Effect of fracture geometric feature and flow velocity on fracture preferential flow

Understanding fluid flow in fractured rock is essential for accurately predicting subsurface transport behavior. This study examines how fracture contact area, fractal dimension, and flow velocity influence the development of preferential flow. A series of controlled simulations was conducted, varying contact area (0%–50%), fractal dimension (2.1–2.5), and flow velocity (0.01–2.5 m/s), to quantify the impact of each parameter. The results show that contact area exerts the strongest influence: as it increases, preferential flow volume declines, especially sharply between 20% and 40% contact area. Flow velocity exhibits distinct threshold behavior linked to the transition from Darcy to non-Darcy flow regimes. Below the critical velocity (non-Darcy effect factor E = 0.1), preferential flow volume increases linearly with velocity. Above this threshold, preferential flow stabilizes as inertial effects emerge and geometric constraints dominate. Notably, this critical velocity decreases with decreasing contact area—at 0% contact, flow immediately enters the non-Darcy regime (E > 0.1), causing preferential flow to stabilize from the onset. Fractal dimension (FD) shows non-monotonic effects, with intermediate roughness (FD = 2.3) consistently producing minimum preferential flow, suggesting optimal geometric complexity for flow resistance. These factors interact through a hierarchical control system: contact area establishes the primary flow framework and determines the transition between flow regimes, fractal dimension modulates internal channel complexity, and flow velocity governs fluid distribution within structurally-determined constraints. These insights deepen our theoretical understanding of fractured media flow and inform more accurate predictive models for environmental and engineering applications.