Conductor casing is required only where surface soils are relatively incompetent, and in areas of soft sand formations it can be set down to 1500 ft. The conductor pipe is used to secure the blowout preventers and wellhead equipment before drilling the surface casing hole.
Conductor pipe is also used to a) seal off shallow freshwater zones from drilling mud, b) to supply a route for drilling fluids to circulate back to the mud pits. c) to protect against shallow gas zones, and d) to prevent washout of unconsolidated sediments a well cave-in. A conductor pipe can be drilled into the seafloor from a semisubmersible or drillship. On a jackup rig, the conductor pipe extends from the cellar deck to about 200 ft below the mudline.