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四川盆地焦石坝地区龙马溪组页岩矿物组成和微裂隙特征.rar

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    AUTHORSRichard M. Pollastro C24 Central EnergyResources Team, U.S. Geological Survey, Box25046, MS 939, Denver, Colorado 80225;[email protected] Pollastro received an M.A. degree in ge-ology from the State University of New Yorkat Buffalo in 1977. Rich joined the U.S. Geo-logical Survey in 1978 and serves as a provincegeologist on the national and world energyassessment projects.His recentaccomplishmentsinclude petroleum system assessments of theFort Worth, Permian, and South Florida basinsand the Arabian Peninsula.Daniel M. Jarvie C24 Humble Instrumentsand Services, Inc., Humble GeochemicalServices Division, P.O. Box 789, Humble, Texas77347; [email protected] Jarvie is an organic geochemist and pres-ident of Humble Geochemical Services. Danearned his B.S. degree from the University ofNotre Dame and was mentored in geochem-istry by Don Baker and Wallace Dow. He hasstudied unconventional oil and gas systemsextensively since 1984. Dan’s work on theBarnett Shale spans much of the last decade,which has resulted in several AAPG awards.Ronald J. Hill C24 Central Energy ResourcesTeam, U.S. Geological Survey, Box 25046,MS 939, Denver, Colorado 80225;[email protected] Hill specializes in petroleum geochem-istry and has more than 12 years of oil industryexperience. Currently, he is a research geolo-gist for the U.S. Geological Survey. His researchinterests include shale-gas resources and pro-cesses that control petroleum generation. Ronholds geology degrees from the Michigan StateUniversity (B.S. degree) and the University ofCalifornia, Los Angeles (Ph.D.), and a geo-chemistry degree from the Colorado Schoolof Mines (M.S. degree).Craig W. Adams C24 ADEXCO ProductionCompany, 309 West 7th Street, Ste. 400, FortWorth, Texas 7610; [email protected] Adams worked as an exploration geolo-gist with Amoco Production Company for13 years before becoming an independentin 1996. As president and co-owner of AdexcoGeologic framework of theMississippian BarnettShale, Barnett-Paleozoic totalpetroleum system, Bendarch–Fort Worth Basin, TexasRichard M. Pollastro, Daniel M. Jarvie, Ronald J. Hill,and Craig W. AdamsABSTRACTThis article describes the primary geologic characteristics and cri-teria of the Barnett Shale and Barnett-Paleozoic total petroleumsystem(TPS)oftheFortWorthBasinusedtodefinetwogeographicareas of the Barnett Shale for petroleum resource assessment. Fromthesetwoareas,referredtoas‘‘assessmentunits,’’theU.S.Geologi-cal Survey estimated a mean volume of about 26 tcf of undiscov-ered, technically recoverable hydrocarbon gas in the Barnett Shale.The Mississippian Barnett Shale is the primary source rock foroilandgasproducedfromPaleozoicreservoirrocksintheBendarch–Fort Worth Basin area and is also one of the most significant gas-producing formations in Texas. Subsurface mapping from well logsandcommercialdatabasesandpetroleumgeochemistrydemonstratethat the Barnett Shale is organic rich and thermally mature for hy-drocarbon generation over most of the Bend arch–Fort Worth Basinarea. In the northeastern and structurally deepest part of the FortWorth Basin adjacent to the Muenster arch, the formation is morethan 1000 ft (305 m) thick and interbedded with thick limestoneunits;westward,itthinsrapidlyovertheMississippianChappelshelfto only a few tens of feet.The Barnett-Paleozoic TPS is identified where thermally ma-ture Barnett Shale has generated large volumes of hydrocarbonsandis(1)containedwithintheBarnettShaleunconventionalcontinu-ous accumulation and (2) expelled and distributed among numer-ous conventional clastic- and carbonate-rock reservoirs ofPaleozoicage.Vitrinitereflectance(Ro)measurementsshowlittlecorrelationwithpresent-dayburialdepth.ContoursofequalRovaluesmeasuredfrom Barnett Shale and typing of produced hydrocarbons indicateAAPG Bulletin, v. 91, no. 4 (April 2007), pp. 405–436 405Copyright #2007. The American Association of Petroleum Geologists. All rights reserved.ManuscriptreceivedJanuary25,2006;provisionalacceptanceMarch 15, 2006;revisedmanuscriptreceivedAugust 2, 2006; final acceptance October 30, 2006.DOI:10.1306/10300606008significant uplift and erosion. Furthermore, the thermal historyof the formation was enhanced by hydrothermal events along theOuachitathrustfrontandMineralWells–NewarkEastfaultsystem.Stratigraphy and thermal maturity define two gas-producingassessment units for the Barnett Shale: (1) a greater Newark Eastfracture-barrier continuous Barnett Shale gas assessment unit, en-compassing an area of optimal gas production where dense imper-meable limestones enclose thick (C21300 ft; C2191 m) Barnett Shalethat is within the gas-generation window (RoC21 1.1%); and (2) anextended continuous Barnett Shale gas assessment unit covering anarea where the Barnett Shale is within the gas-generation window,but is less than 300 ft (91 m) thick, and either one or both of theoverlying and underlying limestone barriers are