19B PURE Technique

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Perforating Research

Schlumberger Reservoir Completions

Enhancing Perforation Productivity Without

Initial Underbalance….A Novel Technique

A PURE

TM

Gun System

“Perforating for Ultimate Reservoir Exploitation”

Ian Walton

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S c h lu m b e rg e r P ri v a te

Current Paradigm

• Perforating underbalance is the technique of choice

for maximizing productivity.

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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

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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?

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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 : Experim ental set-up 1. C onfining cham ber w ith confining fluid (K erosene) 2. Sim ulated w ellbore w ith w ellbore fluid 3. C ore sam ple w ith pore pressure and pore fluid 4. 30 gallon accum ulator w ith pre-determ ined gas pre-charge 5.

Sim ulated reservoir rock sam ples 6. D ifferential pressure gauges 7. G un w ith the shaped charge 8. Shooting leads 9. 5 gallon accum ulator 10. M icrom eter valve 11. PC B gauges 12. Shooting Plate D P D P 1 2 3 4 5 7 8 9 10 11 12 6

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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

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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 2 Test 1 Test 3

Initial underbalance = 1000 psi

D if fe re n tia l P re ss ure , p si 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

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Choose The Best Perforation?

Tests shot at 500 psi overbalance

Test 7 CFE = 0.92 Kc/K=0.79 Test 8 CFE = 0.24 Kc/K=0.09 Test 9 CFE = 0.41 Kc/K=0.19

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S c h lu m b e rg e r P ri v a te 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 2000 2500

Perforation Dynamics

Time, sec D if fe ren ti a l P re ssu re , 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

d e t g a s liquid

Detonation gas pressure in the gun

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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

d e t g a s liquid

Detonation gas pressure in the gun

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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 2 Test 1 Test 3

Initial underbalance = 1000 psi

D if fe re n tia l P re ss ure , p si Time, sec

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S c h lu m b e rg e r P ri v a te 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 2000 2500

Perforation Dynamics

Time, sec D if fe ren ti a l P re ssu re , 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 0 0 -4 0 0 0 -3 0 0 0 -2 0 0 0 -1 0 0 0 0 1 0 0 0 2 0 0 0 3 0 0 0 4 0 0 0 5 0 0 0 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 Time, sec. Pr es su re , p si

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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).

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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 Tests

Gas @ Residual Brine Saturation

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

0 2000 4000 6000 8000 10000 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 Time (sec) P re s s u re ( p s i) Pore SWB

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

0 2000 4000 6000 8000 10000 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 Time (sec) P re s s u re ( p s i) Pore SWB

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S c h lu m b e rg e r P ri v a te CT7 CT7--28 28 Conventional Conventional 2000 psi u/b 2000 psi u/b CT7 CT7--30 PURE30 PURE 1000 psi o/b 1000 psi o/b

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More PURE

TM

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.

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More PURE

TM

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 PURE

TM

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

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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).

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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