Historic scale and persistence of drill cuttings impacts on North Sea benthos

- Industry environmental data from 19 North Sea installations were analysed.
- Ecological impacts of drill cuttings reached 1.2 km away and lasted over 8 years.
- New evidence-based recommendations for drill cuttings monitoring are provided.
- OSPAR is urged to re-consider Decision 98/3 and widen the scope for derogation.

Despite its long history of hydrocarbon exploitation, the United Kingdom lacks scientific protocols to monitor ecological impacts of drill cuttings (mixtures between rocky material excavated from wells and drilling mud). The present study used the UK Benthos industry database to apply standardised variance partitioning and measure the scale and persistence of these effects at 19 sites across the UK sector of the North Sea. Generally, effects were limited to within 1 km from the platform, but two platforms historically drilled with oil-based mud were impacted up to 1.2 km away. Impacts persisted for at least 6-8 years in the northern and central North Sea, but were undetectable in the south where cuttings piles do not accumulate. This study underpins new recommendations to implement regional, phase-based approaches to drill cuttings monitoring, and to apply a precautionary approach in considering decommissioning options that will minimise disturbance to cuttings piles.