Effects of Capillarity and Solubility in Brine on CO2 Injectivity into an Aquifer

This study aims to investigate the effects of the capillary and solubility characteristics of the CO2-brine-rock systems on CO2 injectivity and storage capacity numerically. The general-purpose numerical simulator for multicomponent, multiphase fluid flow, TOUGH2 is used as numerical tool. The EOS module, ECO2N which considers the fluid system consisting of CO2 and brine is incorporated to TOUGH2 for the dynamic phase changes during the transport. A generic axissymmetric 2D aquifer model is created. Two distinct capillary pressure models are used. A CO2 injection rate of 60 kg/s is assured in three injection blocks from the bottom of the model. Due to the high solubility of CO2 into brine, the effect of the capillary forces on injectivity is determined to be less pronounced compared to inert gases. Another important effect of the solubility is on the critical gas saturation which decreases below the determined values of relative permeability curves. The increasing salinity of the aquifer brine increases the effect of the capillary forces on the injectivity. Because of the salting out effect less amount of CO2 dissolves in the brine. The salt precipitation is found to be another factor influencing the injectivity negatively.