GEOTHERMOMETRY FROM BRINE ANALYSES - LESSONS FROM THE GULF-COAST, USA

Geothermometers based on mineral-water equilibria are of limited use at temperatures characteristic of hydrocarbon production from sedimentary basins. Metastable detrital phases such as alkali feldspars and plagioclase persist to temperatures characteristic of the deepest wells sampled (approaching 200-degrees-C), and equilibria involving stable phases such as albite, illite, and quartz are not commonly achieved. Empirical relations, such as that between Mg and Li, are more successful in predicting subsurface formation water temperatures than are equilibrium relations involving quartz, carbonates, or feldspars. The concentrations of most components in saline formation waters seem to be governed by kinetic, rather than by equilibrium considerations.