An essential part of the Carbon Capture and Storage (CCS) supply chain is the transportation of the CO₂ in pipelines from the source to the sink. The understanding of the fluid behaviour as a function of pressure, temperature and composition is essential to ensure a robust and safe design of the transportation system. Within the oil and gas industry, dynamic fluid simulations are routinely performed to assess the requirements for safe- and cost-effective production and transportation systems, including lengthy subsea tie-backs.

The thermodynamic properties of a fluid however change dramatically from a typical hydrocarbon mixture to pure CO₂. Additionally, the presence of impurities in a CO₂-rich mixture has proven to have a major impact on the thermodynamic behaviour of the fluid. A CO₂-rich fluid has a critical point at a pressure and temperature typically within the operating envelope of hydrocarbon production facilities and transportation systems. This thermodynamic characteristic makes the transportation of CO₂-rich systems challenging as non-desired phase transitions may compromise stable operations and / or the mechanical integrity of the pipeline.

Accurate thermodynamic modelling of CO₂-rich systems is therefore crucial. Only when simulation tools are able to predict phase transitions and thermodynamic properties with a higher level of certainty, the dynamic flow simulations will produce robust and reliable thermohydraulic results.

At Wintershall Dea we have developed an internal project to study the behaviour of a CO₂-rich mixture during transportation and injection. In the first part of the presentation we will discuss the phase behaviour of CO₂-rich mixtures in contrast to pure CO₂ and how to describe this with commercial software tools. The second part shows the thermohydraulic behaviour of the system during its transportation along the pipeline and into a typical injection well to store the CO₂ in a depleted gas or oil reservoir.