Numerical simulation of electricity generation potential from fractured granite reservoir using the MINC method at the Yangbajing geothermal field

Abstract

Field tests indicate that after hydrofracturing the fracture spacing in an Enhanced Geothermal System (EGS) reservoir may be within 0.33–300 m. For EGS reservoirs with large fracture spacing, it is unreasonable to assume the local thermodynamic equilibrium between water and rock when simulating the heat production process, and temperature gradient between the rock and circulating water must be considered. The multiple interacting continua (MINC) model is an effective method for calculating the temperature gradient between the rock and the circulating water in the EGS reservoirs. In this work we evaluated the electricity generation potential from the 950–1350 m deep fractured granite reservoir at the Yangbajing geothermal field by the MINC method with TOUGH2 software, and analyzed the main factors influencing the system production performance. The results indicate that the system attains an electric power generation potential of 22.2–19.3MW, a reservoir impedance of 0.25–0.39 MPa/(kg/s), a pump power of 0.93–1.78 MW and an energy efficiency of 23.92–10.82 during an exploitation period of 30 years under reference conditions, showing good heat production performance. The main factors influencing the production performance are fracture spacing, fracture permeability, injection temperature and water production rate. Within a certain range, measures to improve the electricity generation performance are to reduce the average fracture spacing, to increase the fracture permeability, or to adopt more reasonable injection temperature and water production rate.