Basalt reservoirs are attractive geologic CO2 storage repositories, as they also promote mineral trapping of injected CO2 in the form of carbonate minerals. In this study, a long-term core flooding experiment was conducted with in situ X-ray computed tomography (XCT) to evaluate CO2-induced basalt dissolution and carbonate precipitation as functions of injectate alkalinity. A saw-cut, heterogeneous basalt core was subjected to a constant flow of CO2-saturated fluids for 62 days, where step increases in the alkalinity of the CO2-saturated fluids (via increasing NaHCO3) were introduced to promote conditions favoring mineral carbonation. Despite reaching temperature (100 °C), pressure (10 MPa PCO2), and pore fluid chemistry (0.64 M NaHCO3) conditions that have been demonstrated to promote rapid and extensive carbonate precipitation in prior work, minimal precipitation occurred over the 62-day experimental duration, while net dissolution occurred. The results underscore the complexity of interplay among controls of coupled basalt dissolution and carbonate precipitation reactions, where elevated alkalinity will not definitively ensure or enhance CO2 mineralization across all basalt lithologies.
Dong et al. (Tue,) studied this question.