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Enhancement of Geothermal Exploitation In Qiabuqia Geothermal Area Using A Multilateral Horizontal Well System
Hot dry rock, which is one of the most promising and clean renewable energy which can be developed and utilized through enhanced geothermal systems (EGSs). The horizontal and multilateral well EGS has potential for achieving high heat extraction performance in HDR development. In this paper, multilateral horizontal well system is employed to based on the geological data of the GR1 borehole to study the geothermal exploitation performance of the Qiabuqia geothermal area. The simulation results indicate that in the basal granitic reservoir with a depth of 2650 - 3650 m and a corresponding initial temperature of 151 - 190 ℃, the production temperature reaches 178.4 ℃ and decreases by 8.3% in 20 years under the combination of 50 kg/s of injection flow rate, 60 ℃ of the injection fluid temperature and a 400 m of lateral well spacing. The energy analysis showed that the designed geothermal system could yield an electric power of 3.58 - 4.35 MW, with the flow impedance of 0.207 - 0.313 MPa/(kg/s) and energy efficiency of 2.7 - 4.5 over a 20-year period. The operation of such a system could reduce the total greenhouse gas (GHG) emissions by 0.21 - 0.72 Mt when compared to a fossil fuel plant. The results indicate that the production temperature, and electric power of the multilateral horizontal well EGS are higher than those of conventional double vertical wells EGS. The heat production performance of geothermal reservoir highly depend on the well horizon and branch well arrangement. A large number of branch wells brings flow impedance increase and production temperature decrease due to strong well interference. Therefore, under the same total well length, less branches and large spacing between the branch wells is the basic principle for the design of multilateral horizontal well system. This study can lay the foundations for the future development of the EGS programs with multilateral horizontal well systems at the Qiabuqia geothermal area.