Effect of higher H2S concentration over CO2 in acid gas mixtures during geosequestration

Abstract

Decarbonisation of most industrial processes is imperative to achieve climate neutrality. In oil and gas, carbon dioxide (CO2) and natural gas are being discovered together with increasingly higher quantities of hydrogen sulphide (H2S). The negative effects of acid gases (predominantly CO2 and H2S) in that industry mean they have to be separated before both natural gas and petroleum fuels can be classified as safe for transportation and usage. The separated acid gas, usually composed of a higher CO2 volume is stored and utilised in enhanced oil recovery (EOR) or geologically stored (geosequestered) in formations. There are increasingly instances in which higher volume of H2S acid gas mixtures are being discovered and explored. In this work, the effects of a higher mole percentage H2S in an acid gas mixture is investigated using molecular dynamics simulations. The analysis found that it was easier for higher CO2 acid mixtures to reach pressure convergence comparatively. It has also been discovered that higher H2S acid gas mixtures had lower interfacial tension, which makes them more hydrophilic and more miscible with the formation water. The higher H2S acid gas content mixtures also have wider water coverage widths and greater interfacial interactivity between the injected and formation fluids. From the density profiles, H2S gas in the higher H2S acid gas mixture is found to have more influence on the higher H2S acid gas/water injection/sequestration process compared to the effect of CO2 on the higher CO2 acid gas mixture/water. While H2S is slightly more polar than the nonpolar CO2, the carbon of CO2’s ability to form strong dipole–dipole interactions with the oxygen of water increases the CO2's polarity, and this is reflected in the assertion of the primacy of the $${\text{O}}_{{{\text{H}}_{{2}} {\text{O}}}} \cdots {\text{C}}_{{{\text{CO}}_{{2}} }}$$ O H 2 O ⋯ C CO 2 interaction over all other pairs from the radial distribution function in the water/acid gas mixture during geosequestration. This demonstrates also that a reduction in interfacial tension is possible even for hydrophobic phases.