Page 145 - 4714

Cellar

The operator may make additional preparations before moving
in the rig. The terrain, the well’s depth, the underground pressures
expected, and the operator's and contractor's preferences determine
how they start the well. At land sites where the operator has ordered a
deep, high-pressure well, for example, a work crew, using dirt moving
equipment, may dig a rectangular pit, or cellar. Sizes vary, but a typical
cellar is about 10 feet (3 metres) on a side and perhaps 10 feet (3
metres) deep. The exact size and depth depend on the characteristics
of the well and the rig's configuration.
Sometimes, the workers line the cellar with boards or pour
concrete walls to keep it from caving in. The cellar accommodates a
tall stack of high-pressure control valves under the rig. The bottom of
the stack will sit in the cellar, below ground level. Since the crew
installs the stack below ground level, the rig’s substructure – the base of
the rig – does not have to be as tall to allow the rig floor to clear the
stack. In short, a cellar provides more working room under the rig.
Rathole
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. Or, after the rig is set up (rigged up), the drilling crew may drill
the rathole with special equipment. Offshore, if the rig needs a rathole,
it is a large-diameter length of pipe that extends below the rig floor. In
the case of drilled ratholes, the crew extends pipe from the drilled part
of the rathole up to the rig floor. The rathole goes through the rig floor
and protrudes a few feet, or a half metre or so, above it.
During drilling, the crew uses the rathole to store the kelly
temporarily. A kelly can be up to 54 feet, or 17 metres, long. Even the

144