The Magnetic Resonance Imaging (MRI) log and the Nuclear magnetic resonance (NMR) are resourceful in addressing various scientific questions in petroleum geology, and they have been universally utilized in estimating total porosity due to its repeatability. Notwithstanding, the field applicability of NMR in lieu of MRI logs to estimate total porosity, have not been fully explored. The objective of our study is to develop a novel correlation between the NMR core analyses performed in the laboratory and the field MRI logs. In this study, firstly, we examined various core samples using 2MHz Geospec NMR core analyzer, and our results are compared to results from magnetic resonance imaging (MRI) log taken at 1MHz. Secondly, we performed a detailed analysis of the MRI logs, and NMR core analysis of Bakken Formation. We then evaluated the petrophysical properties of the investigated cores including its porosity, water saturation, and permeability. Our results show that there is a reasonable degree of concordance between the compared investigated results. The results from our study provided a more efficient correlation between MRI log and NMR core by considering the differences in sample volume and difference in frequency.
The Bakken Formation is one of the most prolific unconventional shale plays in North America (EIA, 2019). This formation was deposited from the Late Devonian to Early Mississippian in the Williston Basin and overlies portions of North Dakota, Montana in the United States, and portions of Manitoba and Saskatchewan in Canadian Provinces (Fig. 1). Bakken consists of four members; the upper and lower member which are black organic-rich shales, the middle member, and Pronghorn members are mixed siliciclastic and carbonates. The Lower Bakken Shale overlies the Pronghorn Member or, where the Pronghorn is absent, it rests uncomfortably upon the Three Forks Formation and overlain by the Lodgepole Formation (Webster, 1984; Meissner, 1978). The upper and lower Bakken are the source rocks while the middle member serves as a reservoir for oil produced from the upper and lower Bakken (Lefever et al., 1991; Nordeng, 2009; Nesheim, 2019) and has low porosity and permeability, particularly for a reservoir rock. Bakken shales exhibit high gammaray response as a result of adsorption of uranium over an extended period from seawater under reducing conditions, hence are easily recognizable and used for correlation purposes. Well-logging tools are used extensively in the petroleum industry to identify physical properties of rocks downhole, for example, resistivity, density which are then converted to provide petrophysical properties of interest (permeability, porosity, oil and gas zone). Nuclear Magnetic Resonance (NMR) is a method used extensively in petroleum geology to total porosity and to measure the pore size distribution (McKenon et al., 1999.)
