Résumé
Carbon trapping in ultramafic (UM) and basaltic basements is one of the options explored to mitigate industrial CO2 emissions in the Earth’s atmosphere. UM rocks and basalts comprise silicates rich in divalent cations (Mg, Ca, Fe) that are dissolved to form carbonates when in contact with CO2-rich fluids, thus trapping CO2 over geological time scales. UM rocks have the highest concentrations in divalent cations and thus they have the highest potential for carbon trapping by CO2-mineralization. Nevertheless, because of their low permeability, UM basements have been overlooked for possible in situ CO2 storage in favor of basaltic basements. Recent research shows that CO2-mineralization is active and efficient in UM basements, and that it is associated to potential benefits, such as the production of H2. However, the hydrodynamic, physical and chemical mechanisms driving CO2-mineralization whilst sustaining fluid flow are still poorly understood and numerous scientific and technological challenges remain before implementing industrial CO2 geological storage in UM basements. Here we present an overview of our recent results on CO2-mineralization in UM rocks combining (i) laboratory experiments, and (ii) field studies of carbonated UM basements with a focus on the Semail ophiolite (Sultanate of Oman), in relation to the recently completed ICDP (International Continental Scientific Program) Oman Drilling Project