复合陆缘盆地成盆机制及其控藏作用

Formation mechanisms of composite continental-margin basins and their control of hydrocarbon accumulation： A case study of the Pearl River Mouth Basin， northern South China Sea

徐长贵 高阳东 刘军 彭光荣 李洪博 邱欣卫 丁琳 龙祖烈 郑金云 姜大朋

Changgui XU Yangdong GAO Jun LIU Guangrong PENG Hongbo Li Xinwei Qiu Lin Ding Zulie Long Jinyun Zheng Dapeng Jiang

中国南海被动陆缘的裂谷盆地研究近年来取得了重要进展，但至今仍没有就盆地属性形成统一认识，缺乏对该类盆地的形成机制及其控藏作用的详细解剖。基于连片的三维地震数据、重磁资料以及超过200口钻遇基底的钻井资料，首次提出珠江口盆地为中生代弧-盆体系与新生代洋-陆体系在动力上转换、空间上叠合、时间上接续的复合陆缘盆地，并根据中生代基底岩浆弧的岩性差异，及其内部先存断裂的几何学和运动学特征对新生代盆地影响程度，将中生代岩浆弧划分为后弧-内弧-前弧“三元”结构。复合陆缘盆地属性及其基底弧结构特征对盆地深部油气成藏有明显控制作用，主要表现在：①中生代岩浆弧的内弧带先存逆断层的发育密度和倾角更大，利于新生代盆地“反转深断”形成大型宽且深的断陷湖盆，其最大湖盆面积可达3 590 km，有利于形成大面积分布的优质烃源岩；②复合陆缘盆地基底岩性的东西差异控制了珠江口盆地深层成岩环境的东西差异特征——“东部贫钾、西部富钾”，同时发现富钾流体抑制高岭石沉淀和贫钾流体抑制伊利石转化的协同保渗机制，有效指导了深部储层预测；③复合陆缘盆地深部复杂流体背景下表现为“超临界CO促运、钙砂薄泥交互联封”的油气高效保存富集机制。提出的复合陆缘盆地概念丰富了大陆边缘盆地类型，对在全球类似盆地内开展成盆机制及其深部研究提供重要参考价值。

In recent years， significant advances have been achieved in research on rift basins along the passive continental margin of the South China Sea. However， consensus on the nature of these basins is yet to be reached， and there is a lack of in-depth studies on the formation mechanisms of these basins and their control of hydrocarbon accumulation. Using 3D seismic data， gravity and magnetic data， and drilling data from over 200 wells encountering basement， we examine the Pearl River Mouth Basin （PRMB） along the passive continental margin of the South China Sea. Specifically， we examine the lithological differences of magmatic arcs in the Mesozoic basement of the basin， as well as the geometric and kinematic characteristics of pre-existing faults within the arcs. Accordingly， we propose for the first time that the PRMB represents a composite continental-margin basin characterized by the dynamic transition， spatial superposition， and temporal succession between the Mesozoic arc-basin system and the Cenozoic ocean-continent system. The Mesozoic magmatic arcs in the PRMB are identified as a ternary structure consisting of back-， inner-， and fore-arc zones. The nature of the PRMB as a composite continental-margin basin and the architectural characteristics of the basement magmatic arcs exert significant controlling effects on the deep hydrocarbon accumulation in the basin. Specifically， pre-existing reverse faults in the inner-arc zone of the Mesozoic magmatic arcs feature higher density and larger dip angles， facilitating the formation of inverted and deep-seated faults in the Cenozoic basins. This contributes to the formation of large-scale， wide， deep faulted lacustrine basins， with the largest measuring up to 3 590 km in area， creating favorable conditions for the generation of extensive， high-quality source rocks. The east-west lithological differences in the basement of the PRMB govern the east-west differences in deep diagenetic environment of the basin， that is， potassium-poor and potassium-rich fluids occur in the eastern and western parts of the basin， respectively. The potassium-rich fluids inhibit the kaolinite precipitation， while the potassium-poor fluids restrain the illite transformation， jointly forming the synergetic permeability preservation mechanism. This finding can effectively guide the mapping of deep reservoirs. In the context of complex deep fluid systems， the PRMB shows an efficient hydrocarbon preservation and enrichment mechanism characterized by supercritical CO-faciliated transport and joint sealing by alternating calcareous sandstones and thin-bedded mudstones. The concept of composite continental-margin basins introduced in this study enriches the types of continental-margin basins， providing a significant reference for in-depth research on the formation mechanisms and deep hydrocarbon accumulation of similar basins worldwide.

10.11743/ogg20250303