Scientific African (Jul 2023)
Zeta potential prediction of dominant sandstone minerals via surface complexation modelling
Abstract
Numerous injection water compositions have been developed by various researchers to optimize the oil recovery via wettability alteration. The ionic composition of the injected brine plays a profound role in the rock/brine and crude-oil/brine interfacial charge thereby its role is pivotal in oil recovery. Numerous experimental techniques have been used to assess the potential of injected brines to optimize wettability via wettability alteration. Notably among them are the spontaneous imbibition, contact angle and core flooding techniques. Zeta potential (ζ-potential) has been used by some researcher to evaluate the wettability alteration during crude oil/brine/rock interactions. However, ζ-potential measurement is relatively expensive and time consuming. Hence, the need for relatively cheap and easy approach of ζ-potential measurements. This was accomplished using Surface Complexation Modelling (SCM) via PHREEQ-C. The focus of this study was to predict ζ-potential using SCM. The qualities and quantities of the materials used during the existing experiment from literature were also used as input in the SCM. Dominant minerals in sandstone reservoir rock notably quartz, calcite, dolomite, kaolinite, illite, montmorillonite, chlorites, ilmenite, muscovite, biotite and anorthoclase were considered in this study. The SCM technique could capture the trend during the ζ-potential measurements. However, out of the 39 mineral-brine ζ-potential measured, the SCM approach could not capture the trend in 5 of these samples namely; dolomite/0.5wt% NaCl (pH = 9.5), microcline/SW (pH = 7.8), muscovite/SW (pH = 7.8), chlorite/SW (pH = 7.8) and ilmenite/20% Dil-SW (pH = 7.6). This was attributed to the effect of atmospheric CO2 on the pH of the brine during the ζ-potential measurement. The ζ-potential of carbonates (calcite and dolomite) were predominantly positive while that of tectosilicates (Quartz, Anorthoclase and Microcline), phyllosilicates (Montmorillonite, Kaolinite, Biotite, Illite, Muscovite and Chlorites) and oxides (Ilmenite) were also predominantly negative. For instance, at the calcite-SW (pH = 7.9) interface, the predicted a ζ-potential value was 20.5 mV while its measured value was observed to be 12.9 mV. The dolomite-SW (pH = 7.9) also predicted 16.7 mV and 19.7 mV for the predicted and the measured ζ-potential value respectively. Considering quartz, anorthoclase and microcline with 0.5wt% NaCl (pH = 7.9), the predicted ζ-potential values were observed to be -11.65 mV, -24.21 mV and -43.00 mV while the measured values were also observed to be -16.9 mV, -33.8 mV and -36.5 mV respectively.
