Morphology of hydraulic fracture surface has significant effects on oil and gas flow, proppant migration and fracture closure, which plays an important role in oil and gas fracturing stimulation. In this paper, we analyzed the fracture surface characteristics induced by supercritical carbon dioxide (SC-CO₂) and water in open-hole and perforation completion conditions under triaxial stresses. A simple calculation method was proposed to quantitatively analyze the fracture surface area and roughness in macro-level based on three-dimensional (3D) scanning data. In micro-level, scanning electron micrograph (SEM) was used to analyze the features of fracture surface. The results showed that the surface area of the induced fracture increases with perforation angle for both SC-CO₂ and water fracturing, and the surface area of SC-CO₂-induced fracture is 6.49%–58.57% larger than that of water-induced fracture. The fractal dimension and surface roughness of water-induced fractures increase with the increase in perforation angle, while those of SC-CO₂-induced fractures decrease with the increasing perforation angle. A considerable number of microcracks and particle peeling pits can be observed on SC-CO₂-induced fracture surface while there are more flat particle surfaces in water-induced fracture surface through SEM images, indicating that fractures tend to propagate along the boundary of the particle for SC-CO₂ fracturing while water-induced fractures prefer to cut through particles. These findings are of great significance for analyzing fracture mechanism and evaluating fracturing stimulation performance.

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Keywords: Supercritical carbon dioxide (SC-CO2) fracturing, Quantitative characterization of surface features, Surface roughness and fractal dimension, Three-dimensional (3D) scanning, Scanning electron micrograph (SEM)