Dissolution kinetics of CO2 and CO2-SO2 mixtures in water and brine at geological storage conditions of 16 MPa and 333 K

Abstract

To minimize the costs of geological storage of carbon dioxide captured from different emitting sources, the purification steps to decrease the concentrations of accessory gases such as sulfur dioxide (SO2) should be optimized according to the needs of the geological storage complexity. SO2 might acidify the formation water and influence chemical reactions in the subsurface reservoir. For adequate predictions of the impact of processes influenced by the accessory gases on the near-well rock integrity, injectivity and long term storage capacity, kinetic data for the mass transfer of CO2 and SO2 into the aqueous formation waters at in situ conditions are crucial.In this study the mass transfer of CO2 and SO2 was investigated from pure CO2 or a CO2-SO2 mixture into pure water or saline water (S = 250 g L−1) at conditions of 16 MPa pressure and a temperature of 333 K in a stirred titanium batch reactor. At the same stirrer speed of 190 rpm the mass transfer coefficient φKL of CO2 into water was determined to be 12.9 cm h−1, which is approximately a third of that of SO2 with φKL(SO2) = 34.9 cm h−1. The presence of SO2 did not affect the dissolved equilibrium CO2 concentration (1.17 ± 0.03 mol L−1 in pure water, 0.50 ± 0.02 mol L−1 in brine) or the mass transfer coefficient for CO2. In less than two hours the equilibrium between the aqueous phase and the CO2-SO2 phase was attained. At equilibrium, ca. 60% of the SO2 was dissolved into the aqueous phase and the rest remained in the supercritical CO2 phase. The Henry constant Hcp for SO2 under the experimental conditions was determined to be 2.7 mol m-³ Pa−1. The different mass transfer coefficients of CO2 and SO2 – and other accessory gases – should be included in geochemical models to adequately describe the distribution of these trace gases in the reservoir and address the impact of reactive trace gas compounds on fluid-rock reactions.