Lacustrine algal limestone reservoir in western Qaidam Basin, China

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Lacustrine algal limestone reservoir in western Qaidam Basin, China

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Lacustrine algal limestone reservoir in western Qaidam Basin, China
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Carbonates and Evaporites
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Zhao, Fan
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Springer
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English
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Earth movements ( lcsh )
Limestone ( lcsh )
Natural gas ( lcsh )
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serial ( sobekcm )

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Compared to marine carbonate around the world, lacustrine carbonate is relatively scarce. Much less attention has been paid to it. Lacustrine carbonate, a product of mixed deposition of continental clastics and carbonate under special conditions, can be both important source rocks, and oil and gas reservoir rocks. Qaidam Basin is a large salt lake basin on the Tibetan Plateau where oil and gas flow has recently been discovered in lacustrine algal limestone. Study of the algal limestone is a potentially valuable target of exploration, and is of great significance to the exploration and development of mixed carbonate formations.

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ORIGINALARTICLE LacustrinealgallimestonereservoirinwesternQaidamBasin, China FanZhao Accepted:16October2013/Publishedonline:6November2013 TheAuthor(s)2013.ThisarticleispublishedwithopenaccessatSpringerlink.com Abstract Comparedtomarinecarbonatearoundthe world,lacustrinecarbonateisrelativelyscarce.Muchless attentionhasbeenpaidtoit.Lacustrinecarbonate,a productofmixeddepositionofcontinentalclasticsand carbonateunderspecialconditions,canbebothimportant sourcerocks,andoilandgasreservoirrocks.Qaidam BasinisalargesaltlakebasinontheTibetanPlateau whereoilandgasowhasrecentlybeendiscoveredin lacustrinealgallimestone.Studyofthealgallimestoneisa potentiallyvaluabletargetofexploration,andisofgreat signicancetotheexplorationanddevelopmentofmixed carbonateformations. Keywords Mixeddeposition Lacustrinecarbonate Algallimestone Porestructure Oilandgas Introduction TheQaidamBasinisnotonlyoneofthecontinentalpetroliferousbasinsofinnorthwesternChinaandanimportant componentofTibetanPlateau.Itisabasinrelatedto forelandonthenortheasternmarginoftheTibetPlateau (Zhu 1986 ;Jia 2005 ;ZhaoandJia 2012 )(Fig 1 ). TheQaidamBasin,aninlandsaltwaterlakeunder droughtconditions,isgenerallyalowpriorityforexploration (Harrisonetal. 1992 ;Allegreetal. 1984 ).Depositionof mixedsedimentofclasticdepositionsandcarbonates (includingallochemicalgrains,etc.)formedavarietyof mixedsedimentaryrocks,whichcanbefoundina combinationofrocklayersystems(Guoetal. 2003 ).Consensushavenotyetreachedabouttheoriginsandclassicationofthemixedsediment(Feng 1993 ;Sha 2001 ;Maand Liu 2003 ;Guoetal. 2003 ;Zhang 2000 ).Thenorthwestern QaidamBasinNeogenesedimentarysourcematerialmainly camefromAltunMountain,adistantsource,formingland faciesandlacustrinefaciesinteractiondepositioninthe westernQaidamBasin.Theresultingreservoirrocksare mixedsedimentaryrocks,formedbyalternatingchemical andmechanicaleffectsinaridtosemi-aridclimaticconditions,andunderslightlybrackishwatertobrackishwater phasesofthelakewaters(Tuoetal. 1995 ;DangandZhao 2004 ;Hansonetal. 2001 ;ZhangandShou 2004 ). Lacustrinealgallimestonematerial Lacustrinealgallimestonestratigraphycharacteristics Accordingtodrillingdata,thewesternQaidamBasinhas undergoneYanshanianandHimalayantectonicmovements sincetheMesozoic(Lee 1984 ;Ulmishek 1984 ;Ritts 1998 ; Wuetal. 2003 ;Zhao 2013 ),whichformedthreesedimentarystratasequences(Fig. 2 ). InthePaleogene,thedepocenterofthebasinwasinthe westernQaidamBasin,thengraduallymigratedeastward. Thisprocesswascontrollednotonlybytectonicmovement inthebasinevolutionprocess,butalsobylatestructure patternsanddistribution(ZhaoandSun 2011 ). Thedevelopmentofthesedimentarysequenceis stronglygovernedbythesequenceoftectonicmovements intheQaidamBasin.Generallytheclimatebecamemore arid,andthewatermoresalty.Intermittentorseasonal oodscarriedne-grainedmudandsiltintothelake.This isthemainreasonforthevariationintheverticalrock F.Zhao( & ) ResearchInstituteofPetroleumExplorationandDevelopmentNorthwest,PetroChina,Lanzhou730020,China e-mail:fan_zh2002@163.com 123 CarbonatesEvaporites(2015)30:127133 DOI10.1007/s13146-013-0182-1

