Abstract: The dissolution process induced by reactive fluid flow in rock fractures significantly impacts geotechnical engineering safety, while the dissolution mechanisms of inclined fractures under gravitational effects induced by solution density differences remain unclear. This study systematically investigates the dissolution patterns and permeability evolution of fractures with different inclinations through pore-scale numerical simulations and visualization experiments. Results indicate that buoyancy-driven convection caused by solution density differences generates “vortex-like” flow structures during inclined fracture dissolution, where buoyancy convection along the fracture length dominates channel development, whereas gravitational effects in the vertical direction can be negligible. A criterion for the transition of dissolution patterns was established using the Richardson number (RiII): When RiII > 10 (buoyancy-dominated regime), increased inclination promotes wormhole growth and reduces the required injection volume for breakthrough; when RiII ≤ 10 (forced convection-dominated regime), dissolution patterns are governed by injection velocity, manifesting as compact dissolution, wormhole dissolution, or uniform dissolution. A theoretical model for optimal injection velocity incorporating gravitational effects was developed, enabling accurate predictions across varying inclinations. This research provides a theoretical guidance for seepage control in underground engineering within soluble rock formations and offers critical insights for safety assessments in CO₂ geological storage, in-situ leaching mining, and related applications.

Key words: buoyancy convection effect, inclined fractures, dissolution pattern, permeability evolution, optimal injection flow rate