Top Banner
I 1Society of Petroleum Engheers SPE 48881 Enhanced Coalbed Methane Recovery Using C02 Injection: Worldwide Resource and C02 Sequestration Potential Scott H. Stevens, SPE; Denis Spector, Advanced Resources International, Inc. Pierce Riemer, IEA Greenhouse Gas R&D Programme Copyright 1998, Sociely of Petroleum Engineers, km This paper was prepared for presentation at the 1998 SPE International Conference and Exhibition in China held in Beijing, China, 2-6 November 1998. This papsr was selected for presentation by an SPE Program Committee following review of information contained in an abstract submitted by the author(s). Contents of the paper, as presented, have not bsen reviewsd by the Swiety of Petroleum Engineers and are subject to coneckm by ha author(s). The material, as presented, does not necessarily reflect any position of the Society of Petroleum Engineem, ita officers, or members. Papers presented at SPE me@Mgs are subject to publication review by Editorial Committees of the Society of Petroleum Engineers. Electronic reproduction, distribution, or storage of any part of this paper for commercial purposes without the written consent of the Society of Petroleum Engineers is pmhibted. Permission to reproduce in print is restricted to an abstract of not more than 300 words illustdcms may ti be copisd. l%e abstract must contain conspicuous acknowledgment of where and by whom the paper was presented. Write Librarian, SPE, P.O. Box 833836, Richardson, TX 73063-%36, U.S.A., fas 01-972-952-9435. Abstract Injeetion of carbon dioxide into deep coal seams has the potential to enhance coalbed methane recovery, while simultaneously sequestering a greenhouse gas. Analysis of production operations from the world’s fwst carbon dioxide-enhanced coalbed methrme (CO,-ECBM) pilot a 4-injector/7-producer pattern in the San Juan Basin, indicates that the process is technically and economically feasible. To date, over 2 Bcf of CO, has been sequestered with negligible breakthrough. Enhancement of gas production can be as high as 1500/0 over conventional pressure-depletion methods. Dewatering of the reservoir is also improved. ECBM development may be profitable in the San Juan basin at wellhead gas prices above $1.75/Met adding as much as 13 Tcf of additional methane resource potential within this mature basin. The key reservoir screening criteria for successful application of C02-ECBM include lateralIy continuous and permeable coal seams, concentrated seam geomeby, and minimal faulting and reservoir compartmentalization. Operational practices for CO,-ECBMreccwery are stiIl being refined. Injection wells should be completed unstimulated, while production wells can be cavitated or hydraulically stimulated. COa injection should be continuous and concurrent with methane production to prevent lateral water encroachment. Apart from the San Juan basin, many other coal basins have signi.tlcant C02-ECBM potential. In the U. S., the Uinta and Raton basins are geologically most favorable, while additional potential exists in the Greater Green River, Appalachian and other coal basins. Coal basins in Australia, Russia, China, India, Indonesia and other countries also have large COZ-ECBM potential. When viewed fi-om a commercial project viewpoint, the total worldwide potential for C02-ECBM is estimated at approximately 68 Tcf, with about 7.1 billion metric tons of associated COZsequestration potential. If viewed purely as a non-commercial COZ sequestration technology, the worldwide sequestration potential of deep coal seams maybe 20 to 50 times greater. Introduction Coalbed methane (CBM) has beeome a significant component of U.S. natural gas supplies. CBM production grew to 2.9 Bcfd of gas supply during 1997, accounting for about 6’70 of total U.S. natural gas production. 1 Essentially all CBM operations still employ prhmiry recovery methods, generally by pumping off large volumes of formation water to lower reservoir pressure and elicit methane deso@ion fi-om the coal. Primary production of coalbed methane recovers onIy 20°/0 to 60°/0 of original gas-in-place, depending on coal seam permeability, gas saturation, and other reservoir properties. Well spacing and other operational practices also will tiect recovery efficiency. Primary recovery thus bypasses a sizeable gas resource. For example, we estimate that primary production in developed areas of the San Juan basin alone may leave behind as much as 10 Tcf of natural gas in areas with completed coal seams. New technologies have been proposed for enhanced coalbed methane recovery (ECBM) to recover a larger &action of gas in place. The two principle variants of ECBM are 1) inert gas stripping using nitrogen injection and 2) displacement resorption employing carbon dioxide injeetion. Simulation and early demonstration projects indicate that N2-ECBM is capable of recovering 90% or more of gas in place, at an average incremental capital and operating cost of about $ 1.00/Mcf. 2 The C02-ECBM process is less well documented but likewise shows signit3cant promise for enhanced coalbed methane recovery. For the past three years, Burlington Resources, the world’s larges~ producer of eoalbed metlume, has been operating an 11-well COZ-ECBM pilot in the San Juan basin. Initial results show improvement in methane recovery in some wells with minimal breakthrough of COZ. However, due to the complex operational history of this pilot, this 489
13

Enhanced Coalbed Methane Recovery Using CO2 Injection ...

Feb 19, 2022

Download

Documents

dariahiddleston
Welcome message from author
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Page 1: Enhanced Coalbed Methane Recovery Using CO2 Injection ...

I

1Society of Petroleum Engheers

SPE 48881

Enhanced Coalbed Methane Recovery Using C02 Injection:Worldwide Resource and C02 Sequestration PotentialScott H. Stevens, SPE; Denis Spector, Advanced Resources International, Inc.Pierce Riemer, IEA Greenhouse Gas R&D Programme

Copyright 1998, Sociely of Petroleum Engineers, km

This paper was prepared for presentation at the 1998 SPE International Conference andExhibition in China held in Beijing, China, 2-6 November 1998.

This papsr was selected for presentation by an SPE Program Committee following review ofinformation contained in an abstract submitted by the author(s). Contents of the paper, aspresented, have not bsen reviewsd by the Swiety of Petroleum Engineers and are subject toconeckm by ha author(s). The material, as presented, does not necessarily reflect any positionof the Society of Petroleum Engineem, ita officers, or members. Papers presented at SPEme@Mgs are subject to publicationreview by Editorial Committees of the Society of PetroleumEngineers. Electronic reproduction, distribution, or storage of any part of this paper forcommercial purposes without the written consent of the Society of Petroleum Engineers ispmhibted. Permission to reproduce in print is restricted to an abstract of not more than 300words illustdcms may ti be copisd. l%e abstract must contain conspicuous acknowledgmentof where and by whom the paper was presented. Write Librarian, SPE, P.O. Box 833836,Richardson, TX 73063-%36, U.S.A., fas 01-972-952-9435.

