Synthesis of intermediate crystal Ba1-xCaxSO4 system via co-precipitation of BaSO4-CaSO4 and partial hindrance of gypsum formation

During the production of hydrocarbons from subterranean reservoirs, calcium sulphate and barium sulphate scaling cause flux decline and dangerous problems in production facilities. Numerous studies have investigated the single salt precipitation in aqueous media. This work is intended to study the co-precipitation of BaSO4-CaSO4, commonly observed salts in the oil sector. The conductometric method was used to follow the progress of the co-precipitation reaction of CaCl2-Na2SO4-barite suspension and BaCl2-CaCl2-Na2SO4 aqueous solutions at acid and alkaline medium. The obtained precipitates were characterized by FTIR, RAMAN, SEM, EDX and XRD. In CaCl2-Na2SO4-barite suspension solution, experiments have showed no difference in gypsum precipitation mode. For BaCl2-CaCl2-Na2SO4 solution at acid medium, it was shown that during the co-precipitation reaction, intermediate mixed crystals Ba1-xCaxSO4 can be formed with an induction time increases in comparison to pure gypsum nucleation. Intermediary solids, which precipitate in dendritic shape, crystallize in both orthorhombic (x < 0.5) and monoclinic (x > 0.5) systems through an insertion and substitution mechanism of calcium in the crystal lattice of barites. Nevertheless, at alkaline medium (pH 8.3), the results have revealed that the presence of Ba2+ has not a significant effect on gypsum precipitation kinetics.