科研之友
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摘要
To recognize the factors which controlled the deeply buried clastic reservoir quality and the distribution of effective reservoirs, the paper takes sandstone reservoirs of the Lower Jurassic Sangonghe Formation in Zhengshacun area, central Junggar Basin as an example for study. Based on the thin sections of core samples, scanning electron microscopy, carbon-oxygen isotopes (C-O isotopes), X-ray diffraction, porosity and permeability, the paper studies the characteristics of petrology and diagenesis of reservoirs, discusses the effects of diagenesis on different lithofacies, establishes the relationship between lithofacies and sedimentary microfacies. The results show that the sandstones of Sangonghe Formation are feldspathic litharenite, and the compositional maturity is really low. The authigenic minerals include carbonate cementation, authigenic clay minerals, anhydrite and siliceous cementation. It is generally a low-ultra-low porosity and permeability reservoir with strong heterogeneity. According to the difference of petrology and diagenesis, sandstones can be divided into three lithofacies: ductile-rich sandstone, calcite-cemented sandstone and ductile-lean sandstone. Different lithofacies undergoes different diagenesis. Ductile-rich sandstone is characterized by strong compaction, weak cementation and dissolution, while calcite-cemented sandstone is characterized by strong cementation, weak compaction and weak dissolution, and the type of sandstones densified during the early diagenesis. Ductile-lean sandstone is moderately compacted, weakly-moderately cemented and strongly dissolved. For the lower degree of compaction and cementation during the early diagenesis, it can not only retain more primary pores, but also be dissolved by acid fluid in the later deep burial, thus forming effective reservoir rocks with good porosity in deep layers. The distribution of different lithofacies is generally controlled by sedimentary microfacies, and ductile-lean sandstone with the best porosity mainly distributes in the middle and lower part of distributary channel or the middle and upper part of mouth bar. This distribution pattern will provide guidance for exploring deep effective reservoirs.
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