Assessing the impact of thermal maturation on the evolution of organic chemistry of Bakken Shale: Insights into oil generation

Abstract

Early development of the Bakken Petroleum System recognized the significance of source rock maturation and the onset of oil generation in determining the geographic limits of production. The process of oil generation kinetics within source rocks involves intricate chemical reactions, where the nature of organic matter and thermal history influence the production of petroleum products. While simple models work well for some kerogen types (Type I), they fail for others (Type II and III), revealing the limitations of assuming invariant kinetic properties. This study explores the complexity of oil generation kinetics and its significance, particularly in the context of the Bakken Formation. Various methods have been used to identify the boundaries of oil sources, yet many are inductive. This research introduces a novel method to distinguish between catagenesis and diagenesis in Bakken's organic matter.A common linear relationship between activation energy (Ea) and frequency factor (ln(A)) appears in kinetic studies of source rocks, often attributed to statistical errors. This study investigates these relationships, revealing non-statistical compensation effects. Furthermore, extended kinetic models uncover a range of behaviors, highlighting the complexity of oil generation pathways. Notably, a kinetic compensation effect (KCE) is observed in the Bakken Formation, closely resembling findings for Type II kerogen. These compensation effects are not statistically forced, emphasizing their physiochemical origins. This research sheds light on the diverse KCEs within the Bakken Formation through a combination of experimental maturation, core analyses, and kinetic modeling. The study suggests that provenance, particularly for Type II kerogen, plays a crucial role in these effects. The data reveal multiple KCE patterns, including linear, inclined arch, and random clusters, with some transitioning between patterns during the oil generation process. These findings underscore the complexity of oil generation kinetics and its dependency on organic provenance. They also provide valuable insights for understanding oil reservoirs in the Bakken Formation and beyond.