High CO2 Depressurization

Dry Ice Risk Analysis and Mitigations

Increasingly, operators are looking to exploit oil & gas fields rich in CO₂ (>50-60 mol%). The main challenges introduced by high content of CO₂ in the design of safety depressurization systems are:

• Complex thermodynamic behaviour:
  • Physical properties that are not accurately predicted by standard equation of state methods
  • Narrow phase envelope with dense phase depressurization – These result in large amounts of “boiling” liquid accumulated across the system, with a significant effect on metal wall temperatures.
• Formation of dry ice during depressurization leading to blockages.

PSE’s approach:

• Use Validated gFLARE models for predicting fluid and wall temperatures.
  • Use advanced EoS options such as GERG or SAFT-γ Mie, if required for accurate prediction of physical properties.
• Distributed / geometric approach to dry ice risk analysis and mitigations.
  • Identify specific locations where dry ice formation potential exists, from either gas or liquid phase during depressurization.
  • Use saltation correlations to determine if solids deposit in specific locations and whether blockage risks occur.
  • Propose suitable design mitigations and operating philosophies to avoid formation of dry ice.