As a typical unconventional resource located in North America, Bakken Formation has become one of the largest shale oil plays in the world. Pore structures and geochemical properties of the shale rocks are important parameters affecting the storage ability and mechanical properties. In this paper, we collected four shale rocks from Bakken Formation for the analysis. We applied SEM to qualify the microstructures of the shale rocks and then analyzed their mineral compositions by using EDX (Energy-dispersive X-ray spectroscopy). For the geochemical properties, Rock-Eval 6 pyrolysis and optical microscopy armed with reflected white light and UV light were used to get the chemical information of the samples such as organic richness, kerogen type, and thermal maturity. We also cleaned the samples to study the impact of the OBM (oil based mud) on the geochemical properties. The results showed that various pores structures exist in the shale rocks. Shale rocks in Bakken Formation have high TOC. VRo and Tmax indicate that the organic matter is in the oil window and consists of a mixture of Type II and Type III (oil/gas prone). The samples after cleaning have smaller TOC values and S1, S2 values.
Due to the depletion of the conventional resources and increasing energy demand, unconventional reservoir plays are becoming the important contributions to the world oil and gas total production (Liu et al., 2017). The Bakken Formation, located in the Williston Basin in Montana, North Dakota, and southern Saskatchewan is now the second largest oil field in the US and one of the biggest shale oil fields in the world. Based on the lithology difference, The Bakken Formation can be divided into three members. Upper and Lower Bakken Formation are world-class source rocks and the published estimates of oil generated from the source rocks range from 10 to 400 billion barrels (Sonnonberg et al., 2011). Pore structure properties analysis can assist in accurately understanding the storage and migration properties of the gas and oil while geochemical analysis can help us to assess the quantity, quality, and thermal maturity of the sedimentary organic matter (Carvajal-Ortiz and Gentzis, 2015). In this paper, we picked samples from the Upper and Lower Bakken Formation. We applied SEM to visualize the pore structures and utilized Rock-Eval and vitrinite reflectance to characterize the geochemical properties.
