Investigating the Effect of Organic Sulphur Compounds on Oil Generation in Bakken Formation in Saskatchewan

This paper presents the preliminary results from an on-going study of the Madison-Bakken petroleum system of the Williston Basin, particularly with respect to oil-source correlations and Bakken source potential. This study seeks to examine and identify areas of anomalous (i.e., early) generation.

Through the application of petroleum geochemistry, this project aims to improve the present understanding of the Bakken petroleum system within the northern part of the Williston Basin, with a specific focus on southern Saskatchewan. More specifically, this study aims to examine oil-source relationships through the application of gas chromatography-mass spectrometry (i.e. biomarker analysis) and an examination of organic sulphur compounds within oils and source extracts, with the aim of determining the possible role of sulphur in the early generation of oil within potential sources conventionally considered ‘immature’.

Previous studies have characterized the lower and upper Bakken Formation to be organic rich, typically with total organic carbon contents in excess of 10wt%, and generally recognised as immature/marginally mature in the Canadian portion of Williston Basin based on Rock-Eval Tmax and vitrinite reflectance data (%VR). Source characterisation of the Bakken Formation shows that Bakken Formation is also typically composed of mainly Type II kerogen with ‘pockets’ of Type I. It has been suggested that some occurrences of Type II kerogen also contain the highest amount of organic sulphur.

Investigation of Bakken extracts in this study clearly show that the Bakken Formation contain substantial amount of elemental sulphur, with variations within the upper and lower Bakken across the basin. Extractable organic matter was separated using column chromatography into saturate and aromatic hydrocarbon fractions, and the distribution of the various organic sulphur compounds was compared in the aromatic fraction of immature sediments using gas chromatography-mass spectrometry. The variations in sulphur compounds have been mapped, although the search for organic sulphur compounds amenable to the early generation of oil is at present on going.

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