川东南地区龙马溪组一段页岩天然裂缝基本特征及其对页岩气高产富集的影响研究

Fundamental Characteristics of Natural Fractures in the First Member of the Longmaxi Formation Shale in Southeastern Sichuan Basin and Their Implications for High-Productivity Shale Gas Accumulation

摘要: 川东南地区五峰组–龙马溪组页岩为我国页岩气勘探与开发的重要目标层系，其天然裂缝系统作为关键的储集–渗流结构，在页岩气富集与保存中发挥了不可忽视的地质作用。本文系统整理并归纳了该区典型研究成果，从裂缝类型、分布特征、形成机制出发，探讨其对页岩气高产富集的控制机制。研究认为，研究区裂缝类型复杂，宏观裂缝以构造缝为主，微裂缝以顺层页理缝最为优势；裂缝的几何属性与空间展布具有显著的层位分异和构造分区性。裂缝发育受多因素耦合控制，构造应力与脆性层理控制其形成位置与密度，有机质含量和压力系统影响其演化与封闭性。进一步结合典型区块裂缝演化与富集条件，识别出三类裂缝–页岩气富集模式：适度裂缝–封闭压力维持型、过度裂缝–导通逸散型与微裂缝优势–改造潜力型。相关认识可为川东南及类似地区页岩气“富集–保存–开发”一体化研究提供有力支撑。

Abstract: The Wufeng-Longmaxi Formation shales in the southeastern Sichuan Basin represent one of the key target intervals for shale gas exploration and development in China. As critical reservoir and seepage structures, natural fractures play a significant geological role in gas accumulation and preservation. This paper systematically reviews representative research results from the region, focusing on fracture types, spatial distribution, and genetic mechanisms to explore their control on shale gas enrichment. The study shows that the fracture system is complex, with macroscopic fractures dominated by tectonic fractures and microscopic fractures characterized mainly by bedding-parallel fractures. These fractures exhibit significant stratigraphic and structural heterogeneity in their geometry and spatial patterns. Fracture development is jointly controlled by multiple factors: tectonic stress and brittle lamination determine their occurrence and density, while organic content and overpressure influence their evolution and sealing capacity. Further analysis of fracture evolution and enrichment conditions in typical blocks identified three types of fracture-shale gas enrichment patterns: moderate fractures (maintaining confinement pressure), excessive fractures (conductivity and escape), and microfractures (dominant) (potential for stimulation). These insights provide strong support for integrated research on shale gas enrichment, preservation, and development in southeastern Sichuan and similar regions.