DF1-1 gas field in the west of the South China Sea is associated with high concentration of CO2. Many options have been assessed by the operator (CNOOC) in recent years in order to dispose the CO2 separated from the gas stream. In this study, geological storage of CO2 into offshore saline aquifers near the gas separation plant on the Hainan Island is considered, and a demonstration project is proposed and designed in terms of aquifer selection and assessment, CO2 transportation and injection, and project economics. Several aquifer structures around the gas field and near the Hainan Island were investigated and assessed with respect to geological structure, reservoir and trap features, fluid properties, storage capacity and site location. A saline aquifer (namely LT13-1), 60 km offshore the Hainan Island, was chosen as the storage site. CO2 will be transported by a long-distance subsea pipeline at high pressure and injected into the aquifer via a subsea well-head and through a horizontal well. Reservoir simulation and injectivity analysis have been conducted to estimate the injection rate and pressure, and also to predict the movement of CO2 after injection. A scoping economic analysis of the project was also conducted and presented in the paper.