Relative Permeability from Centrifuge Data

ABSTRACT The drainage of a wetting phase (say oil) by a non-wetting phase (say gas) may be simulated in the centrifuge by two liquids. Such experiments were conducted on a number of cores and they are discussed in a companion paper. In this paper we consider two of the cores with available capillary pressure data. Two forms of the relative permeability models are selected and the parameters of these models are obtained by history matching with a numerical simulator developed for this study that properly accounts for the capillary pressure and the boundary conditions in centrifuge experiments. It is shown that; (1) recoveries can be matched with two – and maybe even more – very different sets of relative permeability curves; (2) recoveries are sensitive to the parameters of each relative permeability model; (3) excellent history match is possible with arbitrarily small capillary pressure values, but the resulting relative permeabilities are different from those obtained with experimental values of the capillary pressure; and (4) late time predictions can be improved by using a linear relationship for the wetting phase relative permeability below some arbitrary value of the wetting phase saturation. It is concluded that the capillary pressure (Pc) term should not be ignored in obtaining relative permeability curves from centrifuge data. Analytical or numerical models that do not properly include Pc or ignore Pc should be used with caution.