Operational Flexibility of CO₂ Transport and Storage

Publication Overview

This study has reviewed different transport and storage scenarios to reflect the range of full-scale commercial operations. In addition to a wide ranging literature review a survey of industrial, utility, pipeline and CO₂-EOR operators was also conducted to obtain their insights of CO₂ transport and storage. Owing to the sensitivity of these commercial operations it has not been possible to attribute background information to either individuals or their companies. Anonymity has not prevented the inclusion of real world data on exhaust gas composition from different sources including power generation (coal and natural gas), oil refining, gas processing, cement, hydrogen production, and ethanol production. It also includes background information on actual CO₂ pipeline operation, including network hubs, and CO₂ CO₂-EOR experience in the United States. Experience from different industrial scale injection projects such as Sleipner, Snøhvit and In Salah, has been included. The study has investigated how flexible operation affects CO₂ storage and the measures adopted to accommodate intermittent supply. There are a series of prioritized recommendations based on the gaps in knowledge.

Publication Summary

• Large point sources of CO₂ can deliver relatively pure 99.7% CO₂ after capture and dehydration. However, it is important to recognise that many large-scale industrial processes that generate CO₂ emissions are cyclical and intermittent, therefore, to ensure a consistent and reliable CO₂ supply integrated pipeline networks will be essential.
• Experience from the United States clearly demonstrates that CO₂ with a high level of purity can be effectively and safely delivered using integrated pipeline networks.
• Networks can be a useful means to control flow in a pipeline and can also act as a buffer by supplying CO₂ from several sources to a number of different sinks. Multiple sources also mean that there is less reliance on a single source and intermittent supply from different sources can be accommodated. CO₂ can also be temporarily compressed or ‘packed’ into pipelines as a short term measure.
• This study has shown that most North American CO₂ pipelines are overdesigned for their current application. They are designed for higher flow rates and operating pressures through the use of thicker walls and larger diameters. Future pipeline networks can take advantage of this experience if there is an intention for increased capacity in the future.
• Impurities particularly H₂O and O₂, can have negative impacts on pipelines including fracture propagation, corrosion, non-metallic component deterioration and the formation of hydrates and clathrates. The density and viscosity of fluids can also be affected. Non-condensables like N₂, O₂, Ar, CH₄ and H₂ should be separately limited to <4% because their presence increases the amount of compression work. Compression and transport of CO₂ for CO₂-EOR use in the United States has shown that impurities are not likely to cause transport problems provided CO₂ stream composition standards are maintained and pressures are kept significantly over the critical point (≥10.3 MPa).
• The most significant effect on transport and injection of CO₂ is the water content. The Kinder Morgan specification for pipeline transport of CO₂ is a 600 ppm by weight for H₂O and 10 ppm by weight for O₂. Hydrate formation can lead to the most dramatic interruption to flow but the condition is generally preventable using multistage compression and knock out systems plus the inclusion of chemical dryers such as monoethylene glycol.
• Intermittent flow can have an impact on wellbore integrity, fatigue and corrosion. Changes in gas pressure can result in deleterious phase behaviour including segregation of the component gases leading to corrosive effects. Maintaining sufficient pressure is possible onshore with compressor plants but this option is not possible offshore. Lengthy offshore pipelines may need to be larger in diameter than their onshore equivalents so that pipeline pressure can be maintained.
• CO₂ storage in deep saline formations can be managed by using multiple wells and water pumping to control and releave excess pressure, and control plume geometry.
• CO₂-EOR relies on controlling pressure and flow rate conditions to optimise oil recovery. Restricted injection caused by wells being shut in can result in deleterious changes in reservoir pressure and oil miscibility. Under these conditions the precipitation of minerals or asphaltenes (high molecular weight compounds such as bitumen) or changes in formation fluid saturation properties can occur. Reservoir permeability can be reduced as a result. This study has found that experienced operators can plan for intermittency in both the supply of CO₂ and in CO₂ EOR operations.