The evolution of pore structure during in situ underground exploitation of oil shale directly affects the diffusion and permeability of pyrolysis products. In this study, on the basis of mineral analysis and thermogravimetric results, in combination with the low-pressure nitrogen adsorption (LPNA) and mercury intrusion porosimetry (MIP) technique, the evolution of pore structure from 23 to 650 °C is quantitatively analyzed by simulating in situ pyrolysis under pressure and temperature conditions. Furthermore, based on the experimental results, we analyze the mechanism of pore structure evolution. The results show the following: (1) The organic matter of Fushun oil shale has a degradation stage in the temperature range of 350–540 °C, and there is no obvious temperature gradient between decomposition of kerogen and the secondary decomposition of bitumen. The thermal response mechanisms of organic matter and minerals are different in each temperature stage, and influence the change of pore structure. (2) Significant changes occur in pore shape at 350 °C, where thermal decomposition of kerogen begins. The ink-bottle pores are dominant when the temperature is less than 350 °C, whereas slit pores dominate when the temperature is greater than 350 °C. (3) The change in pore structure of oil shale is much less significant from 23 to 350 °C. The pore volume, porosity, and specific surface area (SSA) of samples increase rapidly with temperature varying from 350 to 600 °C. The variation of each parameter is dissimilated from 600 to 650 °C: the porosity and pore volume increases with a small gradient from 600 to 650 °C, and SSA decreases significantly. (4) The lithostatic pressure does not cause change in the evolution discipline of the pore structure, but the inhibitory effect on the pore development is significant.

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.