One of the coming great leaps forward for the subsea industry will be the separation of water from the wellstream on the seabed. A key joint industry project in the development of this technology is entitled CoSWaSS - Configurable Subsea Water Separation System. The project is sponsored by Amerada Hess, BP Exploration, Elf Norge, Mobil Exploration Norway, Norsk Agip, Norsk Hydro, Statoil, and Texaco.
CoSWaSS was to culminate in 1999 in an offshore demonstration of the system. But such is the enthusiasm in the industry to realise the benefits of subsea water separation that this demonstration will be replaced by the first use of the technology on a live field - Norway's Troll.
Troll Oil operator Norsk Hydro was due in early April to award a contract for the development of a pilot subsea separation station to be installed on one of the subsea well clusters included in the current phase of Troll Oil development. Two of the three companies understood to be bidding for this job were Norwegian - Kvaerner Oilfield Products and ABB.
Meanwhile the CoSWaSS project, the first phase of which - conceptual definition - was due to be finished in March, has been modified. The subsequent phases will now be replaced by an on-going technology development programme, to drive the technology forward by managing clusters of technology developments projects, each focusing on the development of specific components or sub-systems.
Subsea separation offers a wide range of benefits. Most fields produce a lot more water than oil, some of them right from start-up. Taking out the water close to the wellhead greatly reduces the volume to be transported back to the host facility, thus reducing both the transport and topside processing requirements. By directly re-injecting the water, the need for topside water injection facilities and associated pipelines is also reduced or even eliminated.
The process of subsea water separation reduces the back pressure on the production tree, thus enhancing the flow from the well. Again, the greatly reduced water content of the two-phase flow exported to the host facility diminishes the problem of hydrate formation, the bane of multiphase transport, and hence also the requirement for chemical injection.
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