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

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.