不同产状裂隙煤样三轴承压下非Darcy渗流特性
|
摘要
裂隙产状是影响瓦斯抽采钻孔孔周煤体渗流状态的重要因素之一。为探究裂隙的不同产状对煤体渗流特性的影响,分别制作了含有1,2,3条裂隙共5种产状的煤样;利用自主设计的三轴渗流试验系统,采用稳态渗透法对煤样进行渗流试验研究,得到了三轴应力下裂隙煤体的渗流雷诺数、渗透率和Forchheimer数变化趋势,并分析了裂隙煤体非Darcy渗流的演化规律。结果表明:(1)渗流试验过程中,42%的渗流雷诺数分布在10～100,且渗流趋势符合非线性渗流特点;说明随着裂隙面面积的增大,流动过程中黏滞阻力和惯性力对流速的影响越来越大,其发生非Darcy渗流的可能性就越高;(2)通过分析裂隙煤体受力状况,得到裂隙煤样渗透率k随着有效应力σ的增加呈下降趋势,且符合k=aσ-b关系;说明随着应力水平的增加,煤样内部部分裂隙发生闭合、渗流通道数目和宽度的减少,最终导致渗透率急剧降低;(3)通过计算各个阶段的Forchheimer数Fo,得到Fo与渗流速度v符合二次曲线规律增长,且随着Fo的增加非Darcy渗流效应也越来越显著,说明裂隙煤样渗透性的增强是导致发生高速非Darcy渗流的根本原因。结合以上结论,可在煤层瓦斯预抽工作中,依据钻孔孔周煤体瓦斯流动规律准确确定抽采钻孔影响范围,从而为钻孔布孔方式的设计提供重要的理论依据。
The fracture occurrence is one of the important factors affecting the seepage state of the coal around the borehole.In order to explore the influence of different occurrences of fissures on the seepage characteristics of coal,five coal samples containing one,two and three fractures were prepared.The self-designed tri-axial seepage test system was used to observe the steady-state infiltration method.The seepage test of the coal sample was carried out,and the regressive Reynolds number,permeability and Forchheimer number of the fractured coal under tri-axial stress were obtained,and the evolution of non-Darcy seepage in the fractured coal was analyzed.The results show that(1) During the seepage test,42% of the seepage Reynolds number is distributed in the range of 10 ～ 100.The seepage trend accords with thenonlinear seepage characteristics; it shows that the viscous drag and the flow process increase with the increase of the fracture surface area.The influence of inertial force on the flow velocity is getting larger and larger,and the possibility of non-Darcy seepage is higher.(2) By analyzing the stress state of the fractured coal,the permeability k of the fractured coal sample decreases with the increase of the effective stress σ.Trend,and in line with the k = aσ-brelationship; indicating that as the stress level increases,the internal crack of the coal sample closes,the number and width of the seepage channel decrease,and finally the permeability decreases sharply.(3) Through the calculation of each stage of Forchheimer the number Foand the seepage velocity v are in accordance with the regular curve growth,and the non-Darcy seepage effect is more and more obvious with the increase of Fo.It indicates that the increase of the permeability of the fractured coal sample is the root cause of the high-speed non-Darcy seepage.Combined with the above conclusions,in the pre-extraction work of coal seam gas,the influence range of the extraction drilling hole can be accurately determined according to the gas flow law of the coal body around the borehole hole,which provides an important theoretical basis for the design of the borehole pattern.
The fracture occurrence is one of the important factors affecting the seepage state of the coal around the borehole.In order to explore the influence of different occurrences of fissures on the seepage characteristics of coal,five coal samples containing one,two and three fractures were prepared.The self-designed tri-axial seepage test system was used to observe the steady-state infiltration method.The seepage test of the coal sample was carried out,and the regressive Reynolds number,permeability and Forchheimer number of the fractured coal under tri-axial stress were obtained,and the evolution of non-Darcy seepage in the fractured coal was analyzed.The results show that(1) During the seepage test,42% of the seepage Reynolds number is distributed in the range of 10 ～ 100.The seepage trend accords with thenonlinear seepage characteristics; it shows that the viscous drag and the flow process increase with the increase of the fracture surface area.The influence of inertial force on the flow velocity is getting larger and larger,and the possibility of non-Darcy seepage is higher.(2) By analyzing the stress state of the fractured coal,the permeability k of the fractured coal sample decreases with the increase of the effective stress σ.Trend,and in line with the k = aσ-brelationship; indicating that as the stress level increases,the internal crack of the coal sample closes,the number and width of the seepage channel decrease,and finally the permeability decreases sharply.(3) Through the calculation of each stage of Forchheimer the number Foand the seepage velocity v are in accordance with the regular curve growth,and the non-Darcy seepage effect is more and more obvious with the increase of Fo.It indicates that the increase of the permeability of the fractured coal sample is the root cause of the high-speed non-Darcy seepage.Combined with the above conclusions,in the pre-extraction work of coal seam gas,the influence range of the extraction drilling hole can be accurately determined according to the gas flow law of the coal body around the borehole hole,which provides an important theoretical basis for the design of the borehole pattern.
