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The AAPG/Datapages Combined Publications Database

AAPG Bulletin

Abstract


Volume: 66 (1982)

Issue: 5. (May)

First Page: 641

Last Page: 641

Title: Analysis of Petroleum Source-Rocks of Bakken Formation (Lowermost Mississippian) in North Dakota: ABSTRACT

Author(s): R. L. Webster

Article Type: Meeting abstract

Abstract:

The Bakken Formation consists of upper and lower, black, organic-rich shales separated by a middle siltstone member. The sediments of the Bakken are marine in origin.

The middle member consists of very fine-grained sandstones, siltstones, silty limestones, and shale. The middle member generally has low porosity (1 to 5%) and permeability (< 0.1 md), except where fracturing is present, as at Antelope field in McKenzie County. The lithologies, fossils, and sedimentary structures of the middle member are indicative of a nearshore marine depositional environment.

The black shales were deposited in quiet, poorly circulated, anaerobic waters. In thin section they exhibit a high degree of orientation of mineral particles and a high kerogen content. Thin-section and chemical analyses show the mineral matter of the shales to be predominantly quartz.

Pyrolysis, total organic carbon determinations, vitrinite reflectance, optical kerogen typing, and chromatography of extractable organic matter were used to determine the depth of onset of hydrocarbon generation, amount of generated hydrocarbons, thermal maturity, kerogen types present, and distribution of organic matter in the black shales of the Bakken Formation. These are extremely rich source rocks, because they contain high amounts of algal kerogen, a prolific source material of oil. Organic carbon values for the black shales average about 13 wt. % and extractable hydrocarbons are typically 4,000 to 5,000 ppm.

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Copyright 1997 American Association of Petroleum Geologists