When high-temperature steam is used as a medium to pyrolyze organic-rich shale, water steam not only acts as heat transfer but also participates in the chemical reaction of organic matter pyrolysis, thus affecting the generation law and release characteristics of gas products. In this study, based on a long-distance reaction system of organic-rich shale pyrolysis via steam injection, the effects of steam temperature and reaction distance on gas product composition are analyzed in depth and compared with other pyrolysis processes. The advantages of organic-rich shale pyrolysis via steam injection are then evaluated. The volume concentration of hydrogen in the gas product obtained via the steam injection pyrolysis of organic-rich shale is the highest, which is more than 60%. The hydrogen content increases as the reaction distance is extended; however, the rate of increase changes gradually. Increasing the reaction distance from 800 to 4000 mm increases the hydrogen content from 34.91% to 69.68% and from 63.13% to 78.61% when the steam temperature is 500 °C and 555 °C, respectively. However, the higher the heat injection temperature, the smaller the reaction distance required to form a high concentration hydrogen pyrolysis environment (hydrogen concentration > 60%). When the steam pyrolysis temperature is increased from 500 °C to 555 °C, the reaction distance required to form a high concentration of hydrogen is reduced from 3800 to 800 mm. Compared with the direct retorting process, the volume concentration of hydrogen obtained from high-temperature steam pyrolysis of organic-rich shale is 8.82 and 10.72 times that of the commonly used Fushun and Kivite furnaces, respectively. The pyrolysis of organic-rich shale via steam injection is a pyrolysis process in a hydrogen-rich environment.

In this paper, the evolution of thermal conductivity, wave velocity and microscopic crack propagation both parallel and perpendicular to the bedding plane in anisotropic rock oil shale were studied at temperatures ranging from room temperature to 600 °C. The results show that the thermal conductivity of the perpendicular to bedding direction (K_PER) (PER: perpendicular to beeding direction), wave velocity of perpendicular to bedding diretion (V_PER), thermal conduction coefficient of parallel to beeding direction (K_PAR) and wave velocity of parallel to beeding direction (V_PAR) (PAR: parallel to bedding direction) decreased with the increase in temperature, but the rates are different. K_PER and V_PER linearly decreased with increasing temperature from room temperature to 350 °C, with an obvious decrease at 400 °C corresponding to a large number of cracks generated along the bedding direction. K_PER, V_PER, K_PAR and V_PAR generally maintained fixed values from 500 °C to 600 °C. 400 °C has been identified as the threshold temperature for anisotropic evolution of oil shale thermal physics. In addition, the relationship between the thermal conductivity and wave velocity based on the anisotropy of oil shale was fitted using linear regression. The research in this paper can provide reference for the efficient thermal recovery of oil shale, thermal recovery of heavy oil reservoirs and the thermodynamic engineering in other sedimentary rocks.

Efficient heat transfer is essential for the in-situ conversion of steeply dipping oil shale reservoirs. In this study, a superheated steam-driven integrated multi-branch well system was proposed, and a coupled thermo-hydro-chemical-mass transport model considering reservoir anisotropy was established in COMSOL Multiphysics-5.6 to investigate heat transfer characteristics and evaluate the effects of key engineering parameters. The numerical model was validated through comparison with an analytical solution and previously published numerical results. The results show that superheated steam preferentially migrates through hydraulic fractures and bedding-parallel high-permeability pathways, resulting in anisotropic heat transfer. Continuous steam injection gradually forms a connected high-temperature region, and most of the reservoir exceeds 500 °C after approximately 600 days. Compared with the conventional well arrangement, the proposed well system achieves more uniform reservoir heating and enlarges the effective pyrolysis region. Parametric analysis indicates that the highest thermal performance among the investigated cases is obtained with a heating well length of 22.5 m, while increasing the inter-well angle, fracture number, and fracture width enhances heat transfer and kerogen conversion. Among the investigated cases, the configuration with three hydraulic fractures achieves the best performance, with the high-temperature region (>500 °C) exceeding 80% of the reservoir after 400 days and a cumulative hydrocarbon production of approximately 4.7 × 10⁷ mol. Sensitivity analysis further demonstrates that fracture-related parameters exert a greater influence on reservoir thermal performance than heating well length and inter-well angle. These findings provide theoretical guidance for the design and performance evaluation of integrated multi-branch well systems for the efficient in-situ conversion of steeply dipping oil shale reservoirs.