Experimental investigation on the anisotropic evolution of the temperature field in oil shale during in-situ conduction heating

The inherent anisotropy of oil shale significantly influences heat transfer efficiency during in-situ conduction heating, yet its spatiotemporal evolution and microscale mechanisms remain poorly understood. In this study, a large-scale physical model of an oil shale enclosure (270 mm × 220 mm × 200 mm) was constructed under simulated in-situ stress conditions (6 MPa axial load). The experimental system integrated a 35-point temperature sensor array, infrared thermal imaging, and a dynamic pore pressure acquisition unit to synchronously capture the spatiotemporal evolution of three-dimensional temperature and pressure fields. Thermal conductivity in both the parallel and perpendicular bedding directions over the range of 25–600 °C was measured using high-temperature laser flash analysis. Additionally, micron-scale CT scanning was employed to characterize the spatial distribution of minerals, organic matter, and fractures, enabling the establishment of a mechanistic link between microstructural features and macroscopic heat-transfer behavior. Results show that, in the parallel-to-bedding plane, the temperature field exhibits concentric isotherms centered on the heat source, indicating isotropic conductivity due to the random microscale distribution of minerals and kerogen. In contrast, in the perpendicular-to-bedding plane, heat transfer efficiency is markedly reduced, with infrared thermography revealing oblate elliptical isotherms—major axis parallel to bedding—attributed to directional sedimentary structures and fracture networks. At ambient temperature, the parallel thermal conductivity (1.99 W·m -1 ·K -1 ) was 2.5 times higher than the perpendicular value (0.81 W·m -1 ·K -1 ), with the disparity increasing to 3.2-fold at 550 °C. Conduction heating alone generated a maximum pore pressure of only 0.025 MPa at ∼640 °C, insufficient to drive hydrocarbon migration. • Measured anisotropic thermal conductivity of oil shale from 25–600 °C. • Concentric vs. elliptical isotherms in parallel and perpendicular bedding. • Microstructure controls anisotropic heat transfer efficiency in conduction heating.