Reservoir stimulation design and evaluation of heat exploitation of a two-horizontal-well enhanced geothermal system (EGS) in the Zhacang geothermal field, Northwest China

A bottom hole temperature of 214 degrees C at 4700 m shows good potential for the development of an enhanced geothermal system (EGS) in the ZR2 well, Zhacang geothermal field, China. A reservoir stimulation plan has to be established to optimize the use of this target reservoir, with the objectives of increasing heat extraction and ensuring the service life. In this study, we used the lab parameters, ZR2 well logging data, and inverted in-situ stress data to conduct a numerical investigation to optimize reservoir stimulation and develop geothermal extraction strategies for the granodiorite reservoir at depths of 4100-4700 m. The results indicate that gel-proppant hydraulic fracturing and a two-horizontal-well system are feasible for this tight and unconfined reservoir. An installed capacity of 5.57MW-6.80 MW and total power generation of 1695GW.h are expected under the optimal combination of an injection temperature of 7.2 degrees C, an injection rate of 50 kg/s, and fracture spacing of 50 m during the 30-year operation period. The final production temperature will be maintained at approximately 171.3 degrees C, and the temperature drop is only 10.7%. The proposed geothermal engineering project will reduce greenhouse gas (GHG) emissions by 0.57-1.98 Mt compared to a fossil fuel plant. The levelized cost of electricity (LCOE) is estimated at 0.0413 $/kW.h, which is much lower than the industrial electricity price of Qinghai province; thus, this project has significant development potential from an economic perspective. (C) 2021 Elsevier Ltd. All rights reserved.