Offshore is a mechanical process where a wellbore is drilled below the seabed. It is typically carried out in order to explore for and subsequently extract petroleum that 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 all environmental challenges, both offshore and onshore 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 (Jack-up 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 or drillship. These are capable of operating in water depths up to 3,000 metres (9,800 ft). In shallower waters the mobile units are anchored to the seabed; however, in water deeper than 1,500 metres (4,900 ft), the semi-submersibles and drillships are maintained at the required drilling location using dynamic positioning.