循环载荷作用下煤体渗透率演化的实验分析
|
摘要
多期次载荷作用下的煤体,其孔隙结构会发生复杂变化,渗透率也随之改变。然而,不同加卸载速率与循环周期决定着煤体渗透率变化路径,影响其应力敏感性,开展循环载荷控制下煤体渗透率演化规律研究,对于解释复杂应力场下煤层渗透率的各向异性特征有理论支撑作用。借助于煤层渗透率应力敏感模型分析,研究了影响煤体渗透率变化的关键表征参数及其函数关系;为验证关键参数对煤体渗透率影响,采用预定轴压和气压、加卸载围压的方式开展煤体三轴循环变载气体渗流实验,分析在不同围压(2.0～12.0 MPa)下煤体渗透率和体应变的演化规律;为研究煤体孔隙结构变化对渗透率的影响,通过低温氮气吸附实验和荧光显微镜煤样观测统计,完成了循环载荷加卸载前后煤体孔隙结构变化对比。研究结果表明,煤体加载/卸载过程中渗透率变化趋势与围压变化负相关,总体可以分为线性段、指数段和稳定段等3个阶段;随循环加载次数的增加煤体应变逐步增大,而渗透率却随之降低;相同条件下,煤体渗透率随体应变增加而升高,增幅在16.79%以上,而渗透率恢复率逐步降低,且与围压变化负相关;3次循环加卸载实验导致煤体孔隙结构发生了显著变化,微孔体积提高71.79%,比表面积增加52.19%,而平均孔径降低32.06%,但循环载荷没有改变煤体的最可几孔径;孔隙结构变化的数据表明,微孔体积增加是煤体渗透率劣化的重要标志之一。对比循环载荷作用前后的孔隙结构实验数据发现,影响气体吸附-解吸的孔隙结构变化,决定了"迟滞环"面积,而决定"迟滞环"形状的关键因素是由煤体最可几孔径控制的突变压力。另外,煤体应变包括裂隙体积变化和孔隙体积变化两部分,其中裂隙影响重要度指标(χ)反映了裂隙体积变化在煤体应变中的权重关系,χ变化随围压升高而降低。
The pore structure and the permeability of coal matrix can be changed complexly under the multi-stage loading.However,the evolution of coal permeability and its stress sensitivity are determined by the different loading/unloading rates and the cyclic cycles.It is of theoretical significance for interpreting the anisotropic characteristics of coal seam permeability under complex stress field by researching the evolution law of coal permeability under cyclic loading.With the aid of the stress sensitive model of coal seam permeability,the key characterization parameters and their functional relationships affecting permeability development were proposed in this study.As for the purpose of verifying the control effect of the key parameters on coal permeability,a triaxial cyclic variable-load gas seepage experiment was carried out by preset axial pressure,gas pressure and loading-unloading confining pressure,and the evolution laws of coal permeability and coal volume strain under different confining pressures(2.0-12.0 MPa) were analyzed.As for the influence of pore structure on permeability,the comparison of pore structure change before and after cyclic loading and unloading was completed by the low temperature nitrogen adsorption experiment and the fluorescence microscope observation.The results showed that the change trend of permeability was negatively correlated with the confining pressure in the process of loading/unloading of coal and it was divided into three stages for the whole process:linear stage,exponential stage and stable stage.With the increase of cyclic loading times,the volumetric strain of coal increased gradually,but the permeability decreased.Under the same experimental conditions,the permeability of coal increased with the increase of volumetric strain,increasing by more than 16.79%,while the permeability recovery rate decreased gradually,and was negatively correlated with the confining pressure.After three cyclic loading and unloading experiments,the pore structure of coal matrix was changed significantly,with the micro-pore volume increased by 71.79%,the specific surface area increased by 52.19%,and the average pore size decreased by 32.06%,but the most probable aperture of coal matrix was not affected by the cyclic stress.The data of pore structure change showed that the increase of micro pore volume was one of the key indicators of coal permeability deterioration.Comparing the experimental data of pore structure before and after cyclic loading,it was found that the change degree of pore structure affected gas adsorption-desorption,determined the area of "hysteresis loop",and the key to determine the shape of "hysteresis loop" was the sudden change pressure controlled by the most probable pore size of coal.In addition,the strain of coal body included the change of fracture volume and pore volume,the important index of fracture influence(χ) showed the weight relationship of the change of fracture volume in the strain of coal body,and decreased with the increase of confining pressure.