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Fig.1 TectonicbackgroundandlocationmapoftheQaidamBasin,arelativelyunstudiedfrontierbasinonthenortheasternmarginofthe TibetanPlateau Fig.2 SeismicsectioninterpretationandstratigraphicframeworkinthewesternQaidamBasinshowingtheformationoffourregional unconformitiesandthecorrespondingthreesedimentarysequences 128 CarbonatesEvaporites(2015)30:127133123

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sequence.TheNeogeneisdividedintosixunitsfromthe bedrockupwards(Table 1 )(WangandCoward 1990 ). Lacustrinealgallimestonetypesanddistribution Onthebasisofwellcoreobservationandsinglewell analysis,theNeogenesedimentaryfaciesinthewestern QaidamBasin(Table 2 )(Fig. 3 )iscomprisedoflacustrine algallimestoneoftheshallowlakesubfacies(Petersand Cassa 1994 ). Shallowlakesubfaciesisthebeltbetweenthelowest lakewatersurface(dryseason)andthewavebase(Peters andCassa 1994 ;Hendrixetal. 1992 ).Thehydrodynamics aremainlywavesandlakeow.Herethemicrofacies include:algalmounds,microfaciescontainingalgallaminatedlimestone,algallimestonemassandalgalmicrite lithofacies.Thelithofaciesoflakebaymicrofaciesis composedofmicrite,marl,mudstoneandshale.Shallow shoalmicrofaciesincludesmanytypesoflimestone lithofacies(Table 2 ). Algallimestoneanalysisresults Algallimestonelithologyanalysisresults ThewesternQaidamBasinismainlyalgallimestone lithology,includingalgallaminatedlimestone,algalclump limestoneandalgalmicritelimestone(Fig. 4 ).Observation ofthecorefromthewesternQaidamBasinwellshowsthat thesurfaceofalgallimestonehasdissolutionporosity, growthformation,goodoil-bearingnature,multi-layer,and largetotalthickness(Table 3 ). Purecarbonatesorpuresiltstoneorpuremudstonehave notbeenfound.Lithologiesincludealgalmicrite,algal clumplimestone,siltymudstoneandgraymatterandother siltstone,showingthisdepositionisthecombinedresultof mechanicalandbio-chemicalprocesses. Algallimestonepropertiesanalysisresults AlgallimestonesinwesternQaidamBasinshowanaverageporosityof6.9%,andanaveragepermeabilityof 1.353mD(Fig. 5 ),whicharebetterthanothertypesof reservoirs. Algallimestoneporestructureanalysisresults Porosityinthereservoirrocksincludeporesandssures. Tondoutporesize,shape,degreeofdevelopmentand interconnection,mercuryanalysisisthemostcommon andmosteffectivemethod.Inthestudyofcarbonate reservoirs,porestructureisespeciallyimportantforoil Table1 MesozoicandCenozoicchronostratigraphicframeworkin westernQaidamBasin EraAgeEpochFormationCode CenozoicQuaternaryHoloceneHubuxunQ4PleistoceneQigequanQ1 ? 3NeogenePlioceneShizigouN2 3Upper Youshashan N2 2Lower Youshashan N2 1MioceneUpperGancaigouN1PaleogeneOligoceneLower Gancaigou E3EoceneLuleheE1 ? 2MesozoicCretaceousLate Cretaceous K2Early Cretaceous QuyagouK1JurassicLateJurassicHongshigouJ3Chaishiling MidJurassicDameigouJ2Xiaomeigou EarlyJurassicHuxishanJ1 Table2 TypicalSedimentarymicrofaciesinwesternQaidamBasin SubfaciesMicrofaciesLithofaciesColorof mudstone Fandelta front Distributary channel SandstoneMulberry MouthbarSiltstone Distalbarsheet sand Siltstone Interdistributary bay Mudstone SharelakeSandatSandstonePurple Brown Red Flesh Gray Dark gray SandmudatMuddysiltstone MudatMudstone PlasteroorMarl GreyatMicrite Shallow lake AlgalmoundAlgallaminated limestone Gray Dark gray Algallimestone-mass Algalmicrite BayMicrite Marl Shale Mudstone ShoalLimestoneparticle CarbonatesEvaporites(2015)30:127133 129123

