Type of Drilling Rigs

Drilling rigs come in various designs to suit different operational needs. Each rig type is tailored for specific environments and challenges, from onshore to offshore, shallow to deep formations, and from stable land-based rigs to ultra-deepwater Drillships. The selection of a rig depends on the project’s technical requirements, operational depth, and geographical conditions. These rigs ensure safe and efficient oil and gas exploration and production.

Here’s a broad category of different types of drilling rigs used for drilling oil & gas wells:

  1. Land-Based Rigs

Land-based rigs are designed to drill wells on solid ground. These rigs are mobile and can be transported to remote locations. They are commonly used for drilling shallow to deep wells in oil and gas fields.

  • Conventional Drilling Rigs: Conventional land drilling rigs feature a fixed derrick or mast and are ideal for prolonged drilling operations. They can drill deeper and larger diameter wells and provide a stable platform for drilling operations. Once finished from one location, the rig components are dismantled, transported to the next drilling site, and assembled to drill the next well.

  • Mobile Rigs: Mobile rigs have most equipment mounted on a truck, trailer, or skid. Hence, moving the rig to the new location is much faster after finishing the current well. Large equipment, like mud tanks, power units, fuel tanks, etc, are usually transported separately and hooked to the rig on site. Mobile rigs are highly portable and less expensive but have lower drilling capacity than conventional ones.

2. Mobile Offshore Drilling Units (MODU):

MODUs are the rigs for drilling a well in an offshore location. Once finishing from a well, they can be moved to another offshore location to drill another well. Different types of rigs are used for drilling in different water depths and are categorized as follows.

  • Barge Rigs: Barge rigs are floating platforms for drilling wells in shallow to ultra-shallow waters, such as swamps, marshes, or inland lakes. They are towed to the drilling site and submerged slightly to stabilize them during drilling. Barges can also sit directly on the seafloor, providing stability and reducing the need for mooring systems. Drilling barges have an extremely shallow draft, allowing them to operate in very shallow water depths of up to 10 - 15 ft.

  • Jack-Up Rigs: These rigs drill wells in shallow offshore waters. A jack-up rig stands on legs that penetrate the seabed to provide stability. After achieving sufficient penetration and completing the load tests, the rig’s deck is elevated above the water, providing safety from tidal motions and waves. Depending on the Rig capacities, they are primarily deployed for developmental or exploratory drilling in water depths up to 500 feet deep. Jack-up rigs require a second vessel to tow them to the location.

  • Semi-Submersible Rigs: A semi-submersible rig is a floating offshore drilling unit. As the name suggests, a semisubmersible rig is partially submerged in water. The rig floats on hollow steel cross-sections called "Pontoons." Some semi-submersible rigs have propulsion systems that allow them to navigate drilling sites under their own power, while others require a second vessel to tow them to the location. Most rigs use several anchors that help maintain the structure's orientation. Computers control the tension on each anchor chain to correct for drift. Since the rig doesn't float on the water surface, it provides a more stable drilling platform than a drillship. Semisubmersible rigs are used for drilling wells in 1,000 feet to 3,500 feet of water depth.

  • Drillships: A Drill Ship, also known as a Floater, is like a ship. It has a drilling rig and all associated equipment for drilling a well. It has a self-propulsion mechanism and can venture into ultra-deepwater to drill remote offshore locations. Drill ships are used for drilling wells in 1,000 feet to 10,000 feet water depths. Drillships use advanced dynamic positioning systems to maintain their position over the drilling location without anchors. These rigs are highly mobile and can be quickly deployed to different locations.

3. Platform Rigs

These rigs are installed on fixed platforms in offshore environments, typically for long-term production and drilling in shallow to moderate depths. They are commonly used in areas where large reservoirs are located beneath the seabed. Platform rigs could be further classified as:

  • Fixed Platforms: Stationary structures anchored to the seabed.

  • Tension-Leg Platforms (TLPs): Use tensioned cables to stay stable in deeper waters.

4. Slimhole Rigs

Slimhole rigs are designed to drill smaller-diameter wells, often used in exploratory drilling to reduce costs. They are lightweight and require less energy and drilling fluid. They provide a cost-effective way to evaluate potential reservoirs before investing more in a drilling project.