Understanding fluid transport through the multiscale pore network of a natural shale

¹ Laboratoire de Mécanique de Lille (LML), FRE CNRS 3723 and Ecole Centrale de Lille, CS 20048, F-59651, Villeneuve d’Ascq Cedex, France
² Metis UMR CNRS 7619, UPMC, Paris, France
³ Changzhou Institute of Technology, Chang Zhou Gong Xue Yuan, Changzhou Shi, Jiangsu Sheng, China, 213000
⁴ Institut d’Electronique, de MicroElectronique et de Nanotechnologie (IEMN), UMR CNRS 8520, BP60069, 59652 Villeneuve d’Ascq, France
⁵ Unité Matériaux et Transformations (UMET), UMR CNRS 8207, Université Lille 1, Bâtiment C6, 59655 Villeneuve d’Ascq, France

^* Corresponding author: catherine.davy@centralelille.fr

Published online: 30 June 2017

Abstract

The pore structure of a natural shale is obtained by three imaging means. Micro-tomography results are extended to provide the spatial arrangement of the minerals and pores present at a voxel size of 700 nm (the macroscopic scale). FIB/SEM provides a 3D representation of the porous clay matrix on the so-called mesoscopic scale (10-20 nm); a connected pore network, devoid of cracks, is obtained for two samples out of five, while the pore network is connected through cracks for two other samples out of five. Transmission Electron Microscopy (TEM) is used to visualize the pore space with a typical pixel size of less than 1 nm and a porosity ranging from 0.12 to 0.25. On this scale, in the absence of 3D images, the pore structure is reconstructed by using a classical technique, which is based on truncated Gaussian fields. Permeability calculations are performed with the Lattice Boltzmann Method on the nanoscale, on the mesoscale, and on the combination of the two. Upscaling is finally done (by a finite volume approach) on the bigger macroscopic scale. Calculations show that, in the absence of cracks, the contribution of the nanoscale pore structure on the overall permeability is similar to that of the mesoscale. Complementarily, the macroscopic permeability is measured on a centimetric sample with a neutral fluid (ethanol). The upscaled permeability on the macroscopic scale is in good agreement with the experimental results.