Bell Creek Field: A Rich Stratigraphic Trap, Powder River and Carter Counties, Montana

Alexander A. McGregor and Charles A. Biggs

The Bell Creek field is located in T8 and 9S, R53 to 55E, in southeastern Montana close to the Montana-Wyoming border. Although more than 15 mi long and up to 3 mi wide, the field still is being developed. On August 1, 1968, 14 months after discovery, there were 329 oil wells, 6 gas wells, and 32 dry holes within the area designated as the Bell Creek field by the Montana Oil and Gas Commission. All drilling has been done since June 1967 when Exter Drilling and Sam Gary completed the discovery well, the No. 33-1 Federal-McCarrell, C NE¼ NE¼, Sec. 3, T8S, R54E, from perforations in the Cretaceous Muddy Sandstone at depths of 4,532 to 4,537 ft; IP was 240 b/d of oil. Since that time, 15,000 productive acres have been proved and the field is still being extended in ll directions except west and northwest. Even on the west and northwest sides of the field (the downdip side), the productive limits are indefinitely known.

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

The reservoir is a series of Lower Cretaceous sandstone lenses called variously the Muddy, Newcastle, or Dynneson Sandstones. The genesis of these sandstone bodies is not clear, but they appear to have formed as a result of the reworking of a previously deposited deltaic complex by an encroaching Early Cretaceous sea. Total thickness of the porous sandstone range from 0 to 40 ft. The sandstone exhibits excellent reservoir characteristics. Many wells have average porosity values of about 30% and average permeability values of several darcys. Productivity of the individual wells ranges from about 100 to 1,000 b/d; most wells are capable of producing more than 500 b/d. The field is presently producing 60,000 b/d. Thus Bell Creek is the largest producing field in the Rocky Mountain area. roved ultimately recoverable reserves are more than 200 million bbl. More than 10 million bbl were produced during the past 14 months. The oil is brown, intermediate-base, and 32°-38° gravity. Gas-oil ratios range from 150:1 to 2,000:1. There appears to be a small gas cap in the updip edge of several of the sandstone lenses.

AAPG Search and Discovery Article #91051©2012 AAPG Rocky Mountain Section Meeting, Albuquerque, New Mexico, 23-26 February 1969