berlin gas storage

7/27/2019 Berlin Gas Storage

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SAFETY AND ENVIRONMENTAL PROTECTION IN THEUNDERGROUND STORAGE INDUSTRY - THE BERLIN GAS

STORAGE

Armin Schneider, GASAG Berliner Gaswerke Aktiengesellschaft

1 INTRODUCTIONBerlin, the capital city today of the Federal Republic of Germany, which was divided up to the

end of 1989, looks back on a turbulent political history that also had a decisive influence on the gassupply of the city. Looking at the political and supply-related island situation of the city at that time,there was initially pressure for proprietary production with regard to the gas supply, i.e., for theproduction of gas based on energy sources such as light gasoline and methanol, that were deliveredvia rail or water.

It took several years to achieve a connection to the German or European integrated energysystem, i.e. in particular a natural-gas transport line through the territory of the former GermanDemocratic Republic. The German-Soviet large-pipe transactions with the gas-delivery treaty thatwas associated with that at the start of the 1980s, as well as the subsequent follow-up meetings, firstopened up the opportunity for the connection of Berlin (West) to the natural-gas supply in the first half

of the 1980s.As a general rule, it was clear to all of the decision-makers in the process that the feasibility

and realization of an underground natural-gas storage were indispensable prerequisites for natural-gas acquisition by Berlin. The attitude of the Allied protection forces had significant weight here; theyhad specified that a year's supply of natural gas be held in reserve .

The area in which the Berlin natural-gas storage was built is in a district of the city that ischaracterized by a medium to high building density, by sport and recreation areas and by nature andwater conservation areas, in addition to having various other problematic issues. Besidesauthorization procedures, intensive technical and cost-related administrative conditions that refer tothe system safety, as well as industrial safety, health protection and environmental protection, resultfrom this.

The following protection goals, which are also documented in a safety analysis from 1990, ordocumented today in a safety report required in accordance with the amended Major Accidents Act(German law), were used as a basis for the construction and the operation of the natural-gas storageincluding all of its technical equipment and structural facilities:

Protection of the facility and of the employees working in the facility against improperoperation conditions and malfunctions, as well as their effects.

Protection of life and health, as well as of physical property, in the environment of the facility.This aspect is of particular importance given the special local conditions in Berlin, with a highdensity of residential buildings at a distance of approx. 110 m. from the property limits of thestorage operating site.

Protection of the environment. The operating facilities of the natural-gas storage are locatedin part in a water conservation area and in a nature conservation area.

Preventative technical and safety-related equipment was installed to achieve the protection goals.The Berlin natural gas storage was originally designed to be a reserve storage unit, i.e. for limited

seasonal quantity equalization between the gas that was acquired and the gas that was needed, dueto the regional and political island situation of Berlin and the restrictions associated with that. It wasprovided with substantial redundancies in the surface facilities for reasons of supply reliability.

The storage is now used to equalize the differences in quantity between the gas acquisition andthe need for gas, and the redundancies have been given up. The operational mode of the storage isoriented towards clipping off the demand peaks in the supply area, or purchasing quantities of gas thatare cheaper, i.e. the saving of costs when acquiring gas and thereby the improvement of the profitsituation of the company.

The requirements in the gas industry are realized with the Berlin natural gas storage system. Theprotection goals have to also be achieved to the same degree a basic prerequisite for the existenceof the storage system at a location of this type. These requirements not only call for technology fortheir realization, but also a methodical system in the organization and process structure, or with regardto the necessary functions and tools for management; not just to be able to adequately cope with the

circumstances, but to also ensure continuous improvement, as well as the capability to quickly andflexibly react to changing requirements.


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2 KEY DATA ON THE BERLIN NATURAL GAS STORAGE

2.1 Gas Supply Situation in the State of BerlinThe company GASAG ensures an entire year's supply of the energy source of natural gas for

more than 700,000 Berlin customers with a network of pipelines having a length of a good 6590 km,five transfer stations and the Berlin natural gas storage with a storage capacity of 1085 * 10

6m (Vn).

The Berlin gas storage serves here to provide equalization between the acquisition and needstructures.

The Berlin gas storage is directly connected to an internal-city, 40-bar natural-gas transport line ofGASAG. This natural-gas transport line first connects, in the form of a half-ring, the Buckow transferstation in the south of Berlin to the southern high-pressure distribution node, the Mariendorfdistribution station, and then to the storage operating site in the Glockenturmstrasse and finally to thenorthern high-pressure distribution node, the Charlottenburg reduction and distribution station. Thefeed into the remaining high-pressure and medium-pressure system, which is designed to be lower interms of pressure levels, is provided through it, apart from the supply of consumers who areconnected to the transport line in a less direct way. The existing network geometry also makes itpossible to use the storage to cover the winter demand peaks of the entire city, among other things.

