CO₂ sequestration in a UK North Sea analogue for geological carbon storage

The Fizzy discovery, a southern North Sea (UK) gas accumulation with ∼50% natural CO₂ content, provides an opportunity to study the long-term quantity of CO₂-related mineral reaction as an analogue for engineered CO₂ storage. The reservoir contains diagenetic dolomite typical of the formation; to identify and quantify any sequestration-related dolomite is challenging. To this end, CO₂ was extracted by stepwise extraction from dolomite from both the Fizzy discovery and equivalent sandstones from a low-CO₂ location. Between 0% and 22% of the dolomite in the Fizzy discovery precipitated due to the high CO₂ concentration. This corresponds to 11% ± 8% of the recent high-CO₂ charge sequestered as dolomite, a relatively low proportion after ∼50 m.y. of potential CO₂-water-rock interaction.