Offshore oil and gas fields have a finite productive life. When production stops, there is a significant amount of infrastructure that cannot be simply left on the seabed: pipelines, umbilicals, wellheads and subsea control systems, to name just some.
Operators remain accountable for safe and environmentally stable subsea decommissioning. Under Australian law, the default expectation is full removal unless the regulator explicitly approves an alternative.
That challenge is neither simple nor optional. Subsea decommissioning involves complex engineering offshore, high-risk waste handling onshore, and a commitment to environmental protection throughout. And as Australia prepares for a surge in decommissioning activity, especially off the WA coast, getting it right has never been more important.
Subsea Infrastructure Used in Oil and Gas Production
Each field looks different, but most subsea oil and gas operations include:
- Pipelines and flowlines transporting hydrocarbons
- Umbilicals carrying hydraulic, electrical or fibre-optic signals
- Risers and flexible hoses
- Manifolds and production templates
- Wellheads and Xmas trees
- Anchoring systems, chains and mooring lines
- Subsea control modules
- Protective structures such as concrete mattresses and grout bags
These systems are built from a mixture of materials. Primarily steel and copper-based alloys, but also plastics, synthetics, composites, concrete coatings and corrosion-resistant materials. Once operations cease, these become a technical challenge – and a recycling opportunity.
NOPSEMA and the Regulatory Landscape
Subsea decommissioning activity in Australia is impacted by a complex landscape of local, national, and international regulatory frameworks. The foremost of these is the Offshore Petroleum and Greenhouse Gas Storage (OPGGS) Act, which sets out a base case of full removal. NOPSEMA, the National Offshore Petroleum Safety and Environmental Management Authority, oversees and enforces the OPGGS Act. NOPSEMA requires operators to:
- Plug and abandon wells
- Remove property unless alternative arrangements are explicitly approved
- Submit environmental management plans
- Conduct ongoing monitoring and reporting
A Snapshot of Australia’s Oil and Gas Regulatory Landscape
(Source: NOPSEMA)
When Infrastructure Can Be Left in Place
In rare cases, NOPSEMA may allow operators to leave items on the seabed if they can demonstrate:
- No feasible removal method without unacceptable environmental harm
- Long-term stability and safety
- No interference with fisheries, navigation or other users
There is an ongoing debate in the global oil and gas industry around leaving structures in place, especially as artificial reefs (called “in-situ decommissioning”). However, Australian policy remains firmly removal-first.
What Happens During Subsea Decommissioning?
A typical subsea offshore program follows a structured, multi-stage lifecycle.
1. Plugging and Abandoning Wells
Wells are sealed with permanent cement and mechanical barriers, and the wellhead is removed. This prevents future leaks and is the most safety-critical stage.
2. Cleaning and Disconnecting Systems
Pipelines and umbilicals are flushed, depressurised, and made safe for handling. This step removes hydrocarbons and residues before lifting begins.
3. Retrieving Equipment
ROVs and heavy-lift vessels cut, detach and raise subsea structures to the surface for barge transport. Vessel time makes this one of the most expensive phases.
4. When Infrastructure Stays in Place
Occasionally regulators allow items to remain on the seabed if removal poses greater environmental risk. Operators must still monitor and manage these assets long-term.
Offshore Decommissioning Continues Onshore
Offshore recovery is only half the story. The moment subsea infrastructure arrives onshore, it enters a second, equally critical phase: dismantling, contamination control and recycling. This is where oil and gas decommissioning specialists like C.D. Dodd play a vital role.
1. Inspection and Hazard Assessment
Each asset is inspected for marine growth, hydrocarbon residue, hazardous coatings, and electrical components. Any contaminants are isolated and materials are processed in line with WA regulations.
2. Dismantling and Materials Separation
Large components are mechanically cut down for transportation. Concrete coatings, insulation, and composite layers are removed. This separation increases recycling yields and reduces landfill.
3. Hazardous Waste Removal
Non-recyclable or hazardous materials, including contaminated growth, chemical residues, and degraded coatings, are contained and managed to prevent environmental contamination.
4. Recycling and Value Recovery
Recyclable metals like steel, copper and specialty alloys are processed for reuse, delivering ESG benefits and supporting the circular economy. Any remaining waste is directed to approved WA facilities for compliant disposal.
Environmental Considerations Throughout the Process
Environmental protection is a crucial and overarching factor in oil and gas decommissioning. Minimising seabed disturbance, protecting delicate marine ecosystems, preventing invasive species transfer, and reducing emissions all shape operational planning.
This also continues onshore. Hazardous material containment, waste segregation, and clean recycling streams prevent the environmental challenge from merely being rerouted from the sea to the land.
Offsetting Subsea Decommissioning Costs With Value Recovery Opportunities
Cost Drivers |
Value Opportunities |
| Specialist teams and decommissioning personnel | Recycling high-value metals |
| Offshore vessel hire | Reduced landfill expenses |
| ROV cutting and subsea interventions | Encouraging investment through ESG leadership |
| Hazardous waste handling and disposal | Automating dangerous and difficult tasks, reducing labour costs and improving safety |
| Heavy lift logistics | Assessing in-situ decommissioning possibilities |
Australia’s oil and gas decommissioning liabilities are close to $67 billion between today and 2070, according to a report from November 2025 commissioned by the Department of Industry, Science and Resources (DISR). The average cost per project could run into the hundreds of millions, depending on the scale of assets and the complexity involved.
As the DISR points out, there are opportunities to improve decommissioning efficiency and control these costs without compromising environmental or safety outcomes:
- Operator cooperation
- Leveraging new technologies
- Investing in onshore disposal and recycling
How a Specialist Recycler Helps You Reduce Costs and Unlock Value in Subsea Decommissioning
Subsea decommissioning is one of the most demanding asset-management tasks in modern industry. It requires an integrated approach to dismantle offshore structures, contain environmental risks, manage hazardous materials, recover recyclable metals, and maintain traceability for regulatory and ESG requirements.
C.D. Dodd brings exactly this combination. We have extensive capabilities and a proven track record across oil and gas, mining, industrial demolition and large-scale asset recovery.
- Specialist equipment for offshore pipeline cutting
- Dedicated large-asset dismantling facilities close to Karratha and Port Hedland
- Hazardous waste processing and contamination control
- Commercial metal recycling for steel, copper, alloys, and even batteries
Our capability, compliance, and sustainability – backed by over 50 years of experience — make us a trusted partner for offshore decommissioning in Western Australia.
Speak to C.D. Dodd to manage onshore processing and recycling of subsea infrastructure from offshore decommissioning projects.