The discharge statistics are given in the latest edition of the DTI's annual "Brown Book" on the UK's oil and gas resources.1 Some of the data will fuel a campaign launched last year by the Marine Conservation Society, which criticised the DTI for "toothless" oversight of the offshore industry (ENDS Report 261, pp 3-4 ).
The oil spill statistics are based largely on reports by offshore operators to the DTI. The number of reported spills increased steeply in the late 1980s and reached a record 345 in 1990 after aerial surveillance flights were initiated by the Dutch and then the UK authorities.
Reported spills have declined since 1990, falling to 145 in 1995. However, last year's total bounced back to 300 - the second highest on record.
The 1996 figure is not strictly comparable with earlier years, since it includes spills detected by aerial overflights for the first time. The report does not say how many spills were spotted in this manner but not reported by operators, commenting only that the surveillance programme has shown that "in the main" operators are quick to report spills to the DTI.
The reported amount of oil spilled from offshore platforms increased by 51% last year to 127 tonnes. Nevertheless, the figure is well down on earlier years.
The industry's biggest source of oil discharges is "produced water" extracted from production wells and discharged to sea with traces of oil. The amount of water extracted in this way increases as oil fields age, helping to explain the upward trend in oil discharges from this source since the late 1980s. However, the industry succeeded in improving the ratio of oil discharged in relation to total water produced last year.
Historically, the largest quantities of oil discharged by the industry have stemmed from the use of oil-based muds (OBM) in drilling operations. In 1988, for example, 18,500 tonnes of oil were legally dumped in the sea with OBM cuttings.
However, the practice has been declining as rules established by the Paris Commission have taken effect. These limited the amount of oil permitted to be discharged with spent OBM to less than 1% for exploration and appraisal wells from January 1994, and for all other wells from 1997. The standard cannot be met with current technology, and dumping of OBM cuttings is now effectively at an end.
Last year saw a 20% increase in the amount of oil discharged on drill cuttings, despite a decline in the number of wells drilled with OBM.