Geochemical calibration for carbonate clay caprock under acidic conditions: experimental and numerical insights

Accurate prediction of possible chemo-mechanical effects on the behaviour of caprocks interacting with carbon dioxide in geological storage operations requires developing models coupling reactive transport and mechanical processes. Determination of the geochemical model parameters is critical to this extent. This work refers to the case of a carbonate clay caprock, where a novel procedure aimed at parameter calibration was based on titration tests, accompanied by mineralogical and chemical analyses. Depending on the value of the equilibrium constants, a competing behaviour between calcite and dolomite dissolution was outlined. The obtained model parameters were used in the simulation of tests where oedometer samples were exposed to acidic solution through diffusion and advection. The simulations were found to provide satisfactory results, helping to assess the specific role of the two carbonates dissolution on the accumulated strains. The advection test was found to be compatible with larger carbonate dissolution characterised by sharp gradients of volumetric fractions, whereas the diffusion test was compatible with smaller carbonate dissolution extending over larger volume with smoother volumetric fraction gradients.