The Research Of Basin Structure And Evolution Of Basin Of Kongdian Formation Of Kongnan Area In Huanghua Depression

There are abundant hydrocarbon resources in Kongnan area of Huanghua Depression, which is a successor battleground of exploratory and exploitation of reservoir in Dagang Oilfield. Predecessors deal with researching Kongdian period basin in Neozoic basin of Huanghua Depression. Their research is lack about the unique feature of evolution of basin of Kongdian period in Kongnan area. By means of further analysis, we think that thoday's basin structure is different from Kongdian period basin, which is folded by multiple-period basin and reformed by later basin.At the same time, there are a lot of disagreements from type of basin, sedimentary boundary, provenance system and evolutional phase of basin etc..These problems not only directly influence awareness about distribution of hydrocarbon, but also seriously restrain deployment and decision of hydrocarbon exploration in Kongnan area.On the basis of predecessors'research, and theoretical guidance with tectonics, sequence stratigraphy and sedimentology, the paper sufficiently uses existing seismic section, core, well logging and else datas because of lacking field crop profile to analyze structural framework, sequence stratigraphy, depositional system, prototype basin structure , palaeotectonics feature, type of basin border and filling pattern ,evolution of basin and provenance system of Kongdian period basin in order to recover and rebuild basin structure and process of lacustrine basin of Kongdian period in study area.Through these analysis,we obtain many important conclusions and new recognitions as follows:1. Utilizing land sequence stratigraphy theory of rifted basin to build up sequence strata framework of deep zone Kongdian Formation in Kongnan area, and to divide out one second-order sequence, four third-order sequences and twelve system tracts.2. On the basis of identifying sedimentary facies indexes including lithologic facies, electrofacies, seismic facies and palaeophyte, types of sedimentary facies and sedimentary system are analyzed. Typical facies sequence of main sedimentary facies is built up.3. According to seismic interpretation sections, the characters of segmentation and activity of main faults-Cangdong Fault and Xuhei Fault in developing period of four sequences are analyzed.4. Four second order structural belts and five depressions can be divided from Kongnan basin according to seismic interpretation sections and relict strata isopach map of Ek in Kongnan basin. Four structural belts include Kongdian, Dongguang, Wang guantun and Shenvsi Salient. Five depressions include Cangdong, Nanpi , Changzhuang, Xiaoji and Nandi depression.Formation time and activity feature of each structural unit has been studied in different geologic time of Ek in study area. The growth relationships of depressions, depression and structural belt, structural belts are analyzed.5. Through analysis of isopachous map of strata and mudrock, centers of subsidence of Ek in Kongnan area are found to distribute along Cangdong Fault and Xuhei, depocenters to distribute in center of basin.Centers of subsidence and depocenters have two direction migration laws. One is migration of NE-SW, which indicates tensional and strike slip kinematics characteristics of Cangdong Fault and Xuhei. The other is migration of NW-SE, which indicates right lateral strike slip kinematics characteristics of two faults.6. On the basis of seismic interpretation sections, the paper analyzed the correspond relationships of fault framework, faults and depressions. Boundary fault controling sedimentation of Kongdian formation is Cangdong fault and Xuhei fault. Activity intensity of Xuhei fault is weaker than that of Cangdong fault. At the same time, Kongdian Salient forms gradually in the north of basin. This results an asymmetrical"a salient between two depressions"graben and horst structure in the north, and asymmetrical graben structure in the south.7. Through analyzing the structural development history of crossing main faults, depressions and structural belts , tectonic deformation series of Kongdian period in Kongnan basin can been built to analyze stages and characters of structural evolution. It is an new visual angle that Kongdian formation basin in Kongnan area is as a indepent basin formation phase in order to bring into studying basin structure and lacustrine basin evolution,and to divide it into four evolutional stages including intial rifting stage, depressing stage, rifting stage and rifting-filling stage.The evolutional characteristic of each stage,type of basin margine and filling.Evolution of lacustrine basin has differentiation and migration of north and south, one of east and west.These differentiations and migrations chiefly display in differentiation and migration of fault activity, center of subsidence, depocenter and lake rim facies.8. The research points out that evolution of Kongdian period basin is mainly influenced by tectonic activity, particularly boundary faults, secondly palaeoclimate, ancient landform, provenance systems and closed property of lacustrine basin. Effection to structure of Kongdian period from pre-palaeogene basement structure and Mesozoic compressional structure and reformation from tectonic action of Shahejie phase has been researched.