Changes of the Multiscale Pore Structure and Connectivity of Organic-Rich Shale during Hydrous Pyrolysis under Different Temperatures and Pressures

Medium–low maturity shale reservoirs are rich in resources and have significant oil production potential, attracting widespread attention. The pore structure and connectivity of organic-rich shale were examined at different temperatures and pressures. In conjunction with mercury intrusion porosimetry and low-temperature N₂ and CO₂ adsorption experiments, organic-rich shale multiscale pore structure alterations were examined. Nuclear magnetic resonance (NMR) investigations were used to assess the pore connectivity. Additionally, the primary mechanisms affecting the pore structure and connectivity in shale subjected to supercritical water were thoroughly explored. The findings revealed that the pore volume reaches 0.52711 cm³/g under supercritical water at 425 °C, which is 2.7 times larger than that of the original shale. Mesopores, transition pores, and micropores are generally more developed in supercritical water environments than in an aqueous medium at a pressure of 15 MPa, enhancing shale connectivity and permeability. Research findings indicate that the pyrolysis of shale organic matter is the key mechanism for pore structure alterations and improved connectivity.