Designing Risk-Based Monitoring for Offshore CO₂ Storage

Monitoring starts with a decision model

A storage-monitoring programme is often described as a list of instruments: seismic surveys, pressure gauges, seabed sensors, water sampling and satellite observations. The harder task comes before technology selection.

The project must first define:

• what behaviour is expected from the storage complex;
• which deviations would be material;
• where those deviations could be observed;
• how evidence from one method would trigger follow-up by another;
• who receives the evidence and what decision it supports.

Without this structure, adding more sensors can increase data volume without improving assurance.

Baseline evidence has more than one purpose

A baseline should establish the natural and operational conditions against which later observations will be interpreted. For offshore projects, that may include subsurface, well, seabed, water-column and ecological evidence.

The baseline also creates a reference for future surveys. Positioning, acquisition parameters, processing assumptions and uncertainty should therefore be recorded in ways that make repeat campaigns genuinely comparable.

Use complementary methods

No single monitoring technology provides complete coverage across space, depth, time and sensitivity. A robust design combines methods with different strengths.

Subsurface imaging

Time-lapse seismic and related geophysical methods can provide broad spatial evidence of changes within the storage complex. Their value depends on repeatability, detectability and a clear interpretation framework.

Well and reservoir observations

Pressure, temperature and downhole measurements provide direct information at specific locations. They are especially useful when connected to reservoir models and operational history.

Seabed and environmental observations

Seabed, water-column and ecological methods help establish whether unexpected migration has produced observable effects in the marine environment. They should be targeted to plausible pathways and natural variability.

Continuous and remote observations

Fiber-optic sensing, permanent seabed systems and remote-sensing methods may improve temporal coverage. They do not remove the need for interpretation, calibration or follow-up methods.

Build escalation logic before operations

A monitoring plan becomes operationally useful when it explains what happens after an observation.

A simple escalation structure can distinguish:

1. expected variation, which is recorded and reviewed;
2. an observation requiring confirmation, which triggers quality checks or repeat acquisition;
3. a credible anomaly, which activates additional monitoring and technical review;
4. a material deviation, which supports operational or regulatory action.

This logic should link data quality, interpretation confidence, responsibilities and communication pathways.

Let the programme evolve with evidence

Risk-based monitoring is not a justification for reducing effort prematurely. It is a way to adjust monitoring intensity when accumulated evidence changes the understanding of the storage complex.

Any change should remain traceable to updated risk assessment, observed performance and applicable regulatory requirements. The programme may become more focused over time, but the evidence chain should become stronger rather than thinner.

OceanHub perspective

OceanHub treats monitoring as an integrated design problem across geophysics, wells, seabed systems, environmental observations and information management. The objective is not to promote one sensor. It is to build a monitoring system in which every method has a defined role in a defensible decision process.