Another Successful Monitoring Campaign Completed

Subacoustech Environmental have successfully completed an underwater noise monitoring campaign during well decommissioning operations in the southern North Sea. Monitoring was undertaken continuously at three locations for the duration of the campaign to capture underwater noise from P&A activities during March and April 2021.

A bespoke deployment and recovery method was devised to enable acoustically silent subsea moorings to be deployed from the platform standby vessel operating inside of the 500 m exclusion zone around the platform. This approach had a number of benefits which contributed to the success of the project:

• The subsea mooring design did not restrict navigation which allowed monitors to be positioned in the optimum locations.
• The lack of a surface buoy made the moorings quieter and much less vulnerable to bad weather with modest sized anchor weights. (No issues in 50+ kt winds and 7-8m waves).
• Deployment inside the 500 m exclusion zone significantly reduced the risk of loss or damage from fishing activity.
• Using a vessel that was already under contract and permitted to operate within the 500 m zone reduced costs and removed the need for additional approvals.

Further Information:

Well decommissioning (known as Plug and Abandon or P&A) involves the use of shaped charges to break the wellbore before placing cement plugs and pressure testing to ensure complete isolation of the well. The process is repeated at progressively shallower depths for each wellbore. There is very little field data available to validate estimates of the underwater noise levels that might result from these operations or to support environmental impact assessments and marine mammal mitigation measures.

Subacoustech Environmental was contracted to assist with addressing this knowledge gap and provide real world data to support a more refined and targeted approach to marine mammal mitigation. Initial analysis has shown good quality data was acquired and detailed analysis is ongoing.

About Subacoustech:

Subacoustech Environmental provide specialist underwater noise measurement and assessment services across all marine sectors. We have particular expertise in designing bespoke solutions that utilise vessels already available to the client in order to reduce the cost and risk associated with additional vessel charter.