Numerical simulation of non-isothermal multiphase tracer transport in heterogeneous fractured porous media

Abstract

We have developed a new numerical method for modeling tracer and radionuclide transport through heterogeneous fractured rocks in a non-isothermal multiphase system. The model formulation incorporates a full hydrodynamic dispersion tensor, based on three-dimensional velocity fields with a regular or irregular grid in a heterogeneous geological medium. Two different weighting schemes are proposed for spatial interpolation of three-dimensional velocity fields and concentration gradients to evaluate the mass flux by dispersion and diffusion of a tracer or radionuclide. The fracture–matrix interactions are handled using a dual-continua approach, such as the double- or multiple-porosity, or dual-permeability. This new method has been implemented into a multidimensional numerical code to simulate processes of tracer or radionuclide transport in non-isothermal, three-dimensional, multiphase, porous/fractured subsurface systems. We have verified this new transport-modeling approach by comparing its results to the analytical solution of a parallel-fracture transport problem. In addition, we use published laboratory results and the particle-tracking scheme to further validate the model. Finally, we present two examples of field applications to demonstrate the use of the proposed methodology for modeling tracer and radionuclide transport in unsaturated fractured rocks.