Analysis of the temperature impact on the calcite surface reactivity in modified salinity water applications

The success of modified salinity waterflooding (MSW) in carbonate reservoirs is dictated by the interactions between the injected brine and the rock. To describe these interactions, different surface complexation models (SCM) have been proposed. These SCMs usually rely on experimental data at room temperature to obtain the equilibrium constants of the surface reactions. However, these conditions diverge from the actual reservoir temperature, e.g. greater than 70oC in the North Sea. Thus, the existing models cannot describe the surface reactivity at real field conditions unless the temperature dependency of the equilibrium constants is included. The conventional approach to account for the impact of temperature on the surface reactivity is to include an extrapolated temperature effect observed for solution complexation. However, this non-validated assumption may lead to misinterpretation of experimental data. We address this issue by first identifying methods that give information on the affinity of ions for the calcite surface at different temperatures. We found that calorimetry, streaming potential, and molecular simulations are potential ways that enable capturing the temperature effect on the surface reactivity. Whereas molecular simulations studies provide directly enthalpy data for each defined interaction, calorimetry and streaming potential require geochemical modelling to interpret and break down the observed temperature effect for individual surface reactions. Thus, we perform the modelling of published data from calorimetry and streaming potential experiments by implementing in Phreeqc a Charge Distribution MultiSite Complexation (CD-MUSIC) model, which includes reactions between the calcite and ions relevant for MSW applications; this model is thoroughly validated with experimental data at room temperature. Next, we infer the enthalpy of the reactions by assuming that the equilibrium constants follow a temperature dependence according to van t Hoff equation. Given the synergy between the interactions, we note that modelling different type of experimental data results in distinct enthalpy values. After a detailed analysis of the experimental methods/simulations, we establish a unique set of enthalpies for the defined reactions. These enthalpies are further verified against flooding experiments in the work of Hosseinzadeh et al. (EAGE IOR 2021) by coupling the reaction module to the single-phase flow equations. The resulting thermodynamic model that accounts for the temperature effect is not only a useful tool for interpreting the laboratory experiments but can also reduce the uncertainty of implementation of MSW projects at the field scale. The study is not only relevant to MSW IOR but also to other non-isothermal reactive transport processes in carbonate formation.