The Paleopressure Evolution And Accumulation Mechanism Of Natural Gas In Upper Paleozoic In The Northeast Of Ordos Basin

North-eastern part of upper paleozonic of Ordos basin is rich in natural gas. Late diagenesis is strong and complex, because of the evolution progress of continental oceanic interaction to delta facies. Hydrodynamic force of Carboniferous - Permian formation presents different feature in different tectonic evolution period, and it affects migration and accumulation of natural gas. It is of important theoretical and practical Significance to analyze migration and accumulation mechanism, though analyzing the history of hydrodynamic force evolution associating description of conducting tissue.Overpressure evolution history and hydrodynamic force distribution were obtained, though basin numerical simulation, for bounding of overpressure of largest buried depth period though compaction curve of mudstone, associating measured pressure and trapping pressure of inclusion. sand body distribution are researched, effectiveness of sand conducting tissue is describing using store coefficient and flow coefficient, and effective conducting tissue area divided, in the condition of delta facies. Accumulation periods are divided using homogenization temperature of inclusion and experiment of carbon-oxygen isotope. In the above, accumulation mechanism of natural gas is analyzed comprehensively.Major recognition including: overpressure occurs in the lower part of Yanchang formation. The peaks appear in Yanchang - Zhifang formation, Shiqianfeng formation and Shangshihezi formation. Two peaks are developed in late Triassic and early Cretaceous, the latter is bigger. Distribution feature is different in different period. High value area of gas potential exists in southeast part in Late Triassic to Late Jurassic, and southwest part in late Early Cretaceous to Late Cretaceous. Dongsheng area in northeast part is lying in low value area for a long time, as pointing direction of gas migration. Nearly to provenance result in physical property conducting tissue in north part is better. Main period of gas accumulation is in middle Jurassic - late early Cretaceous, when diagenism makes reservoir compact. Natural gas is drove to the north along sandstone conducting tissue affected by gas potential of north direction and accumulations in structural nose and bending place. After Structure uplift happened in late Jurassic, the main direction is east until nowadays. Gas accumulates closely of hydrocarbon kitchen.