AbstractInjeetion of carbon dioxide into deep coal seams has the potentialto enhance coalbed methane recovery, while simultaneouslysequestering a greenhouse gas. Analysis of production operationsfrom the world’s fwst carbon dioxide-enhanced coalbed methrme(CO,-ECBM) pilot a 4-injector/7-producer pattern in the San JuanBasin, indicates that the process is technically and economicallyfeasible. To date, over 2 Bcf of CO, has been sequestered withnegligible breakthrough. Enhancement of gas production can beas high as 1500/0over conventional pressure-depletion methods.

Dewatering of the reservoir is also improved. ECBM developmentmay be profitable in the San Juan basin at wellhead gas pricesabove $1.75/Met adding as much as 13 Tcf of additional methaneresource potential within this mature basin.

The key reservoir screening criteria for successful applicationof C02-ECBM include lateralIy continuous and permeable coalseams, concentrated seam geomeby, and minimal faulting andreservoir compartmentalization. Operational practices forCO,-ECBMreccwery are stiIl being refined. Injection wells shouldbe completed unstimulated, while production wells can becavitated or hydraulically stimulated. COa injection should becontinuous and concurrent with methane production to preventlateral water encroachment. Apart from the San Juan basin, manyother coal basins have signi.tlcant C02-ECBM potential. In theU. S., the Uinta and Raton basins are geologically most favorable,while additional potential exists in the Greater Green River,Appalachian and other coal basins. Coal basins in Australia,Russia, China, India, Indonesia and other countries also have large

COZ-ECBM potential. When viewed fi-om a commercial projectviewpoint, the total worldwide potential for C02-ECBM isestimated at approximately 68 Tcf, with about 7.1 billion metrictons of associated COZsequestration potential. If viewed purely as

a non-commercial COZ sequestration technology, the worldwidesequestration potential of deep coal seams maybe 20 to 50 timesgreater.

IntroductionCoalbed methane (CBM) has beeome a significant component ofU.S. natural gas supplies. CBM production grew to 2.9 Bcfd ofgas supply during 1997, accounting for about 6’70of total U.S.natural gas production. 1 Essentially all CBM operations stillemploy prhmiry recovery methods, generally by pumping off largevolumes of formation water to lower reservoir pressure and elicitmethane deso@ion fi-om the coal. Primary production of coalbedmethane recovers onIy 20°/0 to 60°/0 of original gas-in-place,depending on coal seam permeability, gas saturation, and otherreservoir properties. Well spacing and other operational practicesalso will tiect recovery efficiency. Primary recovery thusbypasses a sizeable gas resource. For example, we estimate thatprimary production in developed areas of the San Juan basin alonemay leave behind as much as 10 Tcf of natural gas in areas withcompleted coal seams.

New technologies have been proposed for enhanced coalbedmethane recovery (ECBM) to recover a larger &action of gas inplace. The two principle variants of ECBM are 1) inert gasstripping using nitrogen injection and 2) displacement resorptionemploying carbon dioxide injeetion. Simulation and earlydemonstration projects indicate that N2-ECBM is capable of

recovering 90% or more of gas in place, at an average incrementalcapital and operating cost of about $ 1.00/Mcf. 2 The C02-ECBMprocess is less well documented but likewise shows signit3cantpromise for enhanced coalbed methane recovery. For the pastthree years, Burlington Resources, the world’s larges~ producer ofeoalbed metlume, has been operating an 11-well COZ-ECBM pilotin the San Juan basin. Initial results show improvement in methanerecovery in some wells with minimal breakthrough of COZ.However, due to the complex operational history of this pilot, this

489

Page 2: Enhanced Coalbed Methane Recovery Using CO2 Injection ...

conclusion remains preliminary. The design, operation, and resultsof this pilot are presented here for the first time in print. Theyserve as a benchmark for our larger study of worldwideCOZ-ECBM potential.

A secondary benefit associated with the COZ-ECBM processis that it sequesters large volumes of carbon dioxide, a suspectedgreenhouse gas. Should global restrictions on COZ emissions bepromulgated, COZ-ECBM could be one of the very few profitabletechnologies for sequestering COZ. (The broadly analogousCOZ-EOR process both recycles and sequesters COZ.) Tradeablecredits for COZ sequestration could dramatically improveCOZ-ECBM economics over current performance levels. Thispaper, abstracted from our larger study, presents initial results ofresearch into the technical and economic feasibility of C02-ECBMapplication in worldwide coal basins.3

The C02-ECBM ProcessAt least four patents have been issued during the past two decadesrelating to the process of injecting carbon dioxide intomethane-bearing coal seams. 1.S.QTEach of these patents is based

on the principle that COZadsorbs more readily onto the coal matrixvis-a-vis methane. Injected COZ is preferentially adsorbed (andremains sequestered within the seam) at the expense of the coalbedmethane, which is simultaneously desorbed and thus can berecovered as ffee gas. (Nitrogen injection ECBM works using adifferent physical process by lowering the partial pressure ofmethane to elicit resorption). Because laboratory isothermmeasurements demonstrate that coal can adsorb roughly twice asmuch COZ by volume as methane, our working assumption is thatthe ECBM process stores 2 Mcf of COZ for every 1 Mcf of CH~desorbed and produced. However, the physical chemistry of thisprocess has not yet been fully defined, and there remains thepossibility fiat there are other physical processes active within thereservoir which could alter this ratio.

Allison Unit C02-ECBM PilotBurlington’s Allison Unit field contains the world’s f~st (and todate only) experimental COZ-ECBM recove~ pilot. The AllisonUnit is located within the northern portion of the San Juan basin,in northern New Mexico close to the Colorado border (Fig. 1).The San Juan basin is by far the most prolific coalbed methanedevelopment currently accounting for over 75% of total worldwideCBM production. It is also the most thoroughly studied fi-om areservoir standpoint. Prior to COZ injection, the Allison Unit hadbeen considered a sub-average petiormer, with gas productionrates less than half that of San Juan Basin Fairway wells (whichaverage about 3 MMcf&well), but it was still economically viable.Another reason for selecting the pilot location was its proximity toa major carbon dioxide pipeline that crosses the basin.

