青海聚乎更矿区煤系页岩脆/韧性变形对孔隙结构的影响

Effects of brittle/ductile deformation of coal measure shale on pore structure in Juhugeng Mining Area,Qinghai

煤系页岩的脆/韧性变形对孔隙结构的影响是复杂构造区煤系页岩储层评价的关键因素之一。以青海聚乎更矿区广泛发育的脆/韧性变形页岩为研究对象,挑选出矿物成分相差不大的韧性变形和脆性变形的煤系页岩样品,以扫描电镜、低温液氮实验以及核磁共振为手段,归纳总结了脆/韧性变形的宏观和微观特征,并探讨了其对煤系页岩孔隙结构影响的差异性。结果表明:脆性变形主要使得煤系页岩出现大量的张性或剪性裂隙,并切割了原生孔隙,但并未改变矿物颗粒的排列方式;而韧性变形使得煤系页岩出现大量的揉皱、扭折带、以及不规则翻立等现象,改变了矿物颗粒紧密的排布方式,不仅使得孔容和比表面积增大,也使得原生的孔隙出现受压缩而变形的现象。同时,脆性变形和韧性变形对页岩孔隙类型的影响并未表现出差异性,但韧性变形使得样品的总孔容、比表面积、孔隙度以及有效孔隙度均明显高于脆性变形样品:韧性变形样品总孔容11.970×10^(-3)~13.820×10^(-3) mL/g、比表面积5.779~8.287 m^(2)/g、孔隙度4.39%~7.34%、有效孔隙度1.34%~2.52%;脆性变形样品总孔容5.546×10^(-3)~7.720×10^(-3) mL/g、比表面积4.343~4.545 m^(2)/g、孔隙度1.24%~2.76%、有效孔隙度0.43%~0.72%,且韧性变形引起的孔容和比表面积增大主要出现在小于100 nm的孔段范围内。此外,随着孔径的增大,韧性变形样品中非连通孔所占比例逐渐降低,而韧性变形样品中非连通孔所占比例变化并不明显,可以推断出韧性变形使得小孔径孔隙的连通性降低,但会使得大孔径孔隙的连通性增加,而脆性变形则是无差别影响不同孔径范围内的孔隙连通性。

The effect of brittle/ductile deformation on coal measure shales is one of the key factors in the evaluation of coal measure shale reservoirs in complex structural areas.This paper takes the brittle/ductile deformation coal measure shales in the Juhugeng Mining Area of Qinghai province as the research objects,and selects the shale samples of ductile deformation and brittle deformation with nearly the same mineral compositions,and based on scanning electron microscopy(SEM),low temperature liquid nitrogen adsorption/desorption,and nuclear magnetic resonance(NMR) experiments,the macroscopic and microscopic characteristics of the brittle/ductile deformation of shales and their influence on the pore structure were summarized.The results show that the brittle deformation mainly causes a large number of tensile or shear fractures in coal measure shales,but does not change the arrangement of the mineral particles;while in the ductile deformation shales,there are a large number of wrinkles,kinking zones,and irregular erection of minerals changing the tight arrangement of mineral particles,which not only increases the pore volume and specific surface area,but also causes the original pores to be compressed and deformed.At the same time,the effects of brittle deformation and ductile deformation on the shale pore types did not show any obvious differences,but the total pore volume,specific surface area,porosity,and the effective porosity of the ductile deformation samples were significantly higher than that of the brittle deformation samples:ductile deformation samples werecharacterized by total pore volume of 11.970×10^(-3)-13.820×10^(-3) ml/g,specific surface area of 5.779-8.287 m^(2)/g,porosity of 4.39%-7.34%,and effective porosity of 1.34%~2.52%,while brittle deformation samples were characterized by total pore volume of 5.546×10^(-3)-7.720×10^(-3) mL/g,specific surface area of 4.343-4.545 m^(2)/g,porosity of 1.24%-2.76%,and effective porosity of 0.43%-0.72%,respectively,and the increase of pore volume and specific surface area caused by ductile deformation mainly occur within the range of pores smaller than 100 nm.In addition,as the pore size increases,the proportion of non-connected pores in ductile deformation samples gradually decreases,while that in brittle deformation samples does not change.So it can be inferred that the ductile deformation reduces the connectivity of pores with smaller diameters,but increases the connectivity of pores with larger diameters,while the brittle deformation affects the pore connectivity in different pore sizes without any difference.