两淮煤田煤储层吸附孔孔隙结构及分形特征
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摘要
为了定量表征两淮煤田(淮南和淮北煤田)煤储层吸附孔孔隙结构特征,基于低温氮气吸附实验数据及FHH模型计算了吸附孔分形维数D_1(相对压力0~0.5)和D_2(相对压力0.5~1),讨论了分形维数与孔隙结构、物质组成以及煤变质程度之间的关系。结果表明,研究区煤样低温氮气吸附回线可以划分为3类:Ⅰ类,孔隙以"墨水瓶"或"细瓶颈"形孔为主,煤样具有比表面积大、平均孔径小的特点;Ⅱ类,孔隙多为开放性较好的平行板状孔,煤样比表面积和总孔体积较低;Ⅲ类,孔隙以狭缝形孔为主,煤样总孔体积和平均孔径较大。D_1与比表面积呈较强的正相关关系,代表孔表面积分形维数,D_2和平均孔径、微孔含量分别呈高度的线性正相关和负相关,代表孔结构分形维数,不同吸附脱附曲线类型煤样的分形维数D_1呈现出Ⅰ类>Ⅲ类>Ⅱ类的规律,D_2则呈现出Ⅰ类>Ⅱ类>Ⅲ类的规律,D_1、D_2与水分、灰分均呈正线型相关,与煤的R_(o,max)的关系并不明显。
To quantitatively characterize the coal reservoir adsorptive pore structural features in the Huainan and Huaibei coalfields,based on low temperature nitrogen adsorption experiment and FHH model computed adsorptive pore fractal dimensions D_1( relative pressure 0 ~ 0. 5) and D_2( relative pressure 0. 5 ~ 1); discussed relationship between fractal dimension and pore structure,material composition,as well as degree of coal metamorphism. The result has shown that pores in the study area according to coal sample low temperature nitrogen adsorption loops can be partitioned into 3 types: type Ⅰ pores are mainly "ink bottle"or "narrow neck"shaped pores,coal samples have large specific surface area and small average pore diameter features; type Ⅱ pores have better openness parallel plate-like pores mostly,coal samples have smaller specific surface area and total pore volume; type Ⅲ pores are mainly slit shaped pores,coal samples have larger total pore volume and average pore diameter. Between D_1 and specific surface area presents stronger positive correlation and represents pore surface area fractal dimension; between D_2 and average pore diameter,micropore content presents higher linear positive correlation and negative correlation respectively,represents pore structure fractal dimension. Pore fractal dimension D_1 of coal samples with different adsorption and desorption curve types presents a pattern of type Ⅰ > type Ⅲ > type Ⅱ; while D_2 presents a pattern of type Ⅰ > type Ⅱ > type Ⅲ. Between D_1,D_2 and moisture,ash contents all present linear positive correlation; correlation with coal Ro,maxis not apparent.
To quantitatively characterize the coal reservoir adsorptive pore structural features in the Huainan and Huaibei coalfields,based on low temperature nitrogen adsorption experiment and FHH model computed adsorptive pore fractal dimensions D_1( relative pressure 0 ~ 0. 5) and D_2( relative pressure 0. 5 ~ 1); discussed relationship between fractal dimension and pore structure,material composition,as well as degree of coal metamorphism. The result has shown that pores in the study area according to coal sample low temperature nitrogen adsorption loops can be partitioned into 3 types: type Ⅰ pores are mainly "ink bottle"or "narrow neck"shaped pores,coal samples have large specific surface area and small average pore diameter features; type Ⅱ pores have better openness parallel plate-like pores mostly,coal samples have smaller specific surface area and total pore volume; type Ⅲ pores are mainly slit shaped pores,coal samples have larger total pore volume and average pore diameter. Between D_1 and specific surface area presents stronger positive correlation and represents pore surface area fractal dimension; between D_2 and average pore diameter,micropore content presents higher linear positive correlation and negative correlation respectively,represents pore structure fractal dimension. Pore fractal dimension D_1 of coal samples with different adsorption and desorption curve types presents a pattern of type Ⅰ > type Ⅲ > type Ⅱ; while D_2 presents a pattern of type Ⅰ > type Ⅱ > type Ⅲ. Between D_1,D_2 and moisture,ash contents all present linear positive correlation; correlation with coal Ro,maxis not apparent.
引文
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[20]谢和平.分形-岩石力学导论[M].北京:科学出版社,1996:93-95.
