东海陆架盆地丽水西凹陷油气地球化学特征及其成因和来源  

Geochemical Characteristics and Genesis of Oil and Gas in the Lishuixi Sag,East China Sea Shelf Basin

作　　者：张迎朝 胡森清 刘金水 蒋一鸣 陈忠云 覃军 刁慧 王超 ZHANG Yingzhao;HU Senqing;LIU Jinshui;JIANG Yiming;CHEN Zhongyun;QIN Jun;DIAO Hui;WANG Chao(Shanghai Branch of CNOOC Ltd.,Shanghai 200335,China)

机构地区：[1]中海石油(中国)有限公司上海分公司,上海200335

出　　处：《现代地质》2022年第5期1382-1390,共9页Geoscience

基　　金：中海油“七年行动计划”重大科技专项“东海上产关键技术研究”(CNOOC-KJ 135 ZDXM39 SH)。

摘　　要：东海陆架盆地西部丽水西凹陷油气成因和来源争议较大。根据钻井地球化学分析测试结果、地震勘探资料,运用天然气地球化学、油气成藏过程研究思路,重新认识丽水西凹陷L36气田油气成因和来源,提出下一步油气勘探方向。L36气田天然气组分、干燥系数分析表明,天然气为“凝析油-湿气带”演化阶段产物,天然气成熟度Ro不小于1.1%。通过天然气碳同位素组成与中国近海典型油型气碳同位素特征的对比分析,认为L36气田天然气为油型气,估算天然气成熟度Ro在1.12%~1.14%之间,天然气来源于丽水西凹陷下古新统月桂峰组湖相烃源岩。L36气田产出的凝析油C_(7)轻烃具有甲基环己烷含量占优特征,与湖相烃源岩来源的凝析油C_(7)轻烃组成特征存在显著差异;中古新统灵峰组浅海相烃源岩具有甾烷C_(27)20R/C_(29)20R小于1、不含C_(30)4-甲基甾烷、伽马蜡烷含量低的特征,指示L36气田凝析油来源于下古新统灵峰组浅海相烃源岩,证实了丽水西凹陷除发育下古新统月桂峰组湖相烃源岩外,还发育有中古新统灵峰组浅海相烃源岩。基于以上对烃源岩的分析,提出了丽水西凹陷下一步的油气勘探目标,即凹中断背斜构造背景上的岩性圈闭、凹中断鼻及其构造背景上的岩性圈闭和仙桥构造带,为寻找丽水西凹陷新的油气储量阵地提供新的认识。The genesis and source of gas and condensate oil of Lishuixi sag in the western East China Sea Shelf Basin remain disputed for many years.Based on geochemical and drill well analyses and seismic exploration,the oil and gas genesis,source and exploration direction of L36 gas-field in the Lishuixi sag are reviewed with comprehensive research ideas and methods of natural gas geochemistry and oil and gas accumulation.The study shows that the natural gas in L36 gas-field is the product of“condensate-wet gas zone”evolution stage,and that the natural gas maturity Ro is no less than 1.1%.The carbon isotope composition of natural gas and the carbon isotope comparison with typical oil-type gas in China offshore revealed that the natural gas in L36 gas field is oil-type,with the estimated natural gas maturity Ro=1.12%-1.14%,which was originated from lower Paleocene lacustrine Yueguifeng Formation source rocks in the sag,which enriched the genetic types and sources of natural gas in the East China Sea basin.The C_(7) light hydrocarbons of condensate oil produced in L36 gas-field are dominated by methylcyclohexane,significantly different from the C_(7) light hydrocarbon composition of condensate oil from the lacustrine source rock.The lower Paleocene shallow marine Lingfeng Formation source rocks are characterized by<1 sterane C_(27)20R/C_(29)20R,no C_(30)4-methylsterane and low Gamma wax content.This indicates that the condensate oil of L36 gas-field is from the Lingfeng Formation source rocks.It is confirmed that in addition to the Yueguifeng Formation source rocks,the Lingfeng Formation source rocks were also developed in the Lishuixi sag.The next natural gas exploration direction in the Lishuixi sag may include:(1)lithologic traps in the structural background of fault anticline and fault nose across the sag center;(2)Xianqiao structural belt.This provides theoretical guidance for the exploration of new hydrocarbon resource in the sag.

关 键 词：油气成因 月桂峰组 湖相烃源岩 灵峰组 浅海相烃源岩 丽水西凹陷 东海陆架盆地 

分 类 号：P618.1[天文地球—矿床学] TE122.1[天文地球—地质学]