19B PURE Technique

Enhancing Perforation Productivity Without Initial Underbalance….A Novel Technique A PURETM Gun System “Perforating for Ultimate Reservoir Exploitation”

Ian Walton Larry Behrmann Perforating Research Schlumberger Reservoir Completions

Current Paradigm

• Overbalanced perforating is damaging.

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• Perforating underbalance is the technique of choice for maximizing productivity.

Perforating Strong Rock damaged zone

• perforating creates a low-permeability damaged zone around the perf tunnel • perforating underbalance helps remove the damage

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debris

Three Sources of Damage • Crushed zone reduced permeability. • Mobile fines that plug pores during production. (Minimized by post-perforation injection.) • Fractured rock debris in perforation tunnel. (Removed by late time surge flow, only important where injection is required.)

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(Minimized by shooting underbalanced.)

Crushed Zone Damage Removal • How much underbalance do we need?

• How much underbalance do we get? Depends on ……..

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Depends on rock properties (strength, permeability) and effective stress and maybe on rate of drawdown.

Laboratory Tests • Standard Berea sandstone cores (200 md). Schlumberger Private

• Shot under downhole conditions at Schlumberger’s Productivity Enhancement Research Facility (PERF) in Rosharon Texas.

Single-shot Tests (PERF) 10 DP

8

7

3 1

9 6 DP

12 4

5

11 Figure 2A: Experim ental set-up 1. Confining cham ber with confining fluid (K erosene) 2. Sim ulated wellbore with wellbore fluid 3. Core sam ple with pore pressure and pore fluid 4. 30 gallon accum ulator with pre-determ ined gas pre-charge 5. Sim ulated reservoir rock sam ples 6. Differential pressure gauges 7. G un with the shaped charge 8. Shooting leads 9. 5 gallon accum ulator 10. M icrom eter valve 11. PCB gauges 12. Shooting Plate

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2

Choose The Best Perforation? All tests at 1000 psi underbalance

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Test 1

Test 2

Test 3

CFE = 0.70 Kc/K=0.307

CFE = 0.69 Kc/K=0.304

CFE = 0.61 Kc/K=0.235

Test 4 CFE = 0.21 Kc/K=0.049

Perforation Dynamics Initial underbalance = 1000 psi

1500 1000

Test 4

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Differential Pressure, psi

2000

500 0

Test 3 -500

Test 1

-1000

Test 2

-1500 -2000

0

0.2

0.4

0.6

0.8

1

1.2

Time, sec

1.4

1.6

1.8

2

Static Underbalance Does Not Provide Sufficient Information

• What magnitude and rate of transient underbalance determine perforation cleanup? • Need to identify and then control the parameters that influence the dynamics.

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• Post perforation wellbore dynamics critical.

Choose The Best Perforation? Tests shot at 500 psi overbalance

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Test 7

Test 8

Test 9

CFE = 0.92 Kc/K=0.79

CFE = 0.24 Kc/K=0.09

CFE = 0.41 Kc/K=0.19

Perforation Dynamics 2000

Initial overbalance = 500 psi

1500

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Differential Pressure, psi

2500

1000

Test 9

500 0

Test 8

-500 -1000

Test 7

-1500 -2000 -2500

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Time, sec

0.8

0.9

1

Overbalanced Perforating

• It can also be very damaging.

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• Overbalanced perforating can produce very productive perforations, but …...

Well Underbalance

liquid

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Initial wellbore pressure < pore pressure

Well Overbalance

liquid

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Initial wellbore pressure > pore pressure

Gun Overbalance

g a s liquid

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d e t

Detonation gas pressure in the gun > Initial wellbore pressure

Wellbore Compressibility

dp = c -1 dV/V

V-dV

p

c=2.5 10-6 psi-1

p+dp

If dV/V=0.01

dp= 4000 psi

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V

Gun Underbalance

g a s liquid

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d e t

Detonation gas pressure in the gun < Initial wellbore pressure

Perforation Dynamics Initial underbalance = 1000 psi

1500 1000

Test 4

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Differential Pressure, psi

2000

500 0

Test 3 -500

Test 1

-1000

Test 2

-1500 -2000

0

0.2

0.4

0.6

0.8

1

1.2

Time, sec

1.4

1.6

1.8

2

Perforation Dynamics 2000

Initial overbalance = 500 psi

1500

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Differential Pressure, psi

2500

1000

Test 9

500 0

Test 8

-500 -1000

Test 7

-1500 -2000 -2500

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Time, sec

0.8

0.9

1

Perforating Cleanup • Perforation damage/cleanup determined by wellbore dynamics.

