Page 65 - Drilling Technology in Nontechnical Language

56 Drilling Technology in Nontechnical Language Second Edition

The drillers measure the distance from the drill floor down to the top
of the conductor pipe. Depths in the well while drilling are referenced back

to the drill floor, so the conductor shoe depth = length of conductor in the

ground + distance from drill floor to the top of the conductor.
The derrick has several large sheaves at the top end. Steel wire rope,
called block line, passes over these sheaves and around another set of
sheaves on a massive pulley. By winching in or out on the block line with
an electrically powered drum, the pulley—called the traveling block—
moves up and down the derrick. Below the traveling block is a large steel
hook that can lift whole strings of casing pipe, support the drill string
while drilling, and perform many other tasks. A large land rig would
probably be strong enough for the traveling block to support up to 500
tons (508 tonnes), using block line of commonly 1⅝″ (495 mm) diameter
with a tensile strength of over 100 tons (101 tonnes). (Block line may vary
in size from 1″ [25 mm] to 1¾″ [44 mm] diameter.)
With the rig ready to start operating, the diverter must be attached
to the conductor, which was hammered into position by the location

preparation crew (fig. 3–11). The diverter contains a large rubber seal that
is forced under hydraulic pressure to squeeze in around the drillstring and
seal around it. Underneath this seal are usually two large pipes, at least 10″
in diameter, which should lead away from the rig in opposite directions
with no bends or changes in internal size. Occasionally only one line
will be fitted, leading off downwind of the prevailing wind. If a kick is

experienced while drilling below the conductor pipe, the flow is diverted
away from the rig by closing the diverter and opening the valve on the pipe
leading downwind.

On top of the diverter is a section of pipe (called a bell nipple) that has
an outlet to the side. This side outlet directs mud flow from the rig along

a channel to the solids control equipment and then back to the mud tanks,
from where the pumps circulate it back down the hole.
The space between the inside of the well and the outside of the

drillstring is called the annulus. Mud coming out of the bit flows upwards
in this annulus, lifting drilled cuttings to the surface. It comes out of the

flowline outlet (as shown on fig. 3–11) and is directed to equipment that

separates the drilled solids and the mud, so that clean mud can be pumped
back down the hole.

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