Solute transport at fracture intersections

Abstract

A numerical study of three‐dimensional solute transport at fracture intersections by using a particle tracking technique is presented. Two models of orthogonal fracture intersection are considered, namely, two parallel‐walled channels and two rough‐walled Gaussian fractures. The fluid velocity is calculated by solving the three‐dimensional Stokes equation with no‐slip boundary condition at the solid wall. Examples of individual trajectories of particles are first given in order to illustrate the main features of the phenomenon. Solute mass partitioning between outgoing fracture branches is considered for various transport regimes, characterized by the local Péclet number, and for various ratios of the flow rates in the intersecting channels. Generally speaking, it can be said that at dominant diffusion the influence of the flow rates ratio is weak, while it is important in the opposite situation. Validity of the classical models of solute mixing, stream tube routing, and perfect mixing is analyzed by comparing their predictions with the numerical data. Preliminary recommendations are made for the use of these results in large‐scale modeling.