Offshore Drilling Rigs
Jack-Up
Rigs: Jack-up rigs are similar to drilling barges, with one
difference. Once a jack-up rig is towed to the drilling site, three or
four 'legs' are lowered until they rest on the sea bottom. This allows
the working platform to rest above the surface of the water, as
opposed to a floating barge. However, jack-up rigs are suitable for
shallower waters, as extending these legs down too deeply would be
impractical. These rigs are typically safer to operate than drilling
barges, as their working platform is elevated above the water level.
Submersible Rigs: Submersible rigs, suitable
for shallow water, are like jack-up rigs in that they come in contact
with the ocean or lake floor. The rig consists of a platform with two
hulls positioned on top of one another. The upper hull contains the
living quarters for the crew, as well as the actual drilling platform.
The lower hull works much like the outer hull in a submarine - when
the platform is being moved from one place to another, the lower hull
is filled with air - making the entire rig buoyant. When the rig is
positioned over the drill site, the air is let out of the lower hull,
and the rig submerses to the sea or lake floor.
 Semisubmersible
Rigs: Semisubmersible rigs, the most common type of offshore
drilling rigs, work on the same principle as submersible rigs --
'inflating' and 'deflating' of its lower hull to maintain floating
position. The semisubmersible rig does not fully submerge to the sea
floor when it lets air out of the lower hull.
 Partially submerged, it
still floats above the drill site. When drilling, the lower hull, filled with water,
provides stability to the rig. Huge anchors, each weighing upwards of
ten tons, combined with the added stability of the submerged portion
of the rig, ensure that the platform is stable during drilling
operations in turbulent offshore waters and at much deeper water
depths than other types of offshore drilling vessels. The EXMAR
2500 and EXMAR E-II
are examples of semisubmersibles drilling rigs. Click on the links
above for rig specifications.
 Drillships:
Drillships are ships designed to carry out drilling
operations. Drillships are different from ordinary ships in that
they have drilling platform and derrick located on the middle of its
deck and a hole (or "moonpool") through the ship that allows
the drill string to extend through the boat and water down to the
seafloor. Drillships are held in position over the well site by a
dynamic positioning system using satellite positioning technology, and
they are equipped with electric motors on the underside of the ships
hull that are capable of propelling the ship in any direction. The
position system, along with all other equipment used for drilling, are
integrated into the ships onboard computer system to ensure smooth
operations at all times.
 The EXMAR
STURGEON split-ship drilling vessel, illustrated in the
photo, is an example of a special purpose drilling vessel. It was
design to move into and out of narrow straits with ease. The two
separate hulls are separate during the move to the drilling location,
then locked together for stable drilling operations. Though highly maneuverable,
the Exmar Sturgeon feature state-of-the-art
operational components such as advanced tubular handling, BOP handling, and
well fluids handling systems for deepwater drilling. Click
here for specifications.
Offshore Production Platforms
Moveable rigs, such as the jack-up, submersible, and
semisubmersible drilling rigs and drill ships, are used to drill both exploratory
and production wells.
When exploratory drilling find commercially viable natural gas or
petroleum deposits, a production system is installed above the drill
site. Usually a number
of proven wells have been drilled before a stationary production platform is
build since these are huge and very expensive structures. They are
huge and expensive because they must be able to withstand high winds
and waves as well as turbulent subsurface water conditions. There are
a number of different types of permanent offshore platforms, each
useful for a particular depth range. And there are also movable
production systems when either water depth and conditions or the economics
of the field do not allow a fixed production system.
Fixed Platforms: A fixed platform rig has 'legs' constructed
of concrete or steel, extending down from the platform in a 1500 to
2000 feet of water and fixed to the seafloor with piles. They are
stable because they are attached to the sea floor. However, a fixed
platform cannot be used in deep water. For deeper waters, either a
"compliant tower," with flexible legs to absorb wind or sea
pressures, or a "seastar" platform is used. A seastar is
much like a seim-submersible drilling rig, but uses a tension leg
system. The tension legs are long, hollow tendons that do not allow
for up or down movement of the platform but have flexibility for
side-to-side motion. This allows the platform to withstand ocean and
wind forces without breaking the legs off. Seastar platforms are
typically used for smaller reservoirs in water depths less than 3500
feet when it is not economical to build a larger platform.
 Floating Production Vessels: Floating
production vessels contain petroleum production equipment and if large
enough, they can also contain drilling equipment for dual purpose
operations. Often they use a semi-submersible rig designs although
ships can be used as floating production vessels. The production
platforms are kept in place through large anchors or a dynamic
positioning system just like semisubmersible rigs and drillships. When
drilling operations are complete, a production wellhead is attached at
the seafloor and the extracted petroleum product is transported via
risers from the wellhead to the production facilities on the
semi-submersible or drill ship platform. These production systems now
operate in water depths of up to 6,000 feet.
 The EXMAR OPTI-EX Floating Production Semisubmersible (FPS), a deep-draft ring-pontoon vessel,
is a state-of-the-art design that offers
superb stability and motions for production operations. Like other Exmar designed
drilling rigs and drill ships, the Exmar FPS offer increased maneuverability, deeper
drilling, and improved safety, reliability, and performance.
We Design and Build Drilling
and Production Vessels
Whatever your offshore vessel needs may be, EXMAR can help you move
forward with your drilling, production, and transport projects. EXMAR Offshore
can design ready-to-build state-of-the-art vessels to your specifications, modify
EXMAR
Offshore's proprietary designs to meet your needs, and provide project
management support from conception through launch. The principals of EXMAR Offshore Company Houston, each with
over 25 years experience in the offshore industry and their respective
fields (naval architecture, structural engineering, electrical engineering,
mechanical engineering, systems engineering, and engineering design and
drafting), have designed, managed construction, and operated more than 60
drilling and production vessels worldwide.
Click here for an
EXMAR Capabilities
and Projects summary.
We're EXMAR.
We like a challenge. Let's
Talk.
Call US 281-679-3900 or Email exmar@exmaroffshore.com to discuss your
project.
Drilling and production vessels get hydrocarbons out of the ground.
Transport vessels move them from the production facilities to refineries
to the end user.
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