Pore Structure Alteration of Organic-Rich Shale with Sc-CO2 Exposure: the Bakken Formation

The interaction between various components of shale and CO 2 is interesting since it alters pore structures that are the governing factor in different projects. In this study, samples from the Upper (UB) and Lower (LB) Bakken were exposed to super critical CO 2 for 3, 8, 16, 30, and 60 days. Then, chemical and structural changes during the process of exposure were evaluated with different methods, including X-ray diffraction (XRD), gas adsorption (N 2 ) isotherm, and fractal theory. The results showed that quartz increased in the UB and decreased in the LB, whereas clay and other minerals had a decreasing trend for both UB and LB after CO 2 saturation. After saturation, the pore size distributions (PSDs) were skewed to smaller pore sizes at all diameters, indicating that the number of pores decreased as a result of the reaction. Fractal dimension has an increasing trend as the samples were exposed to CO 2, where the roughness of the pore surface and the complexity of pore structure increased after 8–16 days of CO 2 saturation and then decreased after 30–60 days of saturation to become more homogeneous. Furthermore, clay mineral dissolution enhanced the pore volume, and carbonate dissolution increased the specific surface area. These results provided experimental evidence to further test the mechanisms of geological storage of CO 2 in organic-rich self-sourced plays.