SPESPE 18250

Enhanced Recovery of Coalbed Methane ThroughHydraulic Fracturingby S.A. Holditch, Texas A&M U.; J,W. Eiy, M,E. Semmsibeck, and R.H. Carter, S,A, Holditch &Asaoos.; and J. Hinkei and R.(3. Jeffrey Jr., Dowell Schlumberger

SPE Members

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INTRODUCTION

Hydraulic fracturing haa boon wad toaccelerateremovalof methanefromcoal seamsaheadof undergroundmines. Originally,●ll of the gasthat waa producedwas flared or vented, Over thepast decade, however, there has been a growingawsrenessof the vast potential for recovery ofmethane gas from coal seams, TMa awareness isloading to the commercial exploration anddavelopntentof coalbedmethane reservoirsin manyareasof the U.S.

Coalbedmethaneproductionis viewed 6s a newand significantenergy source, Associatedmethanegas from coal is now the,primarysourceof naturalgaa for the state of Alabama and is rapidlybecominga major sourceof naturalgas i~-I#e SanJuan Basin of New Mexico and Colorado, Thenatural gas industry is still learning how tocomplete wells and produce gaa from coal-seatoreservoirs. Compared to our knowledge oftechniquesfor the completionand production ofsandstoneand limestonereservoirs,our knowledgein coal-seamreservoirsis minimal,at beat.

The success achieved in producing gas fromshallow coal has encouraged some operators toexplore for gas trapped in deep coal seams thatwill never be mined, One araa of significantactivity is the San Juan Basin. ‘fo optimizerecoveryfrom most of the wells drilledinto deapcoal seams, hydraulic fracturing treatmentsarerequired, Experiencehas shownthat the designandexecutionof fracturetreatmentsin coal seams isnot straightforward, High injection pressures,complex fracture systems, screenout and theproductionof proppantand coal

Referencesand illustrationsat end of paper.

fines after the treatment are typical problemsfacingthe operator,

The mechanical properties of coal’ aresignificantlydifferent from conventionalrocks,Conventionalreservoirrockstypicallyhave a valueof Young’smodulus in the range of 3 to 6 millionpsi. It ie not uncommonto see laboratorymeasuredvalues of Young’smodulusfor coal in the range of100,000 to 1,000,000psi. The low valueof Young’smodulus will result in the creationof very widehydraulic fractures, Additionally,it has beenfound from minebackexperimentsthat very complexfracture systems a:e usually created during ahydraulic fracturing treatment. Not only aremultiple vertical fractures often created, butfracturespropagatingin multipledirectionscan bequite common, It is felt that this complexhydraulicfracturebehavioris due to the presenceof the cleat system, the complexstructureof thecoal matrix,and the etratigraphyof the coal seamwith respectto the surroundingsediments,

GAS PRODUCINGMECHANISMS

The mechaniamof gas productionfrom coal issubstantially different than observed fromconventionalreservoirs, There ia little or nofree gas present in the coal, Most of tha porespace in the cleat systemis water saturated. Eventhoughsome free gas may exist in the cleatsystem,most of the gas is adsorbedon the surfaceof thecoal. To produca this-gas, the preaaure in thecleat system must be reducedto cause the gaz todesorb from the surface of the coal to the cleatsystem and diffuse through tbe coal matrix,Normally, significantvolumes of water must beproduced in order to lower the pressure in thecleat system so that gas desorption can begin,Because gas desorption is the primary source ofproduction,the gas flow rate from a coal seam mayincrease with time. It is not mcommon for maximum

EWHAt?C2DRBCOVBRYOF COALBBDIfEl

gaa flow ratom to occur months or ●ven yoara intotho producing history of ● ooal.moamWO1l.

To producegas ●t ●conomicratas from ● coalseam, throo criteria must be met, Fir#t, m●xtoneivecleat systemmet exist in the coal seamto provide the needad formation perme~bility.Second,the gas contentof the coal must be largeenough to provide a resource that is worthdeveloping. Third, the cleat ●yetam met beconnectedto the wellbore, All three criteria mustbe consideredto evaluatethe ●conomicpotentialof~ Particularcoal ve~, If any one of the threecriteria is less than satisfactory,then economicproductionof th~s gas sourcewill be hampered.

