Storage of CO2 at low temperature as liquid or solid gas hydrate Application in the French and Spanish EEZ in North-East Atlantic

André Burnol (1) , Isabelle Thinon (1)

1 BRGM - Bureau de Recherches Géologiques et Minières (BRGM)

Another storage option (the so-called “deep offshore” option) is the trapping of CO2 in deep-sea sediments at lower temperature and higher pressure than the standard options, the onshore and offshore storage options. In those conditions, CO2 may be liquid and denser than seawater. In that case, the injected liquid CO2 may be gravitationally trapped in the deep-sea sediments; either in the liquid state or in the solid state as gas hydrates. The state of stored CO2 (liquid or solid) depends strongly on three parameters: the heat flow, the seafloor depth and the CO2 quality. In order to evaluate their effects, a new numerical tool called “GASCO2” using well-proven accurate modules (GERG-2008, CSMGem and GMT) has been designed and applied previously in the French Exclusive Economic Zone (EEZ) (Burnol et al., 2015). This first estimate has been found to be higher than the onshore storage capacity in the deep saline aquifers of the Paris Basin. In the present study, we firstly improve this first conservative estimate, and then extend the storage area to the Spanish EEZ. This improvement relies on the high resolution of the EMODnet bathymetry (http://www.emodnet-bathymetry.eu), with a gridsize of 1/8 * 1/8 minutes (circa 230 m) instead of the previously used 1km spacing grid. This refined local bathymetry of the deep offshore zone encompasses the abyssal plain and continental rise in the area of the Bay of Biscay and the Galicia Plateau. It was used to define a potential interesting zone for the CO2 storage in both EEZ considering a set of three safety criteria. The French EEZ storage volume estimate is of the same order of magnitude as the total storage volume in the Spanish EEZ estimate. There is however a big difference due to the higher average seafloor depth in the Spanish EEZ: in the French case, almost all the stored volume is occupied by gas hydrate and in the Spanish case, about the half is occupied by CO2 in gas hydrate and the other half by liquid CO2. Large uncertainties remain with regard to the effective storage capacity due to the lack of knowledge of the influence of the sediment composition on the mixed gas hydrates formation kinetics and on the saturation level in the deep-offshore conditions (40-60 Mpa). Thus, more work needs to be done in order to be able to understand and to predict the magnitude of these effects on the CO2 storage capacity in deep offshore sediments.

Mots clés: CO2 hydrates; Liquid CO2; Impurities; Deep offshore; Biscay Bay; Galicia Plateau

Domaines: Sciences de la Terre

André Burnol, Isabelle Thinon. Storage of CO2 at low temperature as liquid or solid gas hydrate Application in the French and Spanish EEZ in North-East Atlantic. GEOCO2, Colloque Franco-Espagnol « Stockage géologique du CO2 et microfluidique », Oct 2016, Bordeaux, France. , 2018, ⟨10.13140/RG.2.2.12554.72640⟩. ⟨hal-01970582⟩