Capillary Pressure and Relative Permeability of Small Cores

Abstract

Abstract This paper presents the results of drainage capillary pressure and relative permeability measurements made on cores of different size – bulk volumes ranging from 0.5 to 12 cm3. The aim of the measurements was to obtain reliable experimental data which can be used to validate the predictive value of micro-CT based network models for capillary pressure and relative permeability. Micro-CT based network models typically use realistic networks constructed from the X-ray images of the rock samples representing bulk volumes of the order of 0.3 cm3. Experimental data for drainage capillary pressure were obtained using the centrifuge technique. The results for the largest cores were comparable to data obtained on the same sample using the porous plate technique. Relative permeability data were obtained by history matching unsteady state displacement data. Homogeneous outcrop sandstones (Berea and Bentheim) and carbonate (Mt. Gambier) were used in the experiments. Air-brine and oil-brine fluid-systems were used for drainage capillary pressure and relative permeability measurements, respectively. The relative permeability data were compared with those predicted from empirical and geometry based models using capillary pressure data. Good agreement was obtained for the drainage capillary pressure measured on all samples used. The residual saturations obtained from the cores used in the displacement experiments were also in good agreement. The models were found to predict relative permeability of oil and water with varying degrees of success. For water relative permeability, the Pirson model predicts the experimental data successfully while the Corey, Corey-Brooks/Burdine and van Genuchten/Burdine models provide the best predictions for oil relative permeability. The results demonstrate for the first time that reliable drainage capillary pressure and relative permeability measurements can be made on small sandstone and carbonate cores of size similar to that used for micro-CT-imaging.