Implications of CO2 mass transport dynamics for large-scale CCS in basalt formations

Flood basalts have the potential for relatively rapid mineral trapping when used as an injection target for CO2 storage. Although CO2 mineral trapping in basalt has been studied in various ways, including two successful small-scale pilot projects, questions remain about how the system will behave during a full-scale CO2 storage project. These questions include whether a full-scale CO2 injection can expect complete mineralization on time scales similar to those observed during small-scale injections, as well as how the properties of the target formation will be altered by decades of geochemical reactions. Recently, we developed VIRTra, a vertically integrated reactive transport model specifically designed for efficient field-scale simulation of CO2 storage in reactive rocks. The present work uses this new method to explore the behavior of the water-CO2-basalt system during large-scale injection of separate-phase CO2 in a deep saline aquifer. Trends in the assembled data indicate that a high rate of CO2 dissolution into the aqueous phase results in faster mineralization. However, the time scales on which full mineralization of the injected CO2 is achieved are on the order of centuries, orders of magnitude larger than those observed in small-scale field tests. This appears to be a direct result of the increase in scale of the injection. During the injection period, changes in porosity are observed to be highly dependent on mineral reaction kinetics. Important areas of further research include the impact of mineralogy and formation water composition on the mineralization process, and the relationship between porosity and permeability in vesicular rock types.