Common Pitfalls of Mini-frac Analysis Robert Hawkes, Director of - - PowerPoint PPT Presentation

1 SPE Calgary, Sept 6, 2012

Common Pitfalls of Mini-frac Analysis

Robert Hawkes,

Director of Completion Technologies

Pure Energy Services

2 SPE Calgary, Sept 6, 2012

What They Didn’t Tell You About G-function and log-log plots

3 SPE Calgary, Sept 6, 2012

Bachman G-function

Reappraisal of the G Time Concept in Mini-Frac Analysis (SPE 160169, Bachman et al)

Thank you Google Images

4 SPE Calgary, Sept 6, 2012

Pre-Frac Diagnostics…. …….are we wasting our time?

Most of our Pitfalls are coming from conventional thinking. Closure Pressure

• Still needs a holistic approach ........and more work!

Leak-off Behaviour

• Pressure diagnostics is interpretive and heavily

influenced by your discipline.

After Closure Analysis

• Be careful how you impose a flow regime on the data.

5 SPE Calgary, Sept 6, 2012

Diagnostic Approach

• Step-up or Step-down (neither)
• Low Rate or Treatment Rate?
• What's the objective
• Interpretation Pitfalls
• ISIP
• Closure Identification
• Think again
• Flow Regime Identification
• Not as easy as it seems
• Specialized Plots
• Completion Considerations
• Hz wellbore (toe), Open Hole, Cemented Liner, Packer Leaks, Fluid Choice.....

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Source of Maybe Some Common Pitfalls

YES !! Maybe not No Maybe not Maybe not sure

7 SPE Calgary, Sept 6, 2012

Fracture Flow Regimes from Cinco-Ley (1978) (Static)

8 SPE Calgary, Sept 6, 2012

√𝑢-𝑢0

h

Fluid Loss Velocity

The idea behind Carter's 1D leakoff coefficient

• if a filter-cake wall is building up it will

allow less fluid to pass through a unit area in unit time

• the reservoir itself can take less and

less fluid if it has been exposed to inflow

• Both of these phenomena can be

roughly approximated as "square-root time behavior"

Carter Leak-off Model

(Dynamic)

9 SPE Calgary, Sept 6, 2012

Who Has Seen This Shape of G-Function Plot??

10 SPE Calgary, Sept 6, 2012

Who Has Seen This Shape of G-Function Plot??

11 SPE Calgary, Sept 6, 2012

Who Has Seen This Shape of G-Function Plot??

12 SPE Calgary, Sept 6, 2012

Who Has Seen This Shape of G-Function Plot??

13 SPE Calgary, Sept 6, 2012

Who Has Seen This Behaviour on the Log-log Plot??

14 SPE Calgary, Sept 6, 2012

SPE 140136 (2011)

Paper identifies 3/2 slope feature and gives some theory _______.

15 SPE Calgary, Sept 6, 2012

So What Does the Welltesting Community Have to Offer to Mini-frac analysis?

16 SPE Calgary, Sept 6, 2012

First Mini-frac Derivative Plot, ~1990, Dr. Ted. Leshchyshyn

17 SPE Calgary, Sept 6, 2012

Well Test Analysis Log-Log Derivative Term (Agarwal Equivalent Time)

Uses radial equivalent time ter for derivative

• This is NOT the same as Dt
• Versatile even when radial flow not present
• This is why it is a universal approach to all well test problems

t t t t t Derivative Log dt P d t

p p er er er

D  D   D _ ) (

18 SPE Calgary, Sept 6, 2012

Nolte G-Function Analysis Using the Nolte G Function construct the various plots

• Assume no closure and the G Function Solution

runs on forever……..

• What do things look like?

√𝑢-𝑢0

h

Fluid Loss Velocity

19 SPE Calgary, Sept 6, 2012

Nolte G Function

20 SPE Calgary, Sept 6, 2012

Classic Nolte behavior with no closure

P vs G GdP/dG vs G dP/dG vs G

Nolte G Function

21 SPE Calgary, Sept 6, 2012

Square root-t plot shows a character change from early time to late time with a constant flow regime. Nolte G Function

22 SPE Calgary, Sept 6, 2012

Nolte G Function Early Time Slope = 1 Late Time Slope = 0.5 Derivative is the logarithmic derivative of ∆t…… …conventional approach. Late Time slope = 0.5 is Carter leak-off, not the conventional linear flow.

23 SPE Calgary, Sept 6, 2012

Early Time Slope = 1 Late Time Slope = 1.5*

*as identified in paper 140136

Derivative is the logarithmic derivative of Agarwal equivalent (radial) time or…… …standard well test derivative. NO linear flow slope, not picked up in paper 140136.

m = 1.0 m = 1.5

Nolte G Function

24 SPE Calgary, Sept 6, 2012

Classic Linear Flow Solution Infinite acting linear flow Injection period - classic linear flow Shut-in period - classic linear flow

• Use superposition to compute fall-off response

25 SPE Calgary, Sept 6, 2012

Linear Flow

26 SPE Calgary, Sept 6, 2012

The G-function plot does not give meaningful results as the character changes from early time to late time with the same flow regime. No closure - infinite acting linear flow Linear Flow

27 SPE Calgary, Sept 6, 2012

Square root-t plot also has a character change from early time to late time with the same flow regime. No closure - infinite acting linear flow Linear Flow

28 SPE Calgary, Sept 6, 2012

Intercept is not closure for the special case 0.5 to -0.5 slope but is instead an artifact of the plot. No closure - infinite acting linear flow

Early Slope = 0.5 Late Slope = -0.5

Linear Flow Delta Time

29 SPE Calgary, Sept 6, 2012

Agarwal Equivalent Time Early Time Slope = 0.5 Late Time Slope = 0.5 Linear Flow

30 SPE Calgary, Sept 6, 2012

Well Test Analysis Approach

The welltest log-log pressure derivative is the best flow regime indicator in our arsenal

• Theory is very well established in traditional PTA

 Cinco-ley and Samaniego, 1981

• You need to dust off those old and forgotten welltesters in

your closet and exploit them in the mini-frac world.

