A Semi- Submersible Rig, also called a Semi-Sub, Semi or Floater, is used to explore and extract oil and gas from beneath the ocean floor. It is used for drilling wells in water depths that are not accessible to jack-up rigs. Semi-Subs are buoyant, unlike the jack-up rigs that rest on the seabed while the latter float.
They are preferred over other alternatives since they offer stability in harsh conditions, provide a larger deck area, possess superior installation and construction features and are highly mobile.
They can float when towed to a position, and their pontoons are then flooded, partially submerging them in water once they reach the destination of their operations. These pontoons also provide them with buoyancy, stability and the capability to float on the water’s surface.
In this article, let us look at the 10 Biggest Semi-Submersible Rigs.
1. The Ocean GreatWhite
In 2016, Hyundai Heavy Industries delivered the world’s largest semi-submersible drilling rig, the Ocean GreatWhite, to the drilling contractor Diamond Offshore.
The ultra-deepwater rig is 123 m or 402 feet long and 78 m or 255 feet wide. It can operate in waters up to 3 kilometres or 10,000 feet deep and can drill down to 10 km or 6.6 miles from the sea surface. It has a 23 m draft and a speed of around 8 knots.
The rig was constructed to operate in harsh environments like the North Sea. It has accommodation facilities for around 200 people and is equipped with advanced equipment for handling exploration and drilling operations in challenging environments.
2. Scarabeo 9
Scarabeo 9 is a ‘Frigstad D90-type ultra-deepwater sixth generation semi-submersible drilling rug’ owned and operated by Saipem. One of the biggest rigs in the world, it can function at a depth of around 12,000 feet or 3600 m. Its drilling depth is 15,200 m or 49,900 ft.
Scarabeo 9 is 115 m long and 78 m wide. It has a gross tonnage of 36,863 and a deadweight tonnage of 23,965. It has 8 Wartsila 12V32 diesel engines and 2 cranes.
It also has living quarters for 200 workers and a helicopter deck for MI8, S61 and EH101 helicopters. Scarabeo 9 also has a dual RamRig and Dynamic Positioning System.
3. Deepwater Nautilus
This semi-sub was constructed in 2000 in South Korea by Hyundai Heavy Industries. It is owned by Transocean, is registered in Vanuatu and currently operating under the Liberian Flag.
The ultra-deepwater semi-sub offshore drilling rig is a sixth-generation RBS-8M design. It is column-stabilised and made to drill subsea wells for oil exploration and production.
Deepwater Nautilus can function at water depths of around 8000 feet or 2400 m. It has a drilling depth down to 30,000 ft or 9100 m. It is 114 m or 374 ft long and 78 m or 256 ft broad. It has a draught of 23 m and has a gross tonnage of 29,051.
In 2000, the rig set a water-depth record for an offshore rig functioning in a moored position at 7,785 ft to 2373 m at Alaminos Canyon block 557, in the US sector of the Gulf of Mexico.
Two years later, the rig found oil at the Shell-operated Great White oil field in Alaminos Canyon block 813.
4. Deepsea Aberdeen
Deepsea Aberdeen was constructed by Daewoo Shipbuilding and Marine Engineering yard, South Korea and was classified by DNV. It was delivered to Odjfell Drilling in 2014.
The rig measures 123 m lengthwise and 96 m breadthwise. It is an enhanced GVA7500 harsh environment design and is Odfjell Drilling’s third rig of the optimised deg. Its sister rigs are the Deepsea Atlantic and Deepsea Stavanger.
It has a highly efficient drilling system, including a dual derrick with a main and auxiliary work centre to enable several simultaneous operations.
The rig has a maximum drilling depth capacity of 40,000 ft or 12,192 m. It can operate at water depths of up to 10,000 ft or 3048 m.
It was made for operating worldwide; however, it is suitable for development drilling. Deepsea Aberdeen will drill new wells in the Svalin field in the fourth quarter of 2023 for about 174 days.
The rig is presently in Norway and is operating under the flag of Bermuda. It has 8 mooring lines and can accommodate 157 people. The Deepsea Aberdeen has operated in the North Sea, West Africa and other regions.
Hercules is a 6th generation deepwater and a harsh environment semi-submersible rig. It is a tall derrick, boasting a GVA 7500 design and is laden with a full conventional mooring spread for operating in water depths of 100-500 m.
Its 5200 mt loading capacity allows efficiency and less need for supply vessels. It has successfully worked in the Barents Sea during the freezing winter and is gearing for winterisation class notation for improved working conditions in an arctic environment.
