Computation and Interpretation of Capillary Pressure From a Centrifuge

Summary Centrifuge capillary pressure measurements usually are conducted at atmospheric air pressure. In such measurements, any capillary pressure exceeding atmospheric pressure requires a negative pressure in the wetting phase. Experiments were conducted to examine the effect of air pressure on air/brine capillary pressure. First, drainage capillary pressure curves were determined for six low-permeability core samples under atmospheric pressure. Then, drainage capillary pressure curves were determined at an elevated air pressure of 112 psia [0.77 MPa] for the same samples. The two capillary pressure curves for each core sample generally are in close agreement. Both measurements reported in this paper and data from the literature indicate stable behavior for the wetting phase under negative pressure conditions.