渤海湾盆地渤南洼陷沙河街组三段下亚段岩相特征及有机质富集成因  

Lithofacies and causal mechanism of organic matter enrichment in the lower submember of the 3rd member of Shahejie Formation,Bonan Sag,Bohai Bay Basin

作　　者：王雨菡 丁伟铭 刘璇 魏韧 董琳[1] Wang Yuhan;Ding Weiming;Liu Xuan;Wei Ren;Dong Lin(School of Earth and Space Sciences,Peking University,Beijing100083,China)

机构地区：[1]北京大学地球与空间科学学院

出　　处：《石油与天然气地质》2019年第5期1106-1114,共9页Oil & Gas Geology

基　　金：国家科技重大专项(2016ZX05034001-007)

摘　　要：渤海湾盆地沾化凹陷渤南洼陷沙河街组三段沉积了面积广、厚度大、含碎屑组分的碳酸盐岩,蕴含着大量页岩油。通过岩相特征描述、陆源碎屑来源分析、初始生产力和氧化还原环境分析,探讨了渤南洼陷有机质富集的成因机制。对L69井进行了连续密集取样,根据岩性特征和沉积构造,主要划分为块状泥晶灰岩、透镜状泥晶灰岩、纹层状泥晶灰岩和纹层状亮晶灰岩;通过主微量元素、有机碳氮同位素、无机碳氧同位素实验对陆源碎屑来源进行讨论,稳定的Al/K和Al/Mg说明L69井碎屑组分的物源均一;通过对比研究全岩和干酪根有机氮同位素,对沉积时水体及沉积物的氧化还原环境进行恢复;通过Ba元素的含量、干酪根有机碳同位素,及其与有机氮同位素的耦合关系探讨生产力的变化。在此基础上对研究区油气生成与保存的机理进行了探讨,推测研究区内的陆源输入带来了营养物质,促进了湖盆中藻类的生长,产生了大量有机质。有机质在沉降过程中不断消耗氧气,导致了水体内部出现还原环境,进而促进了有机质的埋藏和保存。Thick carbonate rocks bearing detrital components are widespread in the 3rd member of Shahejie Formation in Bonan Sag,Bohai Bay Basin,where shale oil resource potential is huge.The causal mechanism of organic matter enrichment in Bonan Sag was investigated drawing on lithofacies description,as well as analyses of terrigenous debris sources,primary productivity and redox environment.The core of Well L69 was systematically sampled,with the samples being mainly classified as massive micrite,lenticular micrite,laminar micrite and laminar sparite in terms of lithofacies features and sedimentary structures.In addition,the terrigenous debris sources were discussed based on analysis of major and trace elements,organic carbon and nitrogen isotopes,and inorganic carbon and oxygen isotopes,and the Al/K and Al/Mg were shown to be stable,indicating that the clastic components of shale in Well L69 are homogeneous.Under the comparison of organic nitrogen isotopes between bulk sample and kerogen,the redox environment of water and sediments was restored;the Ba content,organic carbon isotopes of kerogen,and their coupling relationships with organic nitrogen isotopes were employed to demonstrate the primary productivity variation.On this basis,the generating and preserving mechanisms of hydrocarbon in the study area were investigated.The terrigenous clastic input is supposed to bring nutrients to the study area,promoting the growth of algae,and producing a large amount of organic matter as a result.The sedimentation of organic matter consumed oxygen and resulted in a reducing environment in water,which has in turn facilitated the accumulation and preservation of organic matter.

关 键 词：有机碳同位素 有机氮同位素 古生产力 氧化还原环境 湖相碳酸盐岩 沙河街组三段 渤南洼陷 渤海湾盆地 

分 类 号：TE122.3[石油与天然气工程—油气勘探]