An overview of the thermodynamic models for the chalk surface reactions with brine

Several mechanisms that are suggested for the modified-salinity water flooding in chalk, e.g., calcite dissolution, fine migration, compaction, and wettability alteration are directly affected by the electrostatic properties of the chalk-brine interface. Accurate mathematical modelling of these mechanisms necessitates the development of a thermodynamic model that is representative for the chalk surfaces. We first review the existing thermodynamic models for the calcite (the main constituent of chalk)-brine system, implement them in Phreeqc chemistry package, and compare their results with the reported experimental zeta potential measurements. Our study shows that the CD-MUSIC model developed by Wolthers et al gives the closest fit to the data by only slightly modifying its parameters. Then, we study the effect of the clay particles (that is observed on various outcrop and reservoir chalk surfaces) on the chalk-brine equilibrium and the adsorption of the potential determining ions. The results show that minute amounts of clay particles drastically affect the chalk surface charge, but its impact on the adsorption of Ca2+, Mg2+, and SO42- ions is negligible.