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<p>Porosity is a key parameter for assessing a reservoir’s potential to contain hydrocarbons, with diagenesis being the essential process that influences the development and changes of porosity. In this study, various experiments, including thin-section casting and identification, scanning electron microscopy, grain size analysis, high-pressure mercury intrusion, and Ro determination, were conducted to investigate the diagenetic processes and porosity evolution in the Chang 4 + 5 tight sandstone reservoirs in the Dingbian area. The findings reveal that the reservoir forms in the delta front subfacies, which is mainly composed of underwater distributary channels, interdistributary bays, and mouth bars. The sandstone exhibits a high level of textural maturity, characterized by good sorting and rounding, resulting in relatively high porosity and permeability, which makes it an excellent reservoir for oil and gas. Following intense compaction, the contact between rock particles has mostly shifted from point contact to line contact. Compaction is the main factor reducing porosity, accounting for 76.18% of the total porosity loss. Cementation has two stages: early dissolution and late carbonate cementation, which reduces porosity by 4.91%. As a result, primary pores become smaller, increasing the density of the reservoir. Further, dissolution acts as the primary process for enlarging pores, resulting in a 3.87% increase in porosity. This process has a dual impact; while it creates numerous secondary dissolution pores that increase reservoir porosity, it can also cause clay mineral plugging of pore throats during dissolution, thereby decreasing porosity and permeability. The diagenetic evolution of the Chang 4 + 5 reservoir comprises four stages: an early diagenetic stage A (compaction), stage B (early dissolution and cementation), stage A<sub>1</sub> (dissolution), and stage A<sub>2</sub> (carbonate cementation). This study yields critical insights into the coupling relationship between diagenesis and porosity evolution in delta front tight sandstones, thereby offering guidance for the exploration and evaluation of hydrocarbon resources in the Chang 4 + 5 formation and other analogous reservoirs.</p>

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Study on diagenesis and evolution of porosity in tight sandstone reservoirs

  • 期刊论文

  • 发表日期：

    2025年9月22日

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  • Taping He,
  • Yaoqi Zhou,
  • Zhenwei Zhang,
  • Huanyu Xie,
  • Gaixia Cui

摘要

Porosity is a key parameter for assessing a reservoir’s potential to contain hydrocarbons, with diagenesis being the essential process that influences the development and changes of porosity. In this study, various experiments, including thin-section casting and identification, scanning electron microscopy, grain size analysis, high-pressure mercury intrusion, and Ro determination, were conducted to investigate the diagenetic processes and porosity evolution in the Chang 4 + 5 tight sandstone reservoirs in the Dingbian area. The findings reveal that the reservoir forms in the delta front subfacies, which is mainly composed of underwater distributary channels, interdistributary bays, and mouth bars. The sandstone exhibits a high level of textural maturity, characterized by good sorting and rounding, resulting in relatively high porosity and permeability, which makes it an excellent reservoir for oil and gas. Following intense compaction, the contact between rock particles has mostly shifted from point contact to line contact. Compaction is the main factor reducing porosity, accounting for 76.18% of the total porosity loss. Cementation has two stages: early dissolution and late carbonate cementation, which reduces porosity by 4.91%. As a result, primary pores become smaller, increasing the density of the reservoir. Further, dissolution acts as the primary process for enlarging pores, resulting in a 3.87% increase in porosity. This process has a dual impact; while it creates numerous secondary dissolution pores that increase reservoir porosity, it can also cause clay mineral plugging of pore throats during dissolution, thereby decreasing porosity and permeability. The diagenetic evolution of the Chang 4 + 5 reservoir comprises four stages: an early diagenetic stage A (compaction), stage B (early dissolution and cementation), stage A1 (dissolution), and stage A2 (carbonate cementation). This study yields critical insights into the coupling relationship between diagenesis and porosity evolution in delta front tight sandstones, thereby offering guidance for the exploration and evaluation of hydrocarbon resources in the Chang 4 + 5 formation and other analogous reservoirs.