Improvement of Water Saturation and Formation Factor Parameters in a Clastic Reservoir, Zagros Basin, SW Iran

Abstract

Water saturation (<em>Sw</em>) is one of the most important petro-physical parameter for evaluating the clastic horizons of hydrocarbon reservoir, which can be calculated using Archie's equation. The Archie's parameters (<em>m, a</em>) are the major source of uncertainty in the calculation of Sw. In order to obtain Archie's parameters, a total number of 117 sandstone samples, having resistivity measurements from Asmari Formation were studied. Due to scattered data points on the Log-Log plot of <em>F</em> versus <em>Ø</em> and to obtain reliable values for <em>m </em>and <em>a</em> parameters, the data were classified based on current zone indicator (<em>CZI</em>) into 6 classes of electrical flow unit (<em>EFU</em>). The values of parameters<em> m</em> and <em>a</em> obtained from <em>F-Ø</em> cross plots with excellent correlation coefficient. To avoid from data diversity and to make data applicable, the average values of <em>m</em> and <em>a</em> were obtained with considering the number of samples in each class. To assess the validation of the calculated <em>F</em> based on proposed values of <em>m</em> and <em>a</em>, the measured values of <em>F</em> versus calculated one's using Archie, Tixier and Humble formulas and proposed values were compared. The plot shows that the calculated <em>F</em> using Archie Tixier and Humble formulas are lower than calculated <em>F</em> using proposed and measured values. Applying the determined values seems to reasonably minimize the error in calculating F and therefore Sw%. <br />