A conductor pipe is a relatively short, large-diameter pipe driven into the ground prior to the drilling of bore holes or oil wells. Also known as a drive pipe, this section of tubing serves to support the initial sedimentary part of the well, preventing the looser surface layer from caving in and obstructing the wellbore. The pipe also serves several other purposes, such as protection of water carrying sands and returning cuttings from the drill head. A conductor pipe is most commonly used in this role in onshore wells, although it is often employed for similar reasons when sinking offshore wells. Conductor pipes are usually installed using drilling, pile driving, or a combination of these techniques.
The surface section of any well or borehole is particularly prone to cave-in failures, as the initial strata that the wellbore passes through are typically made up of unconsolidated sedimentary material. Collapse of the top section of the well not only causes protracted periods of down time, but also poses a significant safety hazard. To prevent the collapse of this unstable layer, a short, large-diameter conductor pipe is driven through the sedimentary layer to support the wellbore during drilling. These pipes are used in both onshore and offshore wells, with onshore projects being the more common application. In the case of submarine wells, the conductor pipe may also be used as a foundation for the wellhead.
The installation of a conductor pipe also serves several other secondary purposes apart from supporting the well. It serves to seal off fresh water zones from the ingress of drilling and well fluids. Drill cuttings suspended in drilling mud are also removed via the conductor pipe, while the pipe lends protection and support for the surface casing, which is the next series of outer pipes in the well structure. In addition to these benefits, the pipe also prevents washouts of loose material below the drilling rig during sinking operations.
In most cases, the conductor pipe is installed in one of three ways. The pipe can be run into a hole drilled by an auger drill and then cemented into place, or the second method is pile driving, which sees the pipe driven into the ground by repetitive blows from a heavy pneumatic or diesel hammer known as a pile driver. The third method is a combination of the previous two procedures and is used where pile driving fails to drive the conductor pipe to the correct depth. In this case, the pipe is driven in to the point where it refuses to go any further, the hole is then extended a short distance by drilling, and the pipe driven in again until refusal. This process is repeated until the pipe reaches the correct depth.