Page 319 - Hydrocarbon Exploration and Production Second Edition

306 Facilities

P P spacers
P S
H
H
H H

H H = hydraulic hoses
H P P = power cables
S = signal cables
insulation P P

25 mm

Figure 11.38 Electro-hydraulic control umbilical bundle.

Sensors on the tree allow the control module to transmit data such as tubing
head pressure, tubing head temperature, annulus pressure and production choke
setting. Data from the downhole gauge is also received by the control module. With
current subsea systems more and more data are being recorded and transmitted to
the host facility. This allows operations staff to continuously monitor the
performance of the subsea system.
The pressure to accelerate first oil and to decrease development costs is
continuously demanding innovations in offshore engineering. This has led to the
development of minimum facilities, such as monopods and related systems. Instead
of multilegged jackets, monopods consist of a single central column, the well
protector caisson. The caisson is driven into the seafloor and held in place by an
arrangement of cables anchored to the seafloor. The system can accommodate up to
six wells internally and externally of the caisson and it can carry basic production
facilities. The main advantage of this innovative concept is the low construction
costs and the fact that installation can be carried out by the drilling rig, a diver
support vessel (DSV) and a tug boat in some 3 months. There has been some
concern regarding the stability of monopods, but a number of installations in the
GoM and offshore Australia have been exposed to hurricanes without sustaining
major damage. Water depth is a limiting factor of the system (currently about 300 ft)
(Figure 11.39).

11.2.5.1. Offshore evacuation systems
Crude oil and gas from offshore platforms are evacuated by pipeline or alternatively,
in the case of oil, by tanker. Pipeline transport is the most common means of
evacuating hydrocarbons, particularly where large volumes are concerned.
Although a pipeline may seem a fairly basic piece of equipment, failure to design