页岩油开采外文文献翻译Word下载.docx
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Fandcarbondioxideatvariouscombinationsofpressure(1000psi,2000psi,3000psi,and4000psi)andtemperature(−15°
F,0°
F,32°
F,and74°
F)wasinjectedintothem.OilRFforeachexperimentwasmeasuredafterfivedaysofproductionperiod.Additionally,porosity,permeabilityandultrasonicvelocityofeachcoresampleweremeasuredbothpriortoandafterconductingtheexperiment.
TheresultsindicatethatinjectingCO2
atlowtemperatureresultsinhigheroilrecoveryfactor(upto7%)thaninjectingcarbondioxideatambienttemperature.ItwasalsoobservedthatinjectingcoldCO2
enhancedbothporositiesandpermeabilitiesofthecoresamples.Theporositiesandthepermeabilitiesofthecoresamplesenhancedbyupto3.5%and8.8%,respectively.Also,anoticeablereduction(between100 ft/sand400 ft/s)inP-wavevelocitywasobservedafterinjectingthecoldgasintothecoresamples,whichisanindicationofcreatinginducedfractures.Theresultsalsorevealedthatinjectingthecoldgasincreasedthebrittlenessindicesofthecoresamplesbyupto8.Hence,cycliccoldcarbondioxideinjectioncouldbepotentiallyimplementedintheshaleoilfieldstoimprovetheefficiencyofthecurrentindustrypracticeofcyclicgasinjectiontechnique.
Keywords:
Shaleoilreservoirs,Cyclicgasinjection,Carbondioxide,Oilrecovery,Thermalshock
1.
Introduction
Shaleformationshaveultra-lowpermeabilitiesanddonotproduceeconomicallyunlessfracturingtreatmentsareperformed.Despiteusingcurrentstimulationtechniques,shalereservoirsonlyproduce5–7%oftheirinitialoilinplace.Therefore,researchersarestillworkingonexploringnewtechniquestoimproverecoveryfactor(RF)inshale-oilreservoirs.Consequently,severalEnhancedOilRecovery(EOR)techniqueshavebeenstudiedtoimproveultimateoilRF.Oneofthemostpromisingtechniquesiscyclicgasinjection“HuffandPuff”,whichhasbeensuccessfullyimplementedinbothconventionalandunconventionalreservoirsusingdifferentgases(nitrogenandcarbondioxide).
Inthisstudy,effectsoftemperatureofinjectingCO2
onoilRFinshaleoilformationswasinvestigated.Inthisexperimentalstudy,CO2
wasinjectedintofourcoresamplesatdifferentpressuresandtemperaturesandoilRFattheendofeachtestwascalculated.
Itisbelievedthatrapidlyinjectingcoldgasintohotformationscreatescracksattheexposedsurfaceareaoftherock,whichincreasesoilRF.Thistechniqueiscalledthermalshocking.Sincethermalshockcreatesfracturesattherocksurface,itisbelievedthatporosity,permeabilityandrockmechanicalpropertiesoftherocksampleswillbealteredtoo.So,porosityandpermeabilityofthesamplesweremeasuredbeforeandaftereachinjectiontest.Also,ultrasonicvelocitymeasurementtestswereconductedtoassesschangesindynamicyoung’sModuliandPoisson’sratiosofthecoresamples.
SinceEagleFordisoneofthelargestunconventionalresourcesintheU.S.,coreplugsfromitsoutcropwereobtainedandusedinthisstudy.Additionally,CO2
wasusedinthisexperimentalstudybecauseofitssuccessfulimplementationsinEORoperationsinthepastdecades.
[13]
reportedthatthefollowingparametersmaycontributetoincreaseinoilRFusingcarbondioxide;
reductionofoilviscosity,miscibilityeffects,andinternalsolutiongasdrive.
1.1.
Cyclicgasinjectionmethod
CyclicGasInjectionalsoknownashuff-and-pufftechniqueisanefficientEORmethodinwhichagasisinjectedintoareservoireitherinmiscibleorimmisciblecondition(huffcycle).Thenthewellisshut-infora“soak”periodtoallowtheinjectedgastointeractwiththeformationoilandreachequilibrium.Attheendofthesoakingperiod,theproductionisresumedthroughthesamewell(puffcycle).
Thismethodhasbeensuccessfullyimplementedinshaleoilfields.
[9]
reportedthatCO2
greatlyenhancesthediffusionprocess,whichimproveshydrocarbontransportintightmatrixes(especiallydenselyfracturedshale-oilformations).
