Decarbonisation Technology - February 2025 Issue

Safety of CO₂ transport One of the main public concerns about CCS is the safety of CO₂ transport in pipelines and its secure storage underground. However, in EOR projects, CO₂ has been transported over decades, so it is not an unfamiliar technology. It poses no greater risk than oil and gas transport, which has a long history of safe management. Additionally, transporting CO₂ is much safer than other substances as it is not explosive or flammable when mixed with air (Drax, 2022) . A combination of governmental legislation and international standards will ensure maximum safety in CO₂ transport. Ultimately, one of the most important steps in safeguarding CO₂ transport via pipeline is flow assurance. This critical process involves understanding and mitigating the factors that could disrupt the flow of CO₂ from the capture point to its storage location. ensuring the successful and economical flow of hydrocarbons from the reservoir to their destination. However, this now directly applies to the transport and injection of CO₂ during CCS projects. Flow assurance studies are an essential part of the design process for oil and gas operations, such as the front-end engineering and design (FEED) process. Factors affecting flow assurance include the formation of solids/blockages, pressure drop, temperature variation, and purity of the CO₂. Among the factors involved in flow assurance, the primary concern is the potential for blockages within pipelines, whether it is hydrocarbons or CO₂. Studies focus on preventing and controlling the formation of solids which may block the flow. Many Flow assurance Flow assurance was initially based on things can affect this, especially the pressure, temperature, and chemistry of the product flowing through the pipeline. Pressure drop is one of the key concerns in flow assurance, with many contributing factors affecting wellbore pressure, fluid properties, and temperature. Here again, CO₂ injection projects can use the experience gained from the oil and gas industry. In hydrocarbon production, wellbore pressure is a significant factor in pressure drop, with up to 80% of the

lost pressure occurring during the flow from the subsurface to the surface. Fluid properties, such as viscosity and density, are also crucial. Fluids with lower density flow with less pressure drop, while higher viscosities cause more friction, leading to a greater pressure drop (Böser and Belfroid, 2013) . Temperature also influences flow assurance; higher temperatures typically decrease viscosity and density, which can limit pressure drop. However, temperature variations can also lead to a drop in pressure. While these factors affecting hydrocarbon flow are present in terms of the flow of CO₂, the effects vary. The pressure drop due to the wellbore will not be the same with CO₂ because it is injected rather than produced. The fluid properties of CO₂ differ from hydrocarbons, and CO₂ is usually transported in its dense or supercritical phase. The purity of CO₂ and the presence of impurities can affect its “ Among the factors involved in flow assurance, the primary concern is the potential for blockages within pipelines, whether it is hydrocarbons or CO₂ ” viscosity and density in pipelines, nitrogen (N₂) having the greatest and hydrogen sulphide (H₂S) having the least impact on density and pressure loss. The presence of certain impurities, including water (H₂O), sulphur oxides (SOx), and nitrogen oxides (NOx), can also affect the flow of CO₂ by increasing the risk of corrosion. Any water content within the pipeline can lead to corrosion, so an industry-standard limit of 500 ppm is maintained to minimise the risk (Simonsen, et al., 2024) . Conversely, the presence of other impurities, such as N₂, can bring down the water concentration levels in CO₂. In supercritical CO₂ environments, the addition of O₂ can increase corrosion in carbon steel, with severe corrosion occurring when both O₂ and H₂S are present. Therefore, the capture and processing of CO₂ for storage projects is critically important. Furthermore, some pipelines may need to be designed with specific materials to account for the presence