| Water-in-crude oil emulsions can form during oil production, especially when enhanced-oil recovery (EOR) methods are applied, including Alkaline-Surfactant (AS), Alkaline-Surfactant-Polymer (ASP) flooding and possibly LoSal(TM) water flooding. The pros and cons of emulsion formation have motivated significant research in the oil industry. The ultimate objective of this study is to better understand water-in-crude oil emulsions stabilizing mechanisms. This work is a step further towards engineering and designing conditions that promote recovery based on emulsions for commercially applied and proposed EOR methods.;I carried out water-in-oil emulsion stability analysis based on bottle tests, at controlled centrifugal force and temperature, and an electrorheological technique developed in this project. Several parameters affecting the stability of water-in-oil emulsions were examined including oil-to-water ratio, oil type and rheology, aqueous phase composition and temperature. By changing oil-to-water ratio, we found that the higher the oil fraction used in preparing the emulsions, the more stable the emulsions were. The stability comparison for two crude oils with different asphaltene content showed that the heavier oil with higher asphaltene content produced significantly more stable emulsions for all brines tested. Brine composition for EOR formulations often has to be tuned to allow for the design of stable formulations in chemical flooding. Our results showed that the lower the brine ionic strength, the higher the stability of the crude oil emulsions. The effect of cation species in the brine was examined by comparing the stability of emulsions made with either purely monovalent or divalent salts to yield the same overall ionic strength. It is observed that divalent cations in the brine contributed to the formation of more stable emulsions than monovalent cations, for all oils tested.;The stability of water-in-oil emulsions is controlled by either the oil film rheology between approaching drops, which is mainly a function of the continuous phase viscosity, or/and by the strength of drop interfacial surfaces. In our work, temperature is regulated to control the viscosity of the continuous phase and hence determine its effect on emulsion stability through film drainage, in contrast with interfacial strength control.;Additionally, stabilization mechanisms for water-in-crude oil emulsions were investigated. Given the molecular complexity of crude oils, more than one component is likely responsible for emulsion stability and we speculate that stability is the outcome of competing material adsorption on water-crude oil interfaces. For two oils examined, the presence of soluble acids and their complexes could be the dominant emulsion stabilizing agents, while for the heaviest oil used, asphaltenes are possibly more active than organic acids in crude oil to stabilize emulsions. Our results suggest that divalent cations may form more active surface complexes with naphthenic acid and/or asphaltenes than monovalent cations. |
