琼东南盆地第四系乐东组沉积体系演化特征  

Evolution on sedimentary system of the Quaternary Ledong Formation,Qiongdongnan Basin

作　　者：李文龙 毛雪莲 刘平 廖键 杨振建 LI Wenlong;MAO Xuelian;LIU Ping;LIAO Jian;YANG Zhenjian(CNOOC Zhanjiang Company,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：《天然气勘探与开发》2024年第6期1-7,共7页Natural Gas Exploration and Development

基　　金：中海石油中国有限公司重大科技项目(编号:CNOOC-KJ135ZDXM38ZJ)。

摘　　要：随着油气勘探和天然气水合物研究的不断推进,已证实琼东南盆地第四系乐东组浅部地层不仅是天然气水合物的发育层系,也是浅层油气活跃层系。为此,利用三维地震资料、钻井资料,结合区域海平面变化特征,建立了乐东组高精度层序地层格架,厘清了沉积体系演化及展布规律,为该区浅层气和天然气水合物勘探目标选择提供理论支撑。研究结果表明:(1)琼东南盆地乐东组存在5个三级层序,而S_(14)界面是进积型陆坡向加积型陆坡的转换面,控制着海底扇的发育层系;(2)乐东组沉积充填划分为3个演化阶段,S_(20)—S_(14)以西部物源供给的中央峡谷体系水道化海底扇充填为主,S_(14)—S_(12)以北部物源供给的海底扇和块体流沉积充填为主,S_(12)—今以块体流—席状砂复合沉积充填为主;(3)乐东组下段西物源大型水道化海底扇分布范围广,沉积厚度大,砂岩储层厚度较大、粒度较粗;乐东组上段北物源峡谷体系外的规模较小的海底扇,砂岩储层厚度较薄、粒度偏细。结论认为:陵水凹陷南斜坡带隆起区乐东组下段大型海底扇具有较大的油气资源潜力,是浅层天然气和水合物勘探的有利地区。It is proved that as the sustained advancement of petroleum exploration and gas hydrate research,the shallow Quaternary Ledong Formation of Qiongdongnan Basin is not only developed with gas hydrate,but also an active target of shallow oil and gas.Therefore,based on sea-level fluctuation nature,the sequence stratigraphic framework with high precision was established via 3D seismic and drilling data.Furthermore,both evolution and extension were made clear for sedimentary system,which might help theoretically select exploration targets on shallow gas or gas hydrate in this area.Results show that:(i)there are five third-order sequences in this formation.And the S_(14)interface as the transitional surface from the progradational continental slope to the aggradational one controls the strata developed with submarine fan;(ii)the sedimentary system in Ledong Formation underwent three evolutionary stages.Among which the S_(20)-S_(14)is mainly from the channel submarine fan of central canyon system supplied by the western provenance,the S_(14)-S_(12)from the fan given by the northern provenance and mass flow,and the S_(12)-present from compound deposits of both mass flow and sheet-like sand;and(iii)the channel submarine fan where the western provenance originates from the Lower Ledong Formation is featured by wide extension and large depositional thickness,especially sandstone reservoirs with large thickness and coarser grain size.While the other fan where the northern provenance out of the canyon system comes from the Upper Ledong Formation features smaller extension,in which sandstone reservoirs are characterized by thin thickness and fine grain size.In conclusion,there exists a big outlook in petroleum resources in the Lower Ledong Formation in the uplift area of south slope of Lingshui sag,which is also available for shallow gas or gas hydrate exploration.

关 键 词：琼东南盆地 乐东组 层序地层格架 海底扇 地质意义 

分 类 号：P618.13[天文地球—矿床学]