On the Feasibility of Using Supercritical CO2 as Heat Transmission Fluid in an Engineered Hot Dry Rock Geothermal System

Abstract

Responding to the need to reduce atmospheric emissions of carbon dioxide, Donald Brown (2000) proposed a novel hot dry rock (HDR) concept that would use CO2 as heat transmission fluid, and would achieve geologic sequestration of CO2 as an ancillary benefit. Following up on his suggestion, we have evaluated thermophysical properties and performed numerical simulations to explore the fluid dynamics and heat transfer issues in a HDR reservoir that would be operated with CO2. We find that CO2 is roughly comparable to water in its ability to mine heat from hot fractured rock. CO2 has certain advantages with respect to wellbore hydraulics, where larger compressibility and expansivity and lower viscosity as compared to water would reduce the parasitic power consumption of the fluid circulation system. Chemical interactions induced by CO2 between fluids and rocks suggest a potential for porosity enhancement and reservoir growth. A HDR system running on CO2 has sufficiently attractive features to warrant further investigation.