The Allison Unit pilot comprises four CO#njection wells andseven methane production wells in T32N-R6,7W (Fig. 2). Theproduction wells were drilled on 320-acre spacing. Formerly,these wells had been produced using conventional

pressure-depletion methods over a period of five years prior toinjection of C02. Dtiring mid-l 995, Burlington drilled the fourinjection wells in a diamond-shaped pattern also on 320-acrespacing and initiated COZinjection. Detailed well completion dataare presented in Table 1.

Injection wells for COZ-ECBM are similar to those used inenhanced oil recovery operations, such as the Permian oil fields ofWest Texas. Stainless steel or fiberglass tubulars, which arecorrosion-resistant, are not needed provided that the injected COZhas been dehydrated. In the Allison Unit, all four injection wellswere completed in essentially identical fashion (Fig. 3). Aftersetting 8-5/8 inch surface casing to a depth of about 350 feet,Burlington Resources drilled through the Fruitland coal formationusing a 7-7/8 inch bit to total depth of about 3,300 feet. Productioncasing (5- 1/2 inch) was then cemented across the Fruitland coalzones and perforated. Acidization and hydraulic stimulation wereavoided in order to reduce the risk of connecting to natural conduitsthat could channel injected COZ outside of the targeted coalreservoir.

The production wells at the Allison Unit field were drilledduring the late 1980’s, prior to any plans for ECBM application.The nine producing wells were completed using two dissimilartechniques -- natural completion or cavitation; none of the wellswere hydraulically stimulated. In addition, several of theproduction wells were re-cavitated after COZ injection began. Afin-ther complication is that production has been discontinuous overthe pilot life. This diversity in operation style and history hindersanalysis of the efficacy of the C02-ECBM process at the AllisonUnit. To resolve this, the authors plan to integrate initial resultsti-om the Allison Unit into a field-wide reservoir simulation studyusing ARI’s COMET2 coalbed methane simulator, which iscapable of accurately modeling enhanced recovery using COZ.

As shown in Figure 4, the Allison Unit production wellstypically were spudded using a 12-1/4 inch bit and drilled to adepth of about 250 feet. Surface casing (9-5/8 inch) was thencemented in place. An 8-3/4 inch hole was drilled to just above theFruitland coal (3,000 feet), and 7-inch intermediate casing wastop-set and cemented in place. Finally, a 6-1/4 inch hole wasdrilled through the Fruitland coal to a total depth of about 3,200feet. The well was either completed open-hole or pre-drilled 5- 1/2inch liner was positioned across the coal seams. Five of the wellswere cavitated or re-cavitat~ while the remaining four wells werecompleted without stimulation.

Operation at the Allison Unit pilot began with an initial6-month period of C02 injedion, during which time the productionwells were temporarily shut in. Although initially intended to allowpressure buildup within the reservoir, in order to promotesubstitution of COZ for methane, shutting in the wells may havebeen detrimental to gas production. Injection rates weremaintained at a relatively constant rate of 600 to 750Mcfd/injection well. Breakthrough of CO, has been minimal

490

Page 3: Enhanced Coalbed Methane Recovery Using CO2 Injection ...

ENHANCED COALBED METHANE RECOVERY USING C02 INJECTION:48881 WORLDWIDE RESOURCE AND C02 SEQUESTRATION POTENTIAL 3

during the life of the project: following 3 years of injection currentCOZ concentrations at the production wells average 0.4’%0,whichis only slightly above initial pre-injection levels of 0.3°/0. Thissuggests that tbe physical processes of COZ sequestration and CHArelease indeed are taking place.

Unfortunately, the production record at the Allison Unit pilotis somewhat ambiguous. Some wells exhibit strong productionenhancement whereas others actually declined (Fig. 5). Below, weexamine in detail the response of two of the wells to C02 injection.First, gas production born the #113 well (which was shut in)suffered, probably due to water encroachment. In contrast, theproduction record of the second well (#1 15, which was not shut in)is more favorable, exhibiting a dramatic ( 150°/0) improvement ingas production rate. We conclude that the difference inperformance is largely due to operational procedures, rather thanreservoir variation, and that fhture C02-ECBM pilots can achievesigdcant enhanced recovery as “best practices” operationalprocedures are developed.

Following commencement of COZ injection at the AllisonUnit, CBM production frequently was lower than pre-injectionIevels. For example, the #l 13 weII had exhibited typical inclininggas production during its initial five years of operation, improvingto a plateau of about 2 MMcfd during late 1994, just prior to C02injection (Fig. 6). However, after the well was shut in and thenreturned to production during mid-1996, the gas production ratehad fallen to only one-half of pre-injection levels. Gas productionthen improved gradually, but only to about 1.3 MMcfd by early1997. During the same period, the water production rate rosedramatically to 100 BWPD following injectio~ pre-injection waterproduction levels had been reduced to essentially zero. The reasonfor this initial poor performance is likely due to:

1) Water Encroachment: Shutting in the well for two yearsallowed encroachment of water into the reservoir suxounding thewellbore. Higher reservoir pressure slowed the resorption ofmethane ti-om the coal reservoir. More seriously, higher watersaturation resulted in much less favorable relative permeability togas and thus lower gas production.

2) Improved Contact with Bypassed Reservoir Area:Simultaneously, the injection of COZ at high pressure swept freewater from the coal pore and IYacture systems within the reservoir.This effect was particularly strong in regions of the reservoir thatmay have been isolated under normal pressure depletionoperations.

Continued operation of the pilot is starting to overcome thedeleterious effects of water encroachmentkweep, resulting in

normal declining water and inclining gas production. In a sense,

theeffkctivedewatering is a positive indication, demonstrating thatthe C02 process is efficient and that long-term gas recovery islikely to be enhanced.

