Page 12 - Oil and Gas Production Handbook An Introduction to Oil and Gas Production

unconventional reserves may contain more than double the hydrocarbons
found in conventional reservoirs. The picture shows the Syncrude Mildred
plant at Athabasca, Canada Photo: GDFL Jamitzky/Wikimedia
2.1.2 Offshore

A whole range of different structures are used offshore, depending on size
and water depth. In the last few years we have seen pure sea bottom
installations with multiphase piping to shore and no offshore topside
structure at all. Replacing outlying wellhead towers, deviation drilling is used
to reach different parts of the reservoir from a few wellhead cluster locations.
Some of the common offshore structures are:

A shallow water complex,
which is characterized by a
several independent platforms
with different parts of the
process and utilities linked with
gangway bridges. Individual
platforms include Wellhead
Platform, Riser Platform,
Processing Platform,
Accommodations Platform and
Power Generation Platform.
The picture shows the BP
Valhall complex. Typically found in water
depths up to 100 meters.

A gravity base. This consists of
enormous concrete fixed structures placed
on the bottom, typically with oil storage
cells in the "skirt" that rests on the sea
bottom. The large deck receives all parts
of the process and utilities in large
modules. Large fields at 100 to 500 meters
water depth were typical of the 1980s and
90s. The concrete was poured at an on-
shore location, with enough air in the
storage cells to keep the structure floating
until tow-out and lowering onto the seabed.
The picture shows the world's largest GBS
platform, Troll A, during construction. Photo
StatoilHydro

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