absent.INTRODUCTIONThe Bend arch–Fort Worth Basin area of north-central Texas is amature petroleum province (Figure 1) where exploration and pro-duction of oil and gas has been ongoing since the early 1900s. Priorto about 1998, production was mostly from conventional reser-voirs ranging in age from Ordovician to Permian (Ball and Perry,1996). Of recent importance, however, is the recognition that agiant continuous (unconventional), nonassociated gas accumula-tion exists within the Mississippian Barnett Shale. Since 2000, an-nual gas production from the Barnett Shale has established thegreater Newark East field (Figure 1) as the largest gas-producingfieldinTexas(EIA,2002;Rach,2004).Subsequently,BarnettShaleNewarkEast field now ranks second in the United States in termsof annual gas production (EIA, 2005). Cumulative gas productionfrom January 1993 to January 2006 from the Barnett Shale New-ark East field was about 1.8 tcf; in 2005, gas production was about480 bcf comparedtolessthan 11bcfin1993(TexasRailroadCom-mission, 2006). Proven gas reserves for Newark East field are es-timated to be between 2.5 and 3.0 tcf (Bowker, 2003). In addition,the U.S. Geological Survey recently estimated a total mean volumeof undiscovered, technically recoverable gas of about 26 tcf in twoBarnett Shale gas assessment units within the Fort Worth Basin(Pollastro et al., 2004b; Pollastro, 2007).A geologic framework wasconstructedjointlybythe U.S.Geo-logicalSurveyandAdexcoProductionCompany(FortWorth,Texas)for the Barnett Shale within the Bend arch–Fort Worth Basin areafrom well logs, commercial well databases, and scientific litera-ture to (1) determine the geographic extent and stratigraphic rela-tions of the Barnett Shale with underlying and overlying formationsand (2) define favorable areas for undiscovered recoverable gas andoil resources in the Barnett Shale. A joint petroleum geochemistrystudy of the Barnett Shale was also established between the U.S.Geological Survey and Humble Geochemical Services (Humble,Texas) to identify total petroleum systems (TPS) within the area by(1) identifying major source rocks, (2) characterizing oil and gasProduction Company, his primary focus is con-ventional and unconventional oil and gas inTexas and the mid-continent. Craig has workedthe Barnett Shale for 6 years, where his com-pany was one of the first to expand beyondthe core area of the Newark East field.ACKNOWLEDGEMENTSThis study benefited from contributions ofseveral individuals and independent explora-tion companies. We especially thank RepublicEnergy, particularly Brad Curtis and DanSteward, for discussing the Barnett Shale playand for permissions and arrangements tosample oil and gas from Republic Energy wells.We thank Kent Bowker, David Martineau, TonyCarvalho, and Robert Cluff for their helpfuldiscussions that resulted in a more compre-hensive understanding of the geologic frame-work, production characteristics, and historicalevolution of the Barnett Shale play. We areespecially grateful to the reviews of themanuscript in its early stages made by TomAhlbrandt, Neil Fishman, and Dick Keefer atthe U.S. Geological Survey, and the especiallythorough and critical reviews from an anony-mous AAPG reviewer and AAPG reviewers KenPeters and Barry Katz, all of which have greatlyimproved the manuscript.406 Barnett Shale, Bend Arch–Fort Worth Basin, TexasFigure 1. Map shows the area of U.S. Geological Survey (USGS) Bend arch–Fort Worth Basin province 45, major structural features,location of Newark East and Boonsville fields, extent of Mississippian Barnett Shale and Barnett-Paleozoic TPS, and relation to historicalproduction in north-centralTexas and southwestOklahoma. Oil cells contain only oil wells; gas cells contain only gas wells; and mixed oiland gas cells contain both oil and gas wells. Cell data were derived from IHS Energy (2003). Cell size is equal to 0.25 mi2(0.64 km2).Pollastro et al. 407produced from both Paleozoic-age conventional reser-voirs and from continuous accumulations within theBarnett Shale, and (3) identifying areas where theBarnett Shale is within the oil and thermogenic gas-generation windows. Total organic carbon (TOC) andmeanvitrinitereflectance(Ro)analyseswereperformedby HumbleGeochemicalServices.Samplelocation,de-scriptions,anddetailsandinterpretationsoforganicgeo-chemistry and RooftheBarnettShalearefoundincom-panionarticlesbyJarvieetal.(2007)andHilletal.(2007).The purpose of this article is to present an over-view of the geologic framework and thermal historyof the Barnett Shale in the context of the TPS. Usingthe interpretations of organic geochemistry from com-panion articles by Jarvie et al. (2007) and Hill et al.