Abstract: Volcanic activities are of important effects on the key factors for forming a hydrocarbon field such as hydrocarbon generation, migration, reservoir, trap, accumulation and preservation. Volcanic rocks shaped by a volcanic movement tend to occur vugs and fissures as spaces for hydrocarbon storage during rapid magma condensation; the volcanic debris deposits are characterized by expanding and dispersing in water, being either favorable to packing pores, and becoming good sealing caps, or to preservation of oil/gas fields by resisting destruction from new tectonic movements. In addition, volcanic activity can offer magma up to 1 020~1 200 9C and bring about thermal energy carried by hydrothermal fluid in temperature of 300 ~400 C, they have provided thermodynamic conditions for the hydrocarbon migration and accelerated such a migration. Volcanic activity also brings in both volcanic rock body and intrusive mass to a depositional basin and a nonstructural trap-volcanic lithologic trap to a petroliferous basin. All that shows volcanic activity is so closely related to the above six key factors that has formed a complete petroleum system, which have been reflected or supported from Jiyang depression and Huanghua depression in Bohai Bay basin.

Key words: volcanic action, petroleum, natural gas, sealing cap, oil and gas migration, oil and gas accumulation, reservoir preservation condition, oil and gas distribution