An Experimental Study of the Influence of Interfacial Tension on Water–Oil Two-Phase Relative Permeability

Adding surfactant into the displacing aqueous phase during surfactant-enhanced aquifer remediation of NAPL contamination and in chemical flooding oil recovery significantly changes interfacial tension (IFT) (σ) on water–oil interfaces within porous media. The change in IFT may have a large impact on relative permeability for the two-phase flow system. In most subsurface flow investigations, however, the influence of IFT on relative permeability has been ignored. In this article, we present an experimental study of two-phase relativepermeability behavior in the low and more realistic ranges of IFT for water–oil systems. The experimental work overcomes the limitations of the existing laboratory measurements of relative permeability (which are applicable only for high ranges of IFT (e.g., σ > 10−2 mN/m). In particular, we have (1) developed an improved steady-state method of measuring complete water–oil relative permeability curves; (2) proven that a certain critical range of IFT exists such that IFT has little impact on relative permeability for σ greater than this range, while within the range, relative permeabilities to both water and oil phases will increase with decreasing IFT; and (3) shown that a functional correlation exists between water–oil twophase relative permeability and IFT. In addition, this work presents such correlation formula between water–oil two-phase relative permeability and IFT. The experimental results and proposed conceptual models will be useful for quantitative studies of surfactant-enhanced aquifer remediation and chemical flooding operations in reservoirs.