Although we tend to use “oil and gas decommissioning” as an umbrella term here in Western Australia, Western Australia’s petroleum sector faces two unique decommissioning profiles.
Offshore and onshore oil rig decommissioning both contribute to a national liability now estimated to exceed $60 billion in the coming decades. Both require specialist execution. And both focus on compliance, safety, and environmental responsibility.
However, while the obligations are shared, the methods, risks, and regulatory pathways are not.
Oil Rig Decommissioning Is an Interconnected Process
To understand why offshore vs onshore oil rig decommissioning isn’t a cut-and-dry comparison, it helps to remember that decommissioning is not a single venture but a series of high-consequence, high-risk projects:
- Well plug and abandonment (P&A): Permanently sealing wells with cement and mechanical barriers to prevent hydrocarbon migration.
- Structure removal: Dismantling topsides, jackets, pipelines, pumps, and associated equipment.
- Hazardous waste management: Identifying and safely containing hydrocarbons, asbestos, NORMs, coatings, and electrical waste.
- Transport and dismantling: Moving recovered materials to processing facilities.
- Recycling and disposal: Recovering metals and processing residual waste through compliant pathways.
Offshore Decommissioning in WA
The Scale of the Problem
The Australian Government’s offshore oil and gas decommissioning liability estimate puts the cost of offshore decommissioning at $43.6 billion ($66.8 billion accounting for inflation) between 2025 and 2070.
The infrastructure involved spans fixed steel jacket platforms, Floating Production Storage and Offloading (FPSO) vessels, subsea wellhead assemblies, thousands of kilometres of rigid and flexible pipelines, static umbilicals, and riser systems.
Nearly two-thirds (61%) of that liability is off the Western Australian coast. That makes WA the undisputed epicentre of what could be one of Australia’s largest ever industrial programs.
Key Challenges
The offshore environment is unforgiving:
- Cyclones create narrow operational weather windows.
- Heavy lift crane vessels are globally scarce.
- Decades of marine growth and corrosion complicate structural integrity.
- Subsea cutting requires ROV operations at depth.
Tightening scrutiny around environmental responsibility also creates long-term challenges in monitoring and maintaining a healthy post-asset ecosystem.
Regulatory Requirements
Australia’s oil and gas decommissioning regulations are complex. National Offshore Petroleum Safety and Environmental Management Authority (NOPSEMA) is the primary regulator in Commonwealth waters. State, federal, and international regulations and guidelines add further layers of accountability when material reaches WA waters and eventually lands onshore.
Onshore Decommissioning in WA
The Infrastructure
WA’s onshore petroleum industry is older and more dispersed than many people realise. Exploration in the Perth Basin dates back to the 1940s, and some projects have been in operation since the 1960s.
The infrastructure includes land drilling rigs, pump jacks, wellheads, production separators, processing facilities, flare stacks, storage tanks, and extensive pipeline networks above and below ground.
Key Challenges
Onshore decommissioning is operationally more accessible, but it carries its own complications.
- Decades of production leave contaminated soils and groundwater.
- Legacy infrastructure frequently contains asbestos insulation and lead-based coatings.
- NORMs accumulate in produced-water flowlines.
- Remote logistics add considerable time and cost.
This is the second major point in offshore vs onshore oil rig decommissioning: onshore projects are often easier to access, but not necessarily easier to close.
The Process
Onshore decommissioning follows a well-established sequence. The main deviation from the subsea decommissioning process is soil remediation instead of marine ecosystem monitoring.
Other stages – well P&A, dismantling infrastructure, containing hazards, transport to licensed waste disposal facilities – are broadly similar.
Regulatory Requirements
Since DEMIRS split in 2025, the Department of Mines, Petroleum and Exploration (DMPE) has been the responsible authority for onshore decommissioning. Their oversight is supported by WorkSafe WA, which sits under the spun-out Department of Local Government, Industry Regulation and Safety (LGIRS).
One important link between offshore and onshore oil rig decommissioning is the ‘base case’ of full removal. DMPE and NOPSEMA both expect operators to fully remove all assets and infrastructure, although projects are assessed individually.
