The Molecular Simulation of the Influence of H2O on CH4 Desorption and Diffusion in Pores with Different Size of Coal Reservoirs
Received date: 2014-08-04
Revised date: 2014-10-09
Online published: 2015-05-10
Desorption and diffusion of methane (CH4)under different moistures in different size pores of coal reservoirs were simulated.The relationships between pore size,moisture,temperature,pressure and desorption/diffusion of CH4 were discussed.The results show that (1)the wall superimposed effect of the pore can significantly affect the adsorption/desorption of H2O molecules,so H2O molecules concentrate distribution in the middle of the pore.With increase of pore size,the wall superimposed effect of the pore gradually transforms into surface effect of two sides of the wall so that H2O molecules concentrate distribution on both sides|(2)With the increase of the moisture content,the influence of the moisture on CH4 desorption capacity increases,and CH4 desorption capacity shows a trend of decrease,but the temperature effect is not obvious|(3)In the 1nm slit pore,the influence of the moisture on CH4 desorption under low pressure is greater than that under high pressure|(4)In the 2nm slit pore,when the moisture content increases form 2.35% to 5%,the moisture impact on CH4 desorption under low pressure is less than that of high pressure|(5)In the 5nm slit pore,with the decrease of pressure,the influence of the moisture content on CH4 desorption capacity becomes not obvious,which explains that when the pressure drops to a certain value,changes of the moisture content will not promote CH4 desorption.When the moisture content is more than 2.35%,the increase of the moisture content still affect CH4 desorption,which explains that 2.35% is not the moisture critical value of the graphite slit pore.However,with the increase of the moisture content,CH4 desorption is less affected gradually,so the critical value may exist|(6)Adsorption heat of water in micropores and adsorption potential from micropores to adsorbates will significantly affect the diffusion coefficient of CH4,while temperature and pressure less affect it.
Key words： Coalbed methane; Moisture content; Pore size; Desorption; Diffusion; Molecular simulation
YANG Zhao-zhong，HAN Jin-xuan，FU Qiang，LI Xiao-gang，ZHANG Jian . The Molecular Simulation of the Influence of H2O on CH4 Desorption and Diffusion in Pores with Different Size of Coal Reservoirs[J]. Natural Gas Geoscience, 2015 , 26(5) : 951 -957,985 . DOI: 10.11764/j.issn.1672-1926.2015.05.0951
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