RHEOLOGY OF WATER-IN-CRUDE OIL-EMULSIONS

The present paper deals with the rheological study of simplified sea w ater in crude oil emulsions. This includes viscosity dependence vs. sh ear rate, creep experiments and oscillatory shear measurements. Our re sults show the existence of a critical water volume fraction phi(c), i n addition to the maximum packing fraction phi(m),. This critical frac tion marks the onset of physical contact between water droplets. The d etermined thickness of the hydrodynamic layer due to surfactant molecu les is shown to decrease as the water volume fraction increases. On th e other hand, when emulsions contain an additional surfactant, the los s modulus G '' measured at f= 1 Hz shows a maximum for a given shear s train gamma(max). Such shear strain, however, decreases as the water v olume fraction increases and remains constant above phi similar to phi (c). Finally, we attempt to scale shear rate values with relaxation ti me determined from creep experiments using the analogy with concentrat ed macromolecular solutions. (C) 1998 Elsevier Science B.V. All rights reserved.