Optimization of pore-network characterization of a compacted clay material by TEM and FIB/SEM imaging

In clay-rich sedimentary rocks, the pore network is considered to play a key role in controlling transport properties. The pore size distribution (PSD) of clay-rich rocks, the geometrical features of the pore network, and the clay content are parameters governing the diffusion process through clay formations. In the last few years, research has contributed to improving understanding of some clay-rich rock pore networks by using microscopic imaging techniques (FIB-nt, BIB, X-ray tomography, etc.). These techniques image the mesostructure scale organization of clay materials, but the studies have highlighted several limitations for full pore distribution characterization in terms of geometry and connectivity. Here we demonstrate that we can characterize a clay material's pore network supported by FIB-nt and TEM techniques reliably, to provide useful input data for assessing a future modeling task. The material studied was a compacted clay material mainly composed of illite, a non-swelling mineral. Illite was chosen in order to represent an analog system mimicking the clay matrix of natural clay-rocks. With this compacted clay plug we were able to work on homogeneous systems with controlled porosity, facilitating comparison between different methods. All the techniques used in this work, whether bulk or microscopic, show that all results converge to a similar and full PSD. This project's main improvement was to demonstrate how to improve the usual resolution limitations and data handling of FIB-nt techniques in order to recognize a fully connected pore network. (C) 2015 The Authors. Published by Elsevier Inc.