Quantitative experimental investigation of CO2 enhancement of the desorption rate of adsorbed CH4 in coal

摘要

The injection of COsub2/sub into a coal seam can effectively improve the recovery efficiency of coalbed methane. Existing COsub2/sub-enhanced coalbed methane(ECBM) is mainly focused on improving the physical recovery efficiency of free CHsub4/sub. In macro experiments, it is difficult to simultaneously separate adsorbed CHsub4/sub and free CHsub4/sub; therefore, there are few studies on using COsub2/sub to improve the recovery efficiency of coal seams. In this study, the LF-NMR method was used to evaluate the transformation law of adsorbed and free CHsub4/sub during the COsub2/sub injection process, and the enhancement of adsorbed CHsub4/sub recovery efficiency using COsub2/sub was quantified. The results showed that adsorbed CHsub4/sub and free CHsub4/sub formed separate T 2 peaks, allowing them to be distinguished. The T 2 spectra of adsorbed CHsub4/sub (adsorbed on pore surfaces) were distributed between 0.01 and 2.247806 ms, whereas the T 2 spectrum of free CHsub4/sub (existing between the coal particles and the inner walls of sample cavities) were distributed between 15.702901 and 714.942899 ms. COsub2/sub injection increased the total desorption efficiency of adsorbed CHsub4/sub by 19.89%, the desorption efficiency of adsorbed CHsub4/sub per unit time by 14.108% and the amount of CHsub4/sub desorption per unit mass of coal by 35.23%. The results of the study demonstrate that COsub2/sub injection into a coal seam can significantly improve the recovery efficiency of adsorbed CHsub4/sub and shorten the CHsub4/sub desorption time; findings that are highly significant in relation to enhancing coalbed methane exploitation and COsub2/sub geological storage.