More to Consider than CO2 in CCS Leakage Risks

Researchers from the Technical University of Denmark have highlighted that taking a comprehensive view of the chemical composition of potential fluids leaking from geological CO2 storage reservoirs raises new questions about the potential risks.

The study, published in the Journal of Environmental Management, says, albeit small, the risk of failures during operations and storage does exist.

Different environmental modelling studies have suggested that different annual leakage rates (0.001%–0.01% of stored CO2) are acceptable for the climate mitigation benefits of carbon capture and storage (CCS).

“Despite measures to ensure containment, there is a risk of CO2 leakage,” they say. “Other than the environmental impacts of pure CO2, it is essential to understand the full composition of the fluids reaching shallow and surface environments.”

Impurities can come from several sources:

The captured CO2 may contain impurities that are directly toxic for living organisms (e.g. CO, H2S, SOx, and NOx).

Chemicals such as hydrocarbons or previously injected biocides and surfactants in depleted hydrocarbon fields may accompany the CO2 leaking from a reservoir.

CO2 and some impurities alter the pH when dissolved in water and trigger geochemical reactions, mobilizing or immobilizing harmful chemicals (e.g. trace metals) in the leaking brine.

Microbial activity