Evaluation of thermal properties of geothermal reservoir rocks under high temperature and stress

Abstract

The thermal physical parameters of rocks are the main controlling factors of the temperature field in geothermal engineering. Firstly, the thermal conductivity of Republican granite, Kangding granite, and Songliao sandstone at different high temperatures and axial stress loading were determined based on the steady-state plate method and the mechanism of the evolution of thermal conductivity for rocks with different porosity was further analyzed. Secondly, the evolution of thermal expansion coefficients of the three types of rocks at ultra-high temperatures was determined. Finally, the evolution of the specific heat capacity of the three types of rocks at different temperatures was determined based on the hybrid cooling method. The study shows that the thermal conductivity of all three types of rocks decreases slightly with increasing temperature and increases slightly with increasing stress and that the thermal conductivity of rocks with high porosity is more sensitive to stress and decreases with further increase in stress; the thermal storage capacity and thermal deformation behavior of all three types of rocks increase with increasing temperature. In particular, the larger the mineral grains, the more significant the thermal deformation behavior of the rocks. This study helps to provide a basis for the design and construction of geothermal projects and enriches the study of rock thermal properties.