Evolution mechanism of dynamic thermal parameters of shale

Abstract

In situ conversion is a process that converts organic matter into light oil and gas via underground in situ heating, which leads to changes in shale material composition and dynamic changes in thermal field parameters. At present, there is a lack of understanding of the evolution behavior and mechanism associated with dynamic thermal field parameters of shale. The dynamic thermal field parameters of shale with different organic matter abundances at various temperatures, orientation, heating rates, and pressures are obtained using an improved surface thermal source method and the laser flash method. The results show that the changes in dynamic thermal field parameters of shale are mainly controlled by organic matter abundance. The thermal diffusivity of shale decreases with the increase in temperature, and the thermal conductivity presents an “M-shaped” dynamic evolution with temperature. The thermal conductivity and thermal diffusivity of shale parallel to bedding are higher than those shale that are perpendicular to bedding. The rapid heating rate decreases thermal diffusivity above 200 °C, which is believed to be due to the instantaneous weight loss rate at high temperatures. The thermal conductivity and thermal diffusivity of shale parallel and perpendicular to bedding show the following two-stage evolution characteristics with the increase in pressure. Through matrix analysis, the bi-directional thermal conductivity model of shale with different organic matter abundances under different temperature and pressure conditions is constructed, which provides accurate parameters for studying dynamic thermal field evolution and efficient heat transfer during in situ conversion.