Study On Structural Characteristics And The Favorable Exploration Zones Of The Middle-northern Area In Raoyang Sag

Raoyang sag is a secondary structural unit in Jizhong depression of Bohai bay basin, it has experienced three main stages of tectonic evolution since the Cenozoic, namely the period of formation, the period of expansion and the period of disappearance. The structural features are tensile stretch at early time and shear-slip at late time. Because of the multi-stage tectonic movements of Raoyang sag, it formed the complex fault system and a variety of different oil-bearing structural styles. As a result, difficulties have been brought to geological research and production of oilfield. Therefore, at present, based on interpretation of the new high-precision three-dimensional seismic data, it will has a reality significance for petroleum exploration in the sag to research holistically and systematically characteristics and evolution of faults of Paleogene, to research its control on hydrocarbon accumulation.Taking the theories of structural geology, sedimentology and modern hydrocarbon accumulation as guidance, the author studied tectonic units, characteristics of fault system, tectonic evolution and genetic mechanism, and other aspects for Paleogene of Raoyang sag by using all kinds of data. The research focuses on the analysis of types and structural features of fault systems and genetic mechanism of sag. On this basis, the forming and distributing characteristics of the reservoir was also analyzed, the relationship between the tectonic facies zones and distribution of oil was discussed, and the influence of tectonic evolution on the hydrocarbon migration and accumulation were defined. At last, the further favorable exploration zones were proposed by using the production data.The conclusions have shown that the middle-northern area of Raoyang sag can be divided into three different tectonic regions from north to south: it is tilted basement in northern area, base fault-bend in middle area and detachment fault-fold of cover rock in southern area. The normal faults are main fault in the sag, its strike are mainly NE strike and NNE strike, NW strike and EW strike were secondary. Those faults form grid-like fault systems, and constitutes extensional and strike-slip structural styles, such as forward slip-fault, forward tilted fault block and flower-like structure.According to the different geometry and kinematics features of the main faults, as well as different characteristics of structural styles, the faults in the sag can be divided into five major fault systems, that is, Maxi fault system, Renqiu fault system, Hejian fault system, Liulu fault system and Gaoyang fault system. Within the fault system there are different characteristics and genetic mechanisms, among the various fault systems there are different transfer structures. The fault systems constraints of different structural styles and jointly controls the formation and evolution of Raoyang sag.Through the restoration of erosion thickness caused by the tectonic movement, the author used balanced cross-section to analyze the tectonic evolution. The different phases of tectonic activity have different intensity, which resulted in the different fault activity. The fault activity was analyzed quantitatively by using parameters such as the growth index and fault throws. On this basis, the stages of tectonic evolution of sag were also classified.There are many factors of forming sag. A change of the regional tectonic stress field plays an important role. Researching results suggest that rotation pattern of stretching direction, shear tectonic system, the evolution of extensional faults and depth of decollement structure are the main factors that form the framework of current tectonic. Furthermore, the conclusion was verified by taking advantage of numerical simulation of tectonic stress field.In the last part of thesis, the forming characteristics of petroleum in Raoyang sag were summarized and controlling factors of hydrocarbon accumulation was also analyzed. The author pointed out that activity intensity of fault and unconformity control the oil and gas migration and accumulation. At the same time, beneficial structural facies belts and sedimentary system also have controlling on the stratigraphic-lithologic reservoirs. According to analytical results of production data, one member of Shahejie formation of Lixian Slope and the southern region of Maxi area, three member of Dongying formation of Dawangzhuang-hejian region were taken as the favorable exploration zones.