Impact and applicability of capillary pressure hysteresis on vertically averaged
CO2 migration
Elsa du Plessis1, Helge K. Dahle1, Jan M. Nordbotten1, Sarah E. Gasda2 and Knut-Andreas Lie3
1
Department of Mathematics, University of Bergen, Norway
Uni CIPR,Uni Research, Bergen, Norway
3
SINTEF ICT, Dept. of Applied Mathematics, Oslo, Norway
2
Injection of CO2 into a saline aquifer results in a thin layer of CO2 that overrides and bypasses the
resident brine due to buoyancy and viscous instability. The lateral spread of the plume may be
several kilometers in diameter and may migrate horizontally over tens of hundreds of kilometers
during the post-injection period, while the vertical migration may span only several tens of meters
over the height of the aquifer. Due to this large aspect ratio, CO2 migration may be approximated by
a vertically averaged formulation, which reduces the full three-dimensional model to a twodimensional one. The inclusion of a capillary fringe, as opposed to a sharp interface, has been shown
to significantly affect the plume shape and migration extent during the post-injection period. In
addition, drainage and imbibition hysteresis in the capillary pressure and relative permeability
functions could further alter the plume formation, speed of residual trapping and the eventual
migration extent of injected CO2.
Whereas previous reduced-modeling efforts employed simplified computational implementations of
hysteresis models for the CO2-storage problem, in this work a capillary fringe with a full hysteresis
model is considered that focuses specifically on the path-dependence of capillary pressure and its
implementation within the vertically averaged modeling framework. We investigate the effect of
drainage and imbibition cycles on fine-scale capillarity, and thus on the vertically integrated
equations and parameters, in order to quantify the impact of hysteresis on CO2 migration. A onedimensional formulation is implemented with discussion on the implementation strategy and the
potential implications of using a more complex hysteresis model.