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Charge testing for well concept selection

impact of gun selection on

development concept

April 2013

Eelco Bakker, Al Zanimonsky, NAM

APPS – 13 - 027

Presented at 2nd Asia Pacific Perforating Symposium, 24 – 25 April 2013

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content

Well concept evolution

Case for charge testing

Test set-up / test conditions

Charge test results

Findings charge testing

Impact concepts

Conclusions

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Well concept evolution

Netherlands / Southern UK sector scene setting

Mature area, remaining gas/oil accumulations small size (0.2 – 1 BCM)

Early 2000’s: “step change” in costs required

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Significant changes (down sizing) required in well design, rig selection, well functionality and surface lay-out in order to meet challenge

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Well concept evolution – 1st step

Typical well data

Reservoir depths: 2800- 4600 mAH (1800 – 3500 m TVD)

Reservoir pressure 250 – 360 bar (undepleted)

Reservoir temperature 100 - 125 deg C

permeability : <1 - 50 mD, porosity 8 - 20 %, streaks with higher %

typical features for new standard:

reduced csg sizes

simple wellhead

3½” cemented completion

2” perf guns, static balanced / slight underbalance for trigger interval

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Old design current design

Concept worked for no. of years BUT further steps required reduce costs/increase value

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Well concept evolution – step 1

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FALLBACK

Ο

Current base case

Ο Ο

3 ½” tbg, cemented in 6” – or 4 7/8” OH

2” guns

Proposed “slim” case, low permeability

Proposed “slim” case, high permeability

2 7/8” tbg, cemented in 4 7/8”- or 3 15/16” OH

small guns:

1 9/16” or

1 11/16”

3 ½” * 2 7/8” tbg, cemented in 4 7/8”- or 3 15/16” OH

small guns:

1 9/16” or

1 11/16”

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Slim well concept – impact gun size (base modelling)

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Prod profile

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Cum prod

2” guns

Small guns

IPR

Case for charge testing:

based on initial modeling, impact (Q / NPV) of changing to slim completion could be significant needs further clarification

test DoP assumptions !!

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Charge testing conditions in lab

reservoir UCS = 1000 – 2000 psi (70 – 140 bar)

Res Pressure = 4350 – 5000 psi (180 - 350

bar)

Overburden = approx 9200 psi (634 bar)

UCS of test

sample

Internal Pressure

Field conditions

Confining stress on outside of the sample

Test set-up / test conditions

In order to mimic field conditions as good as possible selected the following parameters:

Carbon Tan material (sandstone)

internal / confining stress

Section 2 only, no flow conditions

Various combinations OH size / tbg – and charge size

Varying cement thickness

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Charge test results 2” charge

Carried out some 33 tests (3 labs, test data randomly plotted !!)

Tests in 7” and 4” Carbon Tan cores, both centralised / excentralised.

In some tests free gun volume ( FGV) reduced to minimise effect DUB (dyn underbalance)

Data used in original

modelling 0

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DoP

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DoP 2" charge

DoP, 2" charge, 6" OH

DoP, 2" charge, 4 7/8" OH

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EHD inch

EH, 2" charge, 6" OH

EH, 2" charge, 4 7/8" OH

Sample no Sample no

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Charge test results small charge

Carried out some 17 tests (3 labs, test data randomly plotted !!)

Tests in 7” and 4” Carbon Tan cores, both centralised / excentralised.

In some tests FGV reduced to minimise effect DUB

Data used in original

modelling

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TCP

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TCP, small charge, 4 7/8" OH

TCP, small charge, 3 15/16"OH

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EH, 4 7/8" OH

EH, 3 15/16" OH

Sample no

Sample no

DoP, inch EHD, inch

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Findings charge testing (1)

Futher analysis of results

For 3 ½” tbg geometry, impact cement thickness clearly seen in majority of tests (6” vs 4 7/8” OH, 4 7/8” vs 3 15/16” OH)

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DoP

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DoP impact cement thickness

2" DoP, 4 7/8" OH

2" DoP, 6" OH

"small" DoP, 3 15/16" OH

"small" DoP, 4 7/8" OH

Sample no

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Well concept evolution – step 2 (ongoing)

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FALLBACK

Ο

Current base case

Ο Ο

3 ½” tbg, cemented in 6” – or 4 7/8” OH

2” guns

Proposed “slim” case, low permeability

Proposed “slim” case, high permeability

2 7/8” tbg, cemented in 4 7/8”- or 3 15/16” OH

small guns not attractive.

