Research On Mechanism Of Artificial Thermal Reservoir Improving Permeability Under Thermal Shock

Clean and renewable geothermal resources are opening up a new trend of geothermal energy development all over the world due to their large reserves,wide reserves,and almost no pollution in the development process.However,geothermal energy is mainly stored in dense and low-permeability dry hot rocks located several kilometers deep in the earth.How to build artificial heat storage in dry hot rocks with low cost and high efficiency has always been the focus and difficulty of the promotion of this technology.Therefore,research on the physical properties and permeability of hot dry rock reservoirs is of great significance to the construction of artificial thermal storage and the promotion of geothermal resources development and utilization.Based on the Qinghai Gonghe Granite Demonstration Project as the engineering background,this paper selects the dry hot rock in the Qinghai Gonghe Basin as the research object.Through physical tests,the physical properties and permeability changes of granite after different thermal shocks are analyzed and studied,and the permeability of granite under thermal shock is studied.The law of characteristic evolution.At the same time,COMSOL Multiphysics5.4 finite element simulation software was used to construct a thermo-fluid-solid coupling numerical calculation model to analyze the seepage field,temperature field,and stress field of the granite model under fluid migration,and to study the reservoir height,fluid temperature and the influence of velocity on reservoir damage,compare the area and distribution characteristics of reservoir damage area.Draw the following main conclusions:(1)After the granite specimen is naturally cooled in the air at 600 ℃,its permeability increases with the increase of rock temperature,and abrupt change occurs at 500-600 ℃.The change of granite with external stress after high temperature can use the same exponential function.Indicates that the temperature sensitivity coefficient is defined,and the exponential relationship between the rock temperature and the temperature sensitivity coefficient is obtained.(2)The permeability of the granite specimens under the thermal shock of 20 ℃、60 ℃and100 ℃ water at 600 ℃ increased in different degrees,and the granite specimens under the impact of 20 ℃ water and 100 ℃ than 60 ℃ water impact the cooling rate is more significant.It can be seen that the thermal shock of the granite specimens in water at 20 °C and 100°C is more significant than that in water at 60°C.(3)Through the numerical calculation of COMs OL5.3 software,in the process of thermal shock,the temperature of the rock surface decreases rapidly and then slowly.The simulation found that the temperature gradient and thermal stress in the rapid cooling stage of the granite in 100 ℃ water thermal shock cooling are the largest,and the thermal shock damage is the strongest.The calculated thermal shock factor and the permeability of the granite under thermal shock can be very good.The fitting relationship.(4)After water injection and heat recovery,the temperature field and stress field inside the rock mass change with the seepage field,and the internal heat of the rock mass is taken away by the fluid,causing the temperature of the rock mass to decrease and forming a temperature gradient,causing thermal shock damage.The water head,fluid temperature,and reservoir height all cause different damages to the rock mass due to thermal shock.