Differences And Influencing Factors Of The Buoyance Controlling Reservoir Limitation In Different Zones Of Nanpu Sag

The theory of buoyancy accumulation was put forward by American scholar White in 1885,and then developed into a theory of trapping and finding oil.The expansion of the exploration field has led to the discovery of continuous tight oil and gas reservoirs that cannot be explained by buoyancy theory.The buoyance controlling reservoir limitation is the location where the buoyancy in the basin does not play a role,and it is the boundary between the free hydrocarbon dynamic field and the confined hydrocarbon dynamic field.The unconventional tight reservoirs in Nanpu Sag have good exploration potential and are the focus of exploration work.Conventional reservoirs and tight reservoirs are formed in the free hydrodynamic field and the confined fluid dynamic field respectively.Different hydrodynamic fields have different accumulation mechanisms and characteristics.Therefore,it is of great significance to study the buoyance controlling reservoir limitation.In this paper,statistical analysis method,example analysis method and numerical simulation method are used to determine the buoyance controlling reservoir limitation in each zone of Nanpu sag.It is found that the buoyance controlling reservoir limitation in Nanpu sag is 3357~3959 meters,and its porosity distribution is 10.3%~11.8%.It is the deepest in the Gaoliu area and the shallowest in the Laoyemiao area.The influencing factors of the buoyance controlling reservoir limitation are tectonic movement,fluid properties,particle size sorting and geothermal gradient.One-by-one univariate analysis showed that tectonic movement and geothermal gradient were the main controlling factors for the buoyance controlling reservoir limitation in Gaoliu area;tectonic movement,particle size separation,and geothermal gradient were the main controlling factors for the buoyance controlling reservoir limitation in Laoyemiao area.The buoyance controlling reservoir limitations of the remaining structures are also the results of the combined effects of these four factors.The conventional reservoirs above the buoyance controlling reservoir limitation have the characteristics of great seal,high position,high porosity and high pressure.The tight reservoirs below the buoyance controlling reservoir limitation have inverted relationship,low position,low porosity and low pressure.