Exotic Carbonate Mineralization Recovered from a Deep Basalt Carbon Storage Demonstration

Abstract

Mitigating climate change requires transformational advances for carbon dioxide removal, including geologic carbon sequestration in reactive subsurface environments. The Wallula Basalt Carbon Storage Pilot Project demonstrated that CO 2 injected into >800 m deep Columbia River Basalt Group flow top reservoirs mineralizes on month-year timescales. Herein, we present new optical petrography, micro-computed X-ray tomography, and electron microscopy results obtained from sidewall cores collected two years after CO 2 injection. As no other anthropogenic carbonates from geologic carbon storage field studies have been recovered, this world-unique sample suite provides unparalleled insight for subsurface carbon mineralization products and paragenesis. Chemically zoned nodules with Ca/ Mn-rich cores and Fe-dominant outer rims are prominent examples of the neoformed carbonate assemblages with ankerite−siderite compositions and exotic divalent cation correlations. Paragenetic insights for the timing of aragonite, silica, and fibrous zeolites are clarified based on mineral texture and spatial relationships, along with time-resolved downhole fluid sampling. Collectively, these results clarify the mineralogy, chemistry, and paragenesis of carbon mineralization, providing insight into the ultimate fate and transport of CO 2 in reactive mafic−ultramafic reservoirs.

Facile Metal Release from Pore-Lining Phases Enables Unique Carbonate Zonation in a Basalt Carbon Mineralization Demonstration

“…28,29 Petrographic studies performed on these smaller carbonate assemblages pointed to the likelihood of a uniform composition throughout the length of these smaller nodules. 29 In contrast, Zone 2 and Zone 3 contained medium to large nodules, ∼200 to 1000 μm diameter in size. Of particular interest are those recovered from Zone 2, where compositional zonation has been reported using petrographic studies and cross-sectional SEM−EDS point scans.…”

“…Of particular interest are those recovered from Zone 2, where compositional zonation has been reported using petrographic studies and cross-sectional SEM−EDS point scans. 21,29 Figure 1 shows a stained thin section of a nodule recovered from Zone 2 (857.1 m bgs), which reveals a central core rich in Ca, while the exterior rim is rich in Fe. Additionally, the Ca-rich core displays uniform extinction, while the outer region displays cross-extinction due to its spherulitic nature.…”

“…This leads to an Fe dominant calcian siderite-like exterior, Ca 0.34 Fe 0.65 Mg 0.01 CO 3 , with only very minor amounts of Mn (<0.01%). As mentioned previously, this Fe-rich composition is very similar to that of the smaller, more uniform nodules found in Zone 1 …”

“…Additionally, pore fluid sampling studies conducted at the Wallula site post-CO 2 injection also showed an aqueous Mn concentration to be extremely low; approximately 1000 times lower than Fe (∼0.1 ppm vs 100 ppm). 29 Insights into Mn-enrichment can be obtained from a comparative pore-scale μ-XRF chemical mapping analysis between pre-and post-injection SWCs, as shown in Figure 4. The Mn elemental distribution maps clearly reveal that a majority of the Mn found in basalt is localized within the pore-lining alteration, in very close proximity to the carbonate nodules formed.…”

Pore-Scale Microenvironments Control Anthropogenic Carbon Mineralization Outcomes in Basalt

“…Some experimental data and stoichiometric models predict that silica as well as aluminosilicates are produced in carbonation reactions with basalt. ,,− Therefore, the co-precipitation of silica and other materials observed in several instances in all three zones suggests that the supercritical CO 2 did react with and dissolve the host rock rather than just precipitating out of solution or from dissolving and reprecipitating pre-existing carbonate minerals.…”