A study of geothermal hydraulic fracture surface morphology and heat transfer characteristics

Abstract

This study analyzed the morphological characteristics of heat-treated granite fracture surfaces subjected to cyclic hydraulic fracturing (CHF) and traditional hydraulic fracturing (THF). The differences in heat transfer characteristics between THF and CHF fracture surfaces were compared using a three-dimensional numerical heat transfer model. The heat transfer properties of CHF fracture surfaces were investigated under varying injection parameters, and corresponding mathematical models were constructed. It was found that the roughness of CHF fracture surfaces was greater than that of THF, and the heat transfer performance was superior. Specifically, the overall heat transfer coefficient (OHTC) for the C1-C3 fracture surfaces increased by 55.71, 63.40, and 75.91 W/m2/K, respectively, compared to the T1-T3 fracture surfaces. The average outlet temperature (Tout) of the CHF fracture surfaces increases with higher injection flow rates and decreases with higher injection temperatures. The OHTC and local heat transfer coefficient (LHTC) exhibit opposite trends. Specifically, injection flow rates have a quadratic polynomial relationship with the Tout and a logarithmic relationship with OHTC. Additionally, the Tout of the CHF fracture surface shows a linear positive correlation with injection temperature, while OHTC has a linear negative correlation.