The application of sorption hysteresis in nano-petrophysics using multiscale multiphysics network models

Abstract

Scanning electron microscopy (SEM) images of organic-rich mudrock (shale) samples show a wide distribution of pore sizes (commonly between 1nm and 1μm) and complex pore spatial configurations (Loucks et al., 2012). Pore size and pore connectivity are important parameters in that they have first order impact on macroscopic flow properties of a porous medium. However, given the significant difficulty in capturing multiscale pores within a single three-dimensional image, and the possible uncertainties in the existence or absence of original throats in an acquired image, it is imperative to explore indirect methods to quantify the pore structure. In this paper, we simulate sorption in heterogeneous pore network models and study sorption and permeability hysteresis analyses as indirect methods for rock characterization.Three network types are introduced to represent the multiscale pore topology of shale rocks; specifically: regular (type 1), series (type 2) and parallel (type 3). We conclude that, in appropriate size ranges, sorption hysteresis can distinguish the three types whereas permeability hysteresis can only separate parallel from series and regular. Furthermore, the simulations show that sorption hysteresis is sensitive to compaction/cementation (closing of throats) in all network types whereas permeability hysteresis is sensitive to the diagenesis in parallel networks only.