Aker Solutions’ success in winning the subsea hardware contract - notably with vertical trees (VXT) - for the latest stage of Total’s Moho area development in the Congo (SEN, 30/2) has come off the back of at least three years of technical work.

The seemingly unstoppable rise of the horizontal xmas tree over 15 years - due in part to the large bore and easy access downhole without a major intervention - slowed five years ago.

This was partly the result of a number of recorded actuator failures and wellhead connector issues which required the tree to be pulled and thus, unfortunately, displacing the completion. There have been a number of other technical issues including changes to tubing head spool designs.

There have also been cost implications related to drilling and tree delivery schedules. The ability to drill the well and install the completion ahead of the delivery of the tree gives the vertical an edge.

Also some operators, with gas fields with expected long production lives, have expressed concerns about having to replace a tree and again displacing the completion.

AkerSol is not exactly a stranger to VXT’s, having begun life many years ago with them, but has not actually delivered any for 13 years since Woodside’s Laminaria project in Australia waters.

What it has developed is not a legacy design, but something new with both deepwater and arctic conditions in mind. What it has added is an annulus isolation valve, the ability to provide gas lift injection bottomhole and a design that is rated for -18oC.

In parallel it has developed what it calls a rigid lockdown wellhead for deepwater with at least two of its customers - Eni and Statoil - have specified with its trees. It is designed to accommodate heavier bops and has a very high fatigue capacity.

The other key part of the supply contract for Moho-Bilondo 1b and Moho Nord is what AkerSol calls its Tulip - the universal light intervention package - developed in conjunction with Total and installed on the lwi unit Skandi Aker.