煤岩塑性软化及扩容特性对钻孔密封性的影响
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摘要
钻孔密封性是钻孔瓦斯抽采的关键基础之一,而煤岩力学特性对钻孔密封参数的选择及密封效果具有重要影响作用。因此,为准确认识钻孔围岩密封环境并深入分析煤岩塑性软化及扩容特性对钻孔密封性的控制作用,进而为钻孔密封参数的合理选择提供可靠的依据。基于煤岩全应力应变曲线及煤层力学参数,通过引入煤层软化系数k及扩容系数η1和η2,在构建煤岩线弹塑性力学软化"三折线"模型的基础上,依据线性Mohr-Coulomb屈服准则,对钻孔围岩弹性区、塑性软化区及塑性流动区半径、钻孔围岩径向位移以及钻孔围岩理论密封半径等参数进行理论数值解析计算,并对相应解析结果进行对比分析。同时结合钻孔成像技术及钻孔瓦斯抽采浓度数据监测等手段,综合分析塑性软化及扩容特性对煤层钻孔密封性的影响作用。研究结果表明,与理想弹塑性模型(Kastner)解相比,受塑性软化及扩容特性共同作用下的煤层钻孔围岩径向位移及理论密封半径分别增加12. 93倍和2. 60倍,且在构造煤层区域内钻孔缩径现象明显。在钻孔密封参数及密封材料相同的条件下,缩径现象明显的钻孔内初始平均抽采瓦斯体积分数较相邻完整钻孔降低59%,在29 d考察期内平均抽采体积分数同比降低64. 92%,瓦斯体积分数衰减率同比增加3倍。因此,塑性软化及扩容效应是造成钻孔初始密封性降低及后期抽采瓦斯衰减的主要原因之一,而采用Kastner方程求解获得的煤层钻孔围岩理论渗透半径及注浆压力等参数并不合理;同时,钻孔密封参数需应根据钻孔围岩特性进行区别选择。
Sealability of borehole is one of the key foundations of efficient gas drainage. The mechanical properties of coal play important roles in the selection of sealing parameters and the results of borehole sealing. Therefore,this paper aims at understanding the environment of surrounding coal and rock of borehole and analyzing the impacts of coal plastic softening and expansion characteristics on borehole sealing and providing a reliable foundation for the selection of borehole sealing parameters. A linear elastic-plastic stress softening model of "three-fold line" was proposed based on the full stress-strain curve and the mechanical parameters of coal. According to the Linear Mohr-Coulomb Yield Criterion,the radius and displacement of elastic zone,plastic softening zone and plastic flow zone and displacement of the model were calculated. Borehole imaging and data monitoring of gas drainage were conducted. The results show that radial displacement and theoretical sealing radius of surrounding of boreholes was increased by 12. 93 and 2. 60 times compared with the calculated results of Kastner solution. Compared with the adjacent borehole which is unbroken and the sealing parameters are the same,the initial average extraction gas concentration of the borehole decreased by 59%,the average extraction gas concentration decreased by 64.92% over the same period of 29 d and gas concentration decay rate increased by 3 times. Based on the results,the influence of plastic-softening and dilatancy is one of the main reasons inducing the decrease of initial sealing performance and the decline of gas extraction in late drainage stage.The theoretical permeability radius and grouting pressure for sealing boreholes obtained from Kastner equation was not reasonable. The sealing parameters of boreholes should be selected according to the characteristics of borehole surrounding rock as well.
Sealability of borehole is one of the key foundations of efficient gas drainage. The mechanical properties of coal play important roles in the selection of sealing parameters and the results of borehole sealing. Therefore,this paper aims at understanding the environment of surrounding coal and rock of borehole and analyzing the impacts of coal plastic softening and expansion characteristics on borehole sealing and providing a reliable foundation for the selection of borehole sealing parameters. A linear elastic-plastic stress softening model of "three-fold line" was proposed based on the full stress-strain curve and the mechanical parameters of coal. According to the Linear Mohr-Coulomb Yield Criterion,the radius and displacement of elastic zone,plastic softening zone and plastic flow zone and displacement of the model were calculated. Borehole imaging and data monitoring of gas drainage were conducted. The results show that radial displacement and theoretical sealing radius of surrounding of boreholes was increased by 12. 93 and 2. 60 times compared with the calculated results of Kastner solution. Compared with the adjacent borehole which is unbroken and the sealing parameters are the same,the initial average extraction gas concentration of the borehole decreased by 59%,the average extraction gas concentration decreased by 64.92% over the same period of 29 d and gas concentration decay rate increased by 3 times. Based on the results,the influence of plastic-softening and dilatancy is one of the main reasons inducing the decrease of initial sealing performance and the decline of gas extraction in late drainage stage.The theoretical permeability radius and grouting pressure for sealing boreholes obtained from Kastner equation was not reasonable. The sealing parameters of boreholes should be selected according to the characteristics of borehole surrounding rock as well.
