川东南地区中二叠统茅口组三段白云岩成因机理

杨浩; 潘磊; 全力; 李让彬; 王广伟; 高俊杰; 周玲; 徐芮

doi:10.11781/sysydz202402311

川东南地区中二叠统茅口组三段白云岩成因机理

doi: 10.11781/sysydz202402311

杨浩^1,,
潘磊²,
全力¹,
李让彬²,
王广伟^1, ,,
高俊杰²,
周玲¹,
徐芮¹

1.
中国石油大学(华东)地球科学与技术学院, 山东青岛 266580
2.
中国石化勘探分公司, 成都 610041

基金项目:

泰山学者工程专项经费 tsqn202211073

详细信息

作者简介:
杨浩(1996—)，男，硕士生，从事碳酸盐岩储层研究。E-mail: stormra@hotmail.com

通讯作者:
王广伟(1986—)，男，博士，副教授，从事储层沉积学研究。E-mail: wanggw@upc.edu.cn

中图分类号: TE122.21
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- 被引次数: 0
出版历程
- 收稿日期: 2023-10-24
- 修回日期: 2024-02-08
- 刊出日期: 2024-03-28

Genetic mechanism of dolomite in third member of Maokou Formation in Middle Permian, southeastern Sichuan Basin

1.
School of Geosciences, China University of Petroleum (East China), Qingdao, Shandong 266580, China
2.
SINOPEC Exploration Company, Chengdu, Sichuan 610041, China

摘要

摘要: 白云岩是四川盆地海相层系最为重要的天然气储层类型之一，也是深层碳酸盐岩油气勘探的重点，白云岩成因机理的研究是预测深层优质白云岩储层分布的基础。通过川东南地区茅口组三段白云岩露头、岩心、薄片等资料，结合碳氧同位素、锶同位素、稀土元素等研究了白云岩的成因机理。川东南地区茅三段白云岩可分为层状粉晶白云岩、层状细—中晶白云岩以及鞍形白云石胶结物。层状细—中晶白云岩是最主要的白云岩类型，未受热液影响的该类型白云岩δ¹⁸O_VPDB值为-7.04‰~-6.08‰，与泥晶灰岩相似，⁸⁷Sr/⁸⁶Sr比值为0.707 550~0.707 740，处于同期海水范围值内，主要成因为准同生—埋藏期封闭局限海水渗透回流白云岩化；受到热液影响的该类型白云岩δ¹⁸O_VPDB值为-7.33‰~-7.11‰，与泥晶灰岩相比略微偏负，⁸⁷Sr/⁸⁶Sr比值为0.707 950~0.708 171，高于同期海水。层状粉晶白云岩未明显受到热液影响改造，其成因与上述未受热液影响的层状细—中晶白云岩一致。而溶洞、裂缝中的鞍形白云石胶结物则是热液流体直接沉淀或重结晶所形成，具有较高的⁸⁷Sr/⁸⁶Sr比值(均值0.707 970)、明显偏负的δ¹⁸O_VPDB值(均值-7.32‰)以及Eu的正异常。从层状粉晶白云岩、层状细—中晶白云岩到鞍形白云石胶结物，呈现出一种受控于封闭局限海水到热液流体的梯度性变化，研究区内的白云岩是由多期次流体、多次成岩作用的结果。
- 地球化学特征 /
- 成因机理 /
- 白云岩 /
- 茅口组 /
- 中二叠统 /
- 四川盆地
Abstract: Dolomite formation is a crucial aspect of natural gas reservoirs in the marine strata of the Sichuan Basin, particularly in the exploration of deep carbonate reserved oil and gas resources. Understanding the genetic mechanism of dolomite is essential for predicting the distribution of favorable dolomite reservoirs in deep formations. Taking the third member of the Maokou Formation in the southeastern Sichuan Basin as an example, present work systematically investigates the genetic mechanism of dolomite by analyzing geochemical characteristics such as carbon and oxygen isotopes, strontium isotopes and rare earth elements. The analysis is based on data from outcrops, core samples and thin sections. The results reveal that the dolomites of the third member of the Maokou Formation in the southeastern Sichuan Basin can be categorized into laminated fine-crystalline dolomite, laminated fine to medium-crystalline dolomite, and saddle dolomite cement. Among these, the laminated fine to medium-crystalline dolomite is the most common type. The δ¹⁸O values of this dolomite type (-7.04‰ to -6.08‰) appeared unaffected by hydrothermal fluids, and are similar to those of mud-crystal limestone. Additionally, the ⁸⁷Sr/⁸⁶Sr ratio (0.707 550 to 0.707 740) locate within the range of contemporaneous seawater, indicating a diagenesis process of quasi-syngenetic to burial-induced restricted marine water infiltration dolomitization. The δ¹⁸O values of hydrothermally influenced dolomite range from -7.33‰ to -7.11‰, showing slightly negative compared to those of mud-crystal limestone. These dolomites also showed relatively higher ⁸⁷Sr/⁸⁶Sr ratios (0.707 950 to 0.708 171) than those of contemporaneous seawater. The laminated fine-crystalline dolomite, which was not affected by hydrothermal fluids, shares a common genetic mechanism with the previously mentioned laminated fine to medium-crystalline dolomite. Saddle dolomite cement found in caves and fractures is either directly precipitated or recrystallized from hydrothermal fluids. This type of dolomite is characterized by higher ⁸⁷Sr/⁸⁶Sr ratios (with a mean value of 0.707 970), significantly negative δ¹⁸O values (with a mean value of -7.32‰), and positive Eu anomalies. A gradient change from laminated fine-crystalline dolomite to laminated fine to medium-crystalline dolomite and finally to saddle dolomite cement is observed, controlled by a transition from marine water to hydrothermal fluids. The dolomite in the study area is proposed to be the product of multi-stage fluid-induced diagenesis.
- geochemical characteristics /
- genetic mechanism /
- dolomite /
- Maokou Formation /
- Middle Permian /
- Sichuan Basin
注释:

