Compact flotation unit cut soil in water to 10-15 ppm
Epcon Offshore's compact flotation unit (CFU) looks to be a winning solution to one of the most troublesome environ-mental challenges faced by offshore operators – cleaning produced water to the increasingly strict standards demanded by regulatory authorities.
By the beginning of 2006, operators in Norway will have to be capable of achieving zero discharge of toxic elements into the sea. Elsewhere, standards are moving in the same direction. The rapid take-up of the CFU technology in both the Norwegian and other sectors testifies to the belief of those acquiring it that it can deliver this goal.
This year, the technology won OTC's Spotlight on New Technology Award. Prior to this, in late 2003, recognition from Statoil. Referring to the results of trials on Snorre A of the produced water from Vigdis, process engineer Olav Dolonen said: "The Epcon method has yielded far better results than any other treatment system we've tried. It's got the proportion of residual oil in the treated water down to 10-15 parts per million (ppm) – well below the official ceiling of 40 ppm." The plant was inexpensive to install and robust in operation, the statement added.
The CFU combines two well-known principles: separation by centrifugal forces and flotation technology. Produced water is sent to the cylindrical CFU chamber after passing through the separator. On entering the chamber through a tangential inlet located near the top, it is subjected to a "soft cyclone" effect, in which the oil and gas float to the surface and are returned to the production process. The clean water is drawn off from the bottom of the chamber and discharged into the sea.
Lasse Jahnsen, Epcon's managing director, describes the solution as simple rather than high-tech. There are no moving parts and no small openings that might get clogged up. No other energy is required than that in the liquid flow. However, the composition of the water, including any chemicals added upstream, has to be known, and if necessary additional gas – nitrogen or fuel gas – is added to make the separation process work efficiently.
The CFU has a short retention time – usually less than a minute. It is therefore able to cope with large flows of up to 500,000 b/d. The nominal capacity of a unit can often be exceeded. The unit installed on Norsk Hydro's Troll C platform is rated at 60,000 b/d but normally operates at 82,000 b/d.
As a small company with limited financial resources, Epcon was not able to follow the conventional course of funding qualification programs and proving its technology in a lab before gaining the opportunity to carry out a field test. The whole development has taken place in an offshore environment. The original idea came from people working offshore, and the system has proved itself in an applied situation.
The history of the CFU is a short one. A small-scale test unit was first trialed on Norsk Hydro's Oseberg field in 2000. Hydro was so impressed by the results that it ordered full-scale test systems for the Brage and Troll C platforms, where the performance was confirmed. Subsequently Statoil became interested.
The 180,000-b/d Vigdis CFU on the Snorre A platform, which Statoil has decided to redeploy to treating Snorre production. Epcon will supply a new unit for Vigdis.
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Extended production
Jahnsen sees two main drivers that explain the CFU's rapid rise in the offshore market. The first is environmental, as already explained, and the second economic. By increasing the volume of water that can be treated to the required standard, it enables production to be maintained at higher levels and for longer periods than would otherwise be possible in the face of the rising water cut.
The key to this is the CFU's modest presence on the platform. It has one-third the weight and bulk of traditional water treatment systems, such as hydrocyclones and degassers, and occupies one-third of the footprint. It can therefore be retrofitted in situations in which it is impossible to expand the existing system. For a newbuild platform, it can be used instead of more conventional equipment, bringing significant weight and space savings.
There is another important economic advantage – returning produced water to the sea is a lot cheaper than pumping it back downhole. On a growing number of fields operators have resorted to the re-injection of produced water as a means of meeting the environmental requirements. But this is an expensive solution, says Jahnsen, requiring compressor capacity, which itself requires additional power, and which increases emissions to air. Re-injection can also cause formation damage.
The CFU is now accepted as proven technology by the two major Norwegian oil companies, says Lasse Jahnsen. The number of installations in the sector is growing. In all, there are five CFU systems in operation in the Norwegian sector and one under construction. In addition to the Brage and Troll C installations, which have become permanent, Statoil has purchased the Vigdis unit, which has 180,000 b/d capacity, to treat the Snorre flow on Snorre A, and a new unit for Vigdis is under construction. Units are also installed on Statoil's Heidrun platform and ConocoPhillips' Ekofisk 2/4 J platform, in the latter case treating the water on the oily side of the degasser.
In the UK sector, a permanent unit is under construction for ChevronTexaco's Alba Northern platform, and another has been ordered for Paladin's Montrose. In the Danish sector Mærsk is testing the system, and tests are also planned for a leading operator in the Dutch sector.
Significant inroads have also been made into the global market. After a mere 18 months of knocking at the door, Epcon has broken into the Brazilian market. It first carried out a small-scale test on Petrobras' Garoupa platform, which so pleased the Brazilian company that it ordered a full-scale unit on a rental basis with the option to buy. The skid-mounted unit, with 75,000 b/d capacity, was due to be shipped to Brazil in August.
Elsewhere extensive tests have been carried out on Waha Oil's Jealo field in Libya and a trial is planned for PetroCanada's Terra Nova floater off Newfoundland.
