黔西上二叠统龙潭组高煤级煤微观孔隙结构特征及其对含气性的影响

为探讨高煤级煤的微观孔隙结构特征及其对含气性的影响，选取黔西地区黔普地1井龙潭组5件高煤级煤样品，分别采用高压压汞、低温N₂吸附和CO₂吸附对各煤样的纳米级孔隙进行定量表征，基于BJH和DFT方程分别计算孔隙的孔径、孔体积和比表面积，分析煤的微孔（孔径<2 nm）、介孔（孔径2~50 nm）和宏孔（孔径>50 nm）的孔径分布特征，并统计各级孔径对孔体积和比表面积的贡献率。在低温N₂吸附实验的基础上，运用FHH模型分析了高煤级煤孔隙结构分形性质及其控制因素。采用线性拟合的方法，讨论了高煤级煤的持续演化对微孔和介孔的影响，以及各级孔径的比表面积对含气性的控制作用。结果表明：微孔、介孔和宏孔对孔体积的贡献率分别为49.47%、33.22%及17.31%，对比表面积的贡献率依次为85.44%、14.35%及0.21%；高煤级煤的孔隙形态可分为2类：小于3.7 nm的孔主要以一端开口的孔为主，大于3.7 nm的孔则主要为两端开口的孔和细颈瓶孔；孔隙分形维数随着地层压力的增加而增大，且以3.7 nm为界，大孔隙比小孔隙具有更加复杂的空间结构；微孔和介孔随镜质体反射率呈现规律性的变化，微孔的大量形成与煤大分子空间结构演化导致的介孔体积缩小有关；微孔对CH₄吸附量的控制作用远超过介孔和宏孔，小于2 nm的微孔为煤层气的吸附提供了主要的空间。

Microscopic pore structure characteristics and its effect on gas-bearing property of high-rank coal in Upper Permian Longtan Formation in western Guizhou

In order to study the micro-pore structure characteristics of high-rank coal and its influence on gas content， five high-rank coal samples were selected from Longtan Formation of Well Qianpudi 1 in western Guizhou Province. Nano-pore of coal samples were quantitatively characterized by high pressure mercury injection， low temperature N₂ and CO₂ adsorption， respectively. The pore size， pore volume and specific surface area of coal were calculated based on the BJH and DFT equations. The pore size distribution characteristics of micropore （pore size <2 nm）， mesopore （pore size 2-50 nm） and macropore （pore size >50 nm） of coal were analyzed. Then the contribution rate of various pore size to pore volume and specific surface area were calculated. On the basis of N₂ adsorption experiment at low temperature， the fractal properties of pore structure of high-rank coal and its controlling factors were examined by FHH model. The influence of continuous evolution of high rank coal to micropore and mesopore， and the effect of specific surface of different pore sizes on gas content were discussed by linear fitting method. The results show that the contribution rates of micropore， mesoporous and macropore to pore volume are 49.47%， 33.22% and 17.31% respectively， and the contribution rates of specific surface are 85.44%， 14.35% and 0.21% successively. The pore morphology of higher rank coal can be divided into two types： Pore with diameter less than 3.7nm is mainly composed of one end opening， while that with diameter larger than 3.7 nm mainly consists of two ends opening and thin neck bottle. The fractal dimension of pore increases with the increase of formation pressure， and is bounded by 3.7 nm. The spatial structure of macropore is more complex than that of small one. Micropores and mesopores vary regulary with vitrinite reflectance. The formation of large number of micropores is related to the reduction of mesoporous volume due to the evolution of the spatial structure of coal macromolecules. The controlling effect of micropore on CH₄ adsorption is far greater than that of mesoporous and macroporous. Micropore with diameter less than 2 nm provides main adsorption space for coal-bed methane.