Page 64 - 4274

2.2 SPAR platforms

A SPAR, named for logs used as buoys in shipping and
moored in place vertically, is a type of floating oil platform
typically used in very deep waters. Spar production platforms have
been developed as an alternative to conventional platforms. A Spar
platform (fig. 2.19) consists of a large-diameter, single vertical
cylinder supporting a deck. It contains a deep-draft floating
caisson, which is a hollow cylindrical structure similar to a very
large buoy. Its four major systems are hull, moorings, topsides and
risers. About 90% of the structure is underwater. The spar design
is now being used for drilling, production, or both. The
distinguishing feature of a spar is its deep-draft hull, which
produces very favorable motion characteristics compared to other
floating concepts. Water depth capability has been stated by
industry as ranging up to 10,000 ft. The first Spar platform was
installed in September of 1996. It follows the concept of a large
diameter single vertical cylinder supporting deck. These are a very
new and emerging concept: the first spar platform, Neptune, was
installed off the USA coast in 1997. Spar platforms have taut
catenary moorings and deep draught, hence heave natural period is
about 30 seconds.
Presently there are 17 SPARs in operation (fig. 2.20):
▫ 3 Classic SPARs;
▫ 13 Truss SPARs;
▫ 1 Cell SPAR.
The different SPAR designs (tab. 2.1) reflect industry
innovations
Each design (fig.2.21) is an improvement on an older
model and offers improved functionality at a reduced cost.

64