Experimental Study On Characteristics Of Convective Fingering In Impure CO₂ Geological Storage

Carbon emission reduction and carbon neutrality are important strategic goals in my country at this stage,and are of great significance to environmental protection and healthy economic development.Carbon dioxide（CO2）geological storage（CO2 geological storage,CGS）,as one of the technologies for permanent storage of impure CO2 emitted from industry,can effectively reduce industrial CO2 emissions.Dissolution sequestration is one of the important sequestration mechanisms in CGS.Among them,the convective mixing process due to CO2 dissolution,also known as the convective fingering phenomenon,is conducive to improving the efficiency and safety of CO2 geological storage.Because the cost of CGS capture increases with CO2 purity,the sequestered CO2 gas stream typically contains small amounts of impurities for economic reasons.However,co-injection of impurities and CO2 may affect the storage efficiency and safety of CGS.Impure CO2 usually contains a variety of impurities（N2,O2 and Ar,etc.）,so it is extremely important to study the effects of single and multiple impurities on the convective fingering phenomenon.In this thesis,a Hele-Shaw cell is used to conduct a visual experimental study,and the characteristic data of convective fingering,including onset time,maximum fingering length,fingering area,and fingering wavelength,are analyzed through experimental images.The influence of common impurities（N2,O2 and/or Ar）on the development of convective fingers can provide effective experimental results for numerical simulation studies.The main research contents are as follows:（1）Study on the onset time and effect of p H indicator concentration.The non-perfect uniformity of the experimental setup and the non-absolute consistency of human operation and environmental conditions will lead to differences in the convective fingering between repeated experiments.In this thesis,the difference of the convective fingering phenomenon in repeated experiments,the convective onset time of a single experiment and the difference of different concentrations of bromocresol green were firstly studied by using the difference analysis model.The study found that the high-concentration bromocresol green solution made the convective fingering limit more obvious than the low concentration bromocresol green solution,which was more conducive to image analysis.Therefore,in this study,experiments were performed in a high-concentration bromocresol green solution.In addition,the study found that the onset time of convection based on the rapid change of fingering is generally later than the onset of convection based on visual observation.（2）Study on the influence of single impurity（N2,O2 or Ar）on the convective fingering phenomenon.The effects of 10% and 15% single impurity on the onset time and fingering development of convective fingering were compared.The experimental results show that the presence of N2,O2 or Ar all delays the onset of convective fingering.A single impurity N2 or O2 slowed down the development of convective finger length and inhibited the longitudinal development of convective finger.Although single impurity Ar inhibited the occurrence of fingering,the effect of Ar on fingering development was promoted or inhibited under different Ar concentrations.（3）Research on the effect of multiple impurities（N2,O2 and Ar）on the convective fingering.Taking the impurity content in the impure CO2 gas stream discharged from the oxy-combustion plant as a reference,the experimental study was carried out using impure CO2 mixtures with different impurity components.At 3600 s,the experimental results show that the binary impurities 10.3% N2 + 4.7% O2 and 5.8% N2 + 9.2% Ar have an inhibitory effect on the maximum length and area development of convective fingers,while 7% O2 + 8%Ar promotes the convection Longitudinal development of fingers.Likewise,the ternary impurity 5.8% N2 + 4.7% O2 + 4.5% Ar promoted the longitudinal development of fingers,but compared with the single impurity 10% Ar or the binary impurity 7% O2 + 8% Ar,the promoted effect of ternary impurity was small,4.5% N2 weakened the promoting effect of O2 + Ar.