In Situ Characterisation of Three-Phase Flow in Mixed-Wet Porous Media
Using Synchrotron Imaging.
Abstract
We use fast synchrotron X-ray imaging to understand three-phase flow in
mixed-wet porous media to design either enhanced permeability or
capillary trapping. The dynamics of these phenomena are of key
importance in subsurface hydrology, carbon dioxide storage, oil
recovery, food and drug manufacturing, and chemical reactors. We study
the dynamics of a water-gas-water injection sequence in a mixed-wet
carbonate rock. During the initial waterflooding, water displaced oil
from pores of all size, indicating a mixed-wet system with local contact
angles both above and below 90 •. When gas was injected, gas displaced
oil preferentially with negligible displacement of water. This behaviour
is explained in terms of the gas pressure needed for invasion. Overall,
gas behaved as the most non-wetting phase with oil the most wetting
phase; however pores of all size were occupied by oil, water and gas, as
a signature of mixed-wet media. Thick oil wetting layers were observed,
which increased oil connectivity and facilitated its flow during gas
injection. A chase waterflooding resulted in additional oil flow, while
gas was trapped by oil and water. Furthermore, we quantified the
evolution of the surface areas and both Gaussian and the total
curvature, from which capillary pressure could be estimated. These
quantities are related to the Minkowski functionals which quantify the
degree of connectivity and trapping. The combination of water and gas
injection, under mixed-wet immiscible conditions leads to both
favourable oil flow, but also to significant trapping of gas, which is
advantageous for storage applications.