琼东南盆地宝岛凹陷南部渐新统陵水组三段三角洲的发现及石油地质意义

Discovery and petroleum geological significance of delta in the third member of Oligocene Lingshui Formation in southern Baodao Sag,Qiongdongnan Basin,South China Sea

基于琼东南盆地三维地震资料及钻井获取的岩性、电性、薄片及测年等分析测试数据,开展宝岛凹陷南部断阶带渐新统陵水组三段(简称陵三段)源-汇体系特征及源-汇耦合定量分析等研究。研究表明:①陵三段沉积期YL10剥蚀区发育东、西2大物源水系,在宝岛凹陷南部形成了2大优势输砂通道及2个三角洲朵叶体,整体具有西大东小的特征,可划分为初始期、昌盛期、间歇期和回春期4个演变阶段;②综合三角洲砂体发育期次、展布面积、碾平厚度及不同类型母岩区面积、成砂系数等参数进行源-汇耦合定量计算,结果显示研究区具备形成规模储集体的物质基础;③钻井揭示陵三段三角洲沉积以细砂岩为主,砂岩总厚度为109~138 m,最大单层厚度为15.5~30.0 m,砂地比为43.7%~73.0%,不同断阶间储层物性差异明显;④断阶带多期隆升背景下小物源区规模三角洲发育模式揭示幕式隆升提供充足的物源供给,物源水系及流域面积控制砂体的规模,多级活动断阶控制砂体的输送通道,局部断槽控制砂体的侧向推进方向。陵三段三角洲砂体与断块耦合形成多类型圈闭,成为凹陷南部重要的勘探突破口和新领域,有望为盆地内其他构造背景相似区域油气勘探及储层研究提供借鉴。

Based on the 3D seismic data and the analysis and test data of lithology,electricity,thin sections and chronology obtained from drilling of the Qiongdongnan Basin,the characteristics and the quantitative analysis of the source-sink system are studied of the third member of the Upper Oligocene Lingshui Formation(Ling 3 Member)in the southern fault step zone of the Baodao Sag.First,the YL10 denudation area of the Ling 3 Member mainly developed two river systems in the east and west,resulting in the formation of two dominant sand transport channels and two delta lobes in southern Baodao Sag,which are generally large in the west and small in the east.The evolution of the delta has experienced four stages:initiation,prosperity,intermittence and rejuvenation.Second,the source-sink coupled quantitative calculation is performed depending on the parameters of the delta sand bodies,including development phases,distribution area,flattening thickness,area of different source rocks,and sand-forming coefficient,showing that the study area has the material basis for the formation of large-scale reservoir.Third,the drilling reveals that the delta of the Ling 3 Member is dominated by fine sandstone,with total sandstone thickness of 109–138 m,maximum single-layer sandstone thickness of 15.5–30.0 m,and net-to-gross ratio of 43.7%–73.0%,but the physical properties are different among the fault steps.Fourth,the large delta development model of the small provenance area in the step fault zone with multi-stage uplift is established.It suggests that the episodic uplift provides sufficient sediments,the river system and watershed area control the scale of the sand body,the multi-step active fault steps dominate the sand body transport channel,and local fault troughs decide the lateral propulsion direction of the sand body.The delta of the Ling 3 Member is coupled with fault blocks to form diverse traps,which are critical exploration targets in southern Baodao Sag.