INVESTIGATING ROCK-FACE BOUNDARY EFFECTS ON CAPILLARY PRESSURE AND RELATIVE PERMEABILITY MEASUREMENTS

This paper covers the experimental study of water-gas capillary pressure and relative permeability in laboratory scale using the centrifuge spinning disk method to investigate the rock-face boundary effects. The capillary pressure wetting-phase saturation data were first generated using both the centrifuge spinning disk setup and the porous plate setup for the same samples. These measurements are performed to validate the accuracy of the centrifuge spinning disk method. Using the measured capillary pressure data, relative permeability relationships were estimated for each sample by history-matching production and saturation distribution data. The production data was monitored for each disk-shaped rock sample using two different experimental conditions-one by sealing the top and bottom faces of the sample and the other without sealing the rock faces. This is done to investigate the effects of sealing the tested samples on the measured data and ultimately on the relative permeability. Results show that the measured capillary pressure data generated using the spinning disk method are in agreement with the capillary pressure data generated with the porous plate method. Results also showed that the gas and brine relative permeabilities are independent of the rock sealing conditions. The average variation between the two methods used was in the order of 2% with a standard deviation of 2.2%. Capillary pressure data measured using cases with unsealed boundaries were practically a reproduction of capillary pressure data for the same core samples with sealed boundaries. The average variation between these methods was approximately 2.3% with a standard deviation of 2.6%. Capillary pressure and relative permeability are of great importance to petroleum engineers attempting to understand and predict the behavior of various petroleum recovery processes. Accurate determination of relative permeability data is essential for estimating the free water saturation, aiding in evaluating drill-stem and production tests, and estimating the residual saturations. This accuracy of the capillary pressure data and the precession of generated relative permeability data is a consequence of the refinement of the spinning disk setup. The improvement consists of modification of the core holder and adaptation of better lighting conditions. With this procedure, direct determination of capillary pressure saturation data is possible for the equilibrium saturation distribution.