冀中坳陷饶阳凹陷留西地区古近系沙河街组沙三上亚段沉积相与隐蔽油藏

通过岩心观察和单井相分析，结合沉积背景资料，认为留西地区古近系沙河街组沙三上亚段发育辫状河三角洲相和湖泊相，以辫状河三角洲前缘亚相和滨浅湖亚相为主，主要发育辫状分流河道、越岸沉积、水下分流河道、河口坝、席状砂等微相。根据层序地层学基本原理，结合前人研究成果，认为本区沙三上亚段为一完整的三级层序，可划分为低位、湖侵和高位3个体系域，分别对应于沙三上亚段沉积时期的早期、中期和晚期，绘制了每个沉积阶段的沉积相图，在此基础上研究了沉积体系的平面展布特征。沙三上亚段沉积时期形成的北高南低的构造背景与辫状河三角洲近东西向展布的砂体形态相互配置，加之良好的油源供给，为后期成藏创造了条件。沙三上亚段沉积早期发育的辫状河三角洲前缘水下分流河道与河口坝砂体是主要的储集体，与沉积中期发育的烃源岩形成了十分有利的生储盖组合，具有优越的隐蔽油藏发育条件。总结了该区隐蔽油藏成藏的4种模式，确定留西地区中南部沙三上亚段沉积早期发育的辫状河三角洲前缘砂体是下一步隐蔽油藏勘探的有利目标。

Sedimentary facies and subtle petroleum reservoirs of the upper submember of Member 3 of Paleogene Shahejie Formation in Liuxi area of Raoyang Sag, Jizhong Depression

Through core observations and single well sedimentary facies analysis,combined with the sedimentary setting,it is concluded that braided fluvial delta and lacustrine facies were developed during the deposition of the upper submember of the Member 3 of Paleogene Shahejie Formation in Liuxi area,and mainly the braided fluvial delta front and shore-shallow lacustrine subfacies were developed.The microfacies mainly include braided fluvial distributary channel,overbank deposit,subaqueous distributary channel,mouth bar and sheet-like sandbody.Based on the principles of sequence stratigraphy and the previous researches,the upper submember of the Member 3 of the Shahejie Formation in the study area is a complete third-order sequence which can be divided into lowstand systems tract,transgressive systems tract and highstand systems tract respectively corresponding to the early,the middle and the late depositional periods of the upper submember.The sedimentary facies maps of each period were compiled and the distribution characters of the sedimentary systems were investigated.The high in north and low in south topography in the depositional period of the upper submember matched well with the east-west trending sandbodies of the braided fluvial delta.The sands,combined with favorable hydrocarbon sources,thus can create profitable conditions for hydrocarbon accumulation in the late period.The main reservoirs include the subaqueous distributary channel and mouth bar sandbodies of the braided fluvial delta developed during the early depositional period of the upper submember of the Member 3 of the Shahejie Formation which form a very profitable source rock-reservoir-cap rock assemblage together with the source rocks developed in the middle depositional period,and are favorable for the formation of subtle hydrocarbon accumulations.Four types of patterns for subtle hydrocarbon accumulations development were established.The analyses indicate that the braided fluvial delta front sandbodies developed during the early depositional period of the upper submember of the Member 3 of Shahejie Formation are the favorable targets for further exploration of subtle hydrocarbon accumulations.