Offshore vs Onshore Oil Rig Decommissioning: Key Differences
Offshore Decommissioning |
Onshore Decommissioning |
|
Environment |
Marine, weather-dependent, often remote from shore | Land-based, often remote, but easier to access with conventional plant |
Access |
Specialist vessels, ROVs, MODUs | Conventional civil and demolition equipment |
Main Risks |
Well integrity, cyclones and weather, NORMs, marine ecology, vessel scarcity, subsea cutting | Soil and groundwater contamination, asbestos, NORM, buried infrastructure, ageing coatings |
Costs |
Vessel time, offshore labour, subsea intervention, marine mobilisation | Remediation, heavy equipment, hazardous waste handling, transport and rehabilitation |
Waste Streams |
Steel, coatings and composites, hydrocarbons, NORMs, marine growth | Contaminated soil, produced-water residues, asbestos, lead-based coatings, tanks, pipework, scrap steel |
Regulators |
Primarily NOPSEMA, with other state, federal, and international guidelines | Primarily DMPE and the WA title surrender framework, with WHS and environmental obligations also applying |
Final Steps |
Onshore downstream processing, monitoring to approved end-state, NOPSEMA sign-off, title surrender | Demolition, remediation, rehabilitation, title surrender and proof that no liability remains to the State |
The Role of Recycling in Offshore and Onshore Decommissioning
Decommissioning produces an enormous volume of recoverable material. How that material is handled – and by whom – determines whether a project delivers its full economic and environmental potential or leaves value on the table.
Recovering Valuable Metals
Both offshore and onshore projects generate recoverable materials. Steel, stainless steel, copper, alloys, batteries, cabling, and electrical components – at sufficient scale, these recovered metals can generate significant revenue to offset project costs.
Flexible risers and umbilicals are particularly metal-rich. However, the multi-layer construction makes manual cutting to retrieve the material hazardous, slow, and expensive.
It’s a problem C.D. Dodd has addressed directly through custom-designed flowline processing machinery that reduces human exposure and significantly improves throughput.
Reducing Waste and Improving Sustainability
By current estimates, more than 5.7 million tonnes of material will need to be decommissioned in the coming decades. The opportunities here are enormous:
- Recycle millions of tonnes of metal into new material.
- Slash carbon emissions compared to virgin production.
- Reduce landfill reliance.
- Contribute directly to Australia’s budding circular economy.
Capturing these benefits will depend on mature recycling infrastructure and operators’ genuine commitment to sustainable practices in oil and gas decommissioning.
Hazardous Waste Management
Offshore and onshore decommissioning both generate complex hazardous waste streams:
- Offshore assets may contain hydrocarbons, chemical residues, mercury, batteries, contaminated marine growth, legacy coatings and electrical waste.
- Onshore projects add contaminated soil, asbestos, lead-based coatings, vehicles, aging structures, and water-based contaminants to the picture.
These require strict segregation, licensed handling, and documented chain-of-custody. Hazardous waste management must be built into every stage of the process, from removal through to final disposal.
Why Onshore Facilities Are Critical
Onshore processing facilities are where the two decommissioning models meet. They are central to both offshore and onshore oil rig decommissioning for several reasons.
Offshore Decommissioning
Offshore infrastructure arrives onshore in a state that still requires significant work: decontamination, structural breakdown, material separation, hazardous waste removal, and compliant disposal or recycling.
That work demands purpose-built facilities, not general industrial yards or laydown areas.
Proximity to the right ports matters too. Long transit adds cost, carbon, and risk.
Onshore Decommissioning
Without the right processing facility, a compliant closure for onshore projects is not possible.
Processing facilities are where dismantled infrastructure is classified and separated for recycling or licensed disposal. Contaminated materials, hazardous waste, and recoverable scrap must be handled through different pathways – and it all needs to be fully documented.
How C.D. Dodd Supports Decommissioning Projects
C.D. Dodd is Western Australia’s specialist partner for oil and gas decommissioning. We have spent more than 50 years building our infrastructure, equipment, and expertise to support both offshore and onshore oil rig decommissioning projects.
- Purpose-built facilities near the Port of Ashburton (Onslow) and Port of Dampier (Karratha).
- Custom flowline and umbilical processing machinery.
- Full hazardous waste capability across hydrocarbons, asbestos, lead paint, NORMs, chemicals, and batteries.
- Land rig demolition and scrap metal recovery for onshore petroleum infrastructure.
- 50+ years of experience across mining, industrial, offshore, and decommissioning sectors.
- ISO 45001, ISO 14001, and ISO 9001 certified.
Offshore vs onshore oil rig decommissioning both demand more than a generalist. They need a partner who has the right capability for the challenge, backed by the chain of custody that’s central to compliance.
Contact C.D. Dodd to plan a safe, compliant, and responsible oil and gas decommissioning project.