Techniques to Maximise Oilfields ProductionIn The Republic of South Sudan

By:Eng. Salah H. WahbiChairman & Founder

Wahbi Consulting Services Co. Ltd.

PlanstoincreaseProductionRates

Planstoincreaseproductionratecanbecategorizedintotwomainareas:

A)ShorttermPlans.

A)MediumandLongtermPlans.

PlanstoincreaseProductionRatesA)ShortTermPlans(Workover)

Workoveroperationsareusedtosolve:

1. Lowreservoirpermeability.

2. Formationdamage.

3. Waterproduction.

4. Casingdamage.

PlanstoincreaseProductionRatesB)MediumandLongTermPlans

Mediumandlongtermplanscanbecategorizedas:

1. IOR(improvedOilRecovery).2. EOR(EnhancedOilRecovery)

PlanstoincreaseProductionRatesB)MediumandLongTermPlans(IOR)

IORincludes:• Infillwells.• WaterInjection.• ArtificialLift.

PlanstoincreaseProductionRatesB)MediumandLongTermPlans(EOR)

EORisconsideredatertiaryrecoverymethod.Itismainlyafterthemobilityrelationshipbetween

waterandoilEORinclude:a) Polymerflooding.b) Surfactants&alkalineinjection.c) Thermalmethods.d) Miscibleflooding(CO2)

A)ShortTermPlans(Workover)

SummaryofCommonProblems&WorkoverOperations

Excessive Water

Production

Squeeze & Re-perforating

Water Shut Off by Plugs

Chemical Water Shut Off

FACTORSINFLUENCEWATERINFLUXTherearemanyfactorsthatcaninfluencewaterinflux:1]Geological

SizeofstructureanditslocationRelativelythinupperlayerswithlateralvariationThinshalebreakwhichwilleasilyallowchanneling

2]WellLocationUpdip/DownorCrest/Flank

3]DriveMechanismStrongorweakwaterdrive

4]Oil-WaterContactBottomoredgewater

5]ThicknessofNetPay6]OperationalParameters

PressuredrawdownPumpfrequencyChokesize– duringtesting.

7]CompletionintervalStandoffOWC

WaterProductionMechanisms

(Curve 1) :- Completion Into Water and theproblemof fresh water resistivity.- Channel behind Casing (weekcurrent behind)(Curve 2) :- CasingLeaks- Channel behindCasing- StimulationOut of Zone- Barrier Breakdown(Curve 3) :- BottomWater- ConingorCresting- ChannelingthroughHighPermeability(Curve 4) :- FractureCommunicationbetweeninjectorandProducer

v Excesswaterproductionisaconcerninviewof:

ü ItiscausingwaterhandlingproblemsatFPFsü Watertreatmentanddisposalproblemsü RestrictingflowoflowP.Iintervals

ü OptimizingESPsinviewofchangeinP.Iü Severesandproductionwhichreflectonsandfillandhenceperforation

coveragev Stepstobetakentoarrestthisexcesswaterproductionproblem

ü Asproperdiagnosistoidentifythesourceofexcesswaterproduction:§ Properwellhistoryisakeyelement.§ Samelikethedoctorstartswithaskingthepatientabouthishealthhistory.

ü Aggressivewatershutofftobetakenuptoreducewatercutandincreaseoilproduction.

ExcessWaterProductionConcernsandChallenges

ReasonsandRouteCauseofhighwatercutProduction

ü AdverseMobilityratioinsuchfieldslikeBamboo,Heglig &Munga

ü Productionmechanism- ESP&PCPcausedHighdrawdown

ü Bottom&Edgewaterencroachment(MidField)

ü InjectionwaterbreakthroughinUnity(Talih WestField)

ü FlowbehindcasingduetopoorCementationinsomewells(BAM-X,NE-X&NE-Y)…

(Howcanwesolvethis?)

OverallWaterCutBehavior

Production Curve - Block 1,2

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Heglig UN Toma-s EL nar Elharr Eltoor Bambo khairat Munga AvargeBack

Addnewtechniquetodetermineexcessivewaterproductionmechanismsasseeninpetroleumproductionwellshasbeendevelopedandverified.

log-logplotsofWOR(Water/OilRatio)vs.timeshowdifferentcharacteristictrendsfordifferentmechanisms.

