An offshore drilling platform is a marine structure primarily used for drilling wells. It is equipped with drilling, power, communication, and navigation systems, as well as safety, lifesaving, and living facilities. It is an indispensable tool for offshore oil and gas exploration and development.
Classification by structure:
(1) Mobile Offshore Drilling Units (MODU): Jack-up Platforms (or Jack-up Rigs), Drillships, Semi-submersible Platforms, Tension Leg Platforms (TLP), Guyed Tower Platforms
(2) Fixed Platforms: Submersible Platforms, Jacket Platforms, Concrete Gravity Based Structures (GBS), Deepwater Compliant Towers
Classification of Offshore Drilling Platforms
1. Jacket Platform
The jacket platform foundation is rigidly anchored to the seabed and capable of supporting dry wellheads. The theoretical operational water depth ranges from 0 meters to 300 meters. Jacket platforms are predominantly wellhead platforms or integrated processing platforms. Some integrated processing platforms are equipped with modular drilling rigs, enabling them to provide drilling and workover services for oil and gas fields.
2. Submersible Platform
Submersible platforms are designed to operate on the seabed and can support dry wellhead systems. The theoretical operational water depth ranges from 300 to 1,000 meters. These platforms are primarily categorized into reinforced concrete and pure steel structures, with the former being the predominant type. Approximately 50 such platforms are currently in service, mostly serving as integrated processing facilities. All platforms are equipped with modular drilling rigs, enabling them to provide drilling and well maintenance services for oil and gas fields.
3. Compliant Tower Platform
The compliant tower platform’s foundation is fixed to the seabed. Under marine environmental loads, the platform can swing within a certain range around its base. It can support dry wellheads. Theoretical operating water depth is greater than 300-1000 meters. There are five compliant tower platforms in service, all of which are integrated processing platforms. Each platform is equipped with a modular drilling rig, providing drilling and workover services for oil and gas fields.
4. Semi-Submersible Platform
The semi-submersible platform floats on the water surface and is moored to the seabed by anchor chains. Under marine environmental loads, the platform can deviate significantly around its center. It supports wet wellheads. Theoretical operating water depth is over 70 meters. Most are integrated processing platforms. Converted platforms often retain drilling rig modules, providing drilling and workover services for oil and gas fields. Newly built platforms in recent years are not equipped with drilling rig modules.
5. Tension Leg Platform
A tension leg platform floats on the water surface and is moored to the seabed using tension legs. Under marine environmental loads, the platform can deviate slightly around its center. It supports dry wellheads. Theoretical operating water depth: 350-1500 meters. Mostly integrated processing platforms. Because most platforms support dry wellheads, they are often equipped with drilling and workover rig modules, providing drilling and workover services for oil and gas fields.
6. Spar Platform
A spar platform floats on the water surface and is moored to the seabed using semi-tensioned mooring. Under marine environmental loads, the platform can deviate slightly around its center. It can support dry wellheads. Theoretical operating water depth: over 400 meters. Mostly integrated processing platforms. Some platforms are equipped with drilling and workover rig modules, providing drilling and workover services for oil and gas fields.
7. Semi-submersible Drilling Rig
A semi-submersible drilling rig floats on the water surface and is positioned using a dynamic positioning system (older platforms still use mooring). Equipped with a drilling rig system, it provides drilling and workover services for oil and gas fields. Theoretical operating water depth: 100-3600 meters. Since its introduction in 1961, the semi-submersible drilling platform has evolved to its seventh generation. Due to its good environmental adaptability, it is very popular with drilling contractors and will continue to play a dominant role in deep water, especially in harsh sea areas.
8. Mono-column Drilling Platform
A mono-column drilling platform floats on the water surface and is positioned using a dynamic positioning system. Equipped with a drilling rig system, it provides drilling and workover services for oil and gas fields. Often classified as a semi-submersible drilling platform, it is listed separately here due to significant differences in structure and performance compared to traditional drilling platforms. Theoretical operating water depth: 100-3600 meters. This type of platform has poor maneuverability but large storage space. There are currently two submersible platforms in operation, and the future of two platforms under construction is uncertain.
9. Drilling Ship
Drilling ships, designed as floating platforms, utilize dynamic positioning systems for navigation and are equipped with drilling rigs to provide drilling and well maintenance services for oil and gas fields. The theoretical operational water depth ranges from 100 meters to 3,600 meters. Currently, there are 163 such vessels in service. Due to their excellent mobility and large storage capacity, they are highly favored by drilling contractors. However, their environmental adaptability remains relatively limited, which suggests they will play a dominant role in deep-water and temperate marine environments in the future.
10. Drilling Barge
The drilling barge floats on the water surface and is moored to the seabed via an anchor chain. The platform is equipped with a drilling rig system capable of providing drilling and well maintenance services for oil and gas fields. The theoretical operational water depth ranges from 5 meters to 50 meters. Currently, there are 50 such vessels in service. Due to their poor maneuverability and limited environmental adaptability, they are primarily used in inland lakes or offshore waters because of their low cost.
11. Jack-up Rig
The jack-up rigs consists of two main components: movable pile legs and a fixed main hull. During operations, the pile legs remain anchored to the seabed while the hull is raised above water level. Equipped with drilling systems, these platforms provide drilling and well maintenance services for oil and gas fields, with theoretical operational depths ranging from 5 meters to 120 meters. Currently, there are 636 operational and under-construction platforms in use. Their mobility and cost-effectiveness have made them highly popular, ensuring continued dominance in shallow-water offshore operations. However, excessive new platform construction in recent years has led to severe overcapacity in the industry.
12. Submersible Drilling Rig
The Submersible Drilling Rig is the predecessor of the semi-submersible platform, mainly consisting of three parts: a pontoon, a column, and a topside module. During operation, the pontoon rests on the seabed. The platform is equipped with a drilling rig system and can provide drilling and workover services for oil and gas fields. The theoretical operating water depth is less than 30 meters. Currently, there are relatively few submersible platforms in operation. Due to its poor water depth adaptability, its function has been largely replaced by jack-up platforms, and it will eventually be phased out of the drilling market.