Alternative: use 2” guns*

3 ½” * 2 7/8” tbg, cemented in 4 7/8”- or 3 15/16” OH

Alternative: use 2” guns*

*: providing swell tests succesful

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Follow-up 1st test phase – 2” gun in “slim” configuration

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Proposed “slim” base case

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DoP 2" charge

DoP, 2" charge, 6" OH, 3.5" tbg

DoP, 2" charge, 4 7/8" OH, 3.5" tbg

DoP, 2" charge, 3 15/16" OH, 2 7/8" tbg

Sample no

Data used in original

modelling

NB: testing 2” charges in 2 7/8” tbg still in progress, includes swell tests under ambient conditions

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Follow-up 1st test phase – 2” gun in “slim” configuration

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FALLBACK

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Proposed “slim” base case

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DoP

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DoP 2" charge

DoP, 2" charge, 6" OH, 3.5" tbg

DoP, 2" charge, 4 7/8" OH, 3.5" tbg

DoP, 2" charge, 3 15/16" OH, 2 7/8" tbg

Sample no

Data used in original

modelling

NB: testing 2” charges in 2 7/8” tbg still in progress, includes swell tests under ambient conditions

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Findings charge testing (2)

Futher analysis of results

3 ½” tbg configurations:

Centralisation / stand-off impact: significant and hence to be included, not directly included in original modeling

Overall “perforation efficiency” (OH tunnel length/TCP tunnel length) from tests some 80%, hence efficiency for actual field conditions lower tentatively set @ 50%

2 7/8” tbg configuration

Small charges disappointing, 2” prelim DoP data: as expected (still work in progress) DoP 2” charge

vertical Deviated Used for original modeling

6” OH 9” 7.7” 7”

4 7/8” OH

11” 9.6”

EH 0.19” 0.17” 0.22”

Eff, % 50 50 80

Small charge

vertical deviated Used for original modeling

4 7/8” OH

2.9” 2.4” 4”

3 15/16” OH

5.1” 4.3”

EH 0.17” 0.17” 0.17”

Eff, % 50 50 80

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Impact charge testing on well concept selection

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Inflow Performance Relationship

2" charge, base model

small charge, base model

2" charge, 6" OH, test results

2" charge, 4 7/8" OH, test results

small charge, 4 7/8" OH, test results

small charge, 3 15/16" OH, test results

Impact 2” charge:

test results impact rel. minor

Higher DoP offset by lower assumed perforation eff.

Impact small charge:

impact clear

Lower DoP + lower assumed perforation eff.

Small charge will result in loss in IPR (value)

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Impact charge testing on well concept selection

Test results 2” charge in 2 7/8” tbg:

No / minor impact on inflow, likely artefact due to testing.

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Inflow Performance Relationship

2" charge, 3 15/16" OH, test results

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Impact charge testing on well concept selection

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250 Mm3 Cumulative Gas Production

BASE BASE

2” charge Minor Impact

Small charge

Major Impact

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Conclusions

Charge testing results

DoP impact cement thickness for smaller charges potentially under-estimated

potential impact on selected drilling practices (OH drilling diameter), well productivity impact small.

Perforation tunnel efficiency possibly overestimated in original modelling

“ideal” lab tests gave results of approx 80%, field conditions (small clearance, low static UB) far from ideal.

Concept selection

Reducing tubing size to 2 7/8” and using smaller charges not attractive given loss of inflow / recovery tests of 2” guns inside 2 7/8” tbg very promising very likely way forward driving development costs down by slimming down wells. Some penalty on initial productivity.

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