Paleogene Structure Evolution Of Offshore Area In Liaohe And Its Control Over Hydrocarbon

Liaohe Basin is a part of Tanlu rifting system,and it belongs to continental rift basin. Offshore area in Liaohe is a transition zone from Liaohe Basin to Liaodong Bay area. It has identical geological features and evolution history with Liaohe Basin and it is an important substitute area for hydrocarbon resources in Liaohe Oilfield.Based on actual data and structural activity view point,by using structural analysis,and simulation experiments,this paper analyzed structural geomeory,structural activity and earth dynamics of structural evolution of Cenozoic of offshore area in Liaohe,and assessed structural evolution and its control over hydrocarbon geological events and hydrocarbon distribution. The following achievements are obtained:There can be concluded three structural patterns in offshore Liaohe. They are extending,sliding and reverse structural pattern. Among them,extending pattern dominates. The extending major fault has a strike of north-east,controlling the forming of depressions and evolution of sedimentation. The nature of the fault is normal in the early stage. Later with the reformation of sliding effect,normal faults are still the main faults,and the plane distribution of the faults occurs sectionally. Sliding structures are recognized appling multiple ways,and they occur in sections in the shape of flowers. The main sliding fault has the characteristics of straightness and sectionality in plane view. In the main displacement belt or its adjacent areas,an echelon faults and an echelon folds appeared. The fold structure or the volcanic bodies on each side of the main faults are displaced 2-4km. Apparent sliding structure activity trace are recognized in the drilling core samples. The reverse structure appears in three styles. They are regional structure reverse occurred as angle unconformity between Paleogene and Neogene,thrush fault and local reverse structures. The structural activity of Offshore Liaohe has the characteristics of multi-periods and multi-episodes. Fault structures with different sizes,different styles and different strikes stack each other,forming composite structure system with extending and sliding features. This area is divided into 12 composite structural belts of five types. Multiple trap types are developed,with the main area being sliding fault semi anticline structure trap,drape semi anticline structure trap,reverse semi anticline structure trap,reverse thrust semi anticline structure trap,fault nose structure trap,fault block structure trap,buried hill trap and stratigraphic overlapping trap,etc. The faulting activity of this area is divided into two phases and four sub-phases. The variation of different faulting activity phase result in different structure evolution history. The structure evolution of Cenozoic experienced rifting subsidence of Paleogene and rifting thermal subsidence of Neogere and Quartenary. Literature named them as rifting arching,rifting subsidence and rifting re-depression periods.Quantitative analysis of Cenozoic structural activity shows that the extension degreeof western depression is far more apparent than that of the eastern depression. The extension is focused on the main fault,however,the differential lifting activity of the eastern depression is more intensive than that of the western depression. The tilting rotation activity of Paleaogene fault block is very obvious. From extension degree,differential lifting,sliding surface depth and modern seismic data analysis,it is concluded that the structural activity of Liaohe Basin moves from west to east,i,e.,the rifting happens in the western depression first,it moves to the eastern depression and now it locates in Bohai area. The long developing major faults controls the subsidence of the depression and the depression of the formation. Different structural location has different extension effects and therefore forming multiple subsidence center. The structural activity has the characteristic of strong-week-strong-week. Tilting activity controls the distribution of depositional f...