Source rocks that are organic-rich have varying mineralogical composition and complex rock fabric. In this study, we aim to characterize the immature and mature Bakken shale's microstructural and elastic properties using, respectively, advanced laboratory analysis, well log data, and rock physics modeling. We perform geochemical and source rock analysis to estimate the total organic carbon (TOC) and organic matter type, followed by an X-ray diffraction analysis (XRD) to obtain the mineral composition with the corresponding volume fractions. Then, we conduct a pore-scale study with NMR T2 and SEM imaging. Finally, we estimate the elastic properties using well log data and rock physics modeling. The results obtained from this study contribute to a better understanding of the source rock microstructural and elastic properties whether in the context of petroleum geology or engineering. Using our approach presented in this study, conclusions can be drawn that there is a need to investigate how the organic content and maturity impact the geophysical properties in source rocks.
Bakken Formation is one of the most prolific unconventional shale plays in the Williston Basin. It was deposited during the Late Devonian to Early Mississippian in the Williston Basin. Bakken is underlain by the Three Forks Formation and overlain by the Lodgepole Formation (Murphy, E C and Nordeng, S H and Juenker, B J and Hoganson, 2009). Bakken Formation is divided into three main members: upper and lower members are black organic-rich shales, and the middle member consists of mixed siliciclastic (LeFever, Julie A and Martiniuk, Carol D and Dancsok, Edward FR and Mahnic, 1991; Lefever, 1990). The Pronghorn is the fourth member of the Bakken Formation but does not exist in all locations of Bakken and not present in the studied wells hence was not discussed in this paper. The Bakken Petroleum System consists of source rocks that have been buried to depths and temperatures that have generated significant volumes of oil. Bakken Shales are characterized by a low porosity, low density, and low permeability (Sarg, 2011; Sorensen et al., 2017; Vernik & Nur, 1992).