In this paper, factors such as key issues (e.g. emulsions), challenges (e.g. water treatment), and best practices (e.g. combination of equipment design and demulsifier to treat emulsions) associated with chemical enhanced oil recovery (CEOR) are presented. During the application of chemical EOR floods, breakthrough of the injection chemicals such as surfactant and polymer or polymer alone periodically occurs resulting in stable emulsions. This paper was compiled from the literature to report the effects of alkali, polymers, surfactants, asphaltenes, resins, and shear rates on emulsion stability. When treated with polymer alone, the produced fluid was not very stable and resolved into two phases: oil and water. However, the water exhibited a high oily content and was difficult to treat due to the adsorption of polymer onto the surface of the oil droplets. Zeta potential measurements indicated that oil droplets were not only stabilized by steric stabilization of the polymer but also by electrostatic stabilization. The effect of polymer on emulsion stability in SP (surfactant and polymer) or ASP (alkali, surfactant, and polymer) floodings is complicated. Polymer can form a "bridge?? between two oil droplets and decrease the emulsion stability; however, polymer can also enhance the emulsion stability via electrostatic and steric stabilization. Asphaltenes and resins present in the crude oil form a rigid film around water droplets, contributing to high BS&W values. Surfactants and alkali decrease the interfacial tension and zeta potential, contributing to the stability of oil droplets. As concentrations of the injection chemicals in the produced fluid varied, the stability of the emulsion also changed. As a result, the selected demulsifier has to be robust. In this paper, water soluble demulsifiers and oil soluble demulsifiers were used to treat the emulsion. The demulsifier greatly lowered water content in the oil phase (BS&W<0.5%) and oil concentration in the water phase (less than 50 ppm). The demulsification mechanism was also investigated in terms of elastic modulus, particle size, and interfacial tension. Application of this novel demulsifier resulted in a much more effective oil/water separations process with the production of dry oil and clean water at a pilot ASP flood that was experiencing very stable emulsions.
In this paper, the stability of oil-in-water emulsions produced from chemical enhanced oil recovery processes was investigated over a wide range of parameters. These parameters are surfactant concentration, polymer concentration, mixing speed, asphaltene concentration, salinity concentration, water cut, temperature, and alkaline concentration. Emulsion stability decreased with an increase in temperature, salinity content, or water cut. Increasing surfactant concentration, polymer concentration, or shear rate enhanced emulsion stability. One of the main contributions for the tight emulsion from alkaline surfactant polymer (ASP) flood was the addition of alkaline. The surfactant, alkaline, and polymer decreased the size of oil droplets, increased the surface charge of oil droplets, and increased the film elasticity, thereby making oil-water separation difficult. Selected cationic surfactants (patents pending) proved much more effective than conventional nonionic resins and polymeric cationic flocculants in separating oil-in-water emulsions. We also studied the effect of alkyl chain length (C8 - C18) of benzyl and methyl quats on demulsifying efficiency and compared the performances of monoalkyl quat with dialkyl quat. As the surfactant concentration in the brine decreased, the concentration of the cationic demulsifier required to separate the emulsion decreased and the optimum chain length of the cationic demulsifier also changed. Particle video microscope and focused beam reflectance measurement probes showed significant increase of the size of oil droplets and reduction in the number of oil droplets in the presence of a cationic surfactant. This is in agreement of a decrease of the anionic charge on the surface of the oil droplets and a reduction of the film elasticity in the cationic system. Application of this novel demulsifier resulted in a much more effective oil/water separations process with the production of dry oil and clean water at a pilot ASP flood that was experiencing very stable emulsions.
In this paper, the importance of five process variables (alkaline, surfactant, polymer, shear rate and oil cut) and their interactions that govern emulsion stability in chemical enhanced oil recovery (CEOR) was investigated. The surfactant, alkaline, and polymer decreased the size of oil droplets, increased the surface charge of oil droplets, and increased the film elasticity, making oil-water separation difficult. Selected cationic demulsifiers (patents pending) when added to a produced emulsion at ambient temperature for alkaline, surfactant, polymer (ASP) and surfactant, polymer (SP) processes yielded oil and water phases with greatly improved quality compared to emulsions treated with conventional nonionic demulsifier resins and polymeric cationic flocculants. Structure and performance relationships of alkyltrimethylammonium bromides and alkyldimethylbenzylammonium bromides (n=C8 to C18) were also studied. Octyltrimethylammonium bromide was the best demulsifier for SP flood and dodecyldimethylbenzylammonium bromide was the most effective for ASP flood. Di-alkyl quaternary ammonium bromides were more effective than mono-alkyl quaternary ammonium bromides of similar molecular weights. The zeta potential became less negative and the size of oil droplets remarkably increased when a cationic demulsifier was added to the emulsion. Application of this novel demulsifier resulted in the production of dry oil and clean water for a pilot field experiencing chemical breakthrough from an ASP flood