Matrix shrinkage and swelling characteristics of European coals

Abstract

Abstract Matrix 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 CO 2 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/ m 3 to 1.0 kg/ m 3 for methane and 0.25 kg/ m 3 to 1.6 kg/ m 3 for carbon dioxide. For the samples tested, matrix swelling due to CO 2 adsorption displayed a positive correlation with coal rank and resulted in a significant decrease in permeability.