Everything you always wanted to know about well test analysis but - - PowerPoint PPT Presentation

Alain C. Gringarten Imperial College London

Everything you always wanted to know about well test analysis but were afraid to ask

• WTA: what, why, how
• Challenges
• Milestones
• Other applications
• Conclusion: a very powerful tool - use it or lose it

Content

2/44

200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800

Time from the start of production (hrs)

1000 2000 3000 4000 5000 6000 7000 8000 9000 10000

Oil Rate q (STB/D)

q

What is well test analysis (WTA)?

• It is the extraction of information from pressure

and rate data measured in a producing well

PIPELINE RESERVOIR WELL BUILD UP DRAWDOWN

2000 3000 4000 5000 6000

Pressure p (psia)

p

3/44

Why do we do well test analysis?

Pressure History

• To obtain information on the well
• Permeability
• Well damage or stimulation (skin effect)
• To obtain information on the reservoir
• Fluid
• Average reservoir pressure
• Reservoir heterogeneities
• Reservoir hydraulic connectivity
• Distances to boundaries

4/44

How do we do well test analysis?

• We select a period at constant rate (usually, a build up)
• We plot some function of pressure vs. some function of time
• We try to identify flow regimes (radial, linear, spherical,…)
• We include these flow regimes into an interpretation model which

can reproduce the pressure given the rate (or vice-versa)

• We verify that the interpretation model is consistent with all other

information (geology, seismic, cores, logs, completion, etc…).

2000 3000 4000 5000 6000 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800

Pressure (psia)

2000 4000 6000 8000 10000

Oil Rate (STB/D)

Time from the start of production (hrs)

FP4 FP76

5/44

consistent

• WTA allows to assess well condition and to estimate reservoir

parameters

• Over the last 50 years, new WTA techniques have been

developed which give more and better results, and more confidence in those results

• Nowadays, WTA potential contribution to reservoir knowledge

has never been greater

• Only WTA provides reservoir hydraulic connectivity
• Well test analysis is the technique of choice in arbitrations

WTA: the Good

6/44

• Interest and knowledge in WTA seems to be fading
• One

reason may be that the latest new techniques (deconvolution) are perceived as too complex

• This fear of complexity is compounded by WTA being often

taught, wrongly, as “basic” and “advanced” which is mistaken for “practical (for everybody)” and “esoteric (for experts only)”

• Reservoir engineers tend to believe they know how to interpret

well tests as a side benefit of knowing how to do simulation

• The Big Crew Change: WTA experts educated by Ramey at

Texas A&M and Stanford, or trained in Flopetrol/Schlumberger during the heyday of WTA have retired or are about to retire, with no systematic replacements

WTA: the Bad

7/44

• Buttonology instead of domain expertise: engineers often

believe software will do the interpretation for them

• Resistance to changes: commercial software vendors are
• ften forced by their clients to include techniques which are
• bsolete or have been proven wrong over 40 years ago
• Pressure from operators: Regular well testing is no longer

mandatory in many oil provinces

• Short term focus: In Unconventionals, data acquisition in

general (and well testing) is considered unnecessary cost

• Economic constraints: Formal WTA teams have disappeared

in many oil companies following the latest oil price drop

WTA: the Ugly

8/44

The challenge

9/44

“Partially, we (the experts) are to be blamed for the decline

• f the importance of testing.

The SPE testing literature is so much polluted that it is difficult to find relevant papers. Many interpretations (80%) even in published papers are incorrect. And MDT has replaced the Testing fluid sampling.”

Expert in WTA, personal communication

The challenge

10/44

It is not because inexperienced hands ask the same questions about the same old problems as 30 years ago, but because they get the same answers as 30 years ago, even though our industry has advanced tremendously and gotten much better answers and solutions, but this knowledge that resides in repositories and in the heads of the experienced and knowledgeable older experts

is not being transmitted effectively.”

“The picture actually looks very gloomy.

