Abstract
Recently, volcanic gas reservoirs in Yaoyingtai (腰英台) and Daerhan (达尔罕) tectonic belts in Changling (长岭) faulted depression of southeastern Songliao (松辽) basin have been discovered. Based on the compositions and isotopic values, the natural gas is characterized by high content of methane, low content of C2 +, and C1/C1–5 beyond 0.95. Also, the natural gas contains nonhydrocarbons including carbon dioxide with the content from 20% to 40% and minor amount of N2. Combined with the isotopic values, the natural gas is generated by humic kerogen and coal-derived type, but in Daerhan, the natural gas is probably mixed by oil type gas. From the measurement of lithology and fluid inclusions in volcanic rocks, the bitumen, liquid hydrocarbon, and gas hydrocarbon inclusions are present. Through the analysis of the single gas inclusion in volcanic reservoir, the content of carbon dioxide is low, so the carbon dioxide and hydrocarbon gas of the reservoirs are not accumulated at the same time. In addition, minor amount of bitumen in the reservoirs is formed by thermal evolution of the crude oils sourced from the Yingcheng (842557CE) Formation mudstones through the characterizations of the biomarkers. The distribution of homogenization temperatures presents two peaks, one with the liquid hydrocarbon filling stage, and the other with gas filling stage. However, in Daerhan tectonic belt, the second peak is gas and carbon dioxide mixed filling period probably. Combined with the homogenization temperatures of salt water inclusions, the oil and gas filling period is from Qingshankou (青山口) Formation to Nenjiang (嫩江) Formation in the research area. During the charging period, minor amount of inorganic carbon dioxide filled into the trap, but plenty of inorganic carbon dioxide from the end of Sifangtai (四方台) to Eogene periods was related with the structural movement.
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