引文
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[11]范文,俞茂宏,陈立伟,等.考虑剪胀及软化的洞室围岩弹塑性分析的统一解[J].岩石力学与工程学报,2004(19):3213-3220.FAN Wen,YU Maohong,CHEN Liwei,et al.Unified elastoplastic solution for surrounding rocks of openings with consideration of material dilatancy and softening[J].Chinese Journal of Rock Mechanics&Engineering,2004,23(19):3213-3220.
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[13]潘阳,赵光明,孟祥瑞.非均匀应力场下巷道围岩弹塑性分析[J].煤炭学报,2011,36(S1):53-57.PAN Yang,ZHAO Guangming,MENG Xiangrui.Elasto-plastic analysis on surrounding rock mass under non-uniform stress field[J].Journal of China Coal Society,,2011,36(S1):53-57.
[14]郝富昌,孙丽娟,刘明举.考虑塑性软化和扩容特性的最短封孔深度研究[J].中国矿业大学学报,2014,43(5):789-793,807.HAO Fuchang,SUN Lijuan,LIU Mingju.Study of shortest sealing depth with considering plastic softening and dilatancy[J].Journal of China University of Mining&Technology,2014,43(5):789-793,807.
[15]武炜.水泥基复合材料带压注浆封孔测压技术研究[D].焦作:河南理工大学,2015:25-29.WU Wei.Study on coal seam gas pressure measuretechnology of grouting with pressure drillingsealing base on the cement compositematerials[D].Jiaozhuo:Henan Polytechnic University,2015:25-29.
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[17]袁文伯,陈进.软化岩层中巷道的塑性区与破碎区分析[J].煤炭学报,1986(3):77-86.YUAN Wenbo,CHEN Jin.Analysis of plastic zone and loose zone around opening in softening rockmass[J].Journl of China Coal Society,1986,11(3):77-85.
[18]李世平,吴振业,贺永年,等.岩石力学简明教程[M].北京:煤炭工业出版社,1996:90-100.
[19]沈明荣,陈建峰.岩体力学[M].上海:同济大学出版社,2006:153-155.
[20]何满潮,景海河,孙晓明.软岩工程力学[M].北京:科学出版社,2002:114-116.
[21]郑颖人,朱合华,方正昌,等.地下工程围岩稳定分析与设计理论[M].北京:人民交通出版社,2012:60-68.
[2]周福宝,孙玉宁,李海鉴,等.煤层瓦斯抽采钻孔密封理论模型与工程技术研究[J].中国矿业大学学报,2016,45(3):433-439.ZHOU Fubao,SUN Yuning,LI Haijian,et al.Research on the theoretical model and engineering technology of the coal seam gas drainage hole sealing[J].Journal of China University of Mining&Technology,2016,45(3):433-439.
[3]王志明,孙玉宁,王永龙,等.瓦斯抽采钻孔动态漏气圈特性及漏气处置研究[J].中国安全生产科学技术,2016,12(5):139-145.WANG Zhiming,SUN Yuning,WANG Yonglong,et al.Study on characteristics of dynamic leakage ring and leakage disposal of gas extraction borehole[J].Journal of Safety Science and Technology,2016,12(5):139-145.
[4]王兆丰,武炜.煤矿瓦斯抽采钻孔主要封孔方式剖析[J].煤炭科学技术,2014,42(6):31-34,103.WANG Zhaofeng,WU Wei.Analysis on major borehole sealing methods of mine gas drainage boreholes[J].Coal Science&Technology,2014,42(6):31-34,103.
[5]郝志勇.材料复合技术及其在钻孔密封中的应用研究[D].徐州:中国矿业大学,2010:14-15.HAO Zhiyong.Research of composite technology and application in bored sealiing[D].Xuzhou:China University of Mining and Technology,2010:14-15.
[6]王振锋,周英,孙玉宁,等.新型瓦斯抽采钻孔注浆封孔方法及封堵机理[J].煤炭学报,2015,40(3):588-595.WANG Zhenfeng,ZHOU Ying,SUN Yuning,et al.Novel gas extraction borehole grouting sealing method and sealing mechanism[J].Journal of China Coal Society,2015,40(3):588-595.
