Impact of mixing induced calcite precipitation on the flow and transport

Abstract

In several hydrogeochemical situations, there is an interaction between the solid matrix and the carbonate species according to calcite dissolution and precipitation reactions (evaporate deposition in Sebkha and Chotts, calcite dissolution in seawater–freshwater mixing zone). The precipitation of such rocks can easily induce a development of the porosity and permeability as a result of the mixing processes of two different solutions. The purpose of this work is to present a relatively complete modeling tool to evaluate the porosity decrease during calcite precipitation and their impacts on the flow and transport. The modeling of such problem requires a set of highly nonlinearly coupled equations. GEODENS code, used in this work, can solve these equations by a finite element procedure. It can handle geochemical reactions such as mineral dissolution-precipitation reaction. The coupled model iteratively calculates the fluid pressure, the ion concentrations and the quantities of the different salts that may precipitate or dissolve in the domain over time. The porosity is calculated by considering the pore volume invaded during calcite precipitation in every node and each time step. The new porosity value is used to update the permeability using empirical model. The new hydrodynamic distribution is the new inputs for the next time step to solve the flow and reactive transport problem.