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<p>The carbonate succession of the Joyan Member of the Jaisalmer Basin, Rajasthan, offers valuable insights into the diagenetic evolution of Bajocian shallow-marine ramp systems. This study aims to assess the impact of diagenetic processes on key reservoir characteristics, especially porosity and permeability, which are critical for effective petroleum exploration. Detailed field investigations and petrographic analyses reveal that multiple diagenetic features significantly control reservoir quality within the basin. The Bajocian carbonates underwent diagenetic alteration in two distinct stages: eodiagenesis and mesodiagenesis, each associated with four key diagenetic settings: marine-phreatic, meteoric-vadose, meteoric-phreatic, and burial environments. The paragenetic evolution began during the eodiagenetic phase and was characterized by modifications within marine-phreatic and meteoric zones, particularly under vadose and phreatic conditions. The marine-phreatic stage is characterized by evidence of bioturbation (disturbance by organisms), micritization (fine-grain alteration), geopetal structures (sediment filling cavities), and the precipitation of marine cements such as isopachous fibrous calcite, syntaxial overgrowth, and botryoidal forms. In the meteoric-vadose zone, pendant calcite cement formation and dissolution are common. The meteoric-phreatic setting is marked by continued dissolution, neomorphism, and the precipitation of meteoric calcite cements, including syntaxial, granular, drusy, and blocky varieties. During mesodiagenesis, the Bajocian carbonates underwent burial diagenesis. Shallow burial diagenesis was characterized by mechanical compaction of allochems, pore-filling dolomite, silicification, and the development of calcite cements, including bladed, blocky, and poikilotopic forms. In contrast, deep burial diagenesis involved chemical compaction, enhanced dissolution, continued silicification, fracturing, calcite vein formation, neomorphism, dolomitization, and extensive poikilotopic cementation. Bioturbation, micritization, cementation, silicification, compaction, calcite vein formation, and neomorphism collectively reduce reservoir quality by decreasing porosity and permeability. In contrast, dolomitization, dissolution, and fracturing exert only a limited positive influence. Porosity in the Bajocian carbonates is predominantly diagenetic, comprising interparticle, intraparticle, shelter, moldic, fracture, and vuggy indicating a reservoir system strongly governed by diagenetic alterations. This study highlights the critical role of diagenetic processes in shaping reservoir characteristics. It provides a valuable framework for understanding similar carbonate systems globally and guiding hydrocarbon exploration in the Jaisalmer Basin.</p>

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Diagenetic pathways and reservoir quality of a Bajocian shallow-water carbonate ramp: an example from the Joyan Member of Jaisalmer Basin, Western Rajasthan, India

  • 期刊论文

  • 发表日期：

    2025年11月2日

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  • Aashna Javed,
  • M. A. Quasim,
  • B. P. Singh,
  • K. F. Khan

摘要

The carbonate succession of the Joyan Member of the Jaisalmer Basin, Rajasthan, offers valuable insights into the diagenetic evolution of Bajocian shallow-marine ramp systems. This study aims to assess the impact of diagenetic processes on key reservoir characteristics, especially porosity and permeability, which are critical for effective petroleum exploration. Detailed field investigations and petrographic analyses reveal that multiple diagenetic features significantly control reservoir quality within the basin. The Bajocian carbonates underwent diagenetic alteration in two distinct stages: eodiagenesis and mesodiagenesis, each associated with four key diagenetic settings: marine-phreatic, meteoric-vadose, meteoric-phreatic, and burial environments. The paragenetic evolution began during the eodiagenetic phase and was characterized by modifications within marine-phreatic and meteoric zones, particularly under vadose and phreatic conditions. The marine-phreatic stage is characterized by evidence of bioturbation (disturbance by organisms), micritization (fine-grain alteration), geopetal structures (sediment filling cavities), and the precipitation of marine cements such as isopachous fibrous calcite, syntaxial overgrowth, and botryoidal forms. In the meteoric-vadose zone, pendant calcite cement formation and dissolution are common. The meteoric-phreatic setting is marked by continued dissolution, neomorphism, and the precipitation of meteoric calcite cements, including syntaxial, granular, drusy, and blocky varieties. During mesodiagenesis, the Bajocian carbonates underwent burial diagenesis. Shallow burial diagenesis was characterized by mechanical compaction of allochems, pore-filling dolomite, silicification, and the development of calcite cements, including bladed, blocky, and poikilotopic forms. In contrast, deep burial diagenesis involved chemical compaction, enhanced dissolution, continued silicification, fracturing, calcite vein formation, neomorphism, dolomitization, and extensive poikilotopic cementation. Bioturbation, micritization, cementation, silicification, compaction, calcite vein formation, and neomorphism collectively reduce reservoir quality by decreasing porosity and permeability. In contrast, dolomitization, dissolution, and fracturing exert only a limited positive influence. Porosity in the Bajocian carbonates is predominantly diagenetic, comprising interparticle, intraparticle, shelter, moldic, fracture, and vuggy indicating a reservoir system strongly governed by diagenetic alterations. This study highlights the critical role of diagenetic processes in shaping reservoir characteristics. It provides a valuable framework for understanding similar carbonate systems globally and guiding hydrocarbon exploration in the Jaisalmer Basin.