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Traditionally well are drilled in sections and a lining, known as casing, is inserted. When a second section is drilled the drill bit must pass through the casing. So each section gets gradually smaller in diameter until the well is too narrow to be drilled. A Shell engineer solved the problem by inventing special casings that can stretch – expandable tubulars.

Expandable tubulars

Expandable tubulars are metal casings that can be stretched once in the well. Each tubular is small enough to pass through the previous section of casing, but then it can be expanded to the same diameter as the previous section.

Longer wells can reach oil and gas that may have otherwise been too expensive or difficult to recover. The tubulars use fewer materials and costs than other solutions and deep wells can be drilled with a smaller diameter in the upper sections

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