The Numerical Simulation And Exploitation Optimization Theory Of Enhanced Geothermal System

The change of the world energy pattern makes the dry-hot rocks with large reserves and small pollution have attracted much attention,in particular,the enhanced geothermal system(EGS)for efficient dry-hot rock development has been widely sought after by researchers.In order to study the changing process of each physical field during the EGS mining process,numerical simulation is used to evolve the complicated changing law of seepage field,temperature field and stress field caused by its development process,and to solve its thermohydro-mechanical(THM)Coupling issues are necessary.At the same time,due to the special thermophysical properties of supercritical carbon dioxide,studying its role in the thermal recovery of EGS is of great significance for the efficient development of EGS and environmental protection.Based on the seepage field,temperature field and stress field equation,the THM coupling mathematical model of enhanced geothermal system is established.According to the function relationship of fluid density,viscosity,atmospheric heat capacity and thermal conductivity under different temperature and pressure conditions,a discrete fracture network model closer to the actual reservoir was established by finite element simulation method to simulate the change of seepage flow field,temperature field and stress field in the reservoir.The effect of different injection parameters on EGS heat transfer efficiency results show that the higher the injection pressure,the lower the production pressure and the higher the injection temperature,the higher the flow rate and the lower the temperature in each production well.In addition,the study found that well locations and pressures in each production well had a significant impact on EGS heat transfer efficiency.Therefore,based on the SPSA optimization algorithm,an EGS mining optimization model with net heat transfer and net power generation as objective functions is established respectively to determine the optimal well position and pressure value of each production well under the function optimal value.According to the special thermophysical properties of supercritical carbon dioxide,numerical simulation is used to compare the flow rate and temperature change of EGS production wells in both cases of water and supercritical carbon dioxide as the heat transfer medium.The results show that the production flow rate of all wells increased to about 4 times Compared to water.At the same time,it is found that the strong fluidity of supercritical carbon dioxide makes the production flow rate and temperature change more sensitive to different injection parameters.The results of EGS using optimization algorithm to optimize the net heat exchange as the objective function show that the EGS has better heat transfer range,more uniform heat transfer and more net heat transfer after optimization.