Porosity and pore size distribution of shales: a case study of the Carynginia Formation, Perth Basin, Western Australia

The evaluation of the gas storage potential of shale reservoirs requires a good understanding of their pore network. Each of the laboratory techniques used for pore characterisation can be applied to a specific range of pore sizes; but if the lithology of the rock is known, usually one suitable method can be selected to investigate its pore system. Shales do not fall under any particular lithological classification and can have a wide range of minerals present, so a combination of at least two methods is typically recommended for a better understanding of their pore network. In the laboratory, the Low-Pressure Nitrogen Gas Adsorption (LP-N2-GA) technique is typically used to examine micropores and mesopores, and Mercury Injection Capillary Pressure (MICP) tests can identify pore throats larger than 3 nm. In contrast, a wider range of pore sizes in rock can be screened with Nuclear Magnetic Resonance (NMR), either in laboratory measurements made on cores or through well logging, provided that the pores are saturated with a fluid. The pore network of a set of shale core samples from the Carynginia Formation was investigated using a combination of laboratory methods. The cores were studied using the NMR, LP-N2-GA and MICP techniques, and the experimental porosity and pore size distribution results are presented. When NMR results were calibrated with MICP or LP-N2-GA measurements, then the pore size distribution of the shale samples studied could be estimated.

Pore Characterisation in Monodisperse Granular Assemblies

The micro-scale geometric arrangement of pores was quantitatively characterised for monodisperse granular assemblies, particularly in relation to pore volume distribution and pore orientation characteristics. Using physical experiments and numerical simulations, the pore volume distribution was uniquely described by the analytical k-gamma distribution function [1-2]. A pore orientation tensor was defined to determine the preferred orientation of individual pores. This was subsequently used to define a global orientation tensor that revealed an isotropic pore network for the monodisperse granular assemblies considered in this study. The global orientation tensor was analytically linked to the parameters defining the pore volume distribution.