Benefits of saturation profiles for estimating gas and liquid relative permeabilities from centrifuge tests

In conventional centrifuge tests, the relative permeability of just one phase is obtained—the phase with the lowest mobility. Consequently, centrifuge tests are most often used for obtaining relative permeabilities of a liquid in a gas–liquid pair. In order to obtain more relative permeability information from a centrifuge test, saturation data in addition to production data must be obtained. Measurements of evolving air–water saturation profiles for spinning-disk geometry are discussed. The saturation profiles were obtained by processing video images of the spinning rock sample, which was held in a transparent rotor assembly. Relative permeabilities of the water and the air were obtained by history-matching the saturation profiles and production data. The critical gas saturation can be approximately estimated from the saturation profiles. In addition to the relative permeability results, comparisons of capillary pressures measured with the centrifuge (standard geometry and the spinning-disk geometry), with a porous plate, and with mercury injection are presented. For one of the samples, the four methods agreed well. For most samples, the spinning-disk, centrifuge, and the porous-plate methods were in good agreement (less than 10% difference). With the spinning-disk method, direct determinations of capillary pressure curves from equilibrium saturation distributions were obtained.