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WaterfloodingA Tried and True Technique for
Secondary Oil Recovery
WilliamM.Cobb&Associates,Inc.
Houston Bar AssociationOil, Gas and Mineral Law Section
March 26, 2013
F. J. Deacon Marek, P.EPresident
William M. Cobb & Associates, Inc.Dallas, Texas
Brian R. Sullivan, P.EAttorney/Petroleum Engineer
McElroy, Sullivan, Miller, Weber & Olmstead, LLPAustin, Texas
General Topics Whatisawaterflood? Howdoesitwork? Whattypesofpropertiesmakebettercandidates? Unitization
Whyisitsometimesneeded? Howdoestheprocesswork? Exampleequityformula
Page 2William M. Cobb & Associates, Inc.
What is a Waterflood? Itistheinjectionofwaterintoawellboretopush,ordriveoiltoanotherwellwhereitcanbeproduced
Recognizedenhancedoilrecoverytechniquesinceearly1900s
Someoilreservoirshavenaturalwaterinflux,whichincreasesoilproduction Calledwaterdrivereservoirs Theyarenaturalwaterfloods
Page 3William M. Cobb & Associates, Inc.
How Does a Waterflood Work?
OilreservoirsandOriginalOilinPlace Oilrecoveryunderprimaryproduction Targetoilforwaterfloodrecovery
Page 4William M. Cobb & Associates, Inc.
Bulk Volume Calculations
Area
Area
Reservoir Area
Reservoir Bulk Volume (BV) :BV = Area x Thickness
h
Page 5William M. Cobb & Associates, Inc.
Calculating Original Oil in Place (OOIP)
BulkVolume Area Thickness
Porosity Porespacewithintherock Generally5%to30%ofthe
bulkvolume
Page 6William M. Cobb & Associates, Inc.
Calculating Original Oil in Place (OOIP)
BulkVolume Area Thickness
Porosity Fluidsaturations
Water(usually10%to50%ofporespace)
Oil
Page 7William M. Cobb & Associates, Inc.
Calculating Original Oil in Place (OOIP)
BulkVolume Area Thickness
Porosity Fluidsaturations
Water Oil
Shrinkage(oilformationvolumefactor)
Page 8William M. Cobb & Associates, Inc.
Formation Volume Factor (Bo)
Oilshrinksasitisproducedfromthereservoirtothesurfacedueto gasevolvingfromtheoil Lowertemperatureatthesurface
Thesalesunitforoilisastocktankbarrel,orSTB,whichisequalto42USgallons
UnitsofBoareRB/STB(reservoirbarrelsperstocktankbarrel)
Bointypicalwaterfloodprojectsrangesfromabout1.1to1.5RB/STB
Page 9William M. Cobb & Associates, Inc.
Calculating Original Oil in Place (OOIP)
OOIP = 7,758*A*h**(1-Sw)/BoWhere:
OOIP = original oil in place, STB
7,758 = factor converting acre-feet to barrels
A = reservoir area, acres
h = average reservoir thickness, feet
= average reservoir porosity, fraction bulk volumeSw = average water saturation, fraction pore volume
Bo = oil formation volume factor, RB/STB
Page 10William M. Cobb & Associates, Inc.
Example Calculation
Problem - Calculate OOIP oil for a new oil well with the following conditions:
Reservoir area = 40.0 acres
average reservoir thickness = 25 feet
average reservoir porosity = 22%
average water saturation = 30%
oil formation volume factor = 1.32 RB/STB
Page 11William M. Cobb & Associates, Inc.
Example Calculation
OOIP = 7,758*A*h**(1-Sw)/BoOOIP = 7,758*40*25*0.22*(1-.30)/1.32
OOIP = 905,100 STB
Page 12William M. Cobb & Associates, Inc.
So once weve calculated OOIP
Page 13William M. Cobb & Associates, Inc.
So once weve calculated OOIP
How much of that oil is recoverable?
Page 14William M. Cobb & Associates, Inc.
The Amount of Recoverable Oil Depends on the Natural (Primary) Reservoir Drive Mechanism
SolutionGasDrive Recovers5%to15%OOIP Leavingbehind85%to95%oftheOOIP
SolutionGasDrive+GasCapExpansion Recovers15%to25%OOIP Leavingbehind75%to85%oftheOOIP
NaturalWaterDrive Recovers25%to50%OOIP Leavingbehind50%to75%oftheOOIP
Page 15William M. Cobb & Associates, Inc.
