HYpersaline Plume Emission and Risk from CO₂ Storage (HYPER-CO2)

Pressure management is an important part of maintaining the integrity and storage capacity of carbon dioxide storage reservoirs. In saline aquifer storage systems, this may require the production and disposal of reservoir brines. These brines can be hypersaline, hot, anoxic, enriched in metals or organic contaminants, and potentially acidified by elevated CO₂ content. In their undiluted form, they may pose a risk to marine ecosystems, but natural mixing in energetic shelf seas can substantially reduce their impact potential.

This study builds on previous work by assessing not only hypersaline brine release, but also a wider hazard-screening source term based on high-end North Sea produced-water and CCS-relevant formation-water properties. A high-resolution FVCOM hydrodynamic model was used to simulate seabed and sea-surface brine release scenarios. The modelled brine fraction was then used to estimate dilution and compare predicted concentrations against regulation-informed screening thresholds for selected hazardous constituents.

Results show that the impacted area increases non-linearly with dilution threshold. At lower dilution thresholds, affected area increases rapidly, but at higher thresholds the footprint begins to level off.  The most demanding dilution requirements are associated with benzene, zinc, lead, arsenic, and phenol, representing intentionally conservative worst-case screening scenarios and not expected to occur as a chemically coherent release from a single reservoir; rather, it is designed to test the upper bound of potential dilution requirements. Overall, the results indicate that natural shelf-sea mixing can substantially reduce brine-release impacts, but site-specific assessment remains essential.