A rapid, simplified, hybrid modeling approach for simulating solute transport in discrete fracture networks

In this paper, a hybrid model is developed to simulate solute transport in discrete fracture networks (DFNs) considering mass exchange between the fracture and the surrounding matrix. The developed model considers three mechanisms: advection and dispersion along the fracture, molecular diffusion within the fracture and into the matrix, and adsorption within the matrix. Furthermore, the developed model can predict solute transport at fracture intersections and at the discrete fracture network outlet for both constant and pulse injections at inlet boundaries. The developed model predictions are compared to those of an existing analytical model; the results indicate the former is approximately 250 times faster than the later, and this efficiency increases with network complexity. In addition, the developed model is compared to a computational fluid dynamics (CFD) model employing Navier Stokes equations, and the comparison indicates the former has a lower dispersion compared to the later. Nonetheless, the developed model can approximately predict solute transport simulated by the CFD model when assuming a higher value of dispersivity. Finally, the results in a high density DFN indicate that large diffusion coefficients, small apertures, and large fracture spacings reduce solute migration in fracture networks.