Surface Characterization of Model, Outcrop, and Reservoir Samples in Low Salinity Aqueous Solutions

Abstract

The purpose of this study was to characterize model, outcrop, and reservoir samples under low salinity, different cationic valency, and pH ranges. Potentiometric titrations and zeta potential measurements were performed in order to determine the surface properties at different pH. The extent of ion adsorption on the mineral surfaces was found by the difference between the two approaches. X-ray diffraction and cation exchange capacity measurements were also performed. All samples except calcite showed high, negative zeta potentials in fresh water at pH > 6, followed by NaCl, low salinity solution (LSS), and solutions with divalent cations. The effect of ion valency on the zeta potential at low pH values was not prominent. Above pH 8, H⁺ and OH⁻ were not potential determining ions for samples that contained calcite and dolomite more than 1.5%. Above pH 8, the presence of carbonates in outcrop and reservoir samples significantly affected the zeta potential by reversing the charge in divalent solutions. The cation exchange capacity of predominant quartz, mixed quartz-clay-carbonate, and quartz-carbonate sandstones was 0.0, 0.2, and 2.2 meqv/100 g, respectively. The compositional differences between the samples were also reflected in the point of zero charge (pzc) values. Samples containing more than 1.5% carbonates had pzc in the range of pH 8–9, while samples with small fractions of carbonates or without carbonates had pzc values in the range of pH 2.9–3.3.

Keywords:

• Ion valency
• low salinity
• particles
• pH
• point of zero charge
• zeta potential

Acknowledgements

The authors acknowledge financial support from VISTA and thank StatoilHydro for providing samples and funding. Bartlomiej Gawel is acknowledged for helping with XRD and specific surface area measurements.