Characteristics and Genesis of Permian Tight Sandstone Reservoirs in Southern Dagang Exploration Area
[Objective]Exploration of Permian sandstone in southern Dagang shows high-yield oil,but the reservoir characteristics and genetic mechanisms remain uncertain.[Methods]Core observations,thin-section identifications,cathodoluminescence analysis,scanning electron microscopy,fluid inclusion analysis,carbon and oxygen isotopic composition analysis,electron probe microanalysis,and in-situ laser ablation,coupled with the consideration of buri-al evolution history and hydrocarbon charging history,were used in this investigation into the deep-seated sandstone reservoirs in the Wangguantun and Wumaying regions of the southern Dagang exploration area.[Results and Discus-sions]It was found that the Permian sandstone in the southern Dagang region has a high compositional maturity,pre-dominantly characterized by quartz sandstone and sublithic sandstone.The storage spaces in high-quality reservoirs consist primarily of secondary intergranular pores and intercrystalline micropores in kaolinite.Influenced by tectonic movements,the reservoirs have undergone early open-system atmospheric-water leaching and dissolution,followed by late closed-system acid dissolution resulting from hydrocarbon source rock interactions.A range of factors influ-enced the development of high-quality reservoirs,with the high compositionally mature medium-to-coarse sandstones being the basic material.Early strata uplift and erosion,which led to significant secondary porosity from atmospheric fresh-water leaching,were critical factors.Early hydrocarbon charging inhibited by cementation processes favored the preservation of secondary porosity.[Conclusions]Reservoirs in the slope and depression zone that were formed in an area of atmospheric water leaching are appropriate exploration targets.This model is also relevant for pre-drilling pre-diction of Permian reservoirs in other regions of the Bohai Bay Basin.
genetic mechanismsdiagenetic evolutionsandstone reservoirsPermiansouthern Dagang exploration area
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