The pore structure and the permeability of coal matrix can be changed complexly under the multi-stage loading.However,the evolution of coal permeability and its stress sensitivity are determined by the different loading/unloading rates and the cyclic cycles.It is of theoretical significance for interpreting the anisotropic characteristics of coal seam permeability under complex stress field by researching the evolution law of coal permeability under cyclic loading.With the aid of the stress sensitive model of coal seam permeability,the key characterization parameters and their functional relationships affecting permeability development were proposed in this study.As for the purpose of verifying the control effect of the key parameters on coal permeability,a triaxial cyclic variable-load gas seepage experiment was carried out by preset axial pressure,gas pressure and loading-unloading confining pressure,and the evolution laws of coal permeability and coal volume strain under different confining pressures(2.0-12.0 MPa) were analyzed.As for the influence of pore structure on permeability,the comparison of pore structure change before and after cyclic loading and unloading was completed by the low temperature nitrogen adsorption experiment and the fluorescence microscope observation.The results showed that the change trend of permeability was negatively correlated with the confining pressure in the process of loading/unloading of coal and it was divided into three stages for the whole process:linear stage,exponential stage and stable stage.With the increase of cyclic loading times,the volumetric strain of coal increased gradually,but the permeability decreased.Under the same experimental conditions,the permeability of coal increased with the increase of volumetric strain,increasing by more than 16.79%,while the permeability recovery rate decreased gradually,and was negatively correlated with the confining pressure.After three cyclic loading and unloading experiments,the pore structure of coal matrix was changed significantly,with the micro-pore volume increased by 71.79%,the specific surface area increased by 52.19%,and the average pore size decreased by 32.06%,but the most probable aperture of coal matrix was not affected by the cyclic stress.The data of pore structure change showed that the increase of micro pore volume was one of the key indicators of coal permeability deterioration.Comparing the experimental data of pore structure before and after cyclic loading,it was found that the change degree of pore structure affected gas adsorption-desorption,determined the area of "hysteresis loop",and the key to determine the shape of "hysteresis loop" was the sudden change pressure controlled by the most probable pore size of coal.In addition,the strain of coal body included the change of fracture volume and pore volume,the important index of fracture influence(χ) showed the weight relationship of the change of fracture volume in the strain of coal body,and decreased with the increase of confining pressure.
引文
[1] 张新民,张遂安,钟铃文.中国的煤层甲烷[M].西安:陕西科学技术出版社,1991:1-7.
[2] 冯文光.煤层气工程[M].北京:科学出版社,2009:3-5.
[3] 琚宜文,姜波,王桂梁,等.构造煤结构及储层物性[M].徐州:中国矿业大学出版社,2005:1-5.
[4] FATT I,DAVIS D H.Reduction in permeability with overburden pressure[J].Journal of Petroleum Technology,1952,4(12):16-16.
[5] 冯增朝,赵阳升,文再明.煤岩体孔隙裂隙双重介质逾渗机理研究[J].岩石力学与工程学报,2005,24(2):236-240.FENG Zengchao,ZHAO Yangsheng,WEN Zaiming.Percolation mechanism of mechanism of fractured coal rocks as dual-continua[J].Chinese Journal of Rock Mechanics and Engineering,2005,24(2):236-240.
[6] YOU M.Comparison of the accuracy of some conventional triaxial strength criteria for intact rock[J].International Journal of Rock Mechanics and Mining Sciences,2011,48(5):852-863.
[7] 彭苏萍,孟召平,王虎,等.不同围压下砂岩孔渗规律试验研究[J].岩石力学与工程学报,2003,22(5):742-746.PENG Suping,MENG Zhaoping,WANG Hu,et al.Testing study on pore ratio and permeability of sandstone under different confining pressures[J].Chinese Journal of Rock Mechanics and Engineering,2003,22(5):742-746.
[8] 孟召平,侯泉林.煤储层应力敏感性及影响因素的试验分析[J].煤炭学报,2012,37(3):430-437.MENG Zhaoping,HOU Quanlin.Experimental research on stress sensitivity of coal reservoir and its influencing factors[J].Journal of China Coal Society,2012,37(3):430-437.
[9] MCKEE C R,BUMB A C,KOENIG A.Stress dependent permeability and porosity of coal[J].Rocky Mountain Association of Geologist,1998:143-153.
[10] 刘永茜,张浪,李浩荡,等.含水率对煤层气渗流的影响[J].煤炭学报,2014,39(9):1840-1844.LIU Yongqian,ZHANG Lang,LI Haodang,et al.Effect of moisture content on CBM seepage[J].Journal of China Coal Society,2014,39(9):1840-1844.
