单轴加载煤孔裂隙各向异性核磁共振特征
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摘要
为了研究煤孔裂隙各向异性,进一步揭示煤微观结构及物性特征。选取平顶山矿区八矿煤样,采用核磁共振(NMR)方法,对比分析单轴加载前后煤样的横向弛豫谱(T2)特征和核磁成像(MRI)特征。实验结果表明,煤的T2谱特征具有显著的各向异性:平行于层理且垂直主裂隙X方向T2谱为3峰谱图,平行于层理且平行主裂隙Y方向T2谱为双峰谱图,垂直层理Z方向T2谱主要以单峰为主;单轴加载后煤样T2谱面积、孔隙度减小,X、Y方向煤样孔隙变化引起的峰面积所占比例下降,裂隙变化引起的峰面积占比例上升;Z方向裂隙变化引起的峰面积占比例下降;MRI揭示出,单轴加载后平行层理方向煤样孔裂隙大部分闭合,部分裂隙产生径向变形;加载方向裂隙大部分闭合,压实效应显著。综上所述,单轴加载下,煤样各向异性特征显著,同时表明核磁共振技术是研究煤孔裂隙微观变化的有效手段。
In order to study the anisotropy of coal pores and fractures, further reveal the microstructure and physical characteristics of coals, coal samples were collected from Pingdingshan eighth mining area for nuclear magnetic resonance(NMR)experiments, transverse relaxation time(T2)and magnetic mesonance imaging(MRI) under uniaxial loading were compared and analyzed. The results showed that T2 was remarkably anisotropic: parallel to bedding and in direction X of vertical main fractures, T2 had three peaks, parallel to bedding and direction Y of main fractures, T2 had two peaks, vertical to direction Z of bedding T2 had one peak. After uniaxial loading, the spectral area of T2 and the porosity decreased, the percentage of peak area induced by porosity variation in direction X and Y declined, but the fracture areas ascended, the fracture area in direction Z declined. The MRI revealed that under uniaxial loading, most pores and fractures parallel to bedding were closed, some fractures had radial deformation, most fractures of loading direction were closed, the compaction effects was remarkable. In summary, under uniaxial loading, the anisotropic characteristics of coal samples were remarkable, and the NMR was an effective method to study microscopic changes of coal pores and fractures.
In order to study the anisotropy of coal pores and fractures, further reveal the microstructure and physical characteristics of coals, coal samples were collected from Pingdingshan eighth mining area for nuclear magnetic resonance(NMR)experiments, transverse relaxation time(T2)and magnetic mesonance imaging(MRI) under uniaxial loading were compared and analyzed. The results showed that T2 was remarkably anisotropic: parallel to bedding and in direction X of vertical main fractures, T2 had three peaks, parallel to bedding and direction Y of main fractures, T2 had two peaks, vertical to direction Z of bedding T2 had one peak. After uniaxial loading, the spectral area of T2 and the porosity decreased, the percentage of peak area induced by porosity variation in direction X and Y declined, but the fracture areas ascended, the fracture area in direction Z declined. The MRI revealed that under uniaxial loading, most pores and fractures parallel to bedding were closed, some fractures had radial deformation, most fractures of loading direction were closed, the compaction effects was remarkable. In summary, under uniaxial loading, the anisotropic characteristics of coal samples were remarkable, and the NMR was an effective method to study microscopic changes of coal pores and fractures.
引文
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[19]石强,潘一山.基于非磁性渗透仪和核磁技术的煤体结构分析[J].采矿与安全工程学报,2006,23(3):302–305.SHI Qiang,PAN Yishan.Analysis of structure of coal based on non-magnetic osmocope and nuclear magnetic imaging technology[J].Journal of Minging&Safety Engineering,2006,23(3):302–305.
[20]姚艳斌,刘大锰.基于核磁共振弛豫谱的煤储层岩石物理与流体表征[J].煤炭科学技术,2016,44(6):14–22.YAO Yanbin,LIU Dameng.Petrophysics and fluid properties characterizations of coalbed methane reservoir by using NMR relaxation time analysis[J].Coal Science and Technology,2016,44(6):14–22.
[21]周世宁,林柏泉.煤矿瓦斯动力灾害防治理论及控制技术[M].北京:科学出版社,2007.
[22]张亚蒲,何应付,杨正明,等.核磁共振技术在煤层气储层评价中的应用[J].石油天然气学报,2010,32(2):277–279.ZHANG Yapu,HE Yingfu,YANG Zhengming,et al.Application of nuclear magnetic resonance technology in coalbed methane reservoir evaluation[J].Journal of Oil and Gas Technology,2010,32(2):277–279.
[2]EBROM D,万有林.各向异性和油藏开发[J].油气藏评价与开发,1995(2):11–16.EBROM D,WAN Youlin.Anisotropy and reservoir development[J].Evaluation and Development of Oil and Gas Reservoirs,1995(2):11-–16.
[3]何樵登,张中杰.3D横向各向同性介质中的体波[J].石油地球物理勘探,1990,25(2):137–147.HE Qiaodeng,ZHANG Zhongjie.Body wave in 3D transversely isotropic medium[J].Oil Geophysical Prospecting,1990,25(2):137–147.
[4]何樵登,熊维纲.应用地球物理教程[M].北京:地质出版社,1991.
