| 黄陵背斜南翼牛蹄塘组二段页岩岩心裂缝脉体成岩环境演化与页岩气保存 |
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| 引用本文： | 刘力,何生,翟刚毅,陈科,刘早学,王亿,韩元佳,董田.黄陵背斜南翼牛蹄塘组二段页岩岩心裂缝脉体成岩环境演化与页岩气保存[J].地球科学,2019,44(11):3583-3597. |
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| 作者姓名： | 刘力 何生 翟刚毅 陈科 刘早学 王亿 韩元佳 董田 |
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| 作者单位： | 1.中国地质大学构造与油气资源教育部重点实验室, 湖北武汉 430074 |
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| 基金项目： | 国家自然科学基金面上项目41672139国家"十三五"科技重大专项2016ZX05034-002-003国家基础地质调查项目DD20160185 |
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| 摘 要： | 岩心观察鄂西黄陵背斜南翼下寒武统牛蹄塘组二段黑色页岩中发育构造挤压成因的高角度裂缝和顺层裂缝.选取不同产状的典型裂缝脉体样品，薄片镜下观察发现高角度裂缝中充填方解石脉，顺层裂缝中充填方解石-白云石复合脉.通过阴极发光、流体包裹体分析以及微区原位元素测定，开展了裂缝脉体成岩环境演化研究，分析了不同产状裂缝对页岩气层局部封闭性的影响.阴极发光结果表明，高角度方解石脉和顺层方解石-白云石复合脉均为2期流体活动形成.根据流体包裹体分析，高角度方解石脉早期成脉流体主要为变质较深的地层卤水，晚期成脉流体混入了低矿化度流体，而顺层方解石-白云石复合脉2期成脉流体均未受低矿化度流体的改造.利用不同阴极发光的裂缝脉体碳酸盐矿物的微区原位微量元素测定结果，对铁锰含量、稀土元素（REE）和氧化还原判别参数分析显示，高角度方解石脉成岩环境经历了由还原环境向氧化环境转化，而顺层方解石-白云石复合脉的成岩环境长期保持了较为还原的环境.因此认为，高角度裂缝对页岩气层的局部封闭条件可能产生破坏作用，从而造成页岩气一定程度的散失，而顺层裂缝对局部封闭条件的破坏作用相对有限，裂缝发育特征及其经历的成岩演化过程研究可为页岩气层自封闭和页岩气微观保存条件的评价提供依据.
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| 关 键 词： | 黄陵背斜南翼 牛蹄塘组二段 裂缝脉体 流体包裹体 脉体成岩环境演化 页岩气保存 油气地质 |
| 收稿时间： | 2019-06-17 |
Diagenetic Environment Evolution of Fracture Veins of Shale Core in Second Member of Niutitang Formation in Southern Limb of Huangling Anticline and Its Connection with Shale Gas Preservation |
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| Abstract: | Core observation shows that high-angle and bed-parallel fractures of tectonic compression origin develop in the black shale of the second member of the Lower Cambrian Niutitang Formation in the southern limb of Huangling anticline,West Hubei. Typical fracture veins with different occurrences were selected,calcite vein was filled in high-angle fractures and calcite-dolomite composite vein was filled in bedding fractures under thin section microscopy. Through cathodic luminescence,fluid inclusion analysis and in-situ element determination,the evolutions of diagenetic environment of fractured veins were studied,and the effects of different occurrence fractures on local sealing of shale gas reservoirs were analyzed. The cathodic luminescence observation indicates that the high-angle calcite vein and bed-parallel calcite-dolomite composite vein were both formed by two phases of fluid activity. According to fluid inclusion analysis,the early vein-forming fluids of high-angle calcite vein were mainly deep-metamorphic stratum brine while the late vein-forming fluids were mixed with low-salinity fluids,however the two-stage vein-forming fluids of bed-parallel calcite-dolomite composite vein were not modified by low salinity fluids. The in-situ element determination results of carbonate minerals with different cathodoluminescence characteristics in fracture veins,and analyses of iron and manganese content,rare earth elements(REE) and redox discriminant parameters,show that the diagenetic environment of high-angle calcite vein has undergone a transformation from reductive environment to oxidative environment,while the diagenetic environment of bed-parallel calcite-dolomite composite vein has maintained a relatively reductive environment for a long time. Therefore,it is considered that high-angle fractures may have destructive effect on the local sealing conditions of shale gas reservoirs,resulting in the loss of shale gas to a certain extent. While bed-parallel fractures may have relatively limited destructive effect on the local sealing conditions. The study of fracture development characteristics and diagenetic evolution process can provide basis for the evaluation of self-sealing conditions of shale gas reservoirs and micro-preservation conditions of shale gas. |
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