南海北部新生代海相烃源岩发育机理再认识  

Rethinking on the development mechanism of Cenozoic marine source rocks in the northern South China Sea

作　　者：李友川 周姗姗 兰蕾 李威 李婧婧 丁文静 杨永才 LI Youchuan;ZHOU Shanshan;LAN Lei;LI Wei;LI Jingjing;DING Wenjing;YANG Yongcai(CNOOC Research Institute Ltd.,Beijing 100028,China)

机构地区：[1]中海油研究总院有限责任公司,北京100028

出　　处：《中国海上油气》2025年第2期45-60,共16页China Offshore Oil and Gas

基　　金：国家自然科学基金青年基金“莺-琼盆地渐新世-中新世气候演变的陆源有机质分子地球化学响应(编号:42202184)”;国家自然科学基金企业创新发展联合基金重点支持项目“南海北部深水区深层温压场差异性演化对优质储层的控制机理(编号:U24B2016)”;中海石油(中国)有限公司科研项目“琼东南和珠江口盆地新生代海相烃源岩形成机理与分布预测(编号:2021-KT-YXKY-01)”部分研究成果。

摘　　要：新生代海相烃源岩是南海北部含油气盆地的主要烃源岩,但钻井揭示少、预测难度大,制约着南海北部尤其是深水区的油气勘探。针对南海北部新生代海相烃源岩有机质来源不清、海洋营养化程度和古生产力不明、有利于海相烃源岩发育的沉积环境不清等问题,利用有机岩石学微观结构确定海相烃源岩的有机质来源和有机质组成,通过地球化学方法重建南海新生代海洋化学环境,揭示新生代海洋的营养化程度和古海洋有机质生产力以及有机质保存条件。研究表明:(1)南海北部新生代海相烃源岩有机质除来源于陆生高等植物及少量低等浮游藻类外,还有来自海草和底栖宏观藻的贡献,其中以海草为主要有机质来源的烃源岩主要发育在滨浅海,而半封闭海湾环境形成的烃源岩底栖宏观藻贡献较大;(2)南海新生代海洋环境总体贫营养,但白云凹陷恩平组沉积时期营养化程度高于琼东南盆地崖城组和陵水组,且海洋生产力与营养化程度呈正相关,在同一盆地或凹陷内,半封闭海湾营养化程度和古生产力最高、陆棚浅海最低、开阔滨浅海介于二者之间;(3)半封闭海湾环境盐度最高,存在次氧化和缺氧的沉积环境,有利于有机质保存,而陆棚浅海和开阔滨浅海环境总体盐度偏低,且偏氧化,不利于有机质保存;(4)半封闭海湾有机质来源丰富、有机质保存条件较好,是南海北部新生代海相烃源岩发育最有利的沉积环境。该项研究成果为南海北部新生代海相烃源岩预测和油气勘探部署提供理论依据。The Cenozoic marine source rocks are the main source rocks in the basin bearing oil and gas in the northern South China Sea.However,due to the limited number of wells drilled and the great difficulty in prediction,the exploration of oil and gas in the northern South China Sea,especially in the deepwater area,is restricted.To address the issues of unclear organic matter sources of Cenozoic marine source rocks in the northern South China Sea,the unknown marine eutrophication level and paleoproductivity,and the undetermined sedimentary environment favorable for the development of marine source rocks,this study used organic petrology to determine the organic matter sources and composition of marine source rocks.Through geochemical methods,the study reconstructed the Cenozoic marine chemical environment of the South China Sea,revealing the eutrophication level,paleoproductivity,and organic matter preservation conditions in the Cenozoic oceans.The results show the followings.①The organic matter of Cenozoic marine source rocks in the northern South China Sea originates not only from terrestrial higher plants and a small amount of lower planktonic algae but also from seagrasses and benthic macroalgae.Seagrasses are the main source of organic matter in source rocks developed in the coastal and shallow marine environments,while benthic macroalgae contribute significantly to source rocks formed in semi-enclosed bay environments.②The overall Cenozoic marine environment in the South China Sea is nutrient-poor.However,the eutrophication level during the Enping Formation deposition in the Baiyun Sag is higher than that of the Yacheng Formation and Lingshui Formation in the Qiongdongnan Basin.Marine productivity is positively correlated with the eutrophication level.Within the same basin or sag,the eutrophication level and paleoproductivity are highest in semi-enclosed bays,lowest in the continental shelf shallow sea,and intermediate in the open coastal and shallow marine environments.③The salinity is highest in semi-enclo

关 键 词：南海北部 海相烃源岩 发育机理 半封闭海湾 营养化程度 古生产力 氧化还原性 

分 类 号：TE121.1[石油与天然气工程—油气勘探]