In contrast, the Allison Unit#115 well exhibits a very ditlerent(and much more positive) production history (Fig. 7). The #115well was completed without stimulation (natural), with 5-1/2 inchpre-drilkxl liner set across the Fruitland coal interval. Prior to COZinjection, the #11 5 well had been a relatively lackluster producer.Although et%ctively dewatered (<5 BWPD), the well had attaineda modest gas rate of just 500 Mcfd by early 1995. However,following COZ injectio~ the gas rate increased dramatically toabout 1.3 MMcfd. Water production also jumped markedly, butthen declined steadily to 50 BWPD. The level of gas productionrate improvement (750 Mcfd) is comparable to the COZ injectionrate for one injection well. The positive petiormance of the #115well is probably due to the fact that it was operated continuouslywithout shut-in throughout the ltie of the pilot, precluding orlimiting water encroachment.

We view the enhanced production achieved in the #l 15 wellas illustrative of “best practices” COZ-ECBM, at least during thecurrent preliminary development of this technology. Future R&Dand operational experience may be expected to lead to furtherimprovements in recovery.

C02 SourcesA variety of C02 sources, both natural and anthropogenic, may beused within COZ-ECBM recovery operations. Naturally occurring,high-pressure CO, from underground reservoirs is likely to be thelowest cost source, provided that the transport distance to the CBMfield is not excessive. The Burlington pilot utilizes approximately3 MMcfd of naturally occurring COT produced at McEhno Dome

field in southwestern Colorado. Shell CO, Co. operates an existingpipeline that transports about 900 MMcfd of COZ fi-om McEhnoDome across the San Juan basin to the Permian basin of WestTexas, where it is injected for enhanced oil recovery operations.A short (30-mile) connector links the Allison Unit to this CO,pipeline. Line pressure of the main Cortez pipeline is

approximately 2,000 psi, which is then reduced to 1,500 psi in theconnector. The C02 is injected at bottom-hole pressures of about1,100 psi, safely below the formation fi-acture gradient. InjectedCOZ is of high purity (99’%.) and essentially dry. Thus, theavailability of high-quality, high-pressure C02 in this portion of theSan Juan basin is particularly favorable. Delivered supply costsare approximately $0.50/Mcf of COZ.

A second option for sourcing COZ is to utilize anthropogenicsources that currently are being vented to the atmosphere. In theSan Juan Fairway, the natural COZ concentration of produced coaIseam gas is 6 to 12Y0. Over 150 MMcfd of C02 is currentlyseparated born produced CBM and vented in the San Juan basin toenable the gas to meet pipeline specitlcations. However, becausethis waste C02 stream is vented at atmospheric pressure,signdlcant compression would be required to boost line pressure

to injection levels. For a small pilot of limited duration, the highercapital costs of compression make McEhno Dome COZ moreattractive than separated C02, although this may not be true for

491

Page 4: Enhanced Coalbed Methane Recovery Using CO2 Injection ...

~4 4a881

commercial operations.

Finally, and of particular relevance to the control of potentialgreenhouse gas emissions, industrial COZ may also be used asinjectant in ECBM operations. Potential industrial COZ sourcesinclude primarily coal- or gas-fwed power plants and other largeindustrial plants. Industrial C02 is not widely available in the SanJuan basin, but could be a viable source in other coalbed methanebasins (particularly the Appalachian basins). Unlike relativelypure natural fxrnation COZ sources, however, industrial emissionsrequire considerable processing to remove water, SOX, and otherundesirable constituents. Industrial CO~ also requires

compression. These considerations probably make industrial COZless economic as a source of injectant than natural deposits orprocessed natural gas streams. Nevertheless, potential titure

restrictions on emissions could make industrial COJ more costeffective. For example, an industrial emitter may find iteconomically attractive to pay a CBM operator to sequester COZ.Under tlis scentio, handling and disposing of CO, injectant couldactually became a revenue stream for a CBM operation, rather justthan a cost.

Reservoir Screening CriteriaReservoir screening criteria are essential for locating favorableareas fm successfid application of COZ-ECBM, these criteria havenot yet been filly defined. Some of these criteria are likely to besimilar to those established for similar injection-based processes,such as watertlood and steamflood operations. We have expandedand refinedthesecriteria, based on the results of scoping reservoirsimulation, to develop a preliminary list of fwst-order reservoircharacttistics that are important for COZ-ECBM application. Thekey criteria are likely to be:

1) Homogeneous Reservoir: The coal seam reservoir(s) shouldbe laterally continuous and vertically isolated from surroundingstrata. This ensures containment of injectant within the reservoiras well as efficient lateral sweep through the reservoir.

2) Siiple Structure: The reservoir should be minimally faultedand folded. Closely spaced faults can compartmentalize thereservoir into isolated blocks, inhibiting effective sweep. Thefaults themselves may divert injectant away from the reservoir,reducing the efficiency of enhanced recovery and sequestration. inadditiom structurally complex areas fi-equently have damaged coalcleat systems and low permeability.

3) Adequate Permeability: Although no minimum permeabilitycriterion can be specifi~ our preliminary simulation indicates thatat least moderate permeability is necessary for effective ECBM (1to 5 mD). Because many coal basins throughout the world havemuch lower permeability, locating adequate permeability is aprimary exploration challenge.

4) Optimal Depth Window Just as for conventional CBM,ECBM recovew is likely to be most successful within a depth

window, which varies by basin. This is because shallow reservoirstend to be low in reservoir pressure and gas content, whereas deepreservoirs sufkr from diminished permeability. For deep settings,COZ injection may actually improve permeability by maintainingpore pressure.

5) Coal Geometry: Concentrated coal deposits (few, thick seams)are generally favored over stratigraphically dispersed (muitiple,thin seams) settings. Likewise, thick “completable” coals arepreferred over thin coals that cannot be etliciently targeted.

6) Gas Saturated Conditions: Coal reservoirs that are saturatedwith respect to methme are preferred from an economic viewpoint,since metlume production is not seriousIy delayed. Undersaturatedareas can experience delay in methane production, although COZinjection could reduce delays by increasing saturation. From asequestration viewpoint, undersaturated coal seams are stilleffective COZ disposal zones.

Other secondary reservoir criteria likely to afi%ct ECBMrecovery include coal rank, coal maceral composition, ash content,gas composition, as ‘-well as numerous other factors. Thesecharacteristics are shared in common with conventional CBMrequirements, but for the most part they are expected to onlymarginally affect ECBM economics.

