Effect of Local Non-Thermal Equilibrium and Thermal Dispersion On Heat Extraction Performance of Egs Based On Modified Edfm

The effective development of hot-dry-rock relies on the complex fracture network formed by the enhanced geothermal system . Due to the complex flow and heat transfer mechanisms between tight matrix and different fractures, it is a challenge for accurate numerical simulation. It is necessary to clarify the influence of complex heat transfer mechanisms and evaluate the sensitivity of parameters required for the model.Based on the modified enhanced direct fracture model method, the local boundary element method is used to accurately calculate the mass and heat transfer between the matrix and the fracture.Unlike the traditional model, this model considers the local thermal non-equilibrium assumption and the influence of thermal diffusion on the heat transfer process. The applicable conditions of the heat transfer mechanism and the importance of the main input parameters are analyzed. The results show that the local thermal non-equilibrium assumption and thermal dispersion can improve the accuracy of the mass and heat transfer process simulation. The low matrix permeability, low fracture permeability, the significant difference in matrix fracture porosity, the sizeable thermal diffusion coefficient of rock and small convective heat transfer coefficient, and the local non-thermal equilibrium hypothesis mechanism should be considered more. The higher the matrix and fracture permeability, the higher the cumulative heat produced. The more significant the underestimation of the early water temperature and cumulative heat produced without considering the thermal dispersion effect, the more the thermal dispersion effect should be considered. This study formed an evaluation method for the critical heat transfer mechanism and key parameters of complex matrix and fracture. The applicable limits of the complex heat transfer mechanism were given, which provided a reference for collecting and collating field data.