Case Study: Degradation Assessments in Decommissioning

Overview

Decommissioning involves the timely, safe, and environmentally responsible removal or management of offshore infrastructure previously used for oil and gas operations. Exceptions to full removal may apply if titleholders can demonstrate that an alternative decommissioning approach provides equal or better environmental outcomes compared to complete removal and complies with all relevant regulations. Consequently, titleholders may consider leaving infrastructure in place but must support this decision with appropriate scientific data and information, and present a compelling case to the regulator.

Challenges

Given the age of some infrastructure that was installed decades ago, there is often not a complete inventory of materials used for pipelines and associated equipment.  In addition, there is a limit to the number of relevant tests that have been completed on chemicals and how they may react subsea.

The potential impacts from infrastructure degrading in situ vary from toxicity impacts relating to plastic and rubber particulates, chemical loading of plastic particles, leaching and degradation of polymers, and micro and macro plastics. 

Solutions

An environmental fate and impact assessment needs to be conducted in a systematic manner. The assessment aims to identify and risk assess chemicals of potential concern associated with the material composition of subsea infrastructure to determine the fate and potential environmental impact pathways. This assessment:

• Identifies those chemicals of potential interest;

• Identifies chemicals of potential concern; and,

• Prioritises risks for each chemical of potential concern. 

The methodology used in this assessment is  consistent with national and international guidance for environmental hazard assessment.  The report is provided to titleholders to demonstrate the potential impact of leaving any part of the infrastructure in situ long term and can then inform their acceptability assessments for regulatory documents and stakeholder consultation discussions.

MCC also uses their expertise in chemistry and environmental impacts to make recommendations for in field sampling that can verify desktop studies. This methodology is unique and created by MCC Sustainable Futures to ensure the best environmental outcome is achieved. 

Implementation

MCC has partnered with an engineering company to perform the full material inventory of in field assets include the material composition of each piece of infrastructure and to produce a timeline of degradation.  MCC then uses this information to undertake the environmental assessment of components in the specific environmental conditions at each location.  This informs the client of the effects of the different sediment types and effects of local oceanographic conditions.

Results

MCC has undertaken degradation assessments on over ten different fields on the north-west shelf of WA providing information to inform titleholders decision making around the best environmental outcome for leaving infrastructure in situ or informing any rehabilitation requirements in the offshore marine environment.  This offering is unique to the market in WA in the combination of both engineering and environmental assessment with a clear understanding of the regulatory requirements.