Worldwide Potentialfor C02-ECBIMFinally, our study examined the potential for application ofC02-ECBM recovery and CO, sequestration in worldwide coalbasins. This analysis was based on a) the petiormance of theAllison Unit pilot as a preliminary benchmark b) the reservoir andbasin screening criteria outlined above; and c) ARI’s proprietarydata base of CBM reservoir properties in international coal basins.We wnclude that the potential for this process is indeed signit3cant,botl from the point of view of enhanced methane recovery and CO,sequestration potential. We focused on geologically favorablebasin settings where CO,-ECBM recovery could be profitablydeveloped. A COZ-supply cost of $0.50/Mcf was assumed. Forthese areas our analysis indicates an ultimate, enhanced-recoverymethane resource of approximately 68 Tcf worldwide. Up to 7.1million tonnes of COZ could be sequestered within these favorablesettings. Far more COt, perhaps 20 to 50 times as much,ultimately wuld be sequestered in less favorable coal settings, butunder sub-economic conditions as a net disposal cost rather than aprofitable venture.

Coal basins were ranked based on a number of diverse criteriathat influence project success. Criteria included both technicalmeasures (reservoir quality/quantity) and project developmentcriteria (development costs/gas market/CO1 availability). Theindividual criteria that influenced overall rank can be grouped intothree general categories:

492

Page 5: Enhanced Coalbed Methane Recovery Using CO2 Injection ...

ENHANCED COALBED METHANE RECOVERY USING C02 INJECTION: I

48881 WORLDWIDE RESOURCE AND C02 SEQUESTRATION POTENTIAL 5

1. CBM Resources: Separately ranked criteria included coalseam eompletable thickness (f&t); gas content and saturation; totalprospective gas in place (Tcf); technically recoverable resources(Tcf); and resource concentration (Bcf/mi2).

2. Costs/Markets: Capital and operating costs ($/Mc~; currentand future natural gas markets (subjective).

3. C02-ECBM PotentiaI: Availability of C02 (subjective);reeovery enhancement factor (related to permeability and structuralsetting).

The results of our assessment of worldwide applicability ofC02-ECBM technology is summarized below for the high-potentialcountries and basins (Table 2).

United States. The U.S. has by far the brightest outlook forsuccessful near-term commercial application of C02-ECBMrecovery technolo~. This is beeause a) CBM resources in severalbasins appem to be geologically suitable for enhanced recoverytechnology b) large COZ resourees are accessible via establishedpipeline systems, and anthropogenic C02 sources also are availablefor injectanc c) the U.S. natural gas pipeline infrastructure andend-use markets are well developd, d) U.S. production companieshave expertise and confidence in investing in CBM technology andfield development and e) service companies and equipmentmantiacturers compete in an efficient supply market, minimizingdevelopment costs. Three U.S. basins (San Juan, Uinta, Raton)appear to have particular potential for COZ-ECBM recovery. Otherbasins (Appalachian, Warrior, etc.) have lower permeability andare not discussed here, but these areas also may be suitable forenhanced reeove~.

San JuanBasin Thismature CBM basin averaged 2.5 Bcfdof gas production from nearly 4,000 producing wells during 1997.Over 14 Tcf of CBM reserves have been booked to date. The SanJuan ranked highest using our ranking scheme for C02-ECBMfeasibility (29 out of a possible score of 30). It is also the site ofthe first eornmercial pilot. We anticipate that operators could applyC02-ECBM on a large scale in this basin during the next decade.The Fruitland Fm. coal seams are thick, concentrated, IateraIIyconsistent, and -permeable. Structural faulting and reservoircompartmentalization are minor. Reservoir data control andcharacterization are excellent. A COZ pipeline carries nearly 1Bcfd across the center of the basin, while additional waste COJ

from gas prwessing is available. Development and operating costsfor CBM are low. Natural gas pipelines are abundant, althoughwellhead prices are not high. We estimate that widespreadapplication of C02-ECBM could add up to 13 Tcf of reserves inthe San Juan basin, while sequestering about 1.4 billion tonnes ofCOT

Uinta and Raton Basins. CBM development in theseemerging basins is not as mature as in the San Juan, although

several hundred CBM wells are currently on line and 0.6 Tcf ofCBM reserves have been added. The Ferron and Vermejoreservoin in these respective basins resemble the Fruitland coal ofthe San Juan, except that coal seams are somewhat thinner andhave lower gas content. We estimate an additional 2.2 Tcf ofpotential for the Uinta basin (ranked 24/30) and 0.8 Tcf for theRaton basin (23/30). CO, sequestration potential in eomrnerciallyviable projects is estimated to be 230 and 85 million tonnes,respectively.

Australia. Atler the U. S., Australia is likely to become the nextcountry to experience widespread commercial development ofCBM. Five large basins in eastern Australia have CBM resourcepotential assessed at over 500 Tcf in place: Bowen, Sydney,Gunnedah, Galilee, and Clarence-Moreton.8 Conoeo’s 20-wellproject in the Bowen basin currently produces about 6 MMcfd, andis the first significant (albeit still modest) CBM project outside theU.S. However, the producibility of Permian coal seams inAustralia has not been as favorable as in the western U. S., dueprimarily to high stress and low permeability. Industrydevelopment costs are significantly higher than in the U. S. Despitethis, two basins have particular potential for C02-ECBMapplication

Bowen Bash Thishugebasin (ranked 24/30) in east-centralQueensland contains over 100 Tcf of targetable CBM resources inthe Moranbah and Rangal Formations. The better portions of thebasin contain thick concentrated coal seams with high gas contentand moderate permeability. However, long-term developmentcosts are likely to be 25°/0 higher than in the San Juan. Pipelineinii-asttucture also is limited and wellhead gas prices currently arebelow US$2.00/Mcf Industrial COZ emissions fi-om coal-fwedpower plants constitute a potential source of injectant, as is 130MMcfd of COZcurrently v_gntedborn gas fields in the Cooper basin(although a CO, pipeline would need to be constructed). Weestimate that widespread application of COZ-ECBM recovery couldadd 8.3 Tcf in the Bowen basin, while sequestering about 870million tonnes of COZ.

