Research On Sequence Stratigraphy And Depositional Systems Of Tongbomiao And Nantun Group In Wuerxun-Beier Depression

With the application of the theory of classic sequence stratigraphy referred to the seismic and logging and the core data, four sequence boundaries (SB) which are SB1, SB2, SB3 and SB4 and three maximum flooding surfaces (MFS) which are F1, F2 and F3 of Tongbomiao and Nantun group are identified within the Wuerxun-Beier depression based on the well to seismic calibration. At the same time, the top boundary of sequence SQn2 was restructured. The sequence framework in the studied area is established on the basis of 12 well-seismic regional profiles and 27 infill well nets profiles were correlated. Based on the detailed core observation and analysis of single well facies and cross sections facies, the sedimentary facies distribution are identified during the phase of sequence SQt, SQn1 and SQn2. This studies show that 5 sedimentary systems were developed in this area, including alluvial fan, fan delta, braided delta, slump turbidite fan and lacustrine. The strata was developed in the Wuerxun depress and western of Sunainuoer sag which developed mainly alluvial fan-fandelta-shallow lake facies during SQt period. In the SQn1-SQn2 period, lake water was rising gradually, fan delta- turbidite fan- shallow-deep lake were developed in the steep slope zone and braided delta- fan delta where in the slope-break– shallow lake were developed in the slope belts.Based on the application of the theory of high-resolution sequence stratigraphy, the middle-term base-level cycle is divided and correlated within the regional sequence stratigraphy framework. At the same time, the schemes of division and the sequence stratigraphic position and correspondence of the high-frequence cycles of reservoir group are determined. Based on these, fine stratigraphic correlation and 45 correlational profiles are established in this area. Finally, regional correlation profile of reservoir group were established by the SQn1 of the slope eatern Wuerxun– oil field Sudeerte- sag of centural Beier and the SQn2 of the slope eatern Wuerxun- oil field Huhenuoren and the LST of SQd1 of S131 fault block and S102 fault block and HC4 fault block.In combination with regional tectonic background and sequence stratigraphic analysis, some points can be got: regional sequence stratum is controlled by the rifting stage. Different steep slope and slope types can cause different sequence stratigraphic filling pattern. The distibutional plane of the depression and the migration of sedimentary center are controlled by the structural accommodation zone. Different types can adjustment the size and direction of the main source which come from the short axis, thereby affecting the development of sedimentary system. Combining paleogeomorphology and synsedimentary faults of features analysis, three potential exploration targets exist in the basin: sand bodies of slump turbidite in the lowstand of sequence SQd1 in the northern Wuerxun; sand bodies of delta in the slope break zones and turbidite sand in the deep water of the eastern Wuerxun slope belts; sand bodies in the grade 2 slope-break of the centural weastern Beier slope belts and the lowstand sand of the northern or sourthern Beier slope belts.