The aim of this proposal is to develop and validate a multi-phase flow model for simulating the highly transient flow phenomena taking place in the well-bore during start-up injection of CO2 mixtures into depleted gas fields. The objectives are to: 1.demonstrate the usefulness of the model developed based on its application to a real system as a test case; 2.use the findings in (1) to propose optimum injection strategies and develop Best Practice Guidelines for minimising the risks associated with the start-up injection of CO2 into depleted gas reservoirs. Grant number: UKCCSRC-C2-183.