Combination String

A casing that has joints of various collapse resistance, internal yield strength and tensile strength designed for various depths in a specific well to best withstand the conditions of that well. In deep wells, high tensile strength is required in the top casing joints to carry the load , whereas high collapse resistance and internal yield strength are needed for the bottom joints. The in the middle of the casing, average qualities are usually sufficient. The most suitable combination of types and weights of pipe helps to ensure efficient production at a minimum cost.

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