The Big Crew Change: Knowledge Loss or Management of Change? Robert Mathes http://oilpro.com/post/22284/big-crew-change-knowledge-loss-management-change

11/44

1960

Well Test papers OnePetro

1927

Well Test papers SPE

100 200 300 400 500 600 700 800 1941 1954 1968 1982 1995 2009 2023

Rig Count U.S./20 Rig Count Total World/40

Number of publications with “well testing”

Publication inflation

2012

Oil price, 2015 $ /Bbl

1972

12/44

SPE Well Test SPE Total 1 10 104 103 102 1927 2023 2009 1995 1982 1968 1954 1941

Number of publications

Publication inflation

30 (1 month) 265 (9 months) 400 (13 months) 4700 (13 years) PowerPoint Word SPE membership/25 SPE membership/50 WT/Total SPE (19%) 10% 7% DL % WTA (~7%)

& WTA undersold

WT/Total SPE (19%) 10% 7% SPE membership/25 SPE membership/50 2012 WT/Total SPE (19%) 10% 7%

13/44

1960

http://www.spe.org/industry/history/oral_archives.php

1935 1940 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 2015

Horizontal wells Electronic gauges Permanent gauges Hardware/Completion MHF IKVF MDT Multiple-fraced horizontal wells

Straight lines Derivatives Type Curve Analysis

Interpretation methods

IOC UNIVERSITIES SERVICE UNIVERSITIES ??????? DEVELOPERS GROUNDWATER

Single well Deconvolution Multiwell Deconvolution

Well test interpretation milestones

Stehfest Laplace transform Green’s functions Mathematical tools

Single well Deconvolution Multiwell Deconvolution

Horner, D. R.: "Pressure Build-ups in Wells", Proc., Third World Pet. Cong., E. J. Brill, Leiden (1951) II, 503-521.

Year

1935 1940 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 2015

Horner MDH MBH

IOC

Shell, Gulf Oil Corp, ARCO…

Straight line methods

Straight Line Methods

4900 5000 5100

Pressure (psia)

Horner Analysis - Flow Period 4

4300 4400 4500 4600 4700 4800 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 11000 12000 13000 14000

Superposition Function (STB/D)

p*= 5000 psia k = 485 mD S = 102

14/44

Year

1935 1940 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 2015

Horner MDH MBH

IOC

Shell, Gulf Oil Corp, ARCO…

Straight Line Methods

4300 4400 4500 4600 4700 4800 4900 5000 5100 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 11000 12000 13000 14000

Pressure (psia) Superposition Function (STB/D)

Horner Analysis - Flow Period 76

15

p*= 4953 psia k = 1060 mD S = 232 p*= 5000 psia k = 485 mD S = 102 FP 4

15/44

Straight line methods

Ramey, H. J., Jr.: "Short-Time Well Test Data Interpretation in The Presence of Skin Effect and Wellbore Storage," J. Pet. Tech. ( Jan., 1970) 97.

Year

1935 1940 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 2015

Horner MDH MBH

IOC

Shell, Gulf Oil Corp, ARCO… 19 years

Type Curve Analysis

UNIVERSITIES

Texas A&M, Stanford Henry J. Ramey, et al.

GROUNDWATER

Theis (1935) , Jacob (1947), Hantush (>1947)

Straight Line Methods

Log-log pressure analysis

16/44

4400 4500 4600 4700 4800 4900 5000 5100 25 26 27 28

Pressure (psia) Production time (hrs)

1000 2000 3000 4000 5000 6000 7000 8000

Oil Rate (STB/D)

FP4 FP3

Dt Dp

Rate Normalised Pressure Change Dp (psi) Elapsed time Dt (hrs)

1 10 100 1000 0.0001 0.001 0.01 0.1 1 10 100 1000

FP4 FP76 Radial flow ?

Pressure log-log plot

17/44

INTERPRETATION MODEL Wellbore storage and Skin Homogeneous behaviour Infinite reservoir

Wellbore storage and skin type curves

1 0.000295 tD CD = kh m Dt C md.ft cp , . hr bbl/psi 24C qB Dp Dt

1 10-1 10-2 103 104 105 106

Earlougher and Kersch (Marathon) 1974

pD tD CD = PRESSURE BUILDUP GROUP 5.6146 Dp C qB ft3 day RBbl ,

10-4 10-3 10-2 10-1 1 10 102

SHUT-IN TIME, Dt, MINUTES kh / m 5.6146 C md ft psi cp ft3 , 500,000 250,000 100,000 50,000 25,000 10,000 5,000 2,500 1,000 500 250 100 50 104 103 102 10 1

McKinley (Exxon) 1971

‘’’’’’’’’’’’’’’’’’

Dimensionless time, tD 102 103 104 105 106 107 108 Dimensionless Pressure, pD 102 10 10-1 10-2

• H. J. Ramey, Jr (1970)

Same interpretation model Different type curves Different results

19 years

Year

1935 1940 1945 1950 1955 1960 1965 1970 1975 1979 1985 1990 1995 2000 2005 2010 2015

Horner

TC with Independent parameters Type Curve Analysis

MDH MBH

IOC

Shell, Gulf Oil Corp, ARCO…

UNIVERSITIES

Texas A&M, Stanford Henry J. Ramey, et al.

