Study of the Heat Extraction Performance of Integrated Enhanced Geothermal Systems Based on a Novel Semi-Analytical Model

Summary An integrated enhanced geothermal system (EGS) includes vertical wells (i.e., injection wells and production wells), horizontal wells, and multiple hydraulic fractures. Due to the limitations in computational efficiency, numerous studies focus on the heat transfer behavior in the fracture section. However, the thermal interactions of the wellbore section have not been hitherto considered, which can result in inaccurate evaluations of heat extraction performance in EGSs. To solve this issue, we propose a novel semi-analytical model, combining numerical solutions for wellbores and fractures with analytical solutions for geothermal formation. Compared with the traditional numerical models, the proposed model achieves a considerable increase in computational efficiency. Subsequently, we conduct a thorough study to investigate the effect of various parameters on the heat extraction performance of the integrated EGSs. The calculation results show that the heat exchange behavior along the wellbore can significantly influence the temperature change in the fractures and the outlet temperature. Especially in the late production period, the wellbore plays a more important role in increasing the fluid temperature compared with the fracture. A lower injection flow rate, as well as a larger geothermal gradient, is more conducive to the heat absorption of the fluid in the wellbore section. Moreover, the anisotropic thermal conductivity presents a more significant impact on the outlet temperature in the early production. With a given extraction area, there is an optimal fracture number (determined as 6 in this study) beyond which the increase in total heat extraction becomes slight. Keywords enhanced geothermal system, semi-analytical model, heat transfer in wellbore, heat extraction performance, rapid simulation​​​​​​