CO2 reaction rates in sub-seafloor basalt for offshore geologic carbon sequestration

Abstract:

Sub-seafloor basalts are Earth-abundant and unique in terms of geologic carbon storage because they allow for the in-situ mineralization of CO_2, captured from the atmosphere or industrial sources, into thermodynamically stable solid carbonates. The dissolution rates of different sub-seafloor basalt samples from the Caribbean and the Cascadia Basin (IODP Hole U1362A) were measured under acidic conditions (pH 3, mimicking CO₂ saturated water). The mineralogical compositions and degree of alteration were correlated to their dissolution behaviors. Experiments were conducted using a differential bed reactor system to determine initial Ca extraction rates for up to 2 hrs and reaching far-from-equilibrium conditions. Results show that massive basalts with moderate to high alteration are more reactive than flow channel basalts with slight to moderate alteration. Also, the dissolution rate of Caribbean and Cascadia Basin basalt samples is relatively fast in comparison with kinetic rate data published in the literature. The published data, however, have been mostly reported for steady-state dissolution rather than initial dissolution rates. These findings suggest that although the reactivity of ocean basalt samples is affected by both mineralogy and the degree of prior alteration, CO₂ may mineralize relatively quickly after injection. Fast in situ reactivity could require site-specific strategies to enable the maximum amount of CO₂ to be injected without clogging the reservoir and subsequently mineralize into carbonates.