Perforating Research

Schlumberger Reservoir Completions

Enhancing Perforation Productivity Without Initial Underbalance….A Novel Technique

A PURETM Gun System“Perforating for Ultimate Reservoir Exploitation”

Ian Walton

Larry Behrmann

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Current Paradigm

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

• Overbalanced perforating is damaging.

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Perforating Strong Rock

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

damaged zone

debris

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Three Sources of Damage

• Crushed zone reduced permeability.

(Minimized by shooting underbalanced.)

• 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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Crushed Zone Damage Removal

• How much underbalance do we need?

Depends on rock properties (strength, permeability) and

effective stress and maybe on rate of drawdown.

• How much underbalance do we get?

Depends on ……..

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Laboratory Tests

• Standard Berea sandstone cores (200 md).

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

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Figure 2A: Experimental set-up 1. Confining chamber withconfining fluid (Kerosene) 2. Simulated wellbore with wellborefluid 3. Core sample with pore pressure and pore fluid 4. 30gallon accumulator with pre-determined gas pre-charge 5.Simulated reservoir rock samples 6. Differential pressure gauges7. Gun with the shaped charge 8. Shooting leads 9. 5 gallonaccumulator 10. Micrometer valve 11. PCB gauges 12. ShootingPlate

DP

DP

12

3

4 5

78

9

10

11

12 6

Single-shot Tests (PERF)

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Choose The Best Perforation?

Test 1 Test 2 Test 3 Test 4

CFE = 0.70 CFE = 0.69 CFE = 0.61 CFE = 0.21

All tests at 1000 psi underbalance

Kc/K=0.307 Kc/K=0.049Kc/K=0.235Kc/K=0.304

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Perforation Dynamics

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2-2000

-1500

-1000

-500

0

500

1000

1500

2000

Test 4

Test 2Test 1

Test 3

Initial underbalance = 1000 psi

Dif f

e re n

ti al P

ress

u re ,

ps i

Time, sec

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Static Underbalance Does Not Provide Sufficient Information

• Post perforation wellbore dynamics critical.

• 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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Choose The Best Perforation?Tests shot at 500 psi overbalance

Test 7

CFE = 0.92Kc/K=0.79

Test 8

CFE = 0.24Kc/K=0.09

Test 9

CFE = 0.41Kc/K=0.19

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0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-2500

-2000

-1500

-1000

-500

0

500

1000

1500

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Perforation Dynamics

Time, sec

Dif

fer e

n ti a

l Pr e

s su r

e, p

si

Test 7

Test 8

Initial overbalance = 500 psi

Test 9

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Overbalanced Perforating

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

• It can also be very damaging.

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Well Underbalance

liquid

Initial wellbore pressure

< pore pressure

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Well Overbalance

liquid

Initial wellbore pressure

> pore pressure

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Gun Overbalance

det

gas

liquid

Detonation gas pressure

in the gun

> Initial wellbore pressure

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Wellbore Compressibility

V

p

V-dV

p+dp

dp = c -1 dV/V

c=2.5 10-6 psi-1

If dV/V=0.01

dp= 4000 psi

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Gun Underbalance

det

gas

liquid

Detonation gas pressure

in the gun

< Initial wellbore pressure

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Perforation Dynamics

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2-2000

-1500

-1000

-500

0

500

1000

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2000

Test 4

Test 2Test 1

Test 3

Initial underbalance = 1000 psi

Dif f

e re n

ti al P

ress

u re ,

ps i

Time, sec

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0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-2500

-2000

-1500

-1000

-500

0

500

1000

1500

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Perforation Dynamics

Time, sec

Dif

fer e

n ti a

l Pr e

s su r

e, p

si

Test 7

Test 8

Initial overbalance = 500 psi

Test 9

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Perforating Cleanup

• Perforation damage/cleanup determined by wellbore dynamics.

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

• 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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More Tests

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

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

• SLB performed two perforation-flow tests (oil):

– Test 1: 4000 psi UB.

– Test 2: 500 psi OB.

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Laboratory Test Results

0 0 .1 0 .2 0 .3 0 .4 0 .5 0 .6 0 .7 0 .8 0 .9 1-5 0 00

-4 0 00

-3 0 00

-2 0 00

-1 0 00

0

1 0 00

2 0 00

3 0 00

4 0 00

5 0 00Tes t 1 4 00 0 p s i U n de r-b a lan c e Tes t 2 5 00 ps i O ve r-b a la n c e TR U S T

Time, sec.

Pres

sure

, psi

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Laboratory Test Results

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

Fines continually reduced productivity.

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

Stable PI.

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Field Results

• Two options:

• Overbalance - required use of a packer.

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

• 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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More Lab TestsGas @ Residual Brine Saturation

CFE = >1CFE = 0.64CFE = 0.61CFE = 0.56CFE = 0.5CFE = 0.59

-1000 psi

overbalance

PURETM

2000 psi

underbalance

1500 psi

underbalance

1000 psi

underbalance

500 psi

underbalance

-1000 psi

overbalance

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

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2000

4000

6000

8000

10000

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

Time (sec)

Pre

ssu

re (

psi

)

Pore

SWB

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

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2000

4000

6000

8000

10000

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

Time (sec)

Pre

ssu

re (

psi

)

Pore

SWB

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CT7CT7--28 28 ConventionalConventional

2000 psi u/b2000 psi u/b

CT7CT7--30 PURE30 PURE

1000 psi o/b1000 psi o/b

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More PURETM Field Tests

Anadarko tight gas well, Weber formation.

• Permeability 0.5 – 1.5 md.

• Reservoir pressure ~3050 psi.

• 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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More PURETM Field Tests

GOM oil well

• Permanent completion, 40 ft. 4.72 HSD guns with MAXR.

• Reservoir pressure ~ 5200 psi.

• Minimum initial underbalance <500 psi.

• Meet production expectations assuming zero formation and

perforation skin.

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More PURETM Field Tests

Caspian Carbonate: hard, tight, oil

• Laboratory Tests

1. Conventional ob with mud in the wellbore,

skin= 25 after perf, 3 after repeated acid flush/ injection/ production cycles

2. 1000 psi initial ub using PURE (3000 psi dynamic ub), killed with mud

skin=1.4 before kill, 2.2 after cleanup (production)

• Field results

– Perforated close to balance using PURE design with mud in hole

– Excellent productivity

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A Few Questions?

• Effectiveness in low pressure wells; no lab data?

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

• Effectiveness in gas wells; limited lab data.

– A recent PURE test gave a CFE > 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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Summary

• Static underbalance is not enough to determine perforation cleanup.

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

• 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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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