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Platform ..................

An oil platform is a fixed marine construction which is used for the exploitation of an oil layer.
It supports mainly the devices necessary for the phase of drilling, of extraction of oil, thus sometimes of the equipment intended to ensure a human presence on board. Certain platforms also make it possible to transform oil extracts so that it is easier to transport and to export.

The first platforms are those of the Gulf of Mexico on the coasts of Texas. These platforms are located in a very low depth of water and not for only function to be a wellhead. They are the prolongation of what had been developed with ground.
At the time of the first oil crisis in 1973, the European governments put the question of their independence with respect to the countries of the Persian Gulf. It becomes essential for them to develop the exploitation of the oil fields and gazifières of the North Sea.

The United Kingdom and Norway thus launched out in the development of techniques of drilling and offshore oil rig production (far from the coasts, in open sea). The European companies, with the assistance of engineering of the whole world develop research programs which lead to the first oil platform and the development of the techniques of drilling since a floating machine.

The challenge is all the more large as the North Sea is a particularly hostile sea. The climate is hard for six months of the year: at the time of the storms, the height of the waves, their peak to their hollow, can reach more than thirty meters (either the equivalent of a building of ten floors). Located far from the coasts, these platforms must shelter men to ensure the exploitation of it.

The safety requirements related to manufacture, the installation and the implementation of these platforms are developed during the years 1970-80 following various accidents. Mentalities in the world of the offshore oil rig exploitation change radically after the accident of the platform Piper-Alpha which cost the life 167 people in 1988.
Once technologies offshore oil rig controlled and developed at sea North, the door is opened with exploration and the exploitation in all the seas of the sphere. Currently, one finds platforms oil in the following areas; The North Sea, Persian Gulf, Gulf of Guinea, China Sea, Caspian Sea, Dimensions of Brazil, Oceania, Gulf of Mexico.

Techniques of drilling and techniques of constructions having evolved/moved, great depths of water (sup. with 1000 meters) are now accessible and exploitable at reasonable cost. The platforms are transformed then into ships and it is more and more often planned to create automatic underwater exploitations. Of or the need for building various types of platforms, the choice of those is done according to their role as well as the environment (depth of water, marine conditions…). A platform is generally made up of two distinct parts: - Topsides (left useful on the surface), made up of prefabricated modules - Jacket, the carrying structure (left being used to maintain the part useful above water), réaliséé out of tubular lattice metal or made up of concrete columns.

Fixed platforms;

- They are used at sea not very deep less 300m. Beyond these depths, they economically become nonviable. Various techniques of construction exist, such as for example Jacket-Deck, the Gravitating Platform, Compliant Tower; they are based on the bottom and can thus be connected in a rigid way to the wellheads and pipelines in Europe, the principal place or one can see of such platformes is the North Sea. Elsewhere, let us quote the GULF Coast American, the bay of campeche in Mexico, the Persian Gulf… golf of Guinea.

Floating units;

- They are primarily used for the exploitation of oil fields in deep seas with more than 300 meters. When the platform is floating, the installations of wellhead are connected to him by flexible conduits.

- FSO, floating unit of storage and loading (Floating Storage and Offloading). It is acted in fact of a transformed tanker, which stock of oil (coming from other platforms, or sometimes from offshore oil rig productions) and loads the tankers of trade.

- the FPU, floating unit of production (Floating Production links). It is a barge which receives the oil and gas of the bottom to treat them (to separate oil, gas and water for example) before sending them towards a storage unit (FSO) or towards a pipeline of export.

- FPSO, floating unit of production, storage and loading (floating production Storage and Offloading): similar to FSO, but also integrating the production. It is a solution sails about it for the development of the deep water layers. The FPSO have two major advantages: they do not need fixed infrastructures (like pipelines) and are redéployables (when the layer is exhausted, they can be repositioned on another).

