Changes in seal capacity of fractured claystone caprocks induced by dissolved and gaseous CO2 seepage

Muriel Andreani (1) , Philippe Gouze (1) , Linda Luquot (1) , P. Jouanna (1)

1 Géosciences Montpellier

Claystone caprocks are often the ultimate seal for CO2 underground storage when residual CO2 gas reaches the reservoir top due to buoyancy. Permeability changes of a fractured claystone due to seepage of CO2-enriched brine and water vapor-saturated CO2 gas are investigated. Results show that brine flow induces a large porosity increase (up to 50%) in the vicinity of the fracture due to dissolution of calcite and quartz, while permeability remains unchanged. Conversely, cyclic flows of CO2-brine and CO2-gas increase the fracture aperture abruptly after each gas flow period, producing a progressive decrease of the caprock seal capacity. Aperture increase is controlled by decohesion of the clay framework within a micrometer-scale-thick layer induced by CO2-gas acidification. Results show that hydraulic aperture increases linearly with duration of the preceding CO2-brine flow period, emphasizing the kinetic control of the quartz grains dissolution during the brine flow periods.

Mots clés: argillaceous rocks; flow; dissolution; cohesion

Domaines: Géophysique [physics.geo-ph]; Géophysique [physics.geo-ph]; Interfaces continentales, environnement; Milieux et Changements globaux

Muriel Andreani, Philippe Gouze, Linda Luquot, P. Jouanna. Changes in seal capacity of fractured claystone caprocks induced by dissolved and gaseous CO2 seepage. Geophysical Research Letters, 2008, 35 (14), pp.L14404. ⟨10.1029/2008GL034467⟩. ⟨hal-00412332⟩