ThetimederivativesofWORwasfoundtobecapableofdifferentiatingwhetherthewellisexpecting

•Waterconing,

•High-permeabilitylayerbreakthrough,

•Nearwellborechannelingand

•LayerConductivity

Fig 5-1 Coning (Numerical SimulationFig 5-2 High Permeability Layer (Numerical Simulation)Fig 5-3 Near Well Bore Flow

The vertical increase at the end (1800 days) is characteristic of a near well bore flow = this is “bad

water” and needs to be treated.

Fig 5-4 Layer Conductivity Good Water

This case WOR and WOR’ increase = layer conductivity = good water.WOR and WOR’ decrease at 3000 days because of an injector shut down in the near area. Note that they resume their increase on the same slopes sometime after when water comes from farther wells.Some sharp increase corresponds to near well bore flow followed by a remedial squeeze treatment

DiagnosisMethodsofExcessWaterProduction

In-Jun-99fromZarqa X(2176-2192.5mkb)

Drop in O/Liq due to Press

Start W-Injection IN Nov-01

Oil Dec wc inc-bad w

WELLPERFORMANCEANALYSISUN-X

WELLPERFORMANCEANALYSISUN-X

LayerConductivityFromWI-XtoUN-XinZCDistance(695m)

PROPOSALACTIONPLANforSEPRATELAYERINJECTIONUN-X

(CURRENT)UN--X

(PROPOSED CHNAGES)

2069 -2074 mkb

2186 - 2198 mkb

2267 - 2275 mkb

Zarqa-A

Zarqa - C

Zarqa - D

2069 -2074 mkb

2186 - 2198 mkb

2267 - 2275 mkb

Zarqa-A

Zarqa - C

Zarqa - D

PLTZone Relat Inj

Rate (%)Zarga A 12.75Zarga C 84.94Zarga D 2.31 Back

HighWaterCutDiagnosisMethods (Operation)

v ClassicMethods:

o SwabTest

ü SwabofMultilayerswillTakelongtimeofRig

ü Sometimesmisleading(itisalmostatstaticcondition)

v OtherMethods:

o RunPLT

ü GetReservoirparameters(pressure,BHP,PI)underdynamiccondition

ü PLTconductedEx:(He-X,TAS-X,Munga-X)

Heglig -XPLTResult

1) No contribution then single layer completion instead of commingling.

B-1AB-1BB-3AB-3B

B-1AB-1B

B-3BB-3A

GeneralWaterShutoftechniques

v ClassicMethods:

o CementSqueeze:

ü Openended tubingSTCEX:MG-X,Y

ü DrillableCementRetainer(DCR)

o WaterShutoffwithDrillableBridgePlug(DBP)EX:HE-X

v OtherTechniques:

ü MechanicalWaterShutoff

ü ChemicalWaterShutoff

ü PlantouseMultiPacker(onprogress)

ClassicWaterShutoffTechniques

vCementsqueezeandreperforate:

ØOpenendedtubingSTCandcementretainerDCR:o Successfully implemented atTY-Xon13August2008

o BentiuXlowerwaspermanently cementsqueezed

o BentiuXupperwascementsqueezedandpartiallyre-perforated

o Aradeibawassqueezedcementandtotallyre-perforated

• WellperformancePre/PostWSOjob:

Pre-WSO Post-WSOTY-X Well Schematic

Back

ClassicWaterShutoffTechniques

vWatershutoffusingDrillableBridgePlugDBPo Wassuccessfully beingutilizedatHE-XinJuly 2008o BentiulowerwasisolatedwithDBPsetat1731.0

mKB

ü Well performancePre/PostWSOjob:

HE-X Well SchematicPre-WSO Post-WSO

v LessonLearnto Betterdiagnosis&GoodreservoirevaluationwillLeadtohaveanexcellentresultinthere-completion

