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.