The Formation And Evolution Of Fault System And Its Control On Basin Structure In The West Area Of Liaodong Bay Depression

The Liaodong Bay Depression is one of the important oil and gas productive areas and favorable exploration areas in the Bohai Sea area.Faults are the main structural deformation in this area,which control the formation and evolution of the basin.The formation and evolution of faults result in the diversity of basin structure.The 3-D seismic data,drilling data,well logging data in the west area of Liaodong Bay Depression are provided by CNOOC,to study the evolution of fault system and its control on basin structure,and establish the genesis relationship between them.Four sag-controlling faults and a strike-slip fault zone are developed in the west area of Liaodong bay depression,which are separated the salients from sags,including Liao Xi sag,Liao Xinan Salient,Liao Xinan Sag,Liao Xi Salient from the west to east.The strike-slip fault zone located in the west slope and 4 main faults located in the east area of the west slope including Liao Xi 1 fault,Liao Xi 2 fault,Liao Xi 3 fault,Liao Xinan 1 fault.The main faults reflect extensional properties in the early stage and strike-slip effect in the late stage.Overall,strike-slip is stronger in the west than that in the east.The evolution of the west area of Liaodong Bay Depression are divided into four periods,Es₄+Ek,Es₃-Es₁,Ed and N+Q.In the Es₄+Ek depositional period,main faults were continuous and large-scale.Secondary faults had weak activities.Extensional faults were stronger than strike-slip faults.Salients and sags were formed.In the Es₃-Es₁ depositional period,secondary faults increased.NEE-trending and nearly EW-trending secondary faults were formed.Extensional stress was strong and strike-slip effect changed from weak to strong.In the Ed depositional period,NEE-trending and nearly EW-trending secondary faults and the strike-slip fault zone of west slope acted strongly.Strike-slip faults were stronger than extensional faults.The salients stopped uplifting.In the N+Q period,which was the depression stage.Main faults were not continuous,which were presented as secondary fractures en echelon arranged.NEE-trending and nearly EW-trending secondary faults acted strongly.Strike-slip effect decreased.Overall,strike-slip is stronger in the west than that in the east.Since Paleogene period,strike-slip effect increased gradually and reached the peak in the Ed depositional period.Generally,the faults reflect extensional properties in the early stage and strike-slip effect in the late stage.The interaction of extension and strike-slip in different evolution stage of faults and the magnitude of different stress in the same evolution stage control the formation and evolution of the basin.In the Es₄+Ek depositional period,extensional stress was stronger than strike-slip.In the Es₃-Es₁ depositional period,strike-slip effect increased.Extension and strike-slip were all strong.In the Ed depositional period,strike-slip was stronger than extension.In the N+Q period,strike-slip and extension decreased.Strike-slip was still the main stress.As a whole,the research area was mainly controlled by extensional stress in the early stage and strike-slip in the late stage.