Capturing Carbon Dioxide: The Feasibility of Re-Using Existing Pipeline Infrastructure to Transport Anthropogenic CO2

Climate change has been attributed to green house gases, with carbon dioxide (CO2) being the main contributor. Sixty to seventy percent of carbon dioxide emissions originate from fossil fuel power plants. Power companies in the UK, along with oil and gas field operators, are proposing to capture this anthropogenic CO2 and either store it in depleted reservoirs or saline aquifers (carbon capture and storage, CCS), or use it for ‘Enhanced Oil Recovery’ (EOR) in depleting oil and gas fields. This would involve extensive onshore and offshore pipeline systems. The decline of oil and gas production of reservoirs beyond economic feasibility will require the decommissioning onshore and offshore facilities post-production. This creates a possible opportunity for using existing pipeline infrastructure. Conversions of pipelines from natural gas service to CO2 service for EOR have been done in the United States. However, the differing sources of CO2 and the differing requirements for EOR and CCS play a significant part in allowing the re-use of existing infrastructure. The effect of compositions, the phase of transportation, the original pipeline specifications, and also the pipeline route require major studies prior to allowing re-use. This paper will first review the requirements for specifying the purity of the CO2 for CCS and to highlight the implications that the presence of impurities and the current water specifications for pipelines has on the phase diagram and the associated physical properties of the CO2 stream. A ‘best’ and ‘worst’ case impurity specification will be identified. Then an analysis on the impact and subsequent validation, of equations of state based on available experimental data on the phase modelling of anthropogenic CO2 is presented. A case study involving an existing 300km gas pipeline in the National Transmission System (NTS) in the UK is then modelled, to demonstrate the feasibility of using this pipeline to transport anthropogenic CO2. The various issues involved for the selected ‘best’ and ‘worst’ case specification are also covered. This is then followed by an investigation of the options for transport in the ‘gas’ phase and ‘supercritical’ phases, and also identifying the limitations on re-using pipeline infrastructure for CCS.