• The complete wellbore, reservoir and gun characteristics must be evaluated to determine the optimum perforating systems/process to minimize perforation damage.

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• Over/Underbalanced perforating can produce clean perforations as well as damaged perforations.

More Tests • Client problem - low permeability, hard rock, low productivity, acidization required to bring wells on.

• SLB performed two perforation-flow tests (oil): – Test 1: 4000 psi UB. – Test 2: 500 psi OB.

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• Client proposed solution - high underbalance: required low wellbore pressure (500 psi).

Laboratory Test Results 5000 Te s t 1 4 0 0 0 p s i U n d e r-b a la n c e Te s t 2 5 0 0 p s i O ve r-b a la n c e TR U S T

4000

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3000

Pressure, psi

2000 1000 0 -1 0 0 0 -2 0 0 0 -3 0 0 0 -4 0 0 0 -5 0 0 0

0

0.1

0.2

0.3

0 .4

0.5

Time, sec.

0.6

0.7

0 .8

0.9

1

Laboratory Test Results

Fines continually reduced productivity.

• Test 2: Single shot skin = 0.79 (CFE=0.56). Stable PI.

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• Test 1: Single shot skin = 3.17 (CFE=0.24).

Field Results • Two options:

• Option two chosen - nipple in string might have created problems. • Results, six horizontal wells: SPE 77364 • Zero skins, eliminated $150K acid jobs on four wells. One well depleted, first well had operational issues.

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• Overbalance - required use of a packer. • Modest underbalance (400 psi) - required modification of gun system, no packer.

More Lab Tests Gas @ Residual Brine Saturation

overbalance

500 psi

1000 psi

1500 psi

2000 psi

underbalance underbalance underbalance underbalance

-1000 psi overbalance PURETM

CFE = 0.59

CFE = 0.5

CFE = 0.56

CFE = 0.61

CFE = 0.64

CFE = >1

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-1000 psi

CT7-28 (Conventional @ 2000 psi u/b)

Pressure (psi)

8000 6000

Pore

4000

SWB

2000 0 0

0.1

0.2

0.3

0.4

0.5

Time (sec)

0.6

0.7

0.8

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10000

CT7-30 (PURE @ 1000 psi o/b)

8000 6000

Pore

4000

SWB

2000 0 0

0.1

0.2

0.3

0.4

0.5

Time (sec)

0.6

0.7

0.8

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Pressure (psi)

10000

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CT7CT7-28 Conventional

CT7CT7-30 PURE

2000 psi u/b

1000 psi o/b

More PURETM Field Tests Anadarko tight gas well, Weber formation. • Permeability 0.5 – 1.5 md.

• Permanent completion; 264 ft. 2-7/8 guns @ 4 spf. • Initial overbalance = 3000 psi. • Production exceeded expectations at 5.5mmcfd without acid stimulation. • All previous wells required acid stimulation to produce.

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• Reservoir pressure ~3050 psi.

More PURETM Field Tests GOM oil well • Reservoir pressure ~ 5200 psi. • Minimum initial underbalance 1 versus positive skins when perforated conventionally from a static 500 psi overbalanced to 2000 psi underbalance.

• Effectiveness in gas wells with gas in wellbore; no lab data?

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– Model shows a potential dynamic underbalance of 80% of reservoir pressure.

Summary •

Static underbalance is not enough to determine perforation cleanup.

• Need to identify and control the parameters that influence the dynamics. • Need data on gas and low pressure wells (gas and liquid in well). • Need to translate the lab results to field application.

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• Need to analyze the wellbore dynamics during and immediately after perforating.

Publications SPE 71642 Laboratory Experiments Provide New Insights into Underbalanced Perforating

•

SPE 77364 New Underbalanced Perforating Technique Increases Completion Efficiency and Eliminates Costly Acid Stimulation

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