Abstract:

This study is focused on the Dongying formation in Nanpu sag. Based on the uniqueness of tectonic activity of the development period of Dongying formation, through the method of spatialtemporal comparison, it is determined that in late Paleogene, both the activity of boundary faults and the depression effect of the whole sag increased simultaneously. Under the combined control of ‘two important elements’ from the intense fault activity and the acceleration of basement subsidence, the subsidence center and depocenter both migrated away from the boundary faults and developed in the central of the sag, which resulted in the development of wide distribution of deep lacustrine facies in Dongying formation and accumulation of thick lacustrine mudstone and turbidity sandbodies. Meanwhile, a great deal of fan delta in the northern steep slope zone and braided river delta in the southern gentle slope zone deposited, which led to well developed and various reservoirs in Dongying formation. The extrathick Neogene strata caused source rocks reaching the threshold of hydrocarbon generation and hydrocarbon expulsion, which formed favorable selfgenerated and selfcontained combination. The tectonic movements during the Dongying formation deposition period and Neotectonic movements caused the activation of many synsedimentary faults and reactivation later. These faults effectively connected reservoir bodies with main hydrocarbon kitchen of Es3, Es2, and Es1 below and vertically transported the lower hydrocarbon to the reservoir bodies in Dongying formation or even shallower strata. All of these lead to the great potential of hydrocarbon exploration in Dongying formation.

Key words: the Nanpu Sag, Dongying Formation, extrathick deposition, high subsidence rate, intense faults activity, petroleum geological significance