The Buffalo Field air injection units, located in northwest South Dakota, are the oldest High-Pressure Air Injection (HPAI) projects currently in operation. In mid 1977, realizing the rapid production decline under primary recovery, the operator initiated an IOR program including laboratory tests, feasibility studies, and a pilot air injectivity test. Because the pilot results were promising, the original 3.5-section Buffalo Red River Unit (BRRU) was formed in September 1978. The results continued to be encouraging and the unit was enlarged to nine sections in September 1980 and to twelve sections in May 1981. Based upon the success of the BRRU HPAI project, the South Buffalo Red River Unit (SBRRU) of 30.5 sections was formed in June 1983 and began to respond to injection in 1985. Furthermore, given the success of the BRRU and SBRRU HPAI projects, the 7-section West Buffalo Red River Unit was formed and started air injection in November 1987. This paper summarizes the performance of the three 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 due to air injection and discusses how the air utilization has changed over time To date, the three HPAI projects in the Buffalo Field continue to be a commercial success. In the last three years, horizontal laterals have been drilled out of over 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 open hole laterals cross a porosity zone that would have taken away some of the injection into non-productive reservoir.
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