Welltest Log-log derivative:

 the time function is NOT dt of the flow period  the time function is with respect to Agarwal equivalent time

– te = tp*dt/(tp+dt)

The Log-log derivatives in Barree’s paper SPE 107877 are all with respect to dt as far as we can tell.

31 SPE Calgary, Sept 6, 2012

Observations and Comments:

1. We need to do flow regime identification before picking closure pressures  Standard well test log-log derivative plot is key  Flow regime dependent plots 2. Do we need replacements for the Combination G Function plot? 3. We need to calculate the correct derivatives 4. Do we even need ACA plots ?  Why not use standard well test plots to calculate properties ?

32 SPE Calgary, Sept 6, 2012

Classic Barree Case

Jean Marie oil well example

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34 SPE Calgary, Sept 6, 2012

35 SPE Calgary, Sept 6, 2012

Conventional Approach

36 SPE Calgary, Sept 6, 2012

Barree log-log dt plot

Pfoc = 8300 kPa

Conventional Approach

37 SPE Calgary, Sept 6, 2012 Pfoc = 8400 kPa

PDL ??

Conventional Approach

38 SPE Calgary, Sept 6, 2012 Pfoc = 8400 kPa

Conventional Approach

39 SPE Calgary, Sept 6, 2012

Proposed Approach

40 SPE Calgary, Sept 6, 2012

1. Early Time Linear Flow (0.5) 2. Middle Time Carter Flow (1.5) 3. Late Time Linear Flow (after closure) Agarwal Equivalent Time

Pfoc = 8400 kPa

41 SPE Calgary, Sept 6, 2012

Carter Equivalent Time

1. Early Time Linear Flow (0.5) 2. Middle Time Carter Flow (1.0) 3. Late Time Linear Flow (0*) *zero slope SPE 160169

42 SPE Calgary, Sept 6, 2012

Over the time range for which Carter leak-off has been identified, the slope does not need to go through the origin. Is a Positive Y-intercept an indictor of PDL, …..not sure.

43 SPE Calgary, Sept 6, 2012

PPD Curve

1. Late Time Linear Flow (after closure: +0.5) 2. PPD: Late Time Linear Flow (-1.5)

44 SPE Calgary, Sept 6, 2012

Agarwal Equivalent Time Function and their Slopes

Derivative Early Time Carter Late Time Carter te 1.0 1.5 PPD

• 0.5

Early Time Linear Late Time Linear te 0.5 0.5 PPD

• 1.5

Early Time Radial Late Time Radial te PPD

• 1
• 2

SPE 160169

45 SPE Calgary, Sept 6, 2012

CRDM Example

46 SPE Calgary, Sept 6, 2012

CRDM Example

Establish breakdown and pump 5.0 m3 of fresh water @ 0.45 m3/min Recorders set @ 1780m KB MD

47 SPE Calgary, Sept 6, 2012

CRDM Example

Establish breakdown and pump 5.0 m3 of fresh water @ 0.45 m3/min See Log-log plot for ISIP determination.

48 SPE Calgary, Sept 6, 2012

CRDM Example

49 SPE Calgary, Sept 6, 2012

CRDM Example

50 SPE Calgary, Sept 6, 2012

∆p = EOJ - Pw

CRDM Example

Conventional Delta Time

51 SPE Calgary, Sept 6, 2012

Adjusted Agarwal Time

m = 1.5

Welltest Log-log CRDM Example

52 SPE Calgary, Sept 6, 2012

Adjusted Agarwal Time

m = 3/2

Delta-Time

m = 1/2 m = -1/2

Overlay Log-log Diagnostic Plot CRDM Example

53 SPE Calgary, Sept 6, 2012

CRDM Example PPD

Adjusted Agarwal Time

54 SPE Calgary, Sept 6, 2012

Observations and Conclusions:

1. The starting point for ANY mini-frac analysis should be the standard welltest Agarwal equivalent time log-log plot.  You must do flow regime identification before picking closure pressure.  The PPD curve has been shown to contain flow regime identification properties – a bonus diagnostic curve to the welltest community.  The industry should discontinue using the delta-time log-log derivative plot. 2. The G-Function and square root-time plots have been shown to be poor flow regime (and closure) identification plots? 3. PDL (pressure dependent leakoff) diagnostics using the G-Function plot needs a holistic approach with the Agarwal equivalent time and PPD log-log plot.  Needs more study

55 SPE Calgary, Sept 6, 2012

Observations and Conclusions:

4. Traditional welltest after-closure analysis techniques can be used for reservoir property determination. 5. Mini-frac analysis should no longer be viewed as an independent discipline. 6. Talk to your software vendor. 7. and finally……..say Flow Regime at least once day when in the office.

56 SPE Calgary, Sept 6, 2012

Fracture Closure

Test Method Interpretation Method Rate Low High Shut-in Surface BHP Both DFIT/MiniFrac/MDT/XLOT Flowback G(t) Sqrt(t)

Pressure vs Returned Volume

Constant Rate Volume Increments

Stabilized Press. vs Returned Volume

Other log(t)

Time Functions

Banff SPE Workshop, April 2012

57 SPE Calgary, Sept 6, 2012

End of Reception

Banff SPE Workshop, April 2012

58 SPE Calgary, Sept 6, 2012

End of April 24

Banff SPE Workshop, April 2012