准噶尔盆地永进油田西山窑组油藏成岩演化及成藏史

Diagenetic Evolution and Hydrocarbon Accumulation History in Reservoirs of Xishanyao Formation in Yongjin Oilfield,Junggar Basin

准噶尔盆地腹部永进油田中侏罗统西山窑组埋深为5600~6400 m,为深层—超深层低孔低渗储集层。为揭示储集层致密化过程及其与油气成藏的关系,通过岩心观察、铸体薄片鉴定、流体包裹体分析、沥青荧光颜色分析等手段,分析了中侏罗统西山窑组储集层特征、成岩作用、成岩演化序列和油气充注史。研究结果表明,永进油田西山窑组经历了3期成岩—油气充注过程,每期成岩作用均因一期油气充注而终止;第一期充注的原油在构造抬升过程中遭受氧化,生成大量碳质沥青占据孔隙;第二期成岩作用末期发生大规模油气充注,形成超压油藏,油气充注抑制了储集层胶结减孔作用,溶解早期孔隙中充填的碳质沥青增加储集层空间,是油气成藏及储集层物性改善和保持的关键期,该期所成油藏是永进油田主要的勘探目标;第三期成岩作用,地层快速深埋压实,储集层物性变差,该期有少量高成熟油气充注。

The Middle Jurassic Xishanyao formation in Yongjin oilfield is generally 5600 m to 6400 m deep in the hinterland of the Jung⁃gar basin,where the reservoirs are deep and ultra⁃deep ones with low porosity and low permeability.In order to reveal the relationship be⁃tween the process of reservoir densification and hydrocarbon accumulation,the reservoir characteristics,diagenesis,diagenetic evolution se⁃quence and hydrocarbon accumulation history of the Middle Jurassic Xishanyao formation were analyzed through core observation,casting thin section identification,fluid inclusion and asphalt fluorescent color analysis.The results show that the Xishanyao formation has under⁃gone three stages of diagenesis-hydrocarbon charging,and each stage of diagenesis was terminated with hydrocarbon charging.The oil charged in the first stage was oxidized in the process of tectonic uplifting,and a large amount of carbonaceous asphalt was generated and oc⁃cupied reservoir pores.At the end of the second stage of diagenesis,large⁃scale hydrocarbon charging took place,resulting in overpressure reservoirs.Hydrocarbon charging obviously inhibited reservoir cementation and pore reduction,dissolved the carbonaceous asphalt in the early pores and increased the reservoir space.That’s the key process of hydrocarbon accumulation and improvement and maintenance of reservoir physical properties.Reservoirs formed in the stage is the primary exploration target in Yongjin oilfield.In the third stage of diagen⁃esis,rapid burying and compaction further worsened the reservoir physical properties,so that only a small amount of highly mature oil and gas accumulated in the stage.