Lagavulin SERPENT final report to Chevron

Abstract

This report covers the work of the SERPENT Project at the deep water Lagavulin well in the Faroe-Shetland Channel (FSC). As with all deep-sea environments, scientific knowledge about this area is limited. The surveys will investigate how sediment conditions and animal communities around the drilling location change from the baseline to a disturbed situation. Our field results will be compared to previous model predictions of sedimentation at Lagavulin.

The baseline sediment is fine and does not have the heterogeneous grain sizes of sediment found in shallower depths in the Faroe-Shetland Channel (e.g. at Rosebank). A total of 18 animal species were observed living on or associated with the seabed at Lagavulin, with megafaunal representatives (i.e. those animals greater than 10 mm) from at least 7 animal groups (phyla). There were species common to other shallower sites (>900m) within the cold water area of the FSC, but no species were common to sites investigated below 600m depth.

After drilling and cementing the tophole section drill spoil (cuttings, mud and cement) was found to extend to nearly 150 m from the centre of drilling (down current; S direction). Approximately 33,750 m2 of seabed was disturbed. It was not possible to determine the vertical height of drill spoil. A new image complexity method was successfully trialled in this study to measure the extent of drill spoil.

Lagavulin had a low number of visible animals, particularly as many species live partially burrowed into the sediments. The number of seabed animals (non-mobile) found at Lagavulin was very low close to the drill site. It is most likely that these animals were covered with drill cuttings, as 60mm deep cuttings were measured at 20m distant from drilling. There was no evidence that the distribution of mobile animals was affected by drilling.

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