Economically offshore oil and gas are the most important reserves in the Exclusive Economic Zones (EEZ) of many countries. They were generated by chemical transformation from the remains of marine plants and animals that sedimented to the bottom of stagnant anoxic shallow seas during past geological eras, and were then buried by movements of the earth. Initially deep within the rocks the high pressures and temperatures of 50–100 °C (122–212 °F) converted the organic remains into kerogen, a solid, waxy, organic substance, a forerunner of oil and gas. Further pressure cooking at temperatures of 100–160 °C (212–310 °F) converted the kerogen to oils and at still higher temperatures to natural gas (methane). The oil and gas then migrated laterally along porous rock strata, sandstones, or salt deposits, eventually becoming trapped where the strata domed or at faults where impermeable layers stopped further migration. In the North Sea the first gas was recovered in 1967, and the first oil in 1975. An example of a North Sea oil field is Forties. Discovered in 1970, it began production in 1975 and in 1982 produced its one billionth barrel of oil. It extends over a distance of 56 kilometres (35 mls.), covers an area larger than the city of Aberdeen, and each of its four main platforms, Alpha, Bravo, Charlie, and Delta, contains four times more steel than the Eiffel Tower.
To date about 132 million tonnes of oil and gas have been recovered in Britain's EEZ, annually contributing £4 billion a year in taxes since 1984, and in 2004 the industry was employing about 300,000 people. Even so UK oil and gas production is only about 4% of global production. The most important reserves are still in the Middle East, but many offshore regions have large untapped reserves, especially in deposits under the Caspian Sea, and under more than 1,000 metres (3,250 ft) of water off Brazil and Angola. Oil pollution remains an unresolved issue, with serious spills from tankers and other sources occurring with depressing regularity. The industry is concerned about what will happen when most reserves eventually run dry, maybe before, or during, the second half of the 21st century, but many environmentalists believe that the climate change induced by burning all these hydrocarbons will by then have disrupted the world as we know it.
M. V. Angel
Subjects: Maritime History.