鄂尔多斯盆地长6油层组准连续型致密砂岩油藏形成机理

Forming mechanism of quasi-continuous tight sandstone reservoir of Chang 6 oil-bearing formation,Ordos Basin

鄂尔多斯盆地陕北斜坡延长组长6油藏为典型的准连续型致密砂岩非常规油藏,主要具有以下7个特点:(1)长6油藏形成和分布对圈闭无严格要求,石油大面积连片分布,油藏分布范围不受圈闭限制;(2)区域相对稳定的大地构造背景条件,以及大面积复合连片分布的致密储集体是长6准连续型致密砂岩油藏形成的外部因素;(3)长7油层组成熟烃源岩大面积连续分布,高强度生、排烃是长6准连续型致密砂岩油藏形成的前提;(4)长6油藏的形成主要是初次运移和短距离二次运移的结果,垂向裂缝和侧向连通砂体有效组合为石油优势运移通道,石油就近运移聚集成藏;(5)石油运移的动力主要是生烃作用产生的异常压力,浮力作用弱,对油藏的形成和分布不起主要作用;(6)长6油藏油水分布规律复杂,无纯油层,油水层、水层、干层共存,无统一的油水界面和压力系统,油藏非均质性强,含油饱和度不均一,储量丰度较低,存在甜点富集区;(7)在石油大规模生成运移时,长6储层已经致密化或同步致密,为形成长6准连续型致密砂岩油藏创造了条件。

The Chang 6 reservoir in the Yanchang Formation in the Shanbei slope of the Ordos Basin is a typical quasi-continuous unconventional tight sandstone reservoir. It has 7 main features as followed. （ 1 ） The formation and distribution of the Chang 6 reservoir were not restricted by traps. Oils spread for big area and were connected. （2） Regional relatively stable tectonic background and tight sand bodies connected for big area were the external factors for the formation and distribution of the Chang 6 reservoir. （3） Matured hydrocarbon source rocks in the Chang 7 formation were connected widely. High-strength hydrocarbon generation and expulsion were the basis for the formation and distribution of the Chang 6 reservoir. （4） The Chang 6 reservoir mainly resulted from primary migration and secondary migration of short distance. Vertical cracks and laterally-connected sand body effective combinations provided favora- ble pathways for petroleum migration. （5） The abnormal overpressure caused by hydrocarbon generation was the main force for petroleum migration. Buoyancy effect was very weak and played an unimportant effect in controlling the formation and distribution of the reservoir. （6） Oil and water distributions were complex in the Chang 6 reservoir. Pure oil was not found. Oil/water, water and dry layers coexisted. There was no unified oil/water boundary or pressure system. The reservoir had strong heterogeneity. Oil saturation was not unified. Reserve abundance was low. Cookies were found locally. （7） The Chang 6 reservoir had been compacted before the mass migration of petroleum, serving foundation for the formation of the Chang 6 quasi-continuous tight sandstone reservoir.