办事指南

Any old oil? - Geologists search for black gold at the dawn of time

点击量:   时间:2018-01-24 08:02:12

By Douglas Palmer OIL could be lurking in rocks that were thought to be too old to contain any more than tiny traces of hydrocarbons. The oldest rocks so far exploited for oil are 2 billion years old. But geologists in Australia are suggesting that rocks which formed up to 3.5 billion years ago might yield commercial quantities of oil. The oil industry has not bothered to investigate ancient sedimentary rocks because its geologists thought there would not have been enough life in these Archaean times to generate oil. But Roger Buick of the University of Sydney, working with Birger Rasmussen and Bryan Krapez of the University of Western Australia in Nedlands, have now found quantities of tiny nodules of bitumen about a tenth of a millimetre across in a variety of ancient sedimentary rocks in Western Australia and South Africa (Bulletin of the American Association of Petroleum Geologists, vol 82, p 50). These nodules form when hydrocarbons are irradiated by isotopes in the sediments. The geologists believe the hydrocarbons were derived from bacteria that were abundant in Archaean seas. If so, there might also be reserves of oil hidden in the rocks. But finding commercial quantities of oil may be another thing altogether. Neil Piggott, a geochemist with British Petroleum in Sunbury, Middlesex, says that most hydrocarbons in such ancient rocks will have been destroyed by heat and pressure. “The Archaean source rocks would have to sit for billions of years with nothing happening to them,” he says. Buick his colleagues agree, but they note that Archaean rocks in Western Australia and the Transvaal region of South Africa seem neither to have been deformed nor heated above 250 °C. David MacDonald, director of the Cambridge Arctic Shelf Project, a research unit at the University of Cambridge, is keeping an open mind. “I would certainly not dismiss the prospect,