The In Situ Formation Of Bitumen-Water Stable Emulsions In Porous Media During Thermal Stimulation

Abstract The formation, production and handling of highly viscous bitumen-water emulsions Is a significant problem in the operation of many heavy oil thermal stimulation projects. This paper documents an extensive study examining the in-situ emulsification of bitumen and water under conditions of simultaneous flow in an unconsolidated preserved state porous media at full reservoir pressure conditions and at a temperature of 200 ° C. Various co-injection ratios from 100% bitumen - 0% water to 100% water and 0% bitumen were examined in both water saturation Increasing and decreasing directions (drainage and imbibition). The test results Indicate that in-situ emulsification does occur, that certain simultaneous flow ratios cause a localized increase in the severity of emulsification, and that the degree of emulsification appears to be related to the relative flowing proportion of fluids inside the porous media. Some evidence of directional hysteresis effects on emulsion quality were also observed. Introduction Evaluations have indicated that as much as 65% of the oil produced in the world today Is In the form of emulsions(1). Emulsions can exhibit complex phase behavior and viscosity effects, and their presence can greatly impact the economics and efficiency of hydrocarbon recovery. Hence a proper understanding of emulsion formation and how it can Impact flow In porous media Is essential. Emulsion formation Emulsions can potentially occur whenever two immiscible fluids come into contact with one another. Emulsions consist of a continuous external phase and an encapsulated, discontinuous Internal phase. In typical oilfield operations water and oil are the primary two fluids of concern when discussing emulsions (although recent studies have also Investigated the existence and effect of gas in oil type emulsions). The two common types of oilfield emulsions are described as water in oil emulsions, where the oil is the continuous external phase and the water is encapsulated as droplets within the oil phase; and oil In water emulsions, where the water Is the continuous external phase and the oil phase Is encapsulated as discontinuous droplets. Water in oil, or water Internal emulsions, are characterized by viscosities greater (sometimes substantially greater) than the actual clean crude oil. In comparison, oil in water, or water external emulsions, are characterized by viscosities much lower than the oil phase. Unfortunately, about 95% of the produced oilfield emulsions are of the high viscosity water in oil (water internal) type. Water internal emulsions can be typified by the size of the droplets of encapsulated water into microemulslons (Dw < 0.1 microns) or macroemulslons (Dw> 0.1 microns)(2,3). Almost all naturally occurring oilfield emulsions are of the macroemulsion type with encapsulated water droplet volumes varying between 0.1 to 10 microns in diameter, Water internal emulsions can be stable at relatively high concentrations of bound water (up to 70%). The bound water content is usually referred to as emulsion quality. When quality in the emulsion becomes too high, the emulsion passes through what is known as the "inversion point".