A comprehensive methodology has been developed for predicting mineral scaling in oil and gas
production environments. The methodology is based on a previously developed model for mixed-solvent
electrolyte systems (MSE). The model relies on a detailed treatment of speciation in the liquid phase. It
represents the standard-state properties of individual species using the Helgeson-Kirkham-Flowers
equation of state and it predicts the species' activity coefficients on the basis of contributions that reflect
long-range electrostatic, short-range ionic, and non-ionic interactions. The model has been designed to
calculate phase equilibria in multicomponent systems containing an aqueous phase, multiple solid
phases, a gas phase, and a second liquid (typically hydrocarbon-dominated) phase. With this
formulation, the model is capable of predicting the formation of scales not only in aqueous systems but
also in environments that contain nonaqueous additives such as methanol or mono-, di-, and triethylene
glycols. The performance of the model has been analyzed for various solids including calcium sulfate,
barium sulfate, calcium carbonate and magnesium carbonate as a function of temperature, brine
composition, pressure and the presence of methanol and glycols. Additionally, the effects of
metastability have been taken into account for scales that may occur in various crystalline forms.
Keywords: Mineral scaling, modeling, thermodynamics, precipitation, mixed solvents