Numerical Investigation on Delaying Thermal Breakthrough by Regulating Reinjection Fluid Path in Multi-Aquifer Geothermal System

Thermal breakthrough time of geothermal system directly affects its service life. When a geothermal system consists of multiple aquifers with different permeability, a highly permeable reservoir may lead to an earlier thermal breakthrough. It is a key issue that how to increase the service life of geothermal system by regulating the hydrothermal cycle to inhibit the preferential passage of the geothermal system. In this paper, an innovative method to delay thermal breakthrough by adjusting fluid viscosity is presented. A THC coupling model with variable viscosity is established, and a PID controller is used to realize the constant flowrate reinjection. The flowrate, temperature and tracer concentration during reinjection are analyzed by numerical simulation. The response mechanism of hydrothermal cycle of geothermal system to changing viscosity condition is discussed, and the regulation of hydrothermal cycle by adding viscosity regulator to reinjection fluid is simulated. The results show that in the multi-aquifer geothermal model in this paper, adding 1.5 % Methyl Cellulose into the reinjection fluid can delay the thermal breakthrough time from 1190 days to 1800 days, increasing the service life of the geothermal system by about 50 %. The research results prove that the method of regulating reinjection fluid pathway by adjusting viscosity can effectively delay the thermal breakthrough of geothermal system, substantially prolong the lifespan of certain geothermal fields.