Formation of carbon dioxide and hydrocarbon gas reservoirs in the Changling fault depression, Songliao Basin

Abstract On the basis of the research on the forming conditions and distribution of inorganic CO2 gas reservoirs and organic hydrocarbon gas reservoirs in the central uplift area of the Changling fault depression, the forming time, stage and sequence of the two gas reservoirs were studied and the pool-forming patterns were established by analyzing fluid inclusions and structural evolution. The organic gas is over-mature coal-derived gas, mainly from source rocks of the Yingcheng Formation, Shahezi Formation and Huoshiling Formation. Inorganic CO2 gas is mainly from mantle, secondarily from the degassing of volcanics. The distribution of gas-source fault systems and the degassing of mantle volcanos are the two main factors controlling the enrichment, migration and accumulation of inorganic CO2 gas reservoirs. The formation of hydrocarbon gas reservoirs is earlier than that of inorganic CO2 gas reservoirs, the former is 81(86 Ma during the depositional period of the Yaojia to early Nenjiang Formations, the latter is 28 Ma in the Late Paleogene. CO2 gas reservoirs mainly exist, alone or mixed with hydrocarbon gas, in the Yingcheng Formation volcanics, and the hydrocarbon gas reservoirs are on the top of the mixed gas reservoirs.