引文
[1]朱南南,张浪,范喜生,等.基于瓦斯径向渗流方程的有效抽采半径求解方法研究[J].煤炭科学技术,2017,45(10):105-110.ZHU Nannan,ZHANG Lang,FAN Xisheng,et al. Study on effective extraction radius method based on gas radial seepage equation[J].Coal Science and Technology,2017,45(10):105-110.
[2]曾春林,岳高伟,王宾宾,等.基于瓦斯渗透异性的煤层抽采钻孔合理布置[J].重庆大学学报,2018,41(6):102-114.ZENG Chunlin,YUE Gaowei,WANG Binbin,et al. Reasonable arrangement of coal seam drainage holes based on gas permeability and alienation[J]. Journal of Chongqing University,2018,41(6):102-114.
[3]许江,苏小鹏,彭守建,等.卸压区不同钻孔长度抽采条件下瓦斯运移特性试验[J].岩土力学,2018,39(1):103-111.XU Jiang,SU Xiaopeng,PENG Shoujian,et al.Gas transport characteristics under different drainage lengths in the unloading zone[J].Rock and Soil Mechanics,2018,39(1):103-111.
[4]谭云亮,尹延春,滕桂荣,等.基于Lattice Boltzmann方法的瓦斯渗流模拟研究[J].煤炭学报,2014,39(8):1446-1454.TAN Yunliang,YIN Yanchun,TENG Guirong,et al.Simulation of gas seepage based on Lattice Boltzmann method[J]. Journal of China Coal Society,2014,39(8):1446-1454.
[5]盛金昌,王璠,张霞,等.格子Boltzmann方法研究岩石粗糙裂隙渗流特性[J].岩土工程学报,2014,36(7):1213-1217.SHENG Jinchang,WANG Fan,ZHANG Xia,et al. Study on seeage characteristics of rock rough cracks by lattice Boltzmann method[J]. Chinese Journal of Geotechnical Engineering,2014,36(7):1213-1217.
[6]胡耀青,赵阳升,杨栋,等.煤体的渗透性与裂隙分维的关系[J].岩石力学与工程学报,2002,21(10):1452-1456.HU Yaoqing,ZHAO Yangsheng,YANG Dong,et al.Relationship between permeability and fracture fractal dimension of coal[J].Chinese Journal of Rock Mechanics and Engineering,2002,21(10):1452-1456.
[7]冯增朝.低渗透煤层瓦斯强化抽采理论及应用[M].北京:科学出版社,2008.
[8]常宗旭,赵阳升,胡耀青,等.三维应力作用下单一裂缝渗流规律的理论与试验研究[J].岩石力学与工程学报,2004,23(4):620-624.CHANG Zongxu,ZHAO Yangsheng,HU Yaoqing,et al. Theoretical and experimental study on the seepage law of single crack under three-dimensional stress[J]. Chinese Journal of Rock Mechanics and Engineering,2004,23(4):620-624.
[9]杨栋,赵阳升,胡耀青,等.三维应力作用下单一裂缝中气体渗流规律的理论与实验研究[J].岩石力学与工程学报,2005,24(6):999-1003.YANG Dong,ZHAO Yangsheng,HU Yaoqing,et al. Theoretical and experimental study on gas seepage in a single crack under three-dimensional stress[J]. Chinese Journal of Rock Mechanics and Engineering,2005,24(6):999-1003.
[10]朱红光,易成,谢和平,等.基于立方定律的岩体裂隙非线性流动几何模型[J].煤炭学报,2016,41(4):822-828.ZHU Hongguang,YI Cheng,XIE Heping. A geometric model of nonlinear flow in rock mass fracture based on cubic law[J].Journal of China Coal Society,2016,41(4):822-828.
[11]许光祥,张永兴,哈秋舲.粗糙裂隙渗流的超立方和次立方定律及其试验研究[J].水利学报,2003(3):74-79.XU Guangxiang,ZHANG Yongxing,HA Qiuling.The hypercube and subcubic laws of rough crack seepage and its experimental study[J].Journal of Hydraulic Engineering,2003(3):74-79.
