e-Digest Statistics about: Coastal and marine waters
Coastal and marine waters
Oil spills and operational discharges
Marine ecosystems and marine life may also be affected by discharges from vessels and offshore installations. Table 15 shows the number of incidents and the estimated volume of discharges attributed to vessels and offshore oil and gas installations in 2004. The geographical distribution of incidents is given by enumeration area, which are based on the UK Pollution Control Zone. Mineral oils were the most frequently recorded polluting substances, identified in 96 per cent of incident reports. The discharges occurred most frequently in the UK Continental Shelf (UKCS) area, followed by Western Scotland and Southern England enumeration areas. Most spills are small, so the pollutant is usually dispersed and degraded naturally.
Table 16 gives additional information on the source of the pollution in 2004. Oil and gas installations operating on the UKCS accounted for 75 per cent of all confirmed discharges. This table excludes all reported incidents from unidentified sources in ports, near-shore and tidal waters so the total number of incidents is lower than that given in Table 15.
The data in Table 15 and Table 16 are not consistent with data on oil spills published in editions of the digest previous to 2000, reflecting revisions to the Maritime and Coastguard Agency's management information requirements. The remit of this survey is broader, including additional types and categories of discharges such as noxious liquid substances and garbage. However discharges from land-based sources such as outfalls or industrial premises are no longer included. Further information on discharges to the sea around the UK, and on specific changes to the information available can be found in the Annual Survey Report by ACOPS. [4]
Additional information on tonnes of oil and oil spills from offshore installations in the North Sea is shown in Table 17. In addition to accidental oil spills, there are also operational discharges of oil from offshore installations in the North Sea, related to discharges of oil in produced water (i.e. oil contaminated water that is extracted with the oil and gas and is discharged following treatment). Prior to 1997 there were also discharges of oil via drill cuttings arising from the use of oil-based drilling muds. The total amount of oil discharged depends on the extent of new exploration, on the stage in the life cycle of the wells in production (quantities of produced water increase significantly towards the end of the working life of a field) and technical improvements. Although amounts shown in Table 17 are relatively large, the oil is considerably diluted.
Discharges of oil from drill cuttings have reduced substantially over several years, partly caused by the greater use of alternatives to oil-based muds. In 1990, 75 per cent of wells drilled (260 out of a total of 348) used oil-based muds but by 1996 this had reduced to 21 per cent (79 out of 374). Since the beginning of 1994, the level of oil permitted to be discharged when drilling using oil based muds must be less than 1 per cent for exploration and appraisal wells. All other wells were required to achieve this target by the beginning of 1997. Since this is not achievable using current technology, offshore operators have had to use alternatives to discharging at sea, including re-injection and shipping to shore. Consequently there have been no discharges of mineral oil contaminated cuttings into the sea in since 1996.
Table 18 shows prosecutions by port authorities and convictions for offences relating to the illegal discharge of oil or of mixtures containing oil between 1988 and 1998. It covers offences committed in harbours and coastal waters and includes deliberate discharges of oil from ships and discharges of ballast water in harbours.
Further Information:
- Data Tables:
- 15 Reported discharges attributed to vessels and offshore oil and gas installations; number of incidents and estimated volume of discharges; 2004 XLS
- 16 Reported source of pollution by enumeration area: 2004 XLS
- 17 Operational discharges of oil and oil spills from offshore installations: 1982-2005, North Sea XLS
- 18 Prosecutions and convictions for oil spills: 1988-2001, United Kingdom XLS
- References, further reading and links to other resources:
- [4] Advisory Committee on Protection of the Sea. Annual Survey of Reported Discharges Attributed to Vessels and Offshore Oil and Gas Installations Operating in the United Kingdom Pollution Control Zone: 2000, ACOPS.
- Internet Links:
- Advisory Committee on Protection of the Sea (ACOPS)
- Department of Trade and Industry (DTI)
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Page last modified: 8 December 2004
Page published: 8 December 2004