SERVICE

Flopetrol Schlumberger

GROUNDWATER

Theis (1935) , Jacob (1947), Hantush (>1947)

Straight Line Methods

Type curve analysis

19/44

9 years SPE 8205, Gringarten, A. C. et al.: "A Comparison between Different Skin and Wellbore Storage Type-Curves for Early-Time Transient Analysis”

102 10 1 10-1

Dimensionless pressure, pD

10-1 1 10 102 103 104 105

Dimensionless time, tD /CD CD e 2S

Approximate end of wellbore storage Approximate start of semi-log radial flow

1979

102 10 1 10-1

Dimensionless pressure, pD

10-1 1 10 102 103 104 105

Dimensionless time, tD /CD CD e 2S

103 5 0.5 1030 1015 106

1

10-1 10-2 102 10-3

Approximate end of wellbore storage Approximate start of semi-log radial flow

Pressure type curve matching

k = 175 mD C = 0.01 Bbl/psi S = 32

1 10 102 103 10-1 10-2 10-3 1 10 102 103

Rate Normalised Pressure Change Dp (psi) Elapsed time Dt (hrs) FP4 FP76

20/44

?

1030

19 years

Year

1935 1940 1945 1950 1955 1960 1965 1970 1975 1981 1985 1990 1995 2000 2005 2010 2015

Horner

Methodology Type Curve Analysis

MDH MBH

IOC

Shell, Gulf Oil Corp, ARCO…

UNIVERSITIES

Texas A&M, Stanford Henry J. Ramey, et al.

SERVICE

Flopetrol Schlumberger

GROUNDWATER

Theis (1935) , Jacob (1947), Hantush (>1947)

Straight Line Methods

Methodology (workflow)

21/44

TC with Independent parameters

11 years

Methodology

IDENTIFICATION VERIFICATION

CONSISTENT WELL TEST INTERPRETATION MODEL YES

ANOTHER MODEL?

NO END Wellbore Storage Skin Fractures Partial Penetration Horizontal Well NEAR WELLBORE EFFECTS Specified Rate Specified Pressure Leaky Boundary BOUNDARY EFFECTS Homogeneous Heterogeneous

• 2-Porosity
• 2-Permeability
• Composite

RESERVOIR BEHAVIOUR

DATA

LATE TIMES MIDDLE TIMES EARLY TIMES

WELL TEST INTERPRETATION MODEL

CONSISTENT? COMPARE WITH DATA NO YES

SPE 102079 Gringarten ATCE San Antonio Sept 2006

22/44

CALCULATE MODEL BEHAVIOUR

(workflow)

0.1 1 10 100 1000 0.0001 0.001 0.01 0.1 1 10 100 1000

Pressure Change (psi) Elapsed time (hrs)

Log-Log Match - Flow Period 76

4300 4400 4500 4600 4700 4800 4900 5000 5100 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 11000 12000 13000 14000

Pressure (psia) Superposition Function (STB/D)

Horner Match - Flow Period 76

3700 3800 3900 4000 4100 4200 4300 4400 4500 4600 4700 4800 4900 5000 5100 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800

Pressure (psia) Production time (hrs)

Simulation (Constant Skin) - Flow Period 76

Verification: wellbore storage and skin model

23/44

k = 175 mD C = 0.01 Bbl/psi S = 32

4000 4100 4200 4300 4400 4930 4940 4950 4960 4970 4980 4990 5000 5010 Pressure (psia)

15 years 13 years Bourdet et al.: "A New Set of Type Curves Simplifies Well Test Analysis," World Oil ( May, 1983) 95-106.

Year

1935 1940 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 2015

Horner

Derivatives Methodology Type Curve Analysis

MDH MBH

IOC

Shell, Gulf Oil Corp, ARCO…

UNIVERSITIES

Texas A&M, Stanford Henry J. Ramey, et al.

SERVICE

Flopetrol Schlumberger

GROUNDWATER

Theis (1935) , Jacob (1947), Hantush (>1947)

Straight Line Methods = dDp / d ln Dt

1983 24/44

TC with Independent parameters

Pressure derivative

No radial flow FP4 FP76

0.1 1 10 100 1000 0.0001 0.001 0.01 0.1 1 10 100 1000

Elapsed time Dt (hrs) PRESSURE Pressure Change and Derivative (psi)

Pressure derivative

FP4 FP76 DERIVATIVE Radial flow Wellbore storage & skin model

25/44

No radial flow FP4 FP76 FP4 FP76

0.1 1 10 100 1000 0.0001 0.001 0.01 0.1 1 10 100 1000

Pressure Change and Derivative (psi) Elapsed time Dt (hrs) No radial flow Closed reservoir?

