冀中坳陷保定凹陷清苑构造带低熟油成因解析  

Genetic Mechanism of Low-Maturity Oil in the Qingyuan Tectonic Belt,Baoding Sag,Jizhong Depression

作　　者：李小冬 李志军 李熹微 马学峰 李晓燕 陈柯童 张霁潮 许梦婷 张瑞雪 秦梦华 王成云 刘佳[2] 张建淼 施倩倩 李素梅[2,3] LI Xiaodong;LI Zhijun;LI Xiwei;MA Xuefeng;LI Xiaoyan;CHEN Ketong;ZHANG Jichao;XU Mengting;ZHANG Ruixue;QIN Menghua;WANG Chengyun;LIU Jia;ZHANG Jianmiao;SHI Qianqian;LI Sumei(Research Institute of Exploration and Development,Huabei Oilfield Company,PetroChina,Renqiu,Hebei 062552,China;National Key Laboratory of Petroleum Resources and Engineering,China University of Petroleum,Beijing 102249,China;Geosciences Institute,China University of Petroleum,Beijing 102249,China)

机构地区：[1]中国石油华北油田分公司勘探开发研究院,河北任丘062552 [2]中国石油大学(北京)油气资源与工程全国重点实验室,北京102249 [3]中国石油大学(北京)地球科学学院,北京102249

出　　处：《现代地质》2024年第5期1338-1353,共16页Geoscience

基　　金：国家自然科学基金项目(42073064);华北油田探区“十四五”油气资源评价项目。

摘　　要：冀中坳陷保定凹陷清苑构造带近年取得了重大油气勘探突破,油气的来源及其成因有待进一步确认。采用色谱-质谱、高分辨率质谱等地球化学途径,对该区油气的主力烃源岩及油气成因进行了精细剖析。清苑构造带主体原油为含蜡(均值8.12%)、含硫(均值0.81%)的重质油,具有低Pr/Ph(0.14~0.24)、高甾烷/藿烷(3.3~5.6)、高伽马蜡烷和三芳甾烷相对丰度(40%~61%)、低甾烷异构化程度(C_(29)甾烷ααα20S/(S+R)=0.23~0.28)等特征,为典型的强还原咸水相原油。油-油、油源对比表明,清苑构造带主体原油和相邻的蠡县斜坡原油特征相似,与蠡县斜坡沙一段咸水相泥页岩具有较好的亲缘关系,主力烃源岩埋深>3000 m,与保定凹陷烃源岩未显示相关性。高分辨率质谱分析表明,清苑构造带原油富含O_(1)、O_(2)类化合物,特别是等效双键数(DBE)为1、5的O_(2)类化合物(分别主要为脂肪酸和甾烷酸),其低温降解成烃是低熟油形成的重要机制,饶阳凹陷蠡县斜坡及相邻的生油洼陷发育处于生油窗阶段的、热演化程度相对不高的沙一段烃源岩是该区低熟油形成的前提。A significant amount of hydrocarbons has been discovered in recent years in the Qingyuan Tectonic Belt of the Baoding Sag,within the Jizhong Depression of the Bohai Bay Basin.However,the origin and primary source rock of the discovered oils remain under debate.Conventional geochemical methods,combined with negative ESI FT-ICR MS,were employed to investigate the origin and formation mechanism of the crude oils.The majority of the crude oils collected from the Qingyuan Tectonic Belt can be classified as heavy oil,characterized by low wax(average 8.12%),low sulfur(average 0.81%),low Pr/Ph(0.14-0.24),high sterane/hopane ratio(3.3-5.6),high relative abundance of gammacerane and triaromatic sterane(40%-61%),and low sterane isomerization(C_(29) steraneααα20S/(S+R)=0.23-0.28).These characteristics suggest a strongly reducing,brackish-saline,and/or water-stratified paleoenvironment during the deposition of the source rocks.Oil-oil and oil-source correlations reveal similar geochemical characteristics between the crude oils in the Lixian Slope of the Raoyang Sag and those in the main body of the Qiyuan Tectonic Belt.The crude oils show a close genetic affinity with the source rocks from the first member of the Shahejie Formation(Es1)in the Lixian Slope.It is suggested that the main source rocks of the crude oils had a burial depth of at least 3,000 m.No correlation was observed between the crude oils and the source rocks in the adjacent Baoding Sag,due to their relatively low hydrocarbon generation potential and thermal evolution.The crude oils were enriched in O_(1) and O_(2) species,particularly those with equivalent double bond equivalent(DBE)of 1 and 5(mainly fatty acids and steric acids,respectively),which could decarboxylate into hydrocarbons at low temperatures.We suggested that both the relatively low thermal evolution(in the early stage of oil generation window)and the enrichment of algal lipids in the Es1 source rocks are responsible for the less mature oils in the Qingyuan Tectonic Belts.

关 键 词：保定凹陷 清苑构造带 低熟油 生物标志物 高分辨率质谱 油气成因机制 

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