Emulsion Characteristics Associated With An Alkaline Water Flooding Process

Abstract

Abstract This paper presents the results of an investigation of emulsions containing an acidic crude oil from Wilmington Field, California, and sodium hydroxide/sodium orthosilicate solutions. The effect of alkaline water formulation on emulsion characteristics was determined. The characteristics of emulsions were evaluated as a function of salinity, alkali type, and alkali concentrations in the aqueous phase. Emulsion stability, as defined by the coalescence rate of oil droplets in water-external emulsions, was determined as a function of salinity and alkali type. Shear viscosity measurements were made for both the oil-external and water external emulsions formed as a result of crude oil/alkaline water interaction. When the emulsions were oil-external, the degree of incorporation of water by the oil was measured in terms of oil phase volume swelling. The effect of divalent ions on shear viscosity and phase volume swelling were also evaluated. phase volume swelling were also evaluated. The results indicate that there is some optimum salinity in the aqueous phase which needs to be maintained to minimize the problems associated with viscous emulsions. Also the emulsions formed with sodium hydroxide are different from those formed with sodium orthosilicate, especially in the presence of divalent ion salts, so that different salinities are required to minimize the shear viscosity of emulsions for the two systems. Introduction In alkaline waterflooding, an alkaline water is injected to cause additional oil recovery from the reservoir. This additional oil recovery is generally attributed to alterations in the wettability characteristics of the porous media, either from oil-wet to water-wet or from water-wet to oil-wet. The recognition of reservoir wettability as a factor in oil recovery efficiency has led to evaluation of wettability characteristics of reservoirs, and has been used as a basis in evaluating alkaline waterflooding potentials. More recently, investigators have potentials. More recently, investigators have studied the applicability of laboratory wettability measurements to the reservoir as well as the relative importance of fractional wettability in determining the oil recovery rate. An alternate approach has been to consider the release of oil as an emulsification process. Two distinct mechanisms have been proposed on the basis of this consideration to date. In the emulsification and entrainment mechanism, first proposed by Subkow in 1942, the released oil remains as dispersed droplets which are entrained and subsequently recovered as an oil-in-water emulsion. In the emulsification and entrapment mechanism, proposed by Jennings et al. in 1973, the oil droplets proposed by Jennings et al. in 1973, the oil droplets are considered to become preferentially entrapped in the more permeable sections of the reservoir, thereby slowing fluid flow through these sections and improving the overall sweep efficiency of the process. process. Several investigators have explained the results of their laboratory alkaline waterfloods by these emulsification mechanisms. However, there has been no systematic study of the types and properties of emulsions that are associated with alkaline water floods and no specific procedure exists for selecting alkaline water procedure exists for selecting alkaline water formulations based on emulsion characteristics. Such a study was recommended by Hill for evaluation of surfactant systems in low tension surfactant flooding. Essentially, Hill proposed that any oil which becomes associated with viscous emulsions will not be displaced as effectively as unemulsified oil, thereby resulting in poor oil recovery. Consideration of alkaline waterflooding processes shows that the oil released from the solid processes shows that the oil released from the solid surfaces can form either oil-in-water or water-in-oil emulsions. According to Taylor's equation for dilute emulsions, the shear viscosity of the emulsion is proportional to that of the continuous phase. phase. P. 255