Effect of intermediate wettability nanoparticles on oil-water emulsion stability

Emulsions are ubiquitous in oil production operations and in general undesirable for various reasons. These include increased pressure losses leading to reduced oil productivity, pipeline and other equipment corrosion, as well as separation difficulties resulting in increased production costs. Surface active agents (also known as surfactants, like asphaltenes, resins, etc.) and solid particles (for example clays) are naturally present in crude oils. These components can act as stabilizers for oil and water emulsions. Therefore in order to mitigate the aforementioned problems related to emulsions, a better understanding of how emulsions are formed and stabilized is essential. This study focuses on nanoparticle stabilized emulsions and aims to contribute to a deeper understanding as it pertains to the effect of solid nanoparticles on the stability of oil and water emulsions. More specifically, the objective of this research is to investigate the separation kinetics of oil-water emulsions stabilized by spherical silica nanoparticles of intermediate wettability and its dependence on solid particle concentration, initial dispersion phase, water-cut, and shearing time. A novel, state-of-the-art, Portable Dispersion Characterization Rig (P-DCR) is used to run the experiments (as compared to the conventional bottle test method) and the relevant software for accurate data acquisition. All tests are conducted at ambient pressure and temperature conditions. Mineral oil and distilled water are used as the test fluids. The initial oil to water ratio in the batch separator is an important parameter. Therefore a broad range of water-cuts is tested. Starting with a 25% water-cut the experimental results indicate that in most cases no emulsion forms and complete phase separation takes place fast. However, when the water-cut increases to 50% and 75% a stable emulsion rag layer phase is always formed and full separation is not achieved within the experimental time frame. For the stirring times examined, faster separation takes place when the nanoparticles are initially dispersed in the oil phase. Using the specific type of nanoparticles, the formation of multiple emulsions (oil in water in oil, O/W/O) is observed. In general, as the nanoparticle concentration increases the rate of the separation process decreases. The size of the solid nanoparticles is also a critical factor and although not studied intentionally, it is inferred from the results that larger particles do not stabilize the formed emulsions as efficiently as smaller particles do.