4. Monitor the pulldown and top-head drive
spindle rotation pressure gauges to avoid overthrust and
monitor the air line pressure to avoid a plugged bit.
5. When the drill hole is complete, shut down the
air and repressurize before “tripping out” the hole.
Down-Hole-Drilling (DHD) (fig. 9-4):
1. Use the percussion button bit.
2. Use the holdback regulator to control feed
forces.
3. Switch on the DHD line oiler before operating
the DHD. (A air line lubrication system injects a
determined rate of oil into the flushing hose to lubricate
the DHD hammer when air hammer drilling.)
4. Use the DHD line oiler regulator to adjust the oil
flow and check the oil flow by placing a piece of
cardboard under the spindle sub and inspect the pattern.
5. Monitor the DHD frequency and cuttings to
determine proper feed force.
Setting Casing:
1. Retract the top-head drive and unpin and swing
out the forward centralizer.
2. Replace the centralizer bushing with casing
clamps.
3. Install the choker sling on the first casing, and
hoist the casing above the drilled hole.
4. Lower the casing into the hole until the top is
about 1 foot above the worktable.
5. Close the centralizer and pin it shut.
6. Remove the choker sling and attach it to the next
casing. Hoist the second casing above the first.
7. If the casing is plastic, install the collar and
cement joint. If weld type, join shoulders and weld. And
if thread type, clean threads and dope and tighten with
a chain wrench or breakout wrench.
8. Set the screen and rest of casing.
9. Unpin and swing out centralizer.
10. Gravel pack and grout as to the construction
specifications.
DRILLING DIFFICULTIES
Lost circulation is one difficulty you may encounter
when drilling. Sometimes it occurs in zones of high
porosity that usually contain large supplies of water. A
test of the well should be made whenever circulation is
lost. Formations that draw off or absorb all or part of the
circulating fluid offer problems, ranging from minor
inconveniences and loss of time to extreme conditions
that render rotary drilling impossible.
Formations that contain joints and fissures, such as
quartzite, sandstone, limestone, and dolomite, present
problems arising from caving, abrasion, and complete
loss of circulation.
Shale that is jointed and fissured seldom draws off
an excessive amount of circulating mud; however,
drilling fluid that is absorbed causes the shale to swell
and heave, filling up the drill hole. This has been
overcome by the use of special drilling fluids. ‘This
condition is rare, and satisfactory drilling progress can
usually be made by using a drilling fluid of high
viscosity and weight.
Sands and gravel often absorb enough drilling fluid
to hinder drilling progress. Fluid loss, which, in most
cases, will be continuous, should be replaced with mud,
not water. Water, when used to maintain sufficient
volume for circulation, soon lowers the viscosity and
weight of the mud-water mixture, and caving results.
Two methods are used to regain lost circulation. The
preferred method is to drill through the zone of lost
circulation and to set a string of conductor casings
below the porous zone. The chief requirement for this
procedure is a plentiful supply of water to circulate the
cuttings away from the bit and into the formation. Mud
is desirable but the quantity needed usually precludes its
use. When using water to carry off the drill cuttings,
always remember to continue to operate the pump for a
few minutes after drilling has stopped. This flushes the
cuttings out of the hole and prevents the drill pipe from
sticking when it is stopped to make a connection. In
extreme cases where it is necessary to drill as much as
100 feet or more through a formation in which
circulation is lost, a small quantity of mud is spotted
around and above the bit while an additional joint of pipe
is installed in the drilling string. This prevents excessive
settling of the drill cuttings and consequent sticking
while the drill pipe is standing. When the bottom of the
zone has been reached, drilling is continued into the
underlying formation for about 50 feet to give room for
cementing the casing. When the casing has been run and
cemented, the ordinary rotary drilling procedure is
resumed.
In the second method, circulation can usually be
regained by mixing a clay-type material with the drilling
fluid that can be bought commercially. The water well
9-13
