A hybrid-mixed finite element method for single-phase Darcy flow in fractured porous media

TL;DR

This paper introduces a hybrid-mixed finite element method for modeling single-phase Darcy flow in fractured porous media, effectively handling both conductive and blocking fractures with nonconforming meshes and producing locally conservative velocity approximations.

Contribution

The novel hybrid-mixed finite element scheme uniquely combines interface and Dirac-$ delta$ approaches, allowing nonconforming meshes and improving computational efficiency for fractured media.

Findings

The method accurately models flow in both 2D and 3D fractured media.

It produces symmetric positive definite systems with pressure on the mesh skeleton.

Numerical results show high competitiveness with existing methods.

Abstract

We present a hybrid-mixed finite element method for a novel hybrid-dimensional model of single-phase Darcy flow in a fractured porous media. In this model, the fracture is treated as an $(d-1)$-dimensional interface within the $d$-dimensional fractured porous domain, for $d=2, 3$. Two classes of fracture are distinguished based on the permeability magnitude ratio between the fracture and its surrounding medium: when the permeability in the fracture is (significantly) larger than in its surrounding medium, it is considered as a {\it conductive} fracture; when the permeability in the fracture is (significantly) smaller than in its surrounding medium, it is considered as a {\it blocking} fracture. The conductive fractures are treated using the classical hybrid-dimensional approach of the interface model where pressure is assumed to be continuous across the fracture interfaces, while the blocking fractures are treated using the recent Dirac-$\delta$ function approach where normal component of Darcy velocity is assumed to be continuous across the interface. Due to the use of Dirac-$\delta$ function approach for the blocking fractures, our numerical scheme allows for nonconforming meshes with respect to the blocking fractures. This is the major novelty of our model and numerical discretization. Moreover, our numerical scheme produces locally conservative velocity approximations and leads to a symmetric positive definite linear system involving pressure degrees of freedom on the mesh skeleton only. The performance of the proposed method is demonstrated by various benchmark test cases in both two- and three-dimensions. Numerical results indicate that the proposed scheme is highly competitive with existing methods in the literature.