| 湘西沅麻盆地印支期以来古流体特征及其对寒武系页岩气勘探方向的指示 |
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| 引用本文： | 刘安,蔡全升,陈孝红,李海,苗凤彬,彭中勤.湘西沅麻盆地印支期以来古流体特征及其对寒武系页岩气勘探方向的指示[J].地球科学,2021,46(10):3615-3628. |
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| 作者姓名： | 刘安 蔡全升 陈孝红 李海 苗凤彬 彭中勤 |
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| 作者单位： | 中国地质调查局武汉地质调查中心, 湖北武汉 430205 |
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| 基金项目： | 国家科技重大专项2016ZX05034001-002中国地质调查局基金项目DD20190781中国地质调查局基金项目DD20179516中国地质调查局基金项目DD20190558 |
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| 摘 要： | 因古隆起周缘页岩生烃时间晚、热演化程度低，目前已成为中扬子地区油气勘探的重要领域.雪峰古隆起形成于加里东末期，经历了后期复杂的沉积-构造演化，白垩系覆盖区勘探方向尚未明确.以雪峰古隆起西侧沅麻盆地北部为主要研究对象，通过对不整合于寒武系页岩之上的白垩系底部方解石脉与寒武系页岩方解石脉地球化学和包裹体对比分析，研究了古流体形成环境、来源及其对寒武系生烃演化过程的指示.研究结果表明:（1）白垩系脉体碳氧同位素与围岩具有相似性，REE无明显的Eu异常，与寒武系脉体Eu强正异常对比鲜明，表明白垩系脉体主要来自白垩系，受寒武系页岩的影响弱；（2）白垩系方解石脉采样位置位于构造高位，但是包裹体类型显示以纯水溶液包裹体为主，形成于弱还原-弱氧化的环境，未见沥青和明显的纯甲烷包裹体，表明寒武系大规模生排烃在白垩系沉积之前；（3）以包裹体均一温度和Ro为制约，结合区域地质特征恢复了沅麻盆地寒武系两种类型埋藏史，即沅麻盆地北部草堂凹陷早期深埋藏，白垩纪以来不具二次生烃的条件；辰溪凹陷南部早期浅埋藏，白垩系以来Ro可能由1.2%升至2.5%，二次生烃潜力较大，是下一步勘探的有利区.
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| 关 键 词： | 湘西 沅麻盆地 古隆起 白垩系 寒武系 古流体 二次生烃 页岩气 |
| 收稿时间： | 2020-04-08 |
Paleofluid Characteristics since Indosinian Movement in Yuanma Basin,West Hunan:Significance for Cambrian Shale Gas Exploration |
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| Liu An,Cai Quansheng,Chen Xiaohong,Li Hai,Miao Fengbin,Peng Zhongqin.Paleofluid Characteristics since Indosinian Movement in Yuanma Basin,West Hunan:Significance for Cambrian Shale Gas Exploration[J].Earth Science-Journal of China University of Geosciences,2021,46(10):3615-3628. |
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| Authors: | Liu An Cai Quansheng Chen Xiaohong Li Hai Miao Fengbin Peng Zhongqin |
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| Abstract: | Paleo-uplifts with late hydrocarbon generation and relatively low maturity of source rock have become important targets for petroleum exploration in the Middle Yangtze region. Xuefeng uplift formed in Late Caledonian, covered by Cretaceous strata, has no clear exploration directions because of complex tectono-sedimentary evolution. In this paper, it focuses on the north part of Yuanma basin located in the north margin of Xuefeng paleo-uplift, two types of calcite vein samples were collected from Cambrian shale and Cretaceous rocks near the unconformity between Cambrian and Cretaceous, in order to discuss the paleo-fluid environment, source, and its significance for hydrocarbon-generation evolution, by comprehensive analysis of geochemical data and inclusions. The following results were obtained. (1) Cretaceous veins with similar carbon and oxygen isotope value to surrounding rocks have no noticeable Eu abnormality of REE, different from strong Eu positive anomaly in Cambrian veins, indicating the source of veins was Cretaceous and little influenced by Cambrian shale. (2)Most inclusions in Cretaceous samples collected from structurally high position are aqueous inclusions, formed in weakly oxic to weakly reducing environment, with no bitumen or pure methane inclusions, indicating that the Cretaceous sediment was formed later than the time of large-scale hydrocarbon generation and expulsion of Cambrian shale. (3) Under the restrains of homogeneous temperature of fluid inclusions and Ro, two types burial history of Cambrian shale are proposed in Yuanma basin combined with regional geological characteristics. In Caotang depression, north of Yuanma basin, Cambrian shale has no secondary hydrocarbon generation due to deeply buried in early stage. However, the Chenxi depression in the south part may be a favorable area for shale gas exploration, where the Cambrian shale was shallow buried in early stage, and its Ro elevated form 1.2% to 2.5% in Cretacous buried stage leading to huge hydrocarbon potential. |
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