北部湾盆地涠西南凹陷始新统流沙港组三段油源对比与源下成藏机理——以涠洲11区为例

李兴; 吴克强; 李明; 胡德胜; 焦立波

doi:10.11781/sysydz2025051075

北部湾盆地涠西南凹陷始新统流沙港组三段油源对比与源下成藏机理——以涠洲11区为例

doi: 10.11781/sysydz2025051075

中海石油(中国)有限公司湛江分公司南海西部石油研究院, 广东湛江 524057

基金项目:

“十四五”全国油气资源评价项目(QGYQZYPJ2022-3)和中海石油(中国)有限公司前瞻基础研究项目(KJQZ-2024-2003)联合资助。

详细信息

作者简介:
李兴(1986—)，男，硕士，工程师，主要从事油气地球化学与成藏研究。E-mail:lixing4@cnooc.com.cn。

中图分类号: TE122.3
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出版历程
- 收稿日期: 2024-12-26
- 修回日期: 2025-08-03
- 刊出日期: 2025-09-28

Oil and source correlation and sub-source hydrocarbon accumulation mechanisms of the third member of Eocene Liushagang Formation in Weixinan Depression, Beibu Gulf Basin: a case study of Weizhou 11 area

Western South China Sea Petroleum Research Institute, Zhanjiang Branch, CNOOC, Zhanjiang, Guangdong 524057, China

摘要

摘要: 北部湾盆地涠西南凹陷始新统流沙港组三段(简称流三段)勘探程度相对较低，是原油增储上产的重要领域。近年来，该凹陷涠洲11区源下流三段首次获得勘探突破，但油源及成藏机理认识不足制约了该区勘探进展。通过烃源岩与原油地化特征对比，结合成藏期次、成藏动力和运聚通道分析，明确源下成藏特征，构建了涠洲11区流三段成藏模式。涠洲11区流三段原油可划分为两类，第一类原油总体上C₃₀4-甲基甾烷丰度高、规则甾烷C₂₇、C₂₈、C₂₉呈“V”字形分布、全油和饱芳烃碳同位素较重，来源于生油高峰阶段的流二下亚段油页岩；第二类原油具C₃₀4-甲基甾烷丰度低、规则甾烷C₂₇、C₂₈、C₂₉呈“L”字形分布、全油和饱芳烃碳同位素偏轻等特征，为生油高峰—高熟阶段的流二下亚段和流三上亚段源岩共同供烃。流三段储层广泛发育石英颗粒内裂纹、愈合裂纹，其中石英颗粒内裂纹捕获的黄绿色、蓝绿色荧光包裹体对应原油成熟度小于1%，石英愈合裂纹捕获的蓝色荧光石油包裹体对应原油成熟度大于1%，揭示关键成藏期分别为25～16 Ma、16～7.5 Ma、7.5 Ma至今。烃源岩剩余压力与浮力是源下成藏的主要动力，流三段储层早期通过断层错开与主洼中心油页岩对接，浮力驱动成藏；中晚期本地油页岩开始进入生烃高峰，通过剩余压力进行源下充注，优质烃源岩与区域性剩余压力共同控制了涠洲11区原油富集。
- 油源对比 /
- 油页岩 /
- 剩余压力 /
- 源下成藏 /
- 流三段 /
- 涠西南凹陷 /
- 北部湾盆地
Abstract: The third member of the Eocene Liushagang Formation (LF) in the Weixinan Depression, Beibu Gulf Basin, has relatively low exploration levels and is an important area for increasing crude oil reserves and production. In recent years, the first exploration breakthrough was achieved in the sub-source reservoirs in the third member of LF in the Weizhou 11 area, but limited understanding of its oil source and accumulation mechanism has restricted exploration progress in this area. By comparing the geochemical characteristics of source rocks and crude oil, combined with analysis of hydrocarbon accumulation history, driving forces, and accumulation and migration pathways, the sub-source accumulation characteristics were clarified, and the accumulation model for the third member of LF in the Weizhou 11 area of the Weixinan Depression was established. The crude oil in the third member of LF could be classified into two types. Type Ⅰ crude oil generally showed high abundance of C₃₀ 4- methylsteranes, V-shaped distribution of regular steranes C₂₇, C₂₈, C₂₉, and relatively heavy carbon isotopes in both whole oil and saturated aromatic hydrocarbons, originating from oil shales of the lower submember of the second member of LF during the peak oil generation stage. Type Ⅱ crude oil exhibited low abundance of C₃₀ 4-methylsteranes, L-shaped distribution of regular steranes C₂₇, C₂₈, and C₂₉, and lighter carbon isotopes of whole oil and saturated aromatic hydrocarbons, indicating mixed contributions from the lower submember of the second member and upper submember of the third member of LF source rocks during the peak and high maturity stages. Intra-granular fractures and healed fractures were widely developed in quartz grains within LF3 reservoirs. The intra- granular fractures of quartz grains contained yellow-green and blue-green fluorescent inclusions, corresponding to crude oil with maturity less than 1%. The healed fractures of quartz grains contained blue fluorescent inclusions, corresponding to crude oil with maturity greater than 1%. This revealed key hydrocarbon accumulation stages at 25-16 Ma, 16-7.5 Ma, and 7.5 Ma to present. The residual pressure and buoyancy of source rocks were the main driving forces for sub-source hydrocarbon accumulation. In the early stage, LF3 reservoirs connected with oil shales in the central sag through fault displacement, with buoyancy-driven accumulation. In the middle to late stages, local oil shales entered the hydrocarbon generation peak, with sub-source injection occurring under residual pressure. High-quality source rocks and regional residual pressure jointly controlled the enrichment of crude oil in the Weizhou 11 area.
- oil and source correlation /
- oil shale /
- residual pressure /
- sub-source hydrocarbon accumulation /
- third member of Liushagang Formation /
- Weixinan Depression /
- Beibu Gulf Basin

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参考文献(34)

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