Back

MechanicalWatershutoffwasnotsuccessful

q Thetoolworksbyapplyingdifferentialhydrostaticpressureagainsttheswitches,whicharecalibratedtoopenandthencloseatcertainpressurevalues(24Mpa,18Mpaand12Mpa)

q LimitationofMechanicalWatershutoffTool:

o Thecandidateshouldbe7”casing(availabilityof7”packer).o No.ofproducingzones(three).o Differentialpressuretooperatetoolswitches(onandoff).o Surfacepressuremustnotexceed24.4MPa.(Wellheadpressurelimitation).o Welldepthshouldbemorethan2200mKB.o Sandproduction inducesprematureswitchesfailure.

q 1st TrialEH-X :v Failurecauseswereduetopackerleakageandswitchcheckvalvemalfunction.

q 2nd TrialEN-X:v Sandproduction causedtheswitchestostuckandledtoconfusioninproducingzones

combinationandhencetestresults.

MechanicalWSOEquipmentdiagram

EH-X1stTrialToolsDiagram

vLessonLearnt:

oSandpresenceaffectedthetoolswitchesoperation.oThetoolshouldmatchtheapplicationGNPOCwellsnotviseversa.oProvisionoffixableESPtoaccommodatedifferentreservoirscenariosfortestandproduction(i.e.formationpressureandPI).

Back

ChemicalWatershutoffTechnique

qThechemicalworksbyapplyingpluggingagent,highconductivityzonescanbeshutoffselectively.

qChemicalWSOchallengeso Chemicalshelflife.o NoorlittleimprovementinoilgainpoststheWSOjob.o Deepstudyshouldbecarriedouttoselectreliablechemicaltype.o Verylimitedcandidatemeetingtheoperationrequirements.o Operationandlogistic.o Effort&longtimeconsumedforpre-jobpreparationandpotablewatersupply.o Itsintensityandinitialgellingtimecanbeadjustedatacertainextentaccordingtothereservoircondition;temp.

o Wellusedtoproduce5712BLPD,407BOPDwith92%WCbeforejobexecution.Ø1st trialHE-X:

v Postjob thewellproduced200BOPDwith84%WCandthegrosswaslimitedtomax.1800 BLPDasperRErecommendation.

v Thewellcontinuedproduction atlowcontrolledrateforsixmonths.v sincenoimprovement inoilgainachieved,REadvisedtorevertbacktothepreviouscondition (currentlythegrossis5159,oil445and91%WC)

Ø2ndtrialHAM-X:vWellusedtoproduce2772BLPD,62BOPDwith98%WCbeforejobexecution.v Thewellwasabandonedafterclassicre-completion job.

EquipmentdiagramofChemicalWSO

Water tank 80M3

Water tank 80M3

Water tank40M3

Blending tank 8m3

Cement truck

Cementtruck Wellhea

d

Blending tank40m3

Blending tank 40m3

Blending tank 40m3

4〞Hose2-1/2〞Hose4〞Hoseconnected when need2-1/2〞Hose

Connected when need

2〞1502 hardpipeline

vLessonLearnt:oDeepstudyshouldbecarriedouttoselectreliablechemicaltype.oVerylimitedcandidatemeetingtheoperationrequirements.oItsintensityandinitialgellingtimecanbeadjustedatacertainextentaccordingtothereservoircondition;temp.

Back

ProductionPerformanceofHE-XAfter(WOJ)

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Avg WATER_RATE (bwpd) Avg WATER_RATE (bwpd)

Decrease in water production before and after WOJB -3A

B-1A

B -1B

1618 - 1624 mkb

1631 – 1638 mkb

1867 - 1872 mkb

HE-6

B -3B 1875 - 1878 mkb

DBP

0200400600800

1,0001,200

Avg OIL_RATE (bopd) Avg OIL_RATE (bopd)

