The role of capillary trapping during geologic CO₂ sequestration

Abstract

Capillary trapping is thought to be one of the primary $CO_{2}$ fixing mechanisms in a porous medium when it is stored. While $CO_{2}$ is injected, gas displaces formation water (brine) in the process called drainage. In the case of the rock mass wetted by water, formation water remains adsorbed in wall pores and micropores. Once the injection process has been completed, gas is displaced by the natural water in the process referred to as imbibition. In that way $CO_{2}$, being a non-wetting phase, is held in the form of dispersed bubbles as an immobile phase. The process occurs fast and allows for a regular storage of large amounts of $CO_{2}$. The process is dependent upon numerous parameters, including capillary pressure and contact angle, but such measurements cannot be easily taken for rock cores in reservoir conditions. Another problem is the fact that it is difficult to separate the impact of such mechanisms as dis-solution and mineral trapping. So far capillary trapping has been deeply analyzed in terms of hydrocarbon recovery and contaminant remediation. The goal of this article is to:– present a physiochemical basis of capillary trapping in CCS context,– simulate the impact of relative permeability hysteresis on geological $CO_{2}$ storage.