Surfactant Flooding in Heterogeneous Formations

Abstract The potential for surfactant flooding of oil fields can be obtained using field-scale surfactant simulation model with capillary number (Nc) dependent relative permeability, kr. Typically, kr(Nc) is solely based on core flood experiments. In this paper, surfactant recovery mechanisms in presence of heterogeneities smaller than the field simulation grid block are investigated. Effects of reducing the interfacial tension, IFT, are investigated in various models by numerical simulation of the displacement process and by steady-state upscaling. It is demonstrated that measured core-scale results should go through appropriate averaging before they are used in a field-scale surfactant model. Macro-scale effects of IFT in presence of small-scale heterogeneities are examined separately. Capillary trapping of oil in heterogeneous formations depends on the geometric distribution of permeability and wettability and on IFT. In general, reduced IFT has little or possibly negative effect on production from water-wet, low-permeability inclusions embedded in a mixed-wet background. Production from mixed-wet, low-permeability inclusions will in general be increased at reduced IFT. The IFT level needed to mobilize capillary trapped oil is proportional to the heterogeneity scale. At normal field flow rates, it was found that oil recovery was sensitive to variation in IFT at scales less than approximately 10 m. IFT reduction down to 1 mN/m was found sufficient for heterogeneities of length scale 10 cm. It is shown that the effect of capillary trapping in heterogeneous formations can be represented as Nc-dependent relative permeability function at the larger scale and that the larger-scale functions can be obtained from rate dependent steady-state upscaling. The macro-scale effects described here comes in addition to the measured core-scale effects, and may increase the potential for surfactant flooding.