泸州区块深层页岩裂缝脉体发育特征及成脉流体活动

Development Characteristics of Deep Shale Fractured Veins and Vein Forming Fluid Activities in Luzhou Block

裂缝脉体中蕴藏着天然裂缝演化与古流体充注活动等重要信息,对于深层页岩气保存条件也有指示意义.针对泸州区块龙马溪组深层页岩裂缝脉体,综合运用光学薄片、阴极发光、流体包裹体及微区原位等分析手段,分析了裂缝脉体的发育特征,研究了成脉流体活动及其成岩环境演化,探讨了页岩气保存条件.研究发现,深层页岩裂缝脉体主要为石英与白云石或方解石组成的复合脉体,不同矿物之间表现出较复杂的切割关系,盐水包裹体与高密度甲烷包裹体大量发育,且裂缝脉体主要形成于还原性环境.整体看来,构造抬升背景下,深层页岩裂缝开始形成且处于不断开启或闭合过程,3期不同性质的古流体多次充注胶结,较封闭的成岩体系对深层页岩气的保存有利.

Fracture veins contain important information such as natural fracture evolution and paleo-fluid injection activities, which is also indicative of the preservation conditions of deep shale gas. In this paper, the development characteristics of fractures and veins in the deep shale of Longmaxi Formation in Luzhou block were analyzed by means of optical thin section, cathode luminescence, fluid inclusion and in-situ microanalysis, and the activity of vein-forming fluid and its diagenetic environment evolution were studied, and the preservation conditions of shale gas were discussed. It is found that the deep shale fracture vein is mainly a composite vein composed of quartz, dolomite or calcite, showing a complex cutting relationship between different minerals, a large number of brine inclusions and high-density methane inclusions are developed, and the fracture vein is mainly formed in a reducing environment. On the whole, under the background of tectonic uplift, the deep shale fractures began to form and were in the process of continuous opening or closing. The three stages of paleo-fluid with different properties were filled and cemented for many times, and the closed diagenetic system was favorable for the preservation of the deep shale gas.