厄瓜多尔奥连特叠合盆地白垩系油气成藏特征与主控因素分析

Controlling Factors of the Cretaceous Hydrocarbon Accumulation in the Oriente Superimposed Basin,Ecuador

厄瓜多尔奥连特盆地是南美地区最重要的含油气盆地之一,油气资源丰富,主要含油气层系为白垩系Napo组、Basal Tena组和Hollion组砂岩;盆地内发育多个油田,但各油田之间,纵向上各砂层之间原油品质差异较大:纵向上,下轻上稠;平面上,南轻北稠。根据奥连特盆地构造演化、烃源分布、埋藏史等资料,结合盆地内原油纵、横向特征,对盆地内原油生烃、运移和成藏运移过程进行分析,认为:奥连特盆地受中生代白垩纪裂谷和新生代前陆盆地叠合影响,由西向东分为三个构造带:西部逆冲带、中部前渊带和东部斜坡带。西部逆冲带受安第斯山脉构造作用强烈,发育叠瓦状高角度逆冲断层和牵引背斜构造,主要储层为早白垩Hollin组砂岩;中部前渊带是强烈造山逆冲终止的构造带,发育近南北向高角度逆冲断层和走滑断裂,圈闭类型以断背斜和低幅构造圈闭为主,主要储层为白垩系Napo组砂岩;东部斜坡带发育大量走滑断裂,以伴生背斜圈闭和岩性、地层圈闭为主。油气富集受盆地构造演化和断裂发育控制,即早期断裂活化反转控制了不同构造带的圈闭类型;不同构造带储层沉积发育控制了油气垂向富集程度。

The Oriente basin is one of the most important petroleum basins in South American.Its main reservoir is sandstone of the Cretaceous Napo Formation.The secondary reservoir is sandstone of Tertiary Basal Tena and Hollion Formations.There are many oilfields in the Oriente basin.The crude oil in the lower reservoir and in the south is low-density oil,while the crude oil in the upper and in the north is heavy crude oil.The source distribution,structure evaluation and burial history of the basin are discussed.The Oriente basin may be divided into three structural zones such as thrust zone in the west,foredeep zone in the center and slope belt in the east.Imbricated high-angle thrust faults and tractional anticlines structures are developed in the thrust zone where major reservoir is sandstone of the Lower Cretaceous Hollin Formation.Nearly longitudinal high-angle thrust faults and strike-slip faults are developed in the foredeep zone where major reservoir is sandstone of the Cretaceous Napo Formation and trap types are mainly faulted anticlines and low-amplitude structural traps.A large number of strike-slip faults are developed in the slope zone where anticline trap,stratigraphic trap and lithologic trap predominate.Oil and gas enrichment is controlled by basin tectonic evolution and fault action.