Speaker
Description
Fractures in rock masses promote discrete, preferential flow paths rather than the diffuse wetting of porous media. This channeling behavior reduces fracture-matrix contact, weakens capillary imbibition, and suppresses the coupling between the two domains, thereby challenging the applicability of traditional retention models such as van Genuchten and Brooks-Corey at larger scales. Here, we present a suite of numerical and analytical models to describe unsaturated flow in complex fractured media. Unsaturated flow is modeled by solving Richards’ equation in combination with a Brooks-Corey retention model. A set of 3D discrete fracture networks (DFNs) with varying fracture densities and length exponents are considered, with fractures represented as lower-dimensional surfaces embedded in a 3D matrix. Both the upscaled relative permeability and capillary pressure exhibit a pronounced two-branch behavior, reflecting the contrasting roles of the matrix and fracture domains across the saturation range. Specifically, with the increase of saturation, the system response exhibits a transition from matrix-dominated to fracture-dominated regimes, with the shift occurring as a critical saturation, S_c. This bifurcating retention behavior and the associated S_c are observed consistently across all DFN realizations spanning a wide range of fracture density and power law length exponents. We then introduced a modified Brooks-Corey formulation that explicitly captures the transition between matrix- and fracture-dominated regimes. We further developed a phase diagram that delineates matrix- and fracture-dominated regimes based on two dimensionless parameters: the percolation parameter and the ratio of fracture to matrix hydraulic capacity. Our results have important implications for understanding and predicting unsaturated flow in fractured porous media.
| Country | Sweden |
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