Numerical simulation of heat extraction performance in enhanced geothermal system with multilateral wells

A novel enhanced geothermal system with multilateral wells is proposed to extract heat from hot dry rock in this study. For this EGS, one main wellbore is drilled to hot dry rock. Several injection and production multilateral wells are side-tracked from the main wellbore in upper and lower formation, respectively. An insulated tubing is installed in the main wellbore. The working fluid is injected from the annulus and injection wells and then extracts heat from the hot dry rock reservoir. Subsequently, the working fluid is produced from production wells and returns to surface through the insulated tubing. In this study, an unsteady-state fluid flow and heat transfer 3D model is presented to investigate the heat extraction performance of the multilateral-well EGS. The model is verified by a known analytical solution. The temperature and velocity fields of the multilateral-well EGS are analyzed and heat extraction performances of four various well types are compared. The results indicate that the output thermal power, production temperature, heat extraction ratio and accumulative thermal energy of the multilateral-well EGS are higher than those of conventional double vertical wells EGS. This study provides a better alternative for EGS to obtain greater heat extraction performance.