Chemical Interactions and Demulsifier Characteristics for Enhanced Oil Recovery Applications

In this study, a design of experiments was used to investigate the importance of several parameters (alkaline concentration, anionic surfactant concentration, polymer concentration, temperature, shear rate, water cut, and salinity) and their interactions (i.e., synergism or antagonism) that govern emulsion stability in chemical enhanced oil recovery (CEOR). Emulsion stability decreased with an increase in salinity or water cut. An increasing surfactant concentration, polymer concentration, temperature, 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 non-ionic resins and polymeric cationic flocculants in separating oil-in-water emulsions. The chemistry was also investigated by studying the effect of alkyl chain length (C8-C18) of benzyl and methyl quaternary compounds (quats) on demulsifying efficiency. 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. The particle video microscope and focused beam reflectance measurement probes showed a 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. Measurements of interfacial properties, such as the interfacial tension reduction rate, interfacial tension, elastic modulus, and zeta potential, at the oil/brine solution interface were also conducted. A qualitative correlation was found between the interfacial tension reduction rate, elastic modulus, zeta potential, and phase separation. The interfacial tension reduction rate decreased, zeta potential became less negative, elastic modulus decreased, and the size of oil droplets remarkably increased when a cationic demulsifier or an amphoteric demulsifier (patents pending) was added to the emulsion. However, there appears to be no direct correlation with interfacial tension. Without direct information, this preliminary correlation may provide guidelines for selecting demulsifiers for emulsions produced by chemical enhanced oil recovery.