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Mousehole

The rathole rig or the main rig itself may also drill a mousehole
on land sites. A mousehole, like a rathole, is also a shallow hole lined
with pipe that extends to the rig floor. The mousehole is a lined hole
into which the crew puts a length, or joint, of drill pipe during drilling
operations. When crew members are ready to add the joint to the drill
string as the hole deepens, they add it from the mousehole. A joint of
drill pipe is around 3o feet (9 metres) long. If the regular rig’s
substructure is appreciably shorter than this height, then the rathole
crew also drills a mousehole.
Conductor Hole

The rathole crew may also drill the first, or top, part of the
main borehole. The operator can, in some cases, save time and money
by having the rathole rig actually start, or spud, the main hole before
moving in the regular rig. The rathole crew backs the rathole rig to the
cellar. A special bit starts the main hole in the middle of the cellar.
This hole is shallow in depth but large in diameter. Termed conductor
hole, it may be 36 inches (91 centimetres) or more in diameter. It may
be only tens of feet (or metres) deep or it may be hundreds of feet (or
metres) deep, depending on the surface conditions.
The rathole crew lines the conductor hole in the cellar with
conductor pipe. Conductor pipe, or casing, keeps the hole from caving
in. It also conducts drilling mud back to the surface when regular
drilling begins. The crew often secures the conductor pipe in the hole
with cement or concrete. With the conductor pipe, rathole, and
mousehole prepared, the drilling contractor can move in the rotary rig
to drill the rest of the hole.
Other Considerations
On drilling locations where the ground is soft, a rathole rig and
crew may not be needed. Instead, the contractor can usually move in

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