Permeability estimation using Poiseuille models: a case study on comparative analysis of characteristic radii in tight rocks.

Permeability, a fundamental petrophysical property controlling fluid flow in porous media, faces measurement challenges in tight rocks due to time-intensive procedures, specialized equipment requirements, and high costs. This study develops a novel Poiseuille-based methodology that systematically identifies optimal characteristic radii from routine mercury injection capillary pressure (MICP) data while revealing the underlying physical mechanisms. Seventeen characteristic pore throat radii were systematically evaluated from compiled datasets of tight sandstones, carbonates, and shales. Model performance, assessed by coefficient of determination (R2), yielded 0.96 for sandstones with Rc (critical radius at percolation threshold), 0.86 for carbonates with r60-r70 (radii at 60-70% mercury saturation), and 0.77 for shales with r5-r10 (radii at 5-10% saturation). These radii provide physical mechanisms beyond empirical fitting: Rc captures early percolation in preserved intergranular networks, r60 to r70 represents cumulative saturation needed for smaller throats to bridge isolated vugs and molds in heterogeneous carbonate systems, and r5 to r10 identifies the largest pores controlling nanoscale connectivity despite being least abundant. For tight reservoirs and CO2 storage projects where direct measurements are impractical, this approach enables rapid characterization using collapsed fragments or drilling cuttings when core recovery is limited, reducing evaluation costs through lithology-specific models.