--> ABSTRACT: Regional Geology and Petroleum Potential of Bakken Formation, Southwestern Manitoba, by Carol D. Martiniuk; #91033 (2010)

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Regional Geology and Petroleum Potential of Bakken Formation, Southwestern Manitoba

Carol D. Martiniuk

The Bakken Formation has been documented as an excellent petroleum source rock within the Williston basin and has, in some localities, been established as a producing zone. Recent exploration in the Daly field of southwestern Manitoba has led to the discovery and subsequent development of several oil pools within the middle member of the Bakken. The 21 active wells within these pools have produced 20,773.8 m3 (130,667.2 bbl) of oil (40.2° API) as of December 31, 1987.

Through much of the Williston basin, the Bakken typically consists of three members: a lower, highly radioactive, black shale member; a middle siltstone member; and an upper black shale member (identical to the lower member).

In southwestern Manitoba, the lower member is absent in most areas due to nondeposition and overstep of the overlying middle member. In these areas, the middle member unconformably overlies eroded red dolomitic shales of the Devonian Lyleton (Three Forks) Formation.

The middle member is a relatively uniform blanket deposit averaging 4 m (13 ft) thick. It consists of interbedded tan to greenish-gray, very fine to medium-grained, well-sorted dolomitic sandstone and siltstone with angular to subrounded grains.

Oil accumulation in the middle member is largely the result of stratigraphic trapping and appears, in part, to be localized where a basal sandstone (associated with middle member thickening) is concentrated in minor erosional lows on the Lyleton surface.

The black shales of the upper member form a thin (2 m or 6.6 ft average), uniform cap throughout the map area and are overlain by the carbonates of the Mississippian Lodgepole Formation (Souris Valley Beds).

Maximum thickness of the Bakken reaches 32 m (105 ft) in the Waskada field area, where the lower shale member is locally present. Variations in thickness and associated structural features affecting each of the three Bakken Members, as well as the Lyleton Formation, are evident through detailed isopach and structure mapping in the Waskada area. These local anomalies are believed to be the result of multistage salt solution and collapse of underlying Devonian salts during Bakken-Lyleton deposition. The pattern of these anomalies offers some insight into the complexities of the salt-collapse process.

AAPG Search and Discovery Article #91033©1988 AAPG Rocky Mountain Section, Bismarck, North Dakota, 21-24 August 1988