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<p>High-quality vuggy reservoirs have been developed in the Upper Carboniferous–Lower Permian Tahaqi Formation in the southwestern Tarim Basin piedmont area, following significant exploration breakthroughs. However, the unclear reservoir genesis has severely constrained exploration efficiency. Integrating petromineralogical data (drilling cores, thin sections, well logs), field outcrops, and geochemical analyses, this study reveals that Tahaqi Formation reservoirs are controlled by early diagenetic karst within a high-frequency sequence framework (instead of traditional weathering crust karst). The formation comprises two third-order sequences (SQ1–SQ2), with fourth-order sequences characterized by platform margin facies progradation. Typical early diagenetic karst markers (e.g., exposure surfaces, mottled brecciated limestones) in the highstand systems tracts of fourth-order sequences are confirmed by geochemical data. Three vertical karst sequence types are classified based on exposure duration and karst intensity. Moderate early diagenetic karstification is critical for high-quality reservoirs—thick oolitic shoals in the SQ2 highstand systems tract (Well Qiqian 2–Artux section) form favorable reservoirs via karst modification. Combined with the Carboniferous–Permian source-reservoir-caprock assemblage, favorable reservoir belts are predicted from the central study area to the Kashgar-Yecheng Sag, providing a key geological basis for reservoir prediction and risk exploration.</p>

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Karst characteristics during the early diagenetic stage and their influences on reservoirs: a case study of the Carboniferous–Permian Tahaqi Formation in the piedmont area of southwestern Tarim Basin

  • 期刊论文

  • 发表日期：

    2026年1月17日

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  • Guang Yang,
  • Zhen-Yu Wang,
  • Yun-Feng Zhang,
  • Hong-Ming Tang,
  • Xing-Zhi Wang

摘要

High-quality vuggy reservoirs have been developed in the Upper Carboniferous–Lower Permian Tahaqi Formation in the southwestern Tarim Basin piedmont area, following significant exploration breakthroughs. However, the unclear reservoir genesis has severely constrained exploration efficiency. Integrating petromineralogical data (drilling cores, thin sections, well logs), field outcrops, and geochemical analyses, this study reveals that Tahaqi Formation reservoirs are controlled by early diagenetic karst within a high-frequency sequence framework (instead of traditional weathering crust karst). The formation comprises two third-order sequences (SQ1–SQ2), with fourth-order sequences characterized by platform margin facies progradation. Typical early diagenetic karst markers (e.g., exposure surfaces, mottled brecciated limestones) in the highstand systems tracts of fourth-order sequences are confirmed by geochemical data. Three vertical karst sequence types are classified based on exposure duration and karst intensity. Moderate early diagenetic karstification is critical for high-quality reservoirs—thick oolitic shoals in the SQ2 highstand systems tract (Well Qiqian 2–Artux section) form favorable reservoirs via karst modification. Combined with the Carboniferous–Permian source-reservoir-caprock assemblage, favorable reservoir belts are predicted from the central study area to the Kashgar-Yecheng Sag, providing a key geological basis for reservoir prediction and risk exploration.