Study On Dissolution Mechanism Of CO₂ In Geological Burial Process

At present,CO₂ geological storage is an effective way to solve the greenhouse effect.During CO₂ injection into formation,a series of geochemical reactions will occur,resulting in changes in reservoir properties,affecting the safety and effectiveness of CO2 storage.In this paper,the CO2-water-rock reaction during geological burial is studied in the following three parts.?1?The CO₂-water-rock interaction in target formation was studied by static dissolution experiment.The CO₂-water-rock reaction in core was analyzed by ICP-OES detection and whole rock mineral test.;?2?Real-time monitoring of core permeability changes in the process of displacement through core displacement experiment.The changes of core surface morphology were observed by SEM,and the changes of reaction porosity before and after displacement were analyzed by NMR.?3?The effects of different temperatures and pressures on CO₂-water-rock were simulated by the equilibrium phase module in PHREEQC software.The experimental results show that:1.The main dissolution minerals in the core are dolomite and feldspar minerals.The dissolution degree of dolomite is more severe than that of feldspar.The reaction rate of dolomite slows down with time and tends to balance in 30 days.Feldspar dissolution mainly produces quartz and kaolinite and other clay minerals.The dissolution rate of core minerals increases with the increase of pressure,mainly due to the effect of pressure on the solubility of CO₂ in formation water and the enhancement of acidity of solution.2.During the dynamic displacement process,the change trend of core permeability varies with the initial permeability.,mainly due to the interaction of dissolution,precipitation and migration.SEM electron microscopy shows that carbonate minerals and feldspars are dissolved,but feldspar dissolution is not obvious,and quartz does not dissolve,but appear phenomenon of quartz overgrowth;CO₂ dissolution increases core porosity,which shows that the size of micro-voids decreases,while the size of macro-voids increases and the number of macro-voids increases.The main reason is that the migration of secondary minerals and clay particles can block the pore,produce invalid pore or dead pore in the roar,and reduce the size of micro-pore,while some particles can increase the size and quantity of pore through macropore and dissolution..3.The degree of dissolution decreases with the increase of temperature and increases with the increase of CO₂ pressure.The main reason is that temperature and pressure affect the solubility of CO₂ in formation water,thus affecting the acidity of the solution and affecting the dissolution rate.The stability of the three feldspars is:k-feldspar>albite>calcium feldspar...