Fig. 1: Gas supply situation in Berlin

The Berlin gas storage was built from the standpoint of a politically-necessary crisis supply forWest Berlin and was only secondarily designed to be a storage facility for seasonal equalization. Thetasks of the storage were changed considerably after the fall of the Wall and the reunification ofGermany in 1990. The high storage capacity of 1085 * 10

6m (Vn) with a supply quantity for approx. 1

year was no longer the decisive factor for the requirements of Gasag with an expanding supplynetwork; the decisive factor was instead the optimization of gas acquisition and thereby thedependable supply of its customers with natural gas at economical prices.

2.2 Geology and Reservoir EngineeringA great deal of attention was paid to the placement of the wells during the development of the

aquifer gas storage. The Berlin gas storage stands out because of the complicated tectonics. The


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reservoir can be divided up into at least 8 areas that communicate more or less with each other. Theyinvolve 2 areas each east and west of a large Graben fault, which still have to be divided up into theupper and lower Detfurth layers. Furthermore, sand layers above the main storage horizonsparticipate in the storage behaviour, if only to a small extent. In a lithological sense, the sand types ofthe upper and lower Detfurth layer also have major differences. The lower layer involves sandstonethat is a little compacted with a high matrix permeability, whereas the upper layer is heavily cemented

with a significantly lower matrix permeability and thickness. The upper layer has a high degree offractures in the central part of the structure, however; relatively high production rates can be realizedbecause of this.

The location of the operating sites and wells is presented in Fig. 2. The topography is providedand the course of the important faults are presented for orientation. The storage horizons are thelower and upper Detfurth layers in the Buntsandstein (Bunter) at a depth of approx. 800 m below sealevel at the top of the storage. The gas-storage layers are covered with layers of clay stone, anhydriteand rock salt that are approx. 200 meters thick . The tightness of the cap rock layers was investigatedand verified before the construction of the underground storage. The confirmation of the suitability ofthe Bunter structure in Berlin for the construction of an underground natural-gas storage was providedin 1992 in the form of a conclusive report on behalf of the mining authorities for the state of Berlin.

Fig. 2: Berlin natural gas storage Location of the operating sites and wells

2.3 Storage WellsTwelve wells that have been drilled in from 3 sites (B, C, D) are available for the storage operation.

Four of the total of 16 wells can only be used in a limited way.The varying formations of the storage sand types also require different methods of completion of

the wells. In the lower layer the wells are equipped with a sand filter and a gravel pack, whereas asimple completion is adequate in the upper layer. The wells also have major differences in theirproduktion behavior.

The wells are equipped for the most part with 5 1/2 tubings; a few of the older wells are onlyequipped with 4 tubings, however.


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The wells are drilled from 4 sites, 3 of which are in operation; Site A with the wells B2 and B3 isnot connected. In the well B2 the gas saturation ist still very low, well B3 has gas saturation in theupper layer and at the top of the lower layer.

A storage production rate of of 450,000 m (Vn)/h can be achieved with the storage wells and theexisting surface facilities.

2.4 Storage Facilities and Well SitesThe surface storage-facilities are distributed over three of the four well sites (A, B, C, D) (Fig. 3).

The construction of the storage plant was established using the four drilling sites that were developedin the course of the exploration; the sites were converted and expanded into gas production sites.Finding other drilling sites with a better structural situation was impossible due to the buildings in thecity and the water and nature conservation area in the development area of the storage. The 16storage wells and the water disposal wells had to therefore be concentrated at four sites and run downwith a strong deviation from there. All of the facilities are housed in buildings due to the locationrequirements, or for reasons of emission protection.

Fig. 3 Facility schematic, Berlin natural gas storage

The well heads of the storage wells and of the water disposal wells are housed in 5.15-meter-deep cellars that are covered with concrete plates. The cellar covers can be removed if necessary.There are special steel covers over the well heads in each case for wireline jobs.

A solution that was even more expensive and technically-complicated had to be chosen at wellSite B due to the even more cramped situation there. Besides the well heads of the storage wells andthe water disposal wells, all of the process-related facilities, as well as the supply and ancillaryequipment, are also housed underground there in a 2500 m cellar. The heating of the regenerationsystem has to be done electrically due to the accommodations in the cellar.

The reciprocated compressors are located at the main operating site (Site D) in theGlockenturmstrae in noise-insulated buildings. The gas is centrally distributed to the well sites fromthere via a field line system for storage. The compressors are likewise driven electrically for emission-

protection reasons.


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The well sites A, B and D are in the Tiefwerder water conservation area of Zone III. Therequirement for decentralized drying of the gas came about due to this. The water that accumulates inthe process is disposed into the Rdersdorf porous lime stone from ever site on a decentralized basis.

The entire electrical-power supply for the facilities is provided via several 10 kV and 400 Vtransfer stations. In addition, emergency-power systems including a no-break power supply areinstalled at every site. The pipeline system of the facility has a length of approx. 4 km. The process-

control system includes approx. 12,000 control, measurement and regulation points with approx.20,000 process variables.

In total, the storage has seven buildings and 2 cellar structures that are supplied with extensiveheating, air-conditioning and ventilation systems.