Pressure derivative

26/44

0.1 1 10 100 1000 0.0001 0.001 0.01 0.1 1 10 100 1000

Pressure Change (psi) Elapsed time (hrs)

Log-Log Match - Flow Period 76

4300 4400 4500 4600 4700 4800 4900 5000 5100 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 11000 12000 13000 14000

Pressure (psia) Superposition Function (STB/D)

Horner Match - Flow Period 76

3700 3800 3900 4000 4100 4200 4300 4400 4500 4600 4700 4800 4900 5000 5100 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800

Pressure (psia) Production time (hrs)

Simulation (Constant Skin) - Flow Period 76

Verification: WB & S, limited entry, closed rectangular reservoir

4000 4100 4200 4300 4400 4930 4940 4950 4960 4970 4980 4990 5000 5010 Pressure (psia)

FP4 FP76 FP4 FP76

27/44

0.1 1 10 100 1000 0.0001 0.001 0.01 0.1 1 10 100 1000

Pressure Change (psi) Elapsed time (hrs)

Log-Log Match - Flow Period 76

3700 3800 3900 4000 4100 4200 4300 4400 4500 4600 4700 4800 4900 5000 5100 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800

Pressure (psia) Production time (hrs)

Simulation (Constant Skin) - Flow Period 76

Verification: WB & S, limited entry, closed rectangular reservoir

FP4 FP76

Initial pressure (pav)i 5000 psia Horizontal permeability k(xy) 470 mD Vertical permeability k(z) 0.54 mD Wellbore storage coefficient C 0.01 bbl/psi Penetration ratio hw/h 0.06 Wellbore skin effect S(w) 0.8 Reservoir area A 6 10

7

ft2 Parameter Analysis

28/44

Typical field uncertainty ± 5 psia ± 20% ± 20% ± 20% ± ± 0.5 ± 30% ± 20% Design Difference 5000 0% 500

• 6%

0.5 8% 0.01 0% 0.05 20% + 0.8 6 107 0%

19 years 13 years SPE 71574: von Schroeter, T., Hollaender, F., Gringarten, A.:"Deconvolution of Well Test Data as a Nonlinear Total Least Square Problem"

Year

1935 1940 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 2015

Horner

Derivatives Methodology Type Curve Analysis

MDH MBH

IOC

Shell, Gulf Oil Corp, ARCO…

UNIVERSITIES

Texas A&M, Stanford Henry J. Ramey, et al.

SERVICE

Flopetrol Schlumberger

??????? GROUNDWATER

Theis (1935) , Jacob (1947), Hantush (>1947) 19 years

Imperial College

Single well Deconvolution Straight Line Methods

Single well deconvolution

Commercial Software

SSI

29/44 2002

What is Deconvolution?

Deconvolution is data processing with an algorithm which converts pressures at variable rates:

2000 3000 4000 5000 6000 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800

Pressure (psia)

2000 4000 6000 8000 10000

Oil Rate (STB/D)

Time from the start of production (hrs) 30/44

72 hrs 168 hrs

What is deconvolution? 2000 3000 4000 5000 6000 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800 Pressure (psia) 2000 4000 6000 8000 10000 Oil Rate (STB/D) Time from the start of production (hrs) Deconvolution converts pressures at variable rates: into a single drawdown at constant rate, with a duration equal to the duration of the test: 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800

into a single drawdown at constant rate

2000 3000 4000 5000 6000

Pressure (psia)

2000 4000 6000 8000 10000

Oil Rate (STB/D)

2644 hrs

, with a duration equal to that of the test:

No radial flow FP4 FP76 FP4 FP76

10-1 1 10 102 103 10-4 10-3 10-2 10-1 1 10 102 103

Elapsed time Dt (hrs) DERIVATIVE PRESSURE Pressure Change and Derivative (psi)

104

Deconvolved derivative

> 1 log cycle

Deconvolved

Radial flow stabilisation

31/44

32/44

100 200 300 400 500

Elapsed time (hrs)

1000 2000 3000 4000 5000

Pressure (psia)

1 2 3

Time-corrected Total Rate (MMscf/D)

FP 39 FP 12

Erroneous rates Suspicious rates

Gas well in UKCS

Correction of erroneous rates

33/44

1000 2000 3000 4000 5000 500

Pressure (psia) Elapsed time (hrs)

1 2 3

Total Rate (MMscf/D)

