Characterization Of CO₂ Dissolution Convective Mixing In Hele-Shaw Cell Under Chemical Action

In recent decades,global energy use has increased dramatically,and industrial emissions are serious.In the context of large-scale energy consumption,a large number of greenhouse gas emissions need to be solved urgently.CO₂,the chief of these,has long been proposed for geological sequestration in order to reduce greenhouse gas emissions.Under the corresponding geological conditions,a large amount of CO₂is injected into the underground salt water layer and dissolved in the salt water to achieve the purpose of storage.In this process,the CO₂will have an obvious chemical reaction with underground minerals:the CO₂will dissolve in the formation water to form an acidic environment,and after the corrosion of the rock wall,other alkaline substances will be released to further react with the CO₂solution.Among many methods to deal with CO₂emission reduction,CO₂sequestration based on stratigraphic structure is the most potential method in the future.In order to understand the storage mechanism and characteristics of CO₂geological storage technology and improve the storage efficiency and safety of CO₂,this paper uses CO₂and Ca（OH）₂solution to simulate the reaction between Ca²⁺and CO₂in formation environment,and uses Hele-Shaw cell to conduct dissolution convection experiments.First,a visualized experimental platform and an image acquisition system at normal temperature and pressure were built.The concentration range of reactants dominated by Ca（OH）₂solution was determined according to the type of brackish water layer.The plume evolution patterns of CO₂dissolved products in Ca（OH）₂solutions with different concentrations were studied experimentally,and the plume flow characteristics and rules such as plume diffusion length and plume evolution mechanism were determined in solutions with different concentrations.According to the chemical reaction principle and the physical characteristics of CO₂in solution,two different plume evolution models were observed under the coupling effect of Ca²⁺concentration and OH^-concentration.The experimental results show that the plume length decreases with the increase of the concentration,and the higher the concentration of the solution,the stronger the inhibition effect on the plume.In Ca（OH）₂solution with low concentration,CO₂is partially consumed in the process of dissolution and accumulation,and calcium carbonate precipitation is not obvious.The plume shape is similar to that of pure water solution,and the size decreases gradually with the increase of Ca（OH）₂concentration.With the increase of solution concentration,plume generation is inhibited due to the increasing influence of chemical reaction.In the high-concentration Ca（OH）₂solution,plume generation is no longer possible,but a whole region of CO₂dissolution exists in the upper solution.At this time,the upper solution tends to move downward through diffusion,resulting in a flow pattern dominated by diffusion.Meanwhile,the plume flow characteristics in Hele-Shaw cell with different permeability of k were studied.The process of plume evolution under different dimensionless parameters is compared,and the characteristics of plume start time and bottoming time are analyzed.The absorption capacity and efficiency of CO₂at different concentrations were measured by titration method,and the gray distribution histogram of the image was obtained by processing the image,so as to summarize the mechanism of chemical reaction on CO₂absorption in brackish water layer.The results show that the higher the solution concentration,the longer the plume start time and bottoming time.The plume start time decreases with the increase of permeability.The higher the permeability,the closer the theoretical value is to the experimental value.The presence of plumes promoted the dissolution and absorption of CO₂,while the chemical reaction inhibited the generation of plumes,resulting in a decrease in the growth rate of the absorption efficiency.The plume velocity at low concentration is faster than that at high concentration,but the absorption of high concentration solution is greater than that of low concentration solution.