Tectonic Evolution Process Of Troughs And Its Control On The Hydrocarbon Accumulation In Hailar Basin

Depressions are secondary negative tectonic units within the sag grade tectonic units of continental faulted basins.Single or multiple depressions can develop in the depressions,and most of them are asymmetrical.In general,one end of the depression is defined as the main stem boundary fault system,and the other end is the lower slope or secondary fault which tends to the main stem boundary fault.In this paper,the present situation of the study area has been fully investigated,and the regional tectonic background and stratigraphic development characteristics of the Hailar basin have been clarified.Based on the latest 3D seismic data,the fracture of the major boundary faults in the Hailar basin is dissected.By drawing and analyzing the throw-distance curve,the throw-depth curve and expansion indices of major boundary faults,the planar and vertical growth mechanisms of the major boundary faults in the study area are fully understood.The structural evolution history and genetic mechanism of the Hailar basin are analyzed by using the method of balanced structural evolution analysis and combining the structural characteristics of faults in different periods.Five stages of tectonic evolution were defined from bottom to top: residual basin stage(Tongbomiao Formation),initial rifting stage(the middle and lower parts of Nantun1),strong rifting stage(the upper part of Nantun1 Formation and the Nantun2 Formation),fault rifting to depression transformation stage(Damoguaihe Formation and Yimin Formation),and depression stage(Qingyuangang Formation),and tectonic stress characteristics in different stages were also defined.At the same time,the maximum slip backstripping method is used to restore the evolution history of fault formation,define the distribution of ancient troughs,and analyze the structural evolution process of troughs in the Hailar basin.Research shows that based on the throw-depth curve and expansion indices,the active period of the major boundary faults in Hailar basin is determined,and the stratigraphic deposition period of the upper part of Nantun1 Formation and the Nantun2 Formation are the main evolution periods of the trough.According to the major boundary fault growth mechanism(Isolated fault growth mechanism and Fault segmentation growth connection mechanism),the trough growth manners in Hailar basin can be divided into isolated fault-controlled trough growth manner and segmental growth fault-controlled trough growth manner.Finally,the controlling effect of the structural evolution of troughs on the accumulation of oil and gas in troughs is analyzed from three aspects :the relationship between troughstructure and distribution of effective source rocks;the relationship between tectonic tilting and the formation and structural deformation of high-quality reservoirs;the relationship between the structural deformation of troughs and the accumulation of oil and gas.According to the different trough growth manners,the methods of controlling the distribution of hydrocarbon source rocks by troughs can be divided into the distribution patterns of source rocks controlled by isolated troughs and by segmental growing troughs.The uplift of the lower plate controlled by the reverse fault,intermittent exposure to the surface,partial weathering and denudation,atmospheric water leaching and transformation form supporting conglomerate,porosity increases,which is conducive to the formation of high-quality reservoir.The activity of the related faults which cause the structural deformation of the troughs determines the different effects of the faults on hydrocarbon migration and accumulation.Systematic analysis of trough structure and structural evolution characteristics of complex small-scale rift lake basin group is of theoretical value and practical significance for restoring paleo-trough to hydrocarbon source rock prediction,submitting high-quality newly proved reserves in oilfields,and accelerating the pace of oil and gas exploration in the rift basin.At the same time,it plays an important guiding role in improving the theory of ‘trough control hydrocarbon' in rift basins and enriching the theory of ‘fault control oil reservoir' in rift basins.