Evaluation of coal swelling‐controlled CO 2 diffusion processes

CO 2 sequestration in deep and unmineable coalbeds is regarded as a viable option for carbon storage. CO 2 diffusion is a key parameter determining the effectiveness of sealing CO 2 in coal seams. By conducting laboratory tests of coal CO 2 desorption and unsteady gas diffusion theory model calculations, the desorption dynamics of Yaojie coal were studied under the condition of constant temperature and varied balance pressures, and the CO 2 diffusion coefficient was obtained using the non‐steady diffusion model at different times. The results show that the higher the balance pressure is, the greater the diffusion coefficient is under the same conditions. As the pressure drops, the CO 2 diffusion coefficient gradually decreases as time increases, and the mass fraction of desorbed CO 2 has a linear relationship with the diffusion coefficient. It was observed that under high pressures, the diffusion coefficient initially increases and then gradually decreases. The non‐steady CO 2 diffusion in Yaojie coal is related to CO 2 ‐induced swelling and to the effect of dissolved CO 2 on the coal's structures and properties, especially under high‐pressure conditions. The glass transition of coal containing CO 2 may be the governing factor leading to the nonlinear diffusion of CO 2 in coal.