Hele-Shaw Cell Experiment On Density-Driven Convective Mixing Of CO₂ And Brine

The concentration of carbon dioxide in the atmosphere,the recognized major contributor to global warming,has already exceeded 400 ppm.The determination not to let the atmospheric carbon dioxide concentration go uncontrolled needs to be strong,though the pattern of the consumption of the fossil fuel based energy would not be changed immediately.The technology of carbon capture and storage is understood to be an effective choice and sequestration of carbon dioxide in aquifers has got great preference among the methods of permanent storage of CO₂ because of the wide distribution and potential storage capacity of saline aquifers.Prediction of the migration process of CO₂ within the aquifer is the key to successful design and implementation of a sequestration project.This requires a good knowledge of the basic flow mechanism within a saline aquifer,which relies on the interaction related to dissolution,capillarity and mineralization.Considering of the complication of the coupling effects of these trapping mechanisms,this study was to seperatedly exam the dissolution of CO₂ into saline aquifers by visualizing the characteristics of the plumes of natural convection caused by heavier solution,based on a Hele-Shaw setup.The quantitative calculation of CO₂?aq?and the discussion of the relation between the morphology of convective plumes and the flux of CO₂ into salt water were accomplished.The study conducted under normal atmospheric pressure showed grown fingers emerge into bigger ones and many new small fingers come into existence during the convective mixing because fresh salty water flows upwards to the interface.The increase of salinity of the solution leads to an increased density which shows inhibition of fingering,reduction of quantity and scale of fingers,thus decreasing the rate of CO₂ migration.The lower viscosity coming from higher temperature promotes the formation and spread of figer plumes.However,restricted by small solubility of CO₂ in brine,higer temperature can result in less and thinner fingers.The visualizaiong of the solving process in situ of supercritical CO₂ into brine demonstrated that the onset time of fingering moves much forward and cannot be capured in this study.The much higher flux of CO₂ into salt water under new conditons accouts for the number of fingers coming down,the scale becoming fat and the speed of spreading downward growing high.Visual examination told an obvious displacement upwards of the interface between the CO₂?sc?and solution,which resulting from the much faster mass transfer flux of convection than that of diffusion.Salinity owns a similar effect on the convective plumes.The solubility in situ of CO₂ in salty water is high,which produces an absolute high value of CO₂ solubility.So temperature going up doesnot spoil the power for convection but lower the viscosity of the solution,both of which promotes fingering.The formation of convective plumes is also couraged by a pressure increase.The proposal to measure the concentration of CO₂?aq?with the help of absorbancy is implemented in this study.The success application of this method may help a lot in later quantitative study on the natural convection in the dissolution of CO₂.