Thermal Compensation of Rocks Encircling Heat Reservoir in Heat Extraction of Enhanced Geothermal System

With a self-developed numerical model, we simulate long-time operation processes of an imaginary doublet enhanced geothermal system (EGS) with different geological conditions and analyze effects of thermal compensation on evolution of production temperature and fluid and rock temperature in the heat reservoir. The model treats heat reservoir as an equivalent porous media while considers thermal non-equilibrium between rock matrix and fluid. It uses two energy equations to describe temperature field of rock and circulating fluid, respectively, enabling thorough investigations on local heat exchange processes of rock and fluid. It reveals that influence of thermal compensation from rocks encircling heat reservoir is strongly correlated with flow pattern in the reservoir, and it does not always have positive effect on EGS production temperature. If there appears an obvious preferential flow in depth direction of the reservoir, thermal compensation can even lower production temperature during early period of EGS operation. With advance of EGS operation, rock temperature in reservoir decreases and thermal compensation gradually brings a pronounced positive effect on production temperature.