Isotopic characteristics and the origin of the coalbed methane in Tunlan minefield, Xishan coalfield, Taiyuan

摘要

Few studies can be found on the origin of coalbed methane in Tunlan minefield of Xishan coalfield, Taiyuan, which leads to incomprehensive understanding of the overall characteristics of coalbed methane genesis in Xishan coalfield. Based on the chemical composition and isotope test data of 6 gas wells in Xishan coalfield, this paper discusses the origin of coalbed methane. The results show that the average volume fractions of methane, ethane, nitrogen, carbon dioxide and argon are 89.93%, 0.03%, 6.64%, 0.30% and 0.12%> respectively, and the values of carbon isotope and hydrogen isotope are -43.85%—41.3% and -238.27%—222.45%. carbon dioxide isotope value is-12.8%—6.0%. Data of chemical composition and isotopic test in Tunlan minefield shows that the coalbed methane has undergone secondary transformation, which is due to coal degradation. Secondary biogenic methane has been formed, which is the mixed genetic coalbed methane, and the secondary biogenic gas accounts for about 35%.