鄂尔多斯盆地西南缘延长组长8段低充注油藏成藏模式——以环西—彭阳地区为例

Hydrocarbon Accumulation Patterns of Chang 8Low-Charging Oil Reservoirs in Southwestern Margin of Ordos Basin:Taking Huanxi-Pengyang Area as an Example

为了厘清鄂尔多斯盆地西南缘环西—彭阳地区长8油藏的成藏机理,通过储层物性分析、烃源岩评价、流体包裹体分析和自生伊利石同位素测年等手段,明确成藏动力机制及成藏过程,并在不同地区油藏充注程度差异性对比的基础上,通过构造演化史、埋藏史、石油充注史研究,明确油藏分布控制因素。研究表明:长8油藏含油饱和度低,油藏分布呈南北分区的特征;低生烃强度耦合较强的储层非均质性是油藏低充注的主要成因;长7段剩余压力总体大于长8段,有利于长7段的烃向长8段充注;油气充注主要发生在早白垩世末期和晚白垩世早期(110~95 Ma);23 Ma以来,喜山期构造运动对西南区域油气聚集起到调整或破坏作用,北部为正常一致型,南部为早充注晚调整型;南北区成藏模式不同,北部环西地区以侧向输导运移成藏为主,南部彭阳地区以垂向运移成藏为主。经综合分析,鄂尔多斯盆地环西—彭阳地区长8油藏属于低生低压近距离低充注成藏模式。

In order to deeply understand the hydrocarbon accumulation mechanism of the Chang 8 reservoir in Huanxi-Pengyang area, southwestern margin of Ordos Basin, the hydrocarbon accumulation dynamic mechanism and process of the reservoirare studied by means of reservoir property analysis, source rock evaluation, fluid inclusion analysis and isotopic dating of autogenetic illite.On the basis of the comparison of hydrocarbon charging difference of different regions, the control factors of reservoir distribution are clarified through the study of tectonic evolution history, burial history and hydrocarbon charging history.The research shows that the oil saturation of the Chang 8 reservoir is low, and its distribution is characterized by north and south areas.The lower the hydrocarbon generation intensity, the stronger the heterogeneity of the reservoir, which is the main cause of the low charging of the reservoir.The residual pressure of Chang 7 member is higher than that of the Chang 8 member, which is conducive to hydrocarbon charging to Chang 8 member.Hydrocarbon charging occurredmainly in the late Early Cretaceous and early Late Cretaceous(110~95 Ma) Since 23 Ma, Himalayan tectonic movement has adjusted or destroyed hydrocarbon accumulation in the southwest region.The northern part is a normal consistent hydrocarbon accumulation process, and the southern part is early charging and late adjustment process.The hydrocarbonaccumulation patterns of different regions are different.The Huanxi area in the north is dominated by lateral migration and accumulation, while the Pengyang area in the south is dominated by vertical migration and accumulation.The Chang 8 oil reservoir in Huanxi-Pengyang area of Ordos Basin has a hydrocarbon accumulation pattern with lowhydrocarbon generation intensity, lowpressure and shortcharging distance.