含瓦斯煤渗透率演化模型和实验分析
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摘要
与气体压力有关的煤层渗透率变化规律是煤矿开采和煤层气开发过程中的重要问题,不同应力条件下,不同类型煤样的渗透率演化特征不同。为了研究瓦斯压力变化过程中煤样渗透性的变化规律,以开滦赵各庄煤矿9号煤层的煤样为研究对象,利用含瓦斯煤热-流-固耦合三轴伺服渗流装置,在恒定温度、轴压和围压,降低瓦斯压力的实验条件下测定了煤样应变和瓦斯渗透率。实验结果表明:随着瓦斯压力的降低,煤样收缩应变加剧,渗透率表现为两种变化趋势:逐渐增大和先减小后增大(渗透率回升对应的瓦斯压力小于1. 0 MPa)。瓦斯压力降低至0. 3 MPa时,渗透率为初始条件下(瓦斯压力2. 0 MPa)渗透率的1. 9～2. 9倍。考虑到煤样在径向和轴向的收缩应变数值接近,针对三维变形煤样建立了渗透率模型,模型同时体现了气体压力和气体解吸对渗透率的影响。理论分析表明,降压过程中煤的渗透率将在某一气体压力(反弹气体压力pr)时由降低转为升高。推导的反弹气体压力pr计算公式显示pr的取值由煤样的体积模量K、与吸附效应有关的Langmuir系数εp和pL共同决定;体积模量K与吸附变形系数εp越大,pr越大。值得注意的是,pr的取值与煤样的外部应力以及内部的气体压力无关。结合本文和前人的实验数据,由本文的渗透率模型计算得到了不同应力和瓦斯压力条件下的煤样渗透率变化曲线以及相应的反弹气体压力pr。模型计算结果与实验数据接近,最大相对误差低于8. 9%。研究表明,实验测得煤样的渗透率表现为何种变化趋势,取决于反弹气体压力pr和实验气体压力的关系。当pr≥pmax(实验测点中最大的气体压力值)时,渗透率随着气体压力增大而降低;当pr≤pmin(实验测点中最小的气体压力值)时,渗透率随着气体压力增大而增大;当pmin The change of coal permeability related to gas pressure is important to coal mining and CBM exploitation.The permeability evolution of various kinds of coal is different and changes with stress conditions. To investigate the permeability evolution of coal samples changed in gas pressure,the strain and permeability of coal samples collected from the No.9 coal seam in Zhaogezhuang mine,Kailuan,China were measured during gas pressure reduction under constant temperature,axial and confining stress by using Triaxial servo-controlled seepage rig.The experimental results showed that coal shrinkage strain increased with the decrease of gas pressure.And the permeability of coal cores may increase gradually or decrease firstly and then increase( The gas pressure cor-responding to permeability rebound is less than 1.0 MPa).When the gas pressure reduced to 0.3 MPa,the perme-ability was 1.9-2.9 times of the initial condition( gas pressure was 2.0 MPa).Considering that coal axial and radial strains are approximately equal,a theoretical model was established to describe the permeability evolution of the three-dimensional deformation coal.The model also reflected the effects of gas pressure and gas desorption on coal permeability.The analysis showed that in the process of reducing gas pressure,the permeability of coal will change from decreasing to increasing at a certain gas pressure( rebound gas pressure pr).The equation of rebound gas pressure pr was derived.It indicated that prwas determined by coal volume modulus,K,and Langmuir coefficients related to the adsorption,εpand pL.The greater volume modulus K and the adsorption deformation coefficient εpare,the higher pris.And prwas independent of the external stress and the internal gas pressure.According to the derived permeability model,the permeability curves and the rebound gas pressure pr of coal samples under various stresses and gas pressures were calculated by referring to the experimental data of this paper and other published articles.The numerical results were close to the experimental data with a maximum relative error less than 8.9%.The trend of coal permeability changing with gas pressure in the experiment depends on the rebound gas pressure prand the experimental gas pressure.When pr≥pmax( the maximum gas pressure in the experiment),coal permeability decreases with gas pressure increasing.When pr≤pmin( the minimum gas pressure value in the experiment),coal permeability increases with gas pressure.When pmin
引文
[1]林柏泉,周世宁.煤样瓦斯渗透率的实验研究[J].中国矿业学院学报,1987,1:21-28.LIN Baiquan,ZHOU Shining. Experimental investigation on the permeability of the coal samples containing methane[J].Journal of China University of Mining&Technology,1987,1:21-28.
