库车前陆盆地玉东地区白垩系油气成藏过程

Cretaceous hydrocarbon accumulation process in Yudong area,Kuqa foreland basin

利用流体包裹体岩相学观察和显微测温、定量荧光分析和盆地模拟技术,研究了库车前陆盆地玉东地区白垩系储集层油气成藏过程。结果表明,玉东地区经历了晚期油、气充注和后期调整富集。其成藏过程:(1)来自库车坳陷中侏罗统的湖相原油在距今4Ma时充注到玉东地区下白垩统储集层,充注量较少,形成的轻质油包裹体丰度较低,黄色荧光轻质油包裹体记录了该期原油充注;(2)来自库车坳陷中—下侏罗统的煤型天然气在距今3.5 Ma时充注进来,天然气对早期原油气洗,轻质组分溶解到天然气中形成次生凝析气,重质组分和沥青质富集残留,蓝白色荧光油包裹体和气烃包裹体记录了该期天然气充注;(3)随着天然气持续充注和库车组沉积晚期构造抬升,天然气与早期原油发生混合作用的同时,在浮力驱动下,向上运移,并在古近系膏泥岩盖层之下富集成藏,形成凝析气藏。现今气水界面位于深度为4 776 m处,该界面之下形成以凝析油、重质油和沥青质为主的残余油藏,残余油水界面位于深度4 798.5 m处,但残余油饱和度较低。

The hydrocarbon accumulation process of Cretaceous reservoirs in Yudong area,Kuqa foreland basin is investigated by petrographic observation and microthermometry of fluid inclusions,quantitative fluorescence analysis and basin modelling.The results show that Yudong area experienced the accumulation process of the late oil and gas charging as well as the later adjustment and enrichment as below:(1)The lacustrine crude oil sourced from Mid-Jurassic Kuqa depression was charged to the Cretaceous reservoirs in Yudong area at 4 Ma,and the charging volume is small,thus forming light oil inclusions with low abundance.This stage of crude oil charging was recorded by the yellowish-fluorescence light oil inclusions.(2)The coal-based natural gas sourced from the MidLower Jurassic Kuqa depression was charged in at about 3.5 Ma.The early crude oil was washed by the gas,and the light compounds were dissolved into natural gas to form the secondary condensate gas with residual heavy compounds and asphaltenes enriched.This stage of natural gas charging was recorded by the blueish fluorescence oil inclusions and gas hydrocarbon inclusions.(3)With the continuous charging of natural gas and the uplift event in the Late Kuqa Stage,natural gas was mixed with early crude oil,then migrated upwards by the buoyancy,and accumulated beneath the Paleogene gypsum mudstone cap to form a condensate gas reservoir with the current gas-water contact at 4 776 m.Below the gas-water contact,a residual reservoir was formed,mainly consisting of condensate oil,heavy oil and asphaltenes.The residual oil-water contact is located at 4798.5 m,presenting a low residual oil saturation.