石油工程英语看.docx
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石油工程英语看.docx
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石油工程英语看
Studyandlearn.
PartAPetroleumEngineeringFundamentals
1-1Petroleum
Petroleumisasubstance,usuallyliquidorgas,consistingoforganicmoleculescomposedofhydrogenandcarbonatoms.Thusthegeneralname“hydrocarbons”isoftenused.Thepossiblevariationsintheconstructionofthemoleculesandmixturesofdifferentmoleculestoformnaturallyoccurringoil(crudeoil)arevirtuallylimitless.Notwocrudeoilsareidentical.Becausethesecomplexmixturesoforganicmatterarefoundinrock,theyarecalled“petroleum”,awordderivedfromtheLatinwordsforrock(petra)andforoil(oleum).
Weusuallybelievethatmostpetroleumisformedfromorganicmatter,tinyparticlesofplantandanimaldebristhataccumulatedwithmuddepositedinstagnantbodiesofwater.Theoriginalorganicmaterialwasmostlymicroscopicmarineplantsandanimalsthatlivedinopenseas,butmuchofitmayhavebeenderivedfromlandplantsandcarriedbystreamstothesiteofdeposition.Depositstoriesyoumighthaveheard,dinosaursdidnotcontributetotheoriginalsoup.Organicmaterialiseasilydestroyedbyexposuretoair.Depositionofthematerialmustberapidinwaterscontaininglittleornooxygenduetowaterstagnation.Wherewaterisoxygendeficientandchemicalreactionstakeoxygenatomsawayfrommoleculesitissaidtobea“reducing”condition,arequirementforthepreservationoforganicmatter.Also,low-oxygenenvironmentsgreatlydecreasethenumberofscavengersthatmightotherwiseconsumeanddestroytheorganicmorsels.Usuallytheproperconditionsoccurinquietmarinebasins,lagoons,andrapidlyburieddeltadeposits,butsimilarconditionsprevailinsomelakes.
Thebedsofsedimentaryrockinwhichthepetroleumisformediscalledthe“sourcerocks”.Theyareusuallydarkgrayorblackshales,butlimestoneisasourceundersomeconditions.Shalehasanabundanceofporespacebetweentheclayparticleswhichcancontainliquid,buttheporesaremuchtootinytoallowthemovementoffluidsundernormalconditions.Inotherwords,shalesarenotpermeable.However,thepressureproducedbytheprocessesofpetroleumgenerationexpelsthefluid,andpetroleumhastomovefromthesourcerockatsomestagesofdevelopmenttobecomeeconomicallyproducible.Theeventiscalled“primarymigration”.Oncedepartedfromthesourcebed,theoilorgaswillenteranynearbyporousandpermeablerock,suchassandstoneorlimestone.
Oilandgasarelessdensethanwaterand,forallpracticalpurposes,areinsolubleinwater.Ifthefluidsaremixed,oilandgasrisetothesurfaceofthewater.Rocksbeneaththewatertableare,bydefinition,saturatedwithwater.Petroleumleavingthesourcerockentersawater-wetrockandmusttrytorisetothetopoftheporouslayer.Iftheporousrockisalsopermeable,thatis,fluidscanpassfromonetinyporetoanotheror“flow”throughthesetinychannelwaysintherock,thepetroleumwillriseuntilitreachesimpermeablerockabove.Keepinmindthatporesinmostrocksconsistoftinyspacesbetweenthesandgrainsorcrystals.Theporesmustbeinterconnectedforfluidstopassfromoneporetothenext,andtheconnectingopeningmustbelargerthanahydrocarbonglobuleformovementtooccur.Suchmovementofpetroleumafterleavingthesourcerockiscalled“secondarymigration”.
Threadandtinyglobulesofoilorbubblesofnaturalgascollectatthetopoftheporous-permeablerocklayer.Suchaccumulationsareusuallytoosmalltoberecoveredpracticallyfromawell.However,iftherocksaretilledsomehow,thepetroleumwillcontinuetomigrateuptheslopingtopofthebeduntilitreachesthesurfaceoranimpermeablebarriertoitsflow.Themeasuresinclinationofrocklayerissaidtobethe“dip”oftherock.Ifthepetroleumreachesthesurfaceoftheearthatan“outcrop”oftherocklayer,itflowsontothesurfaceasanoilorgas“seep”.ThisishowoilwasfirstdiscoveredinKansas,inMiamiCountyin1860,shortlyaftertheDrakediscoveryinPennsylvania.Ifthepetroleumrisestoanimpermeablelimititissaidtobetrapped.An“oiltrap”isanynaturalbarriertotheup-dipmigrationofpetroleum;andhugeamountsofoiland/ornaturalgasmayaccumulate.
1-2GeologyofPetroleum
Sedimentaryrocks
Petroleummayoccurinanyporousrock,butitisusuallyfoundinsedimentaryrockssuchassandstoneorlimestone.Sedimentaryrocksagroupedintothreemajorclasses:
clastic,carbonate,andevaporitic.
