In this study, the solubility of zinc sulfide has been collected from the literature at pH 2 to 11, temperature 23 to 250 °C, pressure 0.6 to 150 bar, and ionic strength 0 to 4.6 m. A solubility model has been developed based on the combination of Pitzer theory calculated activity coefficient and speciation of the Zn-HS-OH-Cl aqueous system. In total, around 230 solubility data were collected as the input database, the model was fitted in Matalab 2020a with the particle-swarm optimization. The updated model is able to predict the ZnS solubility saturation index (SI) with 95% confidence interval 0.04 SI unit, which suggested good accuracy under model conditions. Due to the extremely low solubility of the ZnS itself, these errors correspond to only around 0.07 ppm of [Zn(II)], which is less than the error of measurement for field samples. For all pH conditions, Zn-HS complexes and Zn-Cl complexes have strong influence on the aqueous soluble zinc solubility. This new model with accurate ZnS solubility prediction will help field operators to better control the ZnS scaling and corrosion problem.
The increasing need for fossil fuels has resulted in more aggressive drilling and exploitation in oil and gas production industry 1,2. As new explorations at more extreme conditions (i.e. high temperature and high pressure) become more frequent, new challenges arise in terms of drilling equipment, operation conditions and safe production 3–6. Among those challenges, the mineral scale deposition, as one of the serious problems both for the surface and subsurface oilfields, can cause pipelines plugging, equipment failure and decrease in production efficiency, even emergency shutdown 6–10. Compared to the conventional drilling conditions, the scaling problems in these extreme conditions are mainly caused by changes in temperature and pressure during the production. The rapid temperature and pressure drop from the reservoir to the surface: 1. alters the equilibrium of the ions in the formation water; 2. causes water evaporation; and 3. redistributes the balance with CO2 and/or H2S gases. These changes result in mineral scale formation 6,11,12.
