Oil Platform

A oil platform is a fixed or floating 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 the Pétrole, like 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.

History

The first platforms are those of the Gulf of Mexico on the coasts of the Texas. These platforms are located in a very low depth of water and have for only function to only be a wellhead. They are the prolongation of what had then been developed with ground.

At the time of the first Oil crisis in 1973, the European governments raise 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 gazifères of the the North Sea.

The the United Kingdom and the 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 oil companies, with the assistance of engineering of the whole world develop research programs which lead to the construction of the first oil platforms 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 security standards related to manufacture, the installation and the implementation of these platforms are developed during the Années 1970 - 80 following various accidents. Mentalities in the world of the offshore oil rig exploitation change radically after the accidents of the platforms Alexander Kielland (which caused the death of 123 people) into 1980 and Piper-Alpha (which cost the life 167 people) into 1988.

Once technologies offshore oil rigs 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 techniques of drilling and the techniques of constructions having evolved/moved, the great depths of water (>1000m) 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.

Taking into consideration current legislation, there exist 3 types of platforms: - MODU (offshore oil rig module drilling links) being used only for drilling and which can place of the personnel. - PP (Platform Production) being useful with the production and/or the preprocessing of the crude, but without housing. - the LQ (living room quarters) being used only for housing, and or any storage/transit of hydrocarbre is interdict for safety reasons.

Various types of platforms

The choice enters the various types of platform 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), consisted of prefabricated modules
  • the carrying structure: part being used to maintain the part useful above the water, made out of metal tubular lattice, (jacket) or composed of concrete columns.

Fixed platforms

The fixed platforms are used at sea not very deep (<300m). Beyond these depths, they economically become not-viable. Various techniques of construction exist, such as for example:
  • gravitating Jacket-deck
  • Platform
  • Compliant tower
  • artificial islands

These punts forms are based on the bottom and can thus be connected in a rigid way to the wellheads and the pipelines. In Europe, the principal place where one can see such platforms is the North Sea. Elsewhere, let us quote the GULF Coast American, the Bay of Campeche in Mexico, the Persian Gulf, the Bay of Bohai (China), etc

Floating units

The floating platforms are primarily used for the exploitation of oil fields in deep seas (>300 m approximately). 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 stores oil (coming from another platform, or sometimes from onshore production) and loads the tankers with trade.

  • 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 of unloading (Floating Production Storage and Offloading): similar to a 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 there, 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 platforms) 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 cylindrical float.

  • For important layers, one combines sometimes several solutions: for example, a platform TLP which produces oil and a FSO to store and export oil.

Mobile platforms

  • self-lifting Platforms (Jack-up): they are platforms made up of a hull and legs. The hull enables them to move by floating and supports utilitées. 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 drilling rigs and are used for exploration or drilling of well around platforms which are not equipped with drilling rig. There exist also some of these platforms which are used as " boatel" , floating hotel allowing to place teams which work at sea.
    • Semi-sub
  • : unit made up of 3 distinct parts: the float which is immersed, beams with semi-water and the bridge which must be higher than the " centenaire" vagueness;. This unit balances some as a ludion functions thanks to pumps with sea water which maintain permanently balance vertical, and of the multidirectional propellers or the anchors which maintain positioning horizontal with the top of the well. This type of platform is used for depths going from 100 to 300 meters, or for zones or sea-bed does not allow to pose the feet of a " jack-up" whether it is soft vase or destabilized rocks
  • Swamp-barge: flat-bottomed boats that one " coule" on the spot by filling the boxes with sea water. After drilling, one empties the boxes and the boat can go to drill elsewhere. Is useful in very low depths, between 1 and 4 meters, which is worth the name of " to him; swamp" , English marsh

Criteria of design

Functionalities

An oil platform is designed to meet various needs:
  • Drilling (but not obligatorily of course, because there exist currently special bodies for the drilling)
  • Production
  • Habitation (which depends on platform indeed)
  • Stockage (although some forward to bodies of storage after pumping).

According to the depth of water and safety regulations, these functions can be gathered on the same platform or 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 Raffinerie.

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 it transportable to the coast, where one builds a refinery more developed with less expenses.

(to be developed)

Environment

One of the dominant criteria in the design of the platform is the environment in which it is. The seamen circle is by hostile nature, because of its instability (Marée S, Tempête S, running S, Vent…) 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 the 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.

  • Maritime environment

the swell, the current and the wind induce horizontal efforts on the fixed platforms and of the movements and accelerations on the floating platforms.

the salt water is a source of corrosion for materials (and in particular the Acier) used in the platform.

  • seismic Conditions

the majority of the producing oil sites is located in zone at the strong seismic risk. The platform, when it is fixed, must then be able to survive these events.

  • Sol

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 used only for the anchoring.

Lifespan

The average lifespan of a field is about 20 to 30 ans.
It is directly related to the economic criteria of the field (return on investment…).
Pour 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 the platforms is done with ground or, as in Norway, in especially arranged Fjord S. (to be developed)

Installation

The platform is then tractor drawn on its processing site by means of powerful tug boats of open sea, and more recently by ships of offshore oil rig supply which also have the possibility of towing the platforms. Another solution, more current in the event of long voyage or of special loading, is to use a semi-submersible Navire such as the Blue Marlin . Once on its processing site, the platform is dealt with by ships refuelling tankers and raising devices of anchors says AHTS (Anchor Handling Tug Supply) which will deal with setting up provisional of way for drilling or a permanent way for the exploitation, then to refuel it in products and materials of drilling.

Certain platforms are transported since bank on ships with very high Tonnage. On the place of installation, the ship can be submerged partially and release its load which floats then of it even. In certain cases, a ship equipped with gigantic cranes is used to discharge the ship from transport. The SPAR are transported in this way in two elements which are then assembled Offshore.

Startup

End-of-life

According to the national legislations and international, the oil companies are in the obligation 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, such as for example in the oil-bearing Champ of Frigg exploited by Total, which will be one of the first large fields to be in this situation.

The operation of dismantling of the platforms of this field should be realized current 2006. The new challenge of the engineers thus will be to dismount these thousands of tons of steel and equipment and to bring back them to ground, while trying to respect the constraints of protection of the Environnement.

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 the International water, interest the purchasers because they constitute artificial islands. Certain new owners of such installations made some or try to make of them tax shelters or independent microphone-states whose legislation (when it exists) can show laxist in many connections (on freedom of expression in particular).

The structures carrying (the dépliable part located under the sea level) some platforms of the Gulf of Mexico knew an original destiny: they were towed to barriers of Corail, or simply left places from there if they were already in a favorable zone. They provide a support favorable to the growth of the corals and thus give rise to coral reefs.

In an anecdotic way, the mobile and massive character of the oil platforms allows their use as platform of launching of space launchers. For example, the platform Ocean Odyssey, an old oil platform of the the North Sea with étée refitted in Norway (building sites Stavanger) so as to be able to accommodate the Lanceur Zenit 3SL. This last allows, in others, the setting in Orbite of satellite civil of Télécommunications. Thanks to this original concept, Sea Launch, the operating company this launcher became one of the actors important of the market of the civil launchers. Indeed, in spite of the disadvantage which the routing of the launcher and the equipment appendices to the platform represents, the main advantages lie precisely in its insulation, as well as the possibility of optimizing the positioning of the launching pad compared to the mission of the launcher: on the equator to profit from the Effect Sling, far away from the coasts for the repercussions of the lower stages, etc One can also quote the Plateforme San Marco which was used for probe rocket shootings of Italian-American in the years 1960 for 1980.

Gallery

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