It should be reiteratedthat ●lthough thereare some similaritiesbetween naturallyfracturedsandatone or carbonate reservoirs●nd coal-seamreservoirs,there is etillone major dissimilarity.The major dissimilarityis the largk differenceineffective modulus of eleeticity, T%e very lowYoung’smodului in coals createea situatton whereit is difficultto create●nd prop long fractures.Field experience hae shown that the creation oflonghydraulicfractureeie ●xtremelydifficult,ifnot impossible, Therefore, coal-seam roeowoirswith poorly developed cleat ey&teme, L.c., lowpermeabilitycoal seams,mey not he candidate fordevelopmentbecause they may not be capablo ofsupplyiwj enough gae to the relatively ●horthydra~<licfracture,

PRE-FMCTURE FORMATIONEVALUATION

As ie the case with conventionalreservoirs,it is critical to ascerteinthe propertiesof acoal-seam reservoirprior to planning completionand stimulationoperations, The primaryreservoirpropertiesthat controlthe productionof gas froma coal seam ere adsorbedgas content,desorptionbehavior characteristics,effectivedrainage areasize, reservoir pressure, and the permeability,pore volume, and water saturationof the cleatsystem, In designing a fracture stimulationtreatment for a coal interval, the mechanicalpropertiesof the coal must also be estimated,

Adsorbed gas content can be determinedby acanistertestwhich involvesplacingdrillcuttingsor a core samplein a sealedcanisterand measuzingthe amount of methene that is given off by thesample. This test measuresthe amountof gas givenoff by the core after it is sealed, One must alsoestimate the amount of “lost” gas that ●scapedbetweenthe time the core was cut end the time thesamplewas sealed.

Another test used to determine sorptioncharacteristics of coal involves ●xposing ●

gae-freesampleof caal to methaneunder Increasingpressure and measuring the amount of gas thatadsorbs to the ccal, Once the sample reacheeequilibrium at initial reservoir pressure, theprossurois then decreased ●nd the amount of gasgiven off (or desorbed)by the sample is rneaeured?’. variouspressures, Thie type of testingcan beused to define ●n adsorption/desorptionisothermfor the coal sample,but does not revealthe ●otualgas content of the sample ●t insitu reservoirconditions, The canistar test, if corroctedfor

● ☛

W THROUGHHYDRAULICFRACTURING SPE 182

lost gae, will give the best e$timateof the gascontentof ● particularcoal seam.

Table 1 preeente laboratory data measuredueing a coal eample from ● well in the PiceanceBasin. The ●dsorptionand desorptiondata can becurve fitted to the Lsngmuir isotherm equation.The coefficientsfor the Langmuirequetionsfor gasadsorptionand desorptionwere determinedto be asfollows:

LangmufrEquation: V - Vmax [k P / (1 + k P)]

Lan~uir Coefficients

vmax

(1/p~ia) (scf/ton)

Adsorption 0,00129 595.

Desorption 0.00237 542.

Formationmechanicalpropertiedcan ●lso bedeterminedby laboratorytesting of core s,mples.Table 2 presents the results of ❑echanicaproperties testing on coal and sandstone coresamplesfrom the Fruitlandformationin the easternportionof the San Juan Baein, Poisson’sratio forthese sampleswas measuredIn two directions:u ismeasuredperpend~cularto the beddingplane ●n4 “2is measuredparallelto the beddingplane.

The differencebetween coal and sandstoneisclear from the data in Table 2; however, thedifferencescouldbe ●ven largerin-a%tubecaueeofthe highlycleatednature of most coal seame. Withmany natural fractures, the *rbulkwcoal system

could actuallybe less stiff than suggestedfromcore measurements.

STIMULATIONSTRATEGZ!%&

To produce ga> from coal seams, a hydraulicfracturetreatmen~is normallyrequired, The typeof fracturetreatmentdssignedis dependenton thedapth, thickness, and stratigraphyof the coalseam, Field observationsand theoreticalstudiesindicatek basic scenarioaof fractutegrowth incoalbed methane reservoirs. We feel that thefracturepressurebehaviorexhibitedin each of thescenarioscan be correlatedto the depth of thecoal and the stratigraphy of the coal andsurrounding formations, The following is adescriptionof the 4 basic scenarios.

