Methanol is a common industrial solvent and is added to water to enhance hydrocarbon solubility and to prevent solid hydrate from forming, as well as other applications. One of the side effects of methanol addition to water is it greatly reduces the solubility of ionic solids, particularly divalent solids. The effect of methanol on ionic solubility has been reported only for a few isolated conditions. The effect of hydrate inhibitors on oilfield scale formation has been studied. A semi-empirical approach is proposed to correlate the effect of hydrate inhibitors on scale formation and inhibition from experimental solubility measurements of halite, barite, gypsum, calcite and carbonate equilibrium chemistry. The ion-cosolvent activity coefficients can be used directly in any solution speciation code to evaluate the effect of cosolvent on mineral scale formation. The validity of the equation has been tested between 4-200°C and 1-6 M ionic strength. Barite solubility is significantly reduced, by as much as 20 fold, with 50% (v/v) methanol. Other mineral solubilities are also reduced significantly. Ethylene glycol has much less impact on mineral solubility than methanol. Good agreements between the model prediction versus both experimental and literature results are observed.

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