We presents zeta potential measurements and surface complexation modeling (SCM) of synthetic calcite in various conditions (brine ionic strength, ionic composition, CO2 partial pressure). The systematic zeta potential measurement and the proposed SCM provide insight into the roles of four potential determining ions (Mg2+, SO42- , Ca2+ and CO32-) in calcite surface charge formation and facilitate the revealing of calcite wettability alteration induced by brines with designed ionic composition (“smart water”). In this work, the calcite zeta potential is measured in various brines (Ionic strength from 0.001M to 0.5M) under two different CO2 partial pressure (10-3.4atm and 1atm). Then, a SCM is developed to fit all the zeta potential. After showing our model can accurately predict calcite zeta potential in brines containing mixed PDIs, we apply it to predict zeta potential in ultra-low and pressurized CO2 environments for potential applications in carbonate enhanced oil recovery including miscible CO2 flooding and CO2 sequestration in carbonate reservoirs. Model prediction reveals that pure calcite surface will be positively charged in all investigated brines in pressurized CO2 environment (&gt;1atm). Moreover, the zeta potential of several natural carbonates is measured and compared with the synthetic calcite’s result to investigate the effect of surface impurities, which is shown to significantly lower the carbonate zeta potential.

Surface complexation modeling of calcite zeta potential in mixed brines with varied ionic strength for carbonate wettability characterization

256th National Meeting (2018)

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