This paper presents a numerical simulation study to investigate the risks and economic benefits of co-injection of water and CO2 in saline aquifers. Eclipse 300TM reservoir simulator was used to develop numerical models based on published data. We track CO2 solubility, gas saturation, brine pH, pressure build-up and the lateral displacement at the boundary to analyse the risks associated with co-injection of water and CO2. The simulation results are used in the standard economic model to further evaluate economic feasibility of the co-injection compared to the conventional CO2 injection. The base model scenario involves injecting supercritical CO2 at 0.94 MT/YR in to a 100 meters thick, homogeneous formation. For comparison purposes, two different engineered scenarios were designed to compare the pressure build-up, the CO2 dissolution and residual trapping data. The scenarios include Simultaneous Water and Gas Injection (SWAG) with producer wells in a no flow condition boundaries and SWAG without producer wells with an open boundary condition. The results show that SWAG injection without producer wells in an open boundary aquifer can accelerate the solubility and residual trapping which is comparable to that of SWAG injection in closed aquifer having producer wells. Also, the pressure build-up does not exceed the prescribed limit of the fracture pressure. The results appear optimistic and display a potential to accelerate CO2 dissolution and residual trapping in open saline aquifers by co-injecting water and CO2 in an open boundary formation with no production well. Even though this study was done on simplified aquifer system, the approach can be applied to real time aquifers.