Why would you need to waterflood? MANY(majority?)oilreservoirsaresolutiongasdrive WaterfloodingcanrecovermuchoftheoilleftbehindunderPrimaryproduction,especiallyasolutiongasdrivesystem
Sincewaterfloodingusuallyfollowsprimaryproduction,itisoftencalledasecondaryrecoverytechnique
Page 16William M. Cobb & Associates, Inc.
How does a waterflood work?
Certainoilwellsareconvertedtowaterinjectionwells
Otheroilwellsremainasproducers Theinjectedwaterdisplaces,orpushesoiltotheproducingwells
Page 17William M. Cobb & Associates, Inc.
Page 18William M. Cobb & Associates, Inc.
Waterflood Example
producing well (21)
water injection well (0)
PRIMARY PRODUCTION
Page 19William M. Cobb & Associates, Inc.
Waterflood Example
producing well (8)
water injection well (13)
WATERFLOOD OPERATIONS
Page 20William M. Cobb & Associates, Inc.
Waterflood Example
producing well (8)
water injection well (13)
WATERFLOOD PATTERN5-SPOT
Page 21William M. Cobb & Associates, Inc.
5-Spot Waterflood Pattern
well well
well well
full well
A single 5-Spot pattern has:
One net producer, and one net injector, or twototal wells
Page 22William M. Cobb & Associates, Inc.
Waterflood Progression
Time 1
Early in life of waterflood. Producer making 100% oil.
Page 23William M. Cobb & Associates, Inc.
Waterflood Progression
Time 2
Still relatively early in life of waterflood. Water banks expanding, but producer still making 100% oil.
Page 24William M. Cobb & Associates, Inc.
Waterflood Progression
Time 3
Mid-life of the waterflood. Water has reached the producing well. Producer now makes oil and water.
Page 25William M. Cobb & Associates, Inc.
Waterflood Progression
Time 4
Late in the life of the waterflood. Producer now making large volume of water compared to the oil volume.
Page 26William M. Cobb & Associates, Inc.
Waterflood Progression
Time 4
Late in the life of the waterflood. Producer now making large volume of water compared to the oil volume.
The effectiveness of the water sweeping the area of the pattern is called the areal sweep efficiency, or Ea .
Page 27William M. Cobb & Associates, Inc.
A waterflood also works in the vertical dimension..
Page 28William M. Cobb & Associates, Inc.
Permeability
Permeability,measuredinmilidarcys(md.),isameasurementofarocksabilitytotransmitfluid
Waterinjectionratewillbeafunctionofpermeability
Mostoilreservoirshavemultiplelayerswithvaryingpermeabilityvalues
Page 29William M. Cobb & Associates, Inc.
Injection Well Producing Well
Layer 1
Layer 2
Layer 3
Layer 4
Layer 5
Layer 6
Layer 7
Layer 8
Oil reservoir with eight layers . . . . .
Page 30William M. Cobb & Associates, Inc.
Injection Well Producing Well
Layer 1
Layer 2
Layer 3
Layer 4
Layer 5
Layer 6
Layer 7
Layer 8
200 md.
400 md.
50 md.
500 md.
75 md.
100 md.
10 md.
300 md.
. . . . . with variable permeability.
Page 31William M. Cobb & Associates, Inc.
Injection Well Producing Well
Layer 1
Layer 2
Layer 3
Layer 4
Layer 5
Layer 6
Layer 7
Layer 8
200 md.
400 md.
50 md.
500 md.
75 md.
100 md.
10 md.
300 md.
Waterflood early time
producing 100% oil
Page 32William M. Cobb & Associates, Inc.
Injection Well Producing Well
Layer 1
Layer 2
Layer 3
Layer 4
Layer 5
Layer 6
Layer 7
Layer 8
200 md.
400 md.
50 md.
500 md.
75 md.
100 md.
10 md.
300 md.
Waterflood at water breakthrough
Starts to make some water
Page 33William M. Cobb & Associates, Inc.
Injection Well Producing Well
Layer 1
Layer 2
Layer 3
Layer 4
Layer 5
Layer 6
Layer 7
Layer 8
200 md.
400 md.
50 md.
500 md.
75 md.
100 md.
10 md.
300 md.
Waterflood late life, near abandonment
producing at a high water to oil ratio (WOR)
Page 34William M. Cobb & Associates, Inc.
