SBM Offshore wanted the initial Fast4Ward semi-submersible design to have a light footprint but also be scalable, writes Kathrine Schmidt.

That meant an initial capacity of 60,000 barrels per day, but with the ability to expand to 120,000 bpd without significant redesign.

Gas processing capacity was initially fixed at 70 million cubic feet per day, but can be modified to go as high as 210 MMcfd.

Those specifications also included produced water capacity of 40,000 bpd to 80,000 bpd, as well as future water injection of 60,000 bpd, scaleable to 120,000 bpd.

The hull retains some similarities to existing semis but includes some important changes.

“It looks exactly the same as Thunder Hawk and (Independence Hub) from the outside,” said SBM Offshore US president Tom Ayers.

“But we’ve made it normally unmanned. We’ve taken all the equipment that used to be inside the hull and we’ve taken it out.”

More specifically, caisson pumps in the hull are operated from above, from where routine maintenance is also conducted. The hull is accessible for periodic inspections.

The other major change in hull design also includes the use of in-line mooring connectors, a solution that SBM used on the Turritella FPSO that it provided for Shell at the Stones field in the US Gulf, which drew first oil in 2016.

That represents a 1700-ton weight savings as compared with a traditional chain jack mooring system.

When it came to the topsides design, SBM aimed to take a modular approach not unlike its strategy on the FPSO front.

Instead of custom engineering, the idea was to offer a range of standard modules that can be configured to meet the field’s reservoir properties or throughput requirements.

The company started with the catalogue of FPSO modules developed for the Fast4Ward project and aimed to adapt many of those same functions for the semi configuration.

In the programme's semi design, those modules would be installed on a support frame called a truss deck, where main utilities would also be located.

In a key feature, the modules are designed to be fully commissioned at the yard where they are built, and accordingly require a simpler start-up on integration.

“Once you get all the modules onto the truss deck, then it’s really easy to just do all the final tie-ins and just push the button to go,” Ayers added.

Once all the modules are integrated, the truss deck would then be lifted onto the hull.

The design is aimed at avoiding delays that can be incurred in more traditional semi-submersible or tension-leg platform construction, which requires the stacking of layers of fabricated components or “pancakes”.

So, if a part from the lower decks is delayed, it can hold up the whole process.

SBM also touts the modular approach as allowing for flexibility in construction, letting the company place the module work in one yard or multiple different locations in Asia or the US Gulf.

They could also be sourced to another location if demanded by local content or special technology requirements.

Weekly

Fast4Ward semisub 'light but scaleable'