The purpose of Stove pipe, marine conductor or foundation pile is to:
- protect the incompetent surface soils from erosion by the drilling fluid.
- reduce the wave and current loads imposed on the inner strings.
- may be used to install a full mud circulation system.
- guide the drillstring and subsequent casing into the hole.
Various names can be given:
- Stove Pipe: Onshore drilling.
- Marine Conductor: Offshore drilling with surface BOPs.
- Foundation Pile: Offshore drilling with subsea BOPs.
Stove pipe
Stove pipes and marine conductors are either driven, drilled/driven or cemented in a pre-drilled hole to provide a circulation system for the drilling fluid.
The stove pipe often carries the subsequent conductor casing. Once the conductor string is cemented the stove pipe is released from this axial load and therefore, subsequent casing strings will hang on the conductor casing string.
Marine Conductor
Marine conductors are used offshore when the BOP is above the water. They provide structural strength, to cover soft formations below the sea bed, to serve as a mud circulation system and to guide the strings into the hole. The marine conductor is driven, drilled and driven or cemented in a pre-drilled hole.
Marine conductors are sometimes part of the piling system for a wellhead jacket or piled platform and are therefore often designed by the structural engineers. They provide centralisation for the inner casing strings against column buckling, but do not carry direct axial loads except during initial installation of the conductor string.
The marine conductors reduce the wave and current loads on the inner casing and provide sacrificial protection against oxygen corrosion in the splash zone. On gravity structures, they are also required to minimise the transfer to the inner casings of stresses resulting from platform settlement and rotational movement of the platform.
Foundation pile
Foundation piles are used offshore when the BOP stack is on the sea floor. They provide a mud circulation system and a guidefor the subsequent strings into the hole.
Foundation piles are usually either jetted into place or cemented in a pre-drilled hole. If no Temporary Guide Base is used, they support the Main Guide Base which carries and aligns all future wellhead components, BOPs, Xmas tree and casing/tubing strings for both the drilling and production phases. If a Temporary Base Guide is used, the foundation pile is landed in tension. The foundation pile directly carries both the axial and bending loads imposed on the wellhead by the environment via marine riser and BOP.