Numerical Simulation Of Multi-Field Coupling Process And Analysis In Geothermal Energy Mining

Hot dry/wet rock(HDR/HWR)is a storage form of deep geothermal energy,which has varied advantages:high energy,non-pollution and so on.Many countries have carried out HDR/HWR geothermal power generation experiment and business operation.It will provides guiding suggestions for the development and utilization of high-temperature geothermal energy in China if we learn the advanced experience abroad,carry out numerical simulation and analysis of hydraulic fracturing and geothermal energy extraction.Having much research on geothermal system and based on the multi-field coupling theory,this paper carried out the numerical simulation and analysis of reservoir reconstruction and geothermal energy exploitation.The main contents and conclusions of this paper are as follows:(1)The discontinuous permeability of fractured rock mass can generally be equivalent to a continuous porous medium which has the same permeability coefficient tensor.In this paper,two methods to calculate permeability are introduced.The first one is to calculate permeability by the crack width.The second one is to establish the relationship between the permeability and the main stress difference,then the formula is substituted into COMSOL to carry out numerical simulation.(2)The mathematical model and calculation method of two or three field coupling for thermal-hydraulic-mechanical are introduced,and corresponding numerical examples is established.The numerical results show that the stress has little effect on the temperature distribution,but it has great influence on the distribution of water head.When stress increases seepage velocity,heat exchange between water and surrounding rock increases,resulting in redistribution of temperature field of surrounding rock.(3)Based on the field data of Soultz geothermal field,a THM coupling model of variable permeability is established to simulate the change of permeability and the reconstruction of temperature field during hydraulic fracturing.The analysis results show that thermal stimulation has an important influence on fracking.(4)A geothermal energy mining model was established to analyze the influence of reservoir lithologic parameters and production parameters on the production well temperature,reservoir temperature distribution and heat extraction efficiency.Finally,the parameters of optimized mining can be determined.