Geochemistry Characteristics of Methane in Soils and its Isotope of Carbon

This paper has reported primarily the carbon isotope composition of the methane in the soil of the oil/gas anomalous area and that of non-oil /gas area which are situated in arid and semi-arid environments of China. Geochemistry characteristics of methane and heavy hydrocarbons in soils and casbon isotope of the methane are discussed. The following conclusions are drawn: (1)Methane in soils one of important sources of "greenhouse effect" gas - methane. The soil in the arid northern China has good ability to preserve mehtane and heavy hydrocarbons concentration. In the south of China, climate condition make it easy for plant to grow. Because of abundant organic matter and strong biological activity in soils, a great quantity of methane of biological origin existed so it could be produced that a g. owing to poor preservation of methane, compared with that of the northern part of China, the soils in the sourth of China contributed more methane to the atmosphere. (2)Methane in soil of the oil/gas-bearing area is a mixture of methane produced by microbiology and by-migrating to the surface from the underground reservoirs in different proportion. Its contribution of methane to atmosphere is often greater than that of non-oil/gas area. (3)δ¹³C Values of methane in soil of oil/gas - bearing area are heavier than that of non-oil/gas - bearing, i. e. relatively rich in ¹³C. There are obvious differences of the δ¹³C Values of methane in soils between two different areas. (4)δ¹³C values of methane in soils become heavier because of the surface oxidization and other secondary fractionation. It is valid that the two origin types of methane in soils are judged by δ¹³C values of methane in soils in association with distribution characteristics of hydrocarbons.