Changes in thermomechanical properties due to air and water cooling of hot dry granite rocks under unconfined compression

Water has been used as a working fluid injected into the hot reservoirs during the exploitation of deep geothermal energy, therefore, understanding the thermomechanical properties of reservoir rocks after water cooling is essential. For that reason, we have conducted a series of laboratory tests on air and water cooled granites from normal temperature to 600 degrees C, to reveal the changes in their thermomechanical properties. At 600 degrees C, the average values of uniaxial compressive strength, elastic modulus and P-wave velocity of water cooled granite decrease by 84.9%, 73.1% and 66.2%, which are 11.0%, 17.0% and 17.7% larger than those of air cooled granite. Through optical microscopic analysis, the microcrack density and average width of water cooled granite increase with thermal temperature and are 4.18 mm/mm(2) and 54.62 mu m at 600 degrees C, while the values of air cooled granite are only 1.97 mm/mm(2) and 25.16 mu m. We thus combined the deterioration of the macroscopic mechanical characteristics of air and water cooled granites with the propagation and development of microcracks. Supported by data from international literature, the changes in the thermomechanical characteristics of granite has been systematically compared to international literature, which is hoped to provide technical support for the geothermal energy exploitation. (C) 2021 Elsevier Ltd. All rights reserved.

Automated summary

Laboratory tests revealed significant changes in the mechanical properties of water-cooled granite at high temperatures, with reduced strength and increased microcrack density, which is of great significance for geothermal energy exploitation.