Case Studies Of Emulsion Behavior At Reservoir Conditions

Abstract

Most emulsion studies are conducted with depressurized crude/water samples. Can emulsions form in the reservoir at high pressures and high temperatures? The answer to this question is generally anecdotal. This paper provides a unique method and new data from emulsion studies at high pressures and high temperatures. Two case studies will be presented where emulsions were suspected to be the cause of production challenges in several wells. The experiments were conducted in a special visual PVT cell with the capability of observing emulsion phase behavior at reservoir conditions. The effects of several variables on emulsion behavior were investigated including shear, pressure, temperature, watercuts, and asphaltene precipitation tendency of the crude.The first case study is in a field that produces tight emulsions. The results of this study indicate that emulsions can form at reservoir conditions, with mixing, especially if the crude has a propensity to precipitate asphaltenes. The new data suggests that emulsion behavior is closely linked to the presence of fine solids through in-situ dynamic precipitation of organic (asphaltenes) and inorganic salts (scales) as well as fines migration in the reservoir. In the second case study, a series of emulsion tests were performed on bottomhole and wellhead samples from several wells. The results suggests that the emulsions are relatively loose at bottomhole conditions but become progressively tighter with a reduction in pressure and temperature. The tightness of the emulsions was linked to fine solids that stabilize them. These include primarily calcite and sulfur-rich heavy hydrocarbons like asphaltenes, with trace amounts of silicates (clays and/or fine grained silica), iron-rich precipitates and barite.