Determining water-oil relative permeability and capillary pressure from steady-state coreflood tests

Abstract

This study aims at the simultaneous determination of relative permeability and capillary pressure from steady-state corefloods. Besides using the measurements of pressure-drop across the core and average saturation under steady-state conditions, we use the transient data between the sequential steady states. The inverse algorithm is based on four type curves “stabilizsation period versus water-cut” revealed by asymptotic analysis of the transient solution near end-point saturations, and on the exponential shape of transition data histories observed by direct numerical runs. The transition measurements are approximated in the stabilisation periods by the type curves using non-linear least-square optimisation. The Corey parameters for relative permeability and capillary pressure are fitted for each interval of sequential water-cuts. The inverse solver is applied to three sets of steady-state tests in oil-wet cores, where saturation profiles during steady-state flows have been measured along with the transition data. Extensive sensitivity analysis of the inverse solutions with respect to the small perturbation of the measured data reveals the stability of obtained relative permeability and capillary pressure. The close agreement between the measured stabilised saturation profiles and those obtained by the matched-based modelling in three oil-wet cases validates the method developed.