Fracking involves drilling a borehole before a high-pressure water mixture is directed at the rock to release the gas.

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Transocean engineers wanted to keep the pressure in the borehole under control with heavy mud while Halliburton set the cement plugs.

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The tests will continue for at least 48 hours, during which time engineers will carefully watch the pressure building up in the well to make sure the damaged borehole can hold it in without a new leak popping open somewhere else.

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