INFLUENCE OF H2S AND SO2 IN CO2 FLUID ON REACTIVITY OF SANDSTONE UNDER NEAR-FIELD AND FAR-FIELD CONDITIONS

Deep saline aquifers are considered as repositories for captured CO₂. Here the influence of co-injected H₂S and SO₂ on the reactivity of sand stones was evaluated. Depending on the source of the CO₂, these sulfur compounds are expected to be co-injected. The reactivity of both red and grey sand stones under near-field conditions (supercritical fluid around the point of injection) and far-field conditions (aqueous phase influenced by the injection of CO₂) was studied.

Both flow-through and batch experiments simulating near-field conditions were conducted. Crushed sandstone packed in a column was exposed to a co-mingled stream of supercritical CO₂ and an aqueous H₂S or SO₂ solution (75°C). Batch experiments were conducted in small autoclaves loaded with crushed sandstone, small amount of water, and dry ice heated to 75°C. The study of far-field conditions has been limited thus far to experiments with aqueous solutions containing bicarbonate and sulfite at 75°C. The reacted sandstones were recovered at the conclusion of each type of experiment and analyzed for changes in mineralogical composition using X-ray Diffraction. Selected reaction products were also submitted for Mössbauer spectroscopy.

The addition of H₂S has the most pronounced effect on the sandstones under near-field conditions in batch experiments. The sandstones turn black and siderite formation is confirmed with XRD. Pending Mössbauer data will be used to resolve other changes in iron oxide mineralogy. However, in flow-through experiments with the same sandstone, the material remains red even after exposure to H₂S containing scCO₂. Availability of water at the mineral surface might be a critical factor in the reactivity of co-injected H₂S. Exposure to SO₂ and scCO₂ (near-field experiments) or sulfite and bicarbonate (far-field experiments) appears to have little effect on the iron mineralogy on the basis of XRD analyses.