A drillship is a merchant vessel designed for use in exploratory offshore drilling of new oil and gas wells or for scientific drilling purposes. In recent years the vessels have been used in deepwater and ultra-deepwater applications, equipped with the latest and most advanced dynamic positioning systems.
The first drillship was the CUSS I , designed by Robert F. Bauer of Global Marine in 1955. The CUSS I had drilled in 400-foot-deep waters by 1957. [1] Robert F. Bauer became the first president of Global Marine in 1958. [1]
In 1961 Global Marine started a new drillship era. They ordered several self-propelled drillships each with a rated centerline drilling of 20,000 foot-wells in water depths of 600 feet. The first was named CUSS (Glomar) II, a 5,500-deadweight-ton vessel, costing around $4.5 million. Built by a Gulf Coast shipyard, the vessel was almost twice the size of the CUSS I, and became the world's first drillship built as a new construction which set sail in 1962. [1]
In 1962, The Offshore Company elected to build a new type of drillship, larger than that of the Glomar class. This new drillship would feature a first-ever anchor mooring array based on a unique turret system. The vessel was named Discoverer I. The Discoverer I had no main propulsion engines, [1] meaning it needed to be towed out to the drill site.
A drillship can be used as a platform to carry out well maintenance or completion work such as casing and tubing installation, subsea tree installations, and well capping. Drillships are often built to the design specifications set by the oil production company and/or investors. [2]
From the first drillship CUSS I to the Deepwater Asgard, the fleet size has been growing ever since. In 2013 the worldwide fleet of drillships topped 80 ships, more than double its size in 2009. [3] Drillships are not only growing in size but also in capability, with new technology assisting operations from academic research to ice-breaker class drilling vessels. U.S. President Barack Obama's decision in late March 2010 to expand U.S. domestic exploratory drilling seemed likely to increase further developments of drillship technology. [4]
Drillships are just one way to perform various types of drilling. This function can also be performed by semi-submersibles, jackups, barges, or platform rigs. [5]
Drillships have the functional ability of semi-submersible drilling rigs and also have a few unique features that separate them from all others, first being the ship-shaped design. [6] A drillship has greater mobility and can move quickly under its own propulsion from drill site to drill site in contrast to semi-submersibles and jackup barges and platforms. Drillships have the ability to save time sailing between oilfields worldwide. A drillship takes 20 days to move from the Gulf of Mexico to offshore Angola, whereas a semi-submersible drilling unit must be towed and takes 70 days. [7] Drillship construction costs are much higher than that of a semi-submersible. Although mobility comes at a high price, the drillship owners can charge higher day rates and get the benefit of lower idle times between assignments. [7]
The table below depicts the industry's way of classifying drill sites into different vintages, depending on their age and water depth. [7]
| Drillship | Launch Date | Water Depth (ft.) |
|---|---|---|
| CUSS I | 1961 | 350 |
| Discoverer 534 | 1975 | 7,000 |
| Enterprise | 1999 | 10,000 |
| Inspiration | 2009 | 12,000 |
The drilling operations are very detailed and in-depth. A simple way to understand what a drillship does to drill, is that a marine riser is lowered from the drillship to the seabed with a blowout preventer (BOP) at the bottom that connects to the wellhead. The BOP is used to quickly disconnect the riser from the wellhead in times of emergency or in any needed situation. Underneath the derrick is a moonpool, an opening through the hull covered by the rig floor. Some of the modern drillships have larger derricks that allow dual activity operations, for example, simultaneous drilling and casing handling. [8]
There are different types of offshore drilling units such as the oil platform, jackup rig, submersible drilling rig, semi-submersible platform and of course drillships. [9] All drillships have what is called a ”moon pool”. The moon pool is an opening on the base of the hull and depending on the mission the vessel is on, drilling equipment, small submersible crafts and divers may pass through the moon pool. Since the drillship is also a vessel, it can easily relocate to any desired location. Due to their mobility, drillships are not as stable compared to semi-submersible platforms. To maintain its position, drillships may utilize their anchors or use the ship's computer-controlled system on board to run off its dynamic positioning. [10]
One of the world's best-known drillships is Japan's ocean-going drilling vessel Chikyū , which actually is a research vessel. The Chikyū has the remarkable ability to drill to a depth of 7.0 kilometres (23,000 ft) below the seabed, bringing that to two to four times that of any other drillship. [11]
In 2011 the Transocean drillship Dhirubhai Deepwater KG1 set the world water-depth record at 10,194 feet of water (3,107 meters) while working for Reliance – LWD and directional drilling done by Sperry Drilling in India. [12]
An oil platform is a large structure with facilities to extract and process petroleum and natural gas that lie in rock formations beneath the seabed. Many oil platforms will also have facilities to accommodate the workers, although it is also common to have a separate accommodation platform bridge linked to the production platform. Most commonly, oil platforms engage in activities on the continental shelf, though they can also be used in lakes, inshore waters, and inland seas. Depending on the circumstances, the platform may be fixed to the ocean floor, consist of an artificial island, or float. In some arrangements the main facility may have storage facilities for the processed oil. Remote subsea wells may also be connected to a platform by flow lines and by umbilical connections. These sub-sea facilities may include one or more subsea wells or manifold centres for multiple wells.
A semi-submersible platform is a specialised marine vessel used in offshore roles including as offshore drilling rigs, safety vessels, oil production platforms, and heavy lift cranes. They have good ship stability and seakeeping, better than drillships.
Transocean Ltd. is an American company. It is the world's largest offshore drilling contractor based on revenue and is based in Vernier, Switzerland. The company has offices in 20 countries, including Canada, the United States, Norway, United Kingdom, India, Brazil, Singapore, Indonesia, and Malaysia.
