Evaluation of Sub-Bubble Point Production in the …devex-conference.org/pdf/Presentations_2012/EvaluationofSub-Bubble... · Verlinden, Vincent Created Date: 6/11/2012 2:10:05 PM

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Evaluation of Sub-Bubble Point

Production in the Chestnut Field

V. Verlinden


Outline

• Introduction

• Sector models

• Full field simulation model

• Results

• Conclusions & recommendations










Background

• Discovery

• 1986: 22/2-5 (Premier)

• Appraisal

• 1988: 22/2a-7, -y and –z (Premier)

• 1987: 22/2a-8 and –z by (Premier)

• 2001: 22/2A-11x, -y, -z, tested 1.1 mmstb (Hess)

• Development

• 2006: 22/2a-12 water injector (Venture)

• 2008: start of production

– Hummingbird FPSO

– 22/2a-11x

• 2008: 22/2a-16y drilled


Background

• Geology

– Eocene Nauchlan formation

– Deepwater turbidite

– Post depositional re-mobilization

– Complex structure mapped with

seismic AVO inversion

• Reservoir properties

– Permeability; 1-2 Darcy

– Porosity: ~30%

– 30 API / 600scf/stb oil

– Initial pressure close to bubble

point


Background

• Start of production Sep 2008, start injection Dec 2008

• Injectivity decline from June 2010 – Related to sand screen failure

– 2 frac attempts in April 2011 unsuccessful, injection stopped

– New injection well planned for Q4 2011

Could production continue with less or no water injection before

the replacement water injection well was drilled?

no injection reduced injection


Background

• Could production continue with less or no water injection before a

new water injector was drilled?

– Without negative environmental effects (excessive gas flaring)

– Without reducing ultimately recoverable reserves

• Simulation study

– Mechanistic sector models around production wells

– Full field simulation model


16y sector model

• 16y area

• Vertical well drilled in local high

• Initial well encountered local gas cap, sidetracked to lower location

• Not much support from aquifer

• Formation water breakthrough

• Sector model

• 16y area only

• 1 producer, 1 injector

• Effect on cumulative production

– Water injection rate

– Voidage replacement ratio


60%

70%

80%

90% 100%

16y sector model results

• Fixed water injection (6000 bbl/d)

• Voidage replacement ratio changed by choking production

time

oil

rate

(bbl/d)

voidage

replacement

ratio

60%

70%

80%

90%

100%

Cum

ula

tive o

il

60%

100%

60%

100%

cross over timing

before EOFL?


11x sector model

• Attempts to history match sector model unsuccessful

• Complex geology

• Interaction between injector and producer

• Significant aquifer influx

• Full field model to match behaviour


Full field simulation model

• Geocellular model based on seismic inversion products

• Constant reservoir properties

• Good history match


Full field simulation results

time

voidage

replacement

ratio

0%

60%

70%

80%

90%

100%

• Simulation result with 10,000 bbl/d water injection and changing

voidage replacement ratios

– Low voidage replacement ratio accelerates production

– Does not reduce recoverable reserves before expected end of field life

cum

ula

tive o

il pro

duction

0%

100% cross over after

expected EOFL


Chestnut remaining reserves vs voidage replacement

20,000 bwpd

15,000 bwpd

10,000 bwpd

6,000 bwpd

0 bwpd

Voidage replacement

Tota

l oil

pro

duction

depletion

6,000 bbl/d injection

Unconstrained EUR ~ equal for all voidage replacement %

Downside: increased gas production

Replacement injector

- reduce gas flaring

- add reserves


Effect of local gas caps

• Why does EUR not change significantly with lower voidage ratios?

– Local gas caps are formed almost instantly due to reservoir architecture

and excellent quality, these provide pressure support. Energy remains

in field 11x

16y


What we did

• During period without water injection we;

– Remained within flare consent by shutting-in one of two producers

– Continued production with one well

– Planned new water injection well in a very short time frame

• Drilled replacement water injection well to restore water injection to;

– Reduce flaring

– Improve recovery


Conclusions

• Low voidage replacement ratios & production below bubble point do

not automatically reduce EUR and if needed can accelerate

production

• Reservoir architecture and low solution GOR important

• Formation of local gas caps has a large impact under production conditions

below bubble point

• Learning's especially relevant for similar fields with gas export route

• We have managed a period with no water injection by shutting in a

production well to limit gas flaring and in this way stayed within our

flare consent

• Drilled new injection well which fully restored water injection,

reduces environmental impact and improves recovery


Acknowledgements

• Atlantic Petroleum, Dana Petroleum.

• Shahbaz Sikandar, Gerry Coghlan, Tatiana Kiryushkina, Sam

Murphy, Steve Furnival, Peter Wood, Ram Nutakki, Oilfield

Production Consultants (OPC).


Questions?

Documents

Evaluation of Sub-Bubble Point Production in the …devex-conference.org/pdf/Presentations_2012/EvaluationofSub-Bubble... · Verlinden, Vincent Created Date: 6/11/2012 2:10:05 PM