| The Qikou sag is located in the middle and north of the Bohai Bay Basin,a typical rift basin in China.The development characteristics of faults in the rift basin are not only an important part of the basin structure research,but also play an important role in controlling the hydrocarbon accumulation.Located in the transitional zone between sea and land,the Binhai area is rich in oil and gas resources and is an important deployment area for Petro China oil and gas exploration.In this paper,guided by generalized fault theory and based on high-resolution 3D seismic data,through the fine interpretation of fault characteristics in the study area,the plane-section combination characteristics of faults are described,and statistical methods are used to quantitatively study the fault strike,size and fracture density of different layers in the Paleogene-Neogene.Then the activity regularity of the main fault in the study area is analyzed.Finally,based on the above research results,the active stages of faults in the study area are divided,which lays a foundation for the subsequent study on the control law of faults on oil and gas accumulation,and the following understanding is obtained:（1）In terms of flat-section fault assemblages,the plane assemblages of faults are mainly parallel,echelon,broom and oblique.The fracture profiles are combined to form stepped,"Y"shaped and spade fan styles.（2）Main fault activity:The secondary faults（the Binhai fault,the Gangdong fault and the Qidong fault）began to develop in the third member of the Shahejie formation（Es3）period.During the second member of the Shahejie formation（Es2）period,the faults activities decreased.The faults reached their peak in the first member of the Shahejie formation（Es1）period and the Dongying formation（Ed）period.Enter the Guantao formation（Ng）of Neogene,the faults activitivies were decreased.During the Minghuazhen formation（Nm）,faults activities strengthened again.The tertiary faults（the Qizhong fault,the Tangjiahe fault and the Dazhangtuo fault）developed late,and began to develop from Es1 period（but developed downward to Es3 member）.The faults activities continued to increase in the Ed period,significantly decreased in the Ng period,and strengthened again in the Nm period.（3）Fault tectonic evolution:the active stages of the fault can be divided into four stages:the main fault was initially formed in the first fault depression（Es3）;In the Es2 period,the faults stopped activities and entered into the structural quiet period,and the strata were uniformly deposited.During the second fault depression period（Es1+Ed）,the pre-existing main faults revived and formed new faults.At the later stage（Ng-Nm）,a few faults were active again.（4）In terms of hydrocarbon accumulation controlled by faults,the active period of faults is well matched with the hydrocarbon generation and expulsion period of source rocks,and the faults generally control the vertical migration and accumulation of oil and gas.The oil and gas in the study area mainly migrated vertically along the main faults,which were controlled by the secondary faults.The formation of middle-shallow（Ed-Nm）oil and gas reservoirs was due to the tectonic action in the second fault depression period,which making the oil and gas in the Es3 or Es1 migrated upward along the newly active or newly formed faults. |