[11] ALAM A K M Badrul,MASAKI Niioka,YOSHIAKI Fujii,et al.Effects of confining pressure on the permeability of three rock types under compression[J].International Journal of Rock Mechanics & Mining Sciences,2014,65:49-61.
[12] 尹光志,李文璞,李铭辉,等.加卸载条件下原煤渗透率与有效应力的规律[J].煤炭学报,2014,39(8):1497-1503.YIN Guangzhi,LI Wenpu,LI Minghui,et al.Permeability properties and effective stress of raw coal under loading-unloading conditions[J].Journal of China Coal Society,2014,39(8):1497-1503.
[13] 左建平,陈岩.卸载条件下煤岩组合体的裂纹张开效应研究[J].煤炭学报,2017,42(12):3142-3148.ZUO Jianping,CHEN Yan.Investigation on crack recovery effect of coal-rock combined body under the influence of unloading[J].Journal of China Coal Society,2017,42(12):3142-3148.
[14] DAVID C,WONG T F,ZHU Wenlu,et al.Laboratory measurement of compaction-induced permeability change in porous rocks:implications for the generation and maintenance of pore pressure excess in the crust[J].Pure and Applied Geophysics,1994,143(1/3):425-456.
[15] 王伟,徐卫亚,王如宾,等.低渗透岩石三轴压缩过程中的渗透性研究[J].岩石力学与工程学报,2015,34(1):40-47.WANG Wei,XU Weiya,WANG Rubin,et al.Permeability of dense rock under triaxial compression[J].Chinese Journal of Rock Mechanics and Engineering,2015,34(1):40-47.
[16] 葛家理.现代油藏渗流力学原理[M].北京:石油工业出版社,2006:12-27.
[17] 张东明,郑彬彬,张先萌,等.含瓦斯砂岩卸围压变形特征与渗透规律试验研究[J].岩土力学,2017,38(12):3475-3483,3490.ZHANG Dongming,ZHENG Binbin,ZHANG Xianmeng,et al.Experimental study on the deformation characteristics and permeability laws of gas infiltrated sandstone under unloading confining pressure condition[J].Rock and Soil mechanics,2017,38(12):3475-3483,3490.
[18] 孔茜,王环玲,徐卫亚.循环加卸载作用下砂岩孔隙度与渗透率演化规律试验研究[J].岩土工程学报,2015,37(10):1893-1900.KONG Qian,WANG Huanling,XU Weiya.Experimental study on permeability and porosity evolution of sandstone under cyclic loading and unloading[J].Chinese Journal of Geotechnical Engineering 2015,37(10):1893-1900.
[19] THOMMES M,KANEKO K,NEIMARK A V,et al.Physisorption of gases,with special reference to the evaluation of surface area and pore size distribution (IUPAC Technical Report)[J].Pure and Applied Chemistry,2015,87(9/10):1051-1069.
[20] 张松航,汤达祯,唐书恒,等.鄂尔多斯盆地东缘煤层气储集与产出条件[J].煤炭学报,2009,34(10):1297-1304.ZHANG Songhang,TANG Dazhen,TANG Shuheng,et al.Preservation and deliverability characteristics of coalbed methane in east margin of Ordos Basin[J].Journal of China coal society,2009,34(10):1297-1304.
[21] 刘永茜,侯金玲,张浪,等.孔隙结构控制下的煤体渗透实验研究[J].煤炭学报,2016,41(S2):434-440.LIU Yongqian,HOU Jinling,ZHANG Lang,et al.Permeability experiments of pore structure in coal matrix[J].Journal of China Coal Society,2016,41(S2):434-440.
[22] CHENG Yuanping,JIANG Haina,ZHANG Xiaolei,et al.Effects of coal rank on physicochemical properties of coal and on methane adsorption[J].International Journal of Coal Science & Technology,2017,4(2):129-146.
[23] J Rouquerol,F Rouquerol,K S W Sing,et al.Adsorption by powders and porous solids:Principles,methodology and applications[M].London:Academic Press,2014:10-12.
[24] ROMANOV Vyacheslav N,GRAESER Lauren C,JIKICH Sinisha A,et al.Coal-gas interaction:Implications of changes in texture and porosity[J].International Journal of Coal Science & Technology,2016,3(1):10-19.
[25] 谢和平,鞠杨,黎立云,等.岩体变形破坏过程的能量机制[J].岩石力学与工程学报,2008,27(9):1729-1740.XIE Heping,JU Yang,LI Liyun,et al.Energy mechanism of deformation and failure of rock masses[J].Chinese Journal of Rock Mechanics and Engineering,2008,27(9):1729-1740.
