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 dropletsize 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.

No abstract

Several researchers have proposed that mobility control mechanisms can positively contribute to oil recovery in the case of emulsions generated in Enhanced-Oil Recovery (EOR) operations. Chemical EOR techniques that use alkaline components or/and surfactants are known to produce undesirable emulsions that create operational problems and are difficult to break. Other water-based methods have been less studied in this sense. EOR processes such as polymer flooding and LoSal TM injection require adjustments of water chemistry, mainly by lowering the ionic strength of the solution or by decreasing hardness. The decreased ionic strength of EOR solutions can give rise to more stable water-in-oil emulsions, which are speculated to improve mobility ratio between the injectant and the displaced oil. The first step toward understanding the connection between the emulsions and EOR mechanisms is to show that EOR conditions, such as salinity and hardness requirements, among others, are conducive to stabilizing emulsions. In order to do this, adequate stability proxies are required. This paper reviews commonly used emulsion stability proxies and explains the advantages and disadvantage of methods reviewed. This paper also reviews aqueous-based EOR processes with focus on heavy oil to contextualize in-situ emulsion stabilization conditions. This context sets the basis for comparison of emulsion stability proxies.

No abstract

Two classes of stabilizing oil components in water-in-crude oil emulsions for three oils from the state of Wyoming are investigated in this paper. The associated contributions appear to be different for each crude oil. Given the molecular complexity of crude oils and their properties, more than one oil component is thought to contribute to emulsion stability and we speculate that stability is the outcome of competing materials adsorption on waterÀoil interfaces, in addition to interfacial and bulk rheology. The presence of emulsion-stabilizing acids and their complexes, presumed here to be naphthenic acids for at least one of the crude oils used here, is claimed to stabilize water-in-crude oil emulsions. The presence of acids is inferred from pH changes of the resolved water fraction obtained in centrifuge-bottle tests, as well as in partition tests. The oil wash test, in which oil obtained after emulsification is reused to generate new water-in-crude oil emulsions, is used here to elucidate the role of the water-insoluble fraction. The effect of di-and monovalent cations in solution on emulsion stability is compared for two oils. Results show that stability improves when the aqueous phase contains calcium ions only in contrast with solutions containing sodium ions exclusively at the same ionic strength.