Mineral scale formation during incompatible water injection into aquifer of oil reservoirs is one of most challenging problem in IOR method. Thermodynamic modeling of incompatible mixing of formation and injection brines before water injection operation could prevent the scale formation in oil reservoirs and injection and produced wells. Using the solid-liquid equilibrium, ENRTL activity coefficient model, mass balance and electroneutrality equations a new method for prediction of different mineral scale formation is presented. Using the experimental mean activity coefficient and solubility data, the binary interaction parameters of ENRTL activity coefficient for studied salts are optimized. Also, the correlation of the solubility product of the main sulfate salts such as CaSO4, CaSO4 center dot 2H(2)O, BaSO4, SrSO4 in vast range of pressures are obtained through fitting the solubility data. Once scaling index becomes greater than zero, the precipitation amount of salt(s) is obtained by mass balance and electroneutrality equations. The present model is compared to previous models for different case studies. The results verify the prediction of new model for determination of scale type and amounts. (C) 2014 Elsevier B.V. All rights reserved.