There might not be much pressure to drill now, with plentiful oil on world markets and reasonable prices.

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As the drill progresses through the rock and sand below the seabed, the pressure of the mud in the drill string must be kept within a limited range.

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It is making preparations to drill another well nearby and thereby relieve pressure on the one that is leaking.

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At 8:20 p.m. on the day of the explosion the pressure data suggest there was a constant flow of sea water being pumped into the drill pipe that was displacing the heavier mud system which was the primary pressure control for the well.

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The drill was taken offline for about six hours after it lost pressure while hammering at the tough Chilean rock, officials said.

CNN: STORY HIGHLIGHTS

Once the blowout preventer is replaced to mitigate the risk of pressure in the well, it will take about four days to drill through the relief well and intercept the main well, based on statements from Allen.

CNN: STORY HIGHLIGHTS