[12]冯学敏,陈胜宏.含复杂裂隙网络岩体渗流特性研究的复合单元法[J].岩石力学与工程学报,2006,25(5):918-924.FENG Xuemin,CHEN Shenghong. Composite element method for studying seepage characteristics of rock mass with complex frature network[J].Chinese Journal of Rock Mechanics and Engineering,2006,25(5):918-924.
[13]宋晓晨,徐卫亚.裂隙岩体渗流概念模型研究[J].岩土力学,2004,25(2):226-232.SONG Xiaochen,XU Weiya.Study on conceptual model of seepage in fractured rock mass[J].Rock and Soil Mechanics,2004,25(2):226-232.
[14]张天军,尚宏波,李树刚,等.三轴应力下不同粒径破碎砂岩渗透特性试验研究[J].岩土力学,2018,39(7):1-10.ZHANG Tianjun,SHANG Hongbo,LI Shugang,et al. Experimental study on permeability characteristics of fractured sandstones with different particle sizes under triaxial stress[J]. Rock and Soil Mechanics,2018,39(7):1-10.
[15] LU Ping,LI Ping,CHEN Jian,et al. Gas drainage from different mine areas:Optimal placement of drainage systems for deep coal seams with high gas emissions[J].International Journal of Coal Science&Technology,2015,2(1):84-90.
[16]程宜康,陈占清,缪协兴,等.峰后砂岩非Darcy流渗透特性的试验研究[J].岩石力学与工程学报,2004,23(12):2005-2009.CHENG Yikang,CHEN Zhanqing,MIAO Xiexing,et al.Experimental study on non-Darcy flow permeability characteristics of postpeak sandstones[J].Chinese Journal of Rock Mechanics and Engineering,2004,23(12):2005-2009.
[17] LIU Yingke,ZHOU Fubao,WANG Jianlong,et al.Approach to increasing the quality of pressure-relieved gas drained from protected coal seam using surface borehole and its industrial application[J]. International Journal of Coal Science&Technology,2015,2(1):46-51.
[18] EMINE Celik,LUAN Hoang. Maximum estimates for generaized Forchheimer flows in heterogeneous porous media[J]. Journal of Differential Equations,2017,262(3):2158-2195.
[19] LIU Hailong.The numerical simulation for multistage fractured horizontal well in low-permeability reservoirs based on modified Darcy’s equation[J].Journal of Petroleum Exploration and Production Technology,2017,7(3):735-746.
[20] YUAN Liang. Theory and practice of integrated coal production and gas extraction[J]. International Journal of Coal Science&Technology,2015,2(1):3-11.
[21] ZENG Z,GRIGG R.A criterion for non-Darcy flow in porous media[J].Transport in Porous Media,2006,63,57-69.
[2]曾春林,岳高伟,王宾宾,等.基于瓦斯渗透异性的煤层抽采钻孔合理布置[J].重庆大学学报,2018,41(6):102-114.ZENG Chunlin,YUE Gaowei,WANG Binbin,et al. Reasonable arrangement of coal seam drainage holes based on gas permeability and alienation[J]. Journal of Chongqing University,2018,41(6):102-114.
[3]许江,苏小鹏,彭守建,等.卸压区不同钻孔长度抽采条件下瓦斯运移特性试验[J].岩土力学,2018,39(1):103-111.XU Jiang,SU Xiaopeng,PENG Shoujian,et al.Gas transport characteristics under different drainage lengths in the unloading zone[J].Rock and Soil Mechanics,2018,39(1):103-111.
[4]谭云亮,尹延春,滕桂荣,等.基于Lattice Boltzmann方法的瓦斯渗流模拟研究[J].煤炭学报,2014,39(8):1446-1454.TAN Yunliang,YIN Yanchun,TENG Guirong,et al.Simulation of gas seepage based on Lattice Boltzmann method[J]. Journal of China Coal Society,2014,39(8):1446-1454.
[5]盛金昌,王璠,张霞,等.格子Boltzmann方法研究岩石粗糙裂隙渗流特性[J].岩土工程学报,2014,36(7):1213-1217.SHENG Jinchang,WANG Fan,ZHANG Xia,et al. Study on seeage characteristics of rock rough cracks by lattice Boltzmann method[J]. Chinese Journal of Geotechnical Engineering,2014,36(7):1213-1217.
[6]胡耀青,赵阳升,杨栋,等.煤体的渗透性与裂隙分维的关系[J].岩石力学与工程学报,2002,21(10):1452-1456.HU Yaoqing,ZHAO Yangsheng,YANG Dong,et al.Relationship between permeability and fracture fractal dimension of coal[J].Chinese Journal of Rock Mechanics and Engineering,2002,21(10):1452-1456.
