19b pure technique
DESCRIPTION
Production-Frac-AL 9TRANSCRIPT
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
2000
2500
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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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
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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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
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)
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)
Pre
ssu
re (
psi
)
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)
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.