Study on inclusions and geochemical behaviors of gases from these inclusions in high-CO

2

reservoirs in the Songliao Basin shows that CO

2

inclusions are underdeveloped in the reservoirs and the geochemical behaviors of CO

2

from inclusions differ greatly with that from the reservoirs.The CO

2

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 CO

2

charged too quickly to allow the growth of inclusions and that the reservoir rock was saturated by hydrocarbon gases before CO

2

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 CO

2

charging happened later than hydrocarbon gas charging.