Analysis on terminologies related to coalbed methane

FU Xuehai; KANG Junqiang; CHEN Yilin; DUAN Chaochao; LU Jielin; ZHANG Baoxin

doi:10.13247/j.cnki.jcumt.20240106

Abstract：In coalbed methane(CBM)exploration and development reports,papers,and news,unstandardized terminologies were utilized,such as"coal rock gas",coalbed gas reservoirs,critical depth of gas content,highly saturated/supersaturated gas content,low/medium/high-rank CBM,and gas content of combustible base.The authors consulted relevant standards and textbooks to analyze those terminologies.It is believed that CBM is a hydrocarbon gas mainly composed of methane,and there is no low/medium/high rank CBM.The"coal rock gas"and"gas of coal seam"are actually CBM.The CBM is a continuous unconventional natural gas without traps,and is less affected by buoyancy and hydrodynamic force.There is no real gas-water interface and blocking condition,and rich areas or"sweet areas"can be found.A con-version depth occurs for adsorbed gas content,but not for total gas content.It is more scien-tifically to determine"deep regions"based on the critical depth of geostress,due to the chan-ges in mechanical state and fracturing fracture propagation direction.The adsorbed gas satura-tion cannot represent the total gas saturation,and the proportion of water-soluble gas and free gas in shallow low-rank coal reservoirs increases exponentially with the increasing equilibrium moisture content and porosity,respectively.As volatile matter and ash are the conversion products of the original components in coal under specific conditions,it is inappropriate to uti-lize volatile matter content and ash content,which should be replaced by volatile matter yield and ash yield.The results provide guidance for standardizing the CBM terminology and analy-zing the phase gas content.