Surface complexation modeling of calcite zeta potential measurements in brines with mixed potential determining ions (Ca2+, CO32−, Mg2+, SO42−) for characterizing carbonate wettability

Abstract

This study presents experiment and surface complexation modeling (SCM) of synthetic calcite zeta potential in brine with mixed potential determining ions (PDI) under various CO partial pressures. Such SCM, based on systematic zeta potential measurement in mixed brines (Mg, SO, Ca and CO), is currently not available in the literature and is expected to facilitate understanding of the role of electrostatic forces in calcite wettability alteration. We first use a double layer SCM to model experimental zeta potential measurements and then systematically analyze the contribution of charged surface species. Calcite surface charge is investigated as a function of four PDIs and CO partial pressure. We show that our model can accurately predict calcite zeta potential in brine containing a combination of four PDIs and apply it to predict zeta potential in ultra-low and pressurized CO environments for potential application in enhanced oil recovery in carbonate reservoirs. Model prediction reveals that calcite surface will be positively charged in all considered brines in pressurized CO environment (>1atm). The calcite zeta potential is sensitive to CO partial pressure in the various brine in the order of NaCO>NaSO>NaCl>MgCl>CaCl (Ionic strength=0.1M).

Simple ions control the elasticity of calcite gels via interparticle forces

“…Calcium Ca 2+ and carbonate CO 2− 3 are known as potential determining ions of calcite [9]. Calcite surface sites are predominantly in their hydrated forms >CaOH −(1−x) and >CO 3 H +(1−x) with x ≈ 0.25 [8,40]. Potential determining ions form complexes with these surface sites, and thereby modify the overall surface charge and potential.…”

“…The corresponding concentrations are presented in Table 2. For pure calcite, the main anion is HCO − 3 , which complexes onto calcite (although more weakly than carbonate CO 2− 3 [8,40]) and thereby makes ζ decrease. In all the solutions containing calcium hydroxide, the main anion is no more bicarbonate but hydroxide, which is not a potential determining ion, and therefore does not affect the ζ potential.…”

A Surface Complexation Model of Alkaline-SmartWater Electrokinetic Interactions in Carbonates

“…The SCM results were qualitatively validated with different carbonate/brine zeta-potential measurements. Song et al [25] applied SCM and reported quantitative agreement with experimental zeta-potential measurements of synthetic calcite and multiple brine recipes. The SCM surface reactions are based on the model proposed in [26], which includes different SCM reactions compared to the models in [21,24].…”

“…For calcite/brine/crude-oil system, the adsorption of ions on crude-oil/brine and calcite/brine interfaces determine the surface charges and the corresponding zeta-potentials. The SCM has been employed to gain insight on the effect of electrokinetics on wettability in the context of brine chemistry in carbonates [20,21,24,25]. Brady et al [21] used SCM based on surface reactions proposed in [22,23] to predict zeta-potentials for both rock/brine and brine/crude-oil interfaces in sandstone and carbonate rocks.…”

“…The SCM surface reactions are based on the model proposed in [26], which includes different SCM reactions compared to the models in [21,24]. The SCM work of Song et al [25] has been recently extended to include surface reactions of organic and inorganic impurities occurring in natural carbonates [27]. In this work, we use SCM with surface reactions similar to the approach in [25] to predict zeta-potentials for pure calcite and different brine recipes with and without alkali chemicals.…”