A comparison study of reservoir boundary conditions of Enhanced Geothermal Systems (EGS)

The effects of boundary conditions on numerical reservoir prediction of Enhanced Geothermal Systems (EGS) are crucial to EGS modeling while have drawn little attention in previous studies. Based on geothermal characteristics of Gonghe Basin, China, we established a thermal-hydraulic-mechanical coupled model to compare the performance of fractured reservoir under "recharge" boundary conditions with that under "no-flow" during the process of heat extraction. The "recharge" boundary conditions allow fluxes of mass and heat to cross reservoir boundaries, whereas the "no-flow" disallow such fluxes. It is indicated that compared with the fractured reservoir under "no-flow" boundary conditions, that under "recharge" has a greater potential for heat extraction and can be more efficiently utilized. Moreover, the EGS has a longer lifespan under "recharge" boundary conditions than under "no-flow". It is also shown that there is a significant decrease of reservoir temperature under both boundary conditions due to thermal depletion. Our results clearly demonstrate the importance of considering reservoir boundary conditions in evaluating EGS and can be beneficial to the following EGS modeling. (C) 2019 The Authors. Published by Elsevier Ltd.