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

Abstract

Subsea pipelines and umbilicals are used for the transportation of fluids and electrical power between subsea installations and floating production systems (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.

Technical–Economic Feasibility Analysis of Subsea Shuttle Tanker

“…In doing so, the external hull need not be designed for the full hydrostatic pressure at the water depth it is operating in. Further details of this system can be found in Xing et al [7] and Ma et al [8]. This 50% payload target is maintained for all sizes of the SST created in this paper.…”

“…In general, the works mentioned above did not go beyond conceptual design proposals. Xing et al [7] and Ma et al [8] closed this knowledge gap by considering the most critical design considerations and defining a baseline SST design that entails detailed global design specifications.…”

“…However, tanker ship operations are weatherdependent and can be difficult to conduct in adverse weather circumstances because of the large dynamic load-effects from the environment (i.e., wind and wave action). On that the account, Subsea Shuttle Tanker (SST) concept was introduced as a potential alternative to subsea pipelines and tankers in order to overcome the limitations mentioned above [5][6][7][8].…”

CFD Investigation on Hydrodynamic Resistance of a Novel Subsea Shuttle Tanker

“…The hull dimensions used in the present study are shown in Figu design parameters of the SST considered are presented in Table 1. In the the Reynolds number is based on the hull length (ReL = u∞·L/ν, where u∞ is th L is the hull length, and ν is the kinematic viscosity of the fluid) is equal R Detailed design considerations and baseline design presented by Xing et al [3] and Ma et al [4] highlighted the importance of low drag resistance to maximize the SST's working range. This paper will compute the resistance coefficient for the concept hull of a version of Equinor's SST travelling with forward speed.…”

“…The operation can be conducted even in severe weather conditions without any interaction with surface vessels. It can also utilize the external hydrostatic pressure and temperature in its design through a pressure compensating system, see Xing et al [3] and Ma et al [4]. Safety of the marine operations will be also enhanced, as the SST can operate remotely or autonomously outside of conventional working conditions which are normally manned.…”