鄂尔多斯盆地陕北地区长8致密砂岩流体包裹体特征与石油成藏

The fluid inclusion characteristics and petroleum accumulation of Chang 8 tight sandstone in northern Shaanxi,Ordos Basin

【研究目的】鄂尔多斯盆地陕北地区延长组长8含油分布范围广,是下步勘探重要的目标领域,但其石油烃类演化和油藏分布的关系尚不清楚。【研究方法】基于流体包裹体产状特征、成分及均一性分析结果,综合地质与地球化学方法,探讨了鄂尔多斯盆地陕北地区长8致密砂岩储层内石油的来源及成藏特征,揭示了长8油藏形成时间以及与油气成藏的关系。【研究结果】长8砂岩储层中的流体包裹体以气液烃包裹体、气液两相盐水包裹体为主,主要分布于细砂岩的石英加大边或裂隙中,可分为早、晚两期,与气液烃包裹体伴生的盐水包裹体均一温度主要存在85~105℃和115~135℃两个峰值区间,分布连续,油气为连续充注;成藏演化史表明,长8石油主要充注时期为110~135 Ma,在晚侏罗世发生早期充注,在早白垩世发生大规模充注。在区域上主要发育长7烃源岩,在最大生排烃阶段烃源岩Ro值接近1.0%,达到生烃门限,大量生烃,长9烃源岩在志丹地区局部分布。【结论】结合包裹体特征与烃类形成的关系,陕北地区长8油藏受烃源岩、储层及充注动力等因素控制,石油充注程度不一,发育平面上分布不均匀的岩性油藏,区域上具有“双源供烃、差异聚集”的成藏特点。

This paper is the result of oil and gas exploration engineering.[Objective]The Yanchang Formation 8 in the northern Shaanxi region of the Ordos Basin has a wide oil distribution range and is an important target area for future exploration.However,the relationship between the evolution of hydrocarbons and the distribution of oil reservoirs is still unclear.[Methods]Based on the analysis of the occurrence characteristics,composition and homogeneity of fluid inclusions,geological and geochemical methods are used,the oil source and reservoir forming characteristics of Chang 8 tight sandstone are discussed,and the formation time of Chang 8 reservoir and its relationship with hydrocarbon accumulation are revealed.[Results]The fluid inclusions in Chang 8 sandstone reservoir are mainly gas-liquid hydrocarbon inclusions and gasliquid two-phase brine inclusions,which are distributed in quartz enlarged edge or fractures of fine sandstone,and can be divided into early and late stages.The homogenization temperature of brine inclusions associated with gas-liquid hydrocarbon inclusions mainly has two peak ranges of 85-105℃and 115-135℃,which shows that oil and gas are continuously filled.The history and evolution of reservoir formation shows that the main filling period of Chang 8 oil is 110-135 Ma,during which the early filling in late Jurassic and large-scale filling in early Cretaceous occurred.The source rocks of Chang 7 in the region are mainly developed,and the Ro value is close to 1.0%in the maximum hydrocarbon generation and expulsion stage,reaching the hydrocarbon generation threshold and generating a large number of hydrocarbons.The source rocks of Chang 9 are locally distributed in Zhidan area.[Conclusions]Combining the characteristics of inclusions with the formation of hydrocarbons,the Chang 8 reservoir in Northern Shaanxi is controlled by factors such as source rock,reservoir and hydrocarbon charging.The oil filling degree is different,and the lithologic reservoir is developed differently,which shows two sets of source rocks hydrocarbon supply and differential accumulation.