中低阶煤孔隙结构特征及其对瓦斯解吸特性影响

Pore structure characteristics of middle and low rank coals and their influence on gas desorption characteristics

煤的孔隙结构是影响瓦斯储存和运移的重要因素。为了进一步研究中低变质程度煤瓦斯解吸特性,选取6组阜康矿区煤样进行压汞试验和瓦斯解吸试验。通过绘制进退汞曲线、统计各孔径段孔隙结构特征以及绘制瓦斯解吸曲线,着重分析了煤的孔隙形态、孔容、孔比表面积和体积分形维数及其对瓦斯解吸量及解吸速率的影响。结果表明:试验煤样均存在不同比例的开放孔,大孔主要以开放孔为主,中孔和小孔主要以半封闭孔为主,微孔主要以封闭孔为主;煤样孔容以微孔和大孔贡献为主,比表面积以微孔贡献为主。通过绘制瓦斯解吸曲线和解吸速率散点图,发现瓦斯解吸量随解吸时间先快速增加后趋于稳定值,进而拟合发现,中低阶煤瓦斯解吸曲线可采用1/Q=m/t^(0.75)+n表示,拟合度在0.995以上,其中参数m为与瓦斯解吸速率相关的参数,参数n为解吸体积常数,系数0.75可能与煤变质程度有关,后期可对不同变质程度的煤样解吸曲线进行分析,解吸速率随解吸时间呈指数式递减。将不同孔径段孔隙结构特征与解吸特性参数拟合发现,在瓦斯解吸初期,大孔中的瓦斯优先被解吸,随着孔径的减小,优先率逐渐降低。中大孔分形维数介于2.8791~2.9915,分形特征明显,解吸初速度与分形维数呈明显正相关关系,n与分形维数关系不明显。

The pore structure of coal is an important factor affecting gas storage and migration.In order to further study the gas desorption characteristics of low and medium metamorphic coals,6 sets of coal samples from the Fukang mining area were selected for mercury intrusion and gas desorption experiment.Mercury intrusion and extrusion curves of coal samples were drawed,the pore structure characteristics of each pore segment were counted,the gas desorption curve was drawed,and the pore morphology,pore volume,pore specific surface area and volume fractal dimension of coal and their influence on the gas desorption capacity and desorption rate were analyzed.The results show that there are different proportions of open pores in coal samples.Macropores are mainly composed of open pores,the middle and small pores are mainly composed of semi-closed pores,and the micropores are mainly composed of closed pores.In addiction,the total pore volume are mainly contributed by micropores and macropores,and micropores contributes the most to the total specific surface area.By drawing the gas desorption curve and the desorption rate scatter diagram,it is found that the gas desorption amount increases rapidly with the desorption time and then tends to a stable value,and then the fitting finds that the gas desorption curve of middle and low rank coal can be expressed by 1/Q=m/t^(0.75)+n,the degree of fitting is above 0.995,where m is a parameter related to the gas desorption rate,n is a parameter related to the desorption volume constant,and the coefficient of 0.75 may be related to the degree of coal metamorphism,and the desorption curves with different degrees of metamorphism can be analyzed in the later stage.And the desorption rate decreases exponentially with the desorption time.Fitting the pore structure characteristics of different pore sizes with the desorption characteristic parameters,it is found that the gas in the macropores is preferentially desorbed in the initial stage of desorption.As the pore size decreases,the priority rate gradually decreases.The fractal dimension of mesopores and macropores is between 2.8791-2.9915,which has obvious fractal characteristics.It is proposed that the initial desorption velocity and fractal dimension show a significant positive correlation.The relationship between n value and fractal dimension is not obvious.