沁水盆地煤储层孔隙分形特征及其对瓦斯吸附的影响

Pore fractal characteristic of coal reservoirs in Qinshui Basin and its influence on methane adsorption property

为研究煤孔隙分形特征及其对瓦斯吸附特性的影响,针对沁水盆地8个煤样开展了低温液氮吸附试验,采用FHH分形理论探讨了煤表面孔隙分形特征,测试了各煤样的瓦斯吸附常数a、b值,并分析了孔隙分形维数对煤体瓦斯吸附的影响。研究结果表明,煤表面孔隙在不同压力段具有不同的分形特征,D1和D2分别代表煤表面微孔、中孔及大孔的分形特征。随变质程度的升高,D1与R0呈现出良好的线性正相关关系,而D2随R0的增加则呈现出先快后慢的抛物线变化。煤体瓦斯吸附特性与煤表面孔隙分形特征密切相关,分形维数D1、D2数值越大,a值越大,煤体瓦斯吸附能力也就越强;分形特征对吸附常数b值的影响较小。

In order to investigate the fractal characteristic of coal pore and its impact on methane adsorption property,low temperature liquid nitrogen gas adsorption experiments were conducted on eight coal samples collected from Qinshui Basin.FHH fractal theory was adopted to explore the pore fractal features of coal surface.The adsorption constants a and b were measured for each coal sample,and the effect of coal pore fractal dimension on methane adsorption was also analyzed.The research results show that different fractal features of coal surface pore were observed at different relative pressure stages.D1 and D2 represent the fractal features of micropore,mesopore and macropore,respectively.As coalification increases,D1 presents a good positively linear relationship with R0,but a parabolic correlation was found between D1 and R0.Methane adsorption is closely related to the pore fractal features of coal surface.The larger values of the fractal dimension D1 and D2,the greater the adsorption constant a,indicating the methane adsorption capacity is stronger.However,the adsorption constant b is less affected by the fractal features.