Scenario I - A shallow coal seam whers a~i-fracture vill be crested.

Scenario 11 . A ser;+s of thtn coal seams in adepth range whare a tingle, planar, varticalfracturewill be created.

Scenario III . A single,thickcoal seamwhare thehydraulicfracturewill be confinsdentirelyin thecoal and ● complex (multipleverticalor T-shapedfrecture systerniscreated.

ScenarioIV - A hydraulicfrscture treatment wherethe fractureis initiallynonfinedwithin ● singlecoal seam but during the later portion of the

-----

S. A. HOLDITCIl,J. W. SLY, M. E. SS3M3LBECK,R. Ii, OARTER------ . . .. ...— ..— . - .-— —. 9L16250 ~A~ ~’ II

trsatmsnt, ths fracturs bagina to propagato to 2,000,000psi or more in the surroundingstrata.verticallyinto the bou~dinglayers, Whan abundantnsturalfractures●re presentin the

coal, the ‘affectiveWYoung’s Modulusmay be evenThe following discuaaion outlina8 the lower, ~is will result in the creationof ● very

strategies which we propose for ●tfmulating wide fractureat early time duringthe treatment.coalbed-methanereaervoira, We first discuea a However, due to the higher values of Young’sgenaraletrategyapplicableto ●ny coalbed-methane 140duluain the boundary layers, the effectivereservoirwhich requires stimulation. Following moduluscontrollingfracturewidth in the coal willthe general strategy, we discuss the specific increaseas the fractureextends(withtime).●erategiesapplicableto ●ach of the four soenariosdescribed above. These discussionsinclude the Theor*tisalcalcu!.ationsfor a 3-layersystem7rock mechanicscontrollingfracturepropagation●nd, show that the ratio of :~,aequivalentmodulus fortheoreticalcalculationsof fracture pressureand the 3-layer system to the actual coal modulus isdimensionswhera ●pplicable. Also includediS an dependanton the ratio of fracturelength to coalexample net-pressure-versus-timegraph whtch wefeal gives a good exampleof the pressurebehavior

seam thicknesswith a limitingupper value beingthe modulus of the bounding layer.

to beFig, 1

expected under ehe spncific scenerio. illustratesehe variation of “equivalentmodulus”Finally, each section ends wi:h the specific to “coal modulus” for values of boundary-to-coalstrategy concerning completion nv~cedures and modulusrattosof 5, 10 and 20. Resultsfor both aexecutionof the treatxaant. Khristianovic,Geertsmaand deKlerk (KGD) fracture

nnd a penny-shapedfractureare illustratedin Fig.GeneralStrategy - Appliesto any coalbedmethane .1,’reservoirrequiringfracturestimulation.

Fig. 2 is a graph of the calculated net1. Hydraulicfracturingof ● coal seam ie mainly pressure during fracture simulation. runs comparing

● process that ineerconnecee the cleat system the cases of conatane Young’s Modulus ●nd aof ehe coal eo the wellbore, Withouta well variable●quivalencemodulus dependant on fracturedevclo’d c:eae ●yetem, creating a long length.fracturein a coal saam will usually not be

The conataneYoung’emodulusvalue of 1000MPa is representative of a coal seam while the

?rofitable. value of 20,000NPa representsthe modulus of theboundarylayer.

2.Note that the net stress for the

If ● long fracture length cannot be created variable equivalentmodulus case increaaes to a●nd propped, then some low-permeability coala value above the line that representsthe higherwill not be commercial●t currentgas prices. modulusboundarylayer, This behavioris causedbyFor ●xtremelylow-permeabilityreservoirs,we fracture fluid storage effects early in the job,must create a long, conductive fracture to Once the equivalentmodulushas reachedIta maximumachiev8 economicflow rates. Because of the and the storage effeces have dissipated,the netnature of coal and the inabilieyto achieve pressurewill begin to decrease. This finalstage,proppedfracturelengthsmore than 200 eo 500 howaver,may not occurduringsmallvolumefractureft, there will be some coal seams with treatmentsor when increasedpressuredrop due topermeabilitiasso low that they cannot be higherproppantconcentrationsmask any decreaseinproducedat commercialflow rates. pressure.

