Water Chemistry for Corrosion Prediction in High-Pressure CO2 Environments

One of the strengths of mechanistic model is its flexibility in extending its validity domain.  It is easy to add new knowledge without major modification of the existing model structure.  Generally, constants of the reactions can be changed and matched to the required operating parameters. Here, the constants for high CO₂ above 10 bars are chosen from open source literatures and implemented in corresponding reactions. Most of the constants are obtained from Spycher (2003) and Duan & Li (2008). The constants from Spycher et al are valid for CO₂-water system in the temperature range of 12-100^oC and pressure up to 600 bar [2] and the constants from Duan & Li 2008 are valid at 1-100^oC and pressure up to 2000 bars. Water chemistry model will be used as the platform for the High pressure corrosion prediction. Here, the experiment was set up to validate the accuracy of the water chemistry model. The most practical and accurate testing is chosen for the model verification. The elements in the water chemistry system are tested as follows:

• Solubility of CO₂ in Water
• Solubility of Water in CO₂
• pH of the system.

Water chemistry will provide the concentration of CO₂ (gas), CO₂ (aqueous), H₂CO₃, H⁺, HCO₃^- and CO₃^2- in the bulk solution system. Once the concentration of these species is known in bulk solution, the corrosion rate and protective film formation can be modeled for high pressure CO₂ systems. H₂CO₃ and H⁺ will serve as the main of oxidizing agents at low pH while HCO₃^- will dominate at high pH. CO₃^2- species will react with Fe²⁺ to form siderite film and precipitate after reaching beyond supersaturation levels 1.