Over the years, legislation regarding the use and discharge of oil-based muds has changed. Shell has to comply with OSPAR Recommendation 2006/5, which aims to reduce the impacts of oil and other substances from historic drill cuttings piles.
The drill cuttings have been surveyed and sampled since the late 1990s – most recently in 2015. Long-term fate modelling based upon the 2007 sample analysis has determined that the GBS seabed cuttings all fall below the OSPAR thresholds. Under OSPAR Recommendation 2006/5, they can be left in place to degrade naturally. A similar outcome was determined for the Delta and Bravo cell top cuttings.
A Comparative Assessment has been carried out for the Alpha seabed cuttings. The decommissioning recommendation is to leave them in place to degrade naturally.
As a result of the higher hydrocarbon content detected in the Charlie cell top cuttings samples, the long-term modelling indicated an oil loss rate above the OSPAR 2006/5 threshold. This meant that further options for the Charlie cell top drill cuttings were considered in more detail by conducting a Comparative Assessment. The decommissioning recommendation is to also leave these cuttings in place.
After decommissioning, Shell will continue to monitor the drill cuttings in a programme that will be agreed with Department for Business, Energy and Industrial Strategy (BEIS).