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High Resolution Organic Facies of the Bakken Formation, Williston Basin, Saskatchewan, Canada

Wrolson, Bree M.*1; Bend, Stephen L.1
(1) Geology, University of Regina, Regina, SK, Canada.

This presentation will present preliminary results of a high resolution organic facies study that is currently being conducted on the Bakken Formation within the Saskatchewan portion of the Williston Basin.

Jones and Demaison (1982) and Jones (1987) defined organic facies as a mappable subdivision of a designated stratigraphic unit, distinguished from the adjacent subdivisions on the basis of the character of its organic matter without regard to the inorganic aspects of the sediments. Tyson (1995) suggested that the concept reflect a body of sediment containing a distinctive assemblage of organic constituents which can either be recognized by microscopy or is associated with a characteristic bulk organic geochemical composition. This study amalgamates both concepts, subdividing a given stratigraphic unit (spatially and temporally) into organic facies that are distinguished by variations in maceral assemblage and geochemical signature, with reference to variations in lithofacies and associated petrophysical log characteristics.

Organic facies is a relatively new concept within the field of petroleum geology and only a few isolated studies have been conducted within the Williston Basin. A high resolution organic facies study of the Bakken Formation incorporates petrographic and geochemical analysis of core-derived samples, selected at closely spaced intervals throughout the Upper, Middle and Lower Bakken. Each core is initially logged and gross characteristics described then subsequently sampled. Petrographic analysis involves point-count analysis of macerals under white and fluorescent light; whereas RockEval is used to geochemically characterize each subdivision. Essentially, the organic petrology data obtained from the epoxy mounted samples is coupled with the RockEval data to define organic facies, which are then plotted on a depth-wise core log and compared to wireline log signature (e.g. GR, Resistivity), TOC, S2, kerogen Type and other key characteristics. Preliminary results, based on this higher resolution approach, show detailed temporal (i.e. depth-wise) variations in maceral/kerogen Type that reflect gross variations in TOC and log signature. Building upon the earlier work of Stasiuk (1991, 1996), who defined the Bakken shales to consist of three organic facies, this work is able to show subtle variations within earlier defined facies that may, in turn, reflect variations in production across the northern part of the basin.

 

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California