利益冲突声明/Conflict of Interests

所有作者声明不存在利益冲突。

All authors disclose no relevant conflict of interests.

作者贡献/Authors’Contributions

杨浩、全力、李让彬参与实验设计；杨浩、徐芮、高俊杰完成实验操作；杨浩、王广伟、周玲、潘磊参与论文写作和修改。所有作者均阅读并同意最终稿件的提交。

The experiment was designed by YANG Hao, QUAN Li and LI Rangbin. The experimental operation was completed by YANG Hao, XU Rui and GAO Junjie. The manuscript was drafted and revised by YANG Hao, WANG Guangwei, ZHOU Ling and PAN Lei. All the authors have read the last version of paper and consented for submission.

HTML全文

图 1 川东南地区中二叠统茅口组三段沉积相与岩性柱状图

Figure 1. Sedimentary facies and lithological column of third member of Maokou Formation in Middle Permian, southeastern Sichuan Basin

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图 2 川东南地区中二叠统茅口组三段白云岩分布对比

Figure 2. Distribution comparison of dolomite in third member of Maokou Formation in Middle Permian, southeastern Sichuan Basin

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图 3 川东南地区中二叠统茅口组三段白云岩宏观特征

a.深灰色泥晶灰岩与灰色粉晶白云岩成层状沉积，分界明显，泰来601井，茅三段；b.层状白云岩，可见明显残余生物碎屑，同时发育硅质条带、方解石条带，放牛坝剖面，茅三段；c.层状白云岩，见斑马状构造，裂缝和溶洞中发育鞍形白云石、方解石和石英胶结物，放牛坝剖面，茅三段；d.层状细—中晶白云岩，偶见生物碎屑残留，泰来6井，茅三段；e.层状细—中晶白云岩，可见大量残余生物碎屑，黄线内部为鞍形白云石胶结物，红线到黄线内部为受热液影响的白云岩，其余部分为未受热液影响的白云岩，泰来7井，茅三段；f.细—中晶白云岩，裂缝、溶洞中充填大量鞍形白云石，泰来7井，茅三段。

Figure 3. Macroscopic characteristics of dolomite from third member of Maokou Formation in Middle Permian, southeastern Sichuan Basin

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图 4 川东南地区中二叠统茅口组三段白云岩微观特征

a.粉晶白云岩，孔隙几乎不发育，偶见残余生物碎屑，泰来601井，茅三段；b.粉晶白云岩，泰来601井，茅三段；c.b所对应的阴极发光照片，白云石发暗红色光，泥质不发光；d.细—中晶白云岩，部分晶体表明污浊，呈自形—半自形晶，可见颗粒幻影，泰来6井，茅三段；e.细—中晶白云岩，晶体呈自形，可见颗粒幻影，放牛坝剖面，茅三段；f.e所对应的阴极发光照片，白云石晶体呈现出两种发光的特点；g.细—中晶白云岩，晶间孔发育，原始结构保存较好，放牛坝剖面，茅三段；h.左侧为溶洞内充填鞍形白云石胶结物，晶体呈粗晶状，右侧为受热液影响的细晶白云岩，泰来6井，茅三段；i.h所对应的阴极发光照片，鞍形白云石发亮红色光，右侧细晶白云岩受热液影响重结晶后也发亮红色光。

Figure 4. Microscopic characteristics of dolomite from third member of Maokou Formation in Middle Permian, southeastern Sichuan Basin

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图 5 川东南地区中二叠统茅口组三段碳酸盐岩碳氧同位素特征

Figure 5. Characteristics of δ¹³C_VPDB and δ¹⁸O_VPDB of carbonate samples from third member of Maokou Formation in Middle Permian, southeastern Sichuan Basin

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图 6 川东南地区中二叠统茅口组三段碳酸盐岩⁸⁷Sr/⁸⁶Sr特征

Figure 6. Characteristics of ⁸⁷Sr/⁸⁶Sr of carbonate samples from third member of Maokou Formation in Middle Permian, southeastern Sichuan Basin

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图 7 川东南地区中二叠统茅口组三段碳酸盐岩稀土元素配分模式

Figure 7. REE characteristics of carbonate samples from third member of Maokou Formation in Middle Permian, southeastern Sichuan Basin

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图 8 川东南地区中二叠统茅口组三段白云岩成岩模式

Figure 8. Diagenetic model of dolomite in third member of Maokou Formation in Middle Permian, southeastern Sichuan Basin

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