3 DETERMINATION AND ASSESSMENT OF THE DANGERS REGARDINGSAFETY AND THE ENVIRONMENT

The new obligation to prepare a safety report that is arising for the operators of undergroundstorage because of the amendment of the Federal Immission Protection Act (BimSchG, German law)and the Major Accidents Act in Germany, triggered by the SEVESO II guideline, is coming up againstthe special set of circumstances at GASAG Berliner Gaswerke Aktiengesellschaft that a safetyanalysis already exists due to the origins of the Berlin natural gas storage.

The safety analysis was arranged for through the resolution of the Berlin parliament with regard to

safety investigations that were to be presented.The safety analysis was prepared in 1986 and updated in 1990. It essentially consisted of two

parts that concerned themselves with the surface area and the sub-surface area. Furthermore,technical measures for the storage operation (both normal operation mode and special operatingmeasures such as workovers, for instance) were also noted and evaluated.

The further construction since 1990 and the operation of the Berlin natural gas storage, as well asall of the measures associated with that, were carried out based on the mining-law authorizationprocess, so there was an update of the safety analysis of 1990 based on the mining-law documents.In the process, the safety plan presented in the safety analysis was pursued further.

The safety report that is necessary due to the requirements of the amended Major Accidents Acttakes the safety analysis of 1990 into consideration, as well as measures that were taken in themeanwhile, and represents as a result the update of the safety analysis of 1990; the new policies ofthe amended Major Accidents Act of April 26, 2000, were taken into account on a formal basis.

The relevant facility areas that were identified in the safety analysis at that time are also givenconsideration in an analog fashion in the safety report. This means that there was a division of thefacility areas into associated, but demarcated, individual facilities for the safety report.

The list of dangers that was prepared at that time, in which the dangerous events, the conditionsfor the danger to become active, and the direct and escalating consequences of the danger werenoted for each identified danger, was checked and included in the same way.

The determination of dangers was done by applying the list of dangers to the facility areas or tothe individual facilities, as the case may be. After possible dangers were identified, there was a riskassessment, followed by an evaluation of the remaining risk. If the risk assessment comes up with arisk that is not reasonable, the process is carried out again after additional protective measures aredetermined (process following DIN EN 1050).

Two methods are used for determining environmental influences / environmental effects. On theone hand, the "effect - cause method", which is usually used, and on the other hand, the "cause -effect method".

In the effect-cause method, the environmental influences / environmental effects (e.g. emissions,waste or waste water) are to be determined, quantified and assigned to the activities, services andproducts that cause them. The environmental influences / environmental effects are to be evaluated.Measures for reducing the environmental influences / environmental effects are to be established, andthe result of the measure is to be determined. Finally, the environmental influence is to be evaluatedagain.

The evaluation of the environmental influences / environmental effects is done according to theABC analysis (A - small effect, B - medium-sized effect, C - strong effect).

In the cause-effect method, the activities, products and services are systematically investigatedwith regard to environmental influences / environmental effects that arise. The subsequent evaluationand establishment of measures are done as they are in the effect-cause method.

The Berlin natural gas storage consists of facility sections and places that are visited with varyingdegrees of frequency and duration by employees for activities. These locations are viewed as being


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work places. The work places are evaluated on the basis of a list of dangers. DIN EN 1050 is used asan instrument for the process of assessing the risk.

Particular attention was paid to only using methods that were already used in comparable facilitieswith good operating experience in the selection of the technical measures for ensuring the protectiongoals. Completely new technical developments that involve the "essential features of the procedure"were not used to rule out from the outset the risk of using systems that are not technically mature.

The residual risk that remains when the set of technical rules is adhered to, which is normallyconsidered to be acceptable, was further reduced through other safety-related equipment andmeasures, above and beyond the requirements of the relevant set of technical rules. The localcircumstances of the facility were taken into consideration here to a great extent.

Operational measures also serve to achieve the protection goals, in addition to preventativetechnical installations.

4 SPECIAL FEATURES OF THE TECHNICAL CONSTRUCTION DESIGN OF THEBERLIN NATURAL GAS STORAGE

4.1 Buildings

The facilities of the Berlin gas storage are in a water conservation area. This had to be taken into

account on a technical basis with regard to the operation, as well as in view of later assembly work.All of the facilities that contain substances that could endanger water are therefore set up withinfluid-tight concrete enclosures with a size of up to 8,500 m. The buildings that are not located withinthe enclosures have their own, water-tight concrete enclosures if fluids that could endanger water arein the buildings.

All of the facilities, especially the compressor equipment, were set up in buildings or cellars thatare equipped with ventilation and smoke-removal systems for reasons involving emission protection.

Large-volume foundations with an anchoring to the ground that extends for up to 14 m belowground ensure that a minimum of vibration will occur when the compressor is operated.

Extensive drainage and waste-water systems with silt traps and oil and gasoline separators areinstalled so that no pollutants will get into the public sewage system. Sunken concrete areas withdrainage systems serve as deployment areas for tank trucks.

All of the operating sites of the Berlin natural gas storage are fenced in; it can only be entered

through the reception area, which is designed in the form of an interlock gate. Furthermore, thefencing is monitored with television cameras with motion sensors; doors and gates are automaticallymonitored by contacts for unauthorized entry. Messages regarding unauthorized entry are visuallyand acoustically signaled in the operations center, which is occupied at all times.