[7]冯增朝.低渗透煤层瓦斯强化抽采理论及应用[M].北京:科学出版社,2008.
[8]常宗旭,赵阳升,胡耀青,等.三维应力作用下单一裂缝渗流规律的理论与试验研究[J].岩石力学与工程学报,2004,23(4):620-624.CHANG Zongxu,ZHAO Yangsheng,HU Yaoqing,et al. Theoretical and experimental study on the seepage law of single crack under three-dimensional stress[J]. Chinese Journal of Rock Mechanics and Engineering,2004,23(4):620-624.
[9]杨栋,赵阳升,胡耀青,等.三维应力作用下单一裂缝中气体渗流规律的理论与实验研究[J].岩石力学与工程学报,2005,24(6):999-1003.YANG Dong,ZHAO Yangsheng,HU Yaoqing,et al. Theoretical and experimental study on gas seepage in a single crack under three-dimensional stress[J]. Chinese Journal of Rock Mechanics and Engineering,2005,24(6):999-1003.
[10]朱红光,易成,谢和平,等.基于立方定律的岩体裂隙非线性流动几何模型[J].煤炭学报,2016,41(4):822-828.ZHU Hongguang,YI Cheng,XIE Heping. A geometric model of nonlinear flow in rock mass fracture based on cubic law[J].Journal of China Coal Society,2016,41(4):822-828.
[11]许光祥,张永兴,哈秋舲.粗糙裂隙渗流的超立方和次立方定律及其试验研究[J].水利学报,2003(3):74-79.XU Guangxiang,ZHANG Yongxing,HA Qiuling.The hypercube and subcubic laws of rough crack seepage and its experimental study[J].Journal of Hydraulic Engineering,2003(3):74-79.
[12]冯学敏,陈胜宏.含复杂裂隙网络岩体渗流特性研究的复合单元法[J].岩石力学与工程学报,2006,25(5):918-924.FENG Xuemin,CHEN Shenghong. Composite element method for studying seepage characteristics of rock mass with complex frature network[J].Chinese Journal of Rock Mechanics and Engineering,2006,25(5):918-924.
[13]宋晓晨,徐卫亚.裂隙岩体渗流概念模型研究[J].岩土力学,2004,25(2):226-232.SONG Xiaochen,XU Weiya.Study on conceptual model of seepage in fractured rock mass[J].Rock and Soil Mechanics,2004,25(2):226-232.
[14]张天军,尚宏波,李树刚,等.三轴应力下不同粒径破碎砂岩渗透特性试验研究[J].岩土力学,2018,39(7):1-10.ZHANG Tianjun,SHANG Hongbo,LI Shugang,et al. Experimental study on permeability characteristics of fractured sandstones with different particle sizes under triaxial stress[J]. Rock and Soil Mechanics,2018,39(7):1-10.
[15] LU Ping,LI Ping,CHEN Jian,et al. Gas drainage from different mine areas:Optimal placement of drainage systems for deep coal seams with high gas emissions[J].International Journal of Coal Science&Technology,2015,2(1):84-90.
[16]程宜康,陈占清,缪协兴,等.峰后砂岩非Darcy流渗透特性的试验研究[J].岩石力学与工程学报,2004,23(12):2005-2009.CHENG Yikang,CHEN Zhanqing,MIAO Xiexing,et al.Experimental study on non-Darcy flow permeability characteristics of postpeak sandstones[J].Chinese Journal of Rock Mechanics and Engineering,2004,23(12):2005-2009.
[17] LIU Yingke,ZHOU Fubao,WANG Jianlong,et al.Approach to increasing the quality of pressure-relieved gas drained from protected coal seam using surface borehole and its industrial application[J]. International Journal of Coal Science&Technology,2015,2(1):46-51.
[18] EMINE Celik,LUAN Hoang. Maximum estimates for generaized Forchheimer flows in heterogeneous porous media[J]. Journal of Differential Equations,2017,262(3):2158-2195.
[19] LIU Hailong.The numerical simulation for multistage fractured horizontal well in low-permeability reservoirs based on modified Darcy’s equation[J].Journal of Petroleum Exploration and Production Technology,2017,7(3):735-746.
[20] YUAN Liang. Theory and practice of integrated coal production and gas extraction[J]. International Journal of Coal Science&Technology,2015,2(1):3-11.
[21] ZENG Z,GRIGG R.A criterion for non-Darcy flow in porous media[J].Transport in Porous Media,2006,63,57-69.