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andgasinformation.Commonparametersinvolvedare displacementpressureandthelargestconnectedpore throatradius. InthewesternQaidamBasinalgallimestonereservoir, displacementpressurerangesfrom0.69to8.966MPa, withmostvalues [ 1MPa.Thelargestconnectedpore Fig.3 SedimentaryfaciesoftheMioceneinthewesternQaidam Basin.PaleogenefaciesinthewesternregionofGanchaigou(N1), QaidamBasin.Ancientstructuralhigherlocationwouldbesuitable forthegrowthofalgaeandbenthicanimals.Alongwiththechangein seasons,theinuxofclasticmaterialwasintermittent.Whenthe inuxwaslow,fairlyclearwaterwasidealforthegrowthofalgae andbenthicanimals,whichformedbiogeniclimestone.Whenthe inuxwasplentiful,thewaterwasmuddy,whichwasnotconducive tothegrowthofalgaeandbenthicanimals,andbiogeniclimestone wasnotlikelytoform.Insteadwiththeinuxofdebris,theamountof energyandenvironmentalinputresultsinothertypesofrocks.Algae andbenthicanimalsmoundfaciesdevelopedinthehighpartofthe shallowlakefacies.Onthesideofsemi-deeplake,strongwavesand lakecurrentcausedstrongagitationofwaterandhigherenergy,which wouldhelpthegrowthofalgaeandbenthicanimals Fig.4 Photomicrographsofalgallimestonereservoirinwestern QaidamBasin. 1 Feng3Well,2,772.8m,algallaminatedlimestone, orthogonalpolarization, 9 100, u = 6%, K = 0.023 9 103l m. 2 Feng3Well,3,017.8m,algaeclumplimestone,orthogonalpolarization, 9 100, u = 13.1%, K = 17.5 9 103l m 130 CarbonatesEvaporites(2015)30:127133123

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throatradiusfallsintherangeof0.0821.065 l m,mostare \ 1 l m(Table 4 ).About17samplesshowasmallerdisplacementpressureandlargerporethroatradius(Fig 6 ). Controllingfactorsofalgallimestone Themaincontrollingfactorsofthealgallimestonereservoirinclude:sedimentarymicrofacies,faulting,dissolution alongfaultsanddissolutionoforganicacids. ThemainreservoirspaceinwesternQaidamBasinis madeupofavarietyofdissolvedpores,withevidenceof exposureandmeteoricwaterleaching.Thesedissolved poresaremostlikelyformedduetodissolutionoverburial time.Ontheotherhand,thewesternQaidamBasinhas manysmallfaults,whichprovidechannelsfortheinvasion offreshwater,makinguparelativelyopensystem. Therefore,poresinalgallimestone,algalmicriteandshale graymicriticwereformedmainlybydissolutionalong Table3 Physicalpropertiesof theAlgallimestonesamples fromwesternQaidamBasin No.Depth (m) LithologyPorosity (%) Permeability (md) Displacement pressure(MPa) Thelargest connected porethroat radius( l m) 22,772.8Algallimestone6.00.0231.0340.711 123,017.6Algallimestone4.40.0291.3790.533 153,017.8Algallimestone13.117.50.691.065 173,019.1Algallimestone101.10.691.065 253,017.7Algallimestone5.40.318.9660.082 273,017.9Algallimestone8.20.873.1030.237 Fig.5 HistogramofaveragepermeabilityandporositybyrocktypeinwesternQaidamBasin Table4 Classicationofpore structureforthecarbonate reservoirinwesternQaidam Basin Typeofpore structure Thelargestconnected porethroatradius( l m) Porosity(%)Permeability (md) Evaluation Coarseporosity Largethroat [ 10Bigthroat [ 12Coarseporosity [ 10Best Middleporosity Middlethroat 20.5Middlethroat126Middleporosity100.25Better Fineporosity Smallthroat 0.50.04Smallthroat62Fineporosity0.250.02Good Fineporosity Microthroat \ 0.04Microthroat \ 2Fineporosity \ 0.02Poor CarbonatesEvaporites(2015)30:127133 131123