Injection Well Producing Well
Layer 1
Layer 2
Layer 3
Layer 4
Layer 5
Layer 6
Layer 7
Layer 8
200 md.
400 md.
50 md.
500 md.
75 md.
100 md.
10 md.
300 md.
producing at a high water to oil ratio (WOR)
The effectiveness of the water sweeping the layers of the reservoir is called the vertical sweep efficiency, or Ev .
Page 35William M. Cobb & Associates, Inc.
Factors Affecting Waterflood Success
Timingofflood earlierisbetter Higherprimarydepletion(lowerpressure)increasesgassaturation
Highgassaturationdecreasesoilrecovery Wellspacing
Tighterwellspacingisbetter IncreasesEa andEv accelerateswaterfloodrecovery
Patternselection BalancedpatternsimproveEa andWORperformance
Page 36William M. Cobb & Associates, Inc.
Waterflood Recovery Potential
Shouldrecoveranadditional10%to40%ofthereservoirOOIP
Atermcommonlyusedisthesecondarytoprimaryratio(S/P) Primaryistheexpectedultimateprimaryoilrecovery
Secondaryistheincrementalwaterfloodrecovery S/Pratioof1+isgenerallyexpected
Page 37William M. Cobb & Associates, Inc.
Types of Oil Reservoirs More Favorable for Waterflood
Shallowerisbetter Cheaperdrillingandoperatingcosts Typicallylowerprimaryrecovery
Lowenergyoil(lowBo) Lowerprimaryoilrecovery Lowergassaturation
Higherpermeabilityisbetter Processthewaterfloodfaster Mayutilizewiderwellspacing(cheaper)
Page 38William M. Cobb & Associates, Inc.
Unitization for Waterflooding Maybeneededwhenreservoirunderliesdifferentleaseswithdifferentownership
Awaterfloodunitcombinestheleasesintoacommonentityforwaterfloodoperations Allowsformoreefficientdevelopmentandoperation
Maximizesoilrecovery Requiresanequityformulatoproperlycompensateallowners
Page 39William M. Cobb & Associates, Inc.
Unitization Example
producing well (8)
water injection well (13)
Lease A Lease B Lease C
Page 40William M. Cobb & Associates, Inc.
Unitization in TexasLegal Perspective
Page 41William M. Cobb & Associates, Inc.
Unitization in Texas AtermfrequentlyusedinterchangeablywithPooling,butmoreproperlyusedtodenominatethejointoperationofallorsomeportionofaproducingreservoir asdistinguishedfrompooling,whichtermisusedtodescribethebringingtogetherofsmalltractssufficientforthegrantingofawellpermitunderapplicablespacingrules.
Williams&Meyers,ManualofOilandGasTerms
Page 42William M. Cobb & Associates, Inc.
Unitization in Texas
UnitizationDOESNOTrequireapprovaloftheTexasRailroadCommission.
PrivateUnits SayNoBoundaries
Page 43William M. Cobb & Associates, Inc.
Unitization in Texas
CommissionapprovedunitsmustcomplywithTexasNaturalResourcesCodeChapter101titledCooperativeDevelopment
Statutefirstpassedin1949 NotUpdated
Page 44William M. Cobb & Associates, Inc.
Unitization in Texas
UnitAgreement NegotiatingtheEquityFormula
blueeyedgrandchildren
UnitOperatingAgreement
Page 45William M. Cobb & Associates, Inc.
Page 46William M. Cobb & Associates, Inc.
Page 47William M. Cobb & Associates, Inc.
Page 48William M. Cobb & Associates, Inc.
Page 49William M. Cobb & Associates, Inc.
Unitization in Texas
RailroadCommissionRequirements 65%RoyaltyInterestSignUptotheUnitAgreement
85%WorkingInterestSignuptotheUnitAgreement
TheTwentyQuestions Allinterestownersofferedtoparticipateonthesameyardstickbasis
Page 50William M. Cobb & Associates, Inc.
Unitization in Texas1. Personsenteringintoandsubmittingagreementownor
controlproduction,leases,royaltyorotherinterestsinsamefield.
2. Agreementwasvoluntarilyenteredinto(a)toestablishpooledunitsforsecondaryrecoveryoperations,or(b)toestablishpooledunitforconservationandutilizationofgas.
3. AgreementisnecessarytoaccomplishpurposesinNo.2.4. Suchagreementisininterestofpublicwelfareas
reasonablynecessarytopreventwasteandpromoteconservation.
