GEOPHYSICAL MONITORING OF THE CO2 PLUME AT SLEIPNER, NORTH SEA

In situ continuous monitoring of dissolved gases (N2, O2, CO2, H2) prior to H2 injection in an aquifer (Catenoy, France) by on-site Raman and infrared spectroscopies: instrumental assessment and geochemical baseline establishment

The establishment of a baseline of gases from an aquifer appears to be an essential prerequisite for monitoring and securing underground storage operations such as the storage of carbon dioxide (carbon capture and storage: CCS), methane or hydrogen. This study describes an innovative metrological technique dedicated to the in situ and continuous quantification of dissolved gases (CO₂, O₂, N₂, CH₄ and H₂) in a shallow aquifer, on the site of Catenoy (Paris Basin) with a water table at a depth of 13 m. Monitoring was carried out from May 7, 2019 to November 19, 2019, before the simulation of H₂ injection. Gases as vapors were collected from the aquifer through a nine-meter long, half-permeable polymer membrane positioned below a packer in a 25-meter deep well. Collected gases were analyzed simultaneously at the surface by fiber Raman (CO₂, O₂, N₂, CH₄ and H₂) and infrared sensors (CO₂). Gas concentrations were determined from Raman and infrared data, and then converted into dissolved concentrations using Henry's law. The dissolved gas concentrations were about constant over the 6 months period with average values of 31-40 mg L^-1 (CO₂), 8 mg L^-1 (O₂), 17 mg L^-1 (N₂), and 0 mg L^-1 (H₂, CH₄) indicating a very low variability in the aquifer. This is believed to allow for rapid detection of any possible abnormal concentration variation, in particular linked to an accidental arrival of gases such as hydrogen. Such an online gas measurement system can be deployed as is on any site type of underground storage without any need for adaptation.

Reducing risk in basin scale CO2 sequestration: a framework for integrated monitoring design

Injection of CO(2) into geological structures is a key technology for sequestering CO(2) emissions captured from the combustion of fossil fuels. Current projects inject volumes on the order of megatonnes per year. However, injection volumes must be increased by several orders of magnitude for material reductions in ambient concentrations. A number of questions surrounding safety and security of injection have been raised about the large scale deployment of geological CO(2) sequestration. They are site specific and require an effective monitoring strategy to mitigate risks of concern to stakeholders. This paper presents a model-based framework for monitoring design that can provide a quantitative understanding of the trade-offs between operational decisions of cost, footprint size, and uncertainty in monitoring strategies. Potential risks and challenges of monitoring large scale CO(2) injection are discussed, and research areas needed to address uncertainties are identified. Lack of clear guidance surrounding monitoring has contributed to hampering the development of policies to promote the deployment of large scale sequestration projects. Modeling provides an understanding of site specific processes and allows insights into the complexity of these systems, facilitating the calibration of an appropriate plan to manage risk. An integrated policy for risk-based monitoring design, prior to large scale deployment of sequestration will ensure safe and secure storage through an understanding of the real risks associated with large scale injection.