According to analyses of the features and hydrocarbon generation history of Paleozoic source rocks

the Lower Paleozoic marine source rocks in North China are basically poor source rocks to non-source rocks due to their low organic matter abundance

though they have good kerogen type and large thickness;moreover

later burial history and thermal evolution history of source rocks are complex after the source rocks getting mature.Therefore exploration risk is high when taking them as the source rocks of a petroleum system.The Lower Paleozoic source rocks have medium to poor hydrocarbon generation potentials only in the southern part of Bohai Bay.After deeply buried in Himalayan

the Lower Paleozoic would be in condition to secondary hydrocarbon generation in Jiyang depression

Linqing depression

Dongpu sag and Huangkou sag

thus certain exploration potentials exist in these areas.The Upper Paleozoic Carboniferous-Permian source rocks are mainly coal measure strata

with thickness in the range of 150～500m

low to medium organic matter abundance

and type Ⅲ kerogen.Secondary hydrocarbon generation in Upper Paleozoic source rocks had occurred mainly at the end of Late Triassic and the end of Early Cretaceous

and hydrocarbons were well preserved

thus there would be large potentials for exploration of primary oil and gas reservoirs.The Upper Paleozoic favorable exploration areas are mainly in the Tertiary sags with large secondary gas generation intensity

such as Dongpu sag

Linnan sag

the southern part of Dezhou sag and the northern part of Xinxian sag in Bohai Bay basin.