Design Considerations of a Subsea Shuttle Tanker System for Liquid Carbon Dioxide Transportation

Subsea pipelines and umbilicals are used for the transportation of fluids and electrical power between subsea installations and floating production units (FPUs). The installation and maintenance of these systems can be expensive. In a conventional subsea field development, the produced fluids can be transported from the well to a FPU where they can be offloaded to a tanker (surface ship). In the case of carbon dioxide (CO₂) injection into the well, the direction of flow is reversed, i.e., CO₂ flows from the tanker to the FPU, down the riser base and through the subsea pipelines to the well. This offloading process is weather-dependent and cannot be performed in severe weather conditions, i.e., strong winds and large waves. This paper presents a novel subsea shuttle tanker system proposed by Equinor ASA designed to be a possible alternative to subsea pipelines, umbilicals, and tanker ships. The subsea shuttle is intended to operate submerged under the sea surface to transport liquid CO₂ from an existing offshore/land facility where CO₂ is captured to a subsea well where the CO₂ is injected into the reservoir. As the shuttle is subsea, it can operate under any type of weather conditions. Even though the subsea shuttle is proposed as a vehicle for liquid CO₂ transport, it can also transport other types of cargo such as hydrocarbons, injection fluids, electrical power, or subsea tools. The paper will discuss the most important design considerations surrounding the subsea shuttle tanker.