4.2 Facilities for Fire and Explosion Protection

4.2.1 Explosion ProtectionThe areas that are subject to a danger of explosion are established in accordance with the

guidelines and acts applicable for facilities of this type.All rooms with system components that transport gas were defined as areas in danger of an

explosion. This goes above and beyond the requirements of the specified regulations to be appliedand takes the high safety requirements of the gas storage into consideration to a special degree.

Air intake and outlet openings of rooms are not in areas in danger of an explosion, so there is nodelay of danger.

All of the rooms in which gas could accumulate are monitored with gas measurement sensors(remote diffusion measurement sensors) that issue a preliminary gas alarm when a certain gasconcentration (25% of the lower explosion limit, LEL) is reached.

When the first alarm threshold is reached, 25% LEL, a visual and acoustical signal is triggered onsite in the gas control center and in the measurement center. Automatic ventilation equipment isstarted up, in order to prevent a further increase in the gas concentration, or to reduce the proportionof gas in the air again. If the gas concentration continues to increase despite this countermeasure, afurther alarm is given when 50% LEL is reached.

The relevant facility is shut off via the EMERGENCY STOP system when the second alarm levelis reached in a compressor section. The shut-off valves on the inlet and outlet sides close in theprocess in accordance with the operations. The ventilation equipment remains in operation.


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Gas accumulations in the well head cellars lead to a startup of the ventilation equipment if it is notyet in operation. Decisions on further measures are to be made by the operating personnel. There isno automatic shutoff of system sections in the well cellar.

The separator cellar, the boiler room, the laboratory, and the calorimeter and gas-measurementroom are only monitored for gas. If gas concentrations accumulate in these rooms, the operatingpersonnel is given an alarm; they have to make a decision on further measures. There are no

automatic, forced shutoffs.

4.2.2 Fire ProtectionFires are automatically recognized via ionization smoke detectors and optical smoke detectors, as

well as UV flame detectors.When one or more ionization smoke detectors of a detector line in the two-line system responds,

a signal arrives in the central fire alarm system that is evaluated as a fire alarm and a preliminaryalarm is triggered. The fire-protection section in which the alarm was triggered is visually andacoustically displayed in the central fire alarm system. Fire-protection doors, gates and flaps areclosed; the ventilation is shut off. An EMERGENCY STOP also takes place for the compressorfacility(ies) when a line responds.

If the fire is detected by a second alarm line, an alarm is automatically sent through to the firedepartment. There is simultaneously a site EMERGENCY STOP. A site EMERGENCY STOP means

an EMERGENCY STOP over the entire operating site, and thus at the compressor section as well.Additional alarm lines with UV flame detectors are also installed for the quickest possible

recognition of open fires and for the quickest possible alarm.When there is visual recognition of fires in fire-protected rooms, alarms can be pressed outside of

the room in direct proximity to the escape doors. The same sequence takes place as if two alarmlines had triggered a fire alarm. Fires in outside facilities or in rooms that are not protected against fire,e.g. the staircase, hallway, basement floor etc. can also be reported with a pushbutton fire alarm in thesame way.

Every gas or fire alarm that is triggered is visually and acoustically displayed in the operatingcenter.

The fire alarm to the public fire department is automatically sent via the main fire alarm line.

4.2.3 Extinguishing Agent Supply

Street hydrants are available to the fire department for extinguishing fires in outside facilities. Thehydrants serve as the initial connecting point for the fire department for general fires.

The minimum water quantity of 3,200 l./min. is provided by two hydrants in each case (1600 l./min.each) with a flow pressure (i.e. at a flow rate of 1600 l./min.) of 2.2 bar (0.22 Mpa).

The extinguishing water lines were designed to have a nominal width of 250 mm and a pressurelevel of 16 bar. Continuing to supply the remaining system with water is possible by shutting off adamaged line section when there is a rupture in the ring line.

The hydrants for fire-extinguishing purposes were positioned next to travel areas for fire-department vehicles in such a way that it is possible to create a connection without problems from thevehicle to the hydrant pipe with a pressure hose that is only 5 m long and vehicle traffic traveling by afire truck that is involved is not obstructed by hoses that are laid out. This hydrant arrangement wasset up according to fire-department specifications, as the case may be.

The line equipment (connection lines, water-meter equipment, consumption lines and shutoff

valves) that is necessary for the hydrants on the site have been installed with the recognized rules ofcurrent technology. The line equipment has been laid in the soil so as to be protected against frost.The required extinguishing-water quantity is adequate to also supply additional equipment, such as asprinkler system, fire-extinguishing hose connection equipment (wall hydrants) or other consumptionunits, with water.

