晋中盆地西南缘石炭-二叠系煤储层孔隙结构及分形特征

Permo-Carboniferous Coal Reservoir Pore Structural and Fractal Features in Jinzhong Basin

以晋中盆地西南缘石炭-二叠系煤储层为研究对象,基于高压压汞试验,分析研究了煤储层的孔隙结构及分形特征,运用Washburn方程和海绵模型计算了大孔(>100nm)分形维数DM,对比讨论了孔隙结构参数与分形维数的关系,以及煤岩工业分析、煤化程度及煤岩显微组分对分形维数的影响。研究结果表明:本区孔径分布在6~10000nm,以“双峰型”为主,墨水瓶状孔发育。孔隙结构以微孔、小孔为主,中孔与大孔次之,其中微孔和小孔对总孔容贡献率最大,吸附孔和渗流孔比表面积贡献率相当,反映本区煤层有利于煤层气的储集、扩散及渗流。本区中变质程度煤储层渗流孔(>100nm)具有分形特征,煤岩总孔容越小、总比表面积越大、分形维数DM越大,即孔隙结构非均质性越强,分形维数DM可以有效反映孔隙结构特征。分形维数DM与Ro,max、水分、镜质组含量呈正相关,与灰分、惰质组含量呈负相关,本区中煤阶烟煤分形维数受煤岩热演化程度影响明显。

Taking the Permo-Carboniferous coal reservoir in the Jinzhong Basin southwestern margin as the subject investigated,on the basis of high-pressure mercury intrusion tested results analytically studied coal reservoir pore structural and fractal features.Through Washburn equation and sponge model have computed macropore(>100nm)fractal dimension DM,comparatively discussed relationship between pore structure parameter and fractal dimension,impacts from coal proximate analyzed result,coalification degree and maceral on fractal dimension.The results have shown that the pore sizes distribution in the area is 6~10,000nm,mainly bimodal,ink bottle shaped pores developed.Pore structure is mainly micropore and minipore,followed by mesopore and macropore;in which,micropore and minipore have largest contribution rate on total pore volume;contribution rate of adsorbable pore and permeable pore on specific surface area is about the same,thus reflected coal seams in the area propitious to CBM accumulation,diffusion and seepage.Permeable pores(>100nm)in the medium metamorphosed coal reservoir in the area have fractal features,the small the coal total pore volume,the large the total specific surface area and fractal dimension DM,that is pore structure anisotropy more stronger;fractal dimension DM can reflect pore structural features effectively.Fractal dimension DM and Ro max,moisture and vitrinite content are positively correlated,while DM and ash content,inertinite content negatively correlated.Fractal dimension of medium ranked bituminous coal in the area has obviously impacted by coal and rock thermal evolution degree.