Page 8 - 4274

1 JACK-UP PLATFORMS

A jack-up platform (fig. 1.1)-- a barge with legs and
a lifting system -- is used for drilling offshore oil and gas wells.
The barge, or hull, is a mobile and floatable platform with
independently moveable legs at its edges. The platform may move
under its own power, or tugboats may tow it to a particular drilling
location. At sea, the legs are elevated so that their bases rest just a
few feet below the water's surface. Once the jack-up is on-site, the
legs are lowered and jacked, or anchored, into the sea floor. The
weight of the barge and additional ballast water secures the
anchoring. The lifting equipment then raises the barge 50 to 60
feet above the water's surface. The barge becomes a working and
accommodation platform.

Figure 1.1 - Jack-up platform
A jack-up platform can drill offshore wells in up to 500 feet
of water. The first jack-up came into operation in the 1950s in the
Gulf of Mexico. These platforms are designed to withstand
hurricane wind speeds of 100 knots and wave heights of 80 feet.
The structure can very quickly position itself on-site or move away
to another location. The type of jack-up that oil company operators
choose depends on water depths, sea bottom conditions and cost.
The leg design of an open-truss platform is a crisscross of
steel tubes, resembling a derrick or electricity pylon. The design
8