Experimental validation of a pore-scale derived dimensionless capillary pressure function for imbibition under mixed-wet conditions

In this work, we validate experimentally a dimensionless capillary pressure function for imbibition at mixed-wet conditionsthat we developed recently based on pore-scale modeling in rock images. The difference to Leverett's traditional J-function is that our dimensionless function accounts for wettability and initial water saturation after primary drainage through area-averaged, effective contact angles that depend on the wetting property and distribution of oil- and water-wet grain surfaces. We hypothesized that describing these effective contact angles as a function of Amott wettability index relates the pore- and core-scale wettability, and that pore-scale imbibition simulations can provide these relations for specific rocks. In the present work, we adopt the dimensionless function to scale imbibition capillary pressure data measured on mixed-wet sandstone and chalk cores. The measured data practically collapse to a unique curve when subjected to the dimensionless capillary pressure function. For each rock material, we employ the average, dimensionless curve to reproduce the measured capillary pressure curves and obtain excellent agreement. We also demonstrate two approaches to generate different capillary pressure curves at other mixed-wettability states than that available from the data used to generate the dimensionless curve. The first approach changes the shape of the spontaneous- and forced-imbibition segments of the capillary pressure curve while the saturation at zero capillary pressure is constant. The second approach shifts the vertical level of the entire capillary pressure curve, such that the Amott wetting index (and the saturation at zero capillary pressure) changes accordingly. Thus, integrating these two approaches with the dimensionless function yields increased flexibility to account for different mixed-wettability states. The validated dimensionless function scales mixed-wet capillary pressure curves from core samples accurately, which demonstrates its applicability to describe variations of wettability and permeability with capillary pressure in reservoir simulation models. This allows for improved utilization of core experiments in predicting reservoir performance. Reservoir simulation models can also employ the dimensionless function together with existing capillary pressure correlations.