Effect of Archie's constants on water saturation Estimation, Nubian Sandstone (Case Study)

Abstract

Estimation of water saturation (Sw) is an important stage of reservoir reserve assessment. Geophysical data recorded of select four wells over studied reservoir depth intervals are processed for presenting this work. Shaly studied reservoir (lower Cretaceous) located Southeast Sirte Basin, has about 410-650 feet thickness, with 30% volume of shale (Vsh) cut off value. It has average total porosity 10%. The reservoir divided into two main units (A and B) according to fluid content (gas and Oil). However, using Archie's standard Tortuosity factor (a=1), Cementation factor (m=2), and Saturation exponent (n=2) parameters effect on water saturation especially shaly reservoir. Therefore, factual parameters of a, m, and n from special core analysis of studied reservoir clarified and comprised water saturation by using different shaly models (Archie, Indonesian and Simandoux) is the main intent. Free and forced fit line technique are used to estimate a and m values. The Simandoux formula gives lowest values of water saturation whether use free or forced Archie's parameters, while the Indonesian has values lower than Archie. Therefore, Shale content (30%) plays performance of various shaly sand saturation equations, which is clearly present by different value between water saturation degrees of average Sw values (ΔSw) where it reach to 3%.