Detecting Seafloor Gas Leakage from Geologic Carbon Storage Sites: A Laboratory-Scale Distributed Acoustic Sensing Evaluation.

Carbon capture and storage (CCS) is a critical technology for mitigating climate change by reducing atmospheric carbon dioxide concentrations. Effective monitoring of CCS sites is essential to ensure that injected CO2 remains securely trapped and does not leak into the shallow subsurface or atmosphere. Large-scale CCS in the Gulf of Mexico could be facilitated by extensive existing infrastructure and suitable geologic containment; however, legacy wells and structurally complex geology remain critical challenges for ensuring storage integrity. Traditional monitoring methods, while effective, often lack the temporal resolution and cost-effectiveness needed for comprehensive leak detection, particularly in shallow seafloor environments. This study explores the potential of distributed acoustic sensing (DAS) as a novel monitoring solution for near-surface CO2 leakage at geologic carbon storage (GCS) sites. We conducted a laboratory-scale controlled nitrogen gas bubble injection experiment to compare DAS responses at varying cable burial depths and evaluated these signals using simultaneous hydrophone measurements. Results indicate that while DAS effectively detects acoustic signals from bubbles in both sediment and water columns, its response amplitude diminishes with increased burial depth. These findings suggest that DAS could serve as a promising technology for long-term monitoring of marine GCS sites, providing insights into near-surface gas flow and leak detection.