Differential diagenetic characteristics and its reservoir formation effect of tight sandstone in the Benxi-Lower Shihezi formations in Jiaxian area,Ordos Basin
To address the geological challenges in tight sandstone gas exploration in Jiaxian area of the Ordos Ba-sin,this study aims to reveal the relationship between differential diagenetic processes and reservoir quality,us-ing a combination of thin section observations,scanning electron microscopy analysis,X-ray diffraction,and flu-id inclusion petrography.Detailed comparisons of reservoir characteristics and differential diagenetic types and features were made among different stratigraphic layers,ultimately establishing a differential diagenetic model for the Jiaxian area.The results indicate that the He 8 section of Lower Shihezi Formation to Benxi Formation reservoirs have experienced intense compaction,two episodes of cementation,and two episodes of dissolution.Compaction is identified as the primary factor contributing to reservoir tightness,while dissolution significantly improves reservoir quality.The intensity and sequence of diagenetic processes vary among different stratigraphic layers.The Shan 2 Member and Benxi Formation,as the lowermost part of the coal-bearing series and in close proximity to the source rocks,have undergone two episodes of dissolution,leading to secondary porosity devel-opment.The Taiyuan Formation consists of multiple thick layers of mudstone and limestone,which consume some acidic diagenetic fluids,resulting in a slightly weaker dissolution intensity.The He 8 Member of the Low-er Shihezi Formation has undergone intense compaction and two episodes of cementation,with primary porosity mostly filled and limited development of secondary dissolution due to its distant proximity to the source rocks,resulting in overall poor reservoir properties.Understanding the differential diagenetic characteristics and their relationship with reservoir quality in tight reservoirs is of great practical significance for identifying favorable ar-eas for exploration and production.
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