5. Rightsofallownersinfield,whethersigningornot,willbeprotected.
Page 51William M. Cobb & Associates, Inc.
Unitization in Texas6. Estimatedadditionalcostwillnotexceedvalueofadditionaloilandgas.
7. Otheravailablemethodsinadequate.8a.Areacoveredcontainsonlysuchpartoffieldasreasonablydefinedbydevelopment.
8b.Theownersofinterestintheoilandgasundereachtractwithinareareasonablydefinedbydevelopmenthavebeengivenopportunitytoenterintosuchagreementonsameyardstickbasisasownersofinterestsinoilandgasinothertractsintheunit.
9. UnitdescribedinunitagreementsufficienttoaccomplishpurposesofUnitizationAct.
Page 52William M. Cobb & Associates, Inc.
Unitization in Texas10. Suchagreementissubjecttoanyvalidorder,rule,orregulationof
theCommissionrelatingtolocation,spacing,proration,conservationorothermatterswithintheauthorityoftheCommission.
11. Suchagreementdoesnotattempttocontainfieldrulesfortheareaorfield.
12. Suchagreementdoesnotprovidefornorlimittheamountofproductionofoilorgasfromtheunitproperties.
13a.Suchagreementdoesnotbindanylandowner,royaltyowner,lessor,lessee,royaltyinterestowneroranyotherpersonwhodoesnotexecutesame,butbindsonlythepersonswhoexecuteit.
13b.Nopersonhasbeencompelledorrequiredtoenterintosuchagreement.
Page 53William M. Cobb & Associates, Inc.
Unitization in Texas14.Suchagreementdoesnotprovidedirectlyorindirectlyfor
thecooperativerefiningofcrudepetroleum.15. Suchagreementdoesnotprovideforthecooperative
refiningofcrudepetroleum,condensate,distillateorgas,oranybyproducethereof.
16. Suchagreementisnotavoluntaryagreementforthejointdevelopmentandoperationofjointlyownedproperties.
17.Suchagreementdoesnotrestrictanyoftherightswhichpersonsnowhavetomakeandenterintounitizationandpoolingagreements.
18a.Suchagreementdoesordoesnotprovideforthelocationandspacingofinputwellsandfortheextensionofleasescoveringanypartoflandscommittedtotheunit.
Page 54William M. Cobb & Associates, Inc.
Unitization in Texas18b.Nosuchagreementshallrelieveanyoperatorfromtheobligationtodevelopreasonablythelandsandleasesasawholecommittedthereto.
19.Agreementmayprovidethatthedrygasafterextractionofhydrocarbonsmaybereturnedtoaformationunderlyinganylandscommittedtotheagreement.
20.WhenitappearsfromsuchagreementorotherwisethatownershipofanylandsorpropertiesdescribedinsuchagreementisanypartyorpartiesnamedinSections2and3ofsaidAct,therequirementsofsaidSectionsofsaidActshouldbecompliedwith.
Page 55William M. Cobb & Associates, Inc.
Unitization in Texas HouseBill100 Taylor OilandGasMajorityRightsProtectionAct ProposedChapter104ofTNRC CompulsoryUnitization
70%RoyaltyInterestSignUp 70%WorkingInterestSignup Appliesto
Repressuring Waterflooding PressureMaintenance Tertiaryrecoveryoperations AnyothersimilaroperationsCommissionmayinvestigatethesoundnessoftheequityformula(remembertheblueeyedgrandchildren)
Page 56William M. Cobb & Associates, Inc.
Unit Tract Participation Factors - Example
T O T A L > 1.000
Phase I 0.100 0.400 0.400 0.100Tract Surface OOIP current useable
Tract Lease Participation acres MSTB BOPD wells
1 Lease 'A' 0.28149773 200 2,100 31 6
2 Lease 'B' 0.28827399 100 1,600 52 7
3 Lease 'C' 0.43022828 220 2,500 74 8
TOTALS 1.00000000 520 6,200 157 21
Page 57William M. Cobb & Associates, Inc.
NetRev. Tract UnitOwner Interest Participation Ownership
GoodOperating,Inc. 0.750000 0.281498 0.211123
JohnGeologist 0.050000 0.281498 0.014075
JamesFarmer 0.120000 0.281498 0.033780
EdithFarmer 0.080000 0.281498 0.022520
1.000000 0.281498
Lease 'A' Ownership
Page 58William M. Cobb & Associates, Inc.
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