PartAPetroleumEngineeringFundamentals1-1PetroleumPetroleumisasubstance,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”.Oncedep