Effect of coal rank on CO2 adsorption induced coal matrix swelling with different CO2 properties and reservoir depths

A. S. Ranathunga, M. S.A. Perera, P. G. Ranjith, T. D. Rathnaweera, X. G. Zhang

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Although the greater adsorption potential of carbon dioxide (CO2) in coal is an appealing fact in relation to the long-term safe storage of CO2 in coal seams, the resulting coal structure modification, particularly through coal matrix swelling, adds several uncertainties to the process. To date, many studies have been initiated, particularly on the effects of injecting CO2 and reservoir properties on this swelling process and the associated reservoir permeability depletion. These influences are largely dependent on the maturity of the coal mass and its structure, including the cleat system. However, minor attention has been given to date to the effect of coal rank on CO2 adsorption-induced coal matrix swelling and was therefore investigated in the present study. The volumetric strain of the Australian brown coal samples for both CO2 and N2 under various confinements (triaxial) and injections was measured at 35 °C constant temperature to investigate the influence of CO2 properties and reservoir depth on CO2-adsorption-induced swelling in coal and was compared with the results in the literature to obtain the effect of coal rank. On the basis of the experimental evaluation of coal matrix swelling under various CO2 and reservoir conditions, supercritical CO2 adsorption leads to greater coal matrix swelling in coal, and the degree of swelling is dependent on reservoir depth and coal maturity. This coal matrix swelling reduces with increasing reservoir depth, due to the associated reduction in CO2 sorption capacity into coal. However, this also depends on the pore pressure conditions, and lower effective stresses leading to greater swelling reduction, regardless of coal rank. The potential of N2 to recover the swelled areas was tested by permeating the coal mass with N2 at different pressures and for different durations (24, 48, and 72 h). The results show a greater potential for recovery at lower effective stresses for any coal type and for longer durations of N2 flooding.

Original languageEnglish
Pages (from-to)5297-5305
Number of pages9
JournalEnergy and Fuels
Issue number5
Publication statusPublished - 18 May 2017

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