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The Ekofisk Bravo Blowout, 1977
Chapter 34
The Ekofisk Bravo Blowout, 1977 Robin J. Law
Chapter Outline 34.1. Case Study
1107
34.1. CASE STUDY On April 22, 1977, a blowout occurred during maintenance operations on the Bravo platform of the Ekofisk oil field in the North Sea and oil began to escape at a rate of 2000e3000 tons per day.1 The release rate was estimated using the flow rate from the well and the elapsed time. As the oil was released high into the air, about 30% had evaporated by the time it reached the sea surface. From April 24 to May 1, Norwegian and UK scientists undertook a coordinated program of research, collecting samples from four research vessels. During this period, samples of subsurface seawater, surface sediments, and fish and shellfish were collected on a grid system around the Ekofisk platform location. Subsurface seawater samples were collected using 2.7 l glass Winchester bottles mounted in a weighted stainless steel frame deployed by means of a nylon rope.2 The bottle is sealed using a Polytetrafluroethylene (PTFE) stopper that can be opened at the sampling depth using a second nylon rope. This avoids contamination from the sea-surface microlayer that would result if the bottle were lowered open. Surface sediments were collected using a 0.1 m2 modified Day grab, previously solvent-cleaned. Fish and shellfish were collected using a Granton trawl. The same analytical methods were used in both national laboratories, which had earlier aligned their procedures.1 This was one of the first incidents in which capillary (high-resolution) gas chromatography-mass spectrometry was deployed in an oil spill investigation, allowing individual alkanes and polycyclic aromatic hydrocarbons (PAH) compounds to be identified and quantified. No sizable quantities of floating oil were encountered by the UK vessel during the survey, but thin sheens of oil Oil Spill Science and Technology. DOI: 10.1016/B978-1-85617-943-0.10034-6 British Crown Copyright Ó 2011.
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PART | XIII Specific Case Studies
were seen at some locations to the east of the platform and about 10e20 miles away.1 Concentrations were low in all the water samples, with maximums of only 3.9 and 8.1 mg/l for the summed aliphatic and aromatic hydrocarbons determined, respectively. Such concentrations are less than 10 times normal background concentrations in the offshore North Sea and of no toxicological significance. Samples of fish and sediments showed only low concentrations of both aliphatic and aromatic hydrocarbons, and the pattern of aliphatics found was predominantly natural in origin. Subsequent studies (May 3e5) undertaken by Scottish scientists using sediment traps suggested that, at that time, particulate oil was probably present in suspension in the water column as a result of natural dispersion. The highest concentrations were observed in the traps closest to the surface. About 9000 to 13,000 tons of oil remained at sea when the well was capped on April 30,3 but none reached land as it dispersed naturally at sea during the next few weeks. There was no evidence that the oil released from the platform contributed significantly to the burden in fish or sediments as a result, and there was only low-level contamination in seawater samples in the area.
REFERENCES 1. Law RJ. Determination of Petroleum Hydrocarbons in Water, Fish, and Sediments Following the Ekofisk Blow-Out. Mar Poll Bull 1978;321. 2. Kelly C, Law RJ, Emerson HS. Methods of Analysing Hydrocarbons and Polycyclic Aromatic Hydrocarbons (PAH) in Marine Samples, Science Series, vol. 12. Cefas, Lowestoft: Aquatic Environment Protection: Analytical Methods; 2000. 3. Berge G. The Ekofisk Bravo Blow Out Part 1. Introduction and Preliminary Findings. ICES C.M. 1977/E:55 1977.
The Ekofisk Bravo Blowout, 1977 Robin J. Law
Chapter Outline 34.1. Case Study
1107
34.1. CASE STUDY On April 22, 1977, a blowout occurred during maintenance operations on the Bravo platform of the Ekofisk oil field in the North Sea and oil began to escape at a rate of 2000e3000 tons per day.1 The release rate was estimated using the flow rate from the well and the elapsed time. As the oil was released high into the air, about 30% had evaporated by the time it reached the sea surface. From April 24 to May 1, Norwegian and UK scientists undertook a coordinated program of research, collecting samples from four research vessels. During this period, samples of subsurface seawater, surface sediments, and fish and shellfish were collected on a grid system around the Ekofisk platform location. Subsurface seawater samples were collected using 2.7 l glass Winchester bottles mounted in a weighted stainless steel frame deployed by means of a nylon rope.2 The bottle is sealed using a Polytetrafluroethylene (PTFE) stopper that can be opened at the sampling depth using a second nylon rope. This avoids contamination from the sea-surface microlayer that would result if the bottle were lowered open. Surface sediments were collected using a 0.1 m2 modified Day grab, previously solvent-cleaned. Fish and shellfish were collected using a Granton trawl. The same analytical methods were used in both national laboratories, which had earlier aligned their procedures.1 This was one of the first incidents in which capillary (high-resolution) gas chromatography-mass spectrometry was deployed in an oil spill investigation, allowing individual alkanes and polycyclic aromatic hydrocarbons (PAH) compounds to be identified and quantified. No sizable quantities of floating oil were encountered by the UK vessel during the survey, but thin sheens of oil Oil Spill Science and Technology. DOI: 10.1016/B978-1-85617-943-0.10034-6 British Crown Copyright Ó 2011.
1107
1108
PART | XIII Specific Case Studies
were seen at some locations to the east of the platform and about 10e20 miles away.1 Concentrations were low in all the water samples, with maximums of only 3.9 and 8.1 mg/l for the summed aliphatic and aromatic hydrocarbons determined, respectively. Such concentrations are less than 10 times normal background concentrations in the offshore North Sea and of no toxicological significance. Samples of fish and sediments showed only low concentrations of both aliphatic and aromatic hydrocarbons, and the pattern of aliphatics found was predominantly natural in origin. Subsequent studies (May 3e5) undertaken by Scottish scientists using sediment traps suggested that, at that time, particulate oil was probably present in suspension in the water column as a result of natural dispersion. The highest concentrations were observed in the traps closest to the surface. About 9000 to 13,000 tons of oil remained at sea when the well was capped on April 30,3 but none reached land as it dispersed naturally at sea during the next few weeks. There was no evidence that the oil released from the platform contributed significantly to the burden in fish or sediments as a result, and there was only low-level contamination in seawater samples in the area.
REFERENCES 1. Law RJ. Determination of Petroleum Hydrocarbons in Water, Fish, and Sediments Following the Ekofisk Blow-Out. Mar Poll Bull 1978;321. 2. Kelly C, Law RJ, Emerson HS. Methods of Analysing Hydrocarbons and Polycyclic Aromatic Hydrocarbons (PAH) in Marine Samples, Science Series, vol. 12. Cefas, Lowestoft: Aquatic Environment Protection: Analytical Methods; 2000. 3. Berge G. The Ekofisk Bravo Blow Out Part 1. Introduction and Preliminary Findings. ICES C.M. 1977/E:55 1977.