Exploration and appraisal well drilling
Once seismic surveys have identified possible reservoirs of hydrocarbons, the next phase of industry activity is to drill an exploration well through the rock beneath the seabed into the geological layer thought to hold oil.
The first exploration well in the Atlantic Margin was drilled by Esso in 1972. Exploration drilling has continued ever since, although levels of activity have varied from year to year. As with every stage of the search for oil, before drilling begins it is essential to assess and analyse all potential environmental sensitivities, in order to reduce the possibility of any adverse effects on marine fauna and flora.
Drilling activities and the seabed
Without sufficient environmental protection measures, drilling through subsea rock can produce debris potentially harmful to some seabed marine wildlife in the localised area. West of Britain operators are fully aware of this and have examined carefully the environmental conditions around proposed well sites.
A number of factors mitigate the potential impact of drilling operations in the Atlantic Margin. Powerful and complex water currents in the region mean that discharges from drilling are dispersed rapidly, thereby minimising impacts on nearby seabed animal life, while the selection of drilling muds used by West of Britain operators is also significant.
Drilling mud serves several purposes. It cools and lubricates the drill bit, maintains pressure, stabilises geological formations and removes rock cuttings from the well bore. Water-based muds are used wherever possible. These are essentially sea water, to which are added small quantities of non-toxic and rapidly biodegradable substances.
If for technical reasons water-based muds cannot be used, synthetic muds -- the latest generation of organic phase drilling fluids -- may be used in some circumstances after consultation with UK Government departments. Drilling muds are an expensive commodity, and are recovered, as far as possible, for economic as well as environmental reasons.
Industry response to oil spillage
Marine flora and fauna on the Atlantic Margin are potentially highly vulnerable to the effects of oil spillage, either as a consequence of well drilling or from any other source. There is understandable public concern about the consequences of a serious incident during the exploration or production processes. However the application of rigorous controls and procedures, developed over several decades in the North Sea, has reduced the possibility of such an incident considerably.
Any incidents, even those involving volumes as low as 0.5 litre, would be reported to all interested parties. In the unlikely event of a more serious incident, operating companies have devised a set of comprehensive oil spill response plans to minimise the environmental impact. Any deployment of oil spill response resources would require the notification and approval of the relevant authorities.
- A Tier 1 spill -- such as a small plant upset or equipment leak -- would be dealt with using infield resources such as dispersant.
- A Tier 2 spill -- more than 100 tonnes, such as the failure of an infield pipeline -- would require additional resources on immediate callout from Shetland, Aberdeen and Dundee.
- In the very unlikely event of a Tier 3 incident -- a very large spill such as a cargo tank rupture or well blow-out -- further substantial resources would be required. Oil Spill Response Ltd (OSRL) in Southampton can respond to two simultaneous large scale spillages anywhere in the world, and could deploy aerial dispersant within 9 hours and sea-borne resources within 36 hours. Local government and the UK Government Marine Pollution Control Unit (MPCU) would also assist, with additional resources including aerial dispersant capability to deal with a major oil spill within hours.
Preparatory work has been undertaken on the Shetland and Orkney coastline should a spill threaten to reach land. Fixed mooring points for booms have been placed at many of the potentially vulnerable locations on the Shetland coast and equipment, including booms, have been stockpiled on both Shetland and Orkney. A third of Scotland's farmed salmon is produced in the region, mostly in deep sheltered inlets on the west coast of Shetland and Orkney. Salmon farmers have been trained in oil spill response techniques by the North Atlantic Fisheries College in Shetland, and local volunteers have been recruited to assist experts on site should a slick reach the coast.
The oil spill response plans for operators in the Atlantic Margin region are drawn up in consultation with organisations including:
- All relevant statutory authorities including UK Government agencies
- Scottish Natural Heritage and Joint Nature Conservation Committee (JNCC)
- Shetland Islands Council, Orkney Islands Council and Western Isles Council
- Royal Society for the Protection of Birds (RSPB)
- Scottish Society for the Prevention of Cruelty to Animals (SSPCA)
- Shetland Fishermen's Association and Shetland Salmon Farmers Association
- Orkney Fishermen's Association
Tarball fingerprinting
Tarballs are small coagulated lumps of oil residue washed ashore onto beaches and rocks. They are usually not found in any significant numbers and, while a nuisance, pose no substantial threat to the environment in themselves. The origin of tarballs can be identified by scientific examination of the type of oil involved. A total of 78 oil residue samples have been analysed to date. The large majority (88%) originated from fuel oil discharges, probably from bilge waters.
Drilling activities and seabirds
The Faeroe, Shetland and Orkney Islands (including the islands of Foula, Fair Isle, Sule Skerry and Sule Stack) are internationally important breeding grounds for several species of seabird. Seabirds from more northerly breeding areas such as Svalbard, Norway and Iceland are also present during migration periods and in the winter months.
It is clearly important for the oil industry to take the breeding and feeding habits of seabirds into account in assessing the potential environmental impact of the exploration drilling and production processes. BP and Shell have therefore sponsored a survey, carried out by the Seabirds at Sea Team (SAST) of the UK statutory body the Joint Nature Conservation Committee (JNCC), to build up a database of birds in the study area. The SAST survey uses methods and protocols pioneered and refined in use around the British Isles since 1979.
The survey logs sightings of all seabirds as well as cetaceans (whales, porpoises and dolphins) and seals. This data is then entered into the JNCC's European Seabirds database, which is in the public domain. West of Britain operators will use this data to help minimise the potential environmental impact of their activities on these varied populations.
More than 10% of the world's
population of guillemots, razorbills, puffins, great skuas and gannets, and more than 1% of kittiwakes and black guillemots breed in these areas. Apart from the great skua, these species, together with fulmars, are numerically the most abundant species in offshore areas of the North Sea and North Atlantic. Large numbers of birds use the Islands for feeding, roosting or preening.
During the pre-breeding season (Mar-April) large numbers of guillemots and puffins and smaller numbers of gannets and great black-backed gulls gather in the area. During March and April many adult puffins are flightless due to the moulting of their feathers. Large numbers of kittiwakes and fulmars can also be found on various parts of the UK Continental Shelf during this period. Large numbers of puffins are found around the study area during the early part of the breeding season.
During the winter period (Oct -- Feb) guillemots are the only auk to gather offshore in moderate numbers within the study area. Although numbers of fulmars and kittiwakes decrease during this period, they are still the most abundant species in the area during the winter months. In May there is a large scale arrival of guillemots and puffins for the breeding season (May-July). Adults and young start moving off to sea in July, and the area is relatively unimportant for most seabirds in the post-breeding season (July-Sept).
Exploration Index