[2]孙培德,凌志仪.三轴应力作用下煤渗透率变化规律实验[J].重庆大学学报(自然科学版),2000,23(S):28-31.SUN Peide,LING Zhiyi.Experimental study of the law for permeability of coal under action of 3-triaxial compression[J]. Journal of Chongqing University(Natural Science Edition),2000,23(S):28-31.
[3]隆清明,赵旭生,孙东玲,等.吸附作用对煤的渗透率影响规律实验研究[J].煤炭学报,2008,33(9):1030-1034.LONG Qingming,ZHAO Xusheng,SUN Dongling,et al.Experimental study on coal permeability by adsorption[J]. Journal of China Coal Society,2008,33(9):1030-1034.
[4]陶云奇,许江,程明俊,等.含瓦斯煤渗透率理论分析与试验研究[J].岩石力学与工程学报,2009,28(S2):3363-3370.TAO Yunqi,XU Jiang,CHENG Mingjun,et al. Theoretical analysis and experimental study on permeability of gas-bearing coal[J].Chinese Journal of Rock Mechanics and Engineering,2009,28(S2):3363-3370.
[5]许江,袁梅,李波波,等.煤的变质程度、孔隙特征与渗透率关系的试验研究[J].岩石力学与工程学报,2012,31(4):681-687.XU Jiang,YUAN Mei,LI Bobo,et al.Experimental study of relationships between metamorphic grade,pore characteristics and permeability of coal[J].Chinese Journal of Rock Mechanics and Engineering,2012,31(4):681-687.
[6]王刚,程卫民,郭恒,等.瓦斯压力变化过程中煤体渗透率特性的研究[J].采矿与安全工程学报,2012,29(5):735-739,745.WANG Gang,CHENG Weimin,GUO Heng,et al. Study on permeability characteristics of coal body with gas pressure variation[J].Journal of Mining&Safety Engineering,2012,29(5):735-739,745.
[7]王登科,魏建平,尹光志.复杂应力路径下含瓦斯煤渗透性变化规律研究[J].岩石力学与工程学报,2012,31(2):303-310.WANG Dengke,WEI Jianping,YIN Guangzhi. Investigation on change rule of permeability of coal containing gas under complex stress paths[J]. Chinese Journal of Rock Mechanics and Engineering,2012,31(2):303-310.
[8]朱卓慧,冯涛,谢东海,等.不同应力路径下含瓦斯煤渗透特性的实验研究[J].采矿与安全工程学报,2012,29(4):570-574.ZHU Zhuohui,FENG Tao,XIE Donghai,et al. Seepage property of coal containing gas under different paths in laboratory[J].Journal of Mining&Safety Engineering,2012,29(4):570-574.
[9]张广洋,胡耀华,姜德义.煤的瓦斯渗透性影响因素探讨[J].重庆大学学报(自然科学版),1995,18(3):27-30.ZHANG Guangyang,HU Yaohua,JIANG Deyi. Study on the factors affecting gas permeability of coal[J].Journal of Chongqing University(Natural Science Edition),1995,18(3):27-30.
[10]曹树刚,郭平,李勇,等.瓦斯压力对原煤渗透特性的影响[J].煤炭学报,2010,35(4):595-599.CAO Shugang,GUO Ping,LI Yong,et al. Effect of gas pressure on gas seepage of outburst coal[J].Journal of China Coal Society,2010,35(4):595-599.
[11]魏建平,秦恒洁,王登科,等.含瓦斯煤渗透率动态演化模型[J].煤炭学报,2015,40(7):1555-1561.WEI Jianping,QIN Hengjie,WANG Dengke,et al.Dynamic permeability model for coal containing gas[J].Journal of China Coal Society,2015,40(7):1555-1561.
