NATURAL BASALT REACTIVITY TOWARDS CO2: IMPLICATIONS FOR GEOLOGIC STORAGE IN MAFIC ROCKS

Keeping atmospheric warming below 2°C not only requires immediate reduction of CO₂ emissions, but also the active removal and sequestration of CO₂ from current point sources. One promising proposed strategy to reduce atmospheric CO₂ levels is geologic carbon sequestration (GCS). During GCS, CO₂ is injected in the deep subsurface, where it reacts with the geologic formation to precipitate carbonate minerals. While mineralization has been predicted to take thousands of years at some proposed GCS sites, rapid mineralization has recently been reported in mafic/ultramafic rocks, such as basalt. In the current study, we delve into the extent of CO₂ geochemical interactions with different types of natural basaltic rocks during 30 days of reaction. Secondary mineral precipitation was investigated on basalt surfaces using Raman spectroscopy and scanning electron microscopy with energy dispersive X-ray analysis (SEM-EDX) and changes to the pore structure were investigated using micro-X-ray computer tomography (µXCT). We found that carbon enrichment of the mineral surface was associated with higher Fe-content, rather than Mg/Ca, and that this enrichment correlated with decreases in the connected porosity. New findings have implications for site selection based on both formation reactivity towards CO₂ and impact on formation injectivity.