准噶尔盆地南缘芦草沟组云质岩储层致密化过程

Study on Densification Process of Dolomitic Reservoir of Lucaogou Formation in the South Margin of Junggar Basin

云质岩是准噶尔盆地芦草沟组重要的致密储油岩类型。通过对博格达地区芦草沟组云质岩的铸体薄片观察、显微荧光分析和孔洞中矿物充填序列的研究,探讨了白云岩储层的致密化过程,揭示了油气成藏与致密化间的匹配关系。结果表明,芦草沟组云质岩储层主要为孔洞型,孔洞中经过多期次油气和热液流体的充注,形成多个世代的矿物充填,从而使白云岩储层孔隙度降低、逐步致密。多期次的热液流体释放和充注可能与构造隆升造成的古油藏破坏密切相关。早期芦草沟组烃源岩排烃时白云岩储层并未致密;中期边致密边成藏,孔隙度有轻微降低;晚期油充注时白云岩开始致密,属于油气成藏过程中和油藏破坏过程中致密。

Dolomitic rock is an important type of tight oil reservoir rock in Lucaogou Formation of Junggar Basin.The densification process of dolomite reservoir and the matching relationship between oil and gas accumulation and densification are revealed through the observation of casting thin sections,micro fluorescence analysis and the study of mineral filling sequence in the pores of the dolomite in Lucaogou formation of Bogda area.The results show that the dolomite reservoir of Lucaogou formation is mainly pore type reservoir,and the pores are charged by hydrocarbon and hydrothermal fluid in multiples stages to form multi-generation mineral filling,which reduces the porosity of dolomite reservoir and gradually makes it densify.The multi-stage release and filling of hydrothermal fluid may be closely related to the damage of paleo reservoir caused by structural uplift.In the early stage,the dolomite reservoir is not dense when the source rock of Lucaogou formation discharges hydrocarbon;in the middle stage,the dolomite is gradually densify in the accumulation of hydrocarbon,and its porosity slightly decreases;in the late stage,the dolomite begins to densify when it is charged by oil,which belongs to the densification in the process of hydrocarbon accumulation and reservoir destruction.