A Conceptual Large Autonomous Subsea Freight-Glider for Liquid CO2 Transportation

The produced fluids in a subsea field development can be transported from the subsea well to a floating production unit using pipelines where they are thereafter offloaded to a tanker (surface ship). The flow direction is reversed in the case of CO2 injection into the subsea well. This CO2 offloading process is highly dependent on the weather conditions and it cannot be performed when the conditions are severe. Furthermore, subsea pipeline systems can be expensive to install and maintain. In the present study, a novel subsea freight-glider system is proposed as a suitable, cost-effective, energy-efficient alternative to tanker ships and pipelines. The proposed vehicle is autonomous, 50 m long, has a 1500 DWT displacement, and can carry approximately 800 tons of cargo. The subsea freight-glider uses variable-buoyancy propulsion instead of traditional propellers/thrusters. It changes ballast to provide positive and negative net buoyancy which allows it to glide subsea through the water using hydrodynamic wings. This is an extremely energy efficient way of transporting large amounts of cargo over medium/long distances. Since the subsea freight-glider operates underneath the sea surface, it is not affected by wind and waves and can operate in any weather condition. Furthermore, subsea fields that are not large enough to justify the installation of subsea pipelines can still be developed. Even though the subsea freight-glider is proposed as a vehicle for liquid CO2 transport, it can also transport different types of cargo such as hydrocarbons, injection fluids and gasses, and even carry electrical power using batteries.