Gas desorption characteristics and related mechanism analysis under the action of superheated steam and pressurized water based on an experimental study

Abstract As a kind of unconventional natural gas, efficient and clean energy, CBM (Coalbed methane) exhibits great potential in adjusting energy structure and formulating energy development strategy. Desorption of methane from coal is essential for CBM production. And the desorption characteristics of methane in coal under different conditions and how to improve the desorption capacity have always been a hot issue of interest to researchers. So, research in this aspect becomes urgent. In this study, a series of desorption experiments of coal samples with various particle sizes under different adsorption pressures were carried out and the influence mechanism of pressurized water and superheated steam on the desorption was analyzed. The results were as follows: 1) The gas desorption capacity is more influenced by the adsorption pressure than the particle size, the particle size mainly affects gas release rate of the desorption process. It can be found that the lower the adsorption pressure, the more obvious the enhancement effect of superheated steam on desorption. 2) The inhibition of desorption by water injection can be attributed to four inhibition mechanisms caused by water, i.e. Water blocking effect, Wetting effect, Capillary effect, and Jamin effect. 3) Superheated steam can provide the energy required for the desorption of methane, intensify the thermal movement of molecules, and can also carry and displace methane, which together increases the desorption capacity and effective diffusion coefficient of gas in coal. These research results can provide a theoretical basis for hydraulic measures and heat injection techniques related to on-site CBM extraction.