ABSTRACT
This paper describes a new technique to simultaneously measure the capillary pressure curves and wettability indices for an oil – brine – rock system. By improving the porous plate method, the full cycle of four capillary pressure curves, i.e. spontaneous and forced drainage and imbibition, is measured in days instead of months. This is achieved by the use of thin oil- and water-wet micropore membranes and short samples with large diameter.
Measurements have been done on sandstone and carbonate cores with wettabilities ranging from strongly water-wet to oil-wet. A reduction in experimental time by a factor of 10 or more is gained by the new method for a full cycle of the four capillary pressure curves.
In addition, a new measure of wettability is suggested as an improvement of the USBM test, incorporating all four areas between the capillary pressure curves and the saturation axis. The new wettability index may be conceived as an extension of the Amott test, with the four saturation intervals weighted by the corresponding areas under the capillary pressure curve and may better discriminate between mixed-wet and spotted-wet samples.
