madhya Pradesh, Central India. The Sohagpur coalfield is

divided into three blocks: SEP-Sohagpur east, SHNP-Sohagpur north & SWP-Sohagpur west. In the SEP & SHNP blocks, 10

CBM wells were drilled (5 in each); the remaining 21 wells were drilled in the SWP block.

Drilling followed two- and three-casing policies. First a 16-inch conductor pipe was driven/run into the 17 1/2-inch hole to a

depth of 13 to 43 ft and cemented with 15.4-ppg bentonite extended slurry. Then a 12 1/4-inch hole was drilled to 162 to 1175 ft

and cemented with 12.5-ppg lead and 15.4-ppg tail cement.Most production holes were drilled with 8 1/2-inch bits, with a few using 7 7/8-inch bits. Then a 5 1/2- or 7-inch casing was

run in to 1224 to 2784 ft. Many were cemented with 11.5-ppg lightweight single slurries and some shallower wells with 12.5-ppg

lead and 15.4-ppg tail cement due to higher fracture gradient at TD.

Discussion:

In most of these wells, cement baskets were used to cement the final casing; no cement was found to have invaded the cleats. Allthe wells were hydraulically fractured with fracture pressures as planned. In the wells that did not use cement baskets, cement

invasion was observed as abnormal pressure build-up during fracturing despite the careful use of 11.5-ppg lightweight cement.

Other ConsiderationsTo combat cement invasion into CBM cleats, engineers worldwide have tried many options, including stage cementing.

However, running a Stage Collar with ECP is often not economical, especially when several devices are required in a single string

between the coal seams.

Cement with lost-circulation material has also been found beneficial3 in other parts of the world and could be tried in theabove cases. Due to logistics and lack of preplanning for the eventuality, cement with such material was not tried in the above

cases.

Multiple streamlined jobs in a single day may not reduce operational costs due to the remoteness of the locations. In these

cases, equipment and materials were mobilised once and stayed with the campaign until it was finished.

Conclusions

Based on the jobs executed and the lessons learned during cementing the above wells over the last six to seven years, and asvarious methods were implemented, the authors derived the below conclusions to execute the cement jobs successfully:

1) Cement designs for CBM wells require extensive/additional considerations compared to conventional oil & gas wellcementing because of CBM economics, fracture gradients, cement invasion in the cleats, cement strengths, fluid loss

control, use of LCM, hole conditions, placement techniques, etc.

2) Study of the CBM cleat system is critical for proper cement system design3) Reducing slurry density is useful if the fracture gradient is low, but the cement must still have good compressive and

tensile strength

4) Gas-tight slurry may not be required if no gas-bearing sand/formation exists5) Instead of designing cement for very low fluid loss, slurries with moderate fluid loss (i.e., 250 ml) has been found to

perform better because they can build cement nodes at the face of the cleats.


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6) Using LCM in the cement may also improve the operations by blocking the entrance of the cleats7) Cement baskets are beneficial and can sustain the cement colum, especially when used with thixotropic slurry designs.8) Ideal properties for CBM slurries are: thixotropic, fluid loss of 250-300 ml (depending on the cleat opening size), with

fibre and graded LCM, light weight. Ideal placement includes a reactive spacer and placement with baskets and other

typical cementing practices.

Acknowledgements

Thanks to BJ Services Company for the permission to publish this paper. Thanks to the operating companies for giving theopportunities to execute and review the jobs. The views and opinions expressed are solely by the authors and do not necessarily

reflect those of any of the companies involved.

NomenclatureAPI > American Petroleum InstituteCBM > Coal Bed MethaneBbl > barrelppg > pound mass per gallonBHT > bottom hole temperatureBHST > bottom hole static temperatureBHCT > bottom hole circulating temperatureHPHT > high pressure high temperatureHT > high temperature

ADC > Automatic Density ControlTOC > top of cementTD > target depthFt > footFrac > FractureECD > Equivalent Circulating DensitySOBM > synthetic oil based mudLCM > Loss circulation materialsQA/QC > quality assurance/quality controlBHA> bottom hole assembliesOD > outside diameterCBL > Cement Bond LogVDL > Variable Density Log

References:

1) David, S. and Trigg, M.: Mathematical Temperature Simulators for Drilling Deepwater HTHP Wells, paper SPE/IADC-105437,presented at the 2007 SPE/IADC Drilling Conference in Amsterdam, The Netherlands.

