Lancaster and Whirlwind SERPENT report

Abstract

SERPENT visited the Borgsten Dolphin semisubmersible drilling rig at Hurricane Exploration’s Lancaster and Whirlwind drilling sites, West of Shetland in 2010. The work at Lancaster was an opportunity to investigate recovery of biodiversity at the drilling site which had been studied by SERPENT nine months previously. At Whirlwind an assessment of biodiversity and initial study of the effects of disturbance were carried out.

At Lancaster background environment data were collected; temperature, salinity and oxygen profiles and seabed current speed and direction. Video surveys and sample collection were used to map disturbance and quantify biodiversity. The size of the area characterised as completely covered by drill cuttings had reduced in the nine months since the initial drilling disturbance commenced. The abundance and diversity of megafaunal organisms was more consistent with distance from the well in 2010 suggesting evidence of some recovery (return to background) from the 2009 situation. There was also some evidence of recolonization in the macrofauna close to the well with organisms present, even in the samples closest to the well. There may however be a change in the macrofaunal community composition, but in order to determine such a change further analysis including a higher number of samples would be essential.

Two visits were made to the nearby but slightly deeper Whirlwind site, where the same background data were collected and an assessment made of the initial effects of disturbance. The megafaunal organisms observed at Whirlwind were similar to Lancaster. The extent of complete cuttings coverage of the seabed at reached a maximum of 70m from the well. There was visible evidence of disturbance (incomplete coverage) reaching beyond the extent of the 100 m video surveys to the SE, W and NW of the well, otherwise incomplete coverage of the seabed reached between 10 and 40m beyond the complete coverage (visit 2). The vertical accumulation of cuttings was measured using marker buoys placed on the seabed. At four metres from the well the cuttings reached over 1m. Ten metres from the BOP the cuttings height was typically 0.2 m. This disturbance affected the megafaunal abundance with significantly fewer megafaunal invertebrates close the BOP during the first visit.

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