3. Bottomholepressure during productionshould Fig. 3 is an excess pressure graph from abe minimized to accelerate desorption of fracture stimulation treatment that appears tonatural gas. A wide, conductive propped reflectScenarioI behavior, Additionof proppanefractureeystemthat can withstandthe maximum causes variation from the theoreticallypredictedclosurestressmust be creaeedto minimizethe prassure behavior from the model since fluidpressuredrop down ehe fracture. viscosity in the model is assumed constant. The

4,strategy suggested for stimulatingthis type of

The engineerin the fieldmust be preparadto reservoiris as follows:make rapid, real-timedesignchangesduring afracture treatment.of a coal seam. In 1.hydraulicfracturingof coal seams,becauaeof

Individualhorizontalfractures(one per coal

the high treatingpressurasand aomplexnatureseam) will have to be created using eitherlimitedentrymethodsor mechanicaldiversion.

of the fracture systems, real-time changeaduring the treatment may become the rule 2. Linear fluidswith a moderatesize pad volumerather than the exception. Cueting proppane shouldbe used to fracturetreaethe interval.and reinitiatingthe pad or changingthe sizeof the pad volume basad upon treating 3, The bottomholetreatingpressure will be inprassureamay be requiredto improveresults, excess of 1 psi/ft. Complax (multiple)

ScenarioI - HorizontalFraceure in ShallowCoalfracturesystemsmay be createdif bottomhole“pressuresincrease subficantiallyduring the

Sa6am treatment.

Undar this scenario, the least principal ScenarioII - A SingleVerticalFractureThroughastrass is in the vertical direceion. Therefore,the hydraulic fracture is initiated in the

Series of Thin Coal.Seams

horizontalplane or parallelto beddingin tha casaof dippingstrata, The Young’sModulusof coal is

This scenario is analogous to a verticalhydraulic fraceure in a layered clastic and/or

on ehe orderof 200,000to 1,000,000psi aa opposed carbonatereservoir, Other than the possibilityof

—.—---— —-- -—-- -- --—— ------- .-.. -... . . . .. . . . . . -“ .“.8...” -S- ‘062,

higher leaksff into coal mosm with w-11 davolopmd 2. Poroelasticeffects - due to the high fluidcleat ●ystwms present, the presence of the coal leakoff that cm occur in ● cleated coal,will have 1ittla off●ct on tho ●ctual fracture backstreases can be increased during thetreatmentdseign. A comsonpracticein stimulating treatment, As backstress increases, thethis typo of reeervoiris to perforatoIn ● claecSc injectionpresauraalso i~creases,zone, (sand or eilt) adjacent to the coal ●ndfracturetraat the coal by allowingthe fractureto 3. Coal finks plugging at the fracture tip, -grow vertically. This usually results in lower This phenomenonhas been thoroughlydiscussedtreating pressures than treating the ooal by Jones et al, If large volumes of coalexclusively. fines are generated,it is possiblethet the

fines could concentrateat the tip of thaFig. 4 is an ●x&mple excess pressure graph fracture and inhibitpropagation,

that exhibits Scensria II behavior, Excesspressuresare modere;~and declinethroughoutmoec 4. Coal fines entrainmentin fluid - Coal finesof the treatmentas the fracturecontinuesto grow will alao remain entrailedin the fluid andvertically. The following four points summarize will cause the apparentviscosityto incraase,our strategyfor stimulatingthesereservoirs: Althougha minor effect, the net resultwill

ks a small increasein injecticnpressure.1, Fracturepropagationgradientsshouldbe less

than 1 psi/ft. A thoroughdiscussionof thesep~~nomencnhavebeen includedin a recentGRI report. Basedupon

2, A single, planar, vertical fracturewill be the theoreticalreeearch performed to date, wecutting through several coal seams, so that believe the primary cause of high treatingconventional3.D fracturedesignmodelscan be pressuresie the complex fracturasystem and theused to ●stimatefracture dimansicm, tortuouspath the fluid and proppantmust travel

aftar it leavesthe wellbore.3, ~akoff is ususlly’not ● problem and nonssl

pad volumes of 30 to 3S8 can be used to The effect of parallelfractureson treatLngfracturetreatthe coal. preesureand width was eetimstedby Jeffrey et al.

