There developed three petroleum systems in the Gaoyou Sag

Subei Basin

including the upper

the middle and the lower petroleum system.The deep reservoirs belong to the lower petroleum system.The basic characteristics of hydrocarbon accumulation and the key factors controlling the formation of deep reservoirs are studied.Hydrocarbon accumulation in the lower petroleum system features in “upper source rock-lower reservoir”.That is

hydrocarbons sourced from the upper E

1

f

2

migrated downward into the E

1

f

1

under abnormal high pressure.The E

1

f

1

reservoirs are mainly delta front sands with large volume but low porosity and low permeability.The result shows that development of the deep effective reservoir was controlled by sedimentary microfacies

burial depth and diagenesis as well as abnormal pressure and hydrocarbon charging.Underwater distributary channel and mouth bar are favorable sedimentary microfacies for effective reservoirs;The reservoirs are in the late diagenetic stage A1 and the secondary pores improved reservoir quality;The abnormal high pressure in the deep reservoirs is favorable for hydrocarbon charging

and the charging is earlier than sandstone densification

being conducive to reservoir space preservation.Among these factors

the favorable sedimentary microfacies and the development of secondary pore zone are the main factors controlling the development of deep effective reservoirs.