Scale control is becoming more important as wells are deeper, as they produce more water, and ironically as wells produce low water cuts (evaporation). There are two levels of scale prediction, one is an absolute prediction of the supersaturation versus temperature and pressure and changing composition. The other is to predict how the supersaturation changes with production conditions. The results of over 10,000 experiments from the past 150 years have been screened and scale prediction modeled for calcium, strontium, and barium sulfates, calcite, and halite using Pitzer theory of electrolyte activity coefficients combined with EOS-based VLE modeling by Prof. Vargas for hydrocarbons, acid gases, and water at various TDS values. In addition, several thousand density values versus T, P, and compositions were used to refine the Pitzer coefficients. All of this information is included in the software ScaleSoftPitzer, supported by a consortium of 26 oil and gas and service companies. A statistical argument related to measurement might be made that these calculated supersaturation results are as accurate as will ever be needed. A summary of these modeling results will be shown along with recent applications to controlling scale formation at HTHP, with some surprising results at HP.
