The Bell Creek field is located in Ts. 8-9 S., Rs. 53-54 E., in southeastern Montana next to the Montana-Wyoming border. It is presently more than 15 mi long, up to 3 mi wide, and is still in an active stage of development. As of February 1, 1968, 7 months after discovery, there were 178 oil wells, 6 gas wells, and 25 dry holes within the area designated as the Bell Creek field by the Montana Oil and Gas Commission. This activity has taken place since June 1967 when Exeter Drilling and Sam Gary completed the discovery well, The Federal-McCarrel No. 33-1, C, NE¼, NE¼, Sec. 3, T.8 S., R.54 E., from perforations in the Lower Cretaceous Muddy sandstone between 4,532 and 4,537 ft. IP was 240 b/d of oil. Since that time more than 12,000 acres have been proved producti e and the field is still expanding in all directions except toward the west and northwest. Even on the west and northwest, the downdip side of the field, the productive limits are not clearly defined.

The field is on the northeast flank of the Powder River basin. The structure is monoclinal with dip of approximately 100 ft/mi toward the northwest. The trap is a facies change from porous sandstone to shale updip toward the east and southeast. The trend of the producing is roughly parallel with the regional strike in this area.

The reservoir is a series of Lower Cretaceous sandstone lenses variously termed the Muddy, Newcastle, or Dynneson sandstones. The precise origin of these sandstone bodies is not clear, but they appear to be reworked from sands previously deposited in a deltaic complex at the margin of an encroaching Early Cretaceous sea. Total thickness of the porous sandstone ranges from 0 to 35 ft and exhibits excellent reservoir characteristics. Many wells have average porosity values of about 30 percent and average permeability values of several darcys. Productivity of the individual wells ranges from approximately 100 to 1,000 b/d of oil. Most wells are capable of producing more than 500 b/d of oil. Productive potential of the field presently is estimated at more than 50,000 b/d but is restricted to about 30,000 b/d by pipeline limitations. Proved ultimately recoverable reserves are in excess of 100,000,000 bbl. The oil is brown, intermediate-base, 32°-38° API gravity with gas-oil ratios ranging from 150:1 to 2,000:1. There appears to be a small gas cap in the updip edge of several of the individual sand lenses.

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