Experimental Investigation on Composition and Pore Structure Evolution of Organic-Rich Shale via Supercritical Water

Abstract

In in situ transformation of organic-rich shale, the evolution of shale composition and internal pore structure not only is directly related to the heat and mass transfer process but also affects the flow and migration of pyrolysis products in shale pores. In this study, the influence of high-temperature and high-pressure N 2 and supercritical water on shale pyrolysis process was compared. The results illustrated that the specific surface area of a shale under N 2 was lower than that under supercritical water. As a pyrolysis medium, supercritical water is more favorable to the development of pores in a shale. As the supercritical water temperature increased, the ratio of the micropores to mesoporous pores changed, leading to a significant increase in the average pore size. The expansion of the pores inside a shale and the development of effective pores are conducive to the formation of more seepage channels inside the shale, thus increasing the connectivity of the shale matrix. In addition, the porosity of the shale under supercritical water increased from 7.0182% at room temperature to 53.1124% at 450 °C, and the porosity increased by 7.6 times, which indicated that the supercritical water temperature could control the change of shale porosity. These phenomena highlight the potential of supercritical water application in in situ shale transformation.