DISPLACEMENT OF OIL BY AQUEOUS SURFACTANT SOLUTIONS FROM CAPILLARIES SEALED AT ONE END

We have investigated the displacement of oil (decane and nonane) by su rfactant solutions from horizontal capillaries sealed at one end. Oil displacement occurs when the hydrostatic pressure is sufficient to ove rcome the Laplace pressure arisng from the curvature of the oil-water interface which is deformed due to gravity. Displacement is possible w hen the oil-water tension is less than a certain critical value gamma( crit). We derive an approximate equation for gamma(crit) in terms of t he capillary radius, the liquid densities and the effective values of the contact angle of the liquid-liquid interface with the wall of the capillary. The equation is found to provide a satisfactory prediction of the feasibility of oil displacement. The rate of displacement is an alysed using a modification of Washburn's treatment of penetration of capillaries by liquids in which it is assumed that all of the energy d issipation occurs within the bulk liquids rather than at the interface . Satisfactory agreement with experimental displacement rate measureme nts is found.