CBM and CO 2-ECBM related sorption processes in coal

Unconventional gas, such as shale gas, tight gas or coalbed methane is able to offer a new and attractive perspective for low-carbon fuel supply. Furthermore, they may provide possibilities for CO2-storage and coevally for enhanced gas recovery. This is suggested by theoretical considerations of displacing the adsorbed methane by a more strongly adsorbing gas such as CO2. Optimizing the development of these unconventional resources, while minimizing their environmental impact, requires a more fundamental understanding of the coupled physico-chemical processes involved. In order to better understand the interaction of gas and water with coal of different maturity, a measuring plan has been developed and executed. The general observation is that CO2 and CH4 sorption capacity of dry coals shows a parabolic trend with rank with a minimum between 1.1 and 1.3% vitrinite reflectance. The CH4 and CO2 sorption capacity of moist coals, in contrast, shows a linear increase with increasing maturity. The sorption capacity ratio of CO2 and CH4 for dry coals has an approximately constant ratio of 2 over the entire maturity range. For moist coals this ratio is higher at low maturity values and decreases to values around 2 with increasing maturity. The highest CO2 to CH4 sorption capacity ratios are observed at low surface coverage. Based on the literature review an extended measuring concept was developed to investigate the competitive interaction between sorbed water and gases such as CH4 and CO2. The determination of the required high-precision CO2 sorption isotherms is challenging because in the temperature and pressure range of interest (T=308-350K) the density of supercritical CO2 increases rapidly with increase pressure. To improve the reliability of the sorption measurements, an inter-laboratory comparison between different European research institutes has been conducted (Chapters 2 and 3). During the first inter-laboratory comparison the comparability between the manometric and the gravimetric sorption methods was ...