Research on monitoring methods and technical systems of CO₂ mineralization in basalt formation

CO₂ storage in basalt formation has received much attention as one of the new CO₂ geological storage methods worldwide. It has been successfully implemented in Iceland and the United States. During the process of carbon storage in basalt, CO₂ is transformed into solid minerals, which differs significantly from carbon storage in sandstone reservoirs in terms of CO₂ injection method, burial depth, and physical property requirements of reservoir cap. Significant differences are also found in both monitoring schemes. By studying the Wallula basalt storage project in the United States and the Carbfix mineralization storage project in Iceland, this study compared and summarized the monitoring schemes of basalt storage for different CO₂ injection phases (supercritical and gas dissolved state). The monitoring systems of basalt storage, saline aquifer storage, oil and gas reservoir storage were further compared. The storage monitoring system for sandstone reservoir focuses on the structural integrity of the CO₂ reservoir and evaluating the change of CO₂ concentration along the potential leakage path. The monitoring period is usually more than 50 years. In contrast, basalt mineralization and storage technology focus on the mineralization reaction of “water-CO₂-basalt”. Its monitoring system is mainly to describe the property changing pattern of each substance from downhole fluid (chemical compositions, tracer concentrations, pH, etc.) during the storage cycle. Moreover, it evaluates the degree of mineralization reaction and the storage efficiency of basalt qualitatively and quantitatively. Finally, based on the systematic and comprehensive monitoring scheme of saline aquifer and oil and gas reservoir storage, the basalt-CO₂ mineralization storage monitoring technology is analyzed systematically and a complete set of basalt-CO₂ mineralization storage monitoring scheme and process is summarized. By comparing different CO₂ storage monitoring systems, this study proposes a universal “subsurface-wellbore-surface-ground” monitoring scheme for basalt-CO₂ mineralization: monitoring scope, purpose, program, and alert system. This provides basic information for the future basalt-CO₂ mineralization storage demonstration project.