2) Haidher, S., Kale, S., Affes, S. and Kumar, S: HPHT Cement System Design - East Coast Case History, paper SPE-104048, presented at

the 2006 IADC conference in Mumbai, India.3) Huff, C.D. and Merritt, J.W.: Coal Seam-Well Cementing in Northeastern Oklahoma, paper SPE-80938, presented at the 2003 SPE

Production and Operations Symposium held in Oklahoma City, Oklahoma, USA.4) Osisanya, S.O. and Schaffitzel, R.F.: A Review of Horizontal Drilling and Completion Techniques for Recovery of Coalbed Methane,

paper SPE-37131 presented at the 1996 SPE International Conference on Horizontal Well Technology, Calgary, Canada.5) Cementing Engineering Support Manual BJ Services6) http://www.glossary.oilfield.slb.com/files/OGL00046.gif7) http://www.davis-lynch.com/stagcem2.JPG

8) Rao, V.K.: Coal Bed Methane A Frontier Energy Source, Potentials and Projections, presentation from Directorate General ofHydrocarbons, New Delhi, India.

9) Fidan, E., Kuru, E. and Babadagli, T.: Foam Cement Applications for Zonal Isolation in Coal Bed Methane Wells, paper 2003-129 was tobe presented at the Petroleum Societys Canadian International Petroleum Conference 2003, Calgary, Alberta, Canada.

10) Philip, A.W., James, M.K., and Charles, E.B.: Improving Cement Bond in the Rocky Mountain area by the use of Spacer, Wash andThixotropic Cement, paper SPE-9031, presented at the SPE Rocky Mountain Regional Meeting 1980, held in Casper, Wyoming, USA.

11) http://energy-alaska.wdfiles.com/local--files/critical-factors-for-coalbed-methane-production/COALBED_METHANE_218.jpg

12) https://reader010.{domain}/reader010/html5/0609/5b1bb97dc2f1a/5b1bb9824a86b.jpg13) http://www.kgs.ku.edu/PRS/publication/2006/2006-13/gif/p2-04.jpg14) Bow Spring Centralizers (Ref-1) > http://www.halliburton.com/public/cem/contents/Data_Sheets/web/H/H05051-A4.pdf15) Bow Spring Centralizers (Ref-2) > http://oilmachinery.win.mofcom.gov.cn/www/6/oilmachinery/img/200842219025.jpg

16) http://www.davis-lynch.com/stagcem.pdf17) http://www.netl.doe.gov/technologies/oil-gas/FutureSupply/Images/CBM_Development.JPG18) Cement Baskets (Ref-1) > http://www.davis-lynch.com/cemenhance.pdf

19) Cement Baskets (Ref-2) > http://www.gauravassociate.com/images/products/cement-basket.jpg20) Cement Baskets (Ref-3) > http://www.cteltd.com/images/260cb.jpg21) http://www.geni.org/globalenergy/library/national_energy_grid/india/graphics/ind-coal.gif


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Figures:

Figure-1: CBM Map, India Figure-2: CBM Fields in India

Figure-3: Cleat System

Figure-4: Cleat System, graphical


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Figure-5: Bow Spring Centralizer Table-1: Worldwide Reserves

Figure-6: Cement Baskets


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Figure-7: Stage Collars

Figure-8: Raniganj Field Table-2: Coal Reserves in India


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Figure-9: CBL/VDL of 12.5 ppg Cement Figure-10: CBL/VDL of 11.5 ppg Cement


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Figure-11: WellTemp Simulation


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