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smallfaults.Inaddition,thedissolutionoforganicacid alsoplayedaroleintheporeformation. Conclusions Thealgallimestoneincludesmainlyalgallaminated limestone,algalclumpsandalgalmicritelimestoneinthe westernQaidamBasin.Thesedimentaryenvironmenthere wasprimarilythelakeshoreandshallowlake.Algal limestoneanalysisresultsindicatedagoodreservoirrock, whichmaybeanimportantexplorationtargetforthe QaidamBasin.OpenAccess Thisarticleisdistributedunderthetermsofthe CreativeCommonsAttributionLicensewhichpermitsanyuse,distribution,andreproductioninanymedium,providedtheoriginal author(s)andthesourcearecredited.ReferencesAllegreCJ,CourtillatV,TapponnierP(1984)Structureandevolution ofHimalayaTibetorogenicbelt.Nature307:1722 DangYQ,ZhaoDS(2004)SedimentaryfaciesofthePaleogeneand NeogeneinwesternQaidamBasin.JPalaeogeogr6(3):297306 (inChinese) FengZZ(1993)SedimentaryPetrology.BeijingPetroleumIndustry Press(inChinese) GuoFS,YanZB,DuCS(2003)Discussaboutadmixturesedimentary,diamictiteandadmixturelayer.EarthSciFront10(3):4044 (inChinese) HansonAD,RittsBD,ZinnikerD,MoldowanJM,BifU(2001) UpperOligocenelacustrinesourcerocksandpetroleumsystems ofthenorthernQaidamBasin,northwestChina.AAPGBull 85(4):601619 HarrisonTM,CopelandP,KiddWSF,YinA(1992)RaisingTibet. Science255:16631670 HendrixMS,GrahamSA,CarrollAR,SobelER,McKnightCL, SchuleinBJ,WangZ(1992)Sedimentaryrecordandclimatic implicationsofrecurrentdeformationintheTianShanevidence fromMesozoicstrataofnorthTarim,southJunggar,andTurpan basins,northwestChina.GeolSocAmBull105:5379 JiaCZ(2005)ForelandthrustfoldbeltfeaturesandgasaccumulationinMidwestChina.PetExplorDev32(2):19 LeeKY(1984)GeologyoftheChaidamubasin,QinghaiProvince, northwestChina.USGeolSurvOpen-FileRep84413:44 MaYP,LiuL(2003)Sedimentaryanddiagenesischaracteristicsof PaleogeneLacustrineHunji''Rockinbeachdistrict.Dagang ActaSedimentologicaSinica21(4):607613(inChinese) PetersKE,CassaMR(1994)Thepetroleumsystem:fromsourceto trap.AAPGMem60:93120 RittsBD(1998)Mesozoictectonicsandsedimentation,andpetroleumsystemsoftheQaidamandTarimbasins,northwestChina. PhDthesis,StanfordUniversity,Stanford,California,p691 ShaAQ(2001)Anexampleofhunjirock-originofsandydoloarenite oftheformationineasternyunnanprovince.JPalaeogeogr 4(3):5660(inChinese) Fig.6 PorestructureanalysisforalgalclumplimestoneinwesternQaidamBasin 132 CarbonatesEvaporites(2015)30:127133123

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TuoJC,ShaoHS,HuangXZ(1995)Lacustrinecarbonatesourcerock anditsorganicgeochemicalcharacteristics:anexamplefromthe NeogeneintheQaidamBasin.ExpPetGeol17(3):273276(in Chinese) UlmishekG(1984)Geologyandpetroleumresourcesofbasinsin westernChina:ArgonneNationalLaboratoryreportANL/ES146.Argonne,Illinois131p WangQ,CowardMP(1990)TheQaidamBasin(northwestChina): formationandhydrocarbonpotential.JPetGeol13:93112(in Chinese) WuYY,JingJQ,LiYT,JiangB,GuoBC,FangX(2003)Trans gressivesystemtractsandrelatedreservoirbodiesofPaleogene inwesternQaidamBasin.JPalaeogeogr5(2):232243(in Chinese) ZhangXH(2000)Classicationandoriginofmixsedimentite.Geol SciTechnolInf19(4):3134(inChinese) ZhangM,ShouJF(2004)Sedimentaryfaciesofcarbonaterocksof thePaleogeneandNeogeneinwesternQaidamBasin.JPalaeogeogr6(4):391400(inChinese) ZhaoF,JiaCZ(2012)Studyonthestrike-slipfaultanditscontrol effectonoilandgasaccumulationinthewesternQaidamBasin, China.GeolRev58(4):18(inChinese) ZhaoF,SunDQ(2011)Applicationofseismicreservoirsresearchin theYingxionglingareaoftheQaidamBasin:acasestudyofSha 37well.JSouthwestPetInst33(7):7378(inChinese) ZhaoF(2013)Meso-CenozoictectonicevolutionofQaidamBasin anditsrelationshipwithoilandgasaccumulation.NatGas Geosci24(5):6168 ZhuX(1986)StructureofpetroliferousbasinsinChina.Petroleum IndustryPress,Beijing(inChinese) CarbonatesEvaporites(2015)30:127133 133123


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