The Late Cretaceous Niobrara Formation of the southern Powder River Basin (PRB) is known as a prominent source rock and oil and gas reservoir. The Formation contains intervals of chalks, marls and calcareous shales. The Niobrara can be defined as a deep-water hemipelagic carbonate mudrock. During the Late Cretaceous, the Western Interior Seaway covered the Powder River Basin depositing calcium carbonate, clay and sand. This deposition included a large amount of total organic carbon (TOC). Present day oil generation for the Niobrara in the PRB is found at approximately 8,000 feet, based on vitrinite reflectance values and burial depths. However, only the Smoky Hill Member is present in the Powder River Basin, making the stratigraphy of this basin different from adjacent basins that contain the Niobrara Formation. The Niobrara Total Petroleum System (TPS) in the southern PRB includes source beds in the Niobrara Formation and reservoirs in the Teckla, Teapot, Parkman, Sussex, Shannon, Frontier, Turner and Niobrara Formations. The Niobrara oil and gas play, is an unconventional chalk, marl and calcareous shale play that extends through Wyoming and Montana in the Powder River Basin Province. It is a continuous-type accumulation of oil and gas that displays different structural and stratigraphic frameworks. There has been a wide range of previous work done on the Niobrara Formation in the Southern PRB. Prior reservoir characterization has been studied to help predict future development in this play, as well as surrounding total petroleum systems that are also thought to be important in the PRB. With an increasing number of studies performed on the Niobrara Formation in the PRB, the Formation is ready to become a well-developed oil and gas play. This is a multidimensional thesis incorporating core descriptions (petrography and porosity), well log data (petrophysics), thermal maturity data, X-ray Florescence (XRF), X-ray Diffraction (XRD), Field Emission Scanning Electron Microscopy (FE-SEM) and pore size analysis to determine the reservoir and source rock potential for oil and gas in the Niobrara Formation. The cyclicity of the chalks and marls within the Niobrara Formation allows for studies to be conducted discovering which intervals are the most prospective based on regional continuity, historical production/shows and thickness. The conclusions of this study will present an outline to characterize the potential for oil and gas reservoirs within the B and C Niobrara benches in the PRB. It will also assist in future research regarding the composition and the oil and gas potential of the Niobrara Formation in the southern PRB. Nine chalk-marl-shale facies were identified in describing the various cores by looking at the lithology, mineralogy, bioturbation, sedimentary structures, and fossil content. The primary reservoir facies include pellet-rich marly chalks and marls, as well as bioturbated marls to marly chalks. SEM photomicrographs indicate that the majority of the pore space is dominated by intergranular pores in the micro to Nano size range. Zones within the B and C Niobrara benches were determined to be the primary reservoir targets based on high carbonate percentage or high quartz percentage, low clay content and high porosity values. The formation also shows very early development of organic porosity. Based on the subsurface mapping, the B bench is thickest through the majority of the area of interest, but does thin to the northeast. The C bench displays a thickening trend through the center of the area of interest. The B and the C Niobrara benches both display promising reservoir characteristics, indicating that these intervals have great potential for hydrocarbon production.
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