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<p>Current research on carbonate reservoir heterogeneity predominantly emphasizes macroscopic depositional facies, yet often lacks systematic analysis of microscale pore-fluid flow mechanisms. This study addresses this gap by integrating cast thin sections, capillary pressure curves, and depositional microfacies analysis to construct a quantitative core data–hydraulic flow unit (HFU) model for the Khasib Formation in Iraq’s B Oilfield. Using a normal probability distribution model, four distinct HFU types were identified: HFU-1 (High-Medium Energy Shoal), composed of arenaceous packstone, exhibits superior high-porosity and high-permeability characteristics resulting from dissolution of fibrous calcite cements; HFU-2 (High-Medium Energy Shoal and Medium-Low Energy Shoal), dominated by green algae–foraminifera assemblages, shows vertically enhanced pore connectivity with increasing bioclast abundance; HFU-3 (Medium-Low Energy Shoal/Back Shoal) displays patchy heterogeneity due to intense bioturbation, with permeability improvements confined to fault-conduit zones; and HFU-4 (Distal/Proximal), characterized by high micrite content and weak hydrodynamic energy, demonstrates the poorest reservoir quality. Results demonstrate that depositional facies (bioclast type and abundance) govern the primary pore structure, diagenetic dissolution (preferential removal of aragonite and high-magnesium calcite) enhances reservoir space, and tectonic activity (fault conduits) exerts a localized influence on permeability. Collectively, these factors drive a gradual reservoir-quality transition from high-energy shoal cores to low-energy margins. The findings offer practical guidance for predicting flow units in analogous carbonate reservoirs.</p>

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Sedimentological and diagenetic effects on hydraulic flow units of ramp carbonates: Khasib Formation, Mesopotamian Basin, Iraq

  • 期刊论文

  • 发表日期：

    2026年2月16日

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  • Ting Wu,
  • Zhongrong Mi,
  • Ahsan Mohammed Saeed,
  • Jianhua Qu,
  • Hui Liu,
  • Ahmed Saeb Rasheed,
  • Xinguo Duan,
  • Haiyue Li,
  • Quanzhen Li

摘要

Current research on carbonate reservoir heterogeneity predominantly emphasizes macroscopic depositional facies, yet often lacks systematic analysis of microscale pore-fluid flow mechanisms. This study addresses this gap by integrating cast thin sections, capillary pressure curves, and depositional microfacies analysis to construct a quantitative core data–hydraulic flow unit (HFU) model for the Khasib Formation in Iraq’s B Oilfield. Using a normal probability distribution model, four distinct HFU types were identified: HFU-1 (High-Medium Energy Shoal), composed of arenaceous packstone, exhibits superior high-porosity and high-permeability characteristics resulting from dissolution of fibrous calcite cements; HFU-2 (High-Medium Energy Shoal and Medium-Low Energy Shoal), dominated by green algae–foraminifera assemblages, shows vertically enhanced pore connectivity with increasing bioclast abundance; HFU-3 (Medium-Low Energy Shoal/Back Shoal) displays patchy heterogeneity due to intense bioturbation, with permeability improvements confined to fault-conduit zones; and HFU-4 (Distal/Proximal), characterized by high micrite content and weak hydrodynamic energy, demonstrates the poorest reservoir quality. Results demonstrate that depositional facies (bioclast type and abundance) govern the primary pore structure, diagenetic dissolution (preferential removal of aragonite and high-magnesium calcite) enhances reservoir space, and tectonic activity (fault conduits) exerts a localized influence on permeability. Collectively, these factors drive a gradual reservoir-quality transition from high-energy shoal cores to low-energy margins. The findings offer practical guidance for predicting flow units in analogous carbonate reservoirs.