Review of Bell Creek Waterflood Performance - Powder River, Montana
Authors: Burt R.A. , Haddenhorst F.A. , Hartford J.C. 
Published: December 2007

This case history of the Bell Creek field reviews the performance of six contiguous Muddy Sand sandstone reservoirs before and during waterflood. An edge-drive waterflood has been in progress for 5 years. Reservoir geology and properties are discussed, along with investigations of the potential for micellar-polymer flooding. potential for micellar-polymer flooding. Introduction
The Bell Creek field consists of six Muddy Sand reservoirs unitized as six units. A line-drive waterflood from the west edge of each reservoir has been in operation since 1970. Oil production in Nov. 1974 was 26,000 B/D. Cumulative production to Dec. 1974 was 66.9 million bbl of oil. Tertiary recovery by a micellar process is under active consideration. process is under active consideration.The Bell Creek field is located 60 miles north of Gillette, Wyo., in Powder River and Carter Counties, Montana (see Fig. 1). The field is 15 miles long and 3 1/2 miles wide, encompassing 17,000 productive acres contuning 305 active producing and injection wells The current 26,000-BOPD rate accounts for nearly one-third of the oil production in Montana.

History
Bell Creek field was discovered June 4, 1967, by Exeter Drilling Co. on a farm-out from Samuel Gary. The discovery well, 33-1 Federal-McCarrel, was completed for an initial pumping potential of 230 BOPD from perforations at 4,524 to 4,537 ft. perforations at 4,524 to 4,537 ft.The Montana Oil and Gas Commission designated 40-acre spacing for Bell Creek field, which resulted in drilling and completing 405 oil wells and 10 gas wells. The average depth of a Bell Creek well is 4,500 ft.
Discovery of the Bell Creek field started extensive exploration of Wyoming's Powder River Basin that led to the discovery of 30 to 40 Muddy Sand reservoirs.

Geology and Reservoir Characteristics
Bell Creek field is located on the northeastern flank of the Powder River Basin. The regional structure dips to the west-northwest at 100 ft/mile. Fig. 2 is a structure map of the Muddy Sand. Geologic data indicate Bell Creek field is a complex of northeast-southwest trending, offshore sand bars and deltaic sand deposits. The Bell Creek Muddy Sand reservoirs, except Unit E, are characteristic of barrier bar complexes. Unit E is a mixture of channel or deltaic deposits and sand bars. The six reservoir sand bodies and the locations of water-oil contacts and gas-oil contacts are shown in Fig. 3.
The gross sand thickness within the field reaches a maximum of 30 ft, with a maximum net pay of 27 ft. Average net pay throughout the units varies from 7.4 ft in Unit E to 12.5 ft in Unit B. Fig. 4 is an isopach map of the Muddy Sand. Table 1 lists average net pay, productive acres, and bulk volume for each unit. productive acres, and bulk volume for each unit.Two distinct sand sections, Zones 1 and 2, are present in all units except Unit E. In comparing the two zones in each unit in order of magnitude, Zone 1, the upper interval, has the higher clay content and a permeability of 100 md. Zone 2 is a cleaner sand with a permeability of 1.5 darcies. Zones 1 and 2 are shown in Fig. 5. Unit E has three distinct zones that vary in permeability from 195 to 1,450 md. These three zones are very lenticular because of the complex geologic deposition.
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