黔北地区牛蹄塘组页岩矿物组成特征与脆性评价

为研究黔北地区下寒武统牛蹄塘组页岩的矿物组成、成因识别的微观特征，并提出适合本区的页岩脆性评价方法，通过薄片鉴定、扫描电镜-能谱分析、阴极发光、元素扫描分析、X射线衍射矿物定量分析和三轴压缩实验等方法，研究了黔北地区XY1井牛蹄塘组页岩的矿物组成，并基于岩石物理与矿物组成评价页岩的脆性特征。结果表明，牛蹄塘组页岩的矿物主要由石英和黏土矿物组成，还含有少量的长石、碳酸盐矿物和黄铁矿，其体积分数分别为43.5%，30.3%，11.6%，8.3%和6.2%。在分析矿物含量与弹性模量、泊松比关系的基础上，认为牛蹄塘组下段较上段岩石脆性好，脆性矿物组合为石英、黄铁矿和碳酸盐矿物，脆性矿物体积分数为41.7%~82.3%。沉积环境的不同是造成牛蹄塘组上、下段页岩脆性差异的原因。

Mineral compositions and brittleness evaluation of shale of Niutitang Formation in northern Guizhou

In order to study mineral composition characteristics and genesis of the shale of Lower Cambrian Niutitang Formation in northern Guizhou,and propose a new method of shale brittleness evaluation for this area, the mineral compositions of Niutitang Formation shale in XY1 well in northern Guizhou were studied by means of thin section identification,scanning electron microscopy-energy spectrum analysis,cathodoluminescence,element scanning analysis,mineral quantitative X-ray diffraction analysis and triaxial compression test,and brittleness characteristics of shale were evaluated based on petrophysics and mineral composition. The results show that the minerals of Niutitang Formation mainly consist of quartz and clay minerals,and also contain a small amount of feldspar,carbonate minerals and pyrite,with volume fractions of 43.5%,30.3%,11.6%,8.3% and 6.2%,respectively. By analyzing the relationships of mineral content with elastic modulus and Poisson's ratio,it is considered that the lower part of Niutitang Formation is more brittle than the upper part,and the brittle minerals are composed of quartz,pyrite and carbonate minerals,with the volume fraction of brittle minerals of 41.7%-82.3%. The difference of sedimentary environment is one of the reasons for the difference in rock brittleness.