The calculation of water saturation from resistivity logs relies on the saturation exponent of Archie’s equation. The accurate determinations of the water saturation in clay-bearing sand reservoirs have been found to be very complicated due to the additional conductivity of the clay minerals, which tend to increase with the increase of porewater conductivity in a nonlinear relationship. Therefore, the aim of this study is to investigate the effects of porewater conductivity and clay minerals on the saturation exponent in different water saturation ranges. A number of digital rock analyses on clay-bearing sandstone were performed in this study using the finite element method. The results indicated that the I-Sw relationship was generally a nonlinear relationship, which changed with the water saturation on a log-log plot. It was observed that the clay volume fractions, as well as the clay minerals in which the conductivity varied with the pore-water conductivity, had displayed significant effects on the saturation exponent.

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