渤海湾盆地东濮凹陷洼陷带油气地质新认识与勘探突破

New insights and exploration breakthroughs in hydrocarbon exploration in sub-sag zones of the Dongpu Sag， Bohai Bay Basin

段金宝 徐田武 杨栋栋 姜振学 高永涛 王德波 李路 袁波

Jinbao DUAN Tianwu XU Dongdong YANG Zhenxue JIANG Yongtao GAO Debo WANG Lu LI Bo YUAN

洼陷带作为油气勘探的重点领域，在渤海湾盆地东濮凹陷40余年的勘探历程中，其勘探面积占东濮凹陷的49 %，但探明石油地质储量仅占东濮凹陷的1 %，呈现出“剩余资源大、探明储量少、有油流无高产、有发现难展开”的勘探困境。近年来，通过持续加强油气富集规律研究，综合利用岩心、测井和分析化验资料，对东濮凹陷不同洼陷开展了烃源岩、源-储配置关系和成藏序列系统研究。研究表明：① 厚度相对薄、有机质丰度相对高（总有机碳含量 1 %）的高效源岩是洼陷带的主要生油岩，打破了洼陷带普遍发育烃源岩的传统认识。② 湖平面高频振荡，形成独特的砂、泥互层“千层饼”式沉积韵律，高效源岩与砂体叠置，近洼储层连片分布，打破了洼陷带泥岩发育而储层不发育的传统认识。③ 烃类充注和流体超压作为近洼成储的主控因素，极大地拓展了有效储层深度下限，打破了3 500 m埋深是传统陆相碎屑岩“死亡界限”储层深度的固有认识。④ 洼陷带油气藏具有“接续成藏”的特点，打破了“水层之下无油气藏”的传统认识。基于上述创新认识，取得了“百方油流、千米含油层段、亿吨资源量”的重大突破，实现了东濮凹陷勘探由构造带向洼陷带的战略转移，落实了规模增储阵地，对渤海湾盆地洼陷带勘探具有重要指导意义。

Over more than four decades of hydrocarbon exploration in the Dongpu Sag within the Bohai Bay Basin， the sub-sag zones， critical targets for hydrocarbon exploration， have accounted for 49 % of the total exploration area. However， their proven geological reserves constitute only 1 % of the total， highlighting an exploration dilemma characterized by abundant residual hydrocarbon resources， low proven geological reserves， limited oil production despite tested oil flow， and difficulties in expanding the development of discovered hydrocarbon resources. Based on the increasingly intensive investigation of hydrocarbon enrichment patterns in recent years， we systematically explore the source rocks， source rock-reservoir configurations， and hydrocarbon accumulation sequences in different types of sub-sags within the Dongpu Sag while integrating various data from core observation， logging， analyses， and laboratory tests. The results indicate that： ① effective source rocks with relatively small thicknesses and high organic matter abundance （ content > 1 %） serve as the major source rocks in the sub-sag zones. This finding challenges the traditional understanding that source rocks are widely developed in sub-sags， facilitating the delineation of exploration targets； ② High-frequency lake-level fluctuations have resulted in a unique sedimentary rhythm of alternating sandstone and mudstone layers. The vertical superimposition of effective source rocks and sand bodies， along with the contiguous distribution of reservoirs near sub-sags， overturns the traditional view that sub-sags contain well-developed mudstones while lacking well-developed reservoirs； ③ Hydrocarbon charging and fluid overpressure are identified as the dominant factors governing the formation of reservoirs near sub-sags， significantly extending the lower depth limit of effective reservoirs. This challenges the long-standing perception that the so-called “death boundary” for the formation of effective reservoirs in continental clastic rocks is 3 500 m； ④ Additionally， hydrocarbon reservoirs in the sub-sag zones feature sequential hydrocarbon accumulation， contradicting the traditional belief that no hydrocarbon reservoirs occur below aquifers. Based on these insights， exploration breakthroughs have been achieved， including high-yield hydrocarbon flow exceeding 100 m oil-gas valent weight on a daily basis in the Gegangji Sub-sag， kilometer-thick oil-bearing intervals in the southwestern sub-sag zone， and the shale/tight oil resources at the hundred-million-ton level in the Qianliyuan Sub-sag. These achievements have driven the strategic shift in hydrocarbon exploration from tectonic zones to sub-sag zones in the Dongpu Sag， facilitating the delineation of exploration targets for large-scale reserve growth. The results of this study provide valuable guidance for hydrocarbon exploration in sub-sag zones within the Bohai Bay Basin.

10.11743/ogg20250204