Highest risk for severe oil spills from exploration and production

The risk of small or medium oil spills from ships, pipelines, storage facilities and refineries is higher than from oil exploration and production. However, the risk of severe oil spills is highest from exploration and production, according to a recent study. Furthermore, the study suggests that the Deepwater Horizon accident, the largest recorded oil spill, cannot be considered as a particularly rare event.
Using information contained in the global Energy Related Severe Accident Database (ENSAD), this study analysed over 1200 accidental oil spills that occurred between the years 1974 and 2010. Severe accidents include those where there are fatalities and where more than 10,000 tons of oil were spilled. This study included oil spills larger than 200 tons in order to make comparisons between incidents of varying scale.
Spill sources were divided into four categories: (i) spills occurring during exploration or production e.g. from oil wells, drilling and exploration platforms and rigs, (ii) spills from tankers transporting crude oil and refined products, (iii) spills from onshore and offshore pipelines carrying crude oil and refined products and (iv) spills from refineries and storage sites.
In this period, a total of 9.8 million tons of oil were spilled in 1213 incidents. While exploration and production was responsible for far fewer spills than ships, storage and refinery and pipelines, it caused far greater quantities of oil to be released. Six million tons of spilled oil came from 888 ship incidents; 870,000 tons from 113 spills at storage and refinery sites and 750,000 tons from 188 spills from pipelines. However, 2.2 million tons were spilled by just 24 incidents during exploration and production.
These figures reveal the severity of spills from exploration and production. While the risk of small or medium spills is generally higher from ships, pipelines and storage/refineries, the risk of large and therefore more severe oil spills is higher from exploration and production as the potential amount of oil that could be released is far greater.
Spills from tankers accounted for around 75% of the total spills and volume of oil spilled during this time. However, over time, the number of spills and volume spilled from oil tankers fell significantly despite more oil being carried. This is probably because better, electronic, navigation systems have been installed in ships and ships are required to have double hulls, which reduce the chance of spillage should the outer hull be damaged. In contrast, the frequency of oil spills from storage or refinery facilities and from pipelines increased over this period.
No particular increases or decreases in the frequency of spills were found for exploration or production operations, although it is possible that studies with a longer time frame could reveal trends. Alternatively, a combination of other risk factors, such as drilling in new locations or changes in regulations and technologies, might explain a lack of trends.
By analysing the data, the study suggests that a severe oil spill on a similar scale as the Deepwater Horizon incident in 2010 could occur every 23 years. The accident at the Deepwater Horizon exploration drilling rig in the Gulf of Mexico killed 11 people and released an estimated 680,000 tons of oil into the sea.

Source: Eckle, P., Burgherr, P. and Edouard Michaux, E. (2012). Risk of Large Oil Spills: A Statistical Analysis in the Aftermath of Deepwater Horizon. Environmental Science & Technology. 46: 13002-13008. Doi.org/10.1021/es3029523
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