Abstract: Geochemical characteristics and genetic identification of low-grade coalbed methane are important foundations for
exploration targets. The origin of coalbed methane in Erlian Basin is discussed by dissecting the composition of gas and water in
coal-seam wells and the characteristics of carbon and hydrogen isotopes. The results show that methane content in coalbed methane
components is 93.41%, and the content of heavy hydrocarbons and carbon dioxide is low, indicating a typical dry gas. The carbon
isotope values of methane are between -62.5‰ and -60.1‰, and the hydrogen isotope values are between -275.1‰ and -270.2‰.
The carbon isotope values of carbon dioxide range from 5.1 to 6.2‰, suggesting that it is biogas. Coal bed water originated from
atmospheric precipitation, showing weak alkalinity and low salinity. The gas and water isotope characteristics of coalbed methane wells
indicate that about 97% of biogas in the study area was formed by carbon dioxide reduction. The biogas reservoir is an important
exploration target for coalbed methane in the Jiergalangtu depression. The suitable groundwater environment is a key factor in the
exploration targets.

Key words: Jiergalangtu depression, coalbed methane, isotope, biogas, carbon dioxide reduction