Experimental Study On The Effect Of Moisture And Salinity On CH₄ Displacement By CO₂ In Medium Rank Coal

With the intensification of meteorological disasters such as global warming,glacier melting,and ozone layer depletion in recent years,the issue of"Carbon Emissions"caused by coal consumption has been paid more and more attention,and energy conservation and carbon reduction are imminent.Under the background of the"Dual Carbon"strategy,coal seam CO₂ geological storage and CH₄ enhanced mining technology（CO₂-ECBM）is a key technology for the Low-Carbon,clean and efficient utilization of Coal-Based fossil energy,and has great development potential.Mine water with high salinity is widely distributed in my country.Coal seam water and its salinity have a significant impact on the physical and chemical properties of coal reservoirs,gas adsorption,desorption,and migration.ignore.However,there are still problems such as lack of data,In-Depth analysis,and unclear impact mechanism for CO₂ displacement of coalbed methane under different moisture and salinity effects,which seriously restrict the popularization and application of this technology.In order to deeply explore the influence mechanism of moisture and salinity on CO₂displacement of coal seam CH₄,and to make up for the lack of data in this area,this thesis takes Medium-Rank coal mined in Huainan mining area as the research object,and carries out coal pore analysis before and after water treatment with different salinity.Experimental studies on structure,wettability,gas adsorption,etc.,discussed the influence mechanism of mineralized water on CO₂ displacement of CH₄,and the main conclusions are as follows:（1）After mineralization water treatment,the peak pore size of pores in coal will be reduced,and the pore volume and specific surface area of coal will be reduced at the same time.The N₂ Adsorption-Desorption curves of the three groups of experimental coal samples have similar characteristics to the type of hysteresis loop.The total pore volume of the original coal sample is 8.09×10^-3 cm³/g,and the total specific surface area is 9.71 m²/g.After water（0g/L）and mineralized water（20g/L）treatment,the peak pore diameters of pores in coal decreased to a certain extent,the pore volume decreased by 13.35%and 16.56%,and the specific surface area decreased by 2.68%and 20.19%,and the reduction mainly comes from the mesopores of 2～10nm.（2）When the salinity increased from 0g/L to 20g/L,the Coal-Water contact angle increased from 59.49°to 82.33°,an increase of 38.4%,indicating that the higher the salinity of water,the more contact with the coal surface The larger the angle,the more hydrophobic the coal surface;the surface tension of water increases from 73.4mN/m to73.91mN/m,indicating that the increase in salinity will increase the surface tension of water,resulting in weakened wettability and fluidity of water.（3）Moisture will reduce the ability of coal to adsorb gas,and the increase of salinity will further lead to a decrease in the adsorption capacity of coal.The isothermal adsorption experiments of CO₂ and CH₄ were carried out on coal samples that were dried,injected with deionized water,and injected with mineralized water（0.5g/L～20g/L）.It is larger than that of saturated coal samples,which verifies the view that the presence of moisture in coal will reduce the coal’s ability to adsorb gas;the adsorption of mineralized Water-injected coal samples to the two gases is less than that of deionized Water-injected coal samples,indicating that the salinity in water increases It will further reduce the adsorption capacity of coal,but there is a limit value,beyond this limit value,the degree of salinity will basically no longer reduce the adsorption capacity of coal,and this limit value is about 8g/L.（4）The increase of salinity in water will have a negative impact on the displacement effect,which is caused by the comprehensive change of mineralized water on coal pore structure characteristics and adsorption capacity.Using columnar coal samples,the physical experiment of CO₂ displacement under water injection with different gas injection pressure and different salinity was carried out.The results show that the higher the gas injection pressure,the more N₂ will be replaced,and the CO₂adsorption will be greater.The average displacement efficiency increased by 5.04%,and the average displacement ratio decreased by 6%,indicating that the displacement effect was improved to a certain extent;the displacement efficiency and displacement ratio of Water-Bearing coal samples were The increase showed a decreasing trend,and the displacement effect decreased to a certain extent.（5）The CO₂ displacement CH₄ numerical simulation study was carried out by using COMSOL software,and it was verified that the increase of salinity in water would have a negative impact on the effect of carbon dioxide displacement of coalbed methane,resulting in a worse displacement effect.In the process of coal displacement,the increase of gas injection pressure can improve the efficiency of CO₂ displacement of coal seam CH₄ to a certain extent;The law of desorption effect is consistent with the law obtained in physical experiments,and the replacement ratio generally decreases with the increase of salinity.There are 53 pictures,20 tables and 92 references in this thesis.