Improvement in oil production Before and after WOJ

Production from Bentiu-X onlyProduction from Bentiu-X & ardeiba

MitigationPlantoDevelopBentiu-X&Bentiu-Y

Mitigation Plan to develop Bentiu-X & Bentiu-Y :Installation of dual ESP can revive production

from Bentiu-3 keeping upper layers un effected

Well PotentialUpper layers= 1035 bopd

Lower layer= 382 bopd

Total= 1473 bopd

Production Tubing

Power cablew/capillary tube

MB Packer

Upper zoneperforations

ESP

Packer

Casing

Lower zoneperforations

Single Production Tubing / Dual ESP System - Annular Flow

ESP

Back

Talih XPLTResult

• Ghazal-Xproduced2500bbl/dwater

üAsifwearewastingeffortof injectordaily

• NoContribution fromZargaatpresenceofGahzal,althoughTAS-Xdowndipwellproduced~250bopd

üCompletionStrategytoberevisedfornewwellsandforexistingwellsonopportunitybasis

PLTMunga-XResult

B-1AB-1B

B-1C

B-1BinterfereB-1A,

ü Actiontakenisreducingperforationintervalto2meter,decreasedthewaterproduction

ü B-1A

ü B-1B

ü Resultisverysuccessful,

ü sameideaconductedinMunga-Xwithverysuccessfulresult

Munga-X Performance after & Recompilation PLT JobClear water production reduced

MG-XPerformanceafterRecompbasedonPLTResultofMG-Y

Back

Strategyforwardinaddressingwaterproduction

Immediate

Medium Term

Ø ApplicationofY-ToolPLT.PermanentinstallationofY-Toolatkeywellsinablocktoreducecost.

Ø Completionstrategy:

ü singlelayercompletionforfuturewells.

ü ExploratorywellsPerforationintervalshouldbeadjusted&optimizedfarawayfromOWC

Ø ContinueDrillingofHorizontalwellstodelaywaterconing

Ø EstablishRMP,optimizeWaterProductionandenhanceRecoveryFactor.

Ø ApplicationofNewTechnology

ü MultipackerCompletion

ü ElectroTreatment

Ø ChemicalWaterShutOffü Indepthstudyandscreeningcriteriashouldbesetupfor

Mechanicalandchemicalwatershutoff

Long Term

MediumandLongTerm(IOR)

IOR

IORdrillinghorizontalwells:- reduceswaterconingduereducedrawdowninthe

reservoir.- Longlengthexposedtopayzoneincreaseproduction.- Moreeffectiveinthesandoilformationwithshort

distancetowater.- Horizontalwellsarenowcompletedwithnewmethods

inadditionaltotraditionalopenhole,casedhole,slottedlineorpre-perforatedpipe.

- Smartcompletioninvolvespermanentzonalsolutionwithexternalpackers,downholechoke&otherdeviceforcontrollingtheinflow.

IOR

WheredoweuseIORwaterinjection?• Waterinjectionwillnotimproverecoveryinareaof

strongwaterdrive.• Itispossiblewheredepletionisobservedandhas

edgewaterinflux.• Itislessexpensivetodrillwatersourcewellinto

shallowaquiferanddirectlytotheinjectorwithoutfurthertreatmentwhileproducedwaterneedstreatmentunit.

IOR(watermanagement)

• Diagnosetheentirewatercycle(reservoir,producers,facilities,injectors).

• Updatedthefielddevelopmentplan.• Identifyworkoveropportunities.• Applysuitabletechnology.

q Producers.q Injectors.q Surface.

MediumandLongTerm(EOR)

EOR Technology for Heavy Oil

Extra heavy oil

EOR

EOR

EOR

EOR

EOR

EOR

EOR

EOR

IOR

IOR

EOR

EOR

ConclusionsandRecommendations

v Declineinoilproductionisattributedmainlyduetohighwatercut,Watercutinmaturefieldsisonrisingtrendwhichhasseverenegativeimpacttofieldsreserve(EUR).

v Excesswaterproductionisheadacheforoperatingcompanyandwillcosttimeandmoneybettertoleaveinreservoir.

v Betterdiagnosis,understandingwillleadtosuccessfulremedialaction

v Diagnosticplotswhichwascarriedouttothatwell(UN-X)ProducedhighWCindicatesthishighwatercutmostlyrelatedtolayerConductivity.

v ControlliquidrateforNewwells&WOwells.