Improvement of thermodynamic modeling of calcium carbonate and calcium sulfates at high temperature and high pressure in mixed electrolytes
Tomson, Mason B.
Master of Science
Pitzer theory is used to predict the solubility of gypsum, anhydrite and calcite over wide ranges of temperature, pressure, and ionic strength with mixed electrolytes, which usually occurs in deep water oil and gas production. Gypsum solubility was measured from 0 to 40 oC, from 14.7 to 20000 psi, with 0 to 4 mol NaCl/kg H2O. Anhydrite solubility in literature was confirmed and adopted in this study. The equilibrium constants of gypsum and anhydrite were incorporated by temperature and pressure dependent parts from different researches. Along with other virial coefficients, virial coefficients for Ca2+-SO42- interactions were fitted, based on which solubility of gypsum/anhydrite is precisely predicted. They are also applied to accurately predict calcite solubility with mixed electrolytes from 0 to 250 oC (except for 100 oC) up to 21000 psi. The Kassoc for CaSO4(0) derived from b2(CaSO4) in this study matches well with other experimental data at 1 atm 25 oC.