Chromatographic partitioning of impurities contained in a CO2 stream injected into a deep saline aquifer: Part 1. Effects of gas composition and in situ conditions

A series of laboratory experiments were carried out to examine the chromatographic partitioning of impurities contained in a stream of CO2 injected into a deep saline aquifer. The experiments were carried out under static (no flow) and dynamic conditions, mainly with H2S as the impurity in the CO2 stream, for 2%, 5% and 30% concentrations, and for in situ conditions of high pressure, temperature and water salinity, and also for pure water at a lower pressure and temperature. In addition, experiments were conducted using CH4, N2 and SO2 at 5% concentration as the ‘Impurity’ in the CO2 stream. The experiments show that gases in an impure stream of CO2 being injected into a deep saline aquifer will chromatographically partition at the leading edge of the gas advancing through the water-saturated porous medium as a result of differential solubility in aquifer water. The solubility of the impurity gas in the CO2 stream compared to that of CO2 is the most dominant factor in regard to the breakthrough time and initial gas concentrations in the effluent. The in situ conditions of pressure, temperature and water salinity also affect the chromatographic partitioning of CO2 and impurities contained in the injection stream through their general effect on the solubility of all gases. The concentration of the impurity gas in the feed gas stream has a secondary effect on the breakthrough and time lag decreasing with increasing concentration of the impurity gas. These experimental findings are significant for understanding the fate of the injected CO2 and associated impurities contained in an injection stream, in devising monitoring procedures and protocols, and in developing emergency response plans in case of leakage of CO2 and associated impurities.