[26] 陈亮,刘建锋,王春萍,等.压缩应力条件下花岗岩损伤演化特征及其对渗透性影响研究[J].岩石力学与工程学报,2014,33(2):287-295.CHEN Liang,LIU Jianfeng,WANG Chunping,et al.Investigation on damage evolution characteristic of granite under compressive stress condition and its impact on permeability[J].Chinese Journal of Rock Mechanics and Engineering,2014,33(2):287-295.
[27] 王向宇,周宏伟,钟江城,等.三轴循环加卸载下深部煤体损伤的能量演化和渗透特性研究[J].岩石力学与工程学报,2018,37(12):2676-2684.WANG Xiangyu,ZHOU Hongwei,ZHONG Jiangcheng,et al.Study on energy evolution and permeability characteristics of damage of deep coal under trixial cyclic loading and unloading conditions[J].Chinese Journal of Rock Mechanics and Engineering,2018,37(12):2676-2684.
[2] 冯文光.煤层气工程[M].北京:科学出版社,2009:3-5.
[3] 琚宜文,姜波,王桂梁,等.构造煤结构及储层物性[M].徐州:中国矿业大学出版社,2005:1-5.
[4] FATT I,DAVIS D H.Reduction in permeability with overburden pressure[J].Journal of Petroleum Technology,1952,4(12):16-16.
[5] 冯增朝,赵阳升,文再明.煤岩体孔隙裂隙双重介质逾渗机理研究[J].岩石力学与工程学报,2005,24(2):236-240.FENG Zengchao,ZHAO Yangsheng,WEN Zaiming.Percolation mechanism of mechanism of fractured coal rocks as dual-continua[J].Chinese Journal of Rock Mechanics and Engineering,2005,24(2):236-240.
[6] YOU M.Comparison of the accuracy of some conventional triaxial strength criteria for intact rock[J].International Journal of Rock Mechanics and Mining Sciences,2011,48(5):852-863.
[7] 彭苏萍,孟召平,王虎,等.不同围压下砂岩孔渗规律试验研究[J].岩石力学与工程学报,2003,22(5):742-746.PENG Suping,MENG Zhaoping,WANG Hu,et al.Testing study on pore ratio and permeability of sandstone under different confining pressures[J].Chinese Journal of Rock Mechanics and Engineering,2003,22(5):742-746.
[8] 孟召平,侯泉林.煤储层应力敏感性及影响因素的试验分析[J].煤炭学报,2012,37(3):430-437.MENG Zhaoping,HOU Quanlin.Experimental research on stress sensitivity of coal reservoir and its influencing factors[J].Journal of China Coal Society,2012,37(3):430-437.
[9] MCKEE C R,BUMB A C,KOENIG A.Stress dependent permeability and porosity of coal[J].Rocky Mountain Association of Geologist,1998:143-153.
[10] 刘永茜,张浪,李浩荡,等.含水率对煤层气渗流的影响[J].煤炭学报,2014,39(9):1840-1844.LIU Yongqian,ZHANG Lang,LI Haodang,et al.Effect of moisture content on CBM seepage[J].Journal of China Coal Society,2014,39(9):1840-1844.
[11] ALAM A K M Badrul,MASAKI Niioka,YOSHIAKI Fujii,et al.Effects of confining pressure on the permeability of three rock types under compression[J].International Journal of Rock Mechanics & Mining Sciences,2014,65:49-61.
[12] 尹光志,李文璞,李铭辉,等.加卸载条件下原煤渗透率与有效应力的规律[J].煤炭学报,2014,39(8):1497-1503.YIN Guangzhi,LI Wenpu,LI Minghui,et al.Permeability properties and effective stress of raw coal under loading-unloading conditions[J].Journal of China Coal Society,2014,39(8):1497-1503.
[13] 左建平,陈岩.卸载条件下煤岩组合体的裂纹张开效应研究[J].煤炭学报,2017,42(12):3142-3148.ZUO Jianping,CHEN Yan.Investigation on crack recovery effect of coal-rock combined body under the influence of unloading[J].Journal of China Coal Society,2017,42(12):3142-3148.
[14] DAVID C,WONG T F,ZHU Wenlu,et al.Laboratory measurement of compaction-induced permeability change in porous rocks:implications for the generation and maintenance of pore pressure excess in the crust[J].Pure and Applied Geophysics,1994,143(1/3):425-456.
