Effects of CO2 thermal properties and local fracture heterogeneity on heat transfer by supercritical CO2 flowing through fractured granite

The exploitation of hot dry rock (HDR) based on supercritical CO2 (SCCO2) is an effective solution to the global energy crisis and climate change. The changes in the thermal properties of SCCO2 and rocks induced by high temperatures (pressures) have significant impacts on the evaluation of the heat extraction rate (HER). In this study, we established the relationship between the rock thermal conductivity and temperature and proposed a local average heat transfer coefficient (HTC), which considered the thermal properties of SCCO2 and the heterogeneity of the rock orthogonal to the flow direction of the SCCO2. Then, we studied the effects of confining pressure, rock sample temperature, SCCO2 injection pressure, and injection temperature on the outlet temperature and the local average HTC through experiments. In addition, we analyzed the influence of these factors on the HER. The results showed that increasing the confining pressure or rock sample temperature would reduce the local average HTC and inhibit the heat extraction of SCCO2. A higher injection pressure or lower injection temperature produced a larger local average HTC, which promoted the heat extraction of SCCO2. The results of this study provide valuable information to increase the HER in HDR reservoir. (C) 2021 The Authors. Published by Elsevier Ltd.

Automated summary

This study established the relationship between rock thermal conductivity and temperature, proposed a local average heat transfer coefficient, and investigated the effects of confining pressure, rock sample temperature, SCCO2 injection pressure, and injection temperature on outlet temperature and local average HTC through experiments. The results provided valuable information for increasing the heat extraction rate in HDR reservoirs.