The original oil saturation of the reservoir is of vital importance for reservoir evaluation and calculation of geological reserves. To determine the original oil saturation of the reservoir and provide a reference for reservoir evaluation and geological reserve calculation, this paper takes the sandstone of the Chang 9 oil layer group in the Zhouchang oil area of Wuqi Oilfield in the Ordos Basin as the research object. Based on core, logging, mud logging and well testing data, combined with experimental data, four methods, namely the closed core method, mercury injection method, relative permeability method and logging interpretation method, are used to calculate the original oil saturation of the Chang 9 oil layer in the northeastern Wuqi area. The advantages and disadvantages of each method are analyzed to determine the original oil saturation that is suitable for the Chang 9 oil layer group in this area and thereby improve the accuracy of reserve calculation. The results show that the comprehensive logging interpretation method is the best method for calculating the original oil saturation in this area, and the original oil saturation is finally determined to be 54.6%.
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