Page 315 - Hydrocarbon Exploration and Production Second Edition

302 Facilities

not licence FPSOs in the Gulf waters due to environmental concerns associated
with such systems.
SPARs can support dry trees and allow conventional access to development
wells. It is also relatively easy to tie in additional wells to a SPAR during its lifetime.
However, the size of buoyancy compartments required to support and tension rigid
steel risers, currently places practical limitations on the water depth in which this
concept can be employed. Like all floating ‘dry tree’ systems, the relative movement
between the risers and SPAR deck also requires flexible ‘jumpers’ that can limit
application in high-temperature reservoir environments. In future, it may be
possible, with subsea trees and flexible riser technology, to deploy SPARs in water
depths as much as 3000 m.
Subsea production systems are an alternative development option for an offshore
field. They are often a very cost-effective means of exploiting small fields which are
situated close to existing infrastructure, such as production platforms and pipelines.
They may also be used in combination with floating production systems.
Typically, a subsea field development or subsea satellite development would consist of a
cluster of special subsea trees positioned on the seabed with produced fluids piped to
the host facility. Water injection, as well as lift gas, can be provided from the host
facility. Control of subsea facilities is maintained from the host facility via control
umbilicals and subsea control modules.
Subsea production systems create large savings in manpower as they are
unmanned facilities. However, these systems can be subject to very high OPEX
from the well servicing and subsea intervention point of view as expensive vessels
have to be mobilised to perform the work. As subsea systems become more reliable
this OPEX will be reduced.
In 1986 when the oil price crashed to $10 a barrel, operators began to look very
hard at the requirements for offshore developments and novel slimline, reduced
facilities platforms began to be considered. The reduced capital outlay and early
production start-up capability, coupled with the added flexibility, ensured that all
companies now consider subsea systems as an important field development option.
Although the interest and investment in subsea systems increased dramatically,
subsea systems still had to compete with the new generation of platforms, which
were becoming lighter and cheaper.
In mature regions, the focus has turned towards developing much smaller fields,
making use of the existing field infrastructure. This, in combination with advances
in subsea completion technology and the introduction of new production
equipment, has further stimulated the application of subsea technology.

11.2.4. Satellite wells, templates and manifolds
Various types of subsea production systems are being used and their versatility and
practicality is being demonstrated in both major and marginal fields throughout the
world. These are illustrated in Figure 11.35.
The most basic subsea satellite is a single subsea wellhead with subsea tree,
connected to a production facility by a series of pipelines and umbilicals. A control