Laboratory Investigations of the Hydro-Mechanical–Chemical Coupling Behaviour of Sandstone in CO₂ Storage in Aquifers

This paper is devoted to experimental investigations of the hydro-mechanical–chemical coupling behaviour of sandstone in the context of CO₂ storage in aquifers. We focused on the evolution of creep strain, the transport properties and the elastic modulus of sandstone under the effect of CO₂–brine or CO₂ alone. A summary of previous laboratory results is first presented, including mechanical, poromechanical and hydro-mechanical–chemical coupling properties. Tests were then performed to investigate the evolution of the creep strain and permeability during the injection of CO₂–brine or CO₂ alone. After the injection of CO₂–brine or CO₂ alone, an instantaneous volumetric dilatancy was observed due to the decrease in the effective confining stress. However, CO₂ alone had a significant influence on the creep strain and permeability compared to the small influence of CO₂–brine. This phenomenon can be attributed to the acceleration of the CO₂–brine–rock reaction by the generation of carbonic acid induced by the dissolution of CO₂ into the brine. The original indentation tests on samples after the CO₂–brine–rock reaction were also performed and indicated that the elastic modulus decreased with an increasing reaction time. The present laboratory results can advance our knowledge of the hydro-mechanical–chemical coupling behaviour of sandstone in CO₂ storage in aquifers.