Alternative Approaches for Transient-Flow Laboratory-Scale Permeametry

Abstract

Although pressure-pulse-decay permeametry has been in wide use for the past 50 years, its standard configuration and design have remained largely intact. To date, almost all implementations of this approach involve the analysis of a pressure response, in either an upstream or downstream reservoir or both, to a disturbance applied to one of the planar faces of a cylindrical sample, which induces a unidirectional flow along its axial coordinate. For characterizing ultra-low permeability materials like shales or caprocks, where this methodology often becomes problematic, many have turned to unsteady-state analyses on crushed particles. A paucity of models exists in the public literature for the latter scenario, most of which are analytical approximations of very simple cases. This study addresses both issues by proposing analytical flow models for alternative experimental schemes. First, new unidimensional flow scenarios are considered as substitutes for the classical pulse-decay techniques for core plugs. These models involve flow along the axial and radial directions of cylindrical core samples, which are shown to decrease testing times by a factor of 7.5 and 17.5, respectively, as compared to conventional pressure-pulse-decay strategies. Monte Carlo analyses are performed on these approaches, which demonstrate comparable accuracy and reliability to the conventional unidirectional strategy under realistic experimental conditions. Second, a model is presented that relaxes a key simplifying assumption inherent to publicly available models for crushed media, namely that the entire collection of particles is of uniform size. Rather, an analytical model for a discrete distribution of sizes is presented that more accurately represents the broad range of particle sizes that are typically seen in crushed materials.