Abstract:
Many processes in the Earth's crust are controlled by the chemical and physical interactions between fluids and geological media where the lattice is usually characterised by a heterogeneous permeability, intrinsic rock permeability and fault networks. Dissolution/precipitation of rock minerals and chemical transport can alter the rock properties, which leads to a change in the flow characteristics and alteration of the geological media with time. In this article, we propose a novel method for modelling heterogeneous reactive transport with a feedback between the flow and chemical alterations. To model fluid flow, we use a modified lattice Boltzmann scheme which facilitates the incorporation of complex boundary conditions and enables us to examine flow in heterogeneous media. In addition, the local update rules of this scheme allow the code to be parallelised on multiple processors. We have coupled transport of chemical species and reactive flow to this scheme using a solution to the advection-diffusion equation. Experimentally derived dissolution/precipitation rates are used to calculate rates of interaction between minerals and the fluids with which they are in contact. Laboratory scale passive and reactive flow-cell experiments from the literature have been used to test and validate the accuracy of the transport of the chemical species in a heterogeneous porous medium. We have also examined the output of our scheme for water-rock interactions in a quartzofeldspathic lithology for relatively long periods of geological time. We have focused on quartz and feldspar reactive flow with associated secondary clay minerals, as these are some of the most abundant minerals in the Earth's crust. In all cases, the numerical results agree well with the experimental results from our numerical scheme. The scheme also reproduces alteration of a quartzofeldspathic lithology over geological time periods, consistent with other numerical work.
