VISCOSITIES OF DISPERSIONS OF SUPERCRITICAL CO₂ IN SURFACTANT/CO₂/H₂O/NaCl SYSTEMS

Abstract

Viscosities have been measured with a capillary viscometer for dispersions (“emulsions”) in surfactant/carbon dioxide/water and surfactant/carbon dioxide/water/NaCl systems at 38°C and at a super-critical pressure (2,000 psi, 13.8 MPa) for CO₂. The effects of shear rate, surfactant structure, and concentrations of the three (or four) components were investigated. Two nonionic, one cationic, and two anionic surfactants were studied

The viscosities were non-Newtonian and exhibited a power-law dependence on the shear rate with the value m = 0.4 for the exponent. Viscosities as large as 500 centipoise (7,000 times the viscosity of CO₂ at 2,000 psi, 38°C) were observed. Viscosities increased exponentially with CO₂ concentration, but with increasing salinity the viscosity passed through a pronounced maximum. Viscosities increased exponentially with surfactant concentration at surfactant/water ratios greater than 0.05, but exhibited more complex behavior at lower surfactant concentrations

The exponential increase of viscosity with CO₂ concentration appears to be a very favorable property for the use of surfactants to control CO₂ mobility in enhanced oil recovery.