GE launches new SVXT S-Series subsea tree
Feature Articles, Nov  27  2009 (Digital Energy Journal)

- GE Oil & Gas has developed a new subsea tree that has a streamlined pre-configured design and promises to be massively more efficient than conventional predecessor subsea trees.

Designed and manufactured in Aberdeen, the SVXT is destined for harsh shallow-waters (i.e. S-Series) up to 90m deep. GE expects it will find a market in the UK North Sea and Asia Pacific, among other places.

New subsea tree from GE Oil and Gas

The new Tree on Mud-line (TOM) equipment merges horizontal and vertical tree technology, reducing weight by 20%, reducing height, and also delivering essential functionality in a pre-engineered, pre-configured 'modular' way. By assessing its entire customized shallow water tree portfolio designed and built over the last 30 months and incorporating the around 85% common denominator elements, GE is confident that the new SVXT unit will offer customers enormous benefits.

Firstly, GE says, by offering all customers pre-engineered quality solutions we will improve clarity during equipment specification. This in turn streamlines the supply chain with rigorously qualified and validated products, and also speeds on-time delivery, driving faster execution in pre and post order phases. Importantly senior engineering expertise is freed-up to focus on customers' most challenging customisation requirements and problems.

Having CapEx and OpEx in mind, makes off-the-shelf equipment attractive to both buyer and seller - the buyer gets the equipment at potentially lower cost with essential elements built-in, thereby reducing upgrade, repair and maintenance needs over the long-term, while the seller gets potentially more profit through efficiency gains.

But it only works if the buyer is prepared to accept that a predominantly standardised piece of equipment meets most of the needs, something which Manuel Terranova, senior VP, subsea product platform, GE Oil and Gas, calls the "standardisation battle".

A typical scenario, he says, is when the client’s engineer initially scoping the equipment, comes up with a list of demands that the equipment must meet, and the contractor works out how much it will cost to meet the demands.

With a standardised piece of equipment, GE can explain that it can have the standard equipment for a certain price, but if it needs the extra special valve then it could mean additional cost and potential time delay.

If a company procurement manager gets involved alongside the engineer, the discussion may get easier, he says. "The procurement manager says to the engineer, do you really want that valve? It's an extra $2m and an extra month’s wait," he says.

The SVXT tree is designed for wells producing up to 50,000 barrels a day, and for shallow waters of up to 90 m depth.

Normally oil and gas companies need to use deepwater equipment for anything over 50m, so if the water is 50m to 90m deep, they can have even bigger cost savings by being able to use shallow water equipment.

The unit weighs 15 tonnes, compared to 25 tonnes for most shallow water trees, Mr Terranova says. Keeping the weight down to 15 tons enables it to be deployed directly from the jack-up rig, without special vessels required.

The company designed the SVXT from a 'blank sheet of paper', not by tweaking its existing designs.

It was also designed from the start as a system, rather than looking at individual components and putting them together. "If you do design from a components mindset, the holistic functioning system can easily become an afterthought," says Mr Terranova.

This means that, for example, the final SVXT unit has a lower weight - it is also perfectly balanced when it is hung from a cable (i.e. being lowered to the seabed) and it does not need any additional ballast to keep it level.

Special consideration has been given to enabling operators to see what they are doing when making connections to the tree unit, because there is often a lot of mud swirling around in harsh shallow waters.

The unit therefore has cameras installed, pointing at the connections, so you don't necessarily need an ROV (remote operated vehicle).

Control system

A whole new control system has been designed for the tree.

The company employs a number of control engineers with experience working in the aviation industry, that know how to make systems super-reliable.

Reliability is very important, because "you would lose the well and your business reputation if you can't operate the tree safely," Mr Terranova says “GE puts environment, health and safety first – this protects our mandate and licence to operate”.

The control system opens and closes electro hydraulic valves, which manage the flow of fluids out of the well.

The control system is housed in a "pod", which can be removed, refurbished and reinstalled if necessary.

Special consideration was given to designing a system that would be ‘future proof’ - using standardised electronic components as much as possible.

Subsea equipment usually has lots of custom-designed electronics, Mr Terranova says, including custom designed microchips, data communications protocols, control systems at the surface and circuit boards, which can cause many problems later when something needs to be replaced and it isn't available, or no-one knows how to do it given the time lag with equipment designed to operate for a generation or more”.

However, the GE tree uses the UNIX operating system, and communications in TCP/IP protocol. "In 20 years, Ethernet will still be a standard," he says.

The unit has the some of the same circuit boards that GE installs in its wind turbines, with around 70,000 in operation.

The chipset maker undertakes to maintain records of what has gone into the chips - the "bill of material" - for 18 years.

The unit has redundant circuit boards, so if a circuit board fails the control system can continue operating.

It is normally possible to update software features; however, it is hardware upgrades that can usually cause the most problems, Mr Terranova says.

Remote monitoring

GE also offers remote monitoring services, assessing the stream of data from the unit and translating the information into performance driven actions that operators can act on.

"We want to be able to say "you've cycled that valve 400 times - after 200 more cycles you have a risk of failure"," he says. "We can tell customers what the remaining life expectancy is in that particular system. This prognostic approach is critical to keeping our equipment in great shape and ultimately helping operators drive greater profitability."

GE has a great deal of expertise in equipment remote monitoring - it conducts remote monitoring for its jet engines, locomotives, medical scanners, turbo compressors and power generation equipment.

The company has a specialist remote diagnostic centre in Nailsea, near Bristol in the UK. The ‘Subsea Monitoring & Remote Technology Center’ (or SmartCenter) is a remote-access data hub connected to subsea field control and instrumentation facilities around the world.

The new state-of-the-art facility will offer assistance & services to the field at every stage of development - from installation & commissioning, through field start up and onwards into routine operation for operational support, condition monitoring, diagnostics, and production optimisation.

"When you have separators and compressors on the seabed, you need to know what's happening on a real time basis," Mr Terranova says.

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