Structural Characteristics And Sealing Assessment Of Faults In Beisantai Swell,Junggar Basin

Taking Beisantai swell in the east part of Junggar basin as research objects,On the premise of knowing the tectonic background of the study area,according to seismic,logging,mud logging,core data,combind with previous research results,systematic study is taken on the fault characteristics and their combination style,fault system,etc.On this basis,the internal structure and fluid diagenetic sealing of the main fault are comprehensively evaluated.Futhermore,the study on the fluid activity period of the fault zone in the study area is carried out.The study shows that Bogeda mountain firstly uplift at Hercynian in southern margin of the Junggar basin,Beisantai swell gradually formed,then it experienced Indosinian period,Yanshan period and muti period tectonic movement,the tectonic background is complex,and the overburden and denudation of stratum is obvious.According to the research of developing characteristics,faults can be divided into two systems for their depth.Deep faults were thrust fault in the early stage,afterwards strike slip faults developed based on reverse faults influenced by the Indosinian movement,they often act paralleled or skew on the plane;Shallow faults are mainly small normal faults,then they connected with deep faults with the properties of tension and slip,and formed composite flower structure with deep faults together,these faults like nets or feather on the plane.The combination styles of faults are often represented by flower structure,"Y" font structure on the profile.The study on the internal structure of fault zone in the study area shows that the fault zone could be identified according to the seismic,logging data and core observation,such as core observation indicates that the rock of slide broken belt are grinded seriously and compact,but induced fracture zone only developed several tectonic fissure without obvious dislocation;the fracture zone reflected a certain width of clutter or blank tape on seismic profile;slide broken belt and induced fracture zone could be recognized by viriation characteristics of different fitting curves in logging data.The internal diagenesis of the fault zone is widely developed,and the cementation is the most important diagenesis in the induced fracture zone on both sides of the fault,which plays an important role in the vertical sealing of the fault.Diagenetic cementation of fault zone is studied through core observation and microscope observation of thin section.The result shows that the cementation of fault zone is obvious and there are various types of cement,mainly calcite,clay minerals,zeolite,quartz and other cement are also found in fractures.Compared with the derived faults,the fracture filling and cementation of large main faults are intenser,and the sealing performance of the oil and gas is stronger.The identification of microscope and the uniform temperature test of fluid inclusion suggests that there are at least three periods of great fluid activity in Beisantai swell,the multiple fluid activity leads to the diagenetic sealing of the faults in this area.