The Cabot G10 was and still is very basic: stainless-steel casing with a black face and luminous numbers.

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"They typically had a steel casing, copper for conducting power down them and optical fibres for collecting data, " he said.

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The high quality brushed stainless steel casing measures 35 x 35 mm.

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The other process, still in use, is to cut a window in an old well's steel casing and then drill horizontally into the oil zone.

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So we are talking a lot of steel casing here.

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To get at the oil and gas trapped in shale, drillers use powerful hydraulic pumps to force water and chemicals through holes punched in the concrete-and-steel well casing.

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The brines in the formation and other corrosive elements will attack the casing steel.

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