by modelingthe extensionof two parallel,vertical.4. viscous, shear stable borate croselink or fracturee and comparing the results with the

delayedcrosslinkfluids (or foams) ehouldbe pressureand width of ● singlevertical fracture,used tc prcvlde adequate proppant transport The einglefracture,in thie amlyels, representsa●nd to minimizeproppantsettling, singlebranchof the two parallelfracturesthat is

far removed frcm the other branch such that noScenario111 . A ComplexHydraulicFracture interactionoccursbetweenthem. Fig. 5 shcws the

Containedin a SingleThickCoal results of those calculations. Plotted on theSeam horizontal axis is the ratio of the distance

betweenthe two parallelfracturesto the lengthofThis scenariois unique to coal eesms and la one of the fractures, Plottedon the verticalaxis

well dccumentad by minebacks. The main are the ratios of fracturepressureand width ofcharacteristicobservedwhen a complexfractureis one of the parallelfracturesto thoseof e singlecontainedin a single,thick coal seam is the high isolatedfracture. Both of the relationship:showntreating pressure observed during the treatment. on this graphreachasymptotesfor smallspacingtoCommonly, the excess preseure in the fracture length ratios at about ,01, i.e., spacingcf therapidly increases when pumpingbegins and ramains parallel fractures of l/100th of the fracturehigh during the treatment, Often, it is difficult length.. These asymptotes indicate a maximumto pump large amountsof sand into the coal, The pressure increaseof 68% over the single fracturemcst logical explanationof the high pressures caee and a 169 decreasein fracturewidth. At thisobserved is the creationof multiplevertical or point in our investigations,we think thatT-shapedfracturasnaar the wellbore, The tortuous Increasingthe number of parallel fractureswillpath for fluid flow creatad by these multiple significantlyincreasethe fracturingpressure.fractureeresultsin a zonewhere the preseuredropis quite large, Fig. 6 is an example excess-pressuregraph

that exhibits tha type cf pressure behaviorIn our research,other phenomenonhave aleo expectedduring a ScenarioIII fracturetreatment

been investigatedthat can help explain the high Trsatingpreeeurerose continuouslythroughoutthistreatingpressurescften associatedwith fractura treatment. Sinceboth high leakoffand high excesetreatment in coal seams, These phenomenoncan be p~qessuresmay occur during fracturetreatment ofsummarizedae follows: thie type, aompleteplanningof the treatmentmuet

include tha contingencyof additionalhorsepower1. Slip zcnes - Slip zone~ are created in the requirements, Our strategy for a Scenario III

highly cleatedareas immediatelyahead of tha fracturetreatmentis as follows:fracturetip, Due to concentrations of streeenear the fracture tip, slip can occur that 1. High injectionrates must be used during thetends tc ●bsorb energythat otherwisewouldbe fracturetreatmentto ccmbathigh leakoff.used to propagatethe fractura, The formationof a slip zone will result in increased 2. In addition to high injec~icn rates, highinjertionpreseureso viscosity,shear stable or delayed crosslink

gels and bridging fluid loss additives arenaededto offsethigh leakoff,

- ..*,?.+S. A. HOLDITCH,J. W. ELY,M. E. SSIQELBIECK, R. E. CARTER

* . .. . . . . . .. . ..l ,. —.” cK AOLJU .J. 9J● 111.muud Mu m. w. .JIirrmx 2

3. Because the coal haa low Young’smodulus ●nd 4. To proporly design a well coispletionand ahigh formationcomprmsnibility,●nd bacausoof fracture treatment, one nust ●nswer suchthe presence of complex fracture●ystema, e quemtion*.hydraulicfracturewill seldompenetratemorethan a few hundredfeat from the wellbore. a. are horizontal or vertical fractures

going to be created? (orboth?);

