考虑时效影响的深部煤层瓦斯运移特性
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摘要
为了考虑长期抽采过程中时间效应对煤体渗透率的影响,结合平均有效应力建立了时间效应和气体解吸效应耦合作用下的深部煤体孔隙率及渗透率演化模型。运用COMSOL Multiphysics对钻孔周围瓦斯运移过程进行了定量计算,结合现场数据对是否考虑时间效应的瓦斯渗流场变化规律进行了对比分析,并对长期抽采过程中深部煤层瓦斯运移规律进行了模拟分析。结果表明:煤层渗透率随瓦斯压力的下降呈指数型上升趋势;考虑时间效应的孔隙率、渗透率模拟结果明显小于未考虑时间效应模型的结果,且随着抽采时间的增长,蠕变本构中的黏弹性元件使得煤体更为致密,深部煤层的时间效应越发明显,考虑时间效应的孔隙率、渗透率模拟结果与未考虑时间效应的结果差值逐渐增大;考虑时间效应的模拟结果与现场数据匹配度较高,更符合深部煤层孔隙率和渗透率的实际演化特征。在同一抽采时刻,随着距钻孔中心距离的减小,渗透率呈现升高的趋势,压力呈现降低的趋势,当模拟抽采时间为1 d时,临近钻孔中心处渗透率较大、瓦斯压力较小;在不同抽采时刻,当抽采时间逐渐增长时,相同位置处的渗透率逐渐增大,瓦斯压力逐渐减小,当抽采时间由1 d增至30 d时,临近钻孔中心处的渗透率增长近1. 4倍,瓦斯压力降低近3. 8倍,且模型内渗透率与瓦斯压力的演化趋于平衡状态。
In order to study the permeability of deep coal seam with time-dependent effect during the long-term extraction process,the improved porosity and permeability model coupling with gas desorption effect and time-dependent effect was developed by incorporating mean effective stress into the gas migration equation. By using COMSOL Multiphysics,the process of gas migration around the borehole was calculated quantitatively.In combination with the field data,the variation law of gas seepage field with or without time-dependent effect was compared and analyzed,and the law of gas migration in deep coal seam during long-term extraction was simulated and analyzed.The results show that coal seam permeability increases exponentially with gas pressure decreasing.The porosity and permeability simulation results considering time-dependent effect are significantly smaller than those without considering the time-dependent effect model,and as the extraction time increases,the viscoelastic elements make the coal body denser in the creep constitutive.With the increase of extraction time,the time-dependent effect of deep coal seam becomes more obvious,and the difference increases gradually between the simulation results of porosity and permeability considering time-dependent effect or not.The time-dependent simulation results are in good agreement with the field data and are more in line with the actual evolutionary characteristics.At the same time,as the distance from the center of the borehole decreases,the permeability shows an increasing trend,while the pressure shows a decreasing trend.When the extraction time is 1 d,the permeability is large and the gas pressure is small near the center of the borehole.At different extraction times,when the extraction time gradually increases,the permeability gradually increases at the same position,and the gas pressure gradually decreases.When the extraction time increases from 1 d to 30 d,the permeability increases by nearly 1.4 times near the center of the borehole,the gas pressure decreases by nearly 3.8 times,and the evolution of permeability and gas pressure tends to balance in the model.
In order to study the permeability of deep coal seam with time-dependent effect during the long-term extraction process,the improved porosity and permeability model coupling with gas desorption effect and time-dependent effect was developed by incorporating mean effective stress into the gas migration equation. By using COMSOL Multiphysics,the process of gas migration around the borehole was calculated quantitatively.In combination with the field data,the variation law of gas seepage field with or without time-dependent effect was compared and analyzed,and the law of gas migration in deep coal seam during long-term extraction was simulated and analyzed.The results show that coal seam permeability increases exponentially with gas pressure decreasing.The porosity and permeability simulation results considering time-dependent effect are significantly smaller than those without considering the time-dependent effect model,and as the extraction time increases,the viscoelastic elements make the coal body denser in the creep constitutive.With the increase of extraction time,the time-dependent effect of deep coal seam becomes more obvious,and the difference increases gradually between the simulation results of porosity and permeability considering time-dependent effect or not.The time-dependent simulation results are in good agreement with the field data and are more in line with the actual evolutionary characteristics.At the same time,as the distance from the center of the borehole decreases,the permeability shows an increasing trend,while the pressure shows a decreasing trend.When the extraction time is 1 d,the permeability is large and the gas pressure is small near the center of the borehole.At different extraction times,when the extraction time gradually increases,the permeability gradually increases at the same position,and the gas pressure gradually decreases.When the extraction time increases from 1 d to 30 d,the permeability increases by nearly 1.4 times near the center of the borehole,the gas pressure decreases by nearly 3.8 times,and the evolution of permeability and gas pressure tends to balance in the model.
