A Review of In Situ Pyrolysis Technologies, Kinetics and Influencing Factors for Oil Shale Based on Thermogravimetric Analysis

As a vital unconventional oil and gas resource, the efficient exploitation of oil shale relies on breakthroughs in pyrolysis conversion technologies. Based on thermogravimetric analysis and related thermal analysis studies, this paper systematically reviews the technologies, kinetics and influencing factors of oil shale pyrolysis, following the framework of “rock properties—pyrolysis technologies and conditions—kinetic characterization—reaction and product formation—engineering factors and responses.” First, typical oil shale deposits, including the Green River (USA), Fushun and Maoming (China), Estonian Kukersite and Brazilian Irati, are compared in terms of kerogen type, mineral composition, oil yield and pyrolysis kinetic parameters. Rock properties are shown to be the fundamental determinant of pyrolysis behaviour. Second, the characteristics of surface retorting (gaseous/solid heat carriers) and in situ pyrolysis (conduction, convection, radiation and reaction-heat heating) are summarized, emphasizing that experimental observations from surface retorting cannot be directly extrapolated to the in situ scale. Third, the applicable conditions and limitations of the Arrhenius, Coats–Redfern, Friedman, FWO and KAS methods are systematically compared. Isoconversional methods (Friedman, FWO and KAS) are shown to effectively capture the dynamic evolution of activation energy with conversion degree, making them more suitable for characterizing the multi-stage and heterogeneous nature of oil shale pyrolysis. Furthermore, hydrocarbon generation pathways and product distribution patterns are analyzed from the perspectives of pyrolysis staging, primary kerogen conversion and secondary cracking. Secondary cracking is identified as the critical process governing oil composition under high-temperature conditions. Finally, the effects of particle size, heating rate, pyrolysis temperature and pressure on product yield and composition are discussed. Future research should advance from “kinetic parameter calculation” toward “product yield prediction,” providing theoretical references for multi-field coupling simulation and engineering-parameter optimization of in situ oil shale pyrolysis.