ScenarioIV - A ComplexHydraulicFracturein a b; how many coal seams are present and areThickCoal Seem That PropagatesLnto theygoing to be perforated?;andBoundingLayers

c. will the fractureremaincontainedin theScenarioIV is a specialcase of Scenario111 coal or will it propagateverticallyout

and, therefore, may iF.-lUdeany of the complex of the coal?fracture geometries previously described. bexcess pressure rises due to complex fracture Based upon the answers to these threegeometry, a vertical component may be initiated questions, one can then define the appropriateinto the boundarylayersat a point of weaknessat scenario end proceed to design the fracturetk$ boundaryinterface. If thishappens,the fluid treatment.escaping to the boundary layer could cause thefracture(s)in the coal to decreasein width which 5. Highly cleated,permeablecoals are needed tocould lead to ● screenoutif high concentrationof justifycompletionand attmulationcoatsbasedsand are being pumped when che vertical growth upon current economic constraints. In suchinitiatea, coals, fracture-fluid leakoff will be a

problem; therefore, high injection rates,Fig. 7 is an excees preesura graph wher* a leakoff control ●dditives, ●nd large pad

sharp drop in treatingpre8sure near the end of the volumes will be needed to successfullytreatment indicates growth out of zone. In thie stimulatecoal seams.particular●xample,the break out occurred near the●nd of the job and the pumping waa finished ●s 6, Additional research is needed to improve ourplanned, In this type of situation,inoreaahg the understandingof the high treat.nentpressurespump rate may give the neceesary fracture width associated with coal seams. If near wellborerequired to finish the job. However, if the tortuosityindeedproves to be the main ceusepressure drop occurs ●arlier in tho job, of the high pressures, then wellborereinitiatingthe pad and pumping fluid without stabilizationmathods can be developed toproppant unttl sufficient fracture width is improve the chances of creating a single,obtainedmay be necessaryprior to continuingthe planer fractureat the wellbore,proppant stages of the treatment. The followingtwo pointscover our strategyfor ScenarioIV which ACKNOWLEDGEMENTalso includethe pointsmade for ScenarioIII:

This work was sponsoredby the Gas Rnsearch1! To be prepared for Scenario IV, extra fluid Inatftute (GRI) under GRI Contrakt No.

shouldbe on locationto reinitiatethe pad if 5087-214-1469, The authors wish to thank GRIthe verticalcomponentbegins to propagate, personneland managementfor theircontributionsto

2.the researcheffort,

If the pad is reinitiated,a largeenoughpadvolume must be pumpnd to develop a fracture REFERENCESthat is wide enough to acceptproppantbeforestartingback with the proppingage~t, 1, Lembert, S. W., Niederhofer, J. D., and

Reeves,S. R.: !tMultipleCoal SesmCompletionCONCLUSIONS Experiencein the DeerlickCreek Field,Black

Warrior Baain,” Proc,, Coalbed Methane1. The design and evaluation of fracture Symposium,Tuscaloosa(1987)81.82,

treatments in coal seams must include thepossibilitythat complex fracturesare often 2, Schraufnagel,R. A., Lambert,S, W., Stubbs,creatednear the wellbore, P. B,, Dobscha,F, X., and Boyer,C. il.,II:

2.“The Rock Creek Field Laboratory--AProject

Although many possibilitiesexist to explain Update,” Proc., Coalbed Methane Symposium,the high treatingpressures aasoclatedwith Tuscaloosa(1987)83-92.coal seams, the most likely cause ia thecreation of multiple fractures near the 3, Wicks,D. E., KcFall,K, S., and Zuber,M. D.:wel-lboreand the tortuous path fluid must *lAnAnalysisof the CoalbedMethaneResourcesfollow between the wellbore and the main of the WarriorBasin,”Proc,,CoalbedMethanehydraulicfracture, Symposium,I’uscaloosa(1987)131-140.

