Effects of intersection and dead-end of fractures on nonlinear flow and particle transport in rock fracture networks

Abstract

Fluid flow tests were conducted on three artificial rock fracture network models to visually investigate the behaviors of fluid flow and solute transport within the fracture intersections, by using the visualization techniques with a CCD camera. Numerical simulations by solving the Navier-Stokes equations were performed to simulate the fluid flow and solute transport based on the experimental models, and to extensively estimate the effects of fracture intersection and dead-end in fracture networks. The results show that for the crossed fracture models, when the Reynolds number (Re) of the inlet is larger than 1, a nonlinear flow regime starts to appear where the proportion of the flow rates in the two outlets change nonlinearly. When calculating the fluid flow in discrete fracture network (DFN) models, it is found that the critical condition of applying the local cubic law to model fluid flow in each single fracture in DFNs is J ≤ 10–5, where J is the hydraulic gradient. Beyond this value, the deviation of applying the cubic law increases remarkably with increasing hydraulic gradient. The effects of dead-ends of fractures on fluid flow are negligible, however, they have a strong impact on the breakthrough curves of particles in DFNs with the relative time deviation rate in the range of 5–35%.