Date of Award

January 2023

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Geology

First Advisor

Stephan H. Nordeng

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. This research project aims to confirm the role of thermal maturation as the dominant mechanism in controlling the oil generation of the Bakken Shale. Additionally, the purpose ofthis research is to test the influence of thermal maturation on the geochemical and mechanical properties of the Bakken Shale. To conduct these investigations, samples from 2-BRENDEN 9-33 1-M, a well in the North Dakota part of the Williston Basin that has experienced the least thermal stress were heated at 340 ℃ for 3, 6, 12, 24, and 48 hours to induce maturity. Bitumen was removed from the experimental samples using the Dean-Stark method. Source rock analysis was used to test the level of maturation and document the changes in the geochemical properties of the untreated and extracted experimental samples. Nonisothermal kinetic experiments using an extended kinetic method were included to better evaluate the point that oil generation begins. To characterize the experimental samples, thin sections prepared from the experimental reaction products were examined under UV light visible fluorescence before and after extraction of bitumen. The changes in the mineralogical composition during maturation were studied through x-ray diffraction (XRD) analysis. Fluid reaction products were evaluated (hydrocarbon composition) using gas chromatography (GC). Scanning electron microscopy (SEM) was used to determine changes in the microstructure as a function of experimentally induced thermal maturation. Finally, the atomic force microscopy (AFM) technique was used to map the mechanical properties of the natural and experimentally matured samples at a nanometer resolution. Data shows that the point of oil generation can be estimated by locating the boundary between a linear, low-gradient maturation series (non-generating) and a nonlinear one (generating). The broadening of reactant temperatures under geologically reasonable subsidence rates further suggests that the reactivity of the Bakken changes throughout oil generation, necessitating the generation of new, immobile, reactive products during catagenesis. Fluorescence shows that amorphous organic matter (AOM) is lost and even more in extracted samples, and solid bitumen is gained because of AOM transformation. Tasmanites alginite is more resistant to transformation than AOM. XRD shows that increased heating time caused more dissolution of calcite than dolomite and textural changes. The results and analyses using the PFQNM approach show a decrease in mechanical properties with an increase in thermal maturation (increased heating time). These research findings show consistency with what is seen in nature and offer an additional metric that can be used to better define the point that marks the beginning of oil generation.

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