A few years ago history was made at the Troll C field offshore Norway when the world's first subsea water injection pump was installed. A lot of water has gone through the system since and the suppliers involved in that project have plans for the future.

Framo Engineering along with ABB helped design, build and install the subsea production system deployed on Troll C oil project, which consisted of a horizontal subsea separator, a water injection pump and a water injection well. Located in 1,148 ft (350 m) of water, about 2.5 miles (4 km) from the Troll C field, the modular system was designed to allow continuous production even if one module malfunctioned.

The complete system was known as SubSis. Framo and ABB together duly won considerable prestige for their achievement back in late 1999.

Framo Engineering is due to present a paper this month at the Underwater Technology conference in Bergen, Norway, focusing on current offshore technology. Hart's E&P asked the company about current and future subsea production technology trends.

"The market has a mixed view on [the] application of traditional subsea production systems in large subsea developments. Typically in West Africa conventional systems are applied to the extent possible," said Nils Arne Sølvik, area sales manager for Framo Engineering based in Norway. "In deepwater fields outside the Gulf of Mexico the willingness to use more novel solutions is higher."

One of the most desirable tools for development in Sølvik's view is subsea production systems with high performance artificial lift capability, such as multiphase boosting. West African markets are also becoming receptive to this technology. Sølvik's company has sold subsea multiphase booster pumps in Equatorial Guinea to the Amerada Hess-operated Ceiba field and others. "In our latest projects, we see that typical manifold functions are integrated with the process control required on the subsea multiphase boosting stations."

Clients are receptive to standardized, integrated and flexible equipment and integrated solutions, he said. Multiphase boosting and metering are generally well received, too, especially when this can be delivered as an integrated system from topsides to the wellhead connection.

Not surprisingly clients are always looking to shorten time to first oil after discovery and project sanction. But Sølvik observed that while drilling and construction of a production platform - often a floating production, storage and offloading (FPSO) vessel - gets priority, parallel activity also requires the utilization of high performance artificial lift systems if as much oil as possible is to be produced in the first 5 to 10 years of field life. He said his company's customers have been reporting "phenomenal production increases" with multiphase pumps.

Looking at the potential demand for subsea production technology 5 to 10 years ahead, Sølvik still reckons FPSOs linked to subsea production equipment will remain a favored formula. "We will see a need for systems that can improve economics from deepwater fields - down to 10,000 ft (3,048 m) as well as enabling solutions for tail-end and existing infrastructure production enhancements. Key words here are long distance tie-backs, approaching +62.5 miles (+100 km) at the end of this period, wet gas compression, raw seawater injection, multiphase boosting and metering, and all required auxiliary systems [including] controls, electrical power, chemical supply etc. to safely and efficiently operate these enhanced production providers." And he does not foresee any major technological barriers which still need to be overcome, "There will be further development in terms of depth capability, power rating and step-out distance, but these challenges are mainly upgrading and further development of the systems and building blocks that we already have developed and installed."

He pointed out Framo already has field experience putting products in stepouts from 3,000 ft to 30,000 ft ( 914 m to 9,146 m) including equipment with a 2 MW power rating. "We will see significant developments in terms of deeper, longer and higher capacity, but the technology, as such, is proven," he said.
Further work is underway to meet anticipated future market demands. These include a:

• Wet gas compressor: a very robust contra-rotating wet gas compressor, fit for both topside and subsea applications. Already a prototype has been extensively tested, and shows impressive results, said Sølvik. "And we are just starting to see the benefits and impact of a compressor that can handle anything from 100% gas to 100% liquid."
• Raw seawater injection: This is an integrated system with high power/high performance subsea injection pumps, filtering and auxiliary systems required to make a reliable and cost efficient subsea raw seawater injection facility.
• Subsea electrical power distribution: Here, Framo has worked with ABB to design, build and test a 3 MW subsea frequency converter designed for 6,000-ft (1,829-m) water depth, and with enhanced reliability.

"In addition there is a continuous development activity on our subsea and topside multiphase products; booster pumps, metering and complete system solutions for the production systems with high performance multiphase technology," Sølvik added.

