Thermal effect on pore characteristics of shale under inert and oxic environments: Insights on pore evolution

Abstract Kerogens are the primary hosts of micropores and mesopores which determine the gas storage capacity in shale. The prime focus of this study is to assess the mode of organic pore development in shale under different heating environments. The clay-rich shales display a reduction in the aliphaticity index from 100 °C to 300 °C, indicating structural changes in kerogen at the higher temperature. Scanning electron microscopic images reveal an increasing interconnectivity of organic pores with increasing temperature. Low pressure gas adsorption analysis confirms appearance of newer micropores and coalescence of micropores into mesopores at 300 °C. Nevertheless, the changes in pore characteristics occur differently when the heating modes are different. Oxic heating causes a noticeable increase in the surface area, and pore volume. Along with that, the pore size distribution peaks become sharper and of higher magnitude. Upon anoxic heating, the presence of bitumen in pores results in pore-blockage, leading to a reduction in surface area and pore volume. The surface roughness does not change in newly formed coarser mesopores upon combustion, whereas, with increasing temperature, the fractal dimensions of both finer and coarser pores suggest new pore formation during inert heating.