SydZey Basin. The Sydney basin (22/30) is particularly wellIoeated to gas markets and industrial C02 sources. Wellhead gas

prices are high, while coal-fired power plants could provide aready source of COZ injectant. However, initial testing hasencountered limited permeability in the Illawarra and equivalentcoal measures, due to high stress and local mineralization. Whileexploration activity has slowed recently, the prospective resourceof over 70 Tcf in place has been only partly tested. C02-ECBMdevelopment in just a few percent of the Sydney basin could addabout 1.4 Tcf of natural gas reserves and sequester 150 milliontonnes of COZ.

Russia. Numerous coal basins exist in Russia, but no commercialCBM development has taken place (apart from in-mine methanerecovery). However, the 30,000-km2 Kuznetsk basin in

493

Page 6: Enhanced Coalbed Methane Recovery Using CO2 Injection ...

south-central Russia appears to have significant potential (24/30).Gas in place is estimated at 400 Tcf, with an attractive averageresource concentration of 35 BcMni2. Structure is favorablysimple, with indications of moderately high permeability.Coal-fued power plants and other industrial C02 sources areabundant witlin the Kuznetsk basin. We estimate about 10 Tcf ofenhanced recovery potential. Approximately 1 billion tonnes ofC02 could be sequestered.

India Two signitlcant CBM areas exist in India.g The Damodarcoal fields (19/30) in eastern India are better known, but are smalland structurally complex. Deliverability fkom the poorly cleatedPermian Gondwana coals is limited by low permeability. TheCambay basin located in heavily industrialized Gujarat state maybe a more favorable area (23/30). The Carnbay contains thick,low-rank coal deposits within the Tertiary Kadi and KalolFormations. Initial testing indicates low-moderate gas content andIirnited permeability, but the unusually thick coal provides kh. TheCambay is a petroleum producing basin with good infrastructureand services, including some gas pipelines; data control also isgood. Wellhead natural gas prices are considered to be favorable(US$3.00/Mcf). We speculate that 0.7 Tcf of methane (out ofabout 35 Tcf in place) may be recovered using COZ-ECBM incommercial projects. About 74 million tonnes of COZ may besequestered.

China. Initial CBM testing in China has coni%med large resourcepotential (500 to 1,000 Tcf in place),’” but most areas appear tohave low permeability. Two very ditlerent settings exist ineast-central China for potential C02-ECBM within thePermo-Carboni?erous coal deposits.

NE China The Northeast China coal region (19/30)comprises a number of small- to medium-sized, discontinuous coalfields that stretch fi-om Anhui Province in the south to Liaoning inthe north. NE China is a heavily industrialized region with rapidlygrowing urban gas demand and numerous coal-fired power plantsfor C02 injectant. Natural CO ~sources also are abundant inpetroleum fields of eastern China. 11 However, there is no existing

gas pipeline infrastructure, apart born local town gas distributionsystems. Despite attractive resource concentration and gas content,permeability in two dozen CBM test coreholes drilled to date hasbeen low (<lmll). Potential reservoirs are tlagmented by intensefaulting. Due to poor producibility, we estimate only about 0.2 Tcfof technically recoverable methane resources in commercialCO,-ECBM projects, with about 21 million tonnes of C02sequestration potential.

Ordos Basin. This large coal basin in north-central China hassuperior reservoir quality compared with NE China, but lessfavorable market and CO, supply outlooks (thus an identical 19/30score). The key geologic distinction is that the Ordos basin isstructurally simple, with minimal faulting and gentle dip.Preliminary testing indicates that permeability is an order ofmagnitude higher than in NE China. A small CBM production

pilot has produced at rates of up to 250 Mcfdlwell. Amoco,Phillips, aud ARCO have CBM exploration programs in the Ordos.Unfortunately, no significant natural COZ sources exist andanthropogenic sources are also limited. Two new natural gaspipelines entered operation during 1997, crossing the CBM areasand improving market access. We estimate that commercialCOZ-ECBM application could add 6.4 Tcf of gas potential, whilesequestering about 660 million tonnes of COZ.

Canada. Technically recoverable CBM resources in CWada aresubstantial, estimated at 135-261 Tcf within the CretaceusManville and Scollard Formations in the Western Canadasedimentary basin in Alberta. 12 Other smaller basins exist inBritish Columbia and eastern Canada but appear to be lessfavorable. However, despite an estimated $40 million investmentin E&P, development in western Canada has not occurred due topoor test results and low wellhead gas prices.’3 Undersaturationand low permeability appear to be widespread reservoir problems.However, the gas pipeline infi-astructure is well developed anddevelopment costs are low. We estimate that the potential forCOZ-ECBM application in commercial projects is about 1.6 Tcf ofenhanced methane production, along with perhaps 170 milliontonnes of carbon sequestration. Non-commercial projects couldsequester far more COZ.

Other Countries. Significant additional potential also existswithin other coal basins for COZ-ECBM application, although theseareas appear to be less favorable for a variety of geologic andmarket reasons. The Donetsk basin in Ukraine is structurallycomplex and probably not suitable for injection of COZ. The Southand Central Sumatra basins in Indonesia may have favorablereservoir, gas market and COZavailability conditions but no testinghas yet taken place. Western and Eastern European coal fieldshave abundant industrial C02, but sutler from complex structure,undersaturated reservoirs, and high costs. The Zambezi and MainKaroo coal fields in Southern A.tiica may have potential but testinghas been limited.

Conclusions/Future R&DTechnology development and application for C02-ECBM recoveryis still at a nascent stage. The potential for simultaneous enhancedmethane recovery and carbon dioxide sequestration using thisprocess appears to be favorable. Based on early projectperformance and preliminary resource assessments, about 68 Tcfof enhanced recovery potential is estimated for favorable(potentially commercial) settings. If successfully applied, anestimated 7.1 billion tons of COZ may be permanently sequesteredin deep, unminable coal seams. A far larger volume of C02 couldbe sequestered in deep coal seams, but at a net operating cost.Additional R&D is needed to confh-m the potential of thistechnology, including:

1) Field-wide reservoir simulation study of the Allison UnitCOZ-ECBM pilot in the San Juan basin to establish theperformance of ECBM;

494

Page 7: Enhanced Coalbed Methane Recovery Using CO2 Injection ...

ENHANCED COALBED METHANE RECOVERY USING C02 INJECTION:48881 WORLDWIDE RESOURCE AND C02 SEQUESTRATION POTENTIAL 7

I

2) Refinement and upgrades to coalbed methane reservoir 9.

simulators to validate existing models and optimize fielddevelopment.

