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Sci Rep. 2018 Aug 3;8(1):11683. doi: 10.1038/s41598-018-30153-x.

Hierarchical integration of porosity in shales.

Author information

1
School of Earth and Environmental Sciences, The University of Manchester, Manchester, M13 9PL, UK. lin.ma@manchester.ac.uk.
2
Manchester X-ray Imaging Facility, School of Materials, The University of Manchester, Manchester, M13 9PL, UK. lin.ma@manchester.ac.uk.
3
Manchester X-ray Imaging Facility, School of Materials, The University of Manchester, Manchester, M13 9PL, UK.
4
School of Earth and Environmental Sciences, The University of Manchester, Manchester, M13 9PL, UK.
5
Research Complex at Harwell, Harwell Campus, Oxfordshire, OX11 0FA, UK.
6
Research Complex at Harwell, Harwell Campus, Oxfordshire, OX11 0FA, UK. peter.lee@ucl.ac.uk.
7
Department of Mechanical Engineering, University College London, London, WC1E 7JE, UK. peter.lee@ucl.ac.uk.

Abstract

Pore characterization in shales is challenging owing to the wide range of pore sizes and types present. Haynesville-Bossier shale (USA) was sampled as a typical clay-bearing siliceous, organic-rich, gas-mature shale and characterized over pore diameters ranging 2 nm to 3000 nm. Three advanced imaging techniques were utilized correlatively, including the application of Xe+ plasma focused ion beam scanning electron microscopy (plasma FIB or PFIB), complemented by the Ga+ FIB method which is now frequently used to characterise porosity and organic/inorganic phases, together with transmission electron microscope tomography of the nano-scale pores (voxel size 0.6 nm; resolution 1-2 nm). The three pore-size scales each contribute differently to the pore network. Those <10 nm (greatest number), 10 nm to 100 nm (best-connected hence controls transport properties), and >100 nm (greatest total volume hence determines fluid storativity). Four distinct pore types were found: intra-organic, organic-mineral interface, inter-mineral and intra-mineral pores were recognized, with characteristic geometries. The whole pore network comprises a globally-connected system between phyllosilicate mineral grains (diameter: 6-50 nm), and locally-clustered connected pores within porous organic matter (diameter: 200-800 nm). Integrated predictions of pore geometry, connectivity, and roles in controlling petrophysical properties were verified through experimental permeability measurements.

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