Disposal of concrete facilities
During the period from 1973 to 1995, 14 concrete facilities were installed for production of petroleum on the Norwegian Continental Shelf (NCS). Two of these are floating (Heidrun A and Troll B), while the remainder are fixed and rest on the seabed.
(Illustration: Norwegian Petroleum Museum)
Ten of these fixed concrete facilities are in operation, while two are shut down and abandoned on site. There are also 12 concrete facilities in the UK sector of the North Sea, one in the Danish sector and two in the Dutch sector.
Some of the fixed concrete facilities on the NCS are approaching the end of their lifetime. In the years to come, the authorities must decide how to dispose these facilities. Statfjord A (Illustration: Norwegian Petroleum Museum) from 1977 is the oldest still in operation, and will be the next removal project involving concrete facilities. Troll A from 1995 is the newest facility. The concrete facilities built prior to 1978 were not designed for removal. This was before the Norwegian Petroleum Directorate (NPD) required that these platforms must also be designed for removal.
A report was prepared in 2012 on the disposal of concrete facilities, based on an initiative from the NPD. The Petroleum Safety Authority (PSA) and the Climate and Pollution Agency were also invited to take a more in-depth look at the agencies’ respective disciplines. The report is also based on knowledge from the engineering and construction of these facilities, and experience from removal of a fixed steel platform on the UK sector. The study assesses and evaluates different technological solutions for disposal of the concrete facilities in relation to consequences for health, safety and the environment.
Removal of shut-down concrete facilities
Under the Oslo-Paris Convention (OSPAR), every offshore installations on NCS that are no longer in use, should be removed from the site. Operators can apply for exemptions from this ban for concrete facilities. To date, two exemptions have been granted on the NCS; the Ekofisk-tank and Frigg TCP2. These facilities are partly left in place.
Removal of fixed concrete facilities resting on the seabed is technically feasible, but will involve extensive work that requires thoroughly planning and risk management. There is little experience, both in Norway and internationally, with disposal solutions other than abandonment of concrete facilities. The above mentioned study from 2012 shows that although some of the facilities have installed equipment which can enable these facilities to refloat, there is significant uncertainty as to whether such operations can be carried out in a controlled manner. The greatest challenge may be to map the condition of the platform and establish an overview of changes that have been made through the years. Solid knowledge about the individual facility is an important precondition for a successful operation.
Bringing the concrete facilities to shore for scrapping and material recovery may entail a risk of discharges to sea, and the dismantling operations on shore will generate noise and dust. Available space is required, both on land and at sea, and conflicts may arise with the local community. The advantage of bringing the facilities to shore will primarily be that the steel and possibly also concrete can be recycled, and that the seabed is returned to its natural state. Using all or parts of the facility, for example as a bridge foundation, or to make artificial reefs, is an alternative to scrapping and material recovery.
Removing concrete facilities is not without risk. At worst, an accident could occur during preparation, refloating, transport or dismantling and entail serious consequences such as loss of life and negative impact on the environment.
Abandonment of concrete facilities on site may have safety benefits and may be environmentally acceptable. Abandonment will not yield much impact on fish populations, but could pose a conflict with fishery interests due to the occupied area. Lights and navigation equipment must be installed on abandoned facilities to reduce the danger of conflict with ship traffic.