鄂尔多斯盆地马岭油田成藏条件与机制

Formation Conditions and Mechanism of Oil Reservoir in Maling Oilfield,Ordos Basin

马岭油田延安组油藏是河流相油气藏的典型代表,认识这类油藏的形成规律,对指导河流相油藏的石油勘探和开发都是重要的。从油气生成、储层、运移、圈闭和聚集成藏诸方面,系统地研究了该油田油藏的形成条件,动态地探讨了油藏的形成机制。研究结果表明,马岭油田原油来自其下覆的延长组烃源岩;储层主要为下侏罗统延安组河道砂体;盖层为煤层、碳质泥岩和泥岩;油气纵向运移受充注点和"石油运移窗"的控制,横向运移输导体为联通的多分支河道砂体,运移动力为地层高异常压力与浮力;圈闭具有构造鼻隆圈闭、差异压实、鼻隆圈闭、古残丘鼻隆圈闭、地层超覆圈闭和岩性圈闭5种类型。

Ordos basin is a large inner continental sedimentary basin in China.Mesozoic crude oils in the basin are derived from nonmarine source rocks,so that it has also been used as a typical model of a nonmarine sedimentary basin generating oil.Maling oilfield is located in the southwestern Yishan slope of Ordos Basin.It was discovered in Lower Jurassic Yanan Formation in 1970 and is one of the earliest-discovered oilfields in Ordos Basin.It also is typical representative of oil reservoir in land fluvial deposits.However,previous geochemical studies of oils from Maling oilfield are limited and the mechanism of hydrocarbons accumulation for this oilfield has not been well known.Understanding the formation law of this kind of oil reservoir is very important for petroleum exploration and production in fluvial deposits.We collected the crude oil samples from different regions of Maling oilfield and source rocks in the Ordos Basin,and analyzed biomarker compounds in the oils and source rocks.In this paper,the formation conditions of oil reservoir in Maling oilfield,such as source rock,reservoir rock,oil migration,traps and accumulation,were systematically studied,and its forming mechanism was discussed dynamically.The results show that crude oil of Maling oilfield was derived from the Yanchang Formation source rocks.Reservoir rocks are mainly the Low Jurassic Yanan Formation fluvial channel sandstones,while coal seam,carbonaceous mudstone and mudstone constituted the cap rock.Hydrocarbon vertical migration was controlled by charging position and migration window.The lateral migration pathway of crude oil is sandbodies of river channels.The force for the vertical migration was likely the capillary pressure and the abnormally high strata pressure.There were five types of traps.