Determine the Capillary Pressure Curve using a pore morphology method to evaluate the distribution of non-wetting and wetting phases for a given (quasi-stationary) capillary pressure and, in this way, determine the saturation . The capillary pressure curve is determined by repeating this calculation for a variety of capillary pressures. The capillary pressure curves for drainage and imbibition are usually not identical but show a hysteresis effect.

SatuDict can calculate the phase distribution for the two types of phase displacement, namely Drainage and Imbibition. Below, they are shown with a digital rock, where the Oil reservoir is at the top and the Water reservoir is at the bottom. The left and right sides of the structure have symmetric boundary conditions.

Drainage displacement occurs when a non-wetting infiltrating fluid (here Oil) enters the porous media and displaces a wetting fluid (here Water) that has saturated the media.

The opposite case, Imbibition, occurs when a wetting fluid invades the space around the material and the material surface, which had been occupied by a non-wetting fluid, displaces it (here, Water displaces Oil).

Not only the pore size, but also the connectivity of the phases to a phase reservoir, determines the final distribution of the phases and has to be accounted for. After Drainage, a residue of the wetting phase or, after Imbibition, a residue of the non-wetting phase can remain trapped in the porous media as Residual Displaced. The Residual is the part of the displaced fluid that is not connected to the displaced fluid outlet anymore during the simulated process.

The mechanisms of the displacements in drainage and imbibition are quite different and the two cases should not be confused. Typically, in drainage the invading non-wetting fluid only enters a pore if the capillary pressure is equal to or greater than the threshold pressure of that pore. The threshold pressure corresponds to the capillary pressure in the narrowest part of the pore. However, in imbibition at low injection rate the invading wetting fluid enters the narrowest pores before any other pore is considered.