Reserch On Coupling Between Structure And Sedimentary System And Its Controlling On Oil-gas Accumulation In Wuerxun-beier Depressions

Wuerxun-Beier depressions are two secondary structural units and major areas of proved oil and gas reserves in the Hailaer Basin.Different structural episode controlled the sequence stratigraphic filling evolution in fault basins.Paleo-morphology resulted from the long-term activity of syndepositional structures controlled the development of the depositional sequence and the distribution of the depositional system tracts and the sand bodies.With the further application of 3D seismic data,structural sequence stratigraphy became a hot issue in the research of sedimentary basin in recent years.With comprehensive analysis of large amount of data and literature,and based on the structure features of Wuerxun-Beier depressions,the features of prototype basin,and sequence and depositional filling characteristics,structural style of codeposition and sequence structure style of different structure belt are analyzed,the response characteristics at different structure evolution stages are observed.Furthermore,the effects of structure events on sequence strata deposition filling are studied;taking the distribution of source rock and formations,the reservoir types in the key areas is studied,the patterns of hydrocarbon concentration and the factors of reservoir formation is analyzed,pool-forming pattern is established,and favorable exploration area is predicted.The paper is not only significant as guiding the exploration,but also theoretically important in the research of exploration application of structural sequence deposition analysis of continental rift basin.The understandings are as follow:1.The structural characteristics of Wuerxun-Beier depressions and restoration of prototype basin shows that Wuerxun-Beier depressions has witnessed three regional structural events,respectively at the end of Nantun formation,the end of Yimin formation,and Qingyuangang formation deposition,i.e.,vertically three structural layers:faulting period,fault-depressed diversionary period,and depression period.Complex depression formation mechanism is clarified.Compound of contemporaneous small dustpan-shaped depressions and congruent of fault depressions of different periods leaded to a multiple concave-convex"compounded dustpan-shaped depression" that is controlled by NE-NEE low-angle extension fracture system.The rudiment of structural belt and effective hydrocarbon distribution is controlled by NEE fault of depression period,and hydrocarbon concentrated towards high point along early NEE depression-controlling fault.The most favorable hydrocarbon concentration area is the pale structure formed by antithetic fault and the related slope.2.Using strata correlation techniques,such as sequence stratigraphy,four-order fine sequence strata correlation is carried out in Wuerxun-Beier depressions within the three-order sequence framework.The observation is that there is a set of special "calcium shale" in Beier depression,which is streak of dark shale and calcium shale,limestone,and shale.The"calcium shale" of Nan 1 member is an important mark strata and good source rock.Wuerxun-Beier depressions are divided into 8 four-order sequence(sandstone formation),and the No.6 sandstone of Nan 1 member formation is the major oil-bearing formation.3.During the establishment of deposition filling evolution model,it is observed that deposition filling evolution is controlled by different structural phase of Beier depression,deposition system distribution is controlled by NEE depression-controlling fault of faulting period,and the decisive factor of reserves in Nan 1 member is the delta and braided frontal sandbody near to macro axis material source.In Wuerxun-Beier depressions,the starting rifting of deposition filling development is shallow lacustrine sequence;the violate rifting is halfdeep-deep lacustrine sequence and rifting-subsiding shallow lacustrine sequence.Nantun formation,the major target formation,is the early violate rifting period,where the activity of depression-controlling fault is relatively weak.The lacustrine basin is widely distributed,water is shallow,thus the universal-basin shallow water deposit.The fan-shaped delta and braided river-delta system are formed near to macro axis.Frontal deposit is well-developed,well sorted and have good properties,thus large good reserves.The statistics show that the most of Nantun formation reserves is located in the fan delta and braided rive delta frontal deposit.4.Controlled by cycle effect of multiple period structural phase,the ravine controlled the distribution of material source system,codeposition fracture slope break has several different compound styles,with different structural paleogeomorphological feature,such as the distribution of sandbody is controlled.Based on codeposition fault development characteristics and compound style,6 codeposition fault compound styles are identified:broom-shaple,fork-shaped,parallel faulted steps,en echelon,comb-shaped,and adjusting type.These codepostion faults made the complicated structural paleogeomorphological feature and fracture slope break,controlled the input of fan-shaped water system in the lake and the distribution path of sandbody.Different fracture slope breaks had adjusting effect on the distribution of multiple period fan-body,and controlled the unload area,scale and path of sandbody.This is the material basis of multiple litho reservoir formation;at mean time,second-order transfer zone sand controlling between the depression near to the material source is adjusted,and worked together with fault area in the paleo structural slope,large braided river delta frontal sandbody distributed near to macro axis is formed,which is a favorable condition for reservoir formation.5.Structrual and sedimentary coupling formed the structural pattern of each depression in convex concave interphase,developed plural sedimentation centers and oil-generating sag had relatively independent petroleum syste.Coupling between structure and sedimentary controlled on the distribution of hydrocarbon source rocks and traps which determined that the distribution of oil and gas has a plurality of migration and accumulation units.Several main hydrocarbon kitchen areas provided a rich,high-quality resources foundation for the accumulation of oil and gas reservoir.Oil and gas migrated and accumulated to all the traps by sand body,fault and unconformity.Structure,lithology and other types of reservoir were symbiosis,the superposition of merging multiple oil gas accumulation zones were formed.6.The hydrocarbon concentration pattern and controlling factors in Wuerxun-Beier depressions is furthered,three models that coupling between structural and sedimentary system and its controlling on oil-gas accumulation in deffrent structural zone are established:compounded dustpan-shaped fault depression concave and uplifting;faulted steps in large slow slope;deep and small stable depression.