It was delivered to Odjfell Drilling in 2008 by DSME, South Korea. It is under the flag of Norway and is currently working for Exxon Mobil. The rig has 2 Liebherr Bos 4200-80 cranes and can accommodate 180 people.
It has a carrying capacity of 40,000 t DWT and has a 16 m draught. Hercules has an LOA of 117 m and a width of approximately 78 m.
6. Sevan Louisiana
The 6th generation Sevan 650 DP Semi-Sub offshore drilling rig, Sevan Louisiana, was constructed in 2013 in the COSCO Nantong Shipyard. It was built for UK-based Seadrill Limited.
The self-propelled rig is equipped with 8 thrusters and can accommodate 150 people. It operates under the flag of Panama and is classed by DNV.
The rig’s carrying capacity is 40,000 t DWT, and her current draught is 12.5 m. Her overall LOA is 99 m, and her width is also 99 m.
It functions at a maximum water depth of 3048 m and has a maximum drilling depth of 10,668 m. It also has a helicopter deck and 2 pedestal cranes, a pipe handling crane and 2 X-Mas Tree cranes with varying load capacities.
7. Island Innovator
Island Innovator is owned by Island Drilling Company AS, which took its delivery from China’s COSCO Zhoushan Shipyard in 2012. The rig used for drilling and heavy, well intervention has successfully dug wells since 2013 and proved its ability to operate in harsh environments such as the North Sea, Norwegian Sea and Barents Sea.
It offers an operational advantage over other rigs. It has an NOV 165-ton crane and NOV 4000 HP ram-rig type cylinder rig, an NOV BOP handling system and a 5 ram BOP stack from Cameron.
The rig is built for production drilling on subsea templates with huge areas for storage and a skidding system. The upgraded hull design increases the deck load capacity.
The rig can operate in water depths from 60m up to 1200m. It has an 8-line mooring system and 6 fixed-pitch variable speed thrusters.
8. Atlantic Star
Atlantic Star is a midwater semi-sub drilling rig originally built in 1976 and was acquired by Constellation Oil Services in 1997. It was upgraded in 2011, can drill at water depths of up to 2000 ft, and has a drilling depth capacity of up to 21,320 ft.
The semi-submersible can accommodate 110 people, per the company. Atlantic Star rig is of an I.F.P. Neptune Pentagone design.
Constellation is a drilling contractor based in Brazil. For its offshore services, it has 8 offshore rigs, 2 semi-submersibles moored to operate at a water depth of up to 1100 m, 3 dynamic positioning rigs for operating in water depths up to 2700 m and 3 drill ships for operating in 3000 m water depth.
9. Norbe VI
Norbe VI is a semi-submersible drilling rig built in 2010 by Gulf Piping- Abu Dhabi, United Arab Emirates. It is sailing under the flag of Panama and has a gross tonnage of 15627 tonnes.
It has a carrying capacity of 12609 t DWT, and its current draught is 17.7 m. It measures 200 m lengthwise and 32 m breadthwise.
This rig, with dynamic positioning, can operate at a water depth of up to 7,874 ft and can drill wells up to 24,606 ft.
10. Hai Yang Shi You 981
Hai Yang Shi You 981, also called Ocean Oil 981/ Ocean Petroleum 981, is a semi-sub platform owned and operated by China National Offshore Oil Corporation.
The semi-sub is equipped with Liebherr Cranes and was designed by Friede & Goldman.
It was built in 2011 and is sailing under the Chinese Flag. It began operating in 2012 in the South China Sea about 320 kilometres southeast of Hong Kong at a 1500 m depth.
Its carrying capacity is 20579 t DWT, and its draught is 13 m. Its overall length is 114.07 m, and it is 89 m wide.
Hai Yang Shi You 981 was designed and built independently in China. It weighs 30,670 tonnes, and this platform is the world’s first rig designed for harsh environments in the South China Sea. After 10 years of operations, the rig went to a shipyard in Shenzen for its first-ever dry docking.
You might also like to read-
- Semi-Submersible Ships and Semi-Submersible Rigs: A General Overview
- What are Jack Up Drilling Rigs?
- What are Semi-Displacement Vessels?
- Top 12 Tanker Shipping Companies in the World
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Zahra is an alumna of Miranda House, University of Delhi. She is an avid writer, possessing immaculate research and editing skills. Author of several academic papers, she has also worked as a freelance writer, producing many technical, creative and marketing pieces. A true aesthete at heart, she loves books a little more than anything else.
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