10.

3) Selection and implementation of a multi-well C02-ECBMdemonstration project within a thoroughly studied coal basin, suchas the San Juan. Controlled field experiments of injection and 11.production well technology could be conducted to optimizeCOZ-ECBM operating procedures (much as the COAL site in theSan Juan basin demonstrated coalbed methane technology).

4) Improved matching of reservoir, gas market, and C02 12.

availability within international coal basins to more rigorouslyestablish the worldwide potential of COZ-ECBM and to target 13.medium-term pilot projects.

AcknowledgmentsThe authors wish to thank the IEA Greenhouse Gas R&DProgramme for their generous support of this study. We also thankCraig McCracken of Burlington Resources and Dan Yee of Amocofor valuable discussions of the ECBM process. Finally, we wish torecognize the contributions of Vello Kuuskraa and JonathanO’Donnell of ARI.

References

1.

2.

3.

4.

5.

6.

7.

8.

Stevens, S.H., Kuuskraa, J.A., and Schraufnagel, R.A., “TechnologySpursGrowthof CoalbcdMethane,” Oil and Gas Journal, January 1,1996, pp. 56-63.

Yee, D. and Puri, R., “Enhanced Coalbed Methane Technology inthe San Juan Basin,” presented at Pittsburgh Coalbed MethaneForum, April 14, 1995.

Stevens, S.H. and Spector, D., “Enhanced Coalbed MethaneRecov~ Worldwide Application and C02 Sequestration Potential,”IEA/CON/97/27, report prepared for IEA Greenhouse Gas R&DProgramme, 1998.

Every, R.L. et al., “Method for Removing Methane from Coal,”Conoco, Inc., U.S. Patent No. 4,043,395, August 23,1977.

Shirley, A.I. et al., “Method of Recovery of Natural Gases fromUnderground Coal Formations,” The BOC Group, Inc., U.S. PatentNo. 5,332,036, July 26, 1994.

Wilson, D.R. et al., “Coal Bed Methane Recovery,” Conoco, Inc.,U.S. Patent No. 5,402,847, April 4, 1995.

Chaback, J.J. et al., “Method for Recovering Methane from a SolidCarbonaceous Subterranean Formation,” Amoco Corp., U.S. PatentNo. 5,566,756, October 22, 1996.

Australian Gas Association, “Coalbed Methane Potential ofAustralia,” 1995.

Kelafmt, J., “Coalbed Methane Development in India,” Oil and GasJournal, May 25, 1998.

Chen, M.H., “Introductory Statement,” United Nations InternationalConference on Coalbed Methane Development and Utilization,Beijing, October 17-21, 1995.

Dai, J.X., Song, Y., Dai, C.S., and Wang, D.R., “Geochemistry andAccumulation of Carbon Dioxide Gases in China,” AmericanAssociationof Petroleum Geologists Bulletin, v. 80, pp. 1615-1626,1996.

Canadian Gas Potential Committee, “Natural Gas Potential inCanada,” pp. 73-74, 1997.

Sinclair, K.G. and Cranstone, J.R., “Canadian Coalbed Methane: theBirth of an Industry,” International Coalbed Methane SymposiumProceedings, May 12-17, 1997, pp. 115-120.

495

Page 8: Enhanced Coalbed Methane Recovery Using CO2 Injection ...

~ S OTT H. STEVE~CE RIEMER 48881

Table 1Well Completion Summary, Burlington Resources Allison Unit C02-ECBM Pilot, San Juan Basin

Allison Unit Wells, Producers

Ll& z % :5 “Fc::“n%‘~:? :~t”Eii?i!d‘x::CZ:-t112 12/31/88 3148 9 5/8 235 7 3030 - - 2318 3111 OPEN HOLE 5/13195 Recavitate

113 7/12/89 3094 9 5/8 235 7 3012 5.5 3095 2318 3062 3011 3093 NA

114 1/15/89 3149 9 5/8 223 7 3077 5.5 3149 2 3/8 3133 3059 3148 NA

115 12/29188 3170 9 5/8 237 7 3083 5.5 3170 2318 3153 3081 3168 NA

120 6/24189 3087 9518 251 7 3001 5.5 3086 2 3/8 3059 2998 3083 4122[96 Underrearn andrecavitate

121 12/22/88 3246 9 5/8 231 7 3178 5.5 3246 2 3/8 3240 3159 3245 NA

130 2/4/89 3200 9 5/8 241 7 3101 - - 2 3/8 3162 OPEN HOLE 5123/93 Cavitated,installed liner

131 1/3 1/89 3245 9518 239 7 3111 4.5 3240 2 3/8 3191 3123 3203 4/4196 Sidetrackcavitate, holeprobs

132 6/24/89 3169 9 5/8 252 7 3111 5.5 3168 2318 3141 3080 3167 1212193 Recavitate

.llison Unit Wells, C02 In,iectors

al General Original Completion Perforations

J1142 11/14/94 3386

14? II 12/S/94 t X379

Csg Set Csg Set Liner Set Tubing(in) (ft) (in) (ft) (in) (ft) (in ) :$ EEIEIE

8 5/8 358 5.5 3435 - - 2718 3062 3090 3110 3119

8 5/8 382 5.5 3426 - - 2 7/8 3050 3090 3138

8 5/8 384 5.5 3385 - - 2718 3022 3049 3078 3092

8 5/8 374 5.5 3376 - - 2 7/8 2950 2996 3018 3082

496

Page 9: Enhanced Coalbed Methane Recovery Using CO2 Injection ...