A separate extinguishing system is available for combating a fire in the area of the productionwells. It essentially consists of a fire-extinguishing basin with a volume of 400 m

3with an inlet from the

public network (max. 1,800 m3/h), two pumps with a pump output of 900 m

3/h each at 7 bar and an

extinguishing ring with 13 connection points for mobile or fixed fire-extinguishing monitors.This system is provided for the hypothetical case of a blowout with an ignited gas flow and serves

to extinguish the flame or to provide cooling in the impacted well area. It is assumed, in the case thatthe system is used, that approx. 80% of the water amount that is pumped will flow back into theextinguishing-water basin via the well site area that is set on edge.


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The power supply of the pumps, each with 300 kW of power requirements, is provided via thepublic electrical-power network and protection is provided via emergency-power units.

Every well cellar is equipped with a line ring with 6 nozzles, each at 16 m3/h. This nozzle system

serves, in the case of a blowout, to flood the impacted cellar, on the one hand, and to spray water intothe "cold" gas flow that is escaping, on the other hand. A preventative system that was built for thehypothetical case of an uncontrolled escape of gas is involved here. When there is a blowout, water is

sprayed into the gas for cooling, in order to prevent ignition of the "cold" flow of gas (Red Adairrecommendation).

The firefighting in buildings is done with water. Wall hydrants, from which the extinguishing watercan be taken, are installed on every floor.

A facade sprinkling system was installed for the rear of the building, and a line system for wateraccumulation on the roof area with a 5-cm water level was installed for the roof, to protect theoperating and control equipment in the operating building. Heat development in and on the operatingbuilding is to be reduced in the case of a blowout.

The rear therefore essentially consists of a back-ventilated shell with no windows made of brick orlimestone walling with insulation and aluminum sheets that are screwed in front and joined in eachother in such a way that a flawless, even and complete wetting of the facade surface is ensured. Thequantity of water introduced over the sheet facade is provided by a pipeline in the area of the edge ofthe roof that extends over the entire length of the building. A separate pipeline with water-outlet

openings has been laid behind the facade in the clinkered area. The layout of the sprinkler systemfollows DIN 14 495.

Fire extinguishers are attached in all of the rooms and outside facilities, in accordance with theregulatory construction specifications.

4.3 Process Monitoring and ControlA programmable-logic process control system with a decentralized structure has been installed for

the functional areas of measurement, control, regulation and monitoring. A central control station(operating center) takes care of the general monitoring and the operation of the individual stations. Allof the equipment that is important for the storage operation is controlled and monitored from there.

The burden has been taken off the operating personnel in their work to a great extent because ofthe high level of automation; they observe and control the processes and only need to intervene whenthere are malfunctions. The process control system, with central processing units and automated

equipment that works on a decentralized basis, makes safe storage operation possible due to itsredundant structure and the safety-oriented control.

It is to also be pointed out that all of the fittings that are electrically, pneumatically or hydraulicallydriven are equipped with manual wheels or other mechanical controls so that functioning is alwaysinsured when the fitting is intact. A mechanical failure of individual measurement, control, regulationand monitoring equipment, or of fittings, is avoided via the testing and servicing that are carried out ona regular basis and, in the case of equipment relevant for safety, via the redundant design that hasalready been mentioned.

4.4 Safety-Oriented Control UnitsA control unit that acts as protective equipment and puts the system into a secure state when

there is a deviation of the operating status from certain specified data, or in the case of a fire alarm,gas alarm, line break or after triggering of the manual EMERGENCY STOP switch, is used for safe

operation of the storage.A safety-oriented control device that consists of several units is used in order to prevent the

dangerous effects of internal system malfunctions towards the outside to persons and facility areas.These units are built up with their own equipment so as to be independent of the process controlsystem and are connected with each other between the facility sections and well sites via twoseparate remote-message cables.

All of the equipment has a self-monitoring, failsafe design, and this ensures that malfunctions thatarise in the individual system are immediately reported and that they always have effects on thesystem that are not dangerous.

The equipment is subjected to a prototype test by the Technical Monitoring Board in Germany andauthorized for use in systems with safety functions. All of the components of the safety equipmentwork in accordance with the closed-circuit current principle.

The transmitter connection lines (activation channels) are monitored by the system in such a way

that interference with safety does not arise due to short circuits or a line break in the connection lines.


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Depending on the triggering criterion, the individual units, facility portions, or the entire facility willbe shut down when this safety equipment triggers.

4.5 Storage WellsThe individual pipe strings of the casing were cemented up to the surface. All of the anulli behind

these pipes are fully sealed because of this. The tubings are sealed with packers in the production

casing, and the anullus is filled with inhibited water.The cementing of a casing string up to the surface prevents a gas migration through the

cemented anulli. The production casing of the storage wells gets two external casing packers in eachcase as an additional sealing element. They are packers with an external, armored rubber sealingring that is pumped up with hole fluid until there is contact with the drill-hole wall directly after thecementing process. The hole fluid remains enclosed in a latching system. The packers are positionedin such a way that the lower one is between the lower Detfurth layer and the upper Detfurth layer, andthe upper one is between the upper Detfurth layer and the Hardegsen or Solling sandstone, therebysealing the storage horizon for the cement.

The cementing was done before the filling of the storage with gas, so gas absorption during thesetting of the cement and an increased permeability because of this can be ruled out.

