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<p>Bioturbation is the reworking of sediments by organisms, which can significantly modify the petrophysical properties of aquifers by introducing burrow-related macro-porosity and enhanced pore connectivity. Many sedimentary formations worldwide contain bioturbated intervals interbedded with less permeable or impermeable strata. Likewise, the Aruma Formation on the Arabian Shelf contains intervals of bioturbated strata with large, open centimetre-scale burrows. Although the geometric characterisation of these burrow networks is well documented, groundwater flow modelling in these aquifers remains poorly understood. The formation contains intervals of intensely bioturbated limestone characterised by large, open, and well-connected burrows, providing an ideal natural analogue to investigate flow behaviour in such systems. This study presents an integrated approach combining high-resolution computed tomography (CT) scans with multi-scale computational fluid dynamics (CFD) modelling to investigate groundwater flow in a bioturbated limestone sample. First, three-dimensional models of connected burrow networks were reconstructed from CT scan images at three different scales. The steady-state single-phase flow was simulated using the Darcy’s Law and the Laminar Flow (Navier–Stokes) interfaces in COMSOL Multiphysics. The Darcy interface results yielded constant permeability values with a linear velocity–pressure relationship across all three scale models, whereas the Laminar Flow results showed strong nonlinearity and yielded varying permeability values across the tested pressure range. High Reynolds number values were observed in the Laminar Flow results, reaching approximately 355 for the small model, 111 for the intermediate model, and 123 for the large model. These results suggest that inertial effects arise at very low driving pressures due to flow concentration within centimetre-scale burrow networks. Forchheimer analysis provided an excellent fit to the simulated data (R<sup>2</sup> ≥ 0.99), confirming that flow is governed by combined viscous and inertial losses rather than by purely viscous behaviour. This study demonstrates that bioturbation altered the hydraulic properties of a limestone rock by creating burrow-dominated systems in which Darcy’s law is not applicable. The findings also highlight the need to incorporate non-linear flow formulations into groundwater and reservoir models for bioturbated samples and to provide a robust framework for linking pore-scale geometry to flow behaviour in heterogeneous systems.</p>

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Scale dependent Forchheimer flow in bioturbated limestone characterised by CT imaging and multi scale CFD analysis

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年7月7日

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  • Ataur Rehman,
  • Marwan Fahs,
  • Husam Musa Baalousha

摘要

Bioturbation is the reworking of sediments by organisms, which can significantly modify the petrophysical properties of aquifers by introducing burrow-related macro-porosity and enhanced pore connectivity. Many sedimentary formations worldwide contain bioturbated intervals interbedded with less permeable or impermeable strata. Likewise, the Aruma Formation on the Arabian Shelf contains intervals of bioturbated strata with large, open centimetre-scale burrows. Although the geometric characterisation of these burrow networks is well documented, groundwater flow modelling in these aquifers remains poorly understood. The formation contains intervals of intensely bioturbated limestone characterised by large, open, and well-connected burrows, providing an ideal natural analogue to investigate flow behaviour in such systems. This study presents an integrated approach combining high-resolution computed tomography (CT) scans with multi-scale computational fluid dynamics (CFD) modelling to investigate groundwater flow in a bioturbated limestone sample. First, three-dimensional models of connected burrow networks were reconstructed from CT scan images at three different scales. The steady-state single-phase flow was simulated using the Darcy’s Law and the Laminar Flow (Navier–Stokes) interfaces in COMSOL Multiphysics. The Darcy interface results yielded constant permeability values with a linear velocity–pressure relationship across all three scale models, whereas the Laminar Flow results showed strong nonlinearity and yielded varying permeability values across the tested pressure range. High Reynolds number values were observed in the Laminar Flow results, reaching approximately 355 for the small model, 111 for the intermediate model, and 123 for the large model. These results suggest that inertial effects arise at very low driving pressures due to flow concentration within centimetre-scale burrow networks. Forchheimer analysis provided an excellent fit to the simulated data (R2 ≥ 0.99), confirming that flow is governed by combined viscous and inertial losses rather than by purely viscous behaviour. This study demonstrates that bioturbation altered the hydraulic properties of a limestone rock by creating burrow-dominated systems in which Darcy’s law is not applicable. The findings also highlight the need to incorporate non-linear flow formulations into groundwater and reservoir models for bioturbated samples and to provide a robust framework for linking pore-scale geometry to flow behaviour in heterogeneous systems.