Production characteristics and reservoir analysis

.InternationalJournalofCoalGeology38199827–45ProductioncharacteristicsandreservoiranalysisofcoalbedmethanereservoirsMichaelD.Zuber)S.A.HolditchandAssociates,1310CommerceDriÍe,ParkRidge1,Pittsburgh,PA15275-1011,USAReceived8July1997;accepted1July1998Abstract.SixAppalachiancoalbedmethaneCBMprojectsarereviewedandevaluatedintermsofreservoirengineeringtechniquesandCBMrecoverability.Theseincludethreenon-mine-relatedprojectsinthenorthernAppalachianbasin,onenon-mine-related,andtwomine-relatedprojectsinthecentralAppalachianbasinofsouthwesternVirginia.Generally,lowproductionratesandlowCBMreservesarecharacteristicofthecentralandnorthernAppalachianbasin;therefore,minimizingproductioncostsisfundamentaltotheeconomicsuccessofaCBMprojectintheseregions.Welldeliverabilityisdeterminedthroughpermeabilitytestingandthroughproductiondataanalysisusingareservoirsimulatortohistorymatchhistoricproductiondata.Allofthenon-mine-relatedprojectsutilizeverticalwellswithwellspacingsof60to100acre0.23–0.402.kmthatproducefrommultiplecoalbedsatdepthsasmuchas762m.ThetargetsarecoalbedsofthePocahontasandNewRiverFormationsandcorrelativeLeeFormation.IntheNoraFieldof.2.VirginiaEquitableResources,developer,wellspacingis60acre0.23m,andrecoverabilityis.high30–60%ofinitialgasinplace.Wellstimulationisbyfoamorwaterasthefracturemedium.Theaveragegasinplaceis675MMscfwelly1,andtheexpectedlifetimeofthewellsis30years.CostofwaterdisposalisamajoreconomicfactorinCBMdevelopmentinthe.Appalachianbasin.Waterdisposalisaccomplishedbyusingwaterdisposalholesinjectionwellsratherthansurfacewaterdischarged,whichisgenerallynotpermitted.Waterdisposalinthey1centralAppalachianbasininvolvesrelativelylowvolumesofwater30STBday,decliningto1y1.to2STBday.InthenorthernAppalachianbasininIndianaCounty,PABeldenandBlake,.developer,verticalCBMholespenetratesixtoeightAlleghenyFormationcoalbeds.Wateranday1y1.sandproppantareusedforstimulation.Productionlevelsarelow-100Mcfdaywell.ThelifeofaverticalCBMholedrilledinadvanceofminingis3to5years.Thistypeofholemaybeconvertedtoagobholeafterminingiscompleted.Gobgasisrecoveredmainlyfromcoalbeds)Tel.:q1-412-787-5403;Fax:q1-412-787-29060166-5162r98r$-seefrontmatterq1998ElsevierScienceB.V.Allrightsreserved..PII:S0166-51629800031-7()M.D.ZuberrInternationalJournalofCoalGeology38199827–4528abovetheminedcoalbedandhashighrecoverabilityofasmuchas10MMscfdayy1welly1.HorizontalCBMholesproducealmostpuremethaneandtypicallyhave1yearofproduction.q1998ElsevierScienceB.V.Allrightsreserved.Keywords:coalbedmethane;productiontechniques;reservoiranalysis;AppalachianBasin1.IntroductionThispaperprovidesanoverviewoftheproductioncharacteristicsofAppalachiancoalbedmethanereservoirsandreviewsthereservoirengineeringtechniquesthatareusedforanalysisofthesereservoirs.TheprimaryareasofproductionofAppalachianbasincoalbedmethanearedirectlyassociatedwithcoal-miningactivity.AvarietyoftechniquesarebeingusedtorecovercoalbedmethanefromAppalachianbasinreservoirsinandaroundactivemineareas,especiallyinsouthwesternVirginia.Welltypesused.includeconventionalverticalcoalbedmethanewells,horizontalin-minedrainholes,gobwells,andwellsdrilledintoabandonedmineareassometimescalledsealedgob.wells.Therearealsoseveralareasthroughoutthebasinwhereconventionalverticalwellsarebeingusedtoproducecoalbedmethane.ThispaperwillreviewtheproductioncharacteristicsofseveralongoingprojectsintheAppalachianbasinanddiscusstherelativecontributionsofvariousdevelopmenttypesontheobservedproductionperfor-mance.BecauseofthevarietyoftechniquesusedtorecoverAppalachiancoalbedmethane,thereservoirengineeringanalysismethodsusedtoanalyseandpredictperformanceforthesereservoirsarealsomorevaried.Reservoirengineeringstudiestypicallyfocuson:..1understandingthereservoirmechanismsthatcontrolproduction,2analysisofwell.productionbehavior,and3predictionoffuturewellandrorreservoirperformance.TheinformationpresentedinthispaperisbasedonpastexperiencesinconductingreservoirstudiesforcoalbedmethanereservoirsinthenorthernandcentralAppalachianbasins.Thiscoversanalysesofawiderangeofprojecttypes,fromfieldsutilizingverticalwellscompletedinmultiplecoalbedstoprojectsprimarilyassociatedwithrecoveryofgasproducedfrommineoperations.ThispaperfocusesonthereservoirengineeringtechniquesutilizedforAppalachiancoalbedmethanereservoirs.Athoroughoverviewofbasicreservoirengineeringtech-.niquesforcoalscanbefoundinMavoretal.1996.Thisreferenceandotherliteratureshouldbeconsultedforspecificequationsandrormethodologiesforreservoiranalysisofcoalbedmethanereservoirs.2.ProductioncharacteristicsofAppalachiancoalbedmethaneprojectsThissectionprovidesareviewoftheproductioncharacteristicsofAppalachiancoalbedmethanereservoirs.ProductionfromAppalachianbasincoalbedscoversawidespectrumofwelltypesandproductiontechniques.Productionfromcoalbedreservoirsin()M.D.ZuberrInternationalJournalofCoalGeology38199827–4529Fig.1.LocationofmajorAppalachiancoalbedmethaneprojects.theAppalachianbasinalsocoversawidegeographicalareaandawiderangeofreservoirtypes.Productionrangesfromfieldsofverticalwel