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Impact of Sorption-Induced Strain and Effective Stress on the Evolution of Coal Permeability under Different Boundary Conditions
Energy & Fuels ( IF 5.2 ) Pub Date : 2021-09-02 , DOI: 10.1021/acs.energyfuels.1c01900 Chunhong Yao 1 , Bobo Li 1, 2, 3 , Zheng Gao 1 , Jianhua Li 1 , Chonghong Ren 1 , Yao Zhang 1 , Bin Wang 1 , Shuai Chen 1
Energy & Fuels ( IF 5.2 ) Pub Date : 2021-09-02 , DOI: 10.1021/acs.energyfuels.1c01900 Chunhong Yao 1 , Bobo Li 1, 2, 3 , Zheng Gao 1 , Jianhua Li 1 , Chonghong Ren 1 , Yao Zhang 1 , Bin Wang 1 , Shuai Chen 1
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Coalbed methane (CBM) is a relatively common unconventional natural gas, which has great exploitation value. Coal permeability is an important parameter that affects the production and production efficiency of CBM, which is mainly controlled by the sorption expansion/contraction strain and effective stress. To study the seepage characteristics of coal in the process of CBM production, we have used CH4 and CO2 as test gases separately and conducted comparative seepage tests of different gases under constant pore pressure conditions. At the same time, the elastic modulus reduction coefficient Rm has been introduced to characterize the sorption strain of coal, following which the permeability models suitable for different boundary conditions were derived according to the stress–strain relationship. Under the two gases, the new model could not only better reflect the law of coal sorption strain but also better reflect the relationship among effective stress, pore pressure, and coal permeability. Under the conditions of constant pore pressure, coal permeability was mainly controlled by effective stress; with the increase of effective stress, permeability decreased sharply initially and then gradually. Under the conditions of uniaxial strain and constant external stress, with an increase of pore pressure and Rm, the matrix sorption expansion strain increased, resulting in a narrowing of the seepage channel, and Rm indirectly inhibited permeability. At this point, coal permeability was mainly controlled by sorption expansion/contraction strain and effective stress. In addition, compared with other permeability models, the new permeability model possesses higher applicability both in theoretical mechanism and in data matching. The general change trend concerning coal permeability, determined by rebound pressure prb, was consistent with the test results, which further verified the applicability of the model. It is believed that the results of this study could provide a basis for subsequent research on the stress–strain–permeability relationship and for the study of efficient development of CBM.
中文翻译：
不同边界条件下吸附诱导应变和有效应力对煤渗透率演化的影响
煤层气（CBM）是一种比较常见的非常规天然气，具有很大的开发价值。煤的渗透率是影响煤层气生产和生产效率的重要参数，其主要受吸附膨胀/收缩应变和有效应力控制。为研究煤层气生产过程中煤的渗流特性，我们分别以CH 4和CO 2作为试验气体，对不同气体在恒定孔隙压力条件下进行了对比渗流试验。与此同时，弹性模量降低系数ř米引入煤的吸附应变表征，然后根据应力应变关系推导出适用于不同边界条件的渗透率模型。在这两种气体下，新模型不仅能更好地反映煤的吸附应变规律，而且能更好地反映有效应力、孔隙压力和煤渗透率之间的关系。在孔隙压力不变的条件下，煤的渗透率主要受有效应力的控制；随着有效应力的增加，渗透率先急剧下降，然后逐渐下降。在单轴应变和恒定外应力条件下，随着孔隙压力和R m的增加，基体吸附膨胀应变增大，导致渗流通道变窄，R m间接抑制渗透率。此时，煤的渗透率主要受吸附膨胀/收缩应变和有效应力的控制。此外，与其他渗透率模型相比，新的渗透率模型在理论机理和数据匹配上都具有更高的适用性。一般变化趋势有关煤的渗透性，通过回弹压力确定p RB，与测试结果一致，进一步验证了模型的适用性。相信该研究结果可为后续应力-应变-渗透率关系研究和煤层气高效开发研究提供依据。
更新日期：2021-09-16
中文翻译：
不同边界条件下吸附诱导应变和有效应力对煤渗透率演化的影响
煤层气（CBM）是一种比较常见的非常规天然气，具有很大的开发价值。煤的渗透率是影响煤层气生产和生产效率的重要参数，其主要受吸附膨胀/收缩应变和有效应力控制。为研究煤层气生产过程中煤的渗流特性，我们分别以CH 4和CO 2作为试验气体，对不同气体在恒定孔隙压力条件下进行了对比渗流试验。与此同时，弹性模量降低系数ř米引入煤的吸附应变表征，然后根据应力应变关系推导出适用于不同边界条件的渗透率模型。在这两种气体下，新模型不仅能更好地反映煤的吸附应变规律，而且能更好地反映有效应力、孔隙压力和煤渗透率之间的关系。在孔隙压力不变的条件下，煤的渗透率主要受有效应力的控制；随着有效应力的增加，渗透率先急剧下降，然后逐渐下降。在单轴应变和恒定外应力条件下，随着孔隙压力和R m的增加，基体吸附膨胀应变增大，导致渗流通道变窄，R m间接抑制渗透率。此时，煤的渗透率主要受吸附膨胀/收缩应变和有效应力的控制。此外，与其他渗透率模型相比，新的渗透率模型在理论机理和数据匹配上都具有更高的适用性。一般变化趋势有关煤的渗透性，通过回弹压力确定p RB，与测试结果一致，进一步验证了模型的适用性。相信该研究结果可为后续应力-应变-渗透率关系研究和煤层气高效开发研究提供依据。
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