Abstract:

Abstract: Based on a comprehensive analysis of gas accumulation conditions and temporalspatial combinations of accumulation elements,in this paper we make a study of enrichment pattern and main controlling factors of volcanic gas reservoirs in the Changling fault depression.The results show that gas pools are mainly distributed in the Yaoyingtai and Da’erhan structures in the low salient of central sag and the Shuanglong structure in the eastern slope belt.Volcanic tuff of explosive phase and rhyolite of overflow phase in the Yingcheng Formation are the most favorable reservoirs.The major controlling factors for gas accumulations are as follows:1)distribution of deep source rocks controls the oil and gas distribution in a macro way;2)volcanic rocks and their favorable reservoir facies control the development and distribution of gas pools;3)discordogenic faults are important conditions for the development of oil/gas pools;4)quality cap rocks and lateral seals determine the vertical distribution of gas;5)the early charged hydrocarbons get mixed with latergenerated CO2 when basement faults have good conductivity,leading to the formation of mixed gas pools with both organic and inorganic origins;6)favorable targets are compound traps formed by largescale inherent palaeohighs(palaeoslope),onlapping pinchouts and volcanic rocks