北部湾盆地乌石凹陷西洼烃源岩特征与勘探前景  

Source rock characteristics and exploration prospect in western subsag of Wushi Sag in Beibu Gulf Basin

作　　者：胡德胜 满晓 高铭恒 李文龙 余敏 HU Desheng;MAN Xiao;GAO Mingheng;LI Wenlong;YU Min(CNOOC China Limited,Zhanjiang Branch,Zhanjiang,Guangdong 524057,China)

机构地区：[1]中海石油(中国)有限公司湛江分公司,广东湛江524057

出　　处：《中国海上油气》2025年第1期13-25,共13页China Offshore Oil and Gas

基　　金：中国海洋石油有限公司“十四五”重大科技项目“中国近海新区新领域勘探技术—地层岩性油气藏高效识别与精细评价技术(编号:KJGG2022-0303)”部分研究成果。

摘　　要：北部湾盆地乌石凹陷西洼为小型边缘洼陷,因生烃潜力不确定性高,多年来勘探进展缓慢。综合应用三维地震资料和已钻井资料,通过对乌石凹陷西洼构造演化、洼陷结构、沉积充填开展研究,分析了西洼烃源岩发育特征及勘探潜力。结果表明:(1)边界断层六号断层分为NNE、NE、NWW、NW、近EW共5段,差异活动明显,流沙港组二段沉积期,NWW段活动性最强,其下降盘流二段沉积厚度最大,可以达到1 000 m;(2)西洼流二段发育好—优质烃源岩,主生烃灶烃源岩成熟度为1.5%~2.8%,TOC平均含量为2.1%,S1+S2平均为7.2 mg/g,有机质类型为Ⅱ1—Ⅱ2型干酪根,以Ⅱ1型为主,为好—优质烃源岩,且处于大量生烃阶段,资源潜力1.1×10^(8) t,具备良好的资源基础;(3)乌石西洼西侧构造脊为下步最有利勘探方向,流一段、涠三段具备良好储盖组合,并发育地层、断块、半背斜等多类型圈闭,为最有利的成藏组合。油气通过洼中EW断裂垂向运移、大型构造脊优势汇聚、砂体-不整合面侧向输导,在有利目标区成藏,整体潜力大,勘探前景好。该成果为乌石西洼下步勘探指明了方向,对类似的小型边缘洼陷的勘探起到指导作用。The western subsag of Wushi Sag in the Beibu Gulf Basin is a small marginal subsag. The high uncertainty of hydrocarbon generation potential makes exploration progress slow down for many years. By comprehensively applying 3D seismic data and drilled well data, research was conducted on the structural evolution, subsag structure, and sedimentary filling of the western subsag of Wushi Sag, and the development characteristics and exploration potential of source rocks in the western subsag were analyzed. The results showed that: ① Boundary fault No. 6 is divided into five segments: NNE, NE, NWW, NW, and near EW, with obvious differential activity. During the sedimentary period of the second member of the Liushagang Formation, the NWW segment has the strongest activity, and its downthrown side has the largest sedimentary thickness of the second member of the Liushagang Formation, which can reach 1 000 m. ② The second member of the Liushagang Formation in the western subsag develops good and high-quality source rocks, with the source rock maturity of the main hydrocarbon generation zone ranging from 1. 5% to 2. 8%. The average TOC content is 2. 1%, and the average S1+S2 is 7. 2 mg/g. The organic matter type is Ⅱ1–Ⅱ2 kerogen, withⅡ1 kerogen dominating, indicating good and high-quality source rocks in a large hydrocarbon generation stage, with a resource potential of 1. 1 × 10^(8) t and excellent resource reserves. ③ The structural ridge on the west side of the western subsag of Wushi Sag is the most favorable direction for subsequent exploration. The first member of the Liushagang Formation and the third member of the Weizhou Formation have good reservoir-cap rock combinations and develop multiple types of traps such as stratigraphic, fault block, and semi-anticline traps, making them the most favorable reservoir-forming combinations. Oil and gas migrate vertically through the EW faults in the subsag, converge preferentially along major structural ridges, and are transported laterally through sand bodies

关 键 词：北部湾盆地 乌石凹陷西洼 边缘洼陷 成藏模式 烃源岩 

分 类 号：TE122[石油与天然气工程—油气勘探]