HOW IT WORKS-2

HowDoesWellAcidizingWorktoStimulateProduction?Stimulationisperformedonawelltoincreaseorrestoreproduction.Sometimes,awellinitiallyexhibitslowpermeability,andstimulationisemployedtocommenceproductionfromthereservoir.Othertimes,stimulationisusedtofurtherencouragepermeabilityandflowfromanalreadyexistingwellthathasbecomeunder-productive.Atypeofstimulationtreatment,acidizingisperformedbelowthereservoirfracturepressureinanefforttorestorethenaturalpermeabilityofthereservoirrock.Wellacidizingisachievedbypumpingacidintothewelltodissolvelimestone,dolomiteandcalcitecementbetweenthesedimentgrainsofthereservoirrocks.Therearetwotypesofacidtreatment:matrixacidizingandfractureacidizing.WellAcidizingSource:MPGPetroleumAmatrixacidjobisperformedwhenacidispumpedintothewellandintotheporesofthereservoirrocks.Inthisformofacidization,theacidsdissolvethesedimentsandmudsolidsthatareinhibitingthepermeabilityoftherock,enlargingthenaturalporesofthereservoirandstimulatingflowofhydrocarbons.Whilematrixacidizingisdoneatalowenoughpressuretokeepfromfracturingthereservoirrock,fractureacidizinginvolvespumpinghighlypressurizedacidintothewell,physicallyfracturingthereservoirrockanddissolvingthepermeabilityinhibitivesediments.Thistypeofacidjobformschannelsthroughwhichthehydrocarbonscanflow.Therearedifferentacidsusedtoperformanacidjobonwells.Acommontypeofacidemployedonwellstostimulateproductionishydrochloricacids(HCI),whichareusefulinremovingcarbonatereservoirs,orlimestonesanddolomites,fromtherock.Also,HCIcanbecombinedwithamudacid,orhydrofluoricacid(HF),andusedtodissolvequartz,sandandclayfromthereservoirrocks.Inordertoprotecttheintegrityofthealreadycompletedwell,inhibitoradditivesareintroducedtothewelltoprohibittheacidfrombreakingdownthesteelcasinginthewell.Also,asequesteringagentcanbeaddedtoblocktheformationofgelsorprecipitateofiron,whichcanclogthereservoirporesduringanacidjob.Afteranacidjobisperformed,theusedacidandsedimentsremovedfromthereservoirarewashedoutofthewellinaprocesscalledbackflush.HowDoesWellFracturingWorktoStimulateProduction?Stimulationtechniquesareusedtoencourageproductiontoflowfromthereservoirrocks.Hydrocarbonsarelocatedinthespacesbetweenporesofreservoirrock.Productionisachievedwhentheseporespacesareconnectedandpermeability,ortheabilitytotransmitfluids,issuchthatthehydrocarbonsflowoutoftherockandintothewell.Insomereservoirs,therockshavelowpermeability,andthehydrocarbonscannotbeextractedforproduction.Othertimes,productionishamperedbyformationdamage,whendrillingintothereservoirrocklessenspermeability.Productioncanbeachievedinthesewellsviaaproductionstimulationmethodcalledwellfracturing.Performedabovethereservoirformationfracturepressure,wellfracturingcausesahighlyconductiveflowpathbetweenthereservoirandthewellbore.Wellfracturingactuallybreaksorsplitsthereservoirrockopentoencouragehydrocarbonstoflowfromtherocksintothewell.AWellBeforeandAfterFracturingSource:AustinExplorationLimitedPerformedafterthewellhasbeencompleted,orafterthecasing,tubingandperforationshavebeenapplied,wellfracturinghasevolvedovertime.Startinginthe1860sandusedthroughthe1940s,explosivefracturingusedtobethemostcommonmethodofwellfracturing.Explosivefracturing,alsoknownaswellshooting,detonatedanexplosivewithinthewelltobreakthereservoirrocks.Successfulatstimulatingproduction,yetdangerous,explosivefracturingintroducedliquidnitrogenintothewellviaatincylinderreferredtoasatorpedo.Thetorpedowasloweredintothewellboreanddetonated.Theexplosioncreatedahugeholethatwasthencleanedoutandcompletedasanopenhole,leavingthebottomofthewellopenintothereservoir.Developedinthelate1940s,hydraulicfracturing,alsoknownasafracjob,isthepracticeofinjectingawellwithlargeamountsoffracfluidsunderhighpressureinordertobreaktherocks.Performedonbothopenholeandcased-wellperforations,hydraulicfracturingquicklyreplacedexplosivefracturing.Usedinagel-likestate,fracfluidsconsistofwaterandpolymers,orlongorganicmoleculesthatformathickliquid.Bothoil-basedandfoam-basedfracfluidsusenitrogenbubblestoachievethefracture.Carbondioxidecanbeused,aswell,tominimizeformationdamage.Afracjobisperformedinthreesteps.First,alargeamountoffracfluidsarepumpedintothewell.Thehigh-pressureofthefracfluidsandthecontinualpumpingincreasesthepressureinthewell,overcomingthestrengthofthereservoirrockstobreakthemapart.Fracingfluidsarepumpedintothewelluntiltherocksarecrackedtoadesiredlength.DifferentTypesofProppantsSource:HexionThen,fracfluidandproppingagentsareintroducedintothewelltoextendthebreaksandpackthemwithproppants,orsmallspherescomposedofquartzsandgrains,ceramicspheresoraluminumoxidepellets,thatholdthefracturesopenafterpumpinghasceased.Thisisimportant,becausethenthehydrocarbonscanflowthroughtheopencracksinthereservoirrocks.Finally,thewellisbackflushedtoremovethefracfluids.Increasingboththerateofproductionandtheoverallproductionofawell,hydraulicfracturingisbestemployedinmediumandhardformations.Infact,hydraulicfracturingisusedinalmostalltightgassandreservoirs.InonshoreUSwells,approximately50%ofthegaswellsand30%oftheoilwellsarefraced.Hyd