Based on composite data of trap formation and evolution

hydrocarbon-generated and hydrocarbon-expulsed process

reservoir saturated pressure and fluid inclusion of diagenetic minerals

the accumulation phase of oil and gas reservoirs in Dongying sag have been divided into two phases

i.e. the late Oliocene phase and the late Miocene to Pliocene phase.Large oil and gas pools were accumulated in late Miocene to Pliocene

especially in the middle-late period deposited in Pilocene Minghuazhen Fm.The main petroleum accumulation phases varies in the oil and gas reservoirs in different stratigraphic horizons and different structural units.In general

it is relatively early in the lithologic pool enclosed in source rocks. There is a tendency for the main accumulation phase of oil and gas reservoirs to become late ordered stratigraphically from the bottom to the top and from the center area to the margin of Dongying sag.