Study on a New Method for Calculating Water Saturation

In order to improve the identification and evaluation accuracy of low resistivity oil layer and complex pore structure oil layer, and to avoid the interpretation error caused by the traditional evaluation mode of “high resistivity is oil layer and low resistivity is water layer”, the method of calculating water saturation by radial resistivity ratio was studied. The results show that the radial resistivity ratio can be used to calculate the reservoir water saturation for completely invaded formation, which can be deduced according to archie formula. The new formula does not evaluate oil and water layers based on high or low of resistivity, but can be used to evaluate low resistivity oil and high resistivity water layers. After testing core experimental data, The new formula can effectively calculate the water saturation and meet the requirement of using. After practical application of data, The average absolute error of the calculated water saturation is 3.55%, which conforms to the industry standard. This method is helpful to improve the coincidence rate of logging interpretation, and is worth popularizing.