Effect of Salinity on Water-in-Crude Oil Emulsion: Evaluation through Drop-Size Distribution Proxy

Abstract

A crude oil and a synthetic reservoir water are used to prepare water-in-oil emulsions. The droplet-size distribution of water-in-oil emulsions is measured by digitally processing optical micrographs. The time evolution of the droplet-size distribution is used as a proxy of emulsion stability. A procedure for obtaining homogeneous aliquots of the initial emulsion is developed. The procedure yields statistical replicas of the initial sample that allow one to measure size distributions through direct observation of optical micrographs for a period of time of up to 7 days. The synthetic reservoir water is diluted by the addition of distilled water to determine how the water ionic strength affected emulsion stability. A detailed droplet-size distribution analysis supports the log-hyperbolic distribution as a better fit to the experimental observations than the Weibull or log-normal distributions. The inferred qualitative rates of coalescence indicate that emulsions are more stable at lower ionic strength of the aqueous phase. This result is consistent with previous emulsion characterization using electrorheology and bottle tests, demonstrating the importance of often overlooked aqueous-phase composition.