Total given approval to drill North Sea relief well

It will take about six months to drill a high-pressure, high-temperature relief well to permanently seal the leaking G4 Elgin well 4,400 metres below the seabed, Britain's energy ministry said.

The relief drilling operation will take place 1,200 metres east of Elgin in waters 90 metres deep.

French oil company Total and the British government are also pursuing their preferred option of a so-called "well kill" - which is cheaper and faster but also more risky - that involves pumping heavy mud into the well from the platform shrouded in explosive gas.

The leak, which has spewed around 200,000 cubic metres of gas daily since March 25, has not directly contaminated the marine environment, the Scottish government said citing the results of tests of water and sediment.

"All data gathered to date continues to demonstrate that the effects on the marine environment of the Elgin gas leak are, so far, minimal," Scottish environment secretary Richard Lochhead said in a statement.

Samples collected on the edge of a two-mile exclusion zone around the evacuated platform found no traces of oil and gas pollution, the Scottish government said.

It said traces of oil-based hydrocarbons that were found in seawater samples were likely the result of other shipping or industrial activities in the area.

"The sediment samples were found to be unaffected by the gas leak, with the samples' chemical indicators being typical of what is found elsewhere in the North Sea," it said.

Total has said the leak was costing it $2.5 million per day.

Britain could be facing as much as a 6 percent cut to gas supplies this summer due to the closure of three large fields following a leak found beneath Total's Elgin platform, National Grid said.

Total's Elgin and Franklin fields and Shell's neighbouring Shearwater site were shut down in late March following the evacuation of the Elgin platform after workers detected a gas leak.