Characteristic Study On Seepage And Thermal Conductivity Mechanism Of Single Fracture Granite Using Supercritical CO₂ In High Temperature And High Pressure Environment

At present,the exploitation of hot dry rock geothermal energy mainly depends on the enhanced geothermal system.The traditional enhanced geothermal system uses water as the working fluid,but there are disadvantages such as the consumption of water resources and the high consumption of circulating pumping energy,so using supercritical carbon dioxide to replace water as the working fluid in the enhanced geothermal system has become an alternative scheme with its unique advantages.In addition,it is a way to achieve carbon sequestration.In this paper,the seepage characteristics and thermal conductivity mechanism of single-fracture granite are studied by using the self-developed supercritical carbon dioxide rock fracture seepage experimental device,and the seepage heat transfer experiments under different temperatures and confining pressures are designed,focusing on the influence of temperature and confining pressure on the permeability and thermal conductivity of single-fracture granite.Meanwhile,the influence of confining pressure and temperature on rock temperature distribution is simulated by COMSOL Multiphysics software.Relevant conclusions of this paper are as follows:（1）Both hydraulic opening and permeability decrease gradually with the increase of confining pressure and temperature.The lower the temperature,the greater the variation of hydraulic opening and permeability with confining pressure.The lower the confining pressure,the greater the variation of hydraulic opening and permeability with temperature.（2）The heat transfer efficiency decreases with the increase of confining pressure and temperature.At a certain temperature,the heat transfer efficiency is mainly affected by the flow rate.When the confining pressure is constant,the effects of temperature difference and mass flow rate on the heat transfer efficiency cancel each other,and the heat transfer efficiency is mainly affected by the specific heat capacity of supercritical carbon dioxide.（3）The convective heat transfer coefficient decreases with the increase of confining pressure and temperature.The confining pressure affects the convective heat transfer area,and temperature affects the physical properties of the fluid itself.In addition,the increase of opening makes the flow velocity and convective heat transfer coefficient increase.（4）With the increase of confining pressure,the effect of fluid on rock temperature distribution becomes slower and the temperature at the outlet increases.With the increase of temperature,the faster the rock temperature decreases in the process of ScCO₂ injection seepage,the greater the temperature difference between the outlet and the stable seepage.