A portion of a study of the B Reservoir of the East Poplar Field made by the East Poplar Unit Engineering Committee is summarized. The study was undertaken to review the performance of the reservoir after five years of operation.
The B Reservoir consisted of two limestone zones and one dolomite zone in good pressure communication. The usual problems of analyzing reservoirs of this type were made more complex by a 200-ft tilt in the original oil-water contact. A thick interval of transition from oil to water also existed which it was necessary to quantitatively define in order to study recovery efficiency.
The B Reservoir contained 213,200,000 bbl of tank oil originally in place[588 bbl/acre-ft]. Calculations have indicated that 39.7 per cent of the tank oil originally in place may be recoverable. Cumulative production as of Jan. 1,1958, was 16.3 per cent of the ultimate recoverable oil.
A pilot pressure maintenance project was initiated in Sept., 1956, testing the feasibility of augmenting a limited natural water drive. Produced saltwater was injected below the original oil-water contact through two wells. Increases in productivity were noted on four wells after the injection of only400,000 bbl of water. The project has been encouraging enough to anticipate future expansion.
The East Poplar Field was discovered in March, 1952, with the completion of the East Poplar Unit No. 1. The field lies in Northeast Montana on the Fort Peck Indian Reservation in Roosevelt County. It is approximately 55 miles south of the International Boundary and 8 miles northeast of the town of Poplar.
There are three oil reservoirs of importance in the field, the Madison A, Band C Zones. In addition, oil production has been established in the Kibby Sandbut has not thus far proved commercial. Minor gas production has also been obtained from the Judith River Sand.
This paper is confined to a discussion of the B Reservoir, occurring at a depth of approximately 5650 ft, and containing most of the reserves of the field.