The Structural Characteristics And Favorable Zones Optimization Of Wunan Depression In Hailar Basin

Located in the south of the Wuerxun Depression,the Wunan Depression is an important potential block in the Hailar Basin and is the focus of exploration in recent years.However,due to the low accuracy of early seismic data and the limitation of single technical means,there are some problems in Wunan area,such as unclear stratigraphic division,lack of systematic research on the development and distribution of internal faults,insufficient understanding of local structures,and unclear structural evolution characteristics.These make it difficult for the research area to carry out effective zone evaluation.This paper uses seismic data reprocessed in 2017,guided by sequence stratigraphy and structural geology,and uses software such as Geo East,Double Fox,and Shiwen to redefine the stratigraphic division scheme in the Wunan Depression and completes its structure and horizon interpretation and mapping.On this basis,the fault system in the depression is re-combed,the characteristics of fault development and distribution are analyzed,the structural characteristics and evolution laws of Wunan Depression are studied,the structural zones are re-divided and the criteria for zone evaluation are established,the oil distribution and exploration potential of each zone are comprehensively evaluated,and the favorable zones are selected.Major achievements have been made in the following aspects:(1)The Cretaceous strata in Wunan are divided into five second-order sequences,eight third-order sequences,and the main strata(K1d,K1 n,K1t)are divided into 14 sand groups,of which the K1 d is composed of three sand groups: d1,d21 and d22.The K1n2 can be divided into two sand groups,namely n21 and n22;the K1n1 is divided into six sand groups,namely n11-n16;K1t can be divided into three sand groups,namely t1,t2 and t3.(2)The faults in Wunan Depression are divided into four levels,and develop three predominant trendings of NNE,NS and NNW.There are four types of normal faults on the profile,and they are shovel,slope,non-rotating and rotating faults.On the profile,there are four types of faults' combination: conjugate,flat,oblique and shovel fan.On the plane,there are six types of faults' combination: fishbone,parallel,grid,rake,root and chain.(3)The depression develops three stages: fault-breaking,transition stage and depression.It has undergone three stages of filling and three stages of transformation.The faults exist six development stages: early,middle,late,early-middle,middle-late,early-middle-late.(4)Affected by stretching,slipping and reversing activities,forward and reverse nose and seven types of anticlines are formed in the depression.The seven types of anticlines are compressive type,extension adjustment type,gravity sliding type,drape type,reverse traction type,transformation type and collapse type.(5)Wunan Depression is divided into five structure zones: the abrupt slope zone of Wuxi fault,the depression zone of Wunan,the upper zone of Wudong slope,the middle zone of Wudong slope and the lower zone of Wudong slope,of which the depression zone and the middle zone have the most exploration potential.