Capillary pressure and heterogeneity for the CO2/water system in sandstone rocks at reservoir conditions

A novel method is presented to measure drainage capillary pressure curves both at the core and sub-core scale using CO2 and water at reservoir conditions. The experimental configuration is very similar to the one used in traditional steady-state relative permeability experiments. Capillary pressure measurements are made at the inlet face of the sample by successively increasing the flow rate of the non-wetting phase while measuring the saturation with a medical X-ray Computed Tomography (CT) scanner. The method requires that the wetting phase pressure is uniform across the core and can be measured in the outlet end-cap. A capillary pressure curve is obtained in less than two days, as compared to weeks for existing methods that use porous plates. Drainage capillary pressure curves of CO2 and water are measured for two sandstones rock cores with different lithology and pore size distribution. Experiments are carried out at 25 and 50 degrees C and at 9 MPa pore pressure, while keeping the confining pressure on the core at 12 MPa. There is excellent agreement between the new method and data from mercury intrusion porosimetry; beside providing confidence in the new technique, such comparison allows for an estimate of the wetting and interfacial properties of the CO2/water system. X-ray CT scanning allows for precise imaging of fluid saturations at a resolution of about (2.5 x 2.5 x 1) mm(3), thus enabling quantification of sub-core scale capillary pressure curves. These measurements provide independent confirmation that sub-core scale capillary heterogeneity plays an important role in controlling saturation distributions during multiphase flow. (C) 2011 Elsevier Ltd. All rights reserved.