Effects of high-pressure supercritical CO2 on fracture morphology and nonlinear flow characteristics of shale

The fracture morphology and seepage properties of shale fractures were altered by stress and CO2 treatment. This has significant implications for enhancing shale gas production and evaluating the viability of the CO2 fracturing technology. This study investigates the chemo-mechanical interactions between supercritical CO2 (ScCO2) and fractured shale through XRD, high-resolution micro-CT imaging, 3D profilometry, and hydraulic tests to quantify ScCO2-induced mineral dissolution, fracture geometry evolution, and nonlinear flow properties under confining stresses (15–40 MPa). Key findings reveal that prolonged exposure to ScCO2 induces chemo-mechanical coupling in shale reservoirs, driving mineral reconfiguration through pyrite oxidation and feldspar dissolution, while promoting secondary fracture branching via quartz liberation and preferential dissolution at pyrite-clay interfaces. These processes enhance fracture network complexity, evidenced by increased volume fraction, roughness, fractal dimension, and aperture, though clay swelling and secondary precipitation cause irreversible permeability reductions. Stress-chemical interactions govern nonlinear flow dynamics: Below 25 MPa confining stress, non-Darcy flow dominates (Re > 1) with a 150 MPa/m pressure gradient threshold, while high stress (30–40 MPa) enhances ScCO2-induced conductivity via dissolution-expanded channels. ScCO2 reduces critical Reynolds number (Rec) through viscosity reduction and interfacial slip, while stress elevates flow resistance via fracture closure. Chemo-mechanical competition is quantified by flow index reduction (n = 0.67–0.83) under microscale vortex dissipation and permeability recovery hysteresis. Key thresholds regulate seepage stability in CO2 sequestration, highlighting the interplay between mineralogical alterations and stress-dependent fracture closure. These findings establish predictive criteria for fracture network evolution and flow regime transitions in subsurface carbon storage systems.