页岩储层脆性特征及其影响因素探讨

Discussion on Brittleness Characteristics and Influencing Factors of Shale Gas Reservoirs

矿物成分与微观结构是页岩储层力学性质的核心影响因素,利用X射线衍射、扫描电镜、能谱、力学测试及薄片观测等实验技术手段,分析了重庆南川三泉剖面泉浅一井龙马溪组下段页岩储层、五峰组页岩储层样品的物质成分、微观结构与脆性特征。结果表明,页岩主要由脆性矿物与黏土矿物组成;储集空间由孔隙—微裂隙—裂隙3级系统构成;应力应变关系曲线表现出了较强的脆性特征,力学性质评价法与矿物组分法的脆性评价结果存在一定差异;脆性矿物含量高的层段微裂隙发育程度更高。沉积环境与成岩作用共同影响着龙马溪组页岩脆性的变化特征,龙马溪组下部页岩储层自生石英与大颗粒的陆源碎屑石英等一起构成页岩刚性力学结构。页岩力学脆性研究应从评价方法向优质脆性的形成机理深入。

Mineral composition and microstructure are the key factors influencing the mechanical properties of shale reservoirs. Characteristics of material composition,microstructure and brittleness of lower Longmaxi Formation and Wufeng Foemation shale samples from Quanqian1 well and Sanquan profile in Chongqing Nanchuan were analysed by experimental methods including X-ray diffraction,scanning electron microscope,energy spectrum,mechanical test and thin section observation,et al. The results show that the mineral components of the test samples are mainly composed of brittle minerals and clay minerals; the reservoir space is composed of three stages including pores,microfractures and fractures; the stress-strain curves show a strong characteristic of brittleness; there exist a certain difference between the mechanical test method and the mineral component method; the development degree of the microfractures with high brittle mineral content is higher. Based on the test results of mechanical brittle characteristics,mineral compositions and reservoir space,the relationship between the mineral composition and the microstructure of the shale gas reservoir and the influence mechanism of sedimentary environment and diagenesis on the brittleness of reservoir is discussed. The research of mechanical brittleness should be made from the evaluation method to the formation mechanism.