Three-dimensional carbon dioxide-induced strain distribution within a confined bituminous coal

Sequestration of carbon dioxide in unmineable coal seams is an option to reduce carbon dioxide emissions. It is well known that the interaction of carbon dioxide with unconfined coal induces swelling. This paper contributes three-dimensional strain distribution in confined coal at microstructural level using high-resolution X-ray computerized tomography data and image analysis. Swelling and compression/compaction of regions in the coal matrix occurs with CO₂ uptake. Normal strain varies between - 1.15% and 0.93%, - 3.11% and 0.94%, - 0.43% and 0.30% along x, y and z axes respectively. Volumetric strain varies between - 4.25% and 1.25%. The positive strains reported are consistent with typical range for unconstrained swelling. However, the average volumetric strains value (- 0.34%) reflect overall volume reduction. Overall swelling is apparently influenced by the confining stresses. The magnitudes of normal strains are heterogeneous and anisotropic. The swelling vs. compression/compaction observed after CO₂ uptake is localized and likely lithotype dependant.