EOR WF Surveillance

Lecture 10Lecture 10

Waterflood SurveillanceWaterflood Surveillance--11

DosenDosen :: IrIr AndryAndry halimhalim, MM, MMDosenDosen : : IrIr Andry Andry halimhalim, MM, MM

STT MIGAS, BalikpapanSTT MIGAS, Balikpapan

20122012

Voidage ControlVoidage Control

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Design of Waterflood ProjectDesign of Waterflood ProjectVoidage ControlVoidage Controlyy Voidage control involves monitoring injection and Voidage control involves monitoring injection and

withdrawal volumes to ensure the correct injection is withdrawal volumes to ensure the correct injection is

o dage Co t oo dage Co t o

added to the reservoir and at the proper locations to added to the reservoir and at the proper locations to maximize secondary recovery maximize secondary recovery

opp BNWsWithdrawalReservoir +=yy Where:Where: BBoo == Oil formation volume factor (RB/STB)Oil formation volume factor (RB/STB)

NNpp == Oil production at stock tank conditionsOil production at stock tank conditions

WWpp == Water productionWater production

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Design of Waterflood ProjectDesign of Waterflood ProjectVoidage ControlVoidage Control

yy If free gas exists & is being produced:If free gas exists & is being produced:


gsppopp )BR-(RNBNWsWithdrawalReservoir ++=

Where:Where: BB == Gas formation volume factorGas formation volume factorWhere:Where: BBgg == Gas formation volume factorGas formation volume factor(RCF/SCF)(RCF/SCF)

RRpp == Surface (produced) gas oil ratioSurface (produced) gas oil ratiopp(SCF/STBO)(SCF/STBO)

RRss == Solution gas oil ratio (SCF/STBO)Solution gas oil ratio (SCF/STBO)

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Design of Waterflood ProjectDesign of Waterflood ProjectVoidage ControlVoidage Control

yy Injection Withdrawal Ratio (IWR)Injection Withdrawal Ratio (IWR) -- commonly usedcommonly used


Injection Withdrawal Ratio (IWR) Injection Withdrawal Ratio (IWR) commonly used commonly used for monitoring waterfloods for monitoring waterfloods

yy Monthly secondary recovery reports should Monthly secondary recovery reports should alwaysalwayscontain calculated IWR for each pattern contain calculated IWR for each pattern

yy Calculated by dividing effective injection by Calculated by dividing effective injection by reservoir withdrawals:reservoir withdrawals:reservoir withdrawals:reservoir withdrawals:

InjectionEffectivesWithdrawalReservoir

InjectionEffectiveRatioWithdrawalEffective =

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Design of Waterflood ProjectDesign of Waterflood ProjectVoidage ControlVoidage Controlyy When injection equals withdrawals, IWR = When injection equals withdrawals, IWR = 11..0 0

IWR illIWR ill d i th t fl d lifd i th t fl d lif


yy IWR will IWR will varyvary during the waterflood life during the waterflood life -- During repressuring early in the life of waterflood, During repressuring early in the life of waterflood,

IWR will be high because reservoir pressure isIWR will be high because reservoir pressure isIWR will be high because reservoir pressure is IWR will be high because reservoir pressure is low & withdrawals have not started increasing low & withdrawals have not started increasing

-- After fillAfter fill--up is reached & waterflood is up is reached & waterflood is ppapproaching steadyapproaching steady--state, IWR will decrease & state, IWR will decrease & approach approach 11..0 0

-- If IWR drops to below If IWR drops to below 11..00, total fluid volume will , total fluid volume will begin to decrease & corrective actions should be begin to decrease & corrective actions should be takentaken

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Design of Waterflood ProjectDesign of Waterflood ProjectVoidage Data SourcesVoidage Data Sourcesyy 2 useful plots are average reservoir pressure 2 useful plots are average reservoir pressure

versus time and average reservoir pressure versus versus time and average reservoir pressure versus

Voidage Data SourcesVoidage Data Sources

cumulative oilcumulative oil

yy Note the pressure change in the late 1970s after a fore destroyed field Note the pressure change in the late 1970s after a fore destroyed field

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p g yp g yinjection facilitiesinjection facilities

yy The effect on reservoir repressuring was significant, but would have been The effect on reservoir repressuring was significant, but would have been difficult to monitor without this average reservoir pressure curvedifficult to monitor without this average reservoir pressure curve

Design of Waterflood ProjectDesign of Waterflood ProjectPattern VoidagePattern Voidageyy Pattern allocation usually Pattern allocation usually

uses a pattern allocation uses a pattern allocation

Pattern VoidagePattern Voidage

factor calculated using factor calculated using angle between injection angle between injection well & two adjacent well & two adjacent offset injection wells in offset injection wells in the pattern the pattern

yy For interior patternsFor interior patternsFor interior patterns, For interior patterns, divide this angle by 360divide this angle by 360ooto obtain factorto obtain factor

F t tiF t tiyy Factors are sometimes Factors are sometimes adjusted (weighted) for adjusted (weighted) for reservoir pay volumesreservoir pay volumes

