长宁地区富有机质页岩脆性及与裂缝发育关系

页岩的脆性控制着裂缝的形成和演化，对页岩气层的体积改造和页岩气的增产极为关键。以川南长宁地区龙马溪组页岩为例，通过岩石矿物、地球化学和岩石力学等实验对龙一₁亚段的矿物组分、有机地球化学、孔隙-裂缝结构以及力学性质进行测试，分析不同脆性矿物、有机质以及埋深的页岩脆性特征及其与裂缝发育的关系。结果表明，龙一₁亚段脆性最高者为富有机质硅质页岩岩相，石英、长石和黄铁矿等脆性矿物的总含量大于50%，它们能够调节岩石断块的剪切滑移，所积累的能量大于完成岩石整体剪切破坏过程所需的能量；有机质及其在成熟过程中所产生的有机孔隙与微裂缝可促进裂缝的拓展、贯通以及连接，有机碳含量越高，裂缝系统越发育；随着埋深增加，页岩的脆性下降，岩石破裂模式由复杂的劈裂型向单一的剪切型转变；龙一₁¹、龙一₁²小层脆性矿物和有机碳含量最高，脆性指数分别达到了61.31%和60.70%，为压裂甜点层段。

Brittleness Characteristics of Organic-rich Shale and Its Relationship with Fracture Development of Changning Area

The brittleness of shale controls the formation and evolution of fractures, which is crucial to the volume transformation of shale gas reservoir and the production increase of shale gas well. Taking Longmaxi Formation in Changning area of South Sichuan as an example, the mineral composition, organic geochemistry, pore fracture structure and mechanical properties of the lower Long 1 sub section were tested by rock and mineral, geochemical and mechanical experiments. Combined with experimental method of scanning electron microscopy, the relationships between the fracture development and different shale characteristics of brittle minerals, organic matter and buried depth were analyzed. The results show that the organic-rich siliceous shale facie has the highest brittleness in lower Long 1sub section. The total content of brittle minerals such as quartz, feldspar, and pyrite is greater than 50%. They can regulate the shear slip of rock blocks, and the energy accumulated in the rock is greater than the energy required to complete the overall rock failure. The organic matter and the organic pores and microfractures produced in the process of maturity can promote the development, connection and connection of fractures. The higher the organic carbon content, the more developed the fracture system. With increasing burial depth, the brittleness of the shale decreases, and the rock failure mode changes from a complex cleavage type to a single shear type. The 1st and 2nd sublayers of lower Long 1 sub section have the highest content of brittle minerals and organic carbon, with brittleness indices of 61.31% and 60.70%, respectively. They can be selected as sweet spot section with good fracturing performance, and complex fractures can be formed after fracturing.