Page 432 - Hydrocarbon

CHA P T E R 1 8

Decommissioning

Introduction and Commercial Application: Eventually every field development will reach
the end of its economic lifetime. If options for extending the field life have been
exhausted, then decommissioning will be necessary. Decommissioning is the process
by which the operator of an oil or natural gas installations will plan, gain approval
and implement the removal, disposal or re-use of an installation when it is no longer
needed for its current purpose.
The cost of decommissioning may be considerable, and comes of course at the
point when the project is no longer generating funds. Some source of funding will
therefore be required, and this may be available from the profit of other projects,
from a decommissioning fund set up during the field life or through tax relief rolled
back over the late field production period.
Decommissioning is often a complex and risky operation. The five key consi-
derations are the potential impact on the environment, potential impact on human
health and safety, technical feasibility, costs of the plan and public acceptability.
Decommissioning may be achieved in different ways, depending on the facilities
type and the location. This section will also briefly look at the ways in which
decommissioning can be deferred by extending the field life, and then at the main
methods of well abandonment and facilities decommissioning.

18.1. Legislation

National governments play an extensive role in assessing and licensing
decommissioning options. Most countries which have offshore oil and natural gas
installations have laws governing decommissioning.
The prime global authority is the International Maritime Organisation (IMO).
The IMO sets the standards and guidelines for the removal of offshore installations.
The guidelines specify that installations in less than 75 m of water with substructures
weighing less than 4000tons be completely removed from the site. Those in deeper
water must be removed to a depth of 55 m below the surface so that there is no hazard
to navigation. In some countries the depth to which structures have to be removed
has already been extended to 100 m.
The planning of decommissioning activities involves extensive periods of
consultations with the relevant authorities and interested parties, such as fishing and
environmental groups.

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