Hybrid solutions look even more attractive to operators since this emerging new breed of tree designs, combined with long-overdue standardization initiatives being undertaken by all the main subsea contractors, also is demonstrably capable of offering substantial savings in development costs.

This emerging subsea technology trend could not have come soon enough. “I have seen a number of crises, but this one looks more like the perfect storm than anything I’ve seen before,” said Per Arne Nilsen, head of subsea technology for Total.

Speaking during a panel session at the Underwater Technology Conference (UTC) in Bergen, Norway, he also bemoaned the lack of standardization over time that had driven up costs. “Every time we have a new project it is a bespoke design. We like to bash ourselves these days to show that we are serious and changing. If you look at Total and our history, we have been very good at one thing, and that is never repeating anything twice.”

Increased efficiency
Nilsen commented that the subsea industry has created an “extremely inefficient” business during the last 10 to 15 years with negative productivity.

“If you look at a [christmas] tree today compared to a [christmas] tree 10 years ago, it’s the same. It has got some more whistles and bells, but today we spend three times the man-hours to engineer and manufacture it compared to 10 years ago, for no obvious reason. We need to increase efficiency,” he said.

Roald Sirevaag, Statoil’s vice president for subsea and diving, at the same event called for greater cooperation on subsea trees. “We are operating with nonstandard specifications. For 5-in. deepwater trees we asked for four completely different solutions doing exactly the same job. I think we should agree on one type of tree.”

HyFleX highlighted
The industry, however, appears to be already heeding the operators’ pleas. A growing number of the main hardware
manufacturers are expanding or are planning to expand upon the traditional vertical and horizontal subsea tree designs. OneSubsea recently unveiled its HyFleX tree, which it said offers the benefits of both types.

The HyFleX system has the tree and the tubing hanger as two separate units in parallel rather than in series, meaning the tree and tubing hanger are completely independent in their installation and recovery.

“The benefit of that is that all that equipment would be more easily recoverable if required,” said James Stewart, OneSubsea’s tree product manager. “The HyFleX tree system offers greater benefits, more flexibility and reduced cost. It gives greater and optimized installation and recovery options by having the tree and the tubing hanger as independent units in parallel rather than in series. Because these units are separate, you have a lower lift weight, and they can be lifted individually rather than in one large assembly.”

The tree system comprises three major components that are integrated. The tubing head spool consists of the wellhead connector main body and valves and forms the barrier on the wellhead.

The system also is designed to be standardized. The tree module integrates onto the tubing head spool, with the tree module designed to be configurable. This is where the project-specific requirements can be accommodated. The module would contain hydraulically actuated valves, chokes, control systems, chemical injection metering, any monitoring and sensors—essentially everything that would be in the tree.

Field-proven
All of the components of the HyFleX tree already exist, including the wellhead connector, the valves and the connection systems, according to Stewart. “It is all field-proven and already existing technology.”

It is not entirely surprising that the first “visible” hybrid tree has emerged from OneSubsea. Its joint founder parent company Cameron was responsible for two highly significant tree advances: the SpoolTree, otherwise known as the horizontal tree, which came onto the market in the early 1990s; and all-electric trees, which appeared in the mid-2000s.

OneSubsea’s own figures suggest that the HyFleX tree could offer savings of $10 million per well, which on a 10-well field can add up to savings of $100 million achieved simply by tree selection alone.

During the Offshore Technology Conference in Houston, the company outlined a case study based on an operator in Malaysia that had a four-well development consisting of four trees, four in-line sleds, jumpers connected to the sleds, jumper connections and pressure caps. The development featured a flowline in a daisy chain arrangement linking each one of these together so the flowline can be installed independently of the tree with four in-line tees.

“Essentially, we can link the flowline into the tubing head spool on the HyFleX tree, and the flowlines can therefore be installed completely independently of the trees,” Stewart said. “We have four trees as before, but now we only have eight jumper connectors and eight pressure caps. We have saved four in-line tee-sleds, four jumpers, eight jumper connectors and four pressure packs. For this field that was a 20% saving just in capital expenditure [capex]. That doesn’t include installation cost savings. That often can be the difference between a field being viable or not.”

Fast-track trees
Mike Garding, OneSubsea’s CEO, also spoke at the UTC event in Norway, where he focused on aspects of tree standardization.

He highlighted the success of a fast-track tree program developed several years ago to meet the requirements for a flexible well solution with reduced lead time and reduced capex. “The uptake of this solution has been particularly successful in the Gulf of Mexico, and we’re expanding this to other regions globally. The pre-engineering components provide a common tree core that can then be configured with key components.”

Garding said the fast-track program, compared with conventional procedures, led to delivery times being shortened
by six months and costs being reduced by between 20% and 30%. “This is a successful example of standardization of
design and manufacturing processes. Bespoke engineering and man-hour costs are down. The reuse of proven solutions
reduces risk, costs and lead times,” he said.

New design debut on Sverdrup
Statoil and its subsea contractors also have been working hard to reduce tree costs and time, putting their heads together to develop a new 7-in. vertical christmas tree that will make its debut on the giant Johan Sverdrup Field project offshore Norway.

The tree has been developed as part of a companywide cost initiative that was actually implemented by Statoil
before the oil price crash.

Kristoffer Dahl, a subsea engineer with Statoil, described the VXT Initiative’s 7-in. christmas tree as a cooperation between Statoil and its four main subsea contractors, Aker Solutions, FMC, GE Oil & Gas and OneSubsea.

“The main intention for developing a new christmas tree at Statoil was to reduce the rig time, especially the maintenance costs of the rig,” Dahl said during UTC. “It is more a cost reduction on the operational side and the life-cycle total cost.”

Hybrid vertical tree
The vertical tree consists of a 7-in. vertical bore that is unlike the horizontal 7-in. unit. “The tree is put on top of the completion,” Dahl said. “The tubing hanger is installed directly in the wellhead and not through the tree, as it is on the horizontal tree. It is not a true vertical tree. It is more of a hybrid [since] the valves are on the horizontal side, but we still call it a 7-in. vertical [christmas] tree.”

He said the main challenge had been to qualify an annulus barrier valve. “As a 7-in. vertical [christmas] tree you don’t have any direct access in the tube on the annulus side, so some sort of plug-in mechanism is needed in the tubing hanger. The Johan Castberg project has been leading the development, but Sverdrup has joined in the financing. Johan Sverdrup will be the first user of this tree,” he said.

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