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

Authors: Thomas A. Dewers; Jason Heath; Russ Ewy; Luca Duranti

Addresses: Geomechanics Department, Sandia National Laboratories, Albuquerque, New Mexico, 87185, USA. ' Geophysics and Atmospheric Sciences Department, Sandia National Laboratories, Albuquerque, New Mexico, 87185, USA. ' Chevron Energy Technology Company, San Ramon, California, 94583, USA. ' Chevron Energy Technology Company, San Ramon, California, 94583, USA

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 formation; Haynesville formation; 3D pore networks; focused ion beam; FIB serial imaging; transport properties; mudstone properties; image analysis; pore properties; topology; tortuosity; pore morphologies; capillary pressure; computational fluid dynamics; CFD; modelling; permeability; clay matrix.

DOI: 10.1504/IJOGCT.2012.046322

International Journal of Oil, Gas and Coal Technology, 2012 Vol.5 No.2/3, pp.229 - 248

Available online: 03 Apr 2012 *

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