Summary
The Buffalo field air-injection units, located in northwest South Dakota,
are the oldest high-pressure-air-injection (HPAI) projects currently in
operation. Air injection began in January 1979, and as of December 2007,
approximately 240 Bscf of air has been injected into the field. A total of 17.2
million bbl of incremental oil has been produced by the HPAI process, which is
equivalent to 9.4% of the original oil in place (OOIP). The cumulative air/oil
ratio (AOR) after 29 years of air injection is approximately 14 Mscf of air/bbl
of incremental oil.
This paper summarizes the performance of the projects and the overall
experience gained by the operators after nearly 30 years of air injection. It
covers almost every aspect of the entire operation since its inception; it
discusses general management practices, technical and operational challenges
encountered, injection and production facilities, and drilling and
well-completion practices. It also includes estimates of incremental oil
recovery caused by air injection and discusses how the air use has changed over
time
To date, the three HPAI projects in the Buffalo field continue to be a
commercial success. In the last 3 years, horizontal laterals have been drilled
out of more than 40 old vertical wells to enhance production, to take advantage
of accumulated reservoir energy, and to improve sweep efficiency. Drilling
injection wells out of old vertical wells was not possible because the openhole
laterals cross a porosity zone that would have taken away some of the injection
into nonproductive reservoir.
© 2009. Society of Petroleum Engineers
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History
- Original manuscript received:
11 February 2008
- Meeting paper published:
20 April 2008
- Revised manuscript received:
31 July 2008
- Manuscript approved:
6 August 2008
- Published online:
20 July 2009
- Version of record:
9 September 2009
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