Feasibility study of heat extraction from a closed-loop fractured geothermal reservoir; A multiphysics problem

Geothermal energy is considered as an attractive alternative source of energy in some parts of the world. In general, geothermal systems can be identified as either open- or closed-loop. In an open-loop system, fluid is produced from the subsurface, while there might be some concurrent fluid injection into the reservoir. The loss of working fluid, surface subsidence, formation compaction, and induced seismicity are major shortfalls of the open-loop systems. To address the indicated challenges, closed-loop geothermal systems can be considered as an alternative option. In this method, a working fluid with low boiling point is circulated through the coaxial sealed pipes to extract the stored heat from the formation rock and fluid. To improve the heat extraction from closed-loop wells, we introduce a highly conductive hydraulic fracture to the system to improve the rate of the heat extraction from the surrounding rocks. Considering the multi-physics nature of the heat extraction from such systems, a comprehensive analysis of this problem requires simultaneous modeling of the interactions between fluid flow, heat transfer and rock deformation. A numerical thermo-poro-elastic model is developed using the finite element methods to simulate this problem. The numerical results suggest that fractured wellbore has significantly larger thermal power and cumulative extracted heat than the unfractured wellbore in the proposed closed-loop configuration.