| Transtensional basin as an important form of oil-gas bearing basin, has been valued more and more as the degree of exploration of domestic major oil-gas fields increases, carrying out relative basic research work is in urgent need. Huimin Sag is a typical transtensional faulted basin, in which Linshang and Xiakou NEE broom fault systems show clear transtensional characteristic. While the petroleum system in Huimin Sag is obviously controlled by transtensional structures, studying the structural features and the structural evolutionary process is very important for understanding the oil-gas accumulation regularity in transtensional basins.Based on logging data, seismic data, core data and related analysis data, with the theory of tectonic geology, tectonic dynamics, petroliferous basin analysis, tectonic numerical simulation etc., this paper has established the dynamic and static geological model of transtensional structure, made the trastensional tectonic evolution regularity of Huimin Sag clear, and summarized its controlling effect on deposition, trap and petroleum accumulation, which provides a basic structural geological reference for petroleum exploration in Huimin Sag and other similar transtensional basins.Before Paleogene, there are three basement fault systems existing in Huimin Sag, the strike of which are mainly NEE, NNE and NW. Under the North-South extensional stress, the NEE striking faults are in more favorable extension direction and have been reactivated with sustained and intensive movements. With high definition interpretations, these faults present broom shaped faults combination on plane and flower-structure on profile, showing classic transtensional tectonic feature, e.g. Linshang fault and Xiakou fault. Numerical simulation results fit well with the distribution of the current distribution of transtensional tectonics which shows it is the NEE striking basement faults reactivities under oblique extension that formed the Huimin transtensional tectonic in Paleogene.The activity rates of main faults is calculated, the extension rate is counted respectively for different geological periods and different parts of Huimin Sag, the slip amount of the two boundary faults which are Linshang and Xiakou faults is calculated. Based on the calculations and statistics mentioned above, the history evolution of Huimin Sag is quantitatively described and the basin dynamic evolution model is built. The result shows that the main period of fault activities is Es3 and Es2, the NS stretching rate of the basin is small in center and large on both west and east sides, the transtensional structure is controlled by the cooperative movements of Linshang and Xiakou faults activity, the evolution of the basin has six stages, in Ek and Es4 periods the half graben faulted basin is formed and Es3 and Es2 are the strongest transtensional rifting periods.Hydrocarbon generation center is controlled by the sustained transtensional tectonics activity of Huimin Sag, the center of Es3 is mainly in Linnan transtensional sub-sag and the center of Es4 is mainly in Yangxin tensional sub-sag. Distribution of sedimentary system is macroscopicly controlled by the palaeogeographic background formed by transtensional tectonic activity, the scale of deltas is large in the weak wrench section of which the vertical drop is large and the scale of deltas is small in the strong wrench section of which the fault throws more and the vertical drop is small. Scale of oil-gas accumulation is controlled by the macro structure background. Oil-gas enrichment is controlled by the intensity of activities, evolutional stages and other differences of transtensional fault systems. |
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