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These structures usually have four to eight legs battered to achieve stability

against toppling in waves. Main piles, which are tubular. are usually carried with

the jackets and driven through the jacket legs into the seafloor.

The term jacket structure has evolved from the concept of providing an

enclosure (“jacket”) for the well conductors. These platforms generally support a

superstructure having 2 or 3 decks with drilling and production equipment and

workover rigs.

The use of these platforms has generally been limited to a water depth of about

500-600 ft (150-180 m) in the harsh North Sea environment (typical design wave

of 100 ft/30 m). In the more intermediate Gulf of Mexico environment (typical

design wave of 75 ft/23 m) half a dozen jackets have been installed in deeper

water. The single piece Bullwinkle jacket weighs 49,375 tons and was installed at a

site with 1350 ft (412 m) water depth in 1988.
For the marginal field development in shallow water, fixed production

platforms with a small deck are often used. At a minimum these structures may
support the following:

* (1) a few wells typically less than 10;
* (2) a small deck with enough space to handle a coil tubing or wireline unit;

* (3) a test separator and a well header;

* (4) a small crane;

* (5) a boat landing;

* (6) a minimum helideck.

Chevron carried out a study to identify and select, among existing production

platform concepts, the ones that would optimise the development of fields in 150 ft

(46 m) and 200 ft (61 m) of water, and for three different design return periods (25,

50 and 100 years).

Next Figure 3/2 depicts three of these concepts.

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