The quality of the casing cement was checked via a cement-bond log. The anullus was openedvia perforation, and there was a supplemental cementing process, when there were indications of poor

cementing.The tightness of the cementing is monitored with a permanent check of the pressure in all of the

anulli.Provisions were made for the installation of sand filters to prevent erosion and corrosion

associated with that. These sand filters (gravel packs) were designed in such a way that the transportfrom the formation sand into the filter is reliably prevented from the start. Co-transport of sand cantherefore be ruled out when there is a filter installation meeting the quality requirements. The sandtransfer is also prevented when there are very high flow rates, even in the case of a hypotheticalblowout.

The filter fittings for salt water with a high proportion of chloride ions were designed to counteractcorrosion.

4.6. Permanent Shear Preventer

This permanently-installed shear preventer can shut off the well, which is under gas pressure,under the X-mas tree (to the gas line connection) in any situation so as to be gas-tight. This shear-preventer is always available in the case of a workover that has become necessary after a fairly longoperating period as an additional safety shutoff device that is always ready to be used and that isintegrated into the well head. The extension pipe (shear joint) that is located above the tubingsuspension unit is sheared through by the closing process of the shear preventer, and the well isclosed up beneath the shearing jaw so as to be gas-tight. All of the shutoff valves on the well head -except for the shear preventer - and the underground safety valve have to be replaced by theworkover prevention system for most of the workover operations. The shear preventer represents anadditional piece of safety equipment that has not been stipulated, especially in the case of thismeasure (Fig. 4).


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Fig. 4 Well head with shear preventer

4.7. Line-Break-Control-System (LBCS)Clear criteria for registering a rupture have been determined via numerical simulation of the flow

events when there is a rupture in a field line of the Berlin gas storage. The operating conditions thatwere investigated can be divided up into the injection process and the withdrawl process. During theinjection process, a flow inversion comes about at the respective well site after a rupture in a field line.This flow condition, which is easy to check, can be determined after a time delay that depends on thedistance of the rupture point to the well site.

The influence of these variables on the flow development was investigated by varying theoperating parameters during the withdrawl process and the distance of the rupture point to the wellsite. It was discovered that the maximum mass flow that is released is determined by the operatingpressure. The number of wells that are open and the maximum mass flow that is thereby triggered inthe field lines, as well as the distance of the rupture point to the tap sites, only influence thechronological development of the flow.

The flow inversion is detected by so-called Anubar sensors. The sensors are (redundantly)equipped with two differential-pressure transmitters for each flow direction. If the remote operationmonitor for "injection" (differential-pressure transmitter for the injection flow direction) responds duringthe storage withdrawl process at the operating site and the remote operation monitor for "storagewithdrawl" simultaneously registers no values, the remote operation monitor assessment of an overallEMERGENCY STOP is triggered. If the remote operation monitor for "storage withdrawl" (differential-pressure transmitter for the storage withdrawl flow direction) responds during the injection process at awell site and the remote operation monitor for "injection" simultaneously registers no values, theremote operation monitor assessment of an overall EMERGENCY STOP is likewise triggered.

All of the valves and fittings are directly closed through the safety-oriented control unit via the"overall EMERGENCY STOP"; the compressors are additionally shut off when the storage process isinvolved, and all of the facility areas (storage withdrawl) are shut down via the control program. Thehydraulic valves are installed in the field lines in the form of quick-closing shutoff valves for the case of

a line break.


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4.8. Gas Displacement System and Residual Gas Compressor

The gas displacement system has the task of collecting gas that accumulates during the injectionand withdrawl and to pump it into the main gas lines. The residual gases involve exhaust gas, stripgas, leakage gas of the compressor lines and gas that accumulates when the facility pressure isrelieved.

Gas release from the quantities of driving-apparatus oil that accumulates during oil changes isalso a part of the residual gases. All of the residual gases are fed into a collection tank.

The residual gases are sucked out of the collection tank and compressed to the pressure of themain gas line with the aid of the residual gas compressor. The removal of the residual gases from thecollection tank is done while the tank pressure is regulated.

The system is designed in such a way that the frequency at which the residual gas compressor isswitched on is not greater than approx. every 4 hours (permitted load alternation frequency of thepipelines and tanks).

The lacking gas volume is fed in from the system's own gas supply when sufficient amounts ofresidual gas are not available. The excess gas pressure of at least 20 mbar (20 hPa) is monitoredand provided with alarm equipment.

5 MANAGEMENT

5.1 Organizational/Process-Structure MeasuresThe economic obligations, but also all of the obligations under public law to protect people, the

environment and physical property, have to be met. This requires a systematic approach to theorganization or process structure for the management, not only to properly handle the existingcircumstances, but also to ensure continuous improvement and to be able to react on short notice tochanges.

The following premises applied to the structuring of the organizational units:Awarding outside contracts for services, as well as the concentration of core tasks to teams and

functional areas. Obtaining know-how, i.e. obtaining the expert knowledge that is necessary anywayunder mining law for the implementation of the requirements.

