孙可明, 李天舒. 超临界CO2作用下煤体膨胀变形理论模型[J]. 煤炭学报, 2020, 45(4). DOI: 10.13225/j.cnki.jccs.2019.0424
引用本文: 孙可明, 李天舒. 超临界CO2作用下煤体膨胀变形理论模型[J]. 煤炭学报, 2020, 45(4). DOI: 10.13225/j.cnki.jccs.2019.0424
SUN Keming, LI Tianshu. Theoretical model of coal swelling deformation under supercritical carbon dioxide action[J]. Journal of China Coal Society, 2020, 45(4). DOI: 10.13225/j.cnki.jccs.2019.0424
Citation: SUN Keming, LI Tianshu. Theoretical model of coal swelling deformation under supercritical carbon dioxide action[J]. Journal of China Coal Society, 2020, 45(4). DOI: 10.13225/j.cnki.jccs.2019.0424

超临界CO2作用下煤体膨胀变形理论模型

Theoretical model of coal swelling deformation under supercritical carbon dioxide action

  • 摘要: 为探讨利用超临界二氧化碳提高低渗透煤层气采收率过程中的煤体膨胀变形规律,解决传统吸附理论以绝对吸附量为基础建立的理论模型在超临界状态下不再适用的问题,根据Elliott-Suresh-Donohue状态方程及简化局部密度模型确定了超临界二氧化碳作用下煤体的过剩吸附量。基于热力学理论和吸附体系的内能关系得出煤体吸附超临界二氧化碳产生的膨胀体积应变,同时考虑温度及孔隙压力作用下煤体的体积应变,建立了超临界二氧化碳作用下煤体膨胀变形理论模型,该模型包括温度应变和孔隙压力产生的应变及吸附应变效应。通过编程计算得出温度变化范围从303.15~330.65 K,孔隙压力变化范围从7.5~9.5 MPa的不同温压条件下理论模型的数值解,并将该数值解与自主研发的具有施加热流力载荷功能的膨胀体积应变测试装置的测量结果进行对比分析,结果表明:理论模型计算数据与试验数据吻合度较高;以过剩吸附量为基础建立的理论模型能较好地反映不同温压条件超临界二氧化碳作用下的煤体膨胀变形规律;超临界二氧化碳作用下,煤体体积应变随超临界温度和超临界孔隙压力变化均呈“S型”Logistic函数规律变化。在利用超临界二氧化碳提高煤层渗透性时,根据膨胀曲线选择合适的超临界温压条件,避免煤体膨胀对煤层渗透性的不利影响。

     

    Abstract: In order to study the law of the coal swelling deformation in the process to enhance coal bed methane recov- ery of the low permeability coal seam by injecting supercritical carbon dioxide,this paper solved the problem that the classical adsorption theory established by absolute adsorption is no longer applicable in the supercritical state. Accord- ing to Elliott-Suresh-Donohue state equation and the Simplified Local Density model,this paper can determine the ex- cess adsorption with supercritical carbon dioxide. Based on the thermodynamic theory and the internal energy relation- ship of the adsorption system,the swelling strain of supercritical carbon dioxide can be obtained. Considering the influ- ence of the compressive strain generated by supercritical pressure and the thermal expansion strain caused by super- critical temperature on the deformation of coal,the theoretical model of coal swelling deformation under supercritical carbon dioxide was established. This model included the thermal strain and the strain and absorption strain effect caused by pore pressure. The numerical solution of the theoretical model under the different conditions of temperature and pressure,relatively ranging from 303. 15 K to 330. 65 K and from 7. 5 MPa to 9. 5 MPa,was found out by pro- gramming. Comparing the numerical solution with the measured results of the independently-developed volume expan- sion strain measurement device with heat flow loading function,the results showed that firstly,the calculated data of the theoretical model coincides with the experimental data to significant extent;secondly,the theoretical model based on excess adsorption can better reflect the law of coal swelling deformation under supercritical carbon dioxide with differ- ent temperature and pressure conditions;finally,under the action of supercritical carbon dioxide,the coal volumetric strain,which varies with the supercritical temperature and pore pressure,presents S-shaped Logistic function pattern. Therefore,when the supercritical carbon dioxide is used to improve the permeability of coal seam,the appropriate su- percritical temperature and pressure conditions should be selected according to the expansion curve to avoid the ad- verse impact of coal swelling on the permeability of coal seam.

     

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