Geothermal energy has the potential to become a widespread reliable energy source. Traditionally, the conventional geothermal systems require a continuous supply of water, which limits their application in dry areas and causes risks such as induced seismicity. To circumvent this shortcoming, closed-loop geothermal systems not requiring water circulation have been proposed in recent years. However, heat extraction efficiency of closed-loop systems is limited due to the small heat exchange area between working fluid in the wellbore and surrounding rock. Therefore, it is of great importance to explore designs to improve heat extraction efficiency, thus increasing economic benefits. To enhance heat extraction efficiency, a fractured closed-loop geothermal system (FCLGS) is discussed in this paper. The objective of FCLGS is to improve heat transfer from hot rock to the wellbore by a conductive fracture. We utilize microscale numerical analysis to determine the best combination of proppants and coatings that yields the highest effective thermal conductivity of a proppant bed. To evaluate heat extraction performance of the FCLGS, a coupled three-dimensional model was established utilizing the finite element method and numerical simulations were conducted. Based on simulation results, the effects of different design factors on heat extraction were determined.

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