The Influence of Capillary Entry-Pressure Representation on CO2 Solubility Trapping

Abstract

The typical shape of a capillary-pressure curve is either convex (e.g., Brooks-Corey model) or S-shaped (e.g., van Genuchten model). The difference between the two models occurs in the representation of the capillary entry pressure. This difference does not lead to significantly different simulation results when modeling CO2 sequestrations in aquifers without considering CO2 dissolution. However, we observe that the van-Genuchten-type capillary- pressure model accelerates CO2 solubility trapping significantly compared with the Brooks-Corey-type model. For the representative examples we study, the differences can be so large as to have complete dissolution of the CO2 plume versus persistence of over 50% of the plume over a 5000-year period. Most CO2 sequestration simulations in the literature employ one of the two capillary-pressure models, and it is important to recognize that these two representations lead to very different predictions of long-term CO2 sequestration.