GEOCHEMISTRY AND ORIGIN OF NATURAL GASES IN XINGCHENG AREA OF DAQING, HEILONGJIANG PROVINCE

The natural gases in Xingcheng area of Daqing, Heilongjiang Province consist of hydrocarbon, CO₂, N₂, H₂, He etc, among which the hydrocarbon, especially the CH4 is the dominating component. The carbon isotopes of the natural gases are commonly heavy and most of the hydrocarbon series are abnormal, which are characteristics of in organic hydrocarbon gases. The chemical composition and isotopes of CO₂ and He gases show that mantle-derived gases exist in the area. Together with the geological setting of Xingcheng area, it is considered that inorganic matter occurs in both non-hydrocarbon and hydrocarbon gases in the area, showing mixed natural gases of organic and in organic origin. The inorganic gases are mainly caused by magmatism and volcanism.