Identifying and Understanding Microbial Methanogenesis in CO Storage.

Carbon capture and storage (CCS) is an important component in many national net-zero strategies. Ensuring that CO can be safely and economically stored in geological systems is critical. To date, CCS research has focused on the physiochemical behavior of CO, yet there has been little consideration of the subsurface microbial impact on CO storage. However, recent discoveries have shown that microbial processes (e.g., methanogenesis) can be significant. Importantly, methanogenesis may modify the fluid composition and the fluid dynamics within the storage reservoir. Such changes may subsequently reduce the volume of CO that can be stored and change the mobility and future trapping systematics of the evolved supercritical fluid. Here, we review the current knowledge of how microbial methanogenesis could impact CO storage, including the potential scale of methanogenesis and the range of geologic settings under which this process operates. We find that methanogenesis is possible in all storage target types; however, the kinetics and energetics of methanogenesis will likely be limited by H generation. We expect that the bioavailability of H (and thus potential of microbial methanogenesis) will be greatest in depleted hydrocarbon fields and least within saline aquifers. We propose that additional integrated monitoring requirements are needed for CO storage to trace any biogeochemical processes including baseline, temporal, and spatial studies. Finally, we suggest areas where further research should be targeted in order to fully understand microbial methanogenesis in CO storage sites and its potential impact.