Abstract: There exist many faults featuring by striped distribution and multiphase activity in Wuerxun sag. This study showed that the deep major faults acted as main passages of deep inorganic CO₂ migrating upward, which controlled the formation and distribution of CO₂ gas reser-voirs the matched relationship between the faulting activity period and the mass expulsion period of hydrocarbon from source rocks controlled the volume of petroleum accumulation into source rocks in Wuerxun sag. There are a great deal of oil and gas expulsed from Nantun source rocks followed by migration and accumulation along late and long-term inherited faults, because of good matched relationship between the second faulting activity period and expulsion period of hydrocarbon in the sag; the major faults extending longer in plane effected as main passages on oil and gas lateral migration in the sag the good vertical sealing faults controlled the accumulation and distribution in the sag;and good lateral sealing faults dominated the formation of faulted block trap, faulted nose trap and fault-screened trap in Wuerxun sag.

Key words: Wuerxun sag, fault, oil-gas reservoir, CO₂ well