Organic matter variation within Upper and Lower Bakken shales of the Williston Basin by extracting kerogen pyrogram information

Activation energy distribution from kerogen kinetics study contains some integral characteristics of the host source rock thermal history over geological time scales. Extracting relevant information from pyrogram is critical for reconstruction of source rock maturation and hydrocarbon generation histories. In this study, in order to improve understanding of the Bakken shale source rock, we present a new quantitative kinetic model by inversion of Rock-Eval pyrograms of the Bakken Formation in Williston Basin. A group of core samples from both Upper and Lower Members of the Bakken Formation were collected for estimating transformation ratio (TR) and pyrolysis analysis, and an inversion method with different kinetic statistic parameters was designed and conducted using the source rock Tmax-Hydrogen Index covariation combined with different burial histories. The analysis of Rock-Eval results on Williston Basin samples from both Canada and US sides demonstrate basin-wide organic matter characteristics of Upper and Lower Bakken and identify variation of hydrocarbon generation histories. The Upper and Lower Bakken shales have different kerogen type characteristics based on activation energy distributions derived from Tmax-HI pair relationship, which suggest variance of the preserved algal materials for Upper and Lower Bakken. The modeling results by the thermal history analysis with the Rock-Eval dataset indicate a higher remanent generable kerogen in Lower Bakken shale, and the thermal maturity results will be valuable for integrated assessment of the hydrocarbon systems of Williston Basin accurately. •Kinetics parameters are calculated by pyrogram inversion for Upper and Lower Bakken Members•Improved pyrolysis reaction model is created by combining Kissinger equation and Tmax-HI modeling•The characteristics of Upper and Lower Bakken suggest different algal input and OM preservation history