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Offshore Drilling Rig Types

There are several types of oil rigs. Each is designed to perform under specific conditions, from shallow water to great depths and areas where the weather is severe or unpredictable. While some oil rigs are built on location over oil deposits, most are constructed or refitted from older ships to create mobile rigs, which can then be towed or propelled into place.

  1. Submersible Oil Rigs

    • In shallow water, where the depth is 80 feet or less, a submersible rig may be used. Submersible rigs are towed to the drilling location and then submerged until they come to rest upon the ocean floor. Some submersible rigs use anchors to secure their place, but many simply stay in place under their own weight.

    Drillships

    • A drillship is a self-propelled oil rig, which may be built new or retrofitted from an older ship. Older drill ships use conventional anchors to stay in place. More modern drill ships use a computer-controlled system of thrusters to maintain their position over a drilling target. Drillships with computer-controlled positioning are capable of drilling in very deep waters, in which other types of rigs can not operate.

    Semi-Submersible Oil Rigs

    • Semi-submersible rigs may be self-propelled or towed, depending on their design. Ballast is used to submerge the rig once it is in position and it is kept in place either by dynamic computer positioning or by conventional anchors. Semi-submersible rigs are designed for harsh weather conditions, which they endure in part due to their sturdy construction and in part via their sheltered position beneath the ocean's surface.

    Jack-Up Oil Rigs

    • Jack-up rigs rest on legs that are jacked down from the surface once they are in position over the drilling target. Jack-up rigs operate at depths of up to 600 feet, and are towed to position prior to deploying their legs. Once the legs of the rig reach the ocean floor, they continue to extend until the body of the rig rests above the water. When the rig rests about fifty feet above the ocean's surface, it is ready to drill.

    Production Platforms

    • Production platforms are permanent structures that are built on-site over deposits of oil or gas. They are commissioned and constructed only after exploratory drilling has lead to the discovery of resources, and cannot be moved once they are in place.

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