Numerical investigation of electricity generation potential from fractured granite reservoir through a single vertical well at Yangbajing geothermal field

Deep geological exploration indicates that there is a high-temperature fractured granite reservoir at depth of 950～1350 m in well ZK4001 in the north of Yangbajing geothermal field, with an average temperature of 248 °C and a pressure within 8.01～11.57 MPa; in this well there mainly produces liquid and steam two-phase flow. In this work we numerically investigated the electricity generation potential from the fractured granite reservoir through a single vertical well, analyzed the process and mechanism of the two-phase flow, and evaluated main factors affecting the heat production and electricity generation. The results show that under the reference conditions the system attains a pump power of 0.02～0.16 MW, an electrical power of 2.71～2.69 MW, and an energy efficiency of 68.06～16.34, showing favorable electricity generation performance. During the production period, the bottomhole production pressure gradually decreases, and this makes the pump power increasing and the energy efficiency decreasing. When the bottomhole pressure is lower than the saturated vapor pressure, the liquid water begins to evaporate and the bottomhole wellbore begins to produce the mixture of liquid and steam. Main factors affecting the performance are reservoir porosity, permeability and fluid production rate. Higher reservoir porosity or higher permeability or lower fluid production rate will increase the bottomehole pressure, decrease the pump power and improve the energy efficiency.