An integrated management system has been introduced and certified according to the standardsDIN EN ISO 9001 and DIN EN ISO 14001 to ensure that the obligations are met and that a continuous

improvement process is ensured; the management system includes in a comprehensive way therequirements, as well as industrial safety and health protection, environmental protection and plantsafety. The processes of the Berlin natural gas storage have been displayed for simplifiedunderstanding as a process landscape, which presents both the sequence and the interaction of theprocesses between each other (Fig. 5).


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Fig. 5: Process landscape of the Berlin natural gas storage

The foundation of the management system is the differentiation of the operating processes intothe core process and support processes. The core process is the "proper operation in accordancewith the regulations" of the Berlin natural gas storage, which is followed by the implementation of thecustomer requirements as a management process, i.e. the provision of the required services andquantities. The processes are backed by process instructions that present the processes in theirsequences.

Quality primarily means meeting the customer requirements for the natural-gas storage.The safety and health of people, safety for the environment and the systems, as well as economic

success for the Berlin natural gas storage, have an equally high level of importance when meeting thecustomer requirements.

A component of the policies for the Berlin natural gas storage is to continually improve, andimprove with lasting effect, the industrial safety, environmental protection and facility safety. Theadherence to the relevant legal regulations and the official regulatory conditions is also a prerequisitefor this, as is the provision of the required resources by the management of GASAG.

All of the employees of the Berlin natural gas storage commit themselves:

To meet the customer expectations and to orient their actions, as the uppermost goal,towards anticipating and exceeding the customer expectations.

To protect the safety and health of all of the employees of the Berlin natural gas storage andthird-parties.

To improve environmental protection with lasting effect.

To safely operate the facilities.

To continuously improve the integrated management system.

5.2 Automated System and Storage-Site MonitoringThe production and pressure data of the storage sensors and of the gas facilities are directly

obtained from the process control system, processed and stored in a central database. The numericalreservoir simulation model can be updated on a daily basis because of this. The results of thesimulation are available on-line. The required data are obtained and organized in the course of theexecution of the core process. Production, log and test data flow into various sub-processes of thestorage-site operations.

Internal auditsContinous improvement

Management review

PoliciesandstrategiesofthecompanyGASAG

Human resource

development

Instructions Control of documents

Meetingthecustomerrequirements

Leadershipandcommunication

PoliciesandgoalsoftheBerlingasstorage

Maintenance

Planning, construction

Managementofresources

Operation of the facilities in accordance with regulations

Storageandwithdrawlplanning

Determinationofthecustomerrequirements

Determinationofcustomersatisfaction

Che

ckoftheorientationtowardsthepoliciesandgoalsofthecompanyGASAG


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5.3 Simulation Models

5.3.1 Geo-SimulationThe best-possible information regarding the geological conditions is necessary for the safe

operation of the storage. One difficulty involved in building up a reservoir model based on seismic datais the low resolution of the seismic data in the area of the reservoir sand. An improvement of the

resolution became possible through a combination of the seismic data with drill-hole data and aconversion of the seismic profiles to impedance profiles (seismic inversion). Other basiccharacteristics such as density and porosity, for instance, were derived from the impedance. Theseismic data acquired during the exploration phase were reprocessed and reinterpreted in accordancewith the improved evaluation processes and computer technology. An improved geological 3-D modelwas prepared with this and with the data from the drill holes. Not only the storage-site simulation wasable to be supplemented with this model; it was also used as a starting point for rock mechanicscalculations, in order to provide further assurance for the maximum authorized storage pressure andthe seal tightness of the cap rock layers.

5.3.2 Storage-Site SimulationThe storage reservoir, storage wells and the entire surface facility are depicted in a simulation

model in which the gas-industry requirements were added.

The history match was calibrated with the well head pressures, the down-hole pressures and thewater cut, and with the aid of the vertical and cross-sectional gas distribution. PLT logs and pulsed-neutron measurements were also used for the vertical sectioning of the block model and thecorresponding assignment of permeability and porosity. Furthermore, pressure build-upmeasurements were utilized, in particular during the development phase, for the listing of relativepermeabilities and for a check of the gas distribution.

The planning, filling and operation of the storage were guided with the help of the simulationmodel. The simulation is an important aid for evaluating the distribution of gas in the reservoir and alsofor calculating possible gas transfers in the Hardegsen and Solling sand lying between the storagehorizons and the cap rock. The simulation thereby serves, on the one hand, to control and optimizethe storage operation from the point of view of production-related aspects and, on the other hand, toensure and monitor the mining safety (Fig. 6).

Fig. 6 Simulation history match of the head pressure of a well

The storage monitoring is done with a comparison to the simulation model and regular gas-saturation measurements through pulsed-neutron logging.


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The geological and storage-site work can never be viewed as being complete. Results from theobservation of the storage make it necessary to work on a more detailed basis, time and time again.This is then helpful for better development of the individual storage areas or the planning of workovertasks.

The precise description of the reservoir behavior is also, in addition to the mining safety, animportant prerequisite for optimizing the storage behavior. The geological risk in the case of

refinishing work or new drilling, for example, can be substantially reduced in this way. Only then arethe forecasts of the storage behavior for long-term, medium-term and short-term planning possible.

