A drillship is a self-propelling marine vessel modified with a drilling apparatus used in the offshore drilling of oil wells. In addition, the ship comes equipped with a drilling derrick, moon pool, and specialized mooring and positioning equipment that helps stabilize the ship in treacherous water or weather conditions. With their great mobility and larger loading capabilities, drillships are used extensively in the drilling of exploratory oil wells. Some even come designed with an on-board heli-pad for transporting crew and supplies.
Drillships were first developed in the late 1940s by marine architects. One of the first drillships was a U.S. surplus Navy patrol ship with cantilevered drilling equipment. The next drillships went on to include a moon pool and a drilling derrick typical of the modern drillships used today. Companies began to order the construction of more drillships to be used for drilling oil wells in open water. Transocean, Pride, Seadrill, Frontier Drilling, and Noble are just some of the companies manufacturing drillships today.
 How it Works
Drillships have the capability to drill oil wells in very deep open water at depths spanning from 2,000 to more than 10,000 feet (610 to 3,048 m). The ship’s drilling equipment, including the drill string, passes through a moon pool and is connected to well equipment located in a riser pipe. The riser pipe is a long flexible pipe that extends from the underside of the drillship down to a subsea oil well. Drillships are self-propelling vessels adept at drilling in multiple open water locations. This makes them highly cost-effective for use in the drilling of exploratory oil wells as opposed to a semisubmersible rig that must be moved with the aid of an another transport vessel.
Agitation by waves, wind, or ocean currents is one of the biggest challenges for an operating drillship, particularly during the drilling process when the ship is attached to equipment located several thousand feet below the sea. Sometimes harsh weather and ocean conditions can result in drillships facing long periods of downtime. This is usually offset, however, by their ability to get from one location to another quickly and with relative ease.
Two types of anchoring systems are used on drillships today. Some drillships use a mooring system of eight to 12 anchors moored to the bottom of the ocean floor. When drillships are operating at deeper depths they must rely on a dynamic positioning system (DPS). A DPS is dependent on the use of multiple thrusters located on the front, mid, and back sections of the ship. An on-board computer monitors weather and ocean conditions, activating the thrusters when necessary to compensate for unexpected changes.
Electric motors positioned on the underside of the ship’s hull are used to maneuver the ship in any direction. The electric motors are also designed to work in combination with the ship’s on-board computer system, which relies on sophisticated satellite positioning technology. Sensors on the drilling template work in conjuction with the computer to ensure the ship stays in place above the drill site in turbulent conditions.