Impacts of Dead-ends on Flow and Transport in Fractured Rocks

Detailed simulation of flow and transport through a rough-walled fracture-matrix system with fracture dead-ends is performed. The analysis demonstrates a significant impact of fracture dead-ends on fluid flow and solute transport processes in the modelled system. Two 2D representative rock fracture-matrix models with and without fracture dead-ends are constructed based on high-resolution laser-scanned measurements of a granite rock fracture surface. Simulations of flow and transport with three Péclet numbers (Pe) ranging from 0.1 to 10 are conducted using a code implementing the finite volume method (FVM) to solve the Navier-Stokes equations (NSE) for water flow in the fracture, and the advection-diffusion equation (ADE) is adopted to solve for transport in the whole fracture-matrix system, also accounting for matrix diffusion. The features of the velocity fields and evolution of concentration distributions as well as breakthrough curves of the two modelled cases are presented and analyzed, with results showing that fracture dead-ends significantly affect solute transport processes and cause important retardation of transport in the fracture. This indicates that overly conservative assessments of solute mass arrivals may be made when fracture dead-ends are ignored in discrete fracture network modelling.