Carbonate and sulphide scales are directly linked together and differ from other inorganic scales because they are intimately linked to the in-situ concentrations of CO2 and H2S, which influence the local pH and availability of reactive species. In previous publications, we described a rigorous workflow (step-by-step procedure) to accurately predict carbonate and sulphide scaling profiles from reservoir to separator using commonly available field data (Verri et al., 2017a). Although the workflow we describe is rigorous, the numerical results produced are of course subject to errors of different types.
In the present paper we identify and describe three key categories of data and procedures that must be correctly gathered and used in order to obtain accurate carbonate and sulphide scale predictions: these relate to field measurements, data handling procedures, choice of software, model equations and parameters. Moreover, in this work we estimate the impact of unreliable field measurements on the final carbonate and sulphide scaling profiles, with particular focus on gas and water chemistry errors. By varying important parameters such as gas phase CO2 and H2S concentration, water pH and alkalinity, Ca2+ and Fe2+ levels, we assess the impact that errors in these measurements could have on the final scale prediction profiles.
This work presents a comprehensive and systematic description of the common errors and challenges associated with the prediction of pH dependent scales (CaCO3, FeS, FeCO3). Moreover, the impact of various parameters on the final scale prediction results is established to distinguish between critical and non-critical data input in PVT and scale prediction software. The results from our analysis suggest that field measurement errors may not play a big role in high scaling risk scenarios, but that they are moreimportant in low/medium scaling systems. In addition, our calculations demonstrate the impact of increasing H2S on calcium carbonate scaling profile, which has not been previously addressed in the literature.