Abstract

The Bakken Formation in the Williston basin consists of the upper and lower (U&L) Bakken shale and the dolomitic siltstones of middle Bakken. The dark colored, organic-rich U&L Shale are world-class source rocks, with total organic carbon (TOC) content varying between 3 to 20 wt. %. The fine-grained dolomitic siltstone of the middle Bakken are the main reservoir in the Bakken Petroleum System. However, recent studies suggest of the U&L shales production contribution to the middle Bakken production. This emphasizes the importance of characterization of the U&L shales.

This study is aimed at understanding the heterogeneity within the U&L Shale using analytical geochemical techniques. Energy dispersive x-ray fluorescence (ED-XRF) data were acquired for several Bakken cores from North Dakota and Montana using a hand-held ED-XRF instrument. Multi-element proxies were used to determine the chemostratigraphic zonation and paleodepositional environment of these mudrocks. The XRF data were integrated with TOC and stable isotope ratios to determine the paleoceanographic controls on deposition of the U&L Shale. This helps to understand the role of productivity, preservation potential and dilution of organic matter, which causes variability of TOC within the U&L Shale.

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