北部湾盆地涠西南凹陷始新统流一段湖底扇发育特征及成藏模式  

Development characteristics and accumulation model of sublacustrine fans of the first member of Eocene Liushagang Formation inWeixinan Sag,Beibuwan Basin

作　　者：满晓 胡德胜 吴洁 宫立园 柳智萱 姜应德 赵晔 MAN Xiao;HU Desheng;WU Jie;GONG Liyuan;LIU Zhixuan;JIANG Yingde;ZHAO Ye(Zhanjiang Branch of CNOOC Ltd.,Zhanjiang 524057,Guangdong,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：《岩性油气藏》2023年第4期137-144,共8页Lithologic Reservoirs

基　　金：中海石油(中国)有限公司重大科技项目“南海西部油田上产2000万方关键技术研究”(编号:CNOOC-KJ135ZDXM38ZJ)资助。

摘　　要：根据三维地震、录井、测井、岩心观察等资料,对北部湾盆地涠西南凹陷始新统流沙港组一段湖底扇沉积特征和主控因素进行了研究,并对该区岩性圈闭发育模式及油气成藏模式进行了刻画。研究结果表明:(1)涠西南凹陷A洼在流一段低位域和湖侵域发育湖底扇沉积体,其中,低位域湖底扇发育于一号断层附近,地震上表现为连续强反射特征;湖侵域湖底扇分布于洼中,地震上具有明显的丘状反射特征。(2)受物源供给和古地貌两大因素的控制,A洼流一段发育2期湖底扇沉积。低位域短轴方向物源供给少,一号断层下降盘为洼陷的堆积中心,发育小规模直接入湖的近岸水下扇体,并形成向物源区方向上倾尖灭的岩性圈闭;湖侵域物源供给逐渐增大,一号断层活动性减弱,A洼堆积中心逐渐迁移至洼中,扇三角洲前缘松散沉积物发生二次搬运,在洼中形成湖底扇,并形成向南斜坡翘倾尖灭的岩性圈闭和被二号断层遮挡形成的构造-岩性复合圈闭。(3)垂向运移条件是研究区岩性油藏成藏的关键要素,A洼烃源层上部发育受早期断层和晚期构造差异沉降两方面因素控制的微裂缝,为油气突破泥岩盖层垂向运移至“源上”岩性圈闭内并聚集成藏提供了良好的运移通道。该区具有“超压驱动、微裂缝运移、低势区汇聚”的成藏模式。Based on the data of 3D seismic,mud-logging,wire-logging and core observation,the sedimentary characteristics and main controlling factors of the sublacustrine fan of the first member of Eocene Liushagang Formation in Weixinan Sag of Beibuwan Basin were studied,and the lithologic trap development model and hydrocarbon accumulation model were determined.The results show that:(1)The sublacustrine fans are developed in lowstand systems tract(LST)and transgressive systems tract(TST)of the first member of Liushagang Formation in subsag A of Weixinan Sag.The sublacustrine fans in LST are developed near the No.1 fault,which is characterized by continuous and strong seismic reflection,while the sublacustrine fans in TST are distributed in the sag,and have obvious mound reflection.(2)Controlled by two major factors of source supply and paleogeomorphology,the first member of Liushagang Formation in subsag A developed two stages of sublacustrine fans.During the period of LST,there was little source supply in short axis direction,the footwall of No.1 fault was the accumulation center of the sag,small scale nearshore submarine fans that directly enter the lake were developed,and lithologic traps that dip upward and pinch out toward the source area were formed.During the period of TST,the source supply gradually increased,the activity of No.1 fault weakened,and the accumulation center of subsag A gradually migrated to the sag.The loose sediments in the fan delta front transported again into the middle of the sag and developed sublacustrine fans.Lithologic traps that dip and pinch out toward the south slope,and structurallithologic traps shielded by No.2 fault were formed.(3)Vertical migration conditions are the key factors for lithologic reservoir accumulation in the study area.Microfractures controlled by early faults and late structural differential settlement developed in the upper part of the hydrocarbon source layer of subsag A,providing a good migration path for oil and gas to vertically migrate through mudstone caprocks

关 键 词：湖底扇 岩性油藏 垂向运移 成藏模式 流一段 始新统 涠西南凹陷 北部湾盆地 

分 类 号：TE122.2[石油与天然气工程—油气勘探] P618.13[天文地球—矿床学]