Three-dimensional pore networks and transport properties of a shale gas formation determined from focused ion beam serial imaging

Abstract

Three-dimensional pore network reconstructions of mudstone properties are made using dual focused ion beam-scanning electron microscopy (FIB-SEM). Samples of Jurassic Haynesville Formation mudstone are examined with FIB-SEM and image analysis to determine pore properties, topology, and tortuosity. Resolvable pore morphologies (>~10 nm) include large slit-like pores between clay aggregates and smaller pores in strain shadows surrounding larger clastic grains. Mercury injection capillary pressure (MICP) data suggest a dominant 1-10 nm or less size of pores barely resolvable by FIB-SEM imaging. Computational fluid dynamics modelling is used to calculate single phase permeability of the larger pore networks on the order of a few nanodarcys (which compare favourably with core-scale permeability tests). This suggests a pore hierarchy wherein permeability may be limited by connected networks of inter-aggregate pores larger than about 20 nm, while MICP results reflect smaller connected networks of pores residing in the clay matrix. [Received: May 12, 2011; Accepted: September 14, 2011] Keywords: shale gas; Haynesville formation; pore networks; focused ion beam; FIB.Reference to this paper should be made as follows: Dewers, T.A., Heath, J., Ewy, R. and Duranti, L. (2012) 'Three-dimensional pore networks and transport properties of a shale gas formation determined from focused ion beam serial imaging ', Int. J. Oil, Gas and Coal Technology, Vol. 5, Nos. 2/3, 230 T.A. Dewers et al.Biographical notes: Thomas A. Dewers is a principal member of the technical staff in the Geomechanics Department at Sandia National Laboratories in Albuquerque, New Mexico. He has over 21 years experience in industry, academia, and government relating to work in the geosciences, and holds a PhD in Geology. His current research interests include nano-to-reservoir scale inquiries into rock mechanics, multiphase flow and reactive transport.Jason Heath is a senior member of the technical staff of the Geophysics and Atmospheric Sciences Department, Sandia National Laboratories, Albuquerque, New Mexico. He has a PhD and MS in Hydrology and Geology, respectively. His research focuses on efficiently estimating well injectivity for large-scale CO 2 storage projects, CO 2 -water-rock interactions, and caprock sealing behaviour.

Quantitative pore characterization and the relationship between pore distributions and organic matter in shale based on Nano-CT image analysis: A case study for a lacustrine shale reservoir in the Triassic Chang 7 member, Ordos Basin, China

“…These techniques (MIP þ LPA) provide quantitative and reproducible porosity data but cannot provide direct information of the actual pore geometry and their connectivity. Direct approaches, such as field emission scanning electron microscopy/transmission electron microscopy (FE-SEM/TEM) (Sondergeld et al, 2010;Loucks et al, 2009), focused ion beam scanning electron microscopy (FIB-SEM) (Curtis et al 2012b;Ma et al, 2015;Dewers et al, 2012;Keller et al, 2011) and smallangle neutron scattering (SANS) and ultra-small-angle neutron scattering (USANS) (Mastalerz et al, 2012;Clarkson et al, 2012a) have been successfully used to observe the shapes, sizes and distributions of pores in shale, and the anisotropy of the microstructure. These methods are intuitive and clear, but the sample heterogeneity and regional differences are ignored because the scanned area is usually tiny (Liu et al, 2011).…”

Simulation and visualization of the displacement between CO2 and formation fluids at pore-scale levels and its application to the recovery of shale gas

“…This method is time-consuming and expensive, but many studies have been performed on nanopore characterization using this method because of its accuracy. At present, FIB-SEM has become the mainstream tool for imaging nanopores (Keller et al 2011;Chalmers et al 2012a, b;Dewers et al 2012;Bai et al 2013). 3D images of shale are first obtained by the FIB-SEM device (Fig.…”

Pore-Scale Simulation and Sensitivity Analysis of Apparent Gas Permeability in Shale Matrix

“…Pore space connectivity is determined by the coordination number, which is a generalized mathematical parameter describing how well the pore spaces are inter-connected in porous media. The average coordination number for sandstone is around 4, and the coordination number decreases with the decrease in porosity [10,11,12,13]. For shale matrix, pore connectivity is relatively low [14], and many isolated pores can be observed from two-dimensional SEM images [3,4].…”