Abstract
Gas Sorption kinetics and hysteresis of coals is crucial for coalbed methane (CBM) resources assessment as well as carbon dioxide (CO2) sequestration potential evaluation in US coal formations. We experimentally studied the sorption kinetics and hysteresis of three different sorbing gases including nitrogen (N2), methane (CH4), and CO2 for Appalachian basin coals. Both experimental data and theoretical results showed that all tested coals have highest CO2 affinity compared to N2 and CH4. It was also found that the diffusion coefficient and equilibrium time are the two most important sorption kinetics parameters for defining gas sorption behaviors. Both diffusion coefficient and parameter k related to equilibrium time are highly gas type and pressure dependent. Sorption hysteresis in the tested coal samples not only gas type dependent but also controlled by pore structure and irreversible deformation of coal matrix due to sorption. We proposed a new theoretical approach to quantify the potential of gas sorption hysteresis by coupling the effects of diffusion coefficient and equilibrium time. Based on the proposed approach, the results demonstrate CO2 has highest hysteresis which well agreed with the experimental results. High irreversibility at high pressure enhances the significant sorption hysteresis in CO2 sorption.
Published Version
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