Projection-based Embedded Discrete Fracture Model

Any endeavour to accurately model flow through fractured porous media at the field-scale must overcome two important challenges. First, the discretized representation of the medium needs to accommodate the complex geometry of intersecting small-scale fractures with various lengths, apertures and orientations. Second, the model formulation must ensure that the conductivity of these fractures, which can be orders of magnitude higher or lower than that of the host rock, is properly taken into account when computing the pressure map. The Embedded Discrete Fracture Model (EDFM) is well known in the literature for its flexibility in representing fractures. More specifically, in EDFM, fractures are lower-dimensional features, discretized independently from the matrix. Their effect on the flow is captured by defining fluxes between the fracture control volumes and the matrix grid cells they intersect. EDFM was proven effective in capturing the flow behaviour through porous media containing highly conductive fractures. However, its formulation fails to represent the effect of low-permeable features, such as embedded flow barriers. In this work, a novel projection-based Embedded Discrete Fracture Model (pEDFM) is introduced for flow simulation in fractured porous media with general conductivity contrasts. Similar to EDFM, pEDFM constructs independent grids for the fracture and matrix domains. As an additional step, the transmissibilities at matrix interfaces are automatically adjusted to account for the conductivity of neighbouring fracture networks, via a scaling factor proportional to their geometric projections. The performance of pEDFM is investigated extensively for two- and three-dimensional scenarios involving single- as well as multiphase flows. These numerical experiments are targeted at determining the sensitivity of the model towards the grid resolution, fracture position and orientation, as well as the conductivity contrast towards the matrix. The results of these studies support the conclusion that pEDFM significantly outperforms the original EDFM model and is a viable method for field-scale simulation of flow in naturally fractured reservoirs.