Study of the enhanced geothermal system (EGS) heat mining from variably fractured hot dry rock under thermal stress

Formation of enhanced geothermal system provides flow and heat transfer paths for heat extraction in HDR (hot dry rock). Based on the local thermal non-equilibrium theory, the THM(thermal-hydraulic-mechanical) coupling is established to describe the interaction of fluid flow, heat transfer and rock deformation in heat mining process. Besides, the randomly generated fractures are adopted to descript the various fracture network. Firstly, the heat mining processes of variably fractured HDR with different fracture network characteristics are researched. Secondly, heat mining performance of multi-well patterns are compared with that of doublet-well pattern. Finally, effect of the key parameters on heat mining are also investigated. The results indicate that the increase of fracture density enhances flow around and retards thermal drawdown. When the angle between fracture orientation and inlet-outlet connection is 45, the optimal heat mining performance can be achieved. The addition of inlets in multi-well pattern conduces to large-scale utilization, and a reasonable well arrangement can avoid the thermal breakthrough. This study provides the support for EGS (enhanced geothermal system) stimulation and well arrangement to obtain better heat mining performance. (C) 2019 Elsevier Ltd. All rights reserved.