PREDICTION OF HALITE, GYPSUM, AND ANHYDRITE SOLUBILITY IN NATURAL BRINES UNDER SUBSURFACE CONDITIONS

Prediction of the solubility of the evaporite minerals halite, gypsum, and anhydrite in brines has numerous scientific and practical applications. This paper presents a Pitzer equation-based model for predicting the solubility of these minerals in Na+-K+-H+-Ca2+-Mg2+Cl--OH--SO42--H2O Solutions of varying composition as a function of temperature and pressure. Model predictions compare well with experimental observations. As an example of the utility of this program, the volume of CaSO4 precipitated as a brine flows up a pipe from 6000 m depth is predicted. This is done as a function of flow distance for different cooling rates of the brine. Results indicate that if the brine can be cooled to near the geothermal gradient no precipitation will take place.