[7]靳钟铭,赵阳升,贺军,等.含瓦斯煤层力学特性的实验研究[J].岩石力学与工程学报,1991,10(3):271-280.JIN Zhongming,ZHAO Yangsheng,HE Jun,et al.An experimental study on the mechanical properties of gas-bearing coal seams[J].Chinese Journal of Rock Mechanics&Engineering,1991,10(3):271-280.
[8]王云飞,龚健,陈赞成.不同围压下煤岩变形与剪胀扩容模型[J].水文地质工程地质,2015,42(1):106-111.WANG Yunfei,GONG Jian,CHEN Zancheng.Deformation characteristics and dilatancy model of coal rock under different confining pressures[J].Hydrogeology&Engineering Geology,2015,42(1):106-111.
[9]陈进,袁文伯.巷道围岩的脆性破坏理论[J].工程力学,1989,6(2):134-137.CHEN Jin,YUAN Wenbo.A brittle failure theory of the rock mass around tunnel[J].Engineering Mechanics,1989,6(2):134-137.
[10]付国彬.巷道围岩破裂范围与位移的新研究[J].煤炭学报,1995(3):304-310.FU Guobin.Recent investigation of extent of fractured zone and displacement of rocks around the roadways[J].Journal of China Coal Society,1995(3):304-310.
[11]范文,俞茂宏,陈立伟,等.考虑剪胀及软化的洞室围岩弹塑性分析的统一解[J].岩石力学与工程学报,2004(19):3213-3220.FAN Wen,YU Maohong,CHEN Liwei,et al.Unified elastoplastic solution for surrounding rocks of openings with consideration of material dilatancy and softening[J].Chinese Journal of Rock Mechanics&Engineering,2004,23(19):3213-3220.
[12]姚国圣,李镜培,谷拴成.考虑岩体扩容和塑性软化的软岩巷道变形解析[J].岩土力学,2009,30(2):463-467.YAO Guosheng,LI Jingpei,GU Shuancheng.Analytic solution to deformation of soft rock tunnel considering dilatancy and plastic softening of rock mass[J].Rock&Soil Mechanics,2009,30(2):463-467.
[13]潘阳,赵光明,孟祥瑞.非均匀应力场下巷道围岩弹塑性分析[J].煤炭学报,2011,36(S1):53-57.PAN Yang,ZHAO Guangming,MENG Xiangrui.Elasto-plastic analysis on surrounding rock mass under non-uniform stress field[J].Journal of China Coal Society,,2011,36(S1):53-57.
[14]郝富昌,孙丽娟,刘明举.考虑塑性软化和扩容特性的最短封孔深度研究[J].中国矿业大学学报,2014,43(5):789-793,807.HAO Fuchang,SUN Lijuan,LIU Mingju.Study of shortest sealing depth with considering plastic softening and dilatancy[J].Journal of China University of Mining&Technology,2014,43(5):789-793,807.
[15]武炜.水泥基复合材料带压注浆封孔测压技术研究[D].焦作:河南理工大学,2015:25-29.WU Wei.Study on coal seam gas pressure measuretechnology of grouting with pressure drillingsealing base on the cement compositematerials[D].Jiaozhuo:Henan Polytechnic University,2015:25-29.
[16]董方庭,宋宏伟,郭志宏,等.巷道围岩松动圈支护理论[J].煤炭学报,1994(1):21-32.DONG Fangting,SONG Hongwei,GUO Zhihong,et.al.Roadway support theory based on broken rock zone[J].Journal of China Coal Society,1994(1):21-32.
[17]袁文伯,陈进.软化岩层中巷道的塑性区与破碎区分析[J].煤炭学报,1986(3):77-86.YUAN Wenbo,CHEN Jin.Analysis of plastic zone and loose zone around opening in softening rockmass[J].Journl of China Coal Society,1986,11(3):77-85.
[18]李世平,吴振业,贺永年,等.岩石力学简明教程[M].北京:煤炭工业出版社,1996:90-100.
[19]沈明荣,陈建峰.岩体力学[M].上海:同济大学出版社,2006:153-155.
[20]何满潮,景海河,孙晓明.软岩工程力学[M].北京:科学出版社,2002:114-116.
[21]郑颖人,朱合华,方正昌,等.地下工程围岩稳定分析与设计理论[M].北京:人民交通出版社,2012:60-68.