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Slide 1 : Jacket based platform - Southern sector North Sea. Slide 2 : Jacket based platform - Northern sector North Sea. Slide 3 : Cantilevered drilling rig: Self-elevating jack-up exploration drilling platform.

Slide 4 : Integrated topside during load out. Slide 5 : Jacket being loaded onto barge by skidding. Previous Next Contents. Deep water. Finite water depth.

Circular orbits. Elliptical orbits. In order to minimize the associated risks and secure safe transport from the fabrication yard to the platform site, it is important to plan the operation carefully by considering, according to API-RP2A [3], the following:.

There are five stages in a launch-upending operation:. Progressive Collapse. Abnormal effects. Damage condition. Value dependent on measures taken. Hammer Weight. Rated Operating. Hydraulic Hammers.

Rated Energy. Ram Weight. Pilecap Weight. Typical Operating. Oil Flow. MHU MH Blows per Minute. Weight including Offshore Cage, if any metric tons. Rated Striking Energy. Expected Net Energy ft-lb x On Anvil. On Pile. Pile Outer Diameter.

Wall Thickness. Hammer Energy. Slide 1 : General arrangement of a load out through skidding. SUMMARY The lecture starts with a presentation of the importance of offshore hydro-carbon exploitation, the basic steps in the development process from seismic exploration to platform removal and the introduction of the major structural concepts jacket-based, GBS-based, TLP, floating.

The major codes are identified. For the fixed platform concepts jacket and GBS , the different execution phases are briefly explained: design, fabrication and installation. Special attention is given to some principles of topside design.

A basic introduction to cost aspects is presented. Finally terms are introduced through a glossary. These figures clearly indicate the challenge for the offshore designer: a growing contribution is required from offshore exploitation, a very capital intensive activity.

Figure 1 shows the distribution of the oil and gas fields in the North Sea, a major contribution to the world offshore hydrocarbons. It also indicates the onshore fields in England, the Netherlands and Germany.

A third type is the floating production unit. The clearance airgap usually is taken at approximately 1,50 m, but should be increased if reservoir depletion will create significant subsidence.

It is necessary to design to limit offshore work to a minimum. The overall cost of a man-hour offshore is approximately five times that of an onshore man-hour. The cost of construction equipment required to handle loads, and the cost for logistics are also a magnitude higher offshore. These factors combined with the size and weight of the items, require that a designer must carefully consider all construction activities between shop fabrication and offshore installation.

The recently issued Lloyds rules [2] and the DnV rules [3] are also important. Specific government requirements have to be complied with, e. In the UK the Piper alpha diaster has led to a completely new approach to regulation offshore. The responsibility for regulatory control has been moved to the Health and Safety Executive HSE and the operator has to produce a formal safety assessment TSA himself instead of complying with detailed regulations. Insurance companies covering transport and installation require the structures to be reviewed by warranty surveyors before acceptance.

The warranty surveyors apply standards, if available, on a confidential basis. After several initial phases which include seismic field surveying, one or more exploration wells are drilled. Jack-up drilling rigs are used for this purpose for water depths up to - m; for deeper water floating rigs are used. The results are studied and the economics and risks of different development plans are evaluated. Factors involved in the evaluation may include number of wells required, fixed or floated production facilities, number of such facilities, and pipeline or tanker off-loading.

The drilling and construction interaction is described below for two typical fixed platform concepts. The wells are then drilled by a jack-up drilling unit standing close by with a cantilever rig extending over the jacket. Slide 3 shows a jack-up drilling unit with a cantilever rig. In this instance it is engaged in exploratory drilling and is therefore working in isolation.

Design and construction of the topside are progressed parallel to the drilling, allowing production to start soon after deck installation. For further wells, the jack-up drilling unit will be called once again and will reach over the well area of the production deck.

As an alternative to this concept the wells are often accommodated in a separate wellhead platform, linked by a bridge to the production platform see Slide 1.

Drilling starts after the platform is built and completely installed. Consequently production starts between one and two years after platform installation. In recent years pre-drilled wells have been used to allow an earlier start of the production. In this case the platform has to be installed exactly above the pre-drilled wells.

They support laterally and protect the inch well conductors and the pipeline riser. The installation methods for the jacket and the piles have a profound impact on the design. The piles are driven approximately 40 - 80 m, and in some cases m deep into the seabed. Skirt piles through pile sleeves at the jacket-base, where the pile is installed in guides attached to the jacket leg.

Skirt piles can be grouped in clusters around each of the jacket legs. Vertical skirt piles are directly installed in the pile sleeve at the jacket base; all other guides are deleted.

This arrangement results in reduced structural weight and easier pile driving. In contrast inclined piles enlarge the foundation at the bottom, thus providing a stiffer structure. The pile accumulates both skin friction as well as end bearing resistance. Lateral load resistance of the pile is required for restraint of the horizontal forces. These forces lead to significant bending of the pile near to the seabed. Number, arrangement, diameter and penetration of the piles depend on the environmental loads and the soil conditions at the location.

The steelwork in the splash zone is usually protected by a sacrificial wall thickness of 12 mm to the members. There are basically two structural types of topside, the integrated and modularized topside which are positioned either on a jacket or on a concrete gravity substructure.

They result from the lifting capacity of crane vessels and the load-out capacity at the yards: the single integrated deck up to approx MN the split deck in two four-leg units the integrated deck with living quarter module the modularized topside consisting of module support frame MSF carrying a series of modules.

Slide 4 shows an integrated deck though excluding the living quarters and helideck being moved from its assembly building. Slide 4 : Integrated topside during load out 5. Low Astronomic Tide. In this case the MSF is a heavy tubular structure Figure 4 , with lateral bracing down to the top of jacket. The backbone of the structure is a system of heavy box-girders with a height of approximately 10 m and a width of approximately 12 - 15 m see Figure 5.

The substructure of the deck is rigidly connected to the concrete column and acts as a beam supporting the deck modules. This connection introduces wave-induced fatigue in the deck structure. A recent development, foreseen for the Norwegian Troll platform, is to provide a flexible connection between the deck and concrete column, thus eliminating fatigue in the deck [10]. The floors are steel plate 6, 8 or 10 mm thick for roof and lower floor, and grating for intermediate floors.

In living quarter modules MN all sleeping rooms require windows and several doors must be provided in the outer walls. This requirement can interfere seriously with truss arrangements. Floors are flat or stiffened plate.


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