Stability of Aqueous Wetting Films in Athabasca Tar Sands

Abstract

Abstract The existence of thin films of water that completely wet the sand grains has long been regarded as an important feature of the Athabasca oil sands deposit. Direct microscopic evidence, however, cannot be relied on to establish whether such films are present, The existence and stability of such films, therefore, must be inferred from the relevant surface chemical forces for the oil/brine/rock system. A detailed analysis of these forces shows that the stability of these thin wetting films is critically dependent on whether the zeta potentials (and charge densities) for the two electrical double layers bounding the film are of like sign. The zeta potential and charge density for the rock/brine interface will in almost all cases be negative in sign. Therefore, a requirement for the stability of a wetting film will be that these quantities are also negative at the brine/oil interface. New measurements of the electrophoretic mobility of small particles of Athabasca bitumen suspended in an aqueous phase are reported. These data show that the zeta potential at the bitumen/water interface is strongly negative. Consequently, these results support the hypothesis that wetting films will be stable in this instance.