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Stability and fracture surface morphology evolution in granite subjected to high-order thermal cycles – Implications for enhanced geothermal systems
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DOI：10.1016/j.jrmge.2026.03.069.png)
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Abstract
En 中文
Granitoid-based enhanced geothermal systems (EGS) undergo cyclic thermal loading during fracture stimulation, increasing fracture complexity and modifying fracture morphology, with direct implications for geothermal productivity. Therefore, understanding the mechanical degradation of rocks under prolonged thermal exposure associated with multiple thermal cycles is highly imperative. In the present study, the impact of high-order thermal cycles (1, 10, 30, and 50) at temperatures of 100 °C, 200 °C, 300 °C, 400 °C, and 500 °C on the physical and mechanical properties, as well as variations in the fracture surface morphology of the granite, is examined. The analysis suggested an escalated impact of thermal cycles under all temperature conditions, indicating thermal weakening due to induced thermal cracks. The strength attributes, such as compressive strength, Brazilian tensile strength, and elastic modulus, showed drops of 71%, 49%, and 82%, respectively, as the temperature approached 500 °C during higher-order thermal cycles. Interestingly, partial thermal strengthening was observed after 300 °C and 30 cycles, indicating a transitional threshold at which granite regains its integrity through thermal cycles, especially at higher thermal loads. This critical condition was influenced by the conversion of wider cracks to a network of thinner, interconnected microcracks due to differential mineral expansion. Additionally, fracture surface roughness values varied notably at higher thermal cycles, particularly above 300 °C. Moreover, fracture toughness and fracture surface roughness showed an inverse relationship, indicating that thermal cycles have a greater influence on both. The study concludes that thermal stimulation promotes long-term efficiency, sustained performance, and reliability of EGS and deep geothermal environments.
Keywords:
Enhanced geothermal system (EGS)
Thermal cycles
Mechanical stability
Fracture surface morphology
Thermal stimulation
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