渤南洼陷沙四下亚段微量元素地球化学特征及其对沉积环境的指示  

Geochemical characteristics of trace elements in the Es4x Formation of the Bonan Sag and their implications for sedimentary

作　　者：张波 郭晓英 孟涛 姜超 刘鹏 陈勇[2,3] ZHANG Bo;GUO Xiaoying;MENG Tao;JIANG Chao;LIU Peng;CHEN Yong(Development Research Institute of Shengli Oilfield Branch Company,SINOPEC,Dongying 257000,Shan-dong,China;National Key Laboratory of Deep Oil and Gas,China University of Petroleum(East China),Qingdao 266580,Shandong,China;School of Geosciences in China University of Petroleum(East China),Qingdao 266580,Shandong,China)

机构地区：[1]中国石油化工股份有限公司胜利油田分公司勘探开发研究院,山东东营257000 [2]深层油气全国重点实验室(中国石油大学(华东)),山东青岛266580 [3]中国石油大学(华东)地球科学与技术学院,山东青岛266580

出　　处：《华东地质》2025年第1期55-67,共13页East China Geology

基　　金：中国石化科技部“济阳坳陷近源领域成藏体系评价与目标优选(编号:P22066)”项目资助。

摘　　要：渤南洼陷是渤海湾盆地重要的油气富集区,为了进一步明确渤南洼陷沙四下亚段烃源岩的沉积环境和生烃潜力,文章对其典型泥岩样品进行了微量元素测试和有机地球化学特征分析。选择对沉积环境较敏感的元素和元素组合(如δCe_(n)、Ce_(anom)、Ni/Co、V/Ni、V/(V+Ni)、V/Cr、B/Ga等)进行分析,并结合有机地球化学特征,明确了渤南洼陷沙四下亚段沉积时期的气候、氧化还原环境和水体盐度等特征,通过对比分析进一步探讨了这些参数在研究区古环境分析中的适用性,以及影响有生烃潜力的烃源岩发育的因素。结果表明,研究区泥岩的La_(n)/Yb_(n)值为1.62~3.00,B/Ga值为1.43~3.73,偏黑色泥岩的Pr/Ph<1、δCe_(n)>1、C_(eanom)>0,偏红色泥岩的δCen值为0.95~0.96、Ce_(anom)<0,这说明渤南洼陷沙四下亚段沉积时期部分区域气候温暖湿润,沉积物沉积速率较慢,整体处于淡水-微咸水环境,且偏红色泥岩沉积于氧化环境,偏黑色的泥岩沉积于弱还原环境。对比分析结果显示,使用δCe_(n)、Ce_(anom)判别氧化-还原环境是可靠的,根据泥岩的Ni/Co值、V/Ni值和V/(V+Ni)值的相对大小可以推断其沉积时环境的缺氧程度,根据B/Ga值可以区分淡水-微咸水和咸水环境。研究区泥岩干酪根类型指数为-26.8~77.1,为Ⅱ型-Ⅲ型干酪根;部分泥岩的TOC、S_(1)+S_(2)、氯仿沥青“A”的含量表明其已经达到一般的烃源岩水平。与研究区的非烃源岩相比,其B/Ga值较小,ETR指数和伽马蜡烷指数较大,这表明在缺氧环境下,能否发育有生烃潜力的烃源岩可能取决于沉积水体的盐度。The Bonan Sag is an important oil and gas-rich region of Bohai Bay basin.In order to clarify the depositional environment and hydrocarbon potential of the hydrocarbon source rocks in the lower subsection of x Es4 in the Bonan Sag,and the hydrocarbon potential of the hydrocarbon source rocks of the Es4x,we analyzed the x typical mudstone samples of the Es4 in the Bonan Sag by trace element testing and organic geochemical charac-teristics.Through selecting the elements and element combinations sensitive to the depositional environment,such asδCen,Ceanom,Ni/Co,V/Ni,V/(V+Ni),V/Cr,B/Ga etc.,in combination with the organic geochemical character-x istics,this paper clarified the climate,redox environment and salinity during the sedimentary period of the Es4 in the Bonan Sag.The applicability of these parameters in the paleoenvironment study for the working area and the factors affecting the development of source rocks with hydrocarbon generation potential were discussed.The re-sults show that the Lan/Ybn values range from 1.62 to 3.00;B/Ga range from 1.43 to 3.73;the blackish mudstones have Pr/Ph<1,δCe_(n)>1,and Ce_(anom)>0,and the reddish mudstones samples have δCe_(n) values ranging from 0.94 to x 0.96,and Ce_(anom)<0.It indicates a warm and humid climate in some areas during the depositional period of the Es4 in the Bonan Sag,a slow sediment deposition rate,and a freshwater-slightly saline environment of the whole area,while that part of the area was in an anoxic environment,except for the oxygen-rich environment.The results of comparative analysis show that usingδCen and Ceanom is reliable to discriminate redox environments,and the rela-tive magnitudes of mudstone Ni/Co,V/Ni,and V/(V+Ni)can infer the anoxicity of environment during their de-position,and the B/Ga ratio can distinguish freshwater-brackish water and brackish water environment.In addi-x tion,the mudstone in the study area of the Es4 has a high content of sapropelinite,the kerogen is type II-III;TOC,S_(1)+S_(2),and chloroform bitumen“A”contents o

关 键 词：渤南洼陷 沙四下亚段 微量元素 沉积环境 

分 类 号：P588.21[天文地球—岩石学] P59[天文地球—地质学]