Geological storage of in deep saline aquifers is achieved by injecting into the aquifers and displacing the brine. Although most of the brine is displaced, some residual groundwater remains in the rock pores. We conducted experiments to investigate factors that influence how much of this residual water remains after is injected. A rock sample was saturated with brines of two different salts. Supercritical was injected into the samples at aquifer temperature and pressure, and the displaced water and water-gas mixtures were collected and measured. The results show that deionized water drains more completely than either of the two brines, and NaCl brine drains more completely than brine. The ranking of the irreducible water saturation at the end of the experiment is deionized brine. The process of drainage can be divided into three stages according to the drainage flow rates; the Pushing Drainage, Portable Drainage, and Dissolved Drainage stages. This paper proposed a capillary model which is used to interpret the mechanisms that characterize these three stages.