Abstract

Present paper is a re-look at the oil industry practices in making use of the Simandoux and Indonesian shaly sand resistivity interpretation models for formation evaluation. Considering the genesis of Indonesian equation to meet the requirements of fresh water formations of Indonesia, application of Indonesian equation in low connate water resistivity regime is examined in contrast to the water saturation (Sw) output of the Simandoux model. It has been shown that the use of the tortuosity prefactor a less than unity is unwarranted if the Simandoux model is used in evaluating low Rw formations. Indonesian equation at low Rw regime demands truncation for the overshooting results of the model (Sw>1) at Sw =1 and yields relatively high values of Sw where Sw<1. Given the critical role of effective porosity, the significance of non-linear Vsh relations which may go neglected when an inappropriate model is used for log evaluation has been pointed out.