Drilling engineers use tons of a thick fluid called drilling mud to lubricate drill bits as they chew through rock.

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At that depth stopping the flow with a deadweight of drilling fluid should create few problems, once the exceedingly difficult challenge of hitting the well is met.

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The effort, called a "top kill, " involved plugging the ruptured deep-sea well by pumping heavy drilling fluid into it from the surface, nearly a mile above.

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In April, Chesapeake suspended work on a clutch of natural gas wells in Pennsylvania temporarily after a well blowout sent thousands of gallons of drilling fluid into local waterways.

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Halliburton said that the report "accurately places responsibility on BP as the well owner for its operational decisions, " which included using a heavy fluid designed to keep gas from entering the well, called drilling mud, that was "too light" and probably mixed with the cement at the bottom of the well, and drilling too narrow a well.

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Then, after carefully drilling a hole into the crystals' walls and removing the few microlitres of fluid from each inclusion, the researchers began testing their samples for life.

ECONOMIST: Old salts