When a facility reaches the end of its economic life and will no longer be used to extract oil and/or natural gas, the facility is decommissioned.

Decommissioning is a normal activity undertaken in the lifecycle of a well – both for onshore and offshore projects.

Decommissioning involves safely shutting down the well and satisfactorily disposing of the infrastructure previously used to support the production phase of a project.

Decommissioning is undertaken in a safe and environmentally responsible way and could involve removing all equipment from the area, or partially removing equipment if arrangements are in place that ensures any remaining equipment meets all legislative requirements.

Regulating decommissioning

As with every aspect of oil and gas exploration or development, decommissioning is approved and overseen by a regulator/s.

Offshore Commonwealth waters

One of the main regulators for offshore works is the National Offshore Petroleum Safety and Environmental Management Authority (NOPSEMA), Australia’s independent regulator for health and safety, well integrity and environmental management for offshore petroleum and greenhouse gas storage activities in Commonwealth waters (comprising the first three nautical miles of the territorial sea) and coastal waters where regulatory powers and functions have been conferred.

Multiple approvals and decision makers are involved in the regulation of decommissioning petroleum facilities in Commonwealth waters.

  • NOPSEMA administers regulations which stipulate the safety, well integrity and environmental management requirements.
  • The Department of Environment and Energy administers the requirements of the Environmental Protection (Sea Dumping) Act 1981, which may apply to decommissioning if any equipment is proposed to be left on the seabed. In circumstances where conditions for decommissioning were applied to an environmental approval under the Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act), before NOPSEMA became the sole regulator for petroleum activities in Commonwealth waters in February 2014, then those conditions must be met for the activity to proceed.
  • The National Offshore Petroleum Titles Administrator (NOPTA) is the day to day administrator of petroleum titles.

Onshore and coastal waters

Each state or territory is regulated by the Government’s respective local department. For example, in Western Australia this is the Department of Mines, Industry Regulation and Safety while in the Northern Territory the Department of Primary Industry and Resources is responsible for the granting, approval and regulation of petroleum titles and activities.

For example, petroleum activities in Western Australia are legislated under the Petroleum and Geothermal Energy Act 1967 (PGERA 67), the Petroleum (Submerged Lands) Act 1982 (PSLA 82) and the Petroleum Pipelines Act 1969 (PPA 69). Regulations under these Acts encompass environment, safety and resource management.[1]

[1] – accessed 21 January 2020

The process

Before decommissioning may begin, an oil and gas company must submit the relevant risk management plans to NOPSEMA for assessment and acceptance.

The plans required for decommissioning can include a safety case, well operations management plan and environment plan. NOPSEMA’s dedicated assessment teams, which comprise of highly qualified and experienced experts, assess each plan against strict criteria as set out in the OPGGS Act and associated regulations – including an occupational health and safety case, an environment plan and for management of well integrity.

A more detailed description regarding the relevant regulatory process can be found on NOPSEMA’s website.

Types of facilities and infrastructure

There is a wide range of offshore facilities because of the technical and environmental conditions for which they are designed.

For example, many offshore Australian oil and gas facilities have been developed using fabricated steel structures fixed to the seabed that support production facilities and accommodation for workers. These are common in Australia on the continental shelf, such as much of the North West Shelf and Bass Strait.

These facilities generally host wells with “dry trees” – i.e. the well control and isolation equipment is all located above the waterline on the facility. Generally, these facilities are installed with “piles” that are either, drilled and grouted into place, or are driven into the seabed.

Other infrastructure such as pipelines may also need to be removed as part of the decommissioning process.

Decommissioning options will be influenced by each individual development and external circumstances at the time of decommissioning and may include:

  • finding an alternative use for part or all of the structure;
  • recycling part or all of the structure;
  • final disposal onshore of part or all of the structure;
  • leaving the structure in place;
  • toppling the structure on location; and
  • disposing of the structure elsewhere at sea, such as an artificial reef or deep-sea disposal.

Decommissioning a petroleum production facility of any sort will always include plugging and abandoning the wells so that no fluids can escape after the site has been decommissioned.[1]


The main objective of plugging and decommissioning a well is to avoid reservoir fluids (oil and gas) leaking to the environment.

This process requires containing the formation fluids (such as oil and gas) within the well and ensuring the correct structure or ‘plug’ is in place to restrict any movement of fluids. A series of barriers is placed inside the well at various depths determined by engineering criteria. These barriers ensure that the well integrity is maintained over time.

Well barriers have the capability to withstand the different loads they will be exposed to during the life of the well.

In plugging and abandoning a well, the objective is to have the determined barriers set in perpetuity.

Several techniques are used to install or set the barriers and different materials qualify for use in constructing these barriers.

The techniques include, but are not limited to, cement placement through pipes, plugs placement through wireline or pipe or cement squeezed into the formation. In recent times, resins have also been used more widely as a plugging material, and sometimes resin is combined with cement to create a flexible mixture.[2]


A range of technical decommissioning and disposal options exists for offshore facilities, each of which must be evaluated on a case-by-case basis. The scope of consideration should include a broad range of aspects and not only focus on the vicinity of the structure.

Decommissioning options include:

  • complete removal, disposal onshore or offshore
  • partial removal, disposal onshore or offshore
  • abandonment in-situ
  • alternate use, either within the oil and gas industry or other industries / purposes.

The method of removing and disposing of a structure depends on factors such as the type of construction, size, distance to shore, weather conditions, the complexity of the removal operation and the environmental impact. It must also consider the safety of workers.




The process for decommissioning a well onshore is much the same as it is for an offshore site. In Western Australia, once decommissioning of infrastructure has been undertaken, the registered holder/operator must restore the petroleum title area to its pre-activity state, unless otherwise agreed with the regulator.

For onshore decommissioning programs, the operator must set rehabilitation completion criteria. The completion criteria should be outlined in the environment plan (EP) and be specific with measurable targets. For example, completion criteria may relate to the stability of landforms, percentage cover of vegetation, and diversity of species compared to the surrounding area.[1]

[1] – Accessed 20 January 2020