The Impact of Field Measurements and Data-Handling Procedures on Carbonate- and Sulfide-Scale Prediction

Abstract

Summary Carbonate and sulfide scales are directly coupled together and differ from other inorganic scales because they are intimately linked to the in-situ concentrations of carbon dioxide (CO2) and hydrogen sulfide (H2S), which influence the local pH and availability of reactive species. The CO2 in aqueous solutions has the most significant effect on the system pH, on the solution content of bicarbonate ion (HCO3–), and on the final alkalinity. However, the presence of H2S in the system also has a direct and important effect on the total-system alkalinity. When calcium carbonate deposition occurs in a depressurized aqueous fluid, the amount of scale (CaCO3) that forms depends on the initial (prescaling) solution alkalinity. Thus, the occurrence and severity of carbonate scale are linked to both the solution carbonate system (CO2/HCO3–/CO32–) and the sulfide system (H2S/HS–/S2–). In previous publications, we have described a rigorous work flow (step-by-step procedure) to accurately predict carbonate- and sulfide-scaling profiles from reservoir to separator using commonly available field data (Verri et al. 2017a). Although, with perfect data, the work flow is rigorous [i.e., it will correctly predict the types and amounts of scale that can occur in some carbonate systems (e.g., CaCO3, FeCO3, FeS)], the numerical results produced are, of course, subject to errors of different types. In this paper, we identify and describe three key categories of data and procedures that must be correctly gathered and used to obtain accurate carbonate- and sulfide-scale predictions: These relate to field measurements, data-handling procedures, choice of software, model equations, and parameters. Moreover, in this work, the impact of unreliable field measurements on the final carbonate and sulfide scaling profiles is estimated, with a specific focus on gas- and water-chemistry errors. By varying important parameters such as Ca2+ concentration and gas-phase CO2 and H2S, it is possible to assess the impact that errors in these measurements have on the final scale-prediction profiles. Because of the closely coupled nature of the carbonate and sulfide systems, it is essential to consider “groups” of variables that change together.

Rigorous Carbonate and Sulfide Scale Predictions: What Really Matters?

“…The authors also looked at field measurement errors and concluded that the three key field measurements for reliable carbonate scale predictions are CO 2(g) , H 2 S (g) , and Ca 2+ …”

“…6,9 The authors also looked at field measurement errors and concluded that the three key field measurements for reliable carbonate scale predictions are CO 2(g) , H 2 S (g) , and Ca 2+ . 10 In this paper, the authors addressed the problem of choosing between different software, EOS, and input (or default) parameters for the PVT calculations.…”

“…Second, the impact of field measurements on carbonate scale predictions was studied, and the authors published for the first time results that show a clear correlation between increasing CaCO 3 scaling risk and increasing H 2 S concentration in produced fluids. 10 The scope of this current work is to address the third and last topic on our research agenda: the impact of software, equation of state (EOS), and parameters on carbonate and sulfide scale predictions.…”

The state of the art in scale inhibitor squeeze treatment

“…needed (Kan and Tomson 2012). The produced water pH is usually determined by a balance between the gas phase acid gases, H 2 S and CO 2 , and the water phase active anions, HCO 3 -, CO 3 2-, carboxylates (such as acetate), HS -, S 2and OHand each of these anions is difficult to measure accurately (for a discussion of these analytical issues, see corresponding references (Kan and Tomson 2012;Kan et al 2019;Ness and Sorbie 2019). Also, for many wells the temperature, pressure, and flow rates are not known accurately enough to support squeeze/resqueeze decisions.…”