Date of Award
Doctor of Philosophy (PhD)
The hydrocarbon potential of the Three Forks Formation in North Dakota is poorly known due to limited stratigraphic, geochemical, and petrophysical data. This study presents a methodology and results of a reservoir characterization study of the stratigraphy, lithofacies distribution, petroleum potential, and paleo-environments of the Three Forks Formation in North Dakota as a potential for hydrocarbon exploration with the principal objective to evaluate the Three Forks Formation’s potential for future developments. The detailed lithology is computed by employing a probabilistic interpretation approach calibrated with lab results and five major lithofacies of the Three Forks Formation in North Dakota, which display a variety of diagenetic characteristics including dolomitization and precipitation of hematite, are identified and presented. These facies correlate well with electrofacies predicted by employing principal component analysis and clustering techniques to selected lithology-sensitive logs. Hydrocarbon source rock analysis, including type and quantity of kerogen, and thermal maturity on all five facies using Rock-Eval 6 pyrolysis and LECO TOC shows that these facies have poor to fair petroleum potential and contain immature Type II and Type III kerogens. In addition, samples from three lithofacies are analyzed by thin section and SEM petrography, plus combined bulk and clay XRD analyses and key aspects controlling the porosity and permeability of this formation are revealed by focusing on the detailed mineralogy, rock type, diagenetic mineral distribution plus overall reservoir quality and the fluid sensitivity. Results show that the Three Forks mineralogy is dominated by dolomite, along with substantial hematite, monocrystalline quartz and mica flakes with trace feldspar, calcite, and pyrite. EDX spectra show that the element distribution is influenced by the lithotype composition, mainly Ca, Mg, and Fe with additional Si, Al, and K. Three stages of the dolomitization process are identified and discussed. Clays mainly consist of illite together with minor chlorite, and kaolinite and are associated with the scattered clasts of quartz and feldspars. The reservoir quality is controlled by intercrystalline, rare micro-vuggy, plus microporosity types that result from diagenetic and depositional events. Six members of the Three Forks are identified and log-derived porosities, water saturations, and net-togross values for each Member calculated and areas with high reservoir quality and potential pay zones highlighted. Also, core data are quantitatively compared with results from the Archie, Simandoux, Modified Simandoux, Indonesia, and Dual-Water models. A proposed depositional model is constructed based on detailed core examination and petrographical analysis and sufficient evidence is provided to show that the Three Forks Formation is of peritidal to sabkha-like origin. A proposed hypothesis is that dolomitization commenced soon after deposition and was pervasive that no original carbonate texture is detectable.
Ashu, Richard A., "Stratigraphy, depositional environments, and petroleum potential of the Three Forks Formation -- Williston Basin, North Dakota" (2014). Theses and Dissertations. 8.