The Magazine for Underwater Professionals

Jul/Aug 2016


Society for Underwater Technology

Feasibility assessment of an all-subsea field development

The Society’s London evening meeting ‘All-Subsea: Feasibility Assessment of the Subsea Factory Concept’ saw the SUT host an industry audience for an interesting presentation delivered by Cranfield MSc students on their MSc group research project. The students discussed the technical feasibility of undertaking an all-subsea field development – a much discussed concept within the industry which seeks to totally eliminate the use of any floating production facilities by transferring all production and processing underwater.

The chairman, Alex Hunt, introduced the topic by referencing a recent DNV GL position paper which discussed various process steps to manage raw fluid streams for an all-subsea scenario. With the simplified process layout being limited in scope, Cranfield MSc students were given the task of expanding the work carried out by DNV GL, by adding as many process steps as possible and critically analysing each step based on technology readiness levels (TRLs) for each process module to in order to determine the maturity of the subsea factory concept.


The project goal was to “assess the technical feasibility and operational desirability of locating each sequential processing step of a full process-facility on the seabed to identify items that require further development and qualification”.

Full wellstream processing generally consists of two or three parallel streams (oil, gas and water). Depending on the field’s characteristics, each stream could consist of a number of processes, such as compression, boosting, separation, heating, etc., (including storage). For each processing step in sequence, students were required to:

  • Identify different possible technology solutions, the major equipment items and monitoring/control requirements.
  • Assess the suitability for subsea deployment based on technical feasibility and operational desirability, providing recommendations on the solution and location (that is to say, subsea or onshore).
  • Identify gaps in the technology and recommend areas for further development.


The students were given parameters based on a large volatile oil field scenario of 150,000 barrels per day (bpd) oil processing, 250 million standard cubic feet of gas per day (MMSCFD) gas processing, 120,000 bpd water processing, 180,000 bpd water injection, 5% CO2, 0.5% H2S, 2200-metre water depth and 100 kilometres from landfall. This was based on a Santos Basin ‘replicant’ FPSO, offshore Brazil.


The students argued the case for the subsea factory concept as it improves personnel safety and solves the problem of space on topside. It was also highlighted that proximity to wells provided by the subsea factory greatly increases hydrocarbon recovery.

The students also assessed existing technologies based on ease of maintenance, flexibility and robustness. Examples were drawn from existing subsea processing developments such as the Statoil’s Åsgard subsea dry-gas compressor which scores high on safety but low on operational expenditure (high cost) due to high power consumption. Other field concepts such as the Gullfaks subsea wet-gas compressor (Statoil) and Ormen Lange subsea dry-gas compressor (Norske Shell) also score high on safety.


The following conclusions were drawn:


  • Oil Stream: Analysis of the oil stream shows that the process chain breaks for subsea processes requiring desalting or mercury removal, as more work is required in technology qualification for subsea deployment. In such situations, the students recommended crude oil transport via single-phase pumps to onshore processing facility. The students also concluded that subsea oil storage may also be a suitable option for smaller fields and remote locations.
  • Gas Stream: For the gas stream, cryogenic requirements cause the process chain to break at the natural gas liquids (NGL) modules (NGL recovery, separation and storage modules). However, it was noted that the removal of gas impurities is feasible with the use of semi-permeable membranes.
  • Water Stream: Although the requirements for water polishing and seawater treatment are largely dependent on reservoir rock properties, the technologies for subsea water processing are fairly mature (moderate to high) as the only major challenge to full scale all-subsea field deployment is water handling for ultra-deepwater applications.
  • Commercial Feasibility: Alex Hunt rounded up the presentation by discussing the major issues surrounding the commercial feasibility of the subsea factory concept. Subsea gas production would generally require a gas reception terminal to be constructed at shore. It would therefore be more practical to have the complicated production processes onshore rather than subsea due to ease of accessibility and lower operational expenditure. For the oil stream, desalting may not be required due to downstream refining processes carrying out this function.


The Q&A session concluded a fascinating presentation, with guests being treated to fine refreshment of cheese and wine.

Samuel Eka

Fugro commits support to Society's eighth OSIG international conference

The SUT’s eighth Offshore Site Investigation & Geotechnics (OSIG) International Conference has received substantial support from Fugro, with the company becoming the principal sponsor for the 2017 event.

The conference, which is titled ‘Smarter Solutions for Future Offshore Developments’, takes place from 12-14 September 2017 at the historic Royal Geographical Society in London. The event is attracting a lot of interest with more than 200 abstracts already submitted from potential speakers.


The conference offers an opportunity for geotechnical engineers, geoscientists and academics specialising in offshore topics to share their knowledge and experience. The 2017 conference will focus on new research and developments in site investigation data acquisition, evaluation and integration, geotechnical analysis and design as well as field operational experience.


Tim Dunne, global business line director for marine site characterisation at Fugro, said: “As a leading global supplier of marine geotechnical site characterisation services, Fugro is delighted to continue its support of OSIG. This major conference event provides an unparalleled platform to exchange knowledge and experience with other experts and we are very pleased to be principal sponsor in 2017.”
Dr Bob Allwood, chief executive officer of SUT, added: “We enjoy a strong relationship with Fugro and I’d like to express my sincere thanks for their support.


“Delegates will hear from a range of high profile speakers on new research findings and innovative ideas as to how we can improve efficiency, develop more collaborative approaches and offer innovation towards ‘Smarter Solutions for Future Offshore Developments’.”

OSIG 2017 will take a detailed look at the challenges currently faced by the offshore oil and gas industry and call for innovative approaches to improve efficiency and rigour in practice.


The 2017 event will also discuss what the offshore renewable energy industry has identified and addressed – through major research programmes – on key technical issues that must be solved to support its growing strength.

The conference will host the fourth Bramlette McClelland Lecture and a special issue of the EAGE Near Surface Geophysics journal will be published preceding the conference with selected papers to be presented in a dedicated session. A conference dinner will also be held at the Natural History Museum.

A number of sponsorship opportunities remain available. For further information, please email or telephone 01224 823637.





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