摘要
河流沉积是陆相沉积环境和地层记录的重要组成部分,也是陆相盆地重要的油气储层。侏罗系延安组是鄂尔多斯盆地重要的含煤和储油层系。延安组早期河流沉积发育,延安一带出露典型沉积剖面,是剖析河流构型特征的难得窗口。采用沉积学理论和构型要素分析方法,在野外露头精细解剖的基础上,分析了延安组下部辫状河、曲流河的沉积构型特征,探讨了古河道规模和河流类型转化的控制因素。研究表明,延安组延10沉积期辫状河发育,主要由河道、顺流加积体和沙质坝等单元组成,多期河道沉积叠置,呈厚层板状分布,泥质隔夹层不发育;延9早期演变为曲流河,发育河道、侧向加积体、废弃河道、泛滥平原及决口扇等构型单元,泥质隔夹层较发育,砂体连续性变差。采用经验公式估算,延10辫状河河道宽度为19.34~373.22 m,延9曲流河河道宽度16.81~99.21 m。延安组早期继承了富县组沉积期的古构造—古地理格局,随着填平补齐的发展和盆地沉积范围的扩大,古地形变缓,物源供给减弱,导致河流类型由辫状河演变为曲流河。研究结果对于深入理解同物源体系供给条件下河流沉积构型特征及类型转换,油气储层预测等具有理论和现实意义。
Fluvial deposits are an important part of the continental sedimentary environment and stratigraphic record and also an important oil and gas reservoir in continental basins.The Jurassic Yan’an Formation is an important oil and coal-bearing reservoir in the Ordos Basin.In the early sedimentary stage of the Yan’an Formation,fluvial sediments were developed,and typical sedimentary sections were exposed in the Yan’an area,providing a valuable window for analyzing the characteristics of river architecture.Based on the detailed analysis of outcrops,the main sedimentary architectural characteristics of the braided river and meandering river in the lower Yan’an Formation are analyzed by employing the sedimentological theory and analysis method of architectural elements.The controlling factors for the scale and type transformation of the ancient channel are discussed further.Our study shows that a braided river was developed during the sedimentary stage of the Yan 10 interval,which was mainly composed of a channel,downstream accretion,and sand bar.The channel unit was compounded in multiple stages,overlapped with each other,and distributed in a thick plate pattern,and the argillaceous interlayer was not well developed.During the sedimentary period of the Yan 9 interval,it evolved into a meandering river,with a mainly developed channel,lateral accretion,abandoned channel,floodplain fine,and crevasse splay units.The muddy interlayer is relatively developed,and the continuity of the sand body is poor.Estimated with an empirical formula,the braided channel width during the Yan 10 stage is 19.34-373.22 m,and the meandering river developed in the Yan 9 stage is 16.81-99.21 m.The paleotectonic and paleogeographic pattern during the early sedimentary stage of the Yan’an Formation is the inheritance of the Fuxian Formation with the progress of filling up the gap,the range of the basin expanded the gradient slowing down,and the sedimentary source recharge decreasing,resulting in the evolution of the river type from braided river to meandering river.The study results have theoretical and practical significances for understanding the typical characteristics of fluvial sedimentary processes,as well as the hydrocarbon reservoir prediction.
作者
王科
赵俊峰
薛锐
闫占冬
李旋
李一凡
WANG Ke;ZHAO JunFeng;XUE Rui;YAN ZhanDong;LI Xuan;LI YiFan(State Key Laboratory of Continental Dynamics/Department of Geology,Northwest University,Xi’an 710069,China;No.12 Oil Production Plant of Changqing Oilfield Company,PetroChina,Heshui,Gansu 745400,China;No.7 Oil Production Plant of Changqing Oilfield Company,PetroChina,Xi’an 710200,China)
出处
《沉积学报》
CAS
CSCD
北大核心
2022年第5期1367-1377,共11页
Acta Sedimentologica Sinica
基金
国家自然科学基金(41330315)
西北大学地质学系科研团队基金项目(DZX-T-3)。
关键词
辫状河
曲流河
构型要素
延安组
鄂尔多斯盆地
braided river
meandering river
architectural element
Yan’an Formation
Ordos Basin
