High-temperature water vapor (H2O) and carbon dioxide (CO2 ) improved the yield and quality of shale oil during oil shale pyrolysis. Aiming to fill knowledge gaps regarding the kinetic mechanism of oil shale pyrolysis in different atmospheres, the pyrolysis behavior and kinetics of Jimusar (JM) oil shale with H2O, CO2 and N2 injections were fully studied in this paper. The results revealed that compared with the N2 injection, the presence of both H2O and CO2 increased the mass loss and mass loss rate, advanced the initial precipitation temperature as well as peak temperature and moved the pyrolysis zone to the low-temperature zone, indicating that both H2O and CO2 injections promoted the pyrolysis behavior of oil shale. The comprehensive release characteristic index of volatiles during oil shale pyrolysis at the heating rate of 20 °C/min with H2O and CO2 injections increased by 37.02% and 18.94%, respectively, which significantly improved pyrolysis reactivity; so, the effect of the H2O injection was higher than that of the CO2 injection. The average activation energy of Jimusar oil shale pyrolysis was as follows: the first stage < the second stage < the third stage. During oil shale kerogen pyrolysis (the second stage), the activation energies with N2 , CO2 and H2O injections exhibited an initial rising trend, then a decreasing trend followed by a constantly decreasing trend and a fluctuating trend with an increase in the conversion rate, respectively. The presence of H2O and CO2 changed the pyrolysis mechanism of oil shale kerogen from a first-order model to a diffusion model. The kinetic mechanism functions of oil shale pyrolysis with N2 , CO2 and H2O injections were f(α) = 1–α, f(α) = [–ln(1–α)]–1, and f(α) = 1.5(1–α)2/3[1–(1–α)1/3]–1, respectively. The pyrolysis conversion curves of Jimusar oil shale with N2, CO2 and H2O injections obtained from the kinetic parameters were consistent with the experimental curves.
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