Investigations on the methane and carbon dioxide sorption capacity of coals from the SW Upper Silesian Coal Basin, Czech Republic

High-pressure sorption experiments with methane (CH4) and carbon dioxide (CO2) were performed on coals from different mines in the SW Upper Silesian Basin in the Czech Republic. The coals were of high- to low-volatile bituminous rank, representing the late stage of catagenesis. The influence of different factors on the sorption capacity of these coals was evaluated by varying the experimental conditions. Excess sorption capacities of moisture-equilibrated coals ranged from 0.3 to 0.8 mmol/g daf for CH4 and from 0.8 to 12 mmol/g, daf for CO2. Excess sorption capacities of as-received (air dried) coals were on average 34% higher for CH4 and 17% higher for CO2 as compared to the moisture equilibrated state. Sorption capacity shows a weak positive correlation with coal rank and a negative correlation with temperature. The CO2/CH4 sorption capacity ratio is larger for moisture-equilibrated coal, while it decreases with increasing pressure as well as increasing coal rank. From the experimental data, correlations were derived between sorption capacity, and coal rank and temperature. These correlations were used to estimate the "static" variation of sorption capacity with coal seam depth. Estimated sorption capacities increase towards a maximum value between 600 and 1000 m depth, followed by a decrease due to the predominance of the temperature effect. Temperature and pressure data derived from the reconstructed (1D) burial history were used to calculate the "dynamic" variation of sorption capacity during basin evolution. These computations show that initial sorption capacity was significantly higher than the one estimated from present day pressure and temperature gradients. Uplift of coal seams resulted in under-saturation of the coal. (C) 2012 Elsevier B.V. All rights reserved.