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天然气地球科学

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煤储层不同尺寸孔中H2O对CH4解吸扩散的分子模拟研究

杨兆中，韩金轩，付蔷，李小刚，张健   

  1. 1.西南石油大学/油气藏地质及开发工程国家重点实验室，四川 成都 610500；
    2.西南油气田分公司采气工程研究院，四川 广汉 618300；
    3.中联煤层气有限责任公司，北京 100011
  • 收稿日期:2014-08-04 修回日期:2014-10-09 出版日期:2015-05-10 发布日期:2015-05-10
  • 作者简介:杨兆中(1969-)，男，四川泸州人，教授，博士生导师，主要从事油气藏增产改造理论,技术和非常规天然气开发等科研和教学工作. E-mail：yzzycl@vip.sina.com.
  • 基金资助:

    “十二五”国家科技重大专项第42项目第2课题(编号：2011ZX05042-002-001)资助.

The Molecular Simulation of the Influence of H2O on CH4 Desorption and Diffusion in Pores with Different Size of Coal Reservoirs

YANG Zhao-zhong，HAN Jin-xuan，FU Qiang，LI Xiao-gang，ZHANG Jian   

  1. 1.State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation,Southwest Petroleum University,
    Chengdu 610500,China;
    2.Gas Recovery Technology Institute of Southwest Oil and Gas Branch,Guanghan 618300,China;
    3.China United Coalbed Methane Corporation Ltd.,Beijing 100011
  • Received:2014-08-04 Revised:2014-10-09 Online:2015-05-10 Published:2015-05-10

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摘要：

模拟煤储层中甲烷(CH4)在不同孔径中不同水分下的解吸和扩散过程，讨论孔径、含水率、温度和压力与CH4解吸扩散的关系。结果表明，狭缝的壁面叠加效应会显著影响H2O分子的吸附/解吸，使H2O分子集中分布在狭缝孔的中间位置。当孔间距逐渐增大时，双侧壁面叠加效应逐渐转化为单侧壁面的表面效应对H2 O分子的吸附，使H2O分子的分布由中间转为两边。含水率的增加对CH4解吸的影响程度增加，CH4的解吸量呈减小趋势，但受温度影响规律不明显。在1nm狭缝孔中，低压时的水分对CH4解吸的影响程度大于高压下的情况。在2nm狭缝孔中，当含水率由2.35%增加至5%时，低压时的水分对CH4解吸的影响程度则开始小于高压下的情况。在5nm狭缝孔中，随着压力的降低，含水率对CH4解吸量的影响变得不明显，说明在解吸过程中，压力降到某一值后，改变含水率并不会促进CH4的解吸；当含水率超过2.35%时，含水率的增加仍然对CH4的解吸产生影响，说明2.35%并不是石墨狭缝孔的水分临界值，但由于随着含水率的增加，CH4所受的影响程度逐渐变小，因此临界值可能存在。微孔中水的吸附热和微孔对吸附质分子的强吸附势使孔径和含水率显著影响CH4的扩散系数，而温度和压力对CH4的扩散系数则影响较小。

关键词: 煤层气, 含水率, 孔径, 解吸, 扩散, 分子模拟

Abstract:

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

中图分类号: 

  • TE122.2

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