Offshore construction
Encyclopedia
Construction
In the fields of architecture and civil engineering, construction is a process that consists of the building or assembling of infrastructure. Far from being a single activity, large scale construction is a feat of human multitasking...
is the installation of structures and facilities in a marine environment, usually for the production and transmission of electricity
Electricity
Electricity is a general term encompassing a variety of phenomena resulting from the presence and flow of electric charge. These include many easily recognizable phenomena, such as lightning, static electricity, and the flow of electrical current in an electrical wire...
, oil
Petroleum
Petroleum or crude oil is a naturally occurring, flammable liquid consisting of a complex mixture of hydrocarbons of various molecular weights and other liquid organic compounds, that are found in geologic formations beneath the Earth's surface. Petroleum is recovered mostly through oil drilling...
, gas
Gas
Gas is one of the three classical states of matter . Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons...
and other resources.
Construction in the offshore environment is a difficult and dangerous activity. Construction and pre-commissioning is typically performed as much as possible on land or inshore areas. To optimize the costs and risks of installing large offshore platforms, different construction strategies have been developed.
One strategy is to fully construct the offshore facility inshore, and tow the installation to site floating on its own buoyancy. Bottom founded structure are lowered to the seabed by de-ballasting (see for instance Condeep
Condeep
Condeep refers to a make of gravity base structure for oil platforms developed and fabricated by Norwegian Contractors in Stavanger, Norway. A Condeep usually consists of a base of concrete oil storage tanks from which one, three or four concrete shafts rise...
or Cranefree
Cranefree
Cranefree is the trademark for offshore foundations marketed by the company Seatower. This technology is focused on the offshore wind sector, and is designed to avoid using heavy-lift crane vessels in order to make offshore construction less risky and costly. Furthermore, the design avoids seabed...
), whilst floating structures
FPSO
FPSO may be:* Fleet Publication Supply Office* Floating Production Storage and Offloading, an offshore oil & gas industry vessel* Forms and Publications Supply Office, by CINCPAC in the United States military* Foster Parent Society of Ontario...
are held in position with substantial mooring systems.
The size of offshore lifts can be reduced by making the construction modular, with each module being constructed onshore
Onshore
Onshore is a term used in finance to denote the jurisdiction in which a company is domiciled and in which it pays a significant rate of tax. It is the opposite of offshore, which denotes a tax haven...
and then lifted using a crane vessel
Crane vessel
A crane vessel, crane ship or floating crane is a ship with a crane specialized in lifting heavy loads. The largest crane vessels are used for offshore construction. Conventional monohulls are used, but the largest crane vessels are often catamaran or semi-submersible types as they have increased...
into place onto the platform. A number of very large crane vessels were built in the 1970s which allow very large single modules weighing up to 14,000 tonnes to be fabricated and then lifted into place.
Specialist floating hotel vessels known as flotel
Flotel
Flotel, a portmanteau of the terms floating hotel, refers to the installation of living quarters on top of rafts or semi-submersible platforms...
s are used to accommodate workers during the construction and hook-up
Hook-up
Hook-up or hook up has several meanings:* Making a connection between components in a system** An electrical connection** An electrical connector** A connection to water, sewer, or electrical utilities at a campsite...
phases. This is a high cost activity due to the limited space and access to materials.
Oil platform
Oil platform
An oil platform, also referred to as an offshore platform or, somewhat incorrectly, oil rig, is a lаrge structure with facilities to drill wells, to extract and process oil and natural gas, and to temporarily store product until it can be brought to shore for refining and marketing...
s are key fixed installations from which drilling and production activity is carried out. Drilling rig
Drilling rig
A drilling rig is a machine which creates holes or shafts in the ground. Drilling rigs can be massive structures housing equipment used to drill water wells, oil wells, or natural gas extraction wells, or they can be small enough to be moved manually by one person...
s are either floating vessels for deeper water or jack-up designs which are a barge with liftable legs. Both of these types of vessel are constructed in marine yards but are often involved during the construction phase to pre-drill some production wells.
Other key factors in offshore construction are the weather window
Weather window
A weather window occurs when weather forecasts indicate that a given set of marine operations or offshore construction activities can be performed within their maximum limits for wave height, wind speeds etc....
which defines periods of relatively light weather during which continuous construction or other offshore activity can take place. Safety
Safety
Safety is the state of being "safe" , the condition of being protected against physical, social, spiritual, financial, political, emotional, occupational, psychological, educational or other types or consequences of failure, damage, error, accidents, harm or any other event which could be...
is another key construction parameter, the main hazard obviously being a fall into the sea from which speedy recovery in cold waters is essential.
The main types of vessels used for pipe laying are the "Derrick Barge (DB)", the "Pipelay Barge (LB)" and the "Derrick/Lay Barge (DLB)" combination. Diving Bells in offshore construction are mainly used in water depths greater than 120 ft, less than that, the divers use a metal basket driven from an "A" frame from the deck. The basket is lowered to the water level, then the divers enter the water from it to a maximum of 120 ft. Bells can go to 1500 ft, but are normally used at 400 to 800 ft.
Offshore construction includes the design, construction, and/or repair of offshore structures, both commercial and military, including:
- Subsea oil and gas developments
- Offshore platforms - Fixed PlatformFixed PlatformA fixed platform is a type of offshore platform used for the production of oil or gas. These platforms are built on concrete and/or steel legs anchored directly onto the seabed, supporting a deck with space for drilling rigs, production facilities and crew quarters. Such platforms are, by virtue of...
s, Semi-submersibleSemi-submersibleA semi-submersible is a specialised marine vessel with good stability and seakeeping characteristics. The semi-submersible vessel design is commonly used in a number of specific offshore roles such as for offshore drilling rigs, safety vessels, oil production platforms and heavy lift cranes.The...
s, SparSparIn sailing, a spar is a pole of wood, metal or lightweight materials such as carbon fiber used on a sailing vessel. Spars of all types In sailing, a spar is a pole of wood, metal or lightweight materials such as carbon fiber used on a sailing vessel. Spars of all types In sailing, a spar is a...
s, TLPTLPTLP refers to:*TLP , reaggea band*Tactical Leadership Programme, a military training unit situated in Albacete, Spain.*Traded Life Policies, the trading, largely in Britain, of second-hand life assurance....
s, FPSOFPSOFPSO may be:* Fleet Publication Supply Office* Floating Production Storage and Offloading, an offshore oil & gas industry vessel* Forms and Publications Supply Office, by CINCPAC in the United States military* Foster Parent Society of Ontario...
s, etc. - Floating Oil and Gas Platforms - Semi-submersibleSemi-submersibleA semi-submersible is a specialised marine vessel with good stability and seakeeping characteristics. The semi-submersible vessel design is commonly used in a number of specific offshore roles such as for offshore drilling rigs, safety vessels, oil production platforms and heavy lift cranes.The...
s, SparSparIn sailing, a spar is a pole of wood, metal or lightweight materials such as carbon fiber used on a sailing vessel. Spars of all types In sailing, a spar is a pole of wood, metal or lightweight materials such as carbon fiber used on a sailing vessel. Spars of all types In sailing, a spar is a...
s, Tension-leg platformTension-leg platformA Tension-leg platform or Extended Tension Leg Platform is a vertically moored floating structure normally used for the offshore production of oil or gas, and is particularly suited for water depths greater than 300 metres and less than 1500 meters...
s (TLP's), FPSOFPSOFPSO may be:* Fleet Publication Supply Office* Floating Production Storage and Offloading, an offshore oil & gas industry vessel* Forms and Publications Supply Office, by CINCPAC in the United States military* Foster Parent Society of Ontario...
's, etc.