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Voidage CalculationVoidage CalculationExample Problem Example Problem 11..66--11

A small waterflood is producing 16,500 BOPD & A small waterflood is producing 16,500 BOPD & 12,500 BWPD. The water injection rate is 30,000 12,500 BWPD. The water injection rate is 30,000 BWIPD The producing GOR is 150 SCF/STBO while BWIPD The producing GOR is 150 SCF/STBO while BWIPD. The producing GOR is 150 SCF/STBO while BWIPD. The producing GOR is 150 SCF/STBO while reservoir solution GOR is 50 SCF/STBO. The reservoir solution GOR is 50 SCF/STBO. The formation volume factors for oil and gas are 1.06 formation volume factors for oil and gas are 1.06 RB/STBO & 0.006 RB/SCF, respectively. RB/STBO & 0.006 RB/SCF, respectively.

-- Calculate the net reservoir voidage (RBPD):Calculate the net reservoir voidage (RBPD):

Calculate the Injection Withdrawal Ratio:Calculate the Injection Withdrawal Ratio:Calculate the Injection Withdrawal Ratio:Calculate the Injection Withdrawal Ratio:

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Pattern Voidage CalculationPattern Voidage CalculationExample Problem 1.6Example Problem 1.6--22

A mature A mature 55--spot waterflood pattern has been under spot waterflood pattern has been under waterflood for waterflood for 15 15 years. The center well produces years. The center well produces 127 127 BOPD and BOPD and 550 550 BWPD with negligible gas The oil BWPD with negligible gas The oil 127 127 BOPD and BOPD and 550 550 BWPD with negligible gas. The oil BWPD with negligible gas. The oil formation volume factor is formation volume factor is 11..1414. The . The 4 4 injection wells injection wells have injection & allocation factors of:have injection & allocation factors of:

ll ll (B P )(B P ) FFWell No. iWell No. iWW (BWIPD)(BWIPD) FactorFactor11 610610 00..25025022 700700 00..26526533 552552 00..22022044 621621 00..271271

Calculate pattern voidage & injection withdrawal ratioCalculate pattern voidage & injection withdrawal ratio

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Voidage CalculationVoidage CalculationExample Problem 1.6Example Problem 1.6--11pp

A small waterflood is producing 16,500 BOPD & 12,500 A small waterflood is producing 16,500 BOPD & 12,500 BWPD. The water injection rate is 30,000 BWIPD. The BWPD. The water injection rate is 30,000 BWIPD. The producing GOR is 150 SCF/STBO while reservoir solution producing GOR is 150 SCF/STBO while reservoir solution producing GOR is 150 SCF/STBO while reservoir solution producing GOR is 150 SCF/STBO while reservoir solution GOR is 50 SCF/STBO. The formation volume factors for GOR is 50 SCF/STBO. The formation volume factors for oil and gas are 1.06 RB/STBO & 0.006 RB/SCF, oil and gas are 1.06 RB/STBO & 0.006 RB/SCF, respectively. respectively.

-- Calculate the net reservoir voidage (RBPD):Calculate the net reservoir voidage (RBPD):

Voidage = Wp + NpBo + Np (Rp Voidage = Wp + NpBo + Np (Rp Rs) BgRs) Bgg p p p ( pg p p p ( p ) g) g= 12,500 + 16,500x1.06 + 16,500 (150= 12,500 + 16,500x1.06 + 16,500 (150--50) x .00650) x .006= 39,890 RBPD = 39,890 RBPD

-- Calculate the Injection Withdrawal Ratio:Calculate the Injection Withdrawal Ratio:Eff Withdrawal Ratio = Eff Injection / Res WithdrawalEff Withdrawal Ratio = Eff Injection / Res Withdrawal

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Eff. Withdrawal Ratio = Eff. Injection / Res. WithdrawalEff. Withdrawal Ratio = Eff. Injection / Res. WithdrawalIWR = 30,000 / 39,890 = 0.75IWR = 30,000 / 39,890 = 0.75

Pattern Voidage CalculationPattern Voidage CalculationExample Problem 1.6Example Problem 1.6--22

A mature 5A mature 5--spot waterflood pattern has been under spot waterflood pattern has been under waterflood for 15 years. The center well produces 127 waterflood for 15 years. The center well produces 127 BOPD and 550 BWPD with negligible gas The oil BOPD and 550 BWPD with negligible gas The oil BOPD and 550 BWPD with negligible gas. The oil BOPD and 550 BWPD with negligible gas. The oil formation volume factor is 1.14. The 4 injection wells formation volume factor is 1.14. The 4 injection wells have injection & allocation factors of:have injection & allocation factors of:

ll ll (B P )(B P ) FFWell No. iWell No. iWW (BWIPD)(BWIPD) FactorFactor11 610610 0.2500.25022 700700 0.2650.26533 552552 0.2200.22044 621621 0.2710.271

