Monitoring and verification of CO₂ plumes is essential in understanding the effectiveness and potential risks associated with Geological Carbon Sequestration (GCS). Despite varying degrees of ambiguity in the regulations for the monitoring requirements in various jurisdictions, all regulators require that the operator monitors the injection, migration, and stabilisation of the plume. Decades of post-injection monitoring can be a costly task that requires careful planning.

The essence of monitoring lies in the regular assessment of the behaviour and movement of the CO₂ plume within the geological storage site. Each risk mechanism component is associated with inherent and operational risks. The assessment of such risks underpins the planned monitoring solution which may include direct or inferred measurements of pressure, temperature, and saturation (or their changes) within the CO₂ storage complex. By monitoring these parameters, the operator can ensure that the stored CO₂ is being contained as intended and is not having an adverse impact (environment, human, reputational) (e.g. significant leakage into the water column).

Verification, on the other hand, focuses on confirming the accurate placement and containment of the CO₂ within the storage complex. This involves the use of various monitoring techniques, such as seismic surveys, well logging, and pressure testing, to assess the integrity of the storage reservoir and detect any potential leaks or migration pathways. Verification is crucial in ensuring the long-term safety and reliability of CCS projects.

Monitoring plans are site-specific, but learnings and best practices can be transferred between projects. This talk aims to introduce some high-level approaches for risk assessment and discuss how this might link to a proposed monitoring plan.