Effect of Salinity and pH on Pickering Emulsion Stability

Abstract

Abstract The stability and morphology of crude-oil emulsions with and without suspended kaolinite or silica were investigated as functions of salinity. First, synthetic reservoir brine with 1, 10 and 100 times dilution was emulsified with crude oils of commercial interest, at several water-oil ratios, on which salinity effect on emulsion stability was studied. Also, the emulsion was prepared by mixing this oil with 100 times dilution dispersed with particles to investigate pH effect on emulsion stability. The clay zeta potential at different pH was measured to estimate the effect of particle charge on emulsion stability. Clay particle-size distribution, which impacts the formation and stability of emulsions, was obtained using light diffraction. The stability of emulsion was determined by simple bottle tests and by using an optical microscope equipped with a digital camera. Our results show that both kaolinite and silica promote emulsion stability. Most emulsions turned out water-in-oil. Also, kaolinite of the order of 1μm in size more easily adsorb at the oil-water interface, while silica with larger diameter, such as 5μm, can form more stable emulsions than with 1μm and 3μm. Zeta potential measurements and bottle tests clearly show that clay particles with zero point of charge (ZPC) at low pH become less effective at stabilizing emulsions in contrast with reservoir conditions, while silica shows the opposite behavior, stabilizing better emulsion at ZPC. Salinity, especially calcium concentration, affects the morphology and stability of emulsions. We can conclude that low-salinity waterflooding provides adequate conditions for formation of relatively stable emulsions, provided kaolinite detachment occurs. This is also apparent in reports of produced water re-injection.