Experimental study on the role of clays as sealing materials in the geological storage of carbon dioxide

• Evaluation of the behaviour of clays as sealing rocks in a CO2 geological storage
• Mg-bentonite and montmorillonite–illite clays are susceptible to attacked by CO2.
• Carbonate precipitation can partially prevent the clay destruction.
• Proposed conceptual model helps to understand the role of clay in cap-rocks.

The aim of this work is to further the knowledge of reactions that can occur between carbon dioxide, diffused or escaped from a geological storage, and the sealing rock (e.g. clay-rich sediments). This research provides experimental data on the reactive behaviour of saponite (Mg-smectite), kaolin and Common Clay (composed of illite with minor montmorillonite) samples with CO2 in the presence of water or under dry conditions. The mechanisms for physical and chemical retention of CO2 were determined, and the influence of pressure, temperature and relative humidity on the effective sealing of the rock was examined. Firstly, the saponite did not physically adsorb CO2, and an amorphous phase was formed due to carbonic acid attack. Nevertheless, the Mg-smectite exchange cations, lead to the precipitation of dolomite and increase the mineral CO2 trapping. Secondly, the smectite and illite of the Common Clay sample were partially destroyed and the smectite destruction leads to the precipitation of some carbonates. Thirdly, kaolin did not physically trap CO2 nor any chemical reaction. This paper has demonstrated that the cannibalization of saponite and Common Clays is not total and the precipitation of carbonates may occur, which could avoid the progressive destruction of the sealing rock.

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