In this paper, effect of matrix permeability and fracture density on flow pattern and overall permeability is presented. According to the literature, dual fracture method (DFM) is an efficient numerical method for investigating the flow in dual porous mediums. In this method, matrix permeability is presented with polygons called voronoi elements (VE) and discrete fracture network (DFN) is used to show fracture system. It is expected that a permeable matrix has to lead to higher overall permeability. Effects of fracture density and aperture patterns on overall permeability and representative elementary volume (REV) have been studied as well. Using a computer code based upon Monte Carlo simulation technique, DFNs with different aperture patterns and densities were generated with regard to real field data. All these models were numerically analyzed via computer code using Distinct Element Method (DEM). The results show that permeability increases with fracture density and with adding permeable matrix to the model, huge increases in overall permeability occur in most cases. Also it was revealed that there is a relationship between overall permeability and DFN aperture pattern. With increasing the density of fractures, REV decreased as well.
Understanding flow process in naturally fractured dual porous media is of interest in environmental engineering applications, in geohydrology or in oil reservoirs engineering, when porous material is made of rocks, which is crossed by networks of fractures. Recently, fractured rocks attracted the attention in connection with the problem of geological isolation of radioactive waste.
Dual porous media often exhibit a variety of heterogeneities, such as fractures, fissures, cracks, and macro-pores or inter-aggregate pores. The granular rock mass consists of solid rock, cut by a network of fractures. Water flows unevenly through an intricate network of paths formed by fracture intersections and micro-channels between matrix blocks or grains (Jourde et al. 2002).
Recently, permeability of the matrix is becoming progressively more important. Previously, due to computing limitations, it was accepted that permeability of the matrix is so low and it can be neglected. But with advances in earth sciences for the past few years, precision and reliability in predicting the overall permeability became more important in earth projects and matrix permeability is an important factor for a precise calculating and predicting of the overall permeability.
There are some methods to study a Dual Permeability Medium. In 1993, Zimmerman (Zimmermann et al. 1993) created a numerical model for dual porosity mediums. In the same year a simple but useful numerical method was developed to estimate the overall permeability in a Dual Porosity-Dual Permeability medium by Priest. Bai expanded an analytical solution for flow in oil reservoirs in 1994. Different types of fracture geometry such as connected and unconnected fracture systems in a Dual Permeability Medium were investigated by Odling (Odling 1997).