[15] 王伟,徐卫亚,王如宾,等.低渗透岩石三轴压缩过程中的渗透性研究[J].岩石力学与工程学报,2015,34(1):40-47.WANG Wei,XU Weiya,WANG Rubin,et al.Permeability of dense rock under triaxial compression[J].Chinese Journal of Rock Mechanics and Engineering,2015,34(1):40-47.
[16] 葛家理.现代油藏渗流力学原理[M].北京:石油工业出版社,2006:12-27.
[17] 张东明,郑彬彬,张先萌,等.含瓦斯砂岩卸围压变形特征与渗透规律试验研究[J].岩土力学,2017,38(12):3475-3483,3490.ZHANG Dongming,ZHENG Binbin,ZHANG Xianmeng,et al.Experimental study on the deformation characteristics and permeability laws of gas infiltrated sandstone under unloading confining pressure condition[J].Rock and Soil mechanics,2017,38(12):3475-3483,3490.
[18] 孔茜,王环玲,徐卫亚.循环加卸载作用下砂岩孔隙度与渗透率演化规律试验研究[J].岩土工程学报,2015,37(10):1893-1900.KONG Qian,WANG Huanling,XU Weiya.Experimental study on permeability and porosity evolution of sandstone under cyclic loading and unloading[J].Chinese Journal of Geotechnical Engineering 2015,37(10):1893-1900.
[19] THOMMES M,KANEKO K,NEIMARK A V,et al.Physisorption of gases,with special reference to the evaluation of surface area and pore size distribution (IUPAC Technical Report)[J].Pure and Applied Chemistry,2015,87(9/10):1051-1069.
[20] 张松航,汤达祯,唐书恒,等.鄂尔多斯盆地东缘煤层气储集与产出条件[J].煤炭学报,2009,34(10):1297-1304.ZHANG Songhang,TANG Dazhen,TANG Shuheng,et al.Preservation and deliverability characteristics of coalbed methane in east margin of Ordos Basin[J].Journal of China coal society,2009,34(10):1297-1304.
[21] 刘永茜,侯金玲,张浪,等.孔隙结构控制下的煤体渗透实验研究[J].煤炭学报,2016,41(S2):434-440.LIU Yongqian,HOU Jinling,ZHANG Lang,et al.Permeability experiments of pore structure in coal matrix[J].Journal of China Coal Society,2016,41(S2):434-440.
[22] CHENG Yuanping,JIANG Haina,ZHANG Xiaolei,et al.Effects of coal rank on physicochemical properties of coal and on methane adsorption[J].International Journal of Coal Science & Technology,2017,4(2):129-146.
[23] J Rouquerol,F Rouquerol,K S W Sing,et al.Adsorption by powders and porous solids:Principles,methodology and applications[M].London:Academic Press,2014:10-12.
[24] ROMANOV Vyacheslav N,GRAESER Lauren C,JIKICH Sinisha A,et al.Coal-gas interaction:Implications of changes in texture and porosity[J].International Journal of Coal Science & Technology,2016,3(1):10-19.
[25] 谢和平,鞠杨,黎立云,等.岩体变形破坏过程的能量机制[J].岩石力学与工程学报,2008,27(9):1729-1740.XIE Heping,JU Yang,LI Liyun,et al.Energy mechanism of deformation and failure of rock masses[J].Chinese Journal of Rock Mechanics and Engineering,2008,27(9):1729-1740.
[26] 陈亮,刘建锋,王春萍,等.压缩应力条件下花岗岩损伤演化特征及其对渗透性影响研究[J].岩石力学与工程学报,2014,33(2):287-295.CHEN Liang,LIU Jianfeng,WANG Chunping,et al.Investigation on damage evolution characteristic of granite under compressive stress condition and its impact on permeability[J].Chinese Journal of Rock Mechanics and Engineering,2014,33(2):287-295.
[27] 王向宇,周宏伟,钟江城,等.三轴循环加卸载下深部煤体损伤的能量演化和渗透特性研究[J].岩石力学与工程学报,2018,37(12):2676-2684.WANG Xiangyu,ZHOU Hongwei,ZHONG Jiangcheng,et al.Study on energy evolution and permeability characteristics of damage of deep coal under trixial cyclic loading and unloading conditions[J].Chinese Journal of Rock Mechanics and Engineering,2018,37(12):2676-2684.
© 2004-2018 中国地质图书馆版权所有 京ICP备05064691号 京公网安备11010802017129号 地址：北京市海淀区学院路29号 邮编：100083 电话：办公室：(+86 10)66554848；文献借阅、咨询服务、科技查新：66554700 |