A moon pool is a feature of marine drilling platforms, drillships and diving support vessels, some marine research and underwater exploration or research vessels, and underwater habitats, in which it is also known as a wet porch. It is an opening in the floor or base of the hull, platform, or chamber giving access to the water below, allowing technicians or researchers to lower tools and instruments into the sea. It provides shelter and protection so that even if the ship is in high seas or surrounded by ice, researchers can work in comfort rather than on a deck exposed to the elements. A moon pool also allows divers, diving bells, ROVs, or small submersible craft to enter or leave the water easily and in a more protected environment.
Chikyū (ちきゅう) is a Japanese scientific drilling ship built for the Integrated Ocean Drilling Program (IODP). The vessel is designed to ultimately drill 7 km beneath the seabed, where the Earth's crust is much thinner, and into the Earth's mantle, deeper than any other hole drilled in the ocean thus far.
Offshore drilling is a mechanical process where a wellbore is drilled below the seabed. It is typically carried out in order to explore for and subsequently extract petroleum that lies in rock formations beneath the seabed. Most commonly, the term is used to describe drilling activities on the continental shelf, though the term can also be applied to drilling in lakes, inshore waters and inland seas.
Ocean Rig UDW Inc. was an operator of semi-submersible oil platforms and underwater drillships and was based in Athens. In 2018, the company was acquired by Transocean.
Subsea technology involves fully submerged ocean equipment, operations, or applications, especially when some distance offshore, in deep ocean waters, or on the seabed. The term subsea is frequently used in connection with oceanography, marine or ocean engineering, ocean exploration, remotely operated vehicle (ROVs) autonomous underwater vehicles (AUVs), submarine communications or power cables, seafloor mineral mining, oil and gas, and offshore wind power.
"Offshore", when used in relation to hydrocarbons, refers to operations undertaken at, or under the, sea in association with an oil, natural gas or condensate field that is under the seabed, or to activities carried out in relation to such a field. Offshore is part of the upstream sector of the oil and gas industry.
Deepwater Horizon was an ultra-deepwater, dynamically positioned, semi-submersible offshore drilling rig owned by Transocean and operated by BP. On 20 April 2010, while drilling at the Macondo Prospect, a blowout caused an explosion on the rig that killed 11 crewmen and ignited a fireball visible from 40 miles (64 km) away. The fire was inextinguishable and, two days later, on 22 April, the Horizon sank, leaving the well gushing at the seabed and causing the largest marine oil spill in history.
A jackup rig or a self-elevating unit is a type of mobile platform that consists of a buoyant hull fitted with a number of movable legs, capable of raising its hull over the surface of the sea. The buoyant hull enables transportation of the unit and all attached machinery to a desired location. Once on location the hull is raised to the required elevation above the sea surface supported by the sea bed. The legs of such units may be designed to penetrate the sea bed, may be fitted with enlarged sections or footings, or may be attached to a bottom mat. Generally jackup rigs are not self-propelled and rely on tugs or heavy lift ships for transportation.
Deepwater drilling, or deep well drilling, is the process of creating holes in the Earth's crust using a drilling rig for oil extraction under the deep sea. There are approximately 3400 deepwater wells in the Gulf of Mexico with depths greater than 150 meters.
Transocean Marianas was an Earl & Wright Sedco 700 design semi-submersible platform drilling unit capable of operating in harsh environments and water depths up to 7,000 feet (2,100 m) using an 47.6 cm (18.75 in), 15,000 psi blowout preventer (BOP), and a 53 cm (21 in) outside diameter (OD) marine riser.
The FPSO Noble Seillean was a dynamically positioned floating oil production, storage and offloading vessel.
The Macondo Prospect is an oil and gas prospect in the United States Exclusive Economic Zone of the Gulf of Mexico, off the coast of Louisiana. The prospect was the site of the Deepwater Horizon drilling rig explosion in April 2010 that led to a major oil spill in the region from the first exploration well, named itself MC252-1, which had been designed to investigate the existence of the prospect.
The Deepwater Horizon drilling rig explosion was an April 20, 2010 explosion and subsequent fire on the Deepwater Horizon semi-submersible mobile offshore drilling unit, which was owned and operated by Transocean and drilling for BP in the Macondo Prospect oil field about 40 miles (64 km) southeast off the Louisiana coast. The explosion and subsequent fire resulted in the sinking of the Deepwater Horizon and the deaths of 11 workers; 17 others were injured. The same blowout that caused the explosion also caused an oil well fire and a massive offshore oil spill in the Gulf of Mexico, considered the largest accidental marine oil spill in the world, and the largest environmental disaster in United States history.
Discoverer Enterprise is a fifth generation deepwater double hulled dynamically positioned drillship owned and operated by Transocean Offshore Deepwater Drilling Inc., capable of operating in moderate environments and water depths up to 3,049 m (10,000 ft) using an 18.75 in (47.6 cm), 15,000 psi blowout preventer (BOP), and a 21 in (53 cm) outside diameter (OD) marine riser. From 1998 to 2005 the vessel was Panama-flagged and currently flies the flag of convenience of the Marshall Islands.
Deepwater Nautilus is an ultra-deepwater, semi-submersible offshore drilling rig.
Appaloosa is an offshore oil field located in the Mississippi Canyon blocks 459, 460, 503, and 504 of the United States sector of the Gulf of Mexico. It is a part of the Greater Longhorn area. The field is developed by the Italian energy company Eni.
Ocean development refers to the establishing of human activities at sea and use of the ocean, as well as its governance.
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