Accuracy analysis of water saturation models in clean and shaly layers

An accurate determination of oil reserve either in virgin or in developed reservoirs represents the main task of petrophysicist and reservoir engineer. Input parameters of Archie's water saturation model in clean formation or suitable shaly water saturation model must be determined as accurately as possible. Archie's parameters a, m and n are the most important parameters to be estimated affecting determination of water saturation, in addition to the empirical constants required for selected empirical shaly water saturation model in case of shaly formations. This paper presents a new technique to determine Archie's parameters called 3-D Technique. This technique is based on the three dimension plot of three parameters; formation water resistivity, water saturation and formation porosity. A comparison study with conventional technique and CAPE technique is conducted to outline the accuracy level of each technique defining Archie's parameters a, m and n. Two field examples are given to show the applicability of three techniques and also to demonstrate the impact the uncertainty of Archie's parameters values on the accuracy of calculated water values using Archie's model or shaly water saturation model.