Characteristics Of Strike-slip Transition Structure And Its Control On Trap In The Liaodong Bay Depression

The Tanlu fault is a large-scale strike-slip fault in the eastern of China,runs through the eastern part of the Bohai Sea,controlling the hydrocarbon accumulation process and hydrocarbon distribution in the Liaodong Bay Depression.Therefore,this thesis studied the strike-slip transition structure in the Liaodong Bay Depression,and clarified the development and distribution characteristics of different types of strike-slip transition structures in the Liaodong Bay Depression.On this basis,The activity of the main fault and the secondary faults is analyzed.Combined with the tectonic evolutionary section and analogue modelling experiments,the formation and evolution model of the typical strike-slip transition structure is established in the Liaodong Bay Depression.Finally,through the fine analysis of the typical tectonic belt,this paper clarified the control of different types of strike-slip transition structures on the traps in the Liaodong Bay Depression.There are six strike-slip transition structures in the Liaodong Bay Depression,including conjugated,S-type,stepover,double,imbricate fan and composite type.Each type is further divided into a restraining and releasing according to the local stress state of the transition structure.The conjugated strike-slip transition structure divides the Liaodong Bay Depression and the Bozhong-Bodong depression,which is the first-class strike-slip transition structure in the study area;The S-type strike-slip transition structure develops in the bending part of the strike-slip fault,and is widely developed in the Liaodong Bay Depression.The fault dip angle of the releasing part is slow,forming a small depression,but the fault dip angle of the restraining part is steep,and the layer is curved and arched in the S-type strike-slip transition structure.The stepover and double strike-slip transition structures are mainly developed in the strike-slip faul stepover part.Secondary faults are relatively developed in the releasing,but in the restraining,secondary faults are not developed or less,and the layer are curved and arched.imbricate fan type strike-slip transition structure develops at the tail end of the main strike-slip fault.Secondary fault is relatively developed,and the main fault is a horsetail or braided structure in the releasing imbricate fan type strike-slip transition structure.The main faults began to strike-slip during the Sha 1 and 2 member sedimentary period in the Liaodong Bay Depression,but the strike-slip activity was very weak at this time.The main faults began to strong strike-slip active during the formation sedimentary period,then strike-slip weaken in the Neogene.The strike-slip activity of the main strike-slip fault controlled the formation and evolution of the strike-slip transition structure.During the sedimentary period of the Dongying Formation,due to the strong strike-slip of the main fault,the strike-slip transition structure has a wide distribution in the liaoodng bay depression,ncluding conjugated,S-type,stepover,double and imbricate fan.At the same time,the releasing strike-slip conversion structure lead to the development of secondary faults with a large scale and a large number,while the secondary faults of the restraining strike-slip transition structure are not developed or less.strike-slip effect is weak,and the strike-slip transition structure is less developed in the Liaozhong sag and the Liaodong sag in the Neogene,including imbricate fan type and S-type.In addition,different types of strike-slip transition structures have different secondary fault growth process.The secondary fault grows and propagates from the both ends to the middle of the step-over zone in the releasing-stepover strike-slip transition structure.While the secondary fault grows and propagates from the the middle to ends of the step-over zone in the releasing-double strike-slip transition structure,and the difference of the secondary fault scale and the activity intensity in the overlying zone is not obvious.The secondary fault grows and propagates from the middle of the fault to the tail end of the fault in the releasing-imbricate fan type strike-slip transition structure.The closer the distance from the main strike-slip fault,the greater the intensity of the secondary fault,and the activity of the secondary fault gradually weakens from the middle to end of the main fault.Different types of strike-slip transition structures have obvious control trap differences in the Liaodong Bay Depression.The restraining strike-slip transition structure develops reverse reversal anticline,semi-anticline,and nose-type trap,and the trap size is larger,and the lateral sealability is better.The releasing strike-slip transition structure develops block-type traps,and the trap size is small and the lateral sealability is poor.In terms of different tectonic layers,the Dongying Formation has a strong strike-slip effect,so the number of traps controlled by the strike-slip transition structure is large and the scale is large.In the Neogene,the strike-slip effect is relatively weak,only a small number of strike-slip transitional structural traps are developed in the Liaodong salient and Liaozhong sag,and the trap size is small.