Abstract:

The deep interval of Lower Sha-Member 4 is characterized by producing condensate oil and gas in the Well Fengshen-1 area,the North Dongying zone,Bohai bay Basin.According to a comprehensive analysis of hydrocarbon gas composition,nitrogen content,gas carbon isotope,microfluorometric reservoir section and thermal simulation experiment,it is revealed that the gas in this area belongs to a type of crude-cracked gas,and that pyrobitumen generated by thermal alteration occurs widely in the reservoir pores.In combination with the geothermal history of the reservoir rocks and hydrocarbon generation history of the source rocks,it can be verified that a latest Paleogene(Es1)fossil oil-reservoir existed in the deep Sha-Member 4 sandstone-conglomerate body,the oil in which was thermally cracked from Neogene Minghuazhen to the present time(Nm-Q),resulting in the formation of a deep condensate gas reservoir.It is also found that a type of gas mixed by source-kerogen-cracked gas and oil-cracked gas occurs along the fossil oil-reservoir margin,such as the Well Fengshen-3 area,and that a lot of releasing microfractures in the reservoir rocks are the main factor to maintain a normal pressure system in the condensate gas reservoir.

Key words: carbon isotope, microfluorescence, pyrobitumen, oil-cracked gas, condensate gas reservoir, North Dongying zone, Jiyang Depression