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[[File:Discoveries-breathe-new-life-in-newfoundland-hero.jpg|thumbnail|The semi-submersible rig West Aquarius, near St. John’s, Newfoundland, drilled Statoil’s Harpoon and Bay du Nord light oil discoveries in 2013. Courtesy of Statoil ASA and the AAPG Explorer. See more in the [http://www.aapg.org/publications/news/explorer/details/articleid/8055/discoveries-breathe-new-life-in-newfoundland#prettyPhoto%5BGallery%201464%5D/0/ AAPG Explorer].]]

[[File:Discoveries-breathe-new-life-in-newfoundland-hero.jpg|thumbnail|300px|The semi-submersible rig West Aquarius, near St. John’s, Newfoundland, drilled Statoil’s Harpoon and Bay du Nord light oil discoveries in 2013. Courtesy of Statoil ASA and the AAPG Explorer. See more in the [http://www.aapg.org/publications/news/explorer/details/articleid/8055/discoveries-breathe-new-life-in-newfoundland#prettyPhoto%5BGallery%201464%5D/0/ AAPG Explorer].]]

 

 

Offshore rigs are similar to [[land rigs]] but with several additional features to adapt them to the marine environment. Those features include

Offshore rigs are similar to [[land rigs]] but with several additional features to adapt them to the marine environment. Those features include

==Types of offshore rigs==

==Types of offshore rigs==

 

[[file:offshore-rigs_fig1.png|left|thumb|{{figure number|1}}Fixed production platforms. From Whittaker.<ref name=pt03r50>Whittaker, A., ed., 1985, Field geologists training guide: Boston, MA, IHRDC, 291 p.</ref>]]

offshore-rigs_fig1.png|{{figure number|1}}Fixed production platforms. From Whittaker.<ref name=pt03r50>Whittaker, A., ed., 1985, Field geologists training guide: Boston, MA, IHRDC, 291 p.</ref>

The various types of offshore rigs include barges, submersibles, platforms, jackups, and floaters (the latter of which include semisubmersibles and drill ships).

The various types of offshore rigs include barges, submersibles, platforms, jackups, and floaters (the latter of which include semisubmersibles and drill ships).

===Platforms===

===Platforms===

''Platforms'' use a ''jacket'' (a steel tubular framework anchored to the ocean bottom) to support the [[surface production equipment]], living quarters, and drilling rig ([[:file:offshore-rigs_fig1.png|Figure 1]]). Multiple [[Wellbore trajectory|directional wells]] are drilled from the platform by using a rig with a movable substructure. The rig is positioned over preset wellheads by jacking across on skid beams. After all the wells are drilled, the rig and quarters are removed from the platform. Smaller platforms use a jackup rig to drill the wells.

''Platforms'' use a ''jacket'' (a steel tubular framework anchored to the ocean bottom) to support the [[surface production equipment]], living quarters, and drilling rig ([[:file:offshore-rigs_fig1.png|Figure 1]]). Multiple [[Wellbore trajectory|directional wells]] are drilled from the platform by using a rig with a movable substructure. The rig is positioned over preset wellheads by jacking across on skid beams. After all the wells are drilled, the rig and quarters are removed from the platform. Smaller platforms use a jackup rig to drill the wells.

''Jackups'' are similar to platforms except that the support legs are not permanently attached to the seafloor ([[:file:offshore-rigs_fig2.png|Figure 2]]). The weight of the rig is sufficient to keep it on location. The rig's legs can be jacked down to drill and jacked up to move to a new location. When under tow, a [[flotation hull]] buoys the jackup. The [[derrick]] is cantilevered over the rear to fit over preset risers if necessary.

''Jackups'' are similar to platforms except that the support legs are not permanently attached to the seafloor ([[:file:offshore-rigs_fig2.png|Figure 2]]). The weight of the rig is sufficient to keep it on location. The rig's legs can be jacked down to drill and jacked up to move to a new location. When under tow, a [[flotation hull]] buoys the jackup. The [[derrick]] is cantilevered over the rear to fit over preset risers if necessary.

===Floaters===

===Floaters===

* They are held on location by anchors or [[dynamic positioning]].

* They are held on location by anchors or [[dynamic positioning]].

* The [[drill string]] and riser are isolated from wave motion by motion compensators.

* The [http://www-odp.tamu.edu/publications/tnotes/tn31/pdf/drill_s.pdf drill string] and riser are isolated from wave motion by motion compensators.

* The wellheads and [[blowout preventer|BOPs]] are on the ocean bottom and are connected to the rig by a riser to allow circulation of [[Drilling fluid|drilling mud]].

* The wellheads and [http://www.glossary.oilfield.slb.com/en/Terms/b/blowout_preventer.aspx BOPs] are on the ocean bottom and are connected to the rig by a riser to allow circulation of [[Drilling fluid|drilling mud]].

There are two categories of floaters: semisubmersibles and drill ships.

There are two categories of floaters: semisubmersibles and drill ships.

===Semisubmersibles===

===Semisubmersibles===

The drilling apparatus on a ''drill ship'' is mounted in the center of the ship over a ''moon pool'', which is a reinforced hole in the bottom of the ship through which the [[drill string]] is raised and lowered ([[:file:offshore-rigs_fig4.png|Figure 4]]). The ship can be turned into the oncoming wind or currents for better stability, and it can operate in water too deep for anchors.

The drilling apparatus on a ''drill ship'' is mounted in the center of the ship over a ''moon pool'', which is a reinforced hole in the bottom of the ship through which the [[drill string]] is raised and lowered ([[:file:offshore-rigs_fig4.png|Figure 4]]). The ship can be turned into the oncoming wind or currents for better stability, and it can operate in water too deep for anchors.

==See also==

==See also==

[[Category:Wellsite methods]]

[[Category:Wellsite methods]]