  Wettability is a pore-scale property that has an important impact on
capillarity, residual trapping, and hysteresis in porous media systems. In many
applications, the wettability of the rock surface is assumed to be constant in
time and uniform in space. However, many fluids are capable of altering the
wettability of rock surfaces permanently and dynamically in time. Experiments
have shown wettability alteration can significantly decrease capillarity in
CO$_2$ storage applications. For these systems, the standard capillary-pressure
model that assumes static wettability is insufficient to describe the physics.
In this paper, we develop a new dynamic capillary-pressure model that takes
into account changes in wettability at the pore-level by adding a dynamic term
to the standard capillary pressure function. We simulate the dynamic system
using a bundle-of-tubes (BoT) approach, where a mechanistic model for
time-dependent contact angle change is introduced at the pore scale. The
resulting capillary pressure curves are then used to quantify the dynamic
component of the capillary pressure function. This study shows the importance
of time-dependent wettability for determining capillary pressure over
timescales of months to years. The impact of wettability has implications for
experimental methodology as well as macroscale simulation of
wettability-altering fluids.
