Development Characteristics of Deep Shale Fractured Veins and Vein Forming Fluid Activities in Luzhou Block
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摘要: 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.Abstract: 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.
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Key words:
- Luzhou block /
- Longmaxi Formation /
- deep shale /
- fractured vein body /
- shale gas /
- preservation condition /
- petroleum geology
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图 2 研究区龙马溪组页岩裂缝脉体特征
Fig. 2. The characteristics of shale fractures in the Longmaxi Formation in the study area
图 3 裂缝脉体镜下光学和阴极发光特征
X1为普通光学特征；X2为阴极发光特征. a.石英颗粒间的孔洞可见细碎白云石颗粒；b.树枝状白云石，且白云石脉中见石英颗粒；c.石英细脉刺穿方解石脉体；d.方解石脉体与石英脉体直接接触；e.白云石脉体发育于石英脉体与围岩间；f.粗宽白云石脉体
Fig. 3. Optical and cathodoluminescence characteristics of the fracture veins
图 4 深层页岩裂缝脉体中流体包裹体产状和形态特征
a~c.龙马溪组，4 080.60 m，石英中气态烃及其伴生盐水包裹体（a、b发育于石英愈合缝中，c发育于石英颗粒中）；d~e.龙马溪组，3 861.00 m，方解石中气态烃及其伴生盐水包裹体；g~i.龙马溪组，3 860.76 m，白云石中气态烃及其伴生盐水包裹体
Fig. 4. Occurrence and morphological characteristics of fluid inclusions in deep shale fracture veins
图 5 石英脉体内甲烷包裹体和盐水包裹体的激光拉曼光谱图
a.甲烷包裹体的激光拉曼图，表现出明显甲烷拉曼散射特征峰；b.盐水包裹体的激光拉曼图，液相部分可见H2O的拉曼散射特征峰，气相部分可见到强度很高的CH4和强度较弱的CO2的拉曼散射特征峰
Fig. 5. Laser Raman spectra of methane and brine inclusions in quartz veins
图 6 裂缝脉体中3种矿物颗粒中盐水包裹体均一温度分布直方图
Fig. 6. Histogram of homogenization temperature distribution of saline inclusions in quartz, dolomite and calcite in the fracture veins
图 7 石英脉中包裹体均一温度‒盐度交汇图
Fig. 7. Plot of inclusion homogenization temperature and salinity in quartz veins
图 8 裂缝脉体氧化还原环境判别参数分布特征
Fig. 8. Distribution characteristics of discriminant parameters in redox environment of fractured veins
图 9 泸州区块埋藏史、热演化史以及均一温度投点图
Fig. 9. Burial, thermal evolution history and homogenization temperature projection of Luzhou block
表 1 样品信息表
Table 1. The sampling location
井号 样品编号 采样层位 深度(m) 主要脉体类型 脉体产状 Y-101 A 龙马溪组 4 080.60 石英脉 高角度 B 龙马溪组 3 861.00 石英脉、石英和方解石复合脉 高角度 C 龙马溪组 3 860.76 石英脉、石英和白云石复合脉 高角度 
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表 2 石英脉体中气液两相盐水包裹体均一温度、盐水包裹体冰点值及盐度统计
Table 2. Statistics of homogenization temperature, freezing point value and salinity of gas-liquid saline inclusions in quartz veins
测试包裹体号 均一温度（℃） 冰点温度（℃） 盐度（%） 赋存矿物 3-1 133.3 ‒5.91 9.1 石英 2-1 141.5 ‒7.32 10.9 石英 2-2 149.2 ‒6.44 9.8 石英 1-1 182.6 ‒12.2 16.2 石英 1-2 188.5 ‒11.4 15.4 石英 1-3 185.4 ‒11.8 15.8 石英 1-4 178.5 ‒12.7 16.7 石英 1-5 234.7 ‒6.8 10.3 石英愈合缝 1-6 237.4 ‒6.5 9.9 石英愈合缝 1-7 220.6 ‒7.5 11.1 石英愈合缝 1-8 235.7 ‒6.3 9.6 石英愈合缝 1-9 238.4 ‒6.1 9.4 石英愈合缝 1-10 223.5 ‒7.2 10.8 石英
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表 3 裂缝脉体微量元素特征参数表(10-6）
Table 3. Characteristic parameters of trace elements in fracture veins (10-6)
测试点位 V/Cr Ni/Co U/Th V/(V+Ni) 氧化还原环境 矿物 捕获流体包裹体的温度 C2-1-4 / 6.524 / 0.501 弱氧化-还原 方解石 较低温度区间 C2-1-6 4.328 11 8.923 1.264 47 0.636 还原 方解石 较低温度区间 C2-1-7 4.708 86 9.943 1.550 5 0.725 还原 方解石 较低温度区间 C3-1-4 4.588 2 8.433 1.190 6 0.704 还原 白云石 中温度区间 C3-1-5 2.216 27 6.269 1.168 48 0.56 弱氧化-还原 方解石 较低温度区间 C3-1-7 3.926 23 7.583 1.389 15 0.605 还原 白云石 中温度区间 C3-2-2 6.007 83 7.176 1.757 75 0.777 还原 方解石 较低温度区间 C3-2-3 7.149 45 8.823 1.323 81 0.616 还原 白云石 中温度区间 C3-2-4 4.482 49 8.108 1.290 14 0.576 还原 白云石 中温度区间 C3-2-5 3.748 66 6.695 0.762 35 0.477 弱氧化-还原 方解石 较低温度区间 C3-2-6 4.523 05 8.271 1.400 31 0.701 还原 白云石 中温度区间 C3-2-7 4.403 73 7.018 1.306 93 0.617 还原 白云石 中温度区间
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