Validation of a multicomponent reactive-transport model at pore scale based on the coupling of COMSOL and PhreeqC

Pore scale modelling in porous media is a field of research where interfaces such as the fluid - mineral boundary are explicitly represented and avoids volume-averaged properties such as porosity, permeability and reaction rates as required in a continuum scale approach. Setting up, running and extracting data from a pore scale model can be complex involving multiple software packages and coding for each problem. A new implementation of a multicomponent reactive-transport model at pore scale is presented using a java interface combining COMSOL and PhreeqC (iCP). The new model is tested using benchmark problems recently published and by simulating a laboratory experiment. The main advantages of this model are the implementation of the aqueous speciation, easy incorporation of different reaction mechanisms and rate laws, parallelization of geochemical calculations and a user-friendly interface. The iCP results agree with the benchmark and experimental results very well confirming its application to reactive-transport problems with dynamic pore geometry evolution. The importance of aqueous speciation and the chosen rate constants are demonstrated for calcite dissolution. Given the model transfers data between two codes and computes the aqueous speciation for every time step, the model is computationally expensive. Its advantages are the user-friendliness and its accuracy in computing local reaction rates and fluid composition.