Clasticrocksarethosethatarefoundbytheaccumulationandcementationofsedimentaryparticlesderivedfromweatheredfragmentsofpreexistingrocks.Weatheringprocesses,suchasfreezingandthawing,rain,wind,andothersimilarevents,breakdowntheparentrockintosmallparticlesthatcanthenbetransportedbywindandrainrunoff.Streamscarrythemud,sand,andgravelfromthesourceareadowntoitsfinalrestingplace,beingthatastreamchannel,floodplain,lake,orultimatelythesea.Thereitaccumulates,isburiedandcompactedbylater-arrivingsediments,andcementedbysilicaorcalcitetoformsandstone,andthegravelsbecomeconglomerates.Sandstones,becauseoftheinherentporositybetweentheirgrains,oftenbecomeexcellentreservoirsforoilornaturalgas.
Carbonaterockarelimestonesanddolomites.Theyusuallyforminwarmseawateratshallowdepth,ankledeeptoabout6m,wherevariousplantsandanimalsthrive.Thehard,usuallycalcareouspartsoftheorganismspileupontheseafloorovertime,formingbedsoflimeparticles.Algae,simpleplants,areoneofthegreatestcontributorsoflimeparticles,butanyshelledanimalmaycontributewholeorfragmentedshellstothepile.Reefs,banksoflimemud,andlimesandbarsarecommonlyfoundpreservedinrocks.
Carbonatesedimentsaresubjecttomanyprocessesinbecomingarock.Iflimemudisexposedtotheair,itsimplydriesoutandalmostovernightbecomesanatural“concrete”,andlimesandsbecomecementedbytheevaporationoflime-richseawatertoform“beachrock”.Rainwater,however,beginstodestroytherockandformsporosityintheprocess.Ifnotexposedtotheair,limesedimentscontinuetoaccumulate,perhapstogreatthickness.Undertheseconditions,theycompactundertheweightofnewsedimentsandeventuallyarecementedtoformlimestone.Theserocksarerarelyporousunlessotherprocessesbecomeinvolved.
Limestoneiscomposedofcalciumcarbonate(calciteoraragonite),thusthegeneralrockterm“carbonate”isused.Magnesium,acommonelementinseawater,canreplacesomeofthecalciumwithinthecrystalstructureofcalcite.Thisoftenhappensbyvariousprocessesthatarenotfullyunderstood;theresultingrockisknownas“dolomite”(calcium-magnesiumcarbonate).Theprocessofchanginglimestonetodolomiteproducessomewhatsmallercrystals,sotheresultingrockhastinyporesbetweenthenewcrystals.Thiskindofporosity,muchlikethatinsandstone,oftencontainsoilandnaturalgas.
Evaporaterocksareformedbythedirectprecipitationofmineralsbyevaporationofseawater.Resultingrocksareordinarysalt(halite-sodiumchloride),gypsum(calciumsulfatewithsomewater),andvariousformsofpotashsalts.Whengypsumisburiedtoconsiderabledepth,thewaterisexpelledfromthecrystalsand“anhydrite”(meaningsimply“withoutwater”),ahardercrystallinerock,results.Evaporatesarenotporous,althoughtheyarereadilydissolvedbywaterandarenotsourcerocksforpetroleum.However,theymaybeformedinhighlystagnantwaterwhereblackmud,richinorganicmatter,mayalsobedeposited,andsoarecommonlyassociatedwithgoodsourcerocks.Becausetheyareimpermeable,evaporatesoftenformsealsonotherreservoirrocks.
Layeredrocks
Geologictimeisnearlyincomprehensibletothehumanmind.Weusuallythinkintermsofafewtensofyears,sincethatmeasuresalifetime.Hundredsorthousandsofyearsareconsideredancienthistory.Butingeology,wemustthinkintimespansofmillionsofyears,hundredsofmillionsofyears,evenbillionsofyears.Geologistsmeasuresuchtremendousspansofgeologictimeinarelativesense,thatis,oneeventoccurredafteranotherandpriortoathirdevent.Inthatsense,ageologictimescalewasdevelopedinthe1800’stomakehardy“boxes”ofrelativetimeperiodsinordertothinkofeventsinanunderstandablemanner.“Period”and“eras”werenamedtodesignatevaryingintervalsoftimethatthenseemedtobeuseful.
Theactualtimeinyears,“absolutetime”ismoredifficulttodetermine.Geologistsarenowabletocalculatetimefromthedecayraysofradioactiveelements,suchasuraniumandpotassium.Radioactivemineralsarerequiredforthisexercise,andtheseonlyoccurincertainrocks,usuallyigneousrockssuchasgranite.Thussedimentaryrockscanonlybedatedrelativetotheoccurrenceofrelatedigneousevents,usuallywithintheaidoffossilsthatfitintoevolutionarysequences.Asonemightguess,datesinyearsforsedimentaryrocksarestillrelativeanduncertainatbest.
TherearemanyreasonstobelievethatEarthformedabout4.5billionyearsago.However,itwasnotuntilthebeginningofCambriantime,about545millionyearsago,thatsedimentaryrockscontainingfossilsbecameabundant.Thefirstfourbillionyearsofearthhistory,lumpedbygeologistintothePrecambrianEra,canonlybedatedwhereradioactivemineralsareavailable.
Structure
Onceformed,sedimentaryrocksaresubjecttovariouskindsofdeformation,suchasfoldingandfaulting.Threegeneraltypesoffoldsareanticlines,synclines,andmonoclines.
Folds
Threegeneraltypesoffoldsareanticlines,synclines,andmonoclines.
Anticlinesareup-foldsinthelayeredroc
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