48881ENHANCED COALBED METHANE RECOVERY USING C02 INJECTION:

WORLDWIDE RESOURCE AND CO. SEQUESTRATION POTENTIAL

Table 2Ranking of World’s Most Prospective Coal Deposits forCOz-ECBM Recovery

9

Coal Basinf Country POtentiaI Resource ECBM Develop. Gas co* Overall RankingRegion

co2- C02Reserves COncen- ProducibiIity costs Sales Avai- Score Enhanced Sequestration

tmdion Market lability Reserves’ Potential

(’r’co (106 tons)

San Juan U.S.A. 5 5 5 5 4 5 29 1 13.0 1,400

Uinta U.S.A. 2 3 5 5 4 5 24 2 2.2 230

Kuznetsk Russia 5 4 4 3 4 4 24 3 10 1,000

Bowen Australia 5 4 4 4 4 3 24 4 8.3 870

Raton U.S.A. 2 3 4 5 4 5 23 5 0.8 90

Cambay India 3 5 3 4 5 3 23 6 0.7 70

Sydney Australia 4 4 3 3 4 4 22 7 1.4 150

Sumatra Indonesia 4 3 3 3 4 4 21 8 3.5 370

Western Canada 4 2 3 4 3 3 19 9 1.6 170Canada

Damodar India 2 3 2 4 4 4 19 10 0.1 10Valley

Donetsk Ukraine/ 1 5 2 3 4 4 19 11 0.3 30

Russia

NE China China 2 4 2 3 4 4 19 12 0.2 20

Ordos China 4 3 4 3 2 2 18 13 6.4 660

*Estimated reserves additional to pressure-depleted recovery Total High-Potential Basins 48.5 5,070

Scale: 1 (lowest) to 5 (highest)

497

Page 10: Enhanced Coalbed Methane Recovery Using CO2 Injection ...

., ,‘ 10 SCOTT H. STEVENS, DENIS SPECTOR, PIERCE RIEMER 48881

Figure 1: Location of Burlington Resources’ COZ-ECBM Pilot, San Juan Basin, USA

LA PLATA CO. [ ARCHULETA CO.

Dome U’)CO, Field ~

=o

ma=.x

----- -----NEW MEXICO

m.,17R

Figure 2: Location of Production and Injection Wells, Allison Unit COZ-ECBM Pilot, San Juan Basin

.!07$224 .m ,, 44 .,,,,.. .1,,M M .,,,m * ..,,.24

-

.W,, 4, .O, a!,

mm.

22 23 ALLISON UNIT 18 17

~

SM.

ma !2

T32NR7\ vALLISON UNr

ALLISON UNITg

T32NR6W+ 4LLISON UNIT

.W.a.

130 ,@142

25 24ALLISON UNIT

19 ~ 20),LLISON UNIT

ALLISON U IT115

ALLISON LINI

*

‘g 9 4LLl# UNIT—141

ALLISON U&l T

*32 143~ .,. s

ALLISON UN1-”

ALLIS

2%

UNIT

*$?. 35 364LL,SC# UNIT30

29—

$20

I

-II >’ 1 31 32—

— — — — — — — —

. . . . . . ---,HJUYU2,LIX

Page 11: Enhanced Coalbed Methane Recovery Using CO2 Injection ...

ENHANCED COALBED METHANE RECOVERY USING C02 INJECTION:

48881 WORLDWIDE RESOURCE AND CO, SEQUESTRATION POTENTIAL 11

Figure 3: Completion Schematic for C02 Injection Wells, Allison Unit Pilot, San Juan Basin

AFO0981 .CDR

ALLISON UNIT #140BASIN FRUITLAND COAL

SEC. 19. T32N.R6W. SAN JUAN COUNTY,NM

CEMENT

2-7/8” TBG SE.T (@3376’

DV TOOL SET @3376’

PACKER SET @3059’

PERFORATED INTERVALS@3109-3376

4-1/2”” CSG SET@ 3436’CMT CIRC. TO SURFACE

:..

;---

499

Page 12: Enhanced Coalbed Methane Recovery Using CO2 Injection ...

12 SCOTT H. STEVENS, DENIS SPECTOR, PIERCE R[EMER 48881

Figure 4: Cross-Sectional Diagram Through Allison Unit C02-ECBM Pilot San Juan Basin, USA

#112 #142 #114

P reduction Well3500ft

Production Well3oooft

o Surface elev.6517’ 4- N05E — — N80E + elev.65 13’0

200 200

~~ 2800

.

!% TMD

3000303s

3124

3200 BMJ3TD=3148’ TD=314!Y

3328,

34003385’> *

TD=3390’

Note: Depths, elevations, thicknesses expressed in feet

3200

3400

_ ——

Figure 5: Gas Production Testing for Allison Unit COZ-ECBM Pilot, Showing Diverse Production Response to C02 Injection

100000T--

90000

800001

70000

60000

Soooo

40000

30000

20000

10000

0

004s7 PI

I

+ALLISON 112

-o--ALLISON 113

-A-ALLISON 114d

*

+ALLISON 115 / ~~—-=1

Aug Jan Jun Nov Apr 86P Feb Jul Dec May Ott Mar Aug Jan

1

un Nov Apr Sep Feb

f

UI Dec

1989 1990 1990 1990 1991 1991 1992 1992 1992 1993 1993 1994 19S4 1995 995 1995 1996 1996 1997 997 1997

TIME

C02 Injection Began Wells Shut-In

500

Page 13: Enhanced Coalbed Methane Recovery Using CO2 Injection ...

ENHANCED COALBED METHANE RECOVERY USING C02 INJECTION:40881 WORLDWIDE RESOURCE AND CO, SEQUESTRATION POTENTIAL 13

Figure 6: Production History of Allison Unit#113 Well, Showing Effects of Water Encroachment

+ Daily Gas +DdY Water

3“0~2”

I ‘r7 J2CC

2500 t J+ II

Aug Jm Jun Nw Apr Sep Feb JLA Dec May Od Mar Aug J= Jun Nw Apr Se$ Feb Tul Dec

1989 1290 1S90 1S90 1S91 1S91 1S92 1S92 1992 1S93 1S93 1S94 1594 1S95 1S95 1S95 1S96 1S96 JS9T 1S97 1S97

Figure 7: Production History for the Allison Unit#115 Well Showing lso~o Production Enhancement, Typical Coz Injection

Rate for One Injection Well Is Also Shown.

2500 120

1’ -=-Gas -8-W&or II● ion2000 III

I. .

Aw 0.. Ac.r Aw 0.. Apr Aw 0.. Ar.r Aw 0.. APr Aw 0.. AW AW 0.. AF.r Aw 0.. Apr Aw 0.. AF.r Aw D..1989 !Se3 1s+0 IN 13s0 1s91 1391 1$91 1992 4s92 !s92 !s93 4593 1s93 !$94 !934 Iw 15$6 4s% 15% !* IWd !s% 1s-37 4s1 4s97