Sensitivity of Joule–Thomson cooling to impure CO2 injection in depleted gas reservoirs

Depleted hydrocarbon reservoirs are key targets for geological storage of CO2. It is well known that Joule–Thomson cooling can potentially occur in reservoirs during CO2 injection. In this paper we investigate the impact of the presence of other gases (impurities) in the injected CO2 stream on Joule–Thomson cooling. A coupled heat and mass transport model is presented that accurately accounts for the pressure-, temperature-, and gas-compositional influences on the thermo-physical transport properties such as density, viscosity, specific heat capacity and Joule–Thomson coefficient. With this model it is shown that impurities affect both the spatial extent of the zone around the well bore in which Joule–Thomson cooling is induced and the magnitude of the cooling. SO2 expands the zone of cooling, O2, N2, and CH4 contract this zone, and H2S has a very small influence on the spatial extent of cooling. These relative behaviours are primarily controlled by the impact of the impurities on the specific heat capacity of the gas mixtures.