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[23]李增学.煤地质学[M].北京:地质出版社,2009:131-132.
[24]赵兴龙,汤达祯,许浩,等.煤变质作用对煤储层孔隙系统发育的影响[J].煤炭学报,2010,35(9):1506-1511.
[2]王战锋.低渗松软煤层地面煤层气开发试验及评价--以淮北矿区芦岭煤矿为例[J].中国煤炭地质,2013,25(6):20-23.
[3]桑树勋,朱炎铭,张时音,等.煤吸附气体的固气作用机理(I)—煤孔隙结构与固气作用[J].天然气工业,2005,25(1):13-15.
[4]Mendhe V A,Bannerjee M,Varma A K,et al.Fractal and pore dispositions of coal seams with significance to coalbed methane plays of East Bokaro,Jharkhand,India[J].Journal of Natural Gas Science and Engineering,2017,38:412-433.
[5]Yao Yanbin,Liu Dameng,Tang Dazhen,et al.Fractal characterization of adsorption-pores of coals from North China:An investigation on CH4 adsorption capacity of coals[J].International Journal of Coal Geology,2008,73(1):27-42.
[6]高迪,刘建国.沁水盆地东南部高阶煤孔隙分形特征及意义[J].河南理工大学学报(自然科学版),2017,36(2):7-15.
[7]敖卫华.淮南煤田深部煤层煤级与煤体结构特征及煤变质作用[D].中国地质大学(北京),2013.
[8]宋立军,李增学,吴冲龙,等.安徽淮北煤田二叠系沉积环境与聚煤规律分析[J].煤田地质与勘探,2004,32(5):1-3.
[9]兰昌益.淮南煤田二叠纪含煤岩系的沉积环境[J].淮南矿业学院学报,1984(2):13-25.
[10]Brunauer S,Emmett P H,Teller E.Adsorption of gases in multimolecular layers[J].Journal of the American Chemical Society,1938,60(2):309-319.
[11]Barret E P,Joyner L G,Halenda P P.The determination of pore volume and area distribution in porous substances.I.Computations from nitrogen isotherms[J].Journal of American Chemical Society,1951,73(1):373-380.
[12]姚艳斌,刘大锰,黄文辉,等.两淮煤田煤储层孔-裂隙系统与煤层气产出性能研究[J].煤炭学报,2006,31(2):163-168.
[13]B.B霍多特.煤与瓦斯突出[M].宋世钊,王佑安,译.北京:中国工业出版社,1966:27-30.
[14]Sing K S W.Reporting physisorption data for gas/solid systems with special reference to the determination of surface area and porosity(Recommendations 1984)[J].Pure and Applied Chemistry,1985,57(4):603-619.
[15]Mandelbrot B B.Stochastic models for the Earth’s relief,the shape and the fractal dimension of the coastlines,and the number-area rule for islands[J].Proceedings of the National Academy of Sciences,1975,72(10):3825-3828,
[16]Pfeifer P,Wu Y J,Cole M W,et al.Multilayer adsorption on a fractally rough surface[J].Physical Review Letters,1989,62(17):1997-2000.
[17]Pfeifer P,Cole M W,Krim J.Pfeifer,Cole,and Krim reply[J].PhysicalReviewLetters,1990,65(5):663.
[18]Lai Jin,Wang Guiwen.Fractal analysis of tight gas sandstones using high-pressure mercury intrusion techniques[J].Journal of Natural Gas Science and Engineering,2015,24:185-196.
[19]Hou Haihai,Shao Longyi,Li Yonghong,et al.The pore structure and fractal characteristics of shales with low thermal maturity from the Yuqia Coalfield,northern Qaidam Basin,northwestern China[J].Frontiers of Earth Science,2018,12(1):148-159.
[20]谢和平.分形-岩石力学导论[M].北京:科学出版社,1996:93-95.
[21]Pyun S I,Rhee C K.An investigation of fractal characteristics of mesoporous carbon electrodes with various pore structures[J].Electrochimica Acta,2004,49(24):4171-4180.
[22]Mahnke M,Mgel H J.Fractal analysis of physical adsorption on material surfaces[J].Colloids and Surfaces A:Physicochemical and Engineering Aspects,2003,216(1-3):215-228.
[23]李增学.煤地质学[M].北京:地质出版社,2009:131-132.
[24]赵兴龙,汤达祯,许浩,等.煤变质作用对煤储层孔隙系统发育的影响[J].煤炭学报,2010,35(9):1506-1511.