Page 13 - Oil and Gas Production Handbook An Introduction to Oil and Gas Production

Compliant towers are much like fixed platforms. They consist of a narrow
tower, attached to a foundation on the seafloor and extending up to the
platform. This tower is flexible, as opposed to the relatively rigid legs of a
fixed platform. This flexibility allows them to operate in much deeper water,
as they can 'absorb' much of the pressure exerted by the wind and sea.
Compliant towers are used between 500 and 1000 meters water depth.
Floating production, where all
topside systems are located on a
floating structure with dry or
subsea wells. Some floaters are:
FPSO: Floating Production,
Storage and Offloading. Their
main advantage is that they are
a standalone structure that does
not need external infrastructure
such as pipelines or storage.
Crude oil is offloaded to a shuttle
tanker at regular intervals, from
days to weeks, depending on
production and storage capacity.
FPSOs today produce from
around 10,000 to 200,000
barrels per day.
An FPSO is typically a tanker
type hull or barge, often
converted from an existing crude
oil tanker (VLCC or ULCC). Due
to the increasing sea depth for
new fields, they dominate new
offshore field development at
more than 100 meters water depth.
The wellheads or subsea risers from the sea bottom are located on a central
or bow-mounted turret so that the ship can rotate freely to point into wind,
waves or current. The turret has wire rope and chain connections to several
anchors (position mooring - POSMOOR), or it can be dynamically positioned
using thrusters (dynamic positioning – DYNPOS). Most installations use
subsea wells. The main process is placed on the deck, while the hull is used
for storage and offloading to a shuttle tanker. May also be used for the
transportation of pipelines.
FPSOs with additional processing and systems such as drilling and
production and stranded gas LNG production are planned.

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