Investigation of temperature effect on permeability of naturally fractured black coal for carbon dioxide movement: An experimental and numerical study

Abstract

Very deep coal seams which are unlikely to be mined may be considered for CO2 sequestration. The main objective of this study is to investigate the effect of temperature on the permeability of naturally fractured coal. Permeability tests were conducted on naturally fractured bituminous coal samples using high pressure triaxial equipment for five different injecting pressures (8–13MPa) under two different confinements (20 and 24MPa) and five different temperatures (25–70°C). The experimental data were then used to develop an appropriate numerical model using the COMET 3 simulator to model the temperature effect on permeability at temperatures up to 200°C. According to the measured permeability values and the developed lab-scale model, there is a clear increase in CO2 permeability with increasing temperature for any confining pressure at high injecting pressures (more then 10MPa). However, for low injecting pressures (less than 9MPa) temperature effect is not so much. With increasing injecting pressure, CO2 permeability decreases at low temperatures (less than around 40°C), and increases at high temperatures (more than 50°C). Interestingly, the temperature effect on permeability is significant only up to around 90°C condition within the 25–200°C temperature limit. These observations are related with the sorption behavior of the adsorbing CO2 during the injection. However, there is no noticeable temperature effect on N2 permeability as it does not create any swelling effect in coal matrix.