[5]赵群,郝守玲.煤样的超声速度和衰减各向异性测试实例[J].地球物理学进展,2006,21(2):531–534.ZHAO Qun,HAO Shouling.Anisotropy test instance of ultrasonic velocity and attenuation of coal sample[J].Progress in Geophysics,2006,21(2):531–534.
[6]董守华.气煤弹性各向异性系数实验测试[J].地球物理学报,2008,51(3):947–952.DONG Shouhua.Test on elastic anisotropic coefficients of gas coal[J].Chinese Journal of Geophysics,2008,51(3):947–952.
[7]周枫.裂隙对煤岩超声波速度影响的实验—以沁水盆地石炭系煤层为例[J].煤田地质与勘探,2012,40(2):71–74.ZHOU Feng.Experiment of influence of fractures on coal/rock acoustic velocity:With Carboniferous seams of Qinshui basin as example[J].Coal Geology&Exploration,2012,40(2):71–74.
[8]徐晓炼,张茹,戴峰,等.煤岩特性对超声波速影响的试验研究[J].煤炭学报,2015,40(4):793–800.XU Xiaolian,ZHANG Ru,DAI Feng,et al.Effect of coal and rock characteristics on ultrasonic velocity[J].Journal of China Coal Society,2015,40(4):793–800.
[9]WERNETT P C,LARSEN J W,YAMADA O,et al.Determination of the average micropore diameter of an Illinois No.6coal by Xenon-129 NMR[J].Energy Fuels,1990,4(4):291–293.
[10]TSIAO C,BOTTO R E.129Xe NMR investigation of coal micropores[J].Energy&Fuels,1991,5(1):87–92.
[11]石强,潘一山.煤体内部裂隙和流体通道分析的核磁共振成像方法研究[J].煤矿开采,2005,10(6):6–9.SHI Qiang,PAN Yishan.A method of nuclear magnetic resonance imaging analyzed in the crack and fluid passageway of coal[J].Coal Mining Technology,2005,10(6):6–9.
[12]YAO Y B,LIU D M,CHE Y,et al.Petrophysical characterization of coals by low-field nuclear magnetic resonance(NMR)[J].Fuel,2010,89(7):1371–1380.
[13]YAO Y B,LIU D M.Comparison of low-field NMR and mercury intrusion porosimetry in characterizing pore size distributions of coals[J].Fuel,2012,95(5):152–158.
[14]YAO Y B,LIU D M,LIU J G,et al.Assessing the water migration and permeability of large intact bituminous and anthracite coals using NMR relaxation spectrometry[J].Transport in Porous Media,2015,107(2):527–542.
[15]郑贵强,凌标灿,郑德庆,等.核磁共振实验技术在煤孔径分析中的应用[J].华北科技学院学报,2014,11(4):1–7.ZHENG Guiqiang,LING Biaocan,ZHENG Deqing,et al.The application of nuclear magnetic resonance on analyzing aperture in coal[J].Journal of North China Institute of Science and Technology,2014,11(4):1–7.
[16]刘彦飞,汤达祯,许浩,等.基于核磁共振的煤岩孔裂隙应力变形特征[J].煤炭学报,2015,40(6):1415–1421.LIU Yanfei,TANG Dazhen,XU Hao,et al.Characteristics of the stress deformation of pore-fracture in coal based on nuclear magnetic resonance[J].Journal of China Coal Soociety,2015,40(6):1415–1421.
[17]刘玉龙,汤达祯,许浩,等.不同围压下中煤阶煤岩孔裂隙核磁共振响应特征[J].煤炭科学技术,2016,44(增刊1):149–153.LIU Yulong,TANG Dazhen,XU Hao,et al.Characteristics of medium rank coal pore-fracture nuclear magnetic resonance under different pressures[J].Coal Science and Technology,2016,44(S1):149–153.
[18]唐巨鹏,潘一山.煤层气赋存运移的核磁共振成像理论及应用[M].沈阳:东北大学出版社,2011.
[19]石强,潘一山.基于非磁性渗透仪和核磁技术的煤体结构分析[J].采矿与安全工程学报,2006,23(3):302–305.SHI Qiang,PAN Yishan.Analysis of structure of coal based on non-magnetic osmocope and nuclear magnetic imaging technology[J].Journal of Minging&Safety Engineering,2006,23(3):302–305.
[20]姚艳斌,刘大锰.基于核磁共振弛豫谱的煤储层岩石物理与流体表征[J].煤炭科学技术,2016,44(6):14–22.YAO Yanbin,LIU Dameng.Petrophysics and fluid properties characterizations of coalbed methane reservoir by using NMR relaxation time analysis[J].Coal Science and Technology,2016,44(6):14–22.
[21]周世宁,林柏泉.煤矿瓦斯动力灾害防治理论及控制技术[M].北京:科学出版社,2007.
[22]张亚蒲,何应付,杨正明,等.核磁共振技术在煤层气储层评价中的应用[J].石油天然气学报,2010,32(2):277–279.ZHANG Yapu,HE Yingfu,YANG Zhengming,et al.Application of nuclear magnetic resonance technology in coalbed methane reservoir evaluation[J].Journal of Oil and Gas Technology,2010,32(2):277–279.