Nonlinear fluid flow regimes in fractured shale: Impact of confining stresses and water-supercritical CO2 interactions

The coupled chemo-mechanical impact of supercritical CO 2 –H 2 O (ScCO 2 –H 2 O) reactions on fracture geometry and nonlinear flow regimes in deep shale under confining pressures remains inadequately quantified. This study systematically investigates the effects of ScCO 2 –H 2 O–shale interactions on fracture morphology and flow properties under confining pressures from 15 MPa to 40 MPa by integrating XRD (X-ray diffraction), micro-CT, 3D surface profilometry, and multistage steady-state flow experiments. The results demonstrate that ScCO 2 –H 2 O exposure drives pyrite/feldspar dissolution and localized clay precipitation, resulting in fracture branching and macroscopic aperture regularization. Critically, confining pressure dictates the net hydraulic response: under low confining pressure (15–25 MPa), dissolution dominates, enhancing permeability, flow efficiency ( Q /∇ P ), and pre-linear flow behavior ( n < 1). At high confining pressures (30–40 MPa) mechanical compaction and mineral precipitation amplify flow resistance, shifting the flow regime toward quasi-linear behavior, as inertial effects become negligible compared to dominant viscous forces and increased flow resistance. Confining pressure thus critically mediates the dissolution–precipitation balance during ScCO 2 –H 2 O treatment, with an optimal window of 15–25 MPa identified for enhancing conductivity while minimizing clogging risk. These findings provide a quantitative framework for predicting stress-dependent flow evolution in chemically altered shale fractures.