Improvement to Water Speciation and FeCO₃ Precipitation Kinetics in CO₂ Environments: Updates in NaCl Concentrated Solutions

Abstract

In the oil and gas industry, the dissolution rate of metal-based materials exposed to an aqueous phase is often controlled by the presence of surface layers such as corrosion products. Knowing the characteristics and rate of formation of these surface layers can help assess the level of protection against corrosion they provide and can permit the development of a successful asset integrity program. The appropriate determination of species concentration is a key aspect of accurately predicting the precipitation rate of corrosion products, more specifically of FeCO3, which is the main product of corrosion of steel in CO2-containing environments. While aqueous speciation in low-salinity brine is well-established, the effects of high NaCl contents (NaCl ≥ 3 wt %) on water chemistry and FeCO3 precipitation are less defined. In this work, two fundamental aspects of H2O/Fe/CO2 system speciation in high salinity brine are discussed: the consumption of Fe2+ due to the formation of ferrous chloride (FeCl+) complex and the dependence of K ca, the first dissociation constant of H2CO3, on ionic strength. This leads to a comprehensive revision of the models used to calculate the solubility product of iron carbonate (FeCO3), K sp,FeCO3 . In parallel, the kinetics of FeCO3 precipitation are experimentally investigated using an electrochemical quartz crystal microbalance (EQCM) in concentrated NaCl solutions at varied temperatures (50–80 °C). This led to the development of a new kinetics model for FeCO3 precipitation that now considers the nonideality of the solutions.

Influence of the Morphology of Eutectoid Steels on Corrosion Resistance in NaCl Aqueous Medium with and without CO2

“…Some authors affirm the existing correlation between temperature increase and susceptibility to siderite formation, depending on the morphology [17][18][19]. Figure 5 indicates that the LC wire OCP showed very similar results between the specimens submitted to CO 2 , demonstrating once again that the influence of temperature is not very important for the established corrosion conditions when it comes to the corrosion potential of the material.…”

“…Some authors affirm the existing correlation between temperature increase and susceptibility to siderite formation, depending on the morphology [17][18][19]. Fe → Fe 2+ + 2e − (1e) Equation (1a) (oxy-reduction) and Equations (1b)-(1d) are cathodic reactions (reduction) and Equation (1e) is anodic (oxidized).…”

Demonstrating a Quartz Crystal Microbalance with Dissipation (QCMD) to Enhance the Monitoring and Mechanistic Understanding of Iron Carbonate Crystalline Films

“…The advantage of using QCMD to study crystallization is both technique sensitivity and in situ monitoring capabilities, without compromising on a controlled environment. Previous efforts to study portions of a crystalline lifecycle using QCM (EQCM, QCMD) have been exceptionally limited. − These studies collectively demonstrate the proof-of-concept capability of this technique to become an important method for studying crystallization phenomena. Herein, we build upon this work to demonstrate that both the frequency and dissipation changes can be utilized to provide insights into not only individual crystals but also the particle population development in a film-like layer on a solid surface.…”