Tubing String

a device made up of pipes that is lowered into a borehole for the extraction of liquid and gaseous minerals. Tubing strings consisting of separate tubing joints screwed together are used for the exploitation of petroleum and gas deposits. The tubing string is suspended at the wellhead by means of a casing head. There is usually one tubing string of constant or variable diameter in a well; multiple wells have two or more parallel tubing strings for simultaneous or separate production from two or more pay zones through the same well.

A tubing string consisting of several strings of pipes lowered in concentric rows is used for compressor-lift petroleum production. The length of a tubing string depends on the strength of the piping materials. In deep wells the tubing string may reach depths of 5,000–6,000 m (USA, 1969).