低-中煤级构造煤纳米孔分形模型适用性及分形特征

Applicability of Fractal Models and Nanopores' Fractal Characteristics for Low-Middle Rank Tectonic Deformed Coals

构造煤纳米孔非均质性研究对于揭示煤层气赋存状态和传输特性具有重要意义.选取低-中煤级典型序列构造煤样品,基于高压压汞和低温液氮相结合的方法计算了构造煤基质压缩系数,并分析了Menger、热力学、Sierpinski和FHH分形模型对构造煤的适用性,进一步揭示了孔隙分形特征,糜棱煤的Menger分形曲线呈现三段式分布,而对于原生煤、碎裂煤、片状煤、鳞片煤和揉皱煤而言,Sierpinski模型、Menger模型、热力学模型以及FHH模型分段点分别为100nm、72nm、72 596nm和8nm.Menger模型分形维数大于3且拟合偏差较大,不适合表征构造煤的孔隙非均质性.Sierpinski模型适合于描述构造煤的纳米孔分形特征;FHH模型适合于表征原生煤及构造煤8~100nm的孔隙非均质性.Sierpinski模型微米孔(>100nm)的分形维数(Ds1)随着构造变形的增强先升高,而后降低,在片状煤中达到最高;Sierpinski模型纳米孔(<100nm,Ds2c)和FHH模型<8nm的孔隙的非均质性随构造变形的增强逐渐升高.原生煤和脆性变形煤中,Ds1>Ds2c,表明为微米孔非均质性强于纳米孔;鳞片煤中,Ds1接近于Ds2c;揉皱煤中,Ds1<Ds2c,表明纳米孔的非均质性强于微米孔.

The investigations of nanopore heterogeneity in tectonically deformed coals are of significance for the study of occurrence state and transmission characteristics of coalbed methane（CBM）.The low-middle rank tectonic deformed coals were screened out firstly in this study and then the matrix compressibility and the applicabilities of Menger,thermodynamics,Sierpinski,and FHH of tectonic deformed coals,as well as the fractal characteristics,were analyzed based on high-pressure mercury intrusion and low-pressure gas adsorption.The fractal curves of Menger model for mylonitic coals can be divided into three stages.However,for primary coals,cataclastic coals,schistose coals,scaly coals,and wrinkle coals,the fractal curves of Sierpinski,Menger,thermodynamics,and FHH can be obviously divided into two stages and the piecewise points locates at100 nm,72 nm,72 596 nm,and 8 nm respectively.The fractal dimensions of Menger model are〉3 and have a fitting deviation,so it is not suitable to characterize the pore heterogeneity.The Sierpinski model is suitable to characterize the fractal characteristics of the nanopore of the tectonic deformed coals whereas the FHH model is for the pores of 8-100 nm in primarycoals and various tectonic deformed coals.The fractal dimension（Ds1）of micron pores at Sierpinski fractal curve（〉100 nm）increases firstly and then decreases with the increase of tectonic deformation,reaching the highest values in schistose coals.The heterogeneity of both nanopores at Sierpinski fractal curve（〈100 nm,Ds2 c）and that of pores of 8-100 nm at FHH fractal curve increase with the enhancement of the tectonic deformation.In primary coals and brittle deformed coals,Ds1〉Ds2 c,indicating that the heterogeneity of micron pores are stronger than that of nanopores.In scaly coals,Ds1 is close to Ds2 c.In wrinkle coals,Ds1〈Ds2 c,indicating that the heterogeneity of nanopores is stronger than that of micron pores.