oa Assessment of Environmental Risk from Brine Disposal Related to Large-Scale CO2 Storage

Large-scale CO2 injection into geological storage will increase pressure in the target formation, potentially leading to decreasing storage capacity and CO2 migration outside the storage complex, and production of formation brine is one out of several mitigation actions. In case of disposal of brine to the marine environment an environmental risk analysis (ERA) is required by the national authorities. In the current study, a greater understanding of the impacts of continuous brine disposal has been achieved using a generic ERA approach. Formation water characteristics vary dependent on the geological formation but will typically have elevated salinity, temperature, dissolved metals, and methane compared to ambient seawater. Metals are of highest environmental concern. Variations in metal concentrations and uncertainties regarding potential contamination of brine samples for a selected area on the NCS are addressed. Preliminary estimate of risk shows a high variability dependent on the metal concentrations and disposal rate of the brine. This highlights the importance of having access to representative and high-quality formation water analyses and models that handle ERA simulation of subsea release of high-saline brine. Nevertheless, using median metal concentrations the environmental risk is negligible.