Offshore drilling refers to a mechanical process where a wellbore is drilled through the seabed. It is typically carried out in order to explore for and subsequently extract petroleum which lies in rock formations beneath the seabed.
Most commonly, the term is used to describe drilling activities on the continental shelf, though the term can also be applied to drilling in lakes, inshore waters and inland seas.
Offshore drilling presents environmental challenges, both from the produced hydrocarbons and the materials used during the drilling operation.
There are many different types of facilities from which offshore drilling operations take place. These include bottom founded drilling rigs (jackup barges and swamp barges), combined drilling and production facilities either bottom founded or floating platforms, and deepwater mobile offshore drilling units (MODU) including semi-submersibles and drillships. These are capable of operating in water depths up to 10,000 ft. In shallower waters the mobile units are anchored to the seabed, however in deeper water (>5,000 ft) the semisubmersibles or drillships are maintained at the required drilling location using dynamic positioning.
[mappress] Subsea World News Staff, February 21, 2013