A number of mud volcanoes exist in the southern Junggar Basin. To date few systematic studies on natural gas geochemistry of mud volcanoes have been conducted in China. In June 1991 and August 2010, the authors invest...A number of mud volcanoes exist in the southern Junggar Basin. To date few systematic studies on natural gas geochemistry of mud volcanoes have been conducted in China. In June 1991 and August 2010, the authors investigated the mud volcanoes in the southern Junggar Basin twice, and the mud volcanism weakened gradually as seen from the variations such as the decrease of gas pressure and output, the downthrow and dry up of the mud pool. The volcanic intensity was significantly weaker than that in Taiwan. The natural gas from the mud volcanoes in the southern Junggar Basin has similar geochemical characteristics, indicating the same source or origin. The main component of the mud volcano gas is alkane gas with contents of 91.15%-97.49%, and the gas is high-quality commercial gas since methane dominates in the alkane. The 513C1 values are -49.1‰-0.6‰, which are in accordance with the peak δ3C1 frequency of mud volcano gas around the world, and the alkane gas displays positive carbon isotopic series, i.e., δ3C1〈δ3C2〈δ13C3, suggesting typical thermogenic origin. The helium in the mud volcano gas is typically crust-derived due to the low R/Ra values of 0.011-0.054. The mud volcano gas is coal-derived since the δ13C2 values are all greater than -28‰, and C1/C1-4 and δ13C1 values are in accordance with those of natural gas derived from the Lower-Middle Jurassic coal-measures. Therefore, alkane gas from mud volcanoes in the southern Junggar Basin is mainly sourced from the Lower-Middle Jurassic coal-measures.展开更多
文摘A number of mud volcanoes exist in the southern Junggar Basin. To date few systematic studies on natural gas geochemistry of mud volcanoes have been conducted in China. In June 1991 and August 2010, the authors investigated the mud volcanoes in the southern Junggar Basin twice, and the mud volcanism weakened gradually as seen from the variations such as the decrease of gas pressure and output, the downthrow and dry up of the mud pool. The volcanic intensity was significantly weaker than that in Taiwan. The natural gas from the mud volcanoes in the southern Junggar Basin has similar geochemical characteristics, indicating the same source or origin. The main component of the mud volcano gas is alkane gas with contents of 91.15%-97.49%, and the gas is high-quality commercial gas since methane dominates in the alkane. The 513C1 values are -49.1‰-0.6‰, which are in accordance with the peak δ3C1 frequency of mud volcano gas around the world, and the alkane gas displays positive carbon isotopic series, i.e., δ3C1〈δ3C2〈δ13C3, suggesting typical thermogenic origin. The helium in the mud volcano gas is typically crust-derived due to the low R/Ra values of 0.011-0.054. The mud volcano gas is coal-derived since the δ13C2 values are all greater than -28‰, and C1/C1-4 and δ13C1 values are in accordance with those of natural gas derived from the Lower-Middle Jurassic coal-measures. Therefore, alkane gas from mud volcanoes in the southern Junggar Basin is mainly sourced from the Lower-Middle Jurassic coal-measures.
