Once all the oil and gas has been extracted, the wells and facilities will all be decommissioned. This involves plugging the well with cement and the dismantling and removal of equipment, plant and machinery. All New Zealand’s offshore fields remain in production so decommissioning is yet to take place in our marine environment.

Prior to decommissioning, surveys are usually undertaken to map the location and quantity of debris, pipelines, power cables and natural marine environments. Post decommissioning surveys can identify any debris left behind during the removal process and confirm any environmental damage. Remote underwater vehicles and divers can be used to remove any debris and to ensure the area is free from any of the operational equipment.

Abandonment of oil rig infrastructure has become a major issue in the North Sea where there are many fields reaching the end of their producing phase. Best practice is to remove as much of the infrastructure as safely as possible. Another option being investigated is the storage of CO2, where some of the existing infrastructure of depleted offshore oil and gas fields might be used for CO2 sequestration after adaptation. 2179

Last updated at 1:41PM on February 25, 2015