Worked

After its installation on Troll C, Subsis has worked almost continuously since August 2001. Now it can boast more than 2 years of successful operation, plus close to 100% system availability over the period.
John Allen, vice president of technology at ABB Lummus, said, "Added production is always welcome, but perhaps the most significant result of the Troll Pilot project was that it greatly exceeded our reliability expectations. This has given us much encouragement as we faced the tasks ahead."
Moving on from there, Framo has been looking at the use of simultaneous water and gas injection called SWAG.

Using the SWAG approach will remove water and gas from the topsides process system and reduce multiphase flow through a pipeline.

Reinjection of the water and gas can be used to increase oil flow through a production line, reduce the capacity constraints on an inlet separator on a host facility and also provide a low cost gas-handling solution for remote fields without any gas-handling infrastructure and a low gas-oil ratio (GOR). This is particularly suitable where gas flaring is either prohibited or if an operator wishes to avoid flaring for environmental reasons.

Furthermore, reinjected water and gas can provide support for or increase oil output.

Avoiding the need for gas-handling on a platform also implies a lower cost for design and construction of topsides process equipment.

Subsea processing and production begins to lead towards the ultimate offshore development - with no surface facility.

Like the removal of gas from the wellstream, the removal of water subsea also has significant implications for the design and cost for a project.

"Subsea removal of water reduces or eliminates the need for water treatment equipment topsides," suggested the Norwegian group. "New, marginal fields may be developed with a minimum of topsides processing equipment."

Also, production from marginal fields or well-testing can be carried out using "very simple" FPSOs.
All of the elements needed for a complete subsea production technology suite are available: Subsea pumps, rated from 400 KW to 2 MW; a wet gas compressor to reduce the volume and increase the pressure of wet gas; and, crucially, a subsea centrifugal separator. Framo's own subsea centrifugal separator (CeSep) produces a treated wellstream with no more than 5% water content, reducing the prospect for hydrate formation in long distance flowlines "significantly," the company said.
In this instance a centrifuge receives direct drive from an electric motor and the device is capable of installation and retrieval with subsea pump tooling. Also the equipment has been field-tested already on a topsides system, on the Ceiba development where subsea pumps have also been installed.
According to Framo's Jan Elde, "When installed, Ceiba will be the world's first 100% subsea pumped field." Elsewhere in the South China Sea, five single-phase subsea booster pumps have been in operation for Statoil since 1997. ExxonMobil is using two centrifugal pumps tied to the FPSO Zafiro Producer offshore Equatorial Guinea.

In order to power this subsea technology, close co-operation has been necessary with ABB for the development of a subsea power distribution system called Sepdis. This involves the utilization of a single high-voltage power cable to the seabed where a step-down transformer at a subsea installation converts electrical power into a low voltage system, which then distributes power throughout subsea architecture.
In a technical bulletin on boosting technologies, Framo discusses the options for further artificial lift technologies based on the premise that they will be required, particularly for marginal oil and gas fields or in mature developments, with the application of multiphase boosting at the subsea wellhead, upstream of a production flowline.

Using this approach, the effect is to lower the back pressure as the pump draws down wellhead pressure. Consequently a decrease in wellhead pressure and increase in pump outlet pressure can have one of several uses.

It can increase production from one or several wells; compensate for higher specific gravity and thus higher back pressure of crude where there is an increased water cut. Also the situation can allow production from an otherwise uneconomic satellite reservoir to a host process facility where the distance and consequent pressure drop prevents natural production.

In fact, Framo goes so far to suggest, "In the near future subsea booster pumps may eliminate floating production facilities."

Given the progress made with subsea production systems in recent years the US Minerals Management Service (MMS) decided December 2003 to establish a formal information gathering process to asses reliability of the technology. As part of the program during 2003 and 2004, the MMS has resolved to approach operators with "significant" subsea operations, including BP, ExxonMobil, Petrobras and Shell to, "Develop an industry state-of-practice regarding the reliability of subsea production systems."

Also key contractors and equipment suppliers, including FMC, ABB, Aker Kværner and Cooper Cameron are to be asked for information on their current programs and practices for measuring subsea equipment reliability.

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