A series of displacement tests was conducted in unconsolidated sand with oil-water pairs exhibiting a range of interfacial tensions from 50 to 0.02 mN/m. Relative permeability behavior and residual saturation levels were measured as a function of the capillary number, List of formula (Available in full paper) which reflects the ratio of viscous to capillary forces. Displacement efficiencies were improved and the shapes of relative permeability curves changed at capillary numbers an order of magnitude lower than those previously reported for less homogeneous media.
Adsorption and aging effects with low concentration petroleum sulfonate solutions were found to have a considerable influence on the displacement behavior. The use of an alcohol co-surfactant markedly improved the long-term stability of the measured interfacial tensions and reduced the adsorption of petroleum sulfonate onto the solid surface.
This report presents the results of an experimental investigation of the effects of interfacial tension reduction on water-oil displacement behavior in water-wet, unconsolidated porous media. The work is part of a study to evaluate the influence of the capillary number, which reflects the ratio of viscous to capillary forces, on the relative permeability characteristics of different types of porous media possessing a variety of wetting properties. Although a prime application of the results is in their utilization for predicting recoveries in low tension waterfloods, such as occur in surfactant and some alkaline floods, the reported data should also provide insight into the displacement behavior with other processes that depend on achieving miscible or near-miscible conditions.
Due to experimental difficulties and the time involved in carrying out displacement measurements at well-defined low interfacial tensions, relatively few definitive studies of relative permeability properties at low interfacial tensions have been reported in the literature. Lefebvre du Prey1 conducted extensive measurements with three types of sintered porous media and fluid pairs having relatively high interfacial tensions, and reported the effect of the ratio of viscous to capillary forces on relative permeabilities and residual saturations. Talash2 has recently provided relative permeability results for water-oil systems containing surfactants, but did not report either the interfacial tensions or the flow rates involved. An earlier investigation by Wagner and Leach3 employing near-miscible hydrocarbon phases indicated that the interfacial tension must be reduced to a value lower than 0.07 mN/m (dyne/cm) to achieve an increased displacement efficiency at field rates. Rosman and Zana4 recently extended this type of study to CO2 – oil systems and showed that low interfacial tension displacement by CO2 is an effective recovery mechanism.
An initial PRI study was conducted by Lo5 to determine the influence of interfacial tension upon oil-water relative permeabilities in sintered oil-wet porous media. It was found that the imbibitions relative permeability curves were more significantly affected by a lowering of the interfacial tension from 50 mN/m to about 0.01 mN/m than were the drainage relative permeability relations. The residual non-wetting phase saturation was also reduced in a manner that generally agreed with previously published correlation between residual oil saturation and the capillary number6.
