The volume of drilling muds ranges from 1,000 to 5,000 cubic metres for each well. Their impact on marine life depends on variables like depth, current, substrate type, and waves.
A single production platform can drill 70 to 100 wells and discharge over 90,000 metric tons of drilling fluids and metal cuttings into the ocean in its lifetime. Over 400 wells have been drilled on the east coast of Canada. Almost 60 wells had to be drilled before Hibernia was discovered.
The compositions of cuttings depends on the rock being drilled and often contains heavy metals such as mercury, lead, cadmium and zinc. Sometimes they contain naturally occurring radioactive materials.
Water-based drilling muds are less toxic then oil-based muds, but barium and bentonite are associated with water-based muds. These two chemicals have been detected as far as 8,000 metres from a well. In one case, barium was detected 65 kilometres west and 35 kilometres east of an exploratory drilling site after drilling stopped. Increases in other trace metals have been associated with water-based muds. These include arsenic, cadmium, chromium copper, mercury, lead and zinc, however, compared to barium, their distribution was much more limited.
Produced waters
Produced waters are one of the main sources of oil pollution from offshore oil and gas production. They are the water which is produced during the production of hydrocarbons.Produced waters are usually polluted by oil, inorganic salts and trace metals but the composition varies between oil fields and can be difficult to predict.
In the North Sea, produced waters are responsible for 20 percent of all oil discharged from the oil and gas activity in the region. The amount of produced waters increase as an oil field ages.
In Cook Inlet, Alaska, industry dumps at least two billion gallons of produced water into the inlet each year. With oil content at 30 to 40 parts per million, it equates to about 70,000 gallons of pure oil dumped into Cook Inlet each year.
Preliminary research by scientists in Norway shows that produced water from offshore oil exploration could be seriously harming cod in the North Sea.
In experimental conditions, chemicals dissolved in waste water from oil platforms stunted the growth of the fish and affected their breeding patterns. Scientists at the Norwegian Marine Research Institute in Bergen found that when cod were exposed to this solution, their eggs became smaller and spawning was delayed. It remains to be seen what this means for wild populations.
