GEOCHEMISTRY AND SP - RESISTIVITY CALIBRATION OF SUBSURFACE WATERS - SURAT BASIN AREA

Abstract

Waters in Early Jurassic strata in the interval pre-Jurassic unconformity to Evergreen Resistivity Marker (ERM) of the Surat Basin and in Triassic Showgrounds Sandstone of the underlying Bowen Basin contain solutions of sodium bicarbonate and sodium chloride in varying proportions. Geochemical classification indicates a range of genetic water types from artesian bicarbonate waters to the more stagnant chloride-sulphate waters. In terms of salinity, waters of the Bowen-Surat Basins range from fresh to brackish and are less than 10000 ppm sodium chloride equivalent concentration.

Significant differences in geochemistry of the waters are noted between the Showgrounds Sandstone, and sandstones within the intervals, pre-Jurassic unconformity to Marker 8 (Precipice Sandstone) and Marker 8 to ERM (Evergreen Formation). These differences facilitate the calibration of the measured water resistivity (Rw) values with values (Rwe) derived from the Self Potential log.

Formation water characteristics such as chloride concentration and sodium chloride equivalent concentration are useful tools in the search for hydrocarbons.