Transport and intersection mixing in random fracture networks with power law length distributions

Abstract

The importance of fracture intersection mixing rules, complete mixing and streamline routing, on simulated solute migration patterns in random fracture networks is assessed. For this purpose, and based on geological evidence, two‐dimensional model networks having power law fracture length distributions and lognormal fracture permeability distributions are considered. Different fracture network structures are accounted for by the power law length distribution, ranging from networks composed of infinite length fractures to percolation networks with constant length fractures. Comparison of solute particle statistics shows that there is no significant difference between the bulk transport properties calculated with the two mixing rules. In fact, it is found that the choice of mixing assumptions has a significant influence in less than 5% of the total number of fracture intersections in most fracture networks. This result can be attributed to the small mean effective coordination number, defined as the number of branches connected to an intersection with nonzero flux. It is concluded that solute transport in fracture networks is strongly influenced by variability and uncertainty in parameters defining the geometrical structure of networks and that, by comparison, the choice of mixing rules at fracture intersections is of little importance.