引文
[1]谢和平,周宏伟,薛东杰,等.煤炭深部开采与极限开采深度的研究与思考[J].煤炭学报,2012,37(4):535-542.XIE Heping,ZHOU Hongwei,XUE Dongjie,et al.Research and consideration on deep coal mining and critical mining depth[J].Journal of China Coal Society,2012,37(4):535-542.
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[13]周长冰,万志军,张源,等.高温三轴应力下气煤蠕变特征及本构模型[J].煤炭学报,2012,37(12):2020-2025.ZHOU Changbing,WAN Zhijun,ZHANG Yuan,et al. Creep characteristics and constitutive model of gas coal mass under high temperature and triaxial stress[J]. Journal of China Coal Society,2012,37(12):2020-2025.
[14]许江,彭守建,陶云奇,等.蠕变对含瓦斯煤渗透率影响的试验分析[J].岩石力学与工程学报,2009,28(11):2273-2279.XU Jiang,PENG Shoujian,TAO Yunqi,et al.Experimental analysis of influence of creep on permeability of gas-bering coal[J].Chinese Journal of Rock Mechanics and Engineering,2009,28(11):2273-2279.
[15]郝富昌,刘彦伟,龙威成,等.蠕变-渗流耦合作用下不同埋深有效抽采半径研究[J].煤炭学报,2017,42(10):2616-2622.HAO Fuchang,LIU Yanwei,LONG Weicheng,et al. Effective gas extraction radius of different burial depths under creep-seepage coupling[J]. Journal of China Coal Society,2017,42(10):2616-2622.
[16] NISHIHARA M. Creep of shale and sandy-shale[J]. The Journal of the Geological Society of Japan,1952,58(683):373-377.
[17] JAEGER J C,COOK N G W,ZIMMERMAN R. Fundamentals of rock mechanics[M].John Wiley&Sons,2009:169-204.
[18] CUI Xiaojun,BUSTIN R M,CHIKATAMARLA LAXMI. Adsorption-induced coal swelling and stress:Implications for methane production and acid gas sequestration into coal seams[J]. Journal of Geophysical Research,2007,112(B10202).
[19] DANESH N N,CHEN Z,AMINOSSADATI S M,et al. Impact of creep on the evolution of coal permeability and gas drainage performance[J].Journal of Natural Gas Science and Engineering,2016,33:469-482.
[20]范超军,李胜,罗明坤,等.基于流-固-热耦合的深部煤层气抽采数值模拟[J].煤炭学报,2016,41(12):3076-3085.FAN Chaojun,LI Sheng,LUO Mingkun,et al. Deep CBM extraction numerical simulation based on hydraulic-mechanical-thermal coupled model[J]. Journal of China Coal Society,2016,41(12):3076-3085.
[21] SHI J Q,DURUCAN S.Exponential growth in San Juan basin Fruitland coalbed permeability with reservoir drawdown:Model match and new insights[J]. SPE Reservoir Evaluation and Engineering,2010,13(6):914-925.
[2]谢和平,周宏伟,薛东杰,等.我国煤与瓦斯共采:理论、技术与工程[J].煤炭学报,2014,39(8):1391-1397.XIE Heping,ZHOU Hongwei,XUE Dongjie,et al.Theory,technology and engineering of simultaneous exploitation of coal and gas in China[J].Journal of China Coal Society,2014,39(8):1391-1397.
[3]谢和平,高峰,周宏伟,等.煤与瓦斯共采中煤层增透率理论与模型研究[J].煤炭学报,2013,38(7):1101-1108.XIE Heping,GAO Feng,ZHOU Hongwei,et al. On theoretical and modeling approach to mining-enhanced permeability for simultaneous exploitation of coal and gas[J].Journal of China Coal Society,2013,38(7):1101-1108.
[4]薛东杰,周宏伟,孔琳,等.采动条件下被保护层瓦斯卸压增透机理研究[J].岩土工程学报,2012,34(10):1910-1916.XUE Dongjie,ZHOU Hongwei,KONG Lin,et al. Mechanism of unloading-induced permeability increment of protected coal seam under mining[J]. Chinese Journal of Geotechnical Engineering,2012,34(10):1910-1916.
[5] SEIDLE J P,JEANSONNE M W,ERICKSON D J. Application of matchstick geometry to stress dependent permeability in coals[A].SPE rocky mountain regional meeting[C].Society of Petroleum Engineers,1992:433-444.
