Subsea Separation: The Way Into the New Millennium
Authors: Gustafson Stig , Norsk William Bakke , Michaelsen Jarle 
Published: October 2008

Short presentation of the Subsea Separation and Injection System (SUBSIS) concept with a discussion around the drivers and benefits for such systems.

Presentation of how the first SUBSIS application was initiated and the reasons behind Norsk Hydro's decisions to go for such a system.

Norsk Hydro is operator for the Oil Development on the Troll Field together with its partners: Statoil, Shell, ELF, Conoco and Total.

New cases introducing new technology into subsea processing are presented.

Finally an example showing the increase production potential by use of subsea separation in deep waters is presented.

Introduction

World wide, the easily available oil and gas resources are rapidly being exhausted. Accordingly, the oil companies have to search for oil and gas in new areas or to develop oil and gas fields that previously have not been profitable or impossible to develop. Main new areas of development are deep water oil and gas fields and previously not profitable, so called marginal fields. This calls for a range of new technology.

This fact was realised by ABB in 1995 and based upon own ideas, a fully internally funded development project was initiated, the SUBSIS project. Based upon this commitment from ABB, Norsk Hydro early gained interest and after 1,5 years, the need for subsea separation was identified by Norsk Hydro at the Troll field and the project developed from a research and development project into a full EPC contract.

Norsk Hydro's Troll Pilot, ABB's and the worlds first subsea separation and water injection station is now installed on the seabed. Start up of the separation and injection system will not appear before late spring this year. Start up point will depend on performance of the wells routed through the unit. The process concepts chosen is robust and simple, mainly a large cylindrical separator, offering a lot of volume, with a minimum of internals.

The business interests for SUBSIS first application is substantial, and the entire oil industry is now waiting for the first operation experiences from Troll Pilot.

A major challenge in the oil industry today is also to reduce the overall cost to ensure economic field developments even with oil prices down to 8–10 $/barrel. Seabed processing has been pointed out as one very interesting solution, which can allow transport of produced oil to remote receiving facilities over long distances or directly to shore.

ABB has completed a number of studies the last two years investigating the feasibility of subsea separation and more advanced subsea processing for both oil and gas fields. The results are very promising.

However, the process functions offered by SUBSIS, do not as per today cover all oil and gas fields expected to be developed by the use of subsea technology in the future. SUBSIS in its current state, should be regarded as first step on the way to establish a complete subsea oil and gas processing concept. The next steps will be, three phase separation, subsea dewatering of oil, subsea compression and subsea gas treatment.