Heat extraction performance analysis of a multilateral wells exploitation system with super-long gravity heat pipe

Super -long gravity heat pipe (SLGHP) system has previously been proven as an environmental and efficient technology in exploiting hot dry rock. This study proposed a multilateral -well SLGHP system to achieve the purposes of improving heat extraction performance and fully utilizing fractured reservoirs. The heat extraction performance was investigated by establishing a 3D thermal-hydrologic (TH) coupling model. It is found that, compared to traditional single -well SLGHP system, after 30 years of operation, multilateral -well SLGHP system has improved the heat extraction rate by 38.1 kW and increased the heat compensation by 61 x 1012 J. The utilization ratio of geothermal reservoirs has been improved by 8.1%. In addition, the effects of different well layouts on heat extraction performance are also studied. Injection wells at the top of fractured reservoir increase the heat extraction rate by 6.4 kW compared to placing them in the bottom area. The relative changes of wellbore location in fractured reservoirs have slight effects on heat extraction performance. This study could provide good suggestions for the SLGHP system to obtain better heat extraction performance.