Micromechanical damage and proppant embedment patterns of fracture surfaces in lacustrine shale CO2 pre-pad energized fracturing

To elucidate the mechanism by which supercritical CO₂ (SCCO₂)-water-shale interactions during CO₂ energized fracturing influence proppant embedment in lacustrine shale, shale samples from the Bohai Bay Basin were selected for SCCO₂-water-shale interaction experiments. X-ray diffraction (XRD), SEM large-area high-resolution imaging, automated mineral identification and characterization system (AMICS), and nanoindentation tests were employed to examine the micro-mechanical damage mechanisms of fracture surfaces and the evolving patterns of proppant embedment characteristics. The results reveal that: Prolonged interaction time reduces the contents of dolomite, feldspar, and clay minerals, while quartz content increases, with dolomite showing the most pronounced dissolution effect. As interaction time increases, the hardness and elasticity modulus of shale follow a power-law decay pattern, with the peak degradation rate occurring at 1 d, followed by a gradual decline of degradation velocity. Increasing interaction time results in growth in both the number and depth of embedment pits on the sample surface. After more than 3 d of interaction, clustered proppant embedment is observed, accompanied by the formation of deep embedment pits on the surface.