UsingCO2
andshalecoresfromMancosandEagleFord,
[4]
conductedalaboratorystudytoinvestigateeffectsofsoakingperiod,soakingpressureandnumberofcyclesonoilRF.TheresultsshowedthatcyclicCO2
injectionisaneffectivemethodtoimproveoilRFfromshaleoilreservoirs.
conductedanexperimentalworkinjectinghigh-pressureCO2
into21coresamplesfromBakkenshaleformationtoenhancethediffusion-dominatedflowinthereservoirmatrix.TheresultsindicatedthatCO2
isabletorecoverupto99%ofoilfrommiddleBakkenformationand68%fromupperandlowerBakkenformations.AnotherCO2
huff-n-puffexperimentalstudyinasupercriticalstatewascarriedoutusinglowpermeabilitycoresamples.TheresultsshowedthatthecyclicCO2
injectioninsupercriticalstatecansignificantlyimprovetheefficiencyofoilfielddevelopmentforlowpermeabilityreservoirs
[15].Incontrast,formationdamagecouldoccurwhenCO2
isinjectedintoformationsduetocalciumcarbonateprecipitationandbrinecontent.SeveralparametersaffecttheinteractionbetweenCO2
andformationrockincludingpressure,temperature,brinecompositionandCO2
injectionrate.ThereactionbetweenCO2
andformationrockcouldresultinpermeabilityreduction
[11].
Inadditiontotheexperimentalstudies,CO2
cyclicgasinjectiontechniquewassuccessfullyimplementedinsomeoilfields.Thismethodwassuccessfullyimplementedon240wellsintheBigSinkingFieldofeasternKentucky,USA.UsingliquidCO2
resultedinadditionalrecoveryof180,000barrelsofoilfromthefield
[10].AnotherfieldimplementationofCO2
cyclicgasinjectionwascarriedoutinJiangsuoilfield,China.TheresultsdemonstratedimprovementinwellproductivityduetodissolutionofCO2
andnearwellboredamageremoval
[20].
1.2.
Lowtemperaturegasinjection
Inthistechnique,gasatalowtemperatureisinjectedintohotreservoirs.Thisprocessiscalledthermalshocktechnique,whichleadstocreatingthermalstressontherock.Thethermalstressresultsincreatingnewfracturesand/orextendingexistingcracksyieldingtohigheroilRF.UsingEq.
(1),thermalstressappliedtoasolidbodyduetotemperaturechangeiscalculated.
Inthelastfewyears,experimentalworkshavebeenconductedtostudythermalshocktechniqueanditsapplicationsintheoilandgasindustry.Usingliquidnitrogen,
[2]
conductedcryogenicfracturingtestsonconcrete,tightsandstone,andNiobrarashalesamples.Theresultsshowedthatinjectingliquidnitrogennotonlyenhancesrocks’permeabilities(especiallyshalesamples),butalso,hasalmostnoformationdamagepotential.
[23]
conductedrockmechanicalpropertiestestsundercryogenicconditions(rocksamplesweresubjectedtoliquidnitrogen).Theresultsshowedthatshearandtensilestrengthsoftherocksamplessignificantlydecreasedafterbeingsubjectedtoliquidnitrogen.Thermalshockcausedbythecryogenictreatmentcouldcreatenewmicrofracturesandextendtheexistingones.
[21]conductedcryogenicfracturingexperimentstoinvestigateitseffectsonthepermeabilitiesofeight-inchcubicsyntheticrocksamples(concrete).Eighttinythermocoupleswereembeddedinthesamplestomonitorchangesintemperatureduringthetest.Liquidnitrogenwascirculatedintothesamplesthrough6-in.-deepholeswhilethesamplesweresubjectedtotriaxialcompression.Theresultsshowedthatthepermeabilitiesoftheaffectedareaincreased.
[3]
concludedthatcryogenicfracturingisastimulationtechnology,whichdeployscryogenicfluidstofractureunconventionaloilandgasreservoirs.
[6]
conductedanon-isothermalcompositionalsimulationstudytoexamineeffectofinjectinglowtemperatureCO2
onoilRFinahightemperaturereservoir.TheresultsshowedthatinjectingliquidCO2
increasesultimateoilRFby8.73%comparedtosupercriticalCO2
injectioninisothermalmode(200°
F)after24 yearsofproduction.
2.
Experimentalwork
Inthisstudy,severalexperimentswereconductedtoinvestigateeffectoftemperatureofinjectingCO2
onoilRFinshaleoilreservoirs.Detaileddescriptionofporosity,permeability,ultrasonicvelocitymeasurementsandcyclicgasinjectionexperimentaregiveninthefollowingsections.FourEagleFordcoreplugswereusedinthisexperimentalstudy.Thesecoreswerecutparalleltothebeddingplanesandwereall1.5″indiameterand3″inlength.
2.1.
Porositymeasurement
Aheliumporosimeterwasusedtomeasuretheeffectiveporositiesofthecoresamples.Theporositiesweremeasuredbothpriortoandafterconductingtheinjectiontests.
2.2.
Permeabilitymeasurement
NewResearchEngland(NER)AutoLab1500(wasusedtomeasurepermeabilitiesusingcomplextransientmethodandhelium.
Fig.
showsajacketedcoresamplemountedbetweenthelow-permeabilitytransducerandthebottomplug.ThepermeabilitiesofallcoresamplesweremeasuredbeforeandafterconductingCO2
injectiontests.Theresultswerethenusedtostudyeffectofthethe