A modified 3D-EDFM method considering fracture width variation due to thermal stress and its application in enhanced geothermal system

Abstract

The successful utilization of hot dry rock is contingent upon the implementation of the development of the enhanced geothermal system (EGS) to create a complex fracture network.However, the fracture is affected by thermal stress, which results from the temperature difference between low-temperature fluid and high-temperature rock. To address this issue, a dynamic model of fracture width that takes thermal stress into account has been proposed. This model is based on the modified three-dimensional embedded discrete fracture model (EDFM) method and is solved by finite volume method coupling local boundary element.This model is based on the modified three-dimensional EDFM method and is solved by finite volume method coupling local boundary element. The proposed method has been validated through comparing with results obtained from commercial finite element software. Furthermore, the method is applied to the simulation of EGS to analyze the parameter sensitivity of the mass and heat transfer process. The results indicate that neglecting the impact of thermal stress on fracture width leads to an underestimation of produced energy. The shape and inclination angle of fractures significantly affect the mass and heat transfer in the reservoir.Moreover, the shape and inclination angle of fractures significantly affect the mass and heat transfer in the reservoir. A larger heat exchange area results in faster temperature decreases and increased heat energy production. High thermal diffusion coefficients improve the performance of EGS, while an increase in the thermal expansion coefficient of rock accelerates thermal breakthrough and enhances heat energy production. It has been found that maintaining a small pressure difference between injection and production and using low-temperature injection water can prolong the system lifetime and increase the final heat energy produced. This study presents an efficient numerical simulation method for mass and heat transfer in fractured reservoirs, expands the original EDFM method's application range and enhances calculation accuracy..