Matrix shrinkage and swelling characteristics of European coals

AbstractMatrix deformation experiments have been performed on a range of different rank coals subjected to carbon dioxide and methane sorption at representative in situ reservoir pressures under unconfined conditions. These experiments were complemented by a set of simultaneous gas permeability and strain measurements. The results were related to coal rank and the mechanical and elastic properties of each coal type tested. The measured CO2 adsorption strains were consistently higher than those for methane, by a factor ranging between 1.3 and 4, depending on the coal type. The corresponding swelling coefficients were estimated in the range of 0.15 kg/ m3 to 1.0 kg/ m3 for methane and 0.25 kg/ m3 to 1.6 kg/ m3 for carbon dioxide. For the samples tested, matrix swelling due to CO2 adsorption displayed a positive correlation with coal rank and resulted in a significant decrease in permeability