Effect of Coal Rank on Various Fluid Saturations Creating Mechanical Property Alterations Using Australian Coals

Abstract

During CO 2 sequestration in deep coal seams, the coal mass may be subjected to various fluid (CO 2 , N 2 , 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 CO 2 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 N 2 saturations compared to CO 2 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 N 2 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 CO 2 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, N 2 saturation slightly enhances coal strength and delays crack propagation in coal and this strength enhancement can be improved by increasing the N 2 saturation pressure.

Effects of Water and Brine Saturation on Mechanical Property Alterations of Brown Coal

“…The mechanical properties of coal mass have been shown to have great influences on coal mining as well as coal seam gas extraction [2][3][4][5]. Many kinds of accidents can happen during coal mining process, among which coal mine outburst is one of the most catastrophic phenomena.…”

“…Many kinds of accidents can happen during coal mining process, among which coal mine outburst is one of the most catastrophic phenomena. Large volumes of CO 2 and/or CH 4 burst out suddenly and violently into coal workings due to strong stress relief, frequently resulting in heavy casualties and serious economic losses. In general, three main factors contribute to coal mine outburst, including stress condition, gas content and physic-mechanical properties of the coal mass [2,[6][7][8], of which the mechanical properties of the coal mass is the key factor affecting outburst accidents.…”

“…In general, three main factors contribute to coal mine outburst, including stress condition, gas content and physic-mechanical properties of the coal mass [2,[6][7][8], of which the mechanical properties of the coal mass is the key factor affecting outburst accidents. One of the most vital factors that determine coal mass strength is the adsorbate type and content in coal as coal may become weaker with the existence of a more reactive potential adsorbate [4].…”

“…The relatively clean-burning nature of CBM has drawn much attention for its potential to provide energy source to a world in need of clean energy supplies. Enhanced coalbed methane (ECBM) technology, which implemented by injecting CO 2 (CO 2 -ECBM) or N 2 (N 2 -ECBM) or flue gas into the coal seam to replace the adsorbed CH 4 , has become a promising technique to recover CBM, with less environmental pollution and higher recovery rates and CO 2 -ECBM has the additional benefit of immobilizing large amounts of CO 2 , which is the main greenhouse gas responsible for global warming [9,10]. However, during this process, the adsorption/desorption of gas/fluids create significant changes in the mechanical properties of coal mass.…”

“…To date, the effects of adsorbates on coal strength changes have received considerable attention in the research literature [3][4][5][11][12][13]. Coal mass mechanical properties can be weakened by the adsorption of a more chemically reactive adsorbate.…”