Subsea processing/boosting choice for deep, ultra deep, harsh environment production

Gene Kliewer - Technology Editor, Subsea & Seismic

Subsea processing, separating, compressing, and pumping are on the leading edge of offshore production technology, especially for deep and ultra deepwater, and also harsh environments. The practice and art of placing such equipment subsea still are in their early stages of use. Nevertheless, the attractions are sufficient that both operators and equipment suppliers are developing subsea systems to accomplish tasks heretofore done above water.

Earlier this year,Offshore published the first ever Worldwide Survey of Subsea Processing, Separation, Compression, and Pumping Systems poster. That poster can be seen online at http://downloads.pennnet.com/os/posters/subseaprocessing_02608.pdf and is contained in the March 2008 issue of the magazine. That poster illustrated and quantifies what is available and already in use. New technology is dynamic, however, so Offshore has gone to several companies to learn what is driving this technology and to get a peek at what the future holds.

Right now, the technology is on a plateau along its industry learning curve. What is needed to move the applications forward is a larger installed base with the attendant comfort level required by the industry before there is common application of any new technology.

For the time being, “nothing new is needed,” says Tom Choate manager, Systems Engineering, INTEQ. “We are at the point where it is time to use (the existing technology) knowingly and with thorough application engineering.”

We need a change in mindset from the operators, adds Neil Holder, VP, Sales & Marketing, Aker Solutions. Experience is needed; more frontrunners to apply the technology. “That brings a willingness to invest in continuing evolvement and deployment of the technology. It might take a change in contracting/business models on the part of operators,” Holder says.

“The technology exists,” says David Morgan, director, Subsea Processing, Cameron. “Some is qualified to some fashion, but the building blocks are there. We need more user base for operator comfort level.”

“Most of all we need more fields where subsea processing is being seriously investigated and evaluated early enough to be considered in the operator’s decision process, and with less penalty for ‘technical uncertainty’ until the installed base produces more reliable uptime/risk data,” says Martin Sorensen, director, Subsea Power & Processing, VetcoGray, now a GE Oil & Gas business.

Driving factors

Some factors currently driving the progress are obvious. Subsea facilities are viewed as a path to bring production to market faster while extending life of the field. Also, such hardware is likely to make otherwise marginal fields economically viable. The shortest answer is simply “more oil.” Here are technical reasons supporting these promises.

“The idea is to get more energy into the flow stream to get more oil from the reserves,” says Morgan. “In deeper waters likewise, free flow the gas and pump the liquids to reduce the head on the well,” in order to increase production.

As with many technological changes, necessity formed part of the equation. For example, BP’s King field in the Gulf of Mexico would not be as productive without multi-phase pumping (MPP), and Shell’s Perdido project “was not going to happen without separation and pumping,” says Choate.

There is another obvious factor at play. Putting the equipment on the seabed cuts topside requirements.

“The rewards are obvious with savings in topside facility costs,” says Jan Olav Hallset, managing director, Poseidon Innovation, part of the Poseidon Group in Stavanger, Norway. This reduced cost raises, “the ability to develop marginal fields.”

“Topside capacity issues are addressed when seawater reinjection is the operation,” says Morgan. “You can separate the production from the water and reinject the water so you do not have to process it. Plus, there is seldom space for more water or more processing hardware on existing platforms, particularly in the North Sea.”

Brownfield operations are included in VetcoGray’s view of the technology.

“By applying subsea boosting and/or separation, in the majority of cases related to brownfields, the operator increases production, meaning earlier and faster earnings from the field,” says Sorensen. “In addition, the recovery rate increases, meaning more earnings over time from existing infrastructure and better use of the reserves.”

Biggest advances

Regardless of the rate of technology uptake into the industry overall, there are significant numbers of working applications proving the concept of subsea boosting and processing.

Two of them are mentioned above, namely King and Perdido.

“The biggest advance in the GoM is the application of MPPs and the use of ESPs (electrical submersible pumps) in seafloor applications,” says Choate of INTEQ. “In the North Sea, StatoilHydro’s full-blown separation/water handling/pumping/compression systems are state of the art.”

For Hallset at Poseidon, the biggest advances to date are subsea boosting and injection pumps, and high-voltage, high-power switching equipment, umbilicals, and connectors.

He also cites StatoilHydro’s Tordis, Ormen Lange, and Snøhvit projects as important advancements.

Sorensen at VetcoGray put the subject into perspective:

“The oil and gas industry has not traditionally been dominated by major technological breakthroughs, but rather careful step-by-step, forward-moving and integrating novel ideas and new technology system solutions consisting of well proven technology and products.

“However, some industry pioneering projects have brought seabed boosting and separation over its first hurdle, such as: the first subsea MPP for the Prizioso field in 1992; the Troll C subsea separation and produced water injection pilot project in 1999; Pazflor as it is the first separation and boosting based field development entirely reliant on the subsea processing functionality; and Ormen Lange where a series of key building blocks for subsea gas compression is being qualified for the next major step in subsea functionality.

“VetcoGray technology played a key role in the Troll C project, developing the first commercially scaled and longest running pilot subsea separation system launched in 340 m (1,115 ft) water depth whereas GE Oil & Gas’ rotating equipment technology is pushing boundaries in the Ormen Lange project through the development of the first subsea compressor able to operate at 900 m (2,953 ft) below sea level.”

Incremental advances can have far-reaching impact. For instance, notes Holder of Aker Solutions, proving pump technology up to 2.5 MW of power to be reliable is significant.

Limiting factors

In the face of its benefits and current applications, and beyond the user base, subsea processing and boosting has some other issues still being worked out. Cost is one. Size and weight of the equipment is another. These are being addressed for subsea hardware just as they have been addressed for platform mounted equipment.

Retrofit, shallow water

Two areas where subsea technology is not typically thought of are in retrofitting existing fields and in shallow water. That could change with time, as well. Cameron, for instance, has several projects which target brownfields. The MARS (Multiple Application Reinjection System) is used to tie back King field by tapping into existing christmas trees with new flowlines without extended shut-in of the field. The system uses isolation valves on the tree and manifold to manage flow during connection. Cameron also is working on an EOR system to improve on raw seawater to charge a reservoir. “Find similar water in another well and send that over as the EOR water in place of seawater,” says Morgan. “That will match the existing reservoir chemistry better. The whole thing is ‘process cooled’ meaning it has no oil loop, just pump and power cable.” Produced fluids as ambient seabed temperature cool the system.

As for shallow water, Choate points out that, for instance, MPPs can add pressure to offset pressure drop regardless of whether the drop is due to elevation or friction. And, operators may find over time that adding subsea equipment in shallow water for boosting and subsea-to-beach solutions becomes less expensive than adding new surface facilities or refurbishing existing platforms.

Subsea market to pass $5 billion

Expenditure on subsea processing systems is increasing rapidly and is expected to total some $5.1 billion over the 2008-2017 period, predicts Douglas-Westwood Ltd. and OTM Consulting. The prospect of improved recovery and production is driving operator uptake. So much so that in 2009 there could be as many seabed pumps installed as were installed in total over the 2003-2007 period, the report continues.