Optimizing micro-foam rheology for soil remediation

Abstract

In situ foam flushing has proved to be an efficient process for removing oil from contaminated soils. The drawback is that foams are thermodynamically unstable and also produce a significant pressure gradient as they pass through porous media. The use of micro-foams, usually called colloidal gas aphrons (CGAs), instead of regular foams minimizes the pressure gradient owing to their reduced size and increased stability. Furthermore, there is a lack of information as far as the micro-foam rheology is concerned. The present paper describes how the formulation and the generation conditions can affect the CGA flow properties. The effects of the surfactant concentration, the bubble size distribution and the gas volume fraction on the rheology of CGAs were quantified using a capillary viscometer. The results showed that CGAs display strong shear-thinning behavior, decreasing their apparent viscosity with increasing shear rate. It was also verified that the apparent viscosity of the CGAs increases as the surfactant concentration is enhanced. Finally, it was observed that there is a significant increment in the apparent viscosity, the yield stress and the mean bubble diameter of CGAs when the gas volume fraction is increased, especially above the critical volume fraction value (φ _c ∼0.65). This behavior confirms that CGAs are able to form packing structures.

Acknowledgements: The authors acknowledge Petróleo Brasileiro, CENPES/Petrobras, the Federal University of Rio de Janeiro, COPPE/UFRJ, the Engineering Research Center (ERC) for Particle Science and Technology at the University of Florida, the National Science Foundation (grant EEC–94–02989), and the industrial partners of the ERC for support of this research.