Summary
The Medicine Pole Hills Unit (MPHU) EOR project is the deepest air-injection/in-situ-combustion project in the Williston basin. A unit comprising 9,600 acres with 13 producing wells was formed in July 1985, and air-injection operations began in Oct. 1987. Laboratory combustion tests and detailed feasibility studies were completed before starting the full scale project. The combination of light oil (39°API), carbonate formation, hot reservoir (230°F), and low permeability (1 to 30 md) makes this a unique air-injection project. Cumulative air injection as of Dec. 1993 was 12 Bscf. This paper reviews production performance of the MPHU to date. Oil production from the unit has shown a significant increase over its historical decline, and a processing plant has been installed to recover the liquids stripped from the oil by the produced flue gas. Although well workovers, acid fracturing, and pump changes in some producers complicate the determination of the oil response to air injection, production decline-curve analysis was used to estimate the incremental oil recovery due to air injection. The current air/oil ratio (AOR) is 8 Mscf/STB. Also discussed are the changes in air utilization over time, the benefits of the liquids recovery from the produced-gas stream in such a light-oil project, and an estimate of the field burned volume.
