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Experimental measurement of adsorption-induced strains and stresses in coal

Adsorption of gases in mesoporous and microporous solids is important for applications in gas capture, gas separation, and gas sorption in sedimentary rocks.
Microporous solids exist in natural sources (e.g., coal, kerogen, zeolites, and gas hydrates) or are the product of synthetic processes (e.g. microcarbon and metal organic frameworks). The adsorption of fluid molecules in micropores can lead to their expansion or contraction depending on the pore size, geometry, and fluid-solid interaction. Macroscopically, sorption-driven changes of pore size or pressure upscale as strains if the solid is free to deform or stresses if strains are prescribed.
We show experimental evidence of strains and stresses developed by coal upon CO2 sorption and desorption.
Experimental measurements summarize data from coal specimens at several length scales including coal matrix, coal cores, and crushed granular coal. Results show that bulk strains and stresses depend on the degree of compactness of the rock, which can be assessed in terms of the ratio between the drained bulk modulus and the matrix bulk modulus. Compact coal cores with low porosity can develop adsorption stresses of several tens of MPa.
Understanding the adsorption-induced strains and stresses in coal is critical for predictable and enhanced coal bed methane production.

Author(s):

D. Nicolas Espinoza    
The University of Texas at Austin
United States

Matthieu Vandamme    
Université Paris-Est, Laboratoire Navier (UMR 8205), ENPC, CNRS, IFSTTAR
France

Jean-Michel Pereira    
Université Paris-Est, Laboratoire Navier (UMR 8205), ENPC, CNRS, IFSTTAR
France

Patrick Dangla    
Université Paris-Est, Laboratoire Navier (UMR 8205), ENPC, CNRS, IFSTTAR
France