Structural Characteristics,Evolution And Formation Mechanism Of Hongqi Sag,Hailar Basin

The Hailar Basin is located in Inner Mongolia on the west side of the Greater Khingan Range in northeast China,and is a large petroleum-bearing basin.The Hongqi Sag is a secondary tectonic unit in the Hailar Basin.It is located in the north part of the central part of the basin and is a typical rift basin.Up to now,the research and exploration degree of Hongqi Sag are very low,but it has good prospects for oil and natural gas exploration.The Hongqi Sag has undergone multi-phase construction and multi-phase reconstruction processes.The tectonic activities in the basin-forming stage are frequent,forming multiple unconformity surfaces at different levels and affected by the division of complex fault systems.It is difficult to compare strata.Strata and faults in the rift period,it is difficult to identify the system.It is complicated by the late tectonic activities,the prototype basin suffered different degrees of damage during the later construction and reconstruction process,and it is difficult to restore the prototype basin.The Hongqi Sag is located at the structural turning point where the tectonic line of the Hailar Basin is deflected from NE to EW,and is distributed in the NEE direction.Due to the complex geological conditions,there has not been any analysis of the plane and section development history of the Hongqi Sag and the restoration of the prototype basin in this area.The lack of analysis of the migration and formation mechanism of the sag during the construction and reconstruction of the basin directly affected the distribution and residual laws of each set of strata Understanding.And evaluation work often uses the residual pattern instead of the prototype pattern,which often leads to misunderstandings.Therefore,the research on the structural characteristics,evolution and formation mechanism of Hongqi Sag has important theoretical and practical significance for further exploration and deployment in the later period.The thesis is guided by the theory and research methods of tectonic stratigraphy,constructing isochronous stratigraphic framework and establishing structural geological model.Applying the comprehensive interpretation method of seismic geology,the regional unconformity interface is determined,and then combined with drilling,logging and seismic data,remake synthetic seismogram,and combine the tectonic interface for layering,and finally complete the whole strata in order to achieve the purpose of more accurate and perfect seismic interpretation.According to the research:Hongqi Sag is a fault-sag combination formed mainly by extensional tectonic background and influenced by three structural reversals.And has long been affected by the western controlling-depression fault--Hongxi fault.On the plane,it has the distribution characteristics of east-west zoning and north-south blocking.The tectonic line is mainly NE-trending,and the controlling-depression fault is mainly characterized by a right-order oblique combination,with two sub-sag nested in the depression and separated by an uplift,which is exactly the location of the transforming slope of the Hongxi fault.On the section,Hongqi Sag is a dustpan fault with faults on the west and overlaps on the east.From west to east,Hongqi Sag is divided into a west steep fault zone,a middle sag zone and a south slope zone.Structural styles in the sag are also well developed,mainly including extensional structural styles in the construction period,compressional structural styles and strike-slip structural styles in the transformation period,and inversion structural styles superimposed by construction and transformation.The extensional structural styles mainly include normal fault-related folds,staircase structures,"Y-type"combinations,"V-type"combinations,normal drag structures and graben-horst structures.The compression structural styles are mainly as follows:detachment fold,propagation fold and thrust structure;Strike-slip structural styles are mainly realized as various types of flower structures.The inversion structure style is mainly positive inversion structure.Since the Jurassic,the Hongqi Sag has undergone superposition of multiple stages of construction and reconstruction.In order to clarify the construction and reconstruction process of the Hongqi Sag and the migration law of the sag,the thesis carried out quantitative restoration of erosion thickness and restoration of the prototype basin,which is an important basic work for basin analysis and oil and gas evaluation of the Hongqi Sag.This is also the first time that this area has carried out research on prototype basin restoration.Based on the establishment of the Hongqi Sag construction model and reconstruction model,the thesis restored the erosion of the sediments in the Tongbomiao Formation,Nantun 1st Member,Yimin 1st Member and Yimin 2nd and 3rd Member.The prototype basins in the above four periods are reproduced.Among them,the prototype basins in the depositional periods of the Nantun 1st Member and Yimin 2nd and 3rd Member have a special structural pattern of"three sags and two uplifts".Sunken.Afterwards,it gradually evolved into the main pattern of today's"two depressions and one up".The sag migration law is clarified and has important guiding significance for oil and gas exploration.The development history of Hongqi Sag was analyzed using the balanced profile technique.The evolution of Hongqi Sag has mainly experienced four tectonic evolution stages,namely,a.initial extension?faulted incubation?stage?T₅-T₄?,b.faulted development stage(T₄-T₂₃),c.fault-depression transition stage(T₂₃-T₀₄),d.depression stage(T₀₄-present).And formed three regional unconformity interfaces:T₅,T₂₃,T₀₄.The structure of Hongqi Sag is complex and the formation mechanism is unclear.In this paper,the first 2D and 3D structural physical simulation experiment was carried out in this area,which successfully solved the problem of the restoration and formation mechanism of the complex faulted prototype basin,and made some new understandings and discoveries.In this paper,through systematic analysis of the geometric correlation between faults and folds in Hongqi Sag,on the basis of the restoration of the evolution history profile,the boundary conditions of 2D and 3D tectonic physical simulations in Hongqi Sag are determined,and tectonic physical simulation experiments are carried out.The simulation result reveals the tectonic dynamic mechanism of Hongqi Sag:the controlled depression fault in Hongqi Sag is formed by two small faults in oblique series.Each small fracture controls a secondary sag,and as the extension increases,two small fractures penetrate through the junction to form a larger controlled depression.The two secondary sag also eventually penetrate to form a unified sag.At the junction of two small faults in Hongqi Sag,there is a very obvious relay fault slope?transition slope?,on which complex small faults,fractures?fissures?and local traps are developed,which is the dominant direction of oil and gas migration and the development area of favorable traps.The only industrial oil flow well in the study area,Hong 7 Well,is in this zone.The relay fault slope is a favorable exploration block.