Subsea Ultrasonic Flowmeter for Fiscal and Allocation Metering in the CCS Value Chain

The world will need to store several gigatons of carbon dioxide per year in 2050 according to the International Energy Agency’s World Energy Outlook (2024). This will require extensive development of carbon capture, transportation, and storage infrastructure. Some of the carbon dioxide will be transported by truck, container, and ship, but the large volumes involved will require pipelines for transportation, similar to existing pipeline systems for oil and gas. Much of the storage will be done subsea. The first subsea pipelines are already in place (Northern Lights JV, 2024), and there are ambitious plans for large, transnational pipelines in the North Sea (Heiberg-Andersen, 2024). At the receiving end, the carbon dioxide will be distributed to different fields for injection via subsea storage wells to the reservoirs where the carbon dioxide will be stored permanently. Carbon dioxide will flow between different operators and across national borders, and the quantity of carbon dioxide will have to be quantified as accurately as possible every time a border is crossed or ownership changes. It is instructive to consider the monetary value of carbon dioxide in terms of emission taxes and tax credits. The average carbon tax rate among the 23 European countries is €49.23 per metric ton as of April 1, 2024 (Mengden, 2024). In the US, the 45Q tax credit for sequestration is $85 per metric ton at the time of writing (Congressional Budget Office, 2023). A single subsea injection well can typically receive up to 1.5 million metric tons of carbon dioxide per year. This is equivalent to nearly 75 million euros in emission taxes in Europe or 127.5 million dollars of tax credits in the US, and these numbers are expected to increase significantly in the coming years. A 1% error in the measurement of carbon dioxide could represent more than 15 million euros or 20 million dollars over a 20-year period for a single well. Government authorities require information about the volumes of carbon dioxide stored in different formations and via different wells. This requires accurate metering and allocation of the injected quantities per well. The Norwegian Offshore Directorate requires for example that the total measurement uncertainty for allocation metering of carbon dioxide is less than 1.5% by mass (2001).