Unloading system for direct CO₂ injection

Background
Nemo Maritime AS has together with its industry partners; Framo, Worley-Rosenberg, Brevik Engineering and NORCE, developed a concept for ship transport of liquid CO₂ with direct injection to storage reservoirs. The project was conducted during 2021- 2024 and supported by the Norwegian Research Council (Forskningsrådet) as a Industri Prosjekt Næringsliv (IPN) The results include the ship design with cargo tanks for CO₂, transfer pumps, design of the process unit fully integrated for injection to the reservoir. NORCE did an in-depth study of the reservoir effects of batch (interval) injection to qualify the concept.

The link from ship to the subsea wells had not been studied and this missing link was the next step to establish a complete solution for a direct injection solution. OneSubsea is the world’s leading subsea technology and solutions provider, focused on accelerating innovation to improve subsea asset performance, while increasing energy efficiency and reducing CO₂ emissions. Over the years, it has delivered
subsea equipment and solutions for submerged loading of oil from offshore fields to shuttle tankers. These loading systems include the basic elements but needed to be made suitable for injection of CO₂ and compatible with the Nemo ship solution.

In addition, OneSubsea has delivered the subsea well for the Northern Lights project, underlining their leading role in designing subsea equipment for CO₂ injection wells
With this background, Nemo established a consortium to develop an offloading solution for CO₂ injection directly from a Nemo ship consisting of OneSubsea, Brevik, OMV and TotalEnergies, with the aim to apply for funding support through the CLIMIT program. The funding was essential for the partners to allocate personnel and budget.

Goal
The goal for the project is to develop and qualify a safe, flexible and cost-effective solution for offloading liquid CO₂ from a ship to a subsea well, based on existing offloading systems used for oil loading.

Activities
The scope describes all the elements for the connection between the ship and the subsea well. The ship will be held on station by mooring or by dynamic positioning (DP) and connected to the hose/riser that will transfer the CO₂ from the ship to the subsea infrastructure and the injection wells, and finally into the reservoir. The project has addressed the challenges related to injection of CO₂ including material challenges that arise from the corrosive nature of CO₂. The challenge is to find solutions to enable safe and cost-effective operations.

The work includes shallow and deepwater solutions for both active station-keeping (dynamic positioning), and passive station-keeping (mooring). The solutions include operational concepts and procedures for connection, disconnection, and emergency situations.

Results
The project has studied the four main cases outlined in the scope and described a solution for emergency disconnect. Throughout the project several technical reports have been produced. The work has been based on experience with offshore oil loading systems and the connection and disconnection systems which have proven to be reliable. The challenges related to CO₂ as corrosive medium and higher pressures have required equipment redesign. Material selection has been addressed but it is very sensitive to the final CO₂ specifications and will need further work to conclude. There are significant costs implications if expensive steel alloys must be selected.

The final report describes the system requirements for the basic design, the operational and safety philosophy, material selection, risk assessment and address the four offloading solutions cases. The work has resulted in a design base for further detailed studies to prepare for prototypes and development. No showstoppers have been identified.

Further Work
Further development is required to confirm costs and commercial feasibility for the various cases. Material selection is one of the main challenges with respect to the CO₂ composition and operational conditions and needs to be further addressed when a CO₂ specification has been standardized.

Direct injection from a ship also requires a control cable from the ship to the well. The design includes an umbilical that can be connected and disconnected. The control system needs further work and will be addressed in the follow- up study that has been recently awarded by Gassnova to a consortium comprising Nemo, OneSubsea and Framo.

Publications
The Nemo ship concept, including offloading solutions that was presented at the NPF-CCS conference in December 2023 and as part of the Carbon Transport Solutions (CETP) presented at the Baltic Forum 2024, Trondheim CCS conference 2025. The project was also presented at the CLIMIT summit February 2025.