Summary
The industry is moving away from overboard discharging of produced water and
is increasingly selecting produced-water reinjection (PWRI) as the preferred
method for waterflooding projects. This does not come without risks because the
produced water usually needs to be supplemented by seawater in order to meet
injection-volume requirements, increasing the risk of both scaling and
souring.
PWRI supplemented by seawater was the selected produced-water-management
strategy for Field M located in West Africa. Produced water from the adjacent
Field K is also being considered for reinjection into Field M. Field M will be
waterflooded from the beginning to maintain reservoir pressure close to the
bubblepoint. Recent experiences of PWRI in other assets have created a
challenging atmosphere because scaling posed a major risk to production. Field
M had to go through very detailed and thorough souring and scaling evaluations
to justify the feasibility of this project.
A consistent formation-water chemistry analysis for these evaluations was
obtained by incorporating thermodynamic equilibrium constraints on
formation-water composition from reservoir mineralogy and using knowledge of
basin formation-water contributions from proximal salt formations. The
evaluation of scaling potential was performed using ScaleSoftPitzer. The
results show a low risk of scaling when the waters are commingled. Periodic
formation scale squeezes are recommended to mitigate the scaling potential.
The souring-potential study was conducted using a full-field
reservoir-souring simulation model (SourSimRL). SourSimRL superimposes criteria
for the generation, partitioning, and transport of H2S. On the basis
of the results, the souring potential is predicted to be generally moderate.
The souring potential for the field is restricted by the availability of carbon
nutrients in the injection waters and the high reservoir temperature of
250°F.
These rigorous technical evaluations were instrumental to obtain the support
for PWRI and could be used as guidance for other PWRI projects.
© 2011. Society of Petroleum Engineers
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History
- Original manuscript received:
22 October 2010
- Meeting paper published:
21 September 2010
- Revised manuscript received:
21 October 2010
- Manuscript approved:
5 February 2011
- Published online:
14 April 2011
- Version of record:
16 May 2011
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