A New Coal-Permeability Model: Internal Swelling Stress and Fracture–Matrix Interaction

We have developed a new coal-permeability model for uniaxial strain and constant confining-stress conditions. The model is unique in that it explicitly considers fracture–matrix interaction during coal-deformation processes and is based on a newly proposed internal swelling stress concept. This conc...

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Bibliographic Details
Published in:Transport in porous media 2010-03, Vol.82 (1), p.157-171
Main Authors: Liu, Hui-Hai, Rutqvist, Jonny
Format: Article
Language:English
Subjects:
Apertures
Basins
Civil Engineering
Classical and Continuum Physics
Coal
Coal transport
Deformation
Earth and Environmental Science
Earth Sciences
Fracture mechanics
Fractures
Geotechnical Engineering & Applied Earth Sciences
Hydrogeology
Hydrology/Water Resources
Industrial Chemistry/Chemical Engineering
Laboratory tests
Model testing
Permeability
Shrinkage
Strain
Stresses
Swelling
Transport
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Summary:We have developed a new coal-permeability model for uniaxial strain and constant confining-stress conditions. The model is unique in that it explicitly considers fracture–matrix interaction during coal-deformation processes and is based on a newly proposed internal swelling stress concept. This concept is used to account for the impact of matrix swelling (or shrinkage) on fracture-aperture changes resulting from partial separation of matrix blocks by fractures that do not completely cut through the whole matrix. The proposed permeability model is evaluated using data from three Valencia Canyon coalbed wells in the San Juan Basin, where increased permeability has been observed during CH 4 gas production, as well as using published data from laboratory tests. Model results are generally in good agreement with observed permeability changes. The importance of fracture–matrix interaction in determining coal permeability, demonstrated in this study using relatively simple stress conditions, underscores the need for a dual-continuum (fracture and matrix) mechanical approach to rigorously capture coal-deformation processes under complex stress conditions, as well as the coupled flow and transport processes in coal seams.
ISSN:0169-3913
1573-1634
DOI:10.1007/s11242-009-9442-x