Influence of Temperature and Pressure on Hydrocarbon Generation During Oil Shale In Situ Conversion (ICP)

Temperature and pressure are critical controlling parameters in the in situ conversion process (ICP) of oil shale. Clarifying the mechanisms governing organic matter pyrolysis is essential for reliably extrapolating laboratory findings to geological conditions. This review systematically summarizes the effects of temperature and pressure on shale pyrolysis and on hydrocarbon generation kinetics. Temperature is the primary factor controlling pyrolysis rates and product distribution, with an optimal temperature window enhancing shale oil yield while suppressing secondary cracking. Low heating rates favor thorough pyrolysis, although their influence on reaction pathways is generally overlooked in current kinetic models. Pressure effects are stage-dependent: during organic matter conversion, they are minor, whereas, in the product expulsion stage, high pressure inhibits hydrocarbon expulsion, prolongs residence time, and promotes secondary cracking, thereby reducing overall oil yield while increasing light fractions. Discrepancies in reported pressure effects arise from variations in experimental systems, sample forms, and medium conditions. The coupling of temperature and pressure is synergistic rather than additive. Given that current kinetic models largely neglect pressure and heating-rate effects, and that temperature–pressure coupling mechanisms remain unclear, future research should focus on thermal simulation experiments across wide ranges of pressures and heating rates, complemented by ReaxFF molecular dynamics to elucidate reaction pathways and guide kinetic model development. Further in situ experiments under high-temperature and high-pressure conditions are needed to characterize coupled pore evolution and fluid migration. Ultimately, integrated thermo-hydro-mechanical-chemical (THMC) models should be developed to capture hydrocarbon generation, retention, and expulsion, providing a robust theoretical framework for optimizing ICP technology.