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Abstract
During CO2 sequestration in deep coal seams, the coal mass may be subjected to various fluid (CO2, N2, etc.) saturations. Therefore, in order to maintain the long-term integrity of the process, it is necessary to identify the mechanical responses of preferable coal seams for various fluid saturations. To date, many studies have focused on the CO2 saturation effect on coal mass strength and less consideration has been given to the influence of other saturation mediums. Hence, this study aims to investigate coal’s mechanical responses to water and N2 saturations compared to CO2 saturation and to determine the effect of coal-rank. A series of unconfined compressive strength (UCS) tests was conducted on Australian brown and black coal samples saturated with water and N2 at various saturation pressures. An advanced acoustic emission (AE) system was utilized to identify the changes in crack propagation behaviors under each condition. According to the results, both CO2 and water act similarly with coal by enhancing the ductile properties of the coal mass and this mechanical weakening is greater for high-rank coal. Conversely, N2 saturation slightly enhances coal strength and delays crack propagation in coal and this strength enhancement can be improved by increasing the N2 saturation pressure.
Highlights
The process of enhanced coal bed methane (ECBM) recovery is being implemented and tested as a viable option to store and reduce the amount of anthropogenic carbon dioxide (CO2 ) in the Earth’s atmosphere, as well as for the recovery of useful coal bed methane (CH4 ) gas [1,2,3,4,5,6,7]
Process involves introducing CO2 through injecting wells into deep coal seams and this CO2 acts as a displacing gas, which allows the already adsorbed CH4 to be desorbed from the coal matrix
According to Perera et al [15], Ranathunga et al [16] and Vishal et al [17], the inherent brittleness of the coal mass becomes ductile with the plasticization effect of coal with the adsorption of CO2, and this phenomena is higher for super-critical CO2
Summary
The process of enhanced coal bed methane (ECBM) recovery is being implemented and tested as a viable option to store and reduce the amount of anthropogenic carbon dioxide (CO2 ) in the Earth’s atmosphere, as well as for the recovery of useful coal bed methane (CH4 ) gas [1,2,3,4,5,6,7]. According to previous studies [1,2,3,6,8,9,10,11,12], this CO2 -ECBM process leads to CO2 adsorption-induced coal matrix alterations, which in turn affect its hydro-mechanical properties. According to Perera et al [15], Ranathunga et al [16] and Vishal et al [17], the inherent brittleness of the coal mass becomes ductile with the plasticization effect of coal with the adsorption of CO2 , and this phenomena is higher for super-critical CO2 (beyond the critical temperature of CO2 -31.8 ̋ C and the critical pressure of CO2 -7.38 MPa)
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