Experimental investigation of thermal cycling effect on fracture characteristics of granite in a geothermal-energy reservoir. (August 2020) - Feng, Gan
Highlights: Thermal cycling effects on granite fracture characteristics were investigated. The number of thermal cycle in the present study were 1, 5, 10, 15, and 20. Crack characteristics in granite was quantitative discussed. Thermal cycling decreases Keff, U, Pv, and increases K . Thermal cycling has effect on the predictive accuracy of MMTS. Abstract: The fracture characteristics of fine-grained granite were examined for a potential geothermal-energy reservoir. The granite was thermally cycled in a furnace between 100 °C and 300 °C and its mechanical behavior and meso-crack characteristics were analyzed. The results indicate that thermal cycling leads to decreased fracture toughness ( Keff ), absorbed energy ( U ), longitudinal wave velocity ( Pv ), and increased permeability ( K ) in granite. These changes can be explained using the thermal fatigue accumulated damage. The ability of granite to resist fracturing is greatly reduced in the first five thermal cycles. Thermal cycling is more conducive to inducing intergranular cracks. The interconnection of intragranular and intergranular cracks causes the structure of granite to become fragmented and more likely to fail. Thus, thermal cycling deteriorates the mechanical stability of fine-grained dense granite, and allows crack networks to form more easily. The correction of crack propagation critical radius ( rc ) can improve the accuracy of the modified maximum tangential stress (MMTS) predictive fracture.