[12]许江,张敏,彭守建,等.不同温度条件下气体压力升降过程中瓦斯运移规律的试验研究[J].岩土力学,2016,37(6):1579-1587.XU Jiang,ZHANG Min,PENG Shoujian,et al. Experimental study of migration laws of gas during loading-unloading process at different temperatures[J]. Rock and Soil Mechanics,2016,37(6):1579-1587.
[13] HARPALANI S,SCHRAUFNAGEL R A.Shrinkage of coal matrix with release of gas and its impact on permeability of coal[J].Fuel,1990,69:551-516.
[14] ROBERTSON E P.Measurement and modeling of sorption-induced strain and permeability changes in coal[D]. Colorado:Colorado School of Mines,2005.
[15] GRAY Ian.Reservoir engineering in coal seams:Part 1-The physical process of gas storage and movement in coal seams[J].SPE Reservoir Engineering,1987,2(1):28-34.
[16] SHI Q,DURUCAN S. Drawdown induced changes in permeability of coalbeds:A new interpretation of the reservoir response to primary recovery[J].Transport in Porous Media,2004,56(1):1-16.
[17] PALMER Ian,MANSOORI John. How permeability depends on stress and pore pressure in coalbeds:A new model[J].SPE Reservoir Engineering,1998,1(6):539-544.
[18] LIU Jishan,CHEN Zhongwei,ELSWORTH Derek,et al.Evolution of coal permeability from stress-controlled to displacement-controlled swelling conditions[J].Fuel,2011,90(10):2987-2997.
[19]祝捷,姜耀东,孟磊,等.载荷作用下煤体变形与渗透性的相关性研究[J].煤炭学报,2012,37(6):984-988.ZHU Jie,JIANG Yaodong,MENG Lei,et al. Pertinence study on deformation and permeability of coal containing methane during loading process[J]. Journal of China Coal Society,2012,37(6):984-988.
[20] ZHU Wancheng,LIU Liyuan,LIU Jishan,et al.Impact of gas adsorption-induced coal damage on the evolution of coal permeability[J].International Journal of Rock Mechanics and Mining Sciences,2018,101:89-97.
[2]孙培德,凌志仪.三轴应力作用下煤渗透率变化规律实验[J].重庆大学学报(自然科学版),2000,23(S):28-31.SUN Peide,LING Zhiyi.Experimental study of the law for permeability of coal under action of 3-triaxial compression[J]. Journal of Chongqing University(Natural Science Edition),2000,23(S):28-31.
[3]隆清明,赵旭生,孙东玲,等.吸附作用对煤的渗透率影响规律实验研究[J].煤炭学报,2008,33(9):1030-1034.LONG Qingming,ZHAO Xusheng,SUN Dongling,et al.Experimental study on coal permeability by adsorption[J]. Journal of China Coal Society,2008,33(9):1030-1034.
[4]陶云奇,许江,程明俊,等.含瓦斯煤渗透率理论分析与试验研究[J].岩石力学与工程学报,2009,28(S2):3363-3370.TAO Yunqi,XU Jiang,CHENG Mingjun,et al. Theoretical analysis and experimental study on permeability of gas-bearing coal[J].Chinese Journal of Rock Mechanics and Engineering,2009,28(S2):3363-3370.
[5]许江,袁梅,李波波,等.煤的变质程度、孔隙特征与渗透率关系的试验研究[J].岩石力学与工程学报,2012,31(4):681-687.XU Jiang,YUAN Mei,LI Bobo,et al.Experimental study of relationships between metamorphic grade,pore characteristics and permeability of coal[J].Chinese Journal of Rock Mechanics and Engineering,2012,31(4):681-687.
[6]王刚,程卫民,郭恒,等.瓦斯压力变化过程中煤体渗透率特性的研究[J].采矿与安全工程学报,2012,29(5):735-739,745.WANG Gang,CHENG Weimin,GUO Heng,et al. Study on permeability characteristics of coal body with gas pressure variation[J].Journal of Mining&Safety Engineering,2012,29(5):735-739,745.
