Problems and Partial Solutions in Using the S.P. Log to Predict Water Salinity in Deep Hot Wells

Abstract

Predictions of formation water salinity from S.P. logs using conventional methods are usually too low in deep, hot wells of the Texas-Louisiana Gulf Coast. We found a standard deviation of 69,000 ppm when comparing predicted salinities with good measured values. The underestimation of salinity leads to an overestimation of the amount of methane which can be dissolved in these waters, an important parameters in assessing the economic feasibility of geothermal geopressured projects. We have developed an improved technique using an inferred RME value, and geologic age correction. This reduces the standard deviation to 21,0000 ppm. Several factors contribute to the high uncertainties in S.P. derived salinities. We believe the two most important factors are variations in Na ion transport efficient of the shales, plus large, erratic variations in mud resistivity.