| On the one hand,coalbed methane is one of the main dangerous sources and serious greenhouse gas,on the other hand,it is a kind of efficient clean energy.However,the gas extraction efficiency in China is seriously affected by the low permeability of coal seam.Gas displacement plays an important role in gas extraction and gas disasters prevention.Therefore,it is of great significance to study the adsorption and desorption characteristics and the mechanism of diffusion and seepage of gases in Coal-CH4-H2O coupling system.?1?Pore structure and surface functional group characteristics of coal samples were analyzed,and the adsorption isotherms and desorption diffusion characteristics curves of gases at different conditions were tested.It was found that value of“a”of anthracite LH were larger than that of bituminous coal PM and HL,while its PL was smaller than two bituminous coals.The PL of CO2 was smallest among three gases.?2?The biggest difference among desorption diffusion curves under different conditions are the desorption amount and desorption rate at the initial stage and the final cumulative desorption amount.The Q?10s?/Q?5400s?and Q?60s?/Q?5400s?of N2 in the three coal bodies are larger than that of CH4 and CO2.With the increase of temperature,Q?10s?/Q?5400s?and Q?60s?/Q?5400s?gradually increase.The relationship between the cumulative desorption amount in the first 10 seconds and time can be fitted well by=6)?+??3?Molecular dynamics method was used to investigate the gas diffusion law of single-component gas in Coal-CH4-H2O system and two-component gas while in the process of injecting CO2 and N2.under different water content,temperature and pressure.Compared with the one-component gas diffusion,it was found that the Dt of CH4 and H2O in the process of two-component gas diffusion?CH4/N2 and CO2/CH4?increased.The water content has a negative correlation with the Dt of each component in the Coal-CH4-H2O system,but temperature is reversed.Compared with the single component gas diffusion,the Dt of CH4 and H2O in the Coal-CH4-H2O system increases more in the process of N2 and CO2 are injected as temperature increases or pressure increases.Under the same conditions,compared with the process of injecting CO2,H2O diffuses faster in the process of injecting N2.It should be noted that the Dt of CO2increases first and then decreases with pressure increasing,this is due to the difference of gas diffusion type and diffusion activation energy at different pressure stages.?4?Permeability law of gas in coal under different conditions is studied.The results show that the permeability of N2 and CH4 varies in a"V"shape with the increase of pressure at different condition.Besides,the higher the temperature and the water content,the weaker the Klingberg effect.The“turning point”pressure of N2 is always less than that of CH4.The higher the moisture content and temperature are,the greater the“turning point”pressure of N2 and CH4 are.The permeability of CO2 decreases with the increase of pressure at different temperatures.In the process CO2 displacement,its injection pressure should be paid special attention because of its significant adsorption deformation.N2 still has strong seepage capacity in the high-constrained environment caused by high temperature and high water content.In the process of gas displacement,the effect of N2 injection with high pressure is more significant.During the phase of Master's degree,3 SCI papers was published. |
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