bachman_dfit_2016-10-26_forpublication

PTA Based After Closure Analysis Gives

Insight to Permeability and SRV Behavior

Bob Bachman, CGG - Taurus Reservoir Solutions

Outline

1. Can we see SRV like behavior in a DFIT Test ?

2. Overlaying DFITS from multiple wells• Can we relate production data to DFIT’s ?

3. After Closure Analysis – Do we need specialized plots ?

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1) Stimulated Reservoir Volume (SRV) Characteristics• Zone of Increase Permeability around Fracture

• SRV is retained permeability after a fracture job

• Should be visible during a DFIT• If Rate High enough ?!

• Late Time

• Not Pressure Dependent Leak-off (PDL)• PDL behavior disappears during the closure process

• Early Time

3

Rate Normalized

Bourdet Derivative

Kinner=0.1 md

Kinner=1.0 md

Kinner=10 md

Kouter=0.001 md

End of unit slope

Starting to see the

true value of the

outer permeability

1/1

Kinner

Kouter

Kinner=0.01 md

Radial Flow – Composite Permeability

Log Deriv DP over Q versus Delta TimeSPE 174454

Radial Composite – Bourdet Derivative

0 – 1 – 0 Slope4

Vertical WellLinear FlowComposite Permeability Concept

Kinner

High Permeability

Due to Influence of Fracture

Kouter

Static Fracture

SPE 174454

Linear Composite – Bourdet Derivative

½ – 1 – ½ Slope

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Vertical WellNolte FlowComposite Permeability Concept

Kinner

High Permeability

Due to Influence of Fracture

Kouter

Open Fracture

SPE 174454

Nolte Composite – Bourdet Derivative

3/2 – 1 – 3/2 Slope

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SPE 163825

Tip Extension ?

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Combination

G Function Plot

Flow Period DT (minutes) Rate (m3/min) Rate (stb/min)

1 0.75 0.30 1.88

2 0.30 0.50 3.14

3 0.20 0.41 2.59

4 4.13 0.40 2.53

5 14.60 0.50 3.18

Total 19.98

Tip Extension ?

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DT Derivative Plot

SPE 163825


1 0.75 0.30 1.88

2 0.30 0.50 3.14

3 0.20 0.41 2.59

4 4.13 0.40 2.53

5 14.60 0.50 3.18

Total 19.98

1/4

-½

3/2

1/1

-1/1

End Nolte Flow at 1.0 days

Composite Permeability at End

This is what an SRV looks like

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SPE 163825


1 0.75 0.30 1.88

2 0.30 0.50 3.14

3 0.20 0.41 2.59

4 4.13 0.40 2.53

5 14.60 0.50 3.18

Total 19.98

Composite Permeability

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DT Derivative Plot

SPE 163825


1 0.75 0.30 1.88

2 0.30 0.50 3.14

3 0.20 0.41 2.59

4 4.13 0.40 2.53

5 14.60 0.50 3.18

Total 19.98

0

1) ConclusionsStimulated Reservoir Volume (SRV) Characteristics

• Look for late time unit slopes on Bourdet derivative

• Tip Extension at late time does not happen

• Replaced with ‘Composite Permeability’ Idea

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2) Overlaying DFITS from Multiple Wells

• Background PTA overlay theory• Single Well/Multiple Tests

• Can we compare wells based on DFITS ?• Multi Well/Single Tests

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Radial Flow during a Buildup Bourdet log-log Derivative Plot

Permeability Decreasing as position of zero slope line moves up

0

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Permeability Decreasing as position of zero slope line moves up

Divide Derivative by Rate Prior to Shut-in to Compare different tests

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Comparing Different TestsExample - Sequential Injection/Fall-off Tests

Formation Linear Flow/Radial Flow during a BU Bourdet log-log Derivative Plot

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Decreasing xf*k0.5

As position of ½ slope line moves up and to the left

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Even if no radial flow one can still calculate maximum permeability

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18

3/2 1/1

0

Definitely closed and rolling over towards linear flow/radial flowPermeability likely similar to Well Duvernay #2

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-½

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Duvernay Oil Wells – Liquid Prod Profiles

Duvernay Oil Wells – Liquid Prod Profiles

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2) ConclusionsOverlaying DFITS from Multiple wells• PTA based Mini-frac interpretations have advantages

• Rate normalized derivative plot overlays are key

• Allows direct comparison of tests from different wells

• Useful even when complex flow regimes occur

• Permeability can be ‘estimated’ even when a rigorous analysis is not possible

• Example shows that 2 wells with similar estimated permeability have similar production behavior

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3) After Closure AnalysisSparky Oil Well - Alberta• Examine different extrapolation techniques for Pi

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End HRTS, DT=0.09125, G=6.62BHP=19,098, Grad=14.0 (Closure)

Combination

G Function Plot

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½

-3/2

PTA based Bourdet Derivative

with Primary Pressure Derivative

(PPD) Plot

0

1) End HRTS, DT=0.09125, G=6.62BHP=19,098, Grad=14.0 (Closure)2) End Linear Flow, DT=1.02439, G=25.563) Radial Flow at endBHP=14,181, Grad=10.4

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-2/1

Linear Soliman/Craig

ACA Plot

0

ExtrapolationP*=12,100, Grad= 8.9 kPa/m

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Linear Superposition

Time Plot

0


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Radial Soliman/Craig

ACA Plot

0


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Radial Superposition

Time Plot

0


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3) ConclusionsLinear/Radial Superposition Time PlotsGeneralized ACA Plots• Has been used in PTA Analysis for 50+ years

• Accounts for rate variations• No ‘Impulse Assumption’• Use with the derivative plot

• Why do we need specialized plots?• PTA techniques only work when Shut-In times are short compared to

injection times ?! (Dake – “Practice of Reservoir Engineering”)• This is INCORRECT

• PTA works on all time scales• Specialized plots are not necessary

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Thank you

Questions?

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Radial Superposition Time (tsr)as pumping time becomes small1 Injection Period + 1 Fall-off

• 𝑡𝑠𝑟 = ln(𝑡𝑝+∆𝑡

∆𝑡) = ln(1 +

𝑡𝑝

∆𝑡) =

𝑡𝑝

∆𝑡-1

2(𝑡𝑝

∆𝑡) 2+ …

• lim𝑡𝑝→0

𝑡𝑠𝑟 = lim𝑡𝑝→0

𝑡𝑝

∆𝑡−

1

2(𝑡𝑝

∆𝑡) 2+ … =

𝑡𝑝

∆𝑡

• For radial flow with short pumping time a plot of Pressure versus 1/Dtor 1/(tp + Dt) is equivalent to a Horner Plot. This is the Radial Soliman/Craig plot

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bachman_dfit_2016-10-26_forpublication

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