Study On Oil Saturation Of Tight Reservoirs In The Ordos Basin

The low permeability sandstone reservoir has poorphysical property, the smallpore throat,the strongpore throat structure heterogeneity and the microscopic seepage mechanism which is different with the conventional reservoir.Therefore, the microstructure of the reservoir rocks is more complicated, and how to interpret the oil saturation of reservoir rocks more accurately is always a concern of the people.Based on research of the domestic and foreign storage layer, oil saturation research methods, this article develop work to realize low permeability reservoir microscopic pore structure in Ordos Basin and revealthe mechanism of low permeability reservoir permeability change from the microscopic pore structure. To establish microcosmic pore structure parameters for method and qualitative analysis of the micro pore structure of the reservoir with the effect of oil saturation. Then a new method for the interpretation of oil saturation is established.The relationship between oil saturation and the percentage of movable fluid is analyzed. Thecompletion of the work and achievements are as follows:(1) The microscopic characteristics of the core are studied by casting thin sections, scanning electron microscopy (SEM), X-ray diffraction;(2) Nuclear magnetic resonance (NMR)experiment was carried out to obtain the percentage of movable fluid in reservoir rocks. Through the experimental data analysis, there is a good power function relationship between the percentage of movable fluid and permeability. Introduced the pore structure complex index of this concept, in value that is approximately equal to the ratio of rock permeability and porosity, porosity units permeability.Through the analysis of the data, the relationship between the percentage of movable fluid and the composite index of pore structure is a power function;(3) By scanning electron microscopy (SEM) experiments the date of capillary pressure curvesand analysing the experimental data of nuclear magnetic resonance (NMR),we can get micro pore parameters:the coordination number z, pore throat radius of H, pore length l and so on. Then by calculating four wellblock permeability and comparising with liquid permeability numerical,we found that the error of the model permeability calculation is acceptable, which means the pore throat radius, the variation coefficient of the model calculation and the throat length values are reasonable;(4) The percentage of movable fluid of reservoir rocks is obtained through the nuclear magnetic resonance experiment. The power function relationship between the percentage of movable fluid and permeability is obtained through the experimental data analysis;(5) Using LTB saturation calculation model to explain four reservoir oil saturation respectively, and compare with the Archie formula which explain oil saturation and the nuclear magnetic logging which explain oil saturation data. The LTB model can avoid the limitation of the Archie formula and the oil saturation in the underground rock can be calculated more accurately;(6) By analyzing the relationship between the oil saturation and the percentage of movable fluid we found that the greater the oil saturation, the greater the percentage of the corresponding movable fluid. For the relationship between the variation coefficient and the percentage of movable fluid have obvious negative correlation, so the greater the degree of oil saturation, the smaller the coefficient of variation of pore throat radius is.