Conductor Pipe
The outermost casing string is the conductor pipe. The main purpose of this casing is to hold back the unconsolidated surface formations and prevent them from falling into the hole. The conductor pipe is cemented back to the surface and it is either used to support subsequent casings and wellhead equipment or the pipe is cut off at the surface after setting the surface casing. Where shallow water or gas flow is expected, the conductor pipe is fitted with a diverter system above the flowline outlet. This device permits the diversion of drilling fluid or gas flow away from the rig in the event of a surface blowout. The conductor pipe is not shut-in in the event of fluid or gas flow, because it is not set in deep enough to provide any holding force.
The conductor pipe, which varies in length from 40 to 500 ft onshore and up to
1,0 ft offshore, is 7 to 20 in. in diameter. Generally, a 16-in. pipe is used in shallow wells and a 20-in. in deep wells. On offshore platforms, conductor pipe is usually 20 in. in diameter and is cemented across its entire length.