Investigation of hydraulic fracture surface morphology and heat transfer characteristics of high-temperature granite under cyclic hydraulic fracturing

Abstract

This study systematically investigated cyclic hydraulic fracturing (CHF) under real-time, high-temperature, true triaxial conditions and combined the results with a three-dimensional rough-fracture heat-transfer model. The results show that increasing the maximum cyclic pressure percentage (MCPP) enhances fracture surface roughness, whereas increasing the injection flow rate reduces it. A mathematical response model between CHF parameters and the fractal dimension of fracture surfaces was established. Gray-level co-occurrence matrix (GLCM) analysis indicates that the angular second moment and correlation are significantly negatively correlated with MCPP, while entropy and contrast are positively correlated; the injection flow rate shows the opposite trend. Increasing the MCPP improves the heat transfer efficiency of fracture surfaces, whereas increasing the injection flow rate weakens their heat exchange capacity. The response model between CHF parameters and the overall heat transfer coefficient (OHTC) suggests that a CHF scheme with high cyclic pressure and low injection flow rate is favorable for enhancing heat extraction efficiency in hot dry rock reservoirs. In addition, the OHTC shows an approximately negative exponential relationship with injection velocity and a linear negative correlation with injection temperature, indicating that, within a certain range, higher injection velocity and lower injection temperature promote fracture heat transfer efficiency.

Keywords

cycle hydraulic fracturing / morphological characteristics / heat transfer / mathematical response model / parameter optimization

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