Accurate Determination of Geopressured Aquifer Salinity from the SP Log

Abstract

The amount of gas dissolved in geopressured brine is water salinity dependant. When water samples are available, water salinity is determined by direct analysis. In the absence of water smnaples, which is often, water salinity is estimated using conventional well logging interpretation techniques. The water resistivity, Rw, is first calculated from the SP log. The salinity is then obtained using available correlations. It is not unusual to obtain poor correlations between the values obtained from water samples and those estimated from the SP especially in deep geopressured south Louisiana formations. The basic SP equation Sp-K log was examined. The parameter K was found to vary with the shale resistivity Rsh. A new interpretation chart relating SP to Rsh, Rmf and Rw was obtained. the use of the new equation resulted in a significant improvement in the correlation between water salinity values obtained from water samples and those estimated from the SP log.