From OTC 2015, Houston: Moves by the main hardware manufacturers to steer away from the traditional ‘vertical’ and ‘horizontal’ subsea trees have been on the agenda for some time and OneSubsea put a spotlight here on its HyFleX tree, billing it as offering 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 the tubing hanger are completely independent in their installation and in their recovery.

OneSubsea’s tree product manager James Stewart said, ‘The benefit of that is that all that equipment would be more easily recoverable if required.

‘The HyFleX tree system offers greater benefits, more flexibility and reduced cost. It gives greater and optimised 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 of three major components that integrate together - the tubing head spool which consists of the wellhead connector main body and valves and this forms the barrier on the wellhead.

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

All of the components of the HyFleX tree exist already, including the wellhead connector, the valves and the connection systems.

‘It is all field proven and already existing technology,’ Stewart added.

It is not surprising that the first ‘visible’ hybrid tree has come out of OneSubsea. In its previous incarnation as Cameron, 1-Sub was responsible for the two earlier important tree advances - the SpoolTree, otherwise known as the horizontal tree which came into the market in the early 1990's and the all-electric trees which appeared in the mid-2000's. Other manufacturers might dispute this view, but the Leeds plant has been a hub for new technology.

1-Sub’s figures suggest that the HyFleX tree could offer a $10mn saving per well, which on a 10-well field would give a ‘significant saving’ of $100mn simply by tree selection alone.

The company carried out a case study based on an operator in Malaysia with a four well development consisting of four trees, four inline sleds, jumpers connected to the sleds, jumper connections and pressure caps. The development has 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 inline tees.

Stewart said, ‘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.

‘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 capex. That doesn’t include installation cost saving. That can be the difference often between a field being viable or not.’

Offshore