- TLP, SPAR, Semi-submersible; they are more traditional platforms, in the sense that they integrate only the production and are connected to pipelines for the export of gas and/or produced oil. The TLP (tension leg plateforms) have an excess of buoyancy and are maintained in place by tended cables connecting them to the bottom. The semi-submersible platforms are inserted in water while filling of the ballasts, which makes them not very vulnerable to the swell. The SPAR rest on an enormous float cyndric. For important layers, one combines sometimes several solutions; parexemple, a platform TLP which produces oil and a FSO to store and export oil.

Mobile platforms;

- Self-lifting Platforms (jack up): they are made up of a hull and legs. The hull enables them to move by floating and supported the utilities. The legs are equipped with toothed racks enabling them to rise or to drop along the hull. In this way these platforms can be spread at multiple places while having a support on the ground. This concept is limited to depths of water about a hundred of meters. The major part of the self-lifting platforms are platforms of drilling and are used for exploration or drilling of well around platforms which are not equipped with drilling rig. There are also some as of the these platforms which are used as boat el, floating hotel making it possible to place teams which work at sea.

Objectives: the oil platforms are conceived to meet various needs, drilling, the production, the dwelling and storage. According to the depth of water and safety requirements, these functions can be gathered on the same platform or be separated on several platforms connected between them by footbridges.

Processes: once the oil brought to surface, it is necessary to separate the liquid and gas phases, to remove the water of the liquid phase. Once the separated gas and oil, they should be made clean to transport by pipeline or tanker to forward them to a refinery.
The cost of a factory on the open sea is such as one often prefers to carry out a treatment limited on oil or the gas only extracts intended to make transportable to the coast, or one builds a refinery more developed with less expenses.

Environment: one of the dominant criteria in the design of the platform is the environment in which it is. The marine environment is by hostile nature, because of its instability (tides, storms, currents, wind.) and of the CORROSION which it causes. The environment especially will influence the structural design carrying the platform (that it is a platform posed on ground or floating). The structure carrying the platform must, in addition to the weight of the topsides, to transmit to the ground the efforts induced by its environment. The swell, the current and the wind induce horizontal efforts on the fixed platforms and of the movements and accelerations on floating platforms. Salted water is a source of CORROSION for materials (and in particular steel) used in the platform.
Seismic; the majority of the producing oil sites are located in zone at the strong seismic risk. The platform, when it is fixed, must then be able to survive these events.
The ground plays a very important part in the design of a fixed platform. The platform rests on the ground and must thus comprise foundations. In the case of a floating platform, the ground is less important because it is not useful which anchoring has.

Lifespan: the lifespan of a field is about 20 to 30 years. It is directly related to the economic criteria of the field (return on investment.). To improve the economic lifespan, one often calls upon the development of satellite layers. When the layer for which a platform was built sees its production strongly declining, the means it has to treat oil find oversize. Moreover, it becomes difficult to make profitable the costs of exploitation. One can then attach to the platform of the small close layers, in general too small to justify a dedicated platform.

Construction: the construction of platform is done with ground or, as in Norway, in especially arranged fjords.

Installation: the platform is then tractor drawn on its processing site by means of powerful tug boats.

After exploitation: according to national and international legislations', the oil companies are obliged to dismantle these platforms when they are not used any more.
The first platforms were installed during the Seventies. They arrive now at the end of the lifetime, which will imply certain field has to be confronted has this situation (Total it field of Frigg).
These operations of dismantling of the platforms will launch a new challenge of the engineers, to dismount these thousands of tons of steel and equipment and to bring back them to ground, signal C by respecting strict constraints relating to the environmental protection.
Certain platforms are not dismantled and remain in the state, the companies being able to resell them with thirds. Such platforms, when they are in international water, interest certain purchasers ........ for operations except tanker.
According to the site or the zone, the jacket can be brought to a rather original destiny; like support for the growth of the corals and to give rise to coral reefs…

Information document.