Effect of water-cooling shock on heat production performance of enhanced geothermal systems

Abstract

ABSTRACT The heat extraction process of the Enhanced Geothermal System (EGS) faces the problem of mechanical property degradation caused by artificial cracks and surrounding rock caused by water-cooling shock. However, there are few studies considering the effect of water-cooling shock on fracture deformation and heat production performance. Therefore, a comprehensive numerical model considering water-cooling shock was established to simulate the heat extraction process of EGS. Four different scenarios were designed to analyze the influence of water-cooling shock on the heat production performance of EGS. The sensitivity analysis of several important variables affecting fracture aperture and heat production performance is carried out. The results show that compared with EGS without considering water-cooling shock, the heat extraction performance of EGS considering water-cooling shock is more reasonable. For a reservoir with an initial temperature of 300°C, the decrease of production temperature after 40 years is 3.35°C. Water-cooling shock changes the fracture aperture by degrading the elastic modulus of rocks and fractures, which affects the heat production performance of EGS. The decrease of fracture elastic modulus means that the fracture aperture increases under the same injection water pressure and confining pressure. The decrease of elastic modulus of bedrock leads to the decrease of stress sensitivity index, which inhibits the expansion of fracture aperture. Comprehensively considering water-cooling shock on reservoirs and fractures will more reasonably predict the heat production performance of EGS.