Using effective medium theory to calculate permeability of rock with complex fractures

Abstract

Dewatering in surface and underground mining is highly dependent on the permeability of fractured rocks, which is usually investigated by analytical and numerical methods. Analytical methods are used for simple, regular joint systems, while for complicated discrete fracture networks, numerical methods are more suitable. However, such numerical simulations demand considerable computation resources and are time-consuming for large-scale models. An attractive approach is to perform a rough mapping of the fractures into a lattice to apply effective medium theory. A computational code based on effective medium theory for calculating the overall permeability of fracture networks was developed. Several stochastic discrete fracture network models were generated with the fracture aperture distributed uniformly, correlated and uncorrelated with fracture trace length. The results showed that when the aperture was correlated or uncorrelated with trace length, the calculated mean permeability values by the effective medium theory method agreed well with numerical modelling. Also, approximated representative elementary volume was well fitted by numerical methods in the constant fracture aperture case. However, the calculated representative elementary volume by the effective medium theory method was smaller than the numerical estimation in the other two cases.