[7]王登科,魏建平,尹光志.复杂应力路径下含瓦斯煤渗透性变化规律研究[J].岩石力学与工程学报,2012,31(2):303-310.WANG Dengke,WEI Jianping,YIN Guangzhi. Investigation on change rule of permeability of coal containing gas under complex stress paths[J]. Chinese Journal of Rock Mechanics and Engineering,2012,31(2):303-310.
[8]朱卓慧,冯涛,谢东海,等.不同应力路径下含瓦斯煤渗透特性的实验研究[J].采矿与安全工程学报,2012,29(4):570-574.ZHU Zhuohui,FENG Tao,XIE Donghai,et al. Seepage property of coal containing gas under different paths in laboratory[J].Journal of Mining&Safety Engineering,2012,29(4):570-574.
[9]张广洋,胡耀华,姜德义.煤的瓦斯渗透性影响因素探讨[J].重庆大学学报(自然科学版),1995,18(3):27-30.ZHANG Guangyang,HU Yaohua,JIANG Deyi. Study on the factors affecting gas permeability of coal[J].Journal of Chongqing University(Natural Science Edition),1995,18(3):27-30.
[10]曹树刚,郭平,李勇,等.瓦斯压力对原煤渗透特性的影响[J].煤炭学报,2010,35(4):595-599.CAO Shugang,GUO Ping,LI Yong,et al. Effect of gas pressure on gas seepage of outburst coal[J].Journal of China Coal Society,2010,35(4):595-599.
[11]魏建平,秦恒洁,王登科,等.含瓦斯煤渗透率动态演化模型[J].煤炭学报,2015,40(7):1555-1561.WEI Jianping,QIN Hengjie,WANG Dengke,et al.Dynamic permeability model for coal containing gas[J].Journal of China Coal Society,2015,40(7):1555-1561.
[12]许江,张敏,彭守建,等.不同温度条件下气体压力升降过程中瓦斯运移规律的试验研究[J].岩土力学,2016,37(6):1579-1587.XU Jiang,ZHANG Min,PENG Shoujian,et al. Experimental study of migration laws of gas during loading-unloading process at different temperatures[J]. Rock and Soil Mechanics,2016,37(6):1579-1587.
[13] HARPALANI S,SCHRAUFNAGEL R A.Shrinkage of coal matrix with release of gas and its impact on permeability of coal[J].Fuel,1990,69:551-516.
[14] ROBERTSON E P.Measurement and modeling of sorption-induced strain and permeability changes in coal[D]. Colorado:Colorado School of Mines,2005.
[15] GRAY Ian.Reservoir engineering in coal seams:Part 1-The physical process of gas storage and movement in coal seams[J].SPE Reservoir Engineering,1987,2(1):28-34.
[16] SHI Q,DURUCAN S. Drawdown induced changes in permeability of coalbeds:A new interpretation of the reservoir response to primary recovery[J].Transport in Porous Media,2004,56(1):1-16.
[17] PALMER Ian,MANSOORI John. How permeability depends on stress and pore pressure in coalbeds:A new model[J].SPE Reservoir Engineering,1998,1(6):539-544.
[18] LIU Jishan,CHEN Zhongwei,ELSWORTH Derek,et al.Evolution of coal permeability from stress-controlled to displacement-controlled swelling conditions[J].Fuel,2011,90(10):2987-2997.
[19]祝捷,姜耀东,孟磊,等.载荷作用下煤体变形与渗透性的相关性研究[J].煤炭学报,2012,37(6):984-988.ZHU Jie,JIANG Yaodong,MENG Lei,et al. Pertinence study on deformation and permeability of coal containing methane during loading process[J]. Journal of China Coal Society,2012,37(6):984-988.
[20] ZHU Wancheng,LIU Liyuan,LIU Jishan,et al.Impact of gas adsorption-induced coal damage on the evolution of coal permeability[J].International Journal of Rock Mechanics and Mining Sciences,2018,101:89-97.