Page 437 - Hydrocarbon Exploration and Production Second Edition

424 Decommissioning Methods

Recycling/disposal
onshore

Deep water disposal
Removal
Toppling on site

Artificial reef

Substructures Leave in Place

Onshore disposal
recycling

Topsides

Refurbishment /
Re-use
Figure 18.3 Decommissioning options.

Each of the main facility types, for example steel jacket, gravity structure,
tension leg and floating platform, have different options for decommissioning. The
main factors which need to be considered and which will impact on costs are type
of construction, size, distance from shore, weather conditions and the complexity of
the removal, including all safety aspects. Figure 18.3 shows the options available.
Tension leg and floating platforms can easily be released and towed away for
service elsewhere, which is cheap and attractive. In the case of the fixed platforms,
the topside modules are removed by lift barge and taken to shore for disposal.
Gravity-based structures can in theory be deballasted and floated away to be re-
employed or sunk in the deep ocean, and steel jackets cut and removed at an agreed
depth below sea level. In some areas jackets are cleaned and placed as artificial reefs
on the seabed. The largest ‘rigs to reefs’ programme involving more than 90
decommissioned installations has been implemented in the GoM.
Subsea facilities are easily decommissioned as they are relatively small and easy to
lift. However, subsea manifolds and templates can weigh in excess of 1000 tons and
will require heavy lift barges for removal.

18.4.4. Land facilities
Onshore processing facilities, and modules brought onshore, have to be cleaned of
all hazardous compounds and scrapped. Cellars of single wells, drilling pads, access
roads and buildings will have to be removed. If reservoir compaction affects the