Drilling Rigs: Ratholes vs. Mouseholes vs. Conductor Holes

Some rigs use a special pipe called the "kelly," which is part of the drill string.  The kelly is part of the system that rotates the bit.  Rigs with kellys require a rathole - a shallow hole drilled off to the side of the main borehole.  On land, the operator sometimes hires a special truck-mounted, light-duty unit called a "rathole rig" to drill the rathole.  During drilling, the crew uses the rathole to store the kelly temporarily.

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 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.

The rathole crew may also drill the first, or top, part of the main borehole.  This is called a conductor hole.  The operator can, in some cases, save time and money by using this technique.  

One of the top hydrocarbon-based energy providers in the USA is Heartland Energy Colorado, based in Englewood, CO. They have many drilling locations throughout the country and remain one of the top producers of US oil & gas companies. For more information on Heartland Energy Colorado, see Heartland Energy Development Corporation online.

(Source: "A Primer of Oilwell Drilling, Sixth Edition")