5.3.3 MaintenanceThe well and storage-site facilities are monitored automatically to a great extent. The goal of the

on-line status monitoring is to get information on the status based on ongoing measurements ofvarious quantities and their analysis. The following improvements were achieved through the use ofthe on-line status diagnosis system:

Doing a clearer diagnosis of operating conditions and thereby improving the facilitysafety

Achieving an increase in the facility and tap availability

Monitoring of the efficiency (economic efficiency) and

Carrying out status-dependent maintenance and tap treatments

The maintenance of the storage wells is done on the basis of a target/actual comparison of thetheoretical drill-hole capacities with the current values.

There is a side-by-side comparison of the theoretical tap capacity (target value) and the actualwell capacity (actual value) for every storage well. The comparison is done in the form of a table.Deviates from the target value are emphasized in a suitable form.

The target value is calculated according to the C&n equation. The calculations are done withhead C&n values of the last multi-rate test that have been stored in the system. A static headpressure that is representative of the well at the point in time of the calculation is used from thesimulation, which is updated daily, as the confinement pressure. The current daily values of the wellfrom the database are used for the flow pressure and flow rate. If no current values are available (the

well is not in operation), the reading of the last operating day is used as a basis and it is appropriatelymarked.

Furthermore, the static well head pressure that is measured in the case of wells that are not inoperation is compared with the simulated static well pressure for quality control. An appropriatemessage is sent to the control system when there are deviations.

If deviations from the target status are discovered during the target/actual comparison of the wellcapacities, further investigation is done to determine the cause (drill-hole measurements, pressurebuild-up measurements). Suitable maintenance measures are taken depending on the results of theinvestigation.

A status-monitoring system (PROGNOST-NT), which is specially designed for the requirementsinvolved in the monitoring, evaluation and diagnosis of piston machines, is used for the on-line statusmonitoring of the piston compressors (Fig. 7).


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Fig. 7. Diagram of the principle of on-line monitoring of a piston compressor

The valves are among the main wearing parts in piston compressors. Special importance isattached to the early recognition and precise determination of a defective valve for this reason. Thesituation in the interior of the compression area can be directly evaluated through the permanentmeasurement of the cylinder chamber pressure. The chronological progression of the pressure that ismeasured is also presented as a p-V diagram (indicator diagram). Various characteristic values thatare each monitored with their own limit value can be calculated from the p-V diagram. The vibrationsmeasured at the cylinders, which are analyzed in 36 segments per 10 of crank angle and monitoredwith limit values, provide additional status information on the valves.

One method for determining the piston-ring wear is the piston-rod position or rod-drop analysis.The lowering of the piston rod is continuously measured here in operation with a proximity sensor. Ameasurable lowering of the piston rod comes about in the course of the operating life because of theabrasion on the piston rings.

The monitoring and control of the maintenance, under public law, as well as in business-technical

terms, are done through the program SAP R3-PM. The entire storage facility, including the storagewells, is portrayed in a way that is oriented towards maintenance in this system. The existing facilityidentification system forms the basis for the structuring. Furthermore, the program permits worksequences for maintenance measures to be stored.

The handling of malfunction messages, i.e. the initiation of repair measures, is to be done withoutpaper in the future. Two possibilities will be available to generate malfunction messages in the SAPsystem. On the one hand, through an input form of the process control system; the data are thentransferred to the SAP system and the message, as well as the work order resulting from that, isautomatically generated. Or, a message can be directly set up via a SAP work station. The work isthen carried out, controlled by priorities, after the messages are analyzed by authorized employees.


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References1. Schneider, A.,Stark M., Littmann, W. (2002). Erdgasspeicher Berlin-Methoden der

Betriebsfhrung. [Berlin Natural Gas Storage - Methods of Management.] Erdl Erdgas Kohle, 118 SXXX

2. Schneider, A., Stark, M., Littmann, W. (2001). Erdgasspeicher Berlin-Betriebsfhrung. [BerlinNatural Gas Storage - Management.] DGMK-Tagungsbericht 2001-2, S. 415

3. Burkowsky, M., Krekler, G. (1999). Erdgasspeicher Berlin. [Berlin Natural Gas Storage.] Gas-Erdgas gwf, 140 S.782.

4. Schmitz, J., Schneider, A. (1998). Erdgasspeicher Berlin. [Berlin Natural Gas Storage.] GEOBerlin 98, Exkursionsfhrer, Terra Nostra, Schriften der Alfred Wegener Stiftung 98/4

5. Krekler, G., Burkowsky, M. (1985). Erkundung der geologischen und lagerstttentechnischenGegebenheiten des Erdgas-Aquiferspeichers Berlin. [Exploration of the Geological and Storage-SiteCircumstances of the Berlin Natural Gas Aquifer Storage.] Gas-Erdgas gwf, 126 S. 151

6. Restin, K. 1984. Erdgas fr Berlin. Gas-Erdgas gwf, 125 S. 914

berlin gas storage

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