Equilibrium partial pressure of CO 2 in Callovian-Oxfordian argillite as a func-tion of relative humidity: experiments and modelling

Arnault Lassin (1, 2, 3) , Nicolas C.M. Marty (2) , Hélène Gailhanou (2) , Benoît Henry (2) , Joachim Trémosa (2) , Catherine Lerouge (2) , Benoît Madé (4) , Scott Altmann (4) , Eric C. Gaucher (2, 5)

1 ISTO - Institut des Sciences de la Terre d'Orléans - UMR7327
2 BRGM - Bureau de Recherches Géologiques et Minières (BRGM)
3 Milieux Poreux - UMR7327
4 ANDRA - Agence Nationale pour la Gestion des Déchets Radioactifs
5 CSTJF - Centre scientifique et Technique Jean Feger

Having previously demonstrated that the mineral assemblage of claystone can impose its pCO2 under saturated conditions, we here study the effect of rock desaturation, i.e. the evaporation of pore water, on the partial pressure of CO2 (pCO2) in Callovian-Oxfordian argillite from the Paris Basin (France). In this new study, which combines experiments at room temperature and geochemical modelling, we examine the primary role of capillary forces on chemical equilibria for relative humidity values ranging between 50% and 100%. In particular we are able, without any fitting parameters, to model the experimental decrease of pCO2 as a function of decreasing water content in the argillite. This application to a complex natural system not only confirms the theoretical concepts of geochemistry in capillary contexts, but is promising with respect to other systems, both natural (soil, rock) and industrial (ceramics, granular material).

Mots clés: Radioactive waste storage; Porous media; Capillary systems; Callovian-Oxfordian argillite; Clay drying; pCO2; Carbon dioxide; Geochemical modelling; Relative humidity; Isobar/anisobar context

Domaines: Géochimie; Stratigraphie

Arnault Lassin, Nicolas C.M. Marty, Hélène Gailhanou, Benoît Henry, Joachim Trémosa, et al.. Equilibrium partial pressure of CO 2 in Callovian-Oxfordian argillite as a func-tion of relative humidity: experiments and modelling. Geochimica et Cosmochimica Acta, 2016, 186, pp.91-104. ⟨10.1016/j.gca.2016.04.028⟩. ⟨insu-01310959⟩