Diagenetic differential evolution of Huagang Formation sandstone reservoir in north-central part of central reversal structural belt in Xihu Sag

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    Huagang Formation sandstone has a great buried depth range in the north-central part of the central reversal structural belt in Xihu Sag,and different layers differ in reservoir quality. In virtue of the data such as mold thin sections,scanning electron microscopes(SEM),X-ray diffraction(XRD),and physical properties,this paper systematically analyzed the fundamental features and the diagenetic differential evolution of different layers of sandstone reservoirs by referring to the regional geological background and burial history. The study shows that the physical properties and pore types of Huagang Formation sandstone reservoirs are distinctly different above and below the vertical demarcation line with a buried depth of 4 100 m. The part above 4 100 m matches H3-H4 reservoirs,which are buried shallowly and relatively rich in volcanic rock debris. The weak compaction and pressure dissolution and the common chlorite coat jointly inhibit the secondary enlargement of quartz and effectively preserve the primary pores,providing conditions for later large-scale organic acid dissolution. As a result,both primary and secondary pores are well developed,and highly porous zones exist in the reservoirs.The part below 4 100 m mainly corresponds to H5-H6 reservoirs,which are buried deeply and rich in metamorphic rock debris. The poorly-developed chlorite coats fail to effectively inhibit the secondary enlargement of quartz. In addition,strong compaction and pressure dissolution result in the large loss of pores in the rapid burial stage,which is inconducive to the pore increasing by organic acid dissolution in the later stage. Exposed to the alkaline diagenetic environment for a long time,pores are filled by a large amount of authigenic mineral cement,which makes the reservoirs relatively dense.

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  • Online: June 21,2022
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