Abstract:

Study on inclusions and geochemical behaviors of gases from these inclusions in high-CO₂ reservoirs in the Songliao Basin shows that CO₂ inclusions are underdeveloped in the reservoirs and the geochemical behaviors of CO₂ from inclusions differ greatly with that from the reservoirs.The CO₂ from inclusions is of organic origin,while that from the reservoirs is of inorganic origin.However,the isotopic characteristics of hydrocarbon gases from gas pools and inclusions show certain consistency.The reasons behind all these include that the mantle-derived CO₂ charged too quickly to allow the growth of inclusions and that the reservoir rock was saturated by hydrocarbon gases before CO₂ charging,forming geological settings unfavorable for inclusion growth due to lack of water needed.Based on the geological settings of the Songliao Basin,it is suggested that CO₂ charging happened later than hydrocarbon gas charging.

Key words: inclusion, gas isotope, CO₂ genesis, Songliao Basin