Miscible water-alternating-gas (WAG) flooding has proven to be an attractive
enhanced-oil-recovery (EOR) method the world over. Successful WAG floods can
yield significant additional oil recovery over waterflooding.
WAG floods are complex in nature since reduction of residual oil in the pore
spaces depends on mass transfer. Optimizing miscibile contact between the
injected gas and the reservoir oil over a large rock volume is challenging.
This challenge is more manageable in a small-scale pilot flood or a coreflood
than in a large field implementation. Numerical-simulation efforts can provide
guidance to designing an optimal flood. However, the field application will
often reveal challenges that are not discovered in the pilot stage or by the
full-field simulation model because the geologic properties and heterogeneity
of the reservoir rock are not accurately represented.
Integrated surveillance of a WAG flood is the only means to determine
whether the flood is working efficiently and the planned additional recovery
will be delivered. A well-implemented surveillance plan allows timely
intervention to improve the efficiency of an underperforming WAG flood.
This paper presents a systematic approach for applying EOR surveillance
tools and methods in large miscible WAG floods in the Ivishak reservoirs at the
Prudhoe Bay and Eileen West End (EWE) of the North Slope, Alaska. Highlights of
these surveillance methods are (1) designed and implemented by a
multidisciplinary team, (2) based on proven theory and corroborated with field
data, (3) requires easily obtainable and relatively inexpensive field data and
analysis, and (4) applied from fault block down to zone levels. Implementation
of these tools has helped to identify the efficiency of flood patterns and
areas of poor performance, which then can be modified through infill drilling,
well recompletion, or WAG-ratio modification to maximize EOR recovery.
© 2011. Society of Petroleum Engineers
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- Original manuscript received:
28 January 2010
- Meeting paper published:
28 June 2010
- Revised manuscript received:
5 January 2011
- Manuscript approved:
19 January 2011
- Published online:
24 May 2011
- Version of record:
7 June 2011