Carbon Mineralization in Reactive Silicate Zones

Basalt reservoirs could provide safe and permanent large-scale carbon sinks, which are critical components of negative emission technologies to meet global CO₂ emission reduction targets. While the expediency and security of CO₂ trapping through mineralization has been proven in the field, the long-term implications of carbonate precipitation on reservoir integrity and fluid transport remain unclear. In this work, we explore carbonate precipitation and alteration patterns induced by CO₂ injection in diffusion-limited zones of reactive basalt silicate minerals where the majority of CO₂ mineralization is expected to occur. Core flooding experiments were designed to optimize the likelihood of achieving rapid and near-complete carbonation by creating packed beds of reactive mineral powders (olivine and wollastonite) within flood basalt cores. All of the packed beds evidenced conversion of silicates to carbonate minerals with up to 58% carbonation efficiency. Consistent with complementary reactive transport model predictions and prior work on packed beds in static systems, carbonation generally reached a local maximum near the center of the packed beds due to opposing geochemical gradients. Despite equivalent initial amounts of Ca- and Mg-silicate powders, Ca-carbonates were the predominant reaction product as Mg-carbonate precipitation was kinetically limited and in direct competition with more favorable hydration (i.e., serpentinization) of Mg-silicates. While volume expansion associated with carbonation reactions has been held critical to optimizing carbonation efficiency through continual renewal of the reactive surface area, no evidence of reaction-induced fracturing was observed in these tests as precipitates were accommodated by the available pore space and simultaneous dissolution of the packed beds.