Abstract

Bakken shales of the Williston Basin are world class source rocks. The shales (upper and lower) have total organic carbon contents (TOC) which average 11 weight percent. Several previous workers have estimated that these shales have generated in excess of 100 billion barrels of oil.

Pyrolysis data (Rock Eval) and total organic carbon content (LECO TOC) for the Bakken shales of the Williston Basin are compiled and analyzed. Onset of intense hydrocarbon generation and mature source rocks correspond to pyrolysis temperatures of 425°C, and production index values of 0.1. The type of kerogen present in the Bakken based on hydrogen and oxygen index values is Type I and II. Type III kerogens are present along the shallow east flank of the basin. Geothermal gradients have dramatic impact on hydrogen index, production index, Tmax values and TOC content. TOC contents are diminished 4 to 6 weight percent in thermally mature areas.

Pyrolysis and TOC data are not constant through a shale interval so several samples are needed to adequately evaluate the intervals.