What are semisubmersibles in oil drilling?


What are semisubmersibles in oil drilling?

Using sonic equipment, oil companies are able to search for oil deep beneath the ocean's floor. Then they use a MODU, or mobile offshore drilling unit, to dig the well in exactly the right location, which their equipment has determined will be the most likely to produce oil.

A “semisubmersible” is a particular kind of MODU that floats above a submerged pontoon boat. Some semisubmersibles need to be towed to drilling sites by another vessel while others use propulsion systems to navigate their own way. Semisubmersibles use up to a dozen anchors to maintain their orientation and stay in one place over the well. The tension on the anchor chains is controlled by computers in order to correct for drift.

A semisubmersible and other types of MODUs use a riser to drill down into the ocean floor. Drilling fluids pass from the ocean floor through the riser and into the rig. Engineers then lower a drill string (a series of 30-foot/9.1-meter pipes) down through the riser. The engineers continue to add pipes to the string as they lower it down. A BOP -- blowout preventer -- seals off the pipe at the sea floor. Metal casings lined with cement walls stabilize the well and keep it from collapsing. When a MODU hits oil, the well needs to be plugged up. Engineers put in a plug, which is held down by seawater or drilling mud. After the well is capped, a permanent rig may come in to capture the oil, or the MODU may convert to a production rig and do the capturing itself.