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Abstract

In the petroleum industry, water and oil emulsion formation presents an on-going production issue receiving considerable technical attention. Crude oil/water demulsification effectiveness has been tested using a new microemulsion-based demulsifier (ME-DeM) with an environmentally improved formulation. This ME-based product, tested on a range of crude oils, has been shown to be more effective than comparable commercially available non-ME based demulsifiers (DeM). Results using ME based products for demulsification have demonstrated significant improvements in field tests. Additional field studies are in preparation.

Introduction

Emulsion Generation and Stabilization

Water and oil emulsions have been the subject of numerous studies in the petroleum industry because of associated operational issues requiring intervention and expense in production, recovery, transfer, transportation and refining processes. A very good summary regarding “a state of the art review” of crude oil emulsions was presented by Sunil Kokai (Kokai 2002). Emulsions, defined as a combination of two or more immiscible fluids that will not easily separate into individual components, which exist as droplets of colloidal sizes or larger, can lead to high pumping cost. In the case that water is dispersed in an oil continuous phase, the emulsion is termed water-in-oil (w/o) emulsion and in the case that oil is dispersed in a water phase, an oil-in-water (o/w) emulsion. If there is no stabilizer between the oil and water interface, the emulsion is not thermodynamically stable. Coalescence of droplets can lead to destabilization of the emulsion (Holmberg, et al. 2007). However components can accumulate at the oil and water interface which stabilize the interface hindering droplet coalescence and the destabilization (demulsification) process. Materials, such as naturally occurring or injected surfactants, polymers, inorganic solids, or wax, can lead to stabilization of the interface. Emulsification formation processes are also influenced by fluid mixing, shear, turbulence, diffusion, surfactant aggregation (Miller 1988), steric stabilization (non-ionic surfactants), temperature and pressure. Surfactants can form lamellar liquid crystals by the growth of multiple layers around the dispersed droplets.

Emulsions can form when fluid filtrates or injected fluids and reservoir fluids mix, or when the pH of the producing fluid changes. Asphaltene, resin and wax composition and concentration (Lissant 1988, Auflem 2002, Sifferman 1976, Sifferman 1980) are factors affecting emulsion creating and stabilization. In oils which contain significant amounts of asphaltene, the asphaltene acts as a surfactant, creating emulsions that can be very difficult to destabilize.

Interfacial tension can be reduced using surfactants which enhance the thermodynamic stability of an emulsion and allowing creation of small droplets. Studies have concluded that emulsion stability is not totally dependent on the interfacial tension value but on the interfacial film properties (Berger, et al. 1988, Posano, et al. 1982) and have shown that lowering the interfacial tension is conducive to emulsion stabilization, but if too low, can lead to destabilization. Surfactants, polymers and adsorbed particles can create strong interfacial films. Increased interfacial film stability also results from greater surface and bulk viscosity. These factors can limit film thinning and rupture by affecting the properties of interfacial viscosity and elasticity.