Calculate pattern voidage & injection withdrawal ratioCalculate pattern voidage & injection withdrawal ratioPattern Inj.= (610x.25)+(700x.265)+(552x.22)+(621x.271)=628 BWIPDPattern Inj.= (610x.25)+(700x.265)+(552x.22)+(621x.271)=628 BWIPDWithdrawals = (127x1 14) + 550 = 695 RBPDWithdrawals = (127x1 14) + 550 = 695 RBPD

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Withdrawals = (127x1.14) + 550 = 695 RBPDWithdrawals = (127x1.14) + 550 = 695 RBPDVoidage = 628 Voidage = 628 695 = 695 = -- 67 RBPD67 RBPDIWR = 628 / 695 = 0.903IWR = 628 / 695 = 0.903

Design of Waterflood ProjectDesign of Waterflood ProjectVoidage MappingVoidage MappingPattern Voidage Map Pattern Voidage Map

yy To view graphically the pattern voidage across a To view graphically the pattern voidage across a field or reservoir, a colored pattern map is field or reservoir, a colored pattern map is sometimes used sometimes used

yy Patterns are classified asPatterns are classified as over balancedover balanced underunderyy Patterns are classified as Patterns are classified as over balancedover balanced, , under under balancedbalanced, , or or balancedbalanced based on injection based on injection withdrawal ratios withdrawal ratios

Under Balanced

13Balanced

Over Balanced

Design of Waterflood ProjectDesign of Waterflood ProjectVoidage MappingVoidage MappingPattern Voidage Bubble MapPattern Voidage Bubble Map

yy Useful pattern voidage tool Useful pattern voidage tool -- Creates bubbles showing positive & negative voidage by Creates bubbles showing positive & negative voidage by

patterns patterns

P iti & ti id h diff t lP iti & ti id h diff t l-- Positive & negative voidages have different colors Positive & negative voidages have different colors

-- Either diameter or area of bubble are proportional to Either diameter or area of bubble are proportional to absolute value of voidage or IWR absolute value of voidage or IWR

Under Balanced

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Over Balanced

Design of Waterflood ProjectDesign of Waterflood ProjectStep for Using Voidage MapStep for Using Voidage Map

yy Set routine schedule for evaluating pattern voidage performanceSet routine schedule for evaluating pattern voidage performanceyy Define optimum data needed & most effective graphical presentation Define optimum data needed & most effective graphical presentation yy Establish baseline of pattern performance:Establish baseline of pattern performance:

Step for Using Voidage MapStep for Using Voidage Map

Establish baseline of pattern performance:Establish baseline of pattern performance:-- What is typical for patterns in this reservoir?What is typical for patterns in this reservoir?-- What is typical for each pattern through time?What is typical for each pattern through time?

yy Evaluate current pattern voidage data:Evaluate current pattern voidage data:-- Clues from general pattern voidage trendsClues from general pattern voidage trends-- Relative magnitude of voidage anomaliesRelative magnitude of voidage anomalies

yy Identify anomaliesIdentify anomaliesyy Determine if voidage anomalies are significantDetermine if voidage anomalies are significantyy Determine conclusions about pattern voidage:Determine conclusions about pattern voidage:

-- Is calculated pattern voidage valid?Is calculated pattern voidage valid?H it b i f ti ?H it b i f ti ?-- Has it been occurring for some time?Has it been occurring for some time?

-- Is it significant?Is it significant?-- What are possible root causes? What are possible root causes?

yy Identify wells which may be contributing to pattern voidage anomalyIdentify wells which may be contributing to pattern voidage anomaly

15Ch 6 - 15

yy Identify wells which may be contributing to pattern voidage anomalyIdentify wells which may be contributing to pattern voidage anomalyyy Identify options Identify options

Voidage MappingVoidage MappingExample Problem 1.6Example Problem 1.6--33E amp ro m .6E amp ro m .6

Given following Pattern Voidage Map, what Given following Pattern Voidage Map, what l d ? l d ?can you conclude?can you conclude?

Balanced

Over Balanced

Under Balanced

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Balanced

Voidage MappingVoidage MappingExample Problem 1 6Example Problem 1 6--44Example Problem 1.6Example Problem 1.6--44

Given following Pattern Voidage Map, what Given following Pattern Voidage Map, what can you conclude?can you conclude?can you conclude?can you conclude?

Balanced

Over Balanced

Under Balanced

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Balanced

Voidage MappingVoidage MappingExample Problem Example Problem 11 66 55Example Problem Example Problem 11..66--55

Given following Pattern Voidage Bubble Map, Given following Pattern Voidage Bubble Map, what can you conclude?what can you conclude?what can you conclude?what can you conclude?

Over Balanced

Under Balanced

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Voidage MappingVoidage MappingExample Problem 1 6Example Problem 1 6 66Example Problem 1.6Example Problem 1.6--66

Given following Pattern Voidage Bubble Map, Given following Pattern Voidage Bubble Map, what can you conclude?what can you conclude?what can you conclude?what can you conclude?

U d B l d

Over Balanced

Under Balanced

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EOR WF Surveillance