[6] PALMER I,MANSOORI J.How permeability depends on stress and pore pressure in coalbeds:A new model[A].SPE Annual Technical Conference and Exhibition[C]. Society of Petroleum Engineers,1998:539-544.
[7] SHI J 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.
[8] CUI Xiaojun,BUSTIN R M.Volumetric strain associated with methane desorption and its impact on coalbed gas production from deep coal seams[J].AAPG Bulletin,2005,89(9):1181-1202.
[9]卢平,朱贵旺.岩样应力应变全程中的渗透性表征与试验研究[J].中国科学技术大学学报,2002,32(6):678-684.LU Ping,ZHU Guiwang. Characterization of and experimental study on the permeability of rock-samples during complete stressstrain course[J].Journal of University of Science and Technology of China,2002,32(6):678-684.
[10]周辉,杨艳霜,刘海涛.岩石强度时效性演化模型[J].岩土力学,2014,35(6):1521-1527.ZHOU Hui,YANG Yanshuang,LIU Haitao. Time-dependent theoretical model of rock strength evolution[J].Rock and Soil Mechanics,2014,35(6):1521-1527.
[11]周宏伟,王春萍,段志强,等.基于分数阶导数的盐岩流变本构模型[J].中国科学:物理学力学天文学,2012,42(3):310-318.ZHOU Hongwei,WANG Chunping,DUAN Zhiqiang,et al. Timebased fractional derivative approach to creep constitutive model of salt rock[J]. Scientia Sinica Physica,Mechanica&Astronomica,2012,42(3):310-318.
[12]尹光志,何兵,王浩,等.深部采动影响下覆岩蠕变损伤破坏规律[J].煤炭学报,2015,40(6):1390-1395.YIN Guangzhi,HE Bing,WANG Hao,et al. Damage law of overlying rock induced by mining[J]. Journal of China Coal Society,2015,40(6):1390-1395.
[13]周长冰,万志军,张源,等.高温三轴应力下气煤蠕变特征及本构模型[J].煤炭学报,2012,37(12):2020-2025.ZHOU Changbing,WAN Zhijun,ZHANG Yuan,et al. Creep characteristics and constitutive model of gas coal mass under high temperature and triaxial stress[J]. Journal of China Coal Society,2012,37(12):2020-2025.
[14]许江,彭守建,陶云奇,等.蠕变对含瓦斯煤渗透率影响的试验分析[J].岩石力学与工程学报,2009,28(11):2273-2279.XU Jiang,PENG Shoujian,TAO Yunqi,et al.Experimental analysis of influence of creep on permeability of gas-bering coal[J].Chinese Journal of Rock Mechanics and Engineering,2009,28(11):2273-2279.
[15]郝富昌,刘彦伟,龙威成,等.蠕变-渗流耦合作用下不同埋深有效抽采半径研究[J].煤炭学报,2017,42(10):2616-2622.HAO Fuchang,LIU Yanwei,LONG Weicheng,et al. Effective gas extraction radius of different burial depths under creep-seepage coupling[J]. Journal of China Coal Society,2017,42(10):2616-2622.
[16] NISHIHARA M. Creep of shale and sandy-shale[J]. The Journal of the Geological Society of Japan,1952,58(683):373-377.
[17] JAEGER J C,COOK N G W,ZIMMERMAN R. Fundamentals of rock mechanics[M].John Wiley&Sons,2009:169-204.
[18] CUI Xiaojun,BUSTIN R M,CHIKATAMARLA LAXMI. Adsorption-induced coal swelling and stress:Implications for methane production and acid gas sequestration into coal seams[J]. Journal of Geophysical Research,2007,112(B10202).
[19] DANESH N N,CHEN Z,AMINOSSADATI S M,et al. Impact of creep on the evolution of coal permeability and gas drainage performance[J].Journal of Natural Gas Science and Engineering,2016,33:469-482.
[20]范超军,李胜,罗明坤,等.基于流-固-热耦合的深部煤层气抽采数值模拟[J].煤炭学报,2016,41(12):3076-3085.FAN Chaojun,LI Sheng,LUO Mingkun,et al. Deep CBM extraction numerical simulation based on hydraulic-mechanical-thermal coupled model[J]. Journal of China Coal Society,2016,41(12):3076-3085.
[21] SHI J Q,DURUCAN S.Exponential growth in San Juan basin Fruitland coalbed permeability with reservoir drawdown:Model match and new insights[J]. SPE Reservoir Evaluation and Engineering,2010,13(6):914-925.