Given rates, time corrected

FP 39 FP 12

Correction of erroneous rates

Estimation of missing rates

34/44

1000 2000 3000 4000 5000 6000 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800

Pressure (psia) Production time (hrs)

1000 2000 3000 4000 5000 6000 7000 8000 9000

Oil Rate (STB/D)

No rates Iteration 1 Iteration 2 Iteration 3 Final

35/44

Sparse WHP Sampling MDT

DATA

Assume a constant rate Apply deconvolution Deconvolved surface rates

Example: Deepwater Horizon oil spill (Macondo)

Assume a constant rate Deconvolved Bottomhole rates Apply deconvolution CUMMULATIVE PRODUCTION Scale bottomhole rates to kh Scale surface rates to kh Apply deconvolution Calculate kh Calculate BHP

36/44

L H L H

Blunt (MB) Gringarten (deconvolution)

L H

Liu, Shah, Mannan, Hasan (Sim)

Spilled Volume (MMSTB) 6 4 2

Compiled by K. Shah from http://www.sciencemag.org/news/2015/01/after-geoscientists-joust-judge-rules-bp-gulf-spill-totaled-319-million-barrels-oil

Judge: 4.0 3.26 L H L H L H L H

Kelkar/Raghavan (MB) Hsieh (Sim) Pooladi-Darvish (Sim) Dykhuizen (Sim) Griffiths (Sim)

5.00

Example: Deepwater Horizon oil spill (Macondo)

19 years 13 years 19 years

Year

1935 1940 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 2015

Horner

Derivatives Methodology Type Curve Analysis

MDH MBH

Commercial Software

IOC

Shell, Gulf Oil Corp, ARCO…

UNIVERSITIES

Texas A&M, Stanford Henry J. Ramey, et al.

SERVICE

Flopetrol Schlumberger

GROUNDWATER

Theis (1935) , Jacob (1947), Hantush (>1947)

Single well Deconvolution Straight Line Methods

??????? Imperial College

Multiwell Deconvolution

13+ years

Multiwell deconvolution

37/33

and two injectors.

N Testing group 2

I14 I12

SPE 174353 Thornton et al., Europec Madrid June 2015

• North Sea oilfield

Multiwell deconvolution: field example

38/44

P12 P15 P10 P11 P13 P14

Six interfering producers

Slope ½ = channel

1.E-04 1.E-03 1.E-02 1.E-01 1.E+00 1.E-03 1.E-02 1.E-01 1.E+00 1.E+01 1.E+02 1.E+03 1.E+04 1.E+05 Δp (psia) Time (hr)

Conventional well test analysis Multiwell deconvolution

Benefits of multiwell deconvolution

3 log cycles Interferences

39/43

I14 P12 P15 P10 P11 P13 I12 P14

N

Increasing Channel width

• Conventional well test analysis impaired by short buildups

WELL P13

• Multiwell deconvolution yields the correct shape

1.E-04 1.E-03 1.E-02 1.E-01 1.E+00 1.E-03 1.E-02 1.E-01 1.E+00 1.E+01 1.E+02 1.E+03 1.E+04 1.E+05 Δp (psia) Time (hr)

Single well deconvolution

• Single well deconvolution impaired by interference
• Multiwell deconvolution provides interference between wells

Fair ( limited) Fair to Good 70’s Pressure Type Curves Poor None ANALYSIS METHOD IDENTIFICATION VERIFICATION 50’s Straight lines Very Good 80’s Pressure Derivative Very Good Much better 00’s Deconvolution Same as derivative Multiwell deconvolution

>>

10’s

>>

40/44

NEXT ?

>>> >>>

WTA Value = Identification Verification

+

41

Other application:

AORTA

WTA of blood pressure

Deconvolved pressure and derivative

• Well test analysis has improved immensely since straight

lines and pressure log-log analysis, and even derivative log-log analysis

• Methodology makes it repeatable and easy to learn
• Derivatives and deconvolution make well test analysis a

reliable tool for reservoir characterization

42/44

Where we are

• Understanding of WTA still required
• Derivatives must be calculated correctly
• Deconvolution requires prior interpretation
• WTA requires other knowledge (geology, etc…)

43/44

But

• MDH instead of Horner
• Horner instead of superposition
• Horner equivalent production time
• Ramey’s one and ½ cycle rule
• Different start of radial flow in Drawdowns and Build ups
• Derivative plotted vs. Agarwal effective time
• Uniform flux vs. infinite conductivity solution
• etc……

44/44

AND concepts proven wrong 30 years ago still used