Effect of Oil/Brine Ratio on Interfacial Tension in Surfactant Flooding

摘要

The difficulty of determining the effective interfacial tension (IFT) in porous media limits the modeling and prediction of surfactant flood performance.Surfactant dilution,adsorption and partitioning - occurring as the aqueous solution is injected into the reservoir and as it contacts the oil - will raise the effective in-situ IFT from the nominal value as measured traditionally.This change will have a corresponding influence on the oil displacement efficiency.A laboratory study of the interfacial tension behaviour of oil/surfactant-brine systems was conducted.The effective equilibrated oil-surfactant IFT - that is,the IFT closest to that actually produced by partitioning effects in the porous medium - was found to change greatly from the nominal values.When the ratio of oil to brine reached 40:60,the effective equilibrated IFT for the systems approached the original value of crude oil/brine without surfactant,apparently losing much of the advantage provided by a surfactant flood.However,the interfacial tensions between equilibrated oils and a fresh surfactant solution indicate that injecting additional chemicals would maintain the IFT at a reasonably low level.This was confirmed with visual micromodel floods:oil displacement efficiency was poor when equilibrated surfactant-brine solution was injected into a model containing equilibrated oil,and then greatly improved by injecting fresh surfactant solution.These findings are important for progress towards designing successful chemical floods.