Anisotropy in Fractured and Porous Media: A Simulation Approach

Subsurface heterogeneity and directional variance in the connectivity of permeable zones influences the movement of fluids which in turn, leads to anisotropy in permeability and flow. Our study investigates this anisotropy in both fractured and porous media by employing a set of synthetic fractal-fracture networks and multifractal models respectively, along with natural datasets. The latter include a high-resolution soil thin-section and a set of outcrop-based fracture maps that are evaluated using a “dynamic” approach. This is achieved by the means of simulating flow using TRACE3D, PFLOTRAN and Processing Modflow. TRACE3D, a streamline simulator, used by reservoir engineers, is employed for generating recovery curves assuming that each flow model is saturated with oil which is “recovered” by injecting water from a series of wells. It essentially serves as an indicator of connectivity, a time-varying “response curve” in our case, a practice not uncommon in the literature where multiple realizations of a pattern are compared using some kind of a “response”.  In order to assess flow in x-direction a series of injection and production wells are placed along the boundaries parallel to the y-axis, with no-flow boundaries along the x-axis. The setup is then rotated 90 degrees to evaluate flow in the y-direction. For evaluating anisotropy in terms of equivalent permeability along x and y-directions, PFLOTRAN and Processing Modflow are used. PFLOTRAN is a high-performance, massively parallel simulator designed for modelling fluid flow and reactive transport in geologic porous media. Processing Modflow, on the other hand, implements Darcy’s law and mass conservation equations to simulate groundwater flow in aquifers. The flow setup used in PFLOTRAN and Processing Modflow is similar to the one used in case of TRACE3D, except that, instead of injection and production wells, PFLOTRAN applies pressure heads and Modflow applies hydraulic heads along the boundaries parallel to the y-axis that facilitate flow along the x-direction. This study adopts a “dynamic” approach for delineating subsurface anisotropy in terms of connectivity, permeability and flow in multifractal porous media and fractal-fracture networks.