Gas Sorption and the Consequent Volumetric and Permeability Change of Coal I: Experimental

Abstract

Experimental and numerical investigations were conducted to study adsorption and desorption of pure and multicomponent gas on coal, and the sorption-induced volumetric strain and permeability change of the coal. This paper presents the experimental work. Using CO\(_2\), N\(_2\), and CO\(_2\) and N\(_2\) binary mixtures of different composition as injection gases, the measurements were conducted on a cylindrical composite coal core at varying pore pressures and constant effective confining pressure. Sorption was measured using a volumetric method. The initial and equilibrium system pressure and gas phase composition were measured. The total amount of adsorption and the composition of the adsorbed phase (for adsorption of binary gas mixtures) were calculated based on material balance. During the process of sorption, the volume of the core was monitored by recording the volume of the water in the confining pressure vessel. Sorption-induced strain was calculated as the ratio of the sorption-induced volumetric change to the initial volume of the core. After adsorption equilibrium was reached, the permeability of the core was measured based on the Darcy equation for gas flow. Sorption and permeability measurements were conducted for each test gas at first increasing and then decreasing pressures. Volumetric strain was only measured while pore pressure increased. To our knowledge, this is the first study measuring adsorption, volumetric strain, and permeability on the same piece of core with the same apparatus.