A research team led by the GEOMAR Helmholtz Centre for Ocean Research Kiel has commenced a critical geophysical survey off the Canadian Pacific coast to establish baseline parameters for sub-seabed carbon capture and storage (CCS) in basalt formations.
Undertaken in collaboration with Ocean Networks Canada and the University of Victoria, the SO321-3 expedition aboard the research vessel SONNE will deploy controlled source electromagnetics (CSEM) to map subsurface electrical resistivity ahead of planned CO₂ injections.
The basalt advantage
While depleted oil and gas reservoirs currently dominate CCS portfolios, sub-seabed basalt formations are attracting significant industry interest. Carbon dioxide injected into these reactive volcanic rocks undergoes rapid natural geochemical reactions, converting into solid carbonate minerals. This permanent in-situ mineralisation significantly reduces long-term containment risks. However, verifying the structural integrity of the reservoir and tracking the CO₂ plume requires high-resolution pre-injection characterisation.
CSEM methodology and measurement uncertainty
To characterise the potential storage site—located near the established IODP drilling site U1362—the team is deploying a proprietary CAGEM transmitter alongside a seabed array of 12 ocean bottom electromagnetic (OBEM) stations. The system measures the varying electrical resistance of subsurface rock layers up to several hundred metres below the seafloor, delineating reservoir structure and identifying potential migration pathways.
A central operational focus of the 72-hour geophysical window is quantifying measurement uncertainty, which is a critical threshold for reliable long-term CCS monitoring. To achieve this, the expedition will survey the initial profile in both directions sequentially.
"Before CO₂ is injected into the subsurface, we need to know exactly how the subsurface is structured," said expedition leader Dr Sebastian Hölz, a geophysicist at GEOMAR. "If we survey the same profile twice under conditions that are as similar as possible, we can estimate which changes occur even after a repeated measurement. This will enable us to ultimately understand which changes could be triggered by an injection."
Future monitoring infrastructure
Data from the dual-directional passes will define the baseline signal-to-noise ratio required for future measurement, monitoring, and verification (MMV) protocols. The expedition's findings are expected to directly inform the engineering and deployment of a permanently installed electromagnetic monitoring system designed to track reservoir evolution following initial CO₂ injection.
