Prevention of sulphate scale in production wells–Challenging the 40 mg/L of sulphate in seawater injection

Wells generally face barium, strontium and calcium sulphates (BaSO4/SrSO4/CaSO4) scaling due to incompatibility of formation water and seawater injected in the reservoir. Barium sulphate deposit was expected in this field due to the high level of barium in the formation water. Scale mitigation is achieved using conventional treatments such as continuous scale inhibitor injection or batch scale inhibitor squeeze treatment; another non-chemical and environmental preventive mitigation is the injection of low sulphate seawater (LWSW). This study showed that the increasing level of heterogeneity (layering permeability contrast), size of aquifer and high initial barium concentration in the formation water, delay the optimal relaxation timing from desulphated seawater to full seawater injection. Sulphate level in the desulphated seawater, the existing of horizontal flow barriers and slow barium sulphate reaction rate, have marginal impact on the optimal relaxation timing from desulphated seawater to full seawater injection. Gradual build-up in the sulphate concentration allows earlier relaxation behavior, with lower degree of risks compared to the direct switch to full seawater injection.