Abstract
This paper aims to study the effect of cyclic heating and flowing-water cooling conditions on the physical properties of granite. Ultrasonic tests, gas measured porosity, permeability, and microscope observations were conducted on granite after thermal treatment. The results showed that the velocity of P- and S-waves decreased as the number of thermal cycles increased. The porosity increased with the number of the thermal cycles attained at 600 °C, while no apparent changes were observed at 200 and 400 °C. The permeability increased with the increasing number of thermal cycles. Furthermore, microscope observations showed that degradation of the granite after thermal treatment was attributed to a large network of microcracks induced by thermal stress. As the number of thermal cycles increased, the number of transgranular microcracks gradually increased, as well as their length and width. The quantification of microcracks from cast thin section (CTS) images supported the visual observation.
Highlights
Geothermal energy is an important component of renewable energy, and most of the deep geothermal resource is stored in hot dry rock (HDR) [1]
Considering that water is the most common fluid used to extract thermal energy from HDR, in this experimental study, we investigate the effects of cyclic heating and water cooling on the physical and mechanical properties of granite, including a quantitative analysis of the resulting microcracks
High temperature thermal treatment could increase the porosity of Porosity and crack density are the most important properties, playing a major role in the structural integrity of a rock [30]
Summary
Geothermal energy is an important component of renewable energy, and most of the deep geothermal resource is stored in hot dry rock (HDR) [1]. HDR is defined as a hot and almost waterless geothermal system. Common HDR systems include granite or other crystalline basement rocks. Rock temperature varies from 150 to 500 ◦ C at maximum depths of 5–6 km [2,3]. HDR resources will contribute to the mitigation of the environmental pollution caused by traditional fossil energy [4]. Enhanced geothermal system (EGS) is an effective engineering method to exploit
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