On the limitations of spot permeability measurements to quantify bulk permeability of bioturbated reservoirs: Insights from digital rock physics modeling

Substantial permeability contrasts between the fine-grained host rock matrix (HRM) and the coarse-grained burrow fillings (BF) are observed in bioturbated reservoirs, which are characterized by burrows that create a dual-porosity system. Consequently, assessing bulk permeability becomes particularly challenging, as these reservoirs often exhibit permeability contrast between HRM and BF spanning several orders of magnitude. To address this issue, the present study utilizes insights from digital rock physics modeling to critically examine the limitations of spot permeability measurements in accurately estimating bulk permeability in bioturbated systems. Specifically, we applied an integrated workflow to examine samples from a bioturbated interval in the upper Hanifa Formation in Saudi Arabia, incorporating spot permeability measurements, petrographic analysis, micro-CT scanning, pore network modeling, and permeability simulations to evaluate the effectiveness of spot permeability data in capturing bulk flow behavior. Our findings revealed that although spot permeability data are valuable for identifying localized permeability trends, they can be misleading when used to infer true bulk permeability, as they may fail to account for isolated or poorly connected pore systems. In particular, our results showed a significant discrepancy emerged between the CT scan data and spot measurements: while the CT imaging showed isolated and poorly connected pores within the burrow fillings—resulting in negligible flow during simulations—the spot measurements indicated substantially higher permeability values, ranging from 2.65 mD to 796.30 mD. This contrast underscores the complexity of relying on localized measurements to characterize bulk reservoir properties. Therefore, achieving more accurate permeability estimations in bioturbated reservoirs necessitates a comprehensive approach that integrates spot permeability data with high-resolution imaging and digital simulation techniques.