A Rapid Laboratory Method for Matrix-Scale Permeability Characterisation in Tight Rocks

Abstract

A rapid laboratory method is presented for estimating gas permeability in tight, fine-grained rocks based on transient gas uptake following controlled pressure expansion between two connected cells. The technique operates under unconfined, isothermal conditions and enforces radial transport through an axially sealed core plug. Pressure-dependent apparent permeability and Klinkenberg-corrected permeability are derived directly from the pressure decay using analytical solutions and established relationships. Analysis was performed on a synthetic ceramic material and a suite of claystones. Method reliability is demonstrated by: (i) resolving fluid dynamic effects; (ii) reproducing published permeability and slip-flow behaviour in the rigid ceramic, serving as an internal benchmark; and (iii) capturing established maturity-related permeability trends in the claystones, supporting geological sensitivity. Klinkenberg-corrected permeability ranged between 10^–19 and 10^–21 m². Slip factors ranged between 1.4 and 9.3 MPa, corresponding to average transport radii of ~ 2–20 nm, smaller in the claystones than in the ceramic and consistent with pore-size measurements. For the ceramic, gas-specific Klinkenberg slopes followed the expected ordering based on kinetic diametre, consistent with classical slip-flow theory. In contrast, the claystones exhibited more complex gas-dependent behaviour: helium and hydrogen showed stronger slip enhancement, whereas methane, nitrogen, and argon deviated from simple slip flow. These deviations are primarily attributed to gas–solid interactions consistent with momentum accommodation behaviour, with methane exhibiting enhanced apparent transport that may reflect additional sorption-related processes. While not intended to replace high-precision permeability measurements under confinement, the proposed method provides a reproducible and physically consistent means of rapidly estimating matrix-scale transport properties in tight rocks. The method confers numerous advantages including simplicity, minimal hardware requirements, and the ability to resolve pressure and gas dependence, making it well suited for early-stage screening, analogue comparison, and resource-limited applications.