Quantitative Raman Spectroscopic Investigation On Non-equilibrium Dissolution And Water-rock Reaction Of SO₂-CO₂ Co-injection Into Pore Space

The reduction of carbon dioxide is an important consensus to control global climate change.Capturing and storing carbon dioxide from combustion sources or reduce the combustion of fossil fuels has become an important means of emission reduction.And greenhouse gases such as carbon dioxide captured from coal-fired power plants or any other source contain impurities,which have potential impacts on health,safety and environmental during the transportation and storage of carbon dioxide.When coal-fired power plants dispose of carbon dioxide,they must spend a lot of money to deal with SO₂ and other impurity gases,so that the flue gas can meet the emission standards and will not cause harm to the environment and human health.Co-capture,co-injection,and co-sequestration of acid gas pollutants like SO₂ together with the CO₂,can reduce the total capture cost,both greenhouse gas emissions can be reduced.Therefore,understanding the impact of impurities on capture,transportation and storage is the primary consideration for co-storage.Injecting carbon dioxide containing SO₂will change the gas-liquid balance and density of the gas stream.These impurity gases will react after injected into the aquifer and produce acidic solution,which is easier to react with minerals than pure carbon dioxide and affect the integrity of the aquifer and cap layer.Understanding the dissolution and reaction behavior of these impurities in storage is critical to the feasibility analysis of the co-storage of impurities and carbon dioxide.This study simulates the multiphase flow reaction process of SO₂ and CO₂injected into the pore medium of the deep aquifer,and obtains the process information of the inconsistent dissolution-migration-reaction process of the CO₂-SO₂ gas mixture in the saturated porous medium.In-situ quantitative Raman Spectroscopy technology was used to detect the content change and distribution of each substance in the pore structure,obtained the concentration of CO₂ and SO₂ in the aqueous and non-aqueous phases,so as to study the inconsistent dissolution of mixed gas on the acidification degree of the solution and the effect of acidic gases on water-rock interaction.The conclusions of this paper are listed as following:(1)In order to obtain the distribution content of the CO₂-SO₂ gas mixture in the non-aqueous phase during the dissolution-diffusion process,based on the calibration experiments of mercury sealing technique and quantitative Raman spectroscopy,the quantitative relationship between the parameters of Raman peak and the contents of SO₂and CO₂ under wide temperature and pressure conditions was established.In the CO₂-SO₂-H₂O system,the SO₂ content in the CO₂phase under the phase equilibrium condition can be obtained by fitting the relationship,and the basic data for simulation of CO₂-SO₂ system is provided;(2)In the co-storage,the solubility and range of SO₂ determine the degree of acidification of the solution.In the SO₂-H₂O system,the solubility of SO₂ in water phase was obtained under the condition of geological storage temperature and pressure.In a homogeneous solution with a known concentration,we determined a specific quantitative relationship between the concentration of SO₂ in water and Raman PAR and found that the quantitative factor is slightly affected by the pressure but increases with elevating temperature.In saturated SO₂ aqueous solution,the pressure and temperature have quite a different effect on the solubility of SO₂ in water when SO₂ is located in the gas phase and the liquid phase.Specifically,when SO₂ is in the gas phase,the pressure exerts a significantly positive influence,while the temperature effect is negligible.When SO₂is in the liquid phase,the solubility of SO₂in water increases remarkably with the increase of temperature.(3)The solubility of SO₂ in water is much higher than that of CO₂ at the same temperature and pressure,and the trend of the solubility-temperature curve is different from that of CO₂.Compared to CO₂ phase,SO₂ is easier to dissolve in H₂O phase.(4)In order to study the non-equilibrium dissolution and diffusion of CO₂-SO₂mixture in the aquifer during displacement process,the experiment simulated the diffusion process of the CO₂-SO₂ mixture in the aquifer at different temperatures.Monitor the concentration of CO₂-SO₂ mixture at different positions in aqueous solution over time in a one-dimensional capillary.The gas composition and Henry's constant ratio restrict the dynamic distribution of SO₂and CO₂ in the solution.The dissolution and migration of SO₂ is quite different from that of CO₂.When the mixed gas diffuses in the aqueous solution,the concentration of CO₂ does not change with time at the gas-liquid interface;because the solubility of SO₂ in water is much greater than that of CO₂,and the dissolution rate is faster,the concentration of SO₂will first increase rapidly with time;and then,with the dissolution of SO₂ in water,the partial pressure in the gas phase gradually decreases,and its concentration tends to be stable and tends to the solubility in water under this condition.The transport rate of gas in water at other locations far from the gas-liquid interface is completely restricted by the concentration gradient.The effect of SO₂ on the diffusion coefficient of CO₂ can be ignored.(5)Raman in situ observed the CO₂-SO₂ mixture injected into the two-dimensional micropore model,and monitored the gas concentration distribution at a closed pore,pore stomach and pore throat changes with the gas dissolved in water,and analyzed the pore structure Influence on mixture distribution.In the closed-end pore,the dissolution and migration of CO₂ and SO₂ are the same as that in one-dimensional capillary.The gas accumulates near the gas-liquid interface and further diffuses under the action of concentration gradient.When the partial pressure of the gas phase is high and the solution reaches saturation quickly,the concentration of SO₂ in the solution continues to increase and the concentration of CO₂ decreases because of the high solubility of SO₂.And in the structure of pore throat,the gas concentration in the middle part is less than that in both sides which means porous throat affects concentration distribution clearly,SO₂ concentration is much higher than CO₂ in the whole pore space and influence of porous throat on concentration distribution is more obvious than CO₂.In the pore,more CO₂ and SO₂ stay in the central part.Different from the pore throat,more gas distributes in the pore abdomen center.SO₂ concentration is little higher than CO₂ in the whole pore space.(6)According to the concentration of gas dissolved in water,the acidity of the solution in porous media medium was calculated.The p H value of the solution is mainly affected by the concentration of SO₂.Injection of CO₂ containing only 1%SO₂,would affect the reaction severely of formation water with minerals.The higher SO₂concentration in the pore will be more acidic,and the pore channel is the more severe acidification area.(7)The water-gas-rock reaction is affected by the gas solubility and spatial distribution.The addition of SO₂ increases the acidity of the fluid,enhances the degree of water-rock reaction,takes priority to the participation of CO₂ in the water-rock reaction,and changes the content of dissolved and precipitated matter in the pore space.In the study of gas-water-rock reaction after the CO₂-SO₂ mixture injection,the reaction process of CO₂-SO₂ mixture with silicate in aqueous solution was simulated by Raman in situ,and reveals the morphologic change and transformation process of the product of CO₂-SO₂ reaction with wollastonite.The water-rock reaction containing SO₂strengthens the trend of heterogeneous changes in the porosity and permeability of the reservoir.The SO₂ impurity will accelerate the water-rock reaction rate and inhibit the formation of HCO₃^-and CO₃^2-ions.Ca SO₄ are preferentially generated on the mineral surface and in solution.When SO₂ is completely consumed,CO₂ will participate in the water-rock reaction,and accumulate Ca CO₃ on the mineral surface,and HCO₃^-ions will appear in the solution.The Ca SO₄ formed by the reaction of SO₂ and water-rock not only covers the surface of minerals,but also precipitates in the solution,and is difficult to dissolve.Combined with the distribution of SO₂ in the pore,the dissolution of SO₂will block the pore channels and closed ends of the pores.In addition,the dissolution and reaction process of SO₂ both occur in the early stage of injection,and SO₂ is mainly concentrated near the interface,so blockage is more likely to occur near the interface,which will significantly affect the injection performance.