石油与天然气地质 ›› 2023, Vol. 44 ›› Issue (5): 1256-1269.doi: 10.11743/ogg20230514

• 油气地质 • 上一篇    

东海陆架盆地西湖凹陷中央反转构造带古近系花港组气藏“先汇后聚”机制及地质意义

张迎朝(), 邹玮, 陈忠云, 蒋一鸣, 刁慧()   

  1. 中海石油(中国)有限公司 上海分公司,上海 200335
  • 收稿日期:2023-02-01 修回日期:2023-05-31 出版日期:2023-10-01 发布日期:2023-10-19
  • 通讯作者: 刁慧 E-mail:zhangyingzh@cnooc.com.cn;diaohui@cnooc.com.cn
  • 第一作者简介:张迎朝(1971—),男,教授级高级工程师,海洋油气勘探。E?mail: zhangyingzh@cnooc.com.cn
  • 基金项目:
    中海油“十四五”重大科技项目(KJGG2022-0301);“十四五”全国油气资源评价项目(QGYQZYPJ2022-3)

The mechanism of “convergence ahead of accumulation” and its geological significance for gas reservoirs in Paleogene Huagang Formation across the central inverted structural zone of Xihu Depression, East China Sea Shelf Basin

Yingzhao ZHANG(), Wei ZOU, Zhongyun CHEN, Yiming JIANG, Hui DIAO()   

  1. Shanghai Branch,CNOOC,Shanghai 200335,China
  • Received:2023-02-01 Revised:2023-05-31 Online:2023-10-01 Published:2023-10-19
  • Contact: Hui DIAO E-mail:zhangyingzh@cnooc.com.cn;diaohui@cnooc.com.cn

摘要:

反转构造带作为圈闭发育的优势构造带在国内外诸多盆地已揭示了丰富的油气资源,但对于海上盆地来说,由于钻井成本较高、钻井较少,对反转构造带油气成藏规律的研究相对薄弱。以西湖凹陷中央反转构造带为例,重点关注烃源岩层系内部的原始汇烃能力及从源到储的动态油气富集过程,以期揭示反转构造带油气富集规律。通过构造演化史-生烃演化史-储层演化史-油气充注史匹配关系分析认为,西湖凹陷中央反转构造带北部地区烃源岩大量生烃期和油气充注时间早于圈闭形成时间,早期天然气在源内层系先形成聚集气或丰度较高的“半聚集”气,即“先汇”;晚期构造运动伴随圈闭形成使得早期气向上运移至圈闭中聚集成藏,即“后聚”,成藏后表现为天然气成熟度由深向浅呈增大的趋势。因此提出“先汇后聚”成藏新机制,该机制不仅阐释了源上古近系花港组主力勘探层系生烃期-圈闭形成期-油气充注期时间不匹配的问题,而且揭示了源内古构造背景对源上现今油气成藏富集的控制作用。在该模式指导下指出了中央构造带大型圈闭天然气成藏的关键因素,并提出B构造具备良好的“先汇后聚”条件。“先汇后聚”成藏模式具有一定普遍性,不仅对西湖凹陷中央反转构造带油气勘探具有指导作用,对有类似地质条件的含油气盆地油气勘探亦具有重要借鉴意义。

关键词: 先汇后聚, 成藏机制, 动态成藏过程, 天然气藏, 花港组, 西湖凹陷, 东海陆架盆地

Abstract:

Inverted structural zones in many onshore basins around the world are frequently found to be home to oil and gas traps and have been the targets for studies for years. However, offshore inverted structural zones, in the contrary, are seldom explored because of less drilling due to high cost. Taking the central inverted structural zone of Xihu Depression as an example, this paper focuses on the original capacity of hydrocarbon convergence in the source rock series and the dynamic accumulation of hydrocarbons from source to reservoir, with the aim of revealing the hydrocarbon enrichment law. The correlation of structural evolution, hydrocarbon generation and reservoir evolution as well as hydrocarbon charging history reveals that the massive hydrocarbon generation and charging of source rocks preceded the formation of traps in the northern part of the zone. The early-generated gas formed “semi accumulation” with high abundance within the series, i.e., “convergence first”; and then migrated upwards and accumulated in traps formed later during tectonic movements, i.e., “later accumulation”. The reservoirs show a trend of increasing natural gas maturity from deep to shallow. Based on these results, the paper proposes the new model of “convergence ahead of accumulation”, which not only reasonably explains the mismatch of timing among the hydrocarbon generation, trap formation and hydrocarbon charging in the Huagang Formation in the series, but also reveals the control effect of ancient tectonic background on the current accumulation of oil and gas. Under the guidance of this model, the key factors for the formation of large-scale natural gas reservoirs in the zone are revealed, and the B structure in the zone is pinpointed to be a perfect place for “convergence ahead of accumulation”. The new model can be applied to other offshore petroliferous basins with similar geological conditions.

Key words: convergence ahead of accumulation, accumulation mechanism, dynamic accumulation process, gas reservoirs, Huagang Formation, Xihu Depression, East China Sea Shelf Basin

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