When offshore lifting, pipelay and drilling firm Huisman decided to redesign the traditional derrick tower on mobile drilling units, it decided to go back to basics—and redesign the whole unit.
Huisman has come up with a vessel layout using a dual, multipurpose drilling tower, allowing the drill floor to be placed about five meters above deck level, lowering the overall center of gravity, increasing stability, reducing vessel size, and therefore reducing costs while increasing deck space. The latest result, vessel number two, of this work will soon start its voyage to offshore Benin, Africa, to drill for supermajor Shell.
It is the 189m long, 32m wide Noble Globetrotter II (GT2), the second of two Huisman designed drillships based on the HuisDrill 12000 design built for Noble Drilling and both on contract to Shell.
The Globetrotter I (GT1), commissioned in 2011, went into service in 2012 and has been drilling for Shell in the Gulf of Mexico.
Joop Roodenburg, chief executive of Huisman, said feedback had been good, with strong uptime. Of the overall downtime less than 2% was attributed to Huisman equipment, he said.
The HuisDrill design is a DP3 drillship. It can conduct drilling operations in water depths up to 12,000ft deep, install Xmas trees, and perform well testing.
The GTs have two ROVs, a service speed of 12kts, 54,000 tons displacement, 20,000 ton payload, and accommodation for 180 in single and twin cabins. Power is from eight 4.6MW engines, with six 3.7MW thrusters. Central to the HuisDrill is the The construction floor can be hoisted in order to skid the BOP or Xmas tree underneath and positioned before lowering into the moonpool. This means the construction floor, and consequently the drill floor, can be low, reducing the center of gravity and minimizing lifting activities.
Due to the lowered tower and drill floor, an exhaust outlet could be placed above a forward accommodation block, the engine rooms could be moved forward of the tower, creating space for up to 9900ft of risers (3000 tons worth) in a hold, and opening deck space covered by a gantry crane.
According to Huisman, these improvements have led to a vessel that is 50% smaller than a conventional drillship, but with the same capacity. It also means it is Panamax size and, thanks to a removable section at the top of the DMPT, it can fit through the Panama canal, the Suez, and also under the Bosphorus’ bridge.
The design idea started when Huisman carried out work on the Pride Amethyst 2 Class semisubmersible rigs, 1995-1998. Huisman was not providing the tower at this stage, but, looking at the interface between the derrick and the vessel, Huisman questioned the point loads created by the derrick’s four legs. This resulted in the idea for a different type of tower to interface and spread load on the vessel better.
The first, a multipurpose tower (MPT), was built in 2000 to go on Helix Energy’s Q4000 well intervention semisubmersible, delivered in 2001. The use of an MPT instead of a traditional drill-derrick structure with its limiting “V-doors,” meant different drilling packages could be skidded in, enabling flexible use.
Then, in 2007, Huisman was contracted to work with Frontier Drilling and Shell to design its first DMPT and related pipe, riser and BOP handling equipment for Frontier’s first drillship, the Bully I (now working in the Gulf of Mexico) and then a year later for a second ship, the Bully II (working off Brazil).
“Shell wanted to not go in with a bigger hammer, but see how it could be done smarter, Shell’s vision was not to use a bigger hammer, but to find a way smarter way,” said Roodenburg.
Both Bully vessels had already been designed (by GustoMSC) with a view to have traditional derricks when Huisman was brought in, which meant retrofitting the tower into the design.
“This was the start,” said Roodenburg. “That gave us the chance to put up our tower and we then saw an opportunity to challenge the whole vessel design using the thinking we had started on the semis, with our tower as the center point.”
Work on the HuisDrill design then started, with Noble Drilling becoming involved ahead of taking over Frontier, in 2011, while the Bully vessels were still being completed in Singapore.
“Together we constructed this drillship,” said Roodenburg. “We used what we had learned on the semis and then worked the ship around it. We always start from a white sheet of paper; that is what we do.”
The GT2’s hull was built at STX Dalian’s yard in China, sailed to Schiedam for fitting out of the topsides equipment last year and completed in March.
Key has been challenging the handling principles and lowering the drilling floor.
“Lowering the floor gives you much more payload capacity, at 20,000 tons on HuisDrill compared to 12,000 tons on the Bully,” said Roodenburg. “That is a big difference because of an integrated design. The tower is easier to integrate, the footprint and load spreading is much easier to integrate on to a hull.”
The smaller size of the vessel reduces its construction cost by $50-$100 million, said Roodenburg. It also has a lower environmental footprint, lower maintenance, and can be built in various yards.
But having built a small vessel, Huisman is now considering going bigger and introducing full automation. Huisman is considering extending the vessel length by 10m so it can handle 150ft lengths of risers, said Precious Nwokoma, drilling engineer at Huisman.
“When you run risers in 3000m water depth at 75ft long, it can take about three to four days,” he said. “The idea is to handle 150ft risers and run them. For that we need extra length in the vessel. It would reduce running time by half.”
While there are no immediate orders for the next HuisDrill, there is interest, says Roodenburg. “We are talking to various potential clients now,” he said. “Major clients and drilling contractors have been on board. All like what they see.”
The Noble Globetrotter I is working for Shell in the Gulf of Mexico.
The Noble Globetrotter II was due to go out on sea trials at the end of April and will be undergoing mobilization before heading to Benin. Following a period there for Shell, it is then potentially going to work in the Black Sea in 2014, also for Shell. OE