3, Other phenomenon, such as slip zones, 4, Kelso,B. S., Decker,A, D,, Wicks,D, E., andporoelasticity,effective modulus, and coal Horner, D, M.: ~@RI Geologic and Economicfines also tend to cause an increase in Appraiaalof CoalbedMethane.inthe San Juaninjection pressure during a stimulation Basin,” Proc,, Coalbad Methane Symposium,treatment, Tuscaloosa(1987)119-130.

muawcm RECOVERYOF COALBEDMBTNANETRROUGHHYDRAULICFRACTURING SPE 1825-.--. -— .—--- —-- -- ---——— ———.—–—

5. Choato, R., Lent, J., ●nd Rightmiro,C. To:“Upper Cretaceous Goolocy, Coal, ●nd thePotantialfor lfothane Recovery From Coal Badsin San Juan Basin-.Colorado●ndNaw Mexico,inRightmiro,C. T., Eddy,G. Et and Kirr, J. N.Eds., CoalbedMethaneRe$ourcesof the UnitedState*: American Association of PetroleumGeologistsStudies in CaologySeries,No. 17,1S5-222.

6. Faaeett, J. E.: “Geometry●nd DepositionalEnvironmentsof FruitlandFormationCoal Beds,San Juan Basin, New Xexico and Colorado:AnaComyof a Giant Coal-BedMethaneDeposit,”Proc., Coalbed Methane Symposium,Tuscaloosa(1987)19;3S,

7. Jeffrey,R. G., Vandamme,L., Hinkel,J. J.,and Horner,D. M.: ‘Propagationof Fracturesin Coal: Equivalent Modulus ●nd ParallelFracture Effects,” Proc., Coalbed MethaneSymposium,Tuscaloosa(1987)113-116.

s, Diamond,V, P. and Oyler,D, C,: ‘Effects ofStimulation Treatment on Coal Beds andSurroundingStrata:EvidenceFrom UndergroundObservations,” U. S. Bureauofl#ines ReportofInvestigation, No, 90s3, United StatesDepartmentof the Interior,

9, Jonee, A. H, et al.: “The Influenceof CoalFines/Chips on the Behavior of HydraulicFracture Stimulation Treatments,” Proc.,Coalbed Methane Symposium,Tuscaloosa(1987)93-102.

10. Holditch, S, A. et al,: ‘Enhanced GasProduction Through Hydraulic Fracturing ofCoal Seams,” Annual Report, Contract No.50S7-214-1669,GRI (Jan198S).

TA8LE 1

EXAHPLEHETHANEADSORPTIONANDLABORATORYTEST

SampleWeight 41.13gm%uspleSize 0.25 in

DESORPTIONISOTHERM ,DATA

Moisture 11.2%Temperature 167*F slumple S

Methane Adsorption RL83766-1

RLS3766-2

Pressure Gas Content(psia) (scf/ton) RL83771

77 53 RLB3775-1314 1761278 369 RL83775-2

2560 457RL83781

Pressure

(psia)

19921488

980757409218173121

753612

MethaneDesorption

Gas Content(scf/ton)

450425382335254185153120824119

RL83785-1

RL83785-2

RL83786

RL83790-1

RLS3790-2

3766

3766

3771

3775

3775

3781

3785

3785

3786

3790

3790

TA8LS 2

TRIAXIALTEST R8SULTS

Porosi tv younR”S Modulus~(percent)

(106psi)

1.8 6.4

3.6 5.4

8.4 2.8

6.3 3.8

7.2 f+.2

6.8 3.3

3.6 0.66

<1 1.0

<1 0.73

<1 2.7

1.3 3.0

0.12

0.12

0.20

0.02

0.07

0.08

0.27

0.40

0.29

0.20

0.44

~

0.12

0.01

0.18

0.02

0.02

0.13

0.52

0.34

0.43

0.09

0.18

Description

sandstone

sandstone

Goal-SS

sandstone

sandstone

Sandstone

Coal

Coal

Coal

SS-Coal

SS-Coal

y!#Y

2.59

2.55

1.91

2.46

2.45

2.44

1.49

1.56

1.41

2.50

2.24

14

12

10

8g

36

4

2

0

1.s

1.6

1.4

1.2

1.0

0.1

Oj

---- KOO

\\ — PEWY-9HAPE0

\‘i,

\ Eb

\. ~EG H

k‘\ Eb

\\

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SPACING TO LENGTH RATIO (s IL)

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PUMP TIME, minutes

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TIME (seconds)

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PUMP TIME, mlnulw

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PUMP TIME, minufes

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