Solubility and phase behavior of polyacrylate scale inhibitors

The phase behavior and precipitation yield of a commercial phosphino-polyacrylate inhibitor (PPAA) widely employed in precipitation squeeze treatments have been characterized as a function of temperature, pH, and the Ca2+ and PPAA concentrations. Contrary to expectations, over a range of conditions the yield of phase-separated PPAA was found to be less than 50% and sometimes as low as 5%. Studies on a sample of isolated precipitate show that it has significant solubility even in brines with high Ca2+ concentration. Ca2+-induced fractionation of the polymeric inhibitor by molecular weight has been identified as the mechanism responsible for both the observed precipitation and re-dissolution behavior. Implications of these results for the optimization of precipitation squeeze treatments are discussed.