(2007), the geologic framework is combined to definethe Barnett-Paleozoic TPS of the Bend arch–Fort WorthBasin to further determine the geographic extent andstratigraphic relations of the Barnett Shale and favor-able areas for undiscovered, technically recoverable gasin the Barnett Shale for resource assessment. Finally,these relations and interpretation are used for the as-sessment of undiscovered gas in the Barnett Shale dis-cussed in a companion article by Pollastro (2007).TOTAL PETROLEUM SYSTEM, RESOURCEASSESSMENT, AND THE BARNETT SHALECONTINUOUS ACCUMULATIONCurrent U.S. Geological Survey assessments to esti-mate undiscovered oil and gas resources are based onthe TPS assessment unit methodology (Klett et al.,2000; Magoon and Schmoker, 2000; Pollastro, 2007).Similar to the petroleum system, principal geologic ele-ments of a TPS include source, reservoir, and seal rocksand hydrocarbon traps. The TPS is different from themoreconventionalpetroleumsystemdefinition.Thecon-ventional definition of a petroleum system by Magoonand Dow (1994) includes an area of all known accu-mulations linked to a specific pod (or pods) of maturesource rock. The TPS, however, is better suitable forresource assessment because it also incorporates areasofpetroleum potential related to the pod(s) of maturesource rock where undiscovered accumulations mayexist because of hydrocarbon migration.In general, the assessment unit is categorized intoone of two primary end-member types of accumula-tions (conventional and continuous) that are identifiedforassessmentpurposes,althoughsomeaccumulationsmay contain characteristics of both, indicating that atransitional-type accumulation may also exist (SchenkandPollastro,2002;Pollastro,2007).Becausethemeth-odology used to assess continuous-type accumulationsismuchdifferentfrom that forconventionalaccumula-tions (Schmoker, 1999, 2002), the characterization ofreservoirswithinaTPSiscriticaltoassessundiscoveredresources. The Barnett Shale of the Fort Worth Basin,Texas, is the foremost example of a continuous-type,shale-gas accumulation.Samplesof(1)oilandgasfromnumerousPaleozoicreservoirs, and (2) cuttings and cores of the Barnett Shale,as well as other potential source rocks, were collectedfromwellsthroughouttheBendarch–ForthWorthBasinarea and analyzed in a joint study by Humble Geochem-ical ServicesandtheU.S. GeologicalSurvey (Figure2A).The study concluded that the organic-rich, MississippianBarnett Shale is the primary source rock for oil and gasproduced from reservoirs of Paleozoic age in the Bendarch–FortWorthBasinarea(Jarvieetal.,2001;2004a,b;2005; 2007; Pollastro et al., 2003; Hill et al., 2007).Although other stratigraphic units show limitedsource potential, including organic-rich facies of Penn-sylvanian age, correlation of oils to both oil producedfrom the Barnett Shale and rock extracts of the BarnettShale indicates that the Barnett is the source of most ofthe oil and gas in the basin (Jarvie et al., 2001, 2004).For example, fingerprinting of oil produced from low-maturity Barnett Shale in Brown County, Texas, usinggas chromatography, biomarkers, and carbon isotopescorrelates with other oils from reservoirs in the westernpart of the basin in Shackelford, Callahan, and Throck-mortoncounties,andthatmostoftheoilsarelowinsulfurandoriginatedfromamarineshalesourcerock.Similar-ly,lighthydrocarbons,biomarkers,andcarbonisotopesof the same oils correlate with condensates in the centralBarnett Shale, producing horizons of Newark East field.Barnett Shale–derived oil and gas are found in allreservoirs of Ordovician (Ellenburger Group) to LowerPermianage(Jarvieetal.,2004a,b;2005;2007;Hilletal.,2007), thus defining the stratigraphic distribution ofthe Barnett-Paleozoic TPS. Ordovician, Mississippian,and lower Pennsylvanian reservoirs are mostly carbon-ate rocks, whereas clastic rocks dominate the middlePennsylvanian to Lower Permian reservoirs (Figure 3).Although new data are available because of recentgas drilling and production in the Barnett Shale play,the distribution of oil and gas within the Bend arch–Fort Worth Basin is generally shown in the 0.25-mi2(0.64-km2)cellmapofFigure1compiledin2003.Here,if a cell contains only oil cells, it is designated as an oilcell. Similarly, if only gas wells fall within the cell, it is408 Barnett Shale, Bend Arch–Fort Worth Basin, TexasFigure 2. (A) Maps shows area of U.S. Geological Survey (USGS) province 45 (termed the ‘‘Bend arch–Fort Worth Basin province’’), geographic extent of the Mississippian BarnettShale, major structural features, Newark East and Boonsville fields, and general locations of wells sampled for oil and gas and total organic carbon analyses. (B) Map showsboundary of Barnett-Paleozoic TPS and major structural elements in the Bend arch–Fort Worth Basin province. Modified from Pollastro (2003).Pollastroetal.409designated asagas cell. If the cell contains both oil andgas wells, it is designated as a mixed oil and gas cell.The distribution of oil, gas, and mixed oil and gasproduced in the Bend arch–Fort Worth Basin on thebasisofthecellmaprevealssomesignificanttrendsthatcanbeattributedtothethermalmaturityoftheBarnettShale source rock. Most gas cells are found along thenortheastern part of the basin or along the Ouachitathrust front. These areas are the deeper and more ther-mally mature parts of the basin. Oil cells a
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