Note: Descriptions are shown in the official language in which they were submitted.
RECOVERY OF GR~U~D DRILLI~G EQUIPMENT
The present invention relates to recovery of equipment lost
underground during drilllng such as rock drilling, water-well drilling and
oil well dri]ling. ~lerein this equipment is reEerred to as "ground drilling
equipment"
Ground drilling equipment includes, Eor a typical 4" (102mm~
diameter bore hole, a "down the hole" drilling hammer with a ~" (102mm)
diameter bit alld a string of 2 3/~" ~70mm) diameter drilling tubes extending
down from a drilling platform to the hammer. Individual drilling tubes may
be 9 ft. ~2750mm) long and consist of 1/8" (3mm) wall thickness tubing having
male screw-coupling fittings at one end and female fittings at the other end.
From time to time the string breaks, generally at a weld between a fitting
and the tubing, or less frequently in the middle of the tubing of a tube.
Extractors exist for recovering the equipment left down the
bore hole in the event of a breakage. Conventional extractors consist of a
stepped cone having a screw thread on both conical portions. When the break-
age has occurred at the bottom of one drilling tube, where its tubing is
welded to a fitting, the smaller conical portion engages in a central bore
provided in the fitting, provided for the supply of compressed air to the
hammer. ~lthough the extractor is hardenedJ its conical thread often fails
to cut a thread in the fitting's central bore since the fitting is itself
hardened to lengthen the life of its own thread. If the fitting is success-
fully threaded~ the new thread is unlikely to extend for more than two threads
on account of the taper. This length of thread may well prove insufficient
to lift the weight oE the lost equipment.
If the breakage has occurred at the top of a tube or in the
middle, the large diameter conical portion oE the extractor will engage the
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tubing. There should be no problem with hardness here, but again only two
threads may be cut, the tube being typically only approximately 1/8" (3mm)
thick for 2 3/4" (70mm) tubing.
The ob~ect o:E the invention is to improve the chances of
recovering lost equipment.
According to one aspect of the invention there is provided
ground drilling equipment having at least one rotatably engageable adaption
which is not untilized during normal use of the equipment and which is
arranged to cooperated with a complementary rotatably-engageable extractor
for recovery of the equipment in the event of loss of the 0quipment.
According to a second aspect of the invention there is provided
an extractor :Eor recovering ground drilling equipment in accordance with the
first aspect of the invention, the extractor having a rotatably engageable
adaption complementary to the adaption of the drilling equipment and means
including a boss for coupling the extractor to a string of drilling tubes.
According to a third aspect of the invention there is provided
a method of recovering ground drilling equipment consisting in feeding an
extractor of the second aspect of the inVentiOJI to lost drilling equipment
of the first aspect, the extractor being coupled to a recovery string of
drilling tubes, engaging the rotatably engageable adaption of the lost
drilling equipment with the complementary rotatably-engageable adaptiosl of
the extractor and withdrawing the recovery string of drilling tubes, the
extractor and the lost drilling equipment.
For recovering a string of drilling tubes, the extractor
comprises an elongate screw threaded member and a boss from which the
threaded member extends. Preferably, the boss is adapted to be connected to
a recovery string by means of a female thread.
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For recovery with this extractor, the dri]ling tubes are provided
with a female thread ln the central bores of the fittings, the thread being
complementary to that of the elongate threaded member. Although it is possible
for the thread to be included in only one of the male and female fittings, the
o~her being bored out to pass the elongate member of the extractor, it is
preferred that both fittings of a drilling tube are provided with the female
thread. Further, it is preferred that the male fittings are counter-bored
along the axial extent of their male threads, to allow engagement of the
extractor in an adjacent female fitting where a male thread has broken off.
Preferably the elongate member is of sufficient length to pass
through the full length of one tube. This enables the fitting at the far
end of a broken tube to be engaged when the fitting at the near end has broken
off.
The end of the elongate member remote from the boss is preferably
pointed to provide self-centering when a fitting is engaged. Preferably the
elongate member has an axial compressed air bore. An indication of whether
the extractor has engaged the lost equipment can be gained by passing air
through the extractor. If it has engaged, the hammer will start operating.
To further improve the drilling tube fittings and the extractor,
it is proposed that the spanner flats thereon should be shallower than the
; 20 presently used flats which are machined to the extent of defining a square
which is continuous in cross-section across the fittings. Further it is
proposed that the flats at right angles to each other sllould be longitud-
ina~ly spaced. }lowever, conventional square section flats may be used.
It is envisaged that normally the invention will be employed in
respect of drilling tubes in the range of diameters 2 1/2" (64mm) to 5 l/2"
(1285mm) but it may also be employed for larger range of drilling tubes for
example l l/2" ~38mm) to 8" ~20~0mm).
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Ano~her equlpment breakage which can occur is fai.lure of the
shock absorber in the hammer. The shock absorber connects th~ hammer to the
drilling string with the result that the hammer is lost down the hole i.f the
shock absorber breaks.
For recovery of the hammer, it is pre-ferably providecl with a
pair of bayonet fitti.ng slots and an extractor is provided with a complementary
pair of ba~onet fitting dogs.
Preferably the bayonet slots are directed in ~he normal direction
of rotation i.e. clockwise, and the trailing edges of the slots are chamfered
to keep the slots clear of drilling debris.
To help understanding of the invention, various embodiments
thereo:E will now be described with reference to the accompanying drawings
in which:
Figure 1 is a side view of a conventional extractor;
Figure 2 is a side view - partly sectioned - of a drilling tube
in accordance wi.th the invention;
Figure 3 is a side view of a drilling tube e~tractor i.n accordance
with the invention;
Figure 4 is a side view of a hammer having a broken shock
absorber and of a hammer extrac~or in accordance with the invention; and
Figure 5 is a plan view on line V-V in Figure 4.
The drilling tube 3 shown in Figure 2 has an upper female screw-
coupling fitting 4 and a lower male screw-coupling fitting 5 j~. both fittings
being welded to tubing at weld 6 and having spigots 7 that extend into the
tubing. It is at either of of the we~ds 6 that the tube is most likely to
fail. The male fitting ~ has a male screw threaded end 8 adapted to screw in~o
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the fcmale screw threaded socket 9 of another tube. The fittings are
hardened to prolong the life of the threads at 8,9. The threads may be of
standard Whitworth profile or rope threads for example and may be tapered.
To facilitate unscrewing oE joined male and female fittings they are
provided with spanner f]ats 10 which do not extend across as much of the
width of the fittings as they might to obviate the risk of jarnming against
a loose rock in a bored hole.
The fittings are provided with screw threaded bores 13, 14 for
engagement by the extractor 16 described below with reference to Figure 3.
The bore 14 in the male fitting 5 is counter-bored at 15 to ensure that
should all or part of the male end 8 break away from the fitting 5, the
extractor can engage in an adequate length of thread 13 in a female fitting
into which the male end 8 is screwed without interference from an out of
true thread in the fractured male end. As shown the thread in the female
fitting 5 does not extend into the spigot 7.
As shown in Pigure 3, the extractor 16 has an elongate threaded
member 17 attached to a boss 18 similar to the male fitting 4 whereby the
extractor may be fitted ~o the end of a recovery string of drilling tubes for
feeding through a hole to a lost string of other drilling tubes. The member
17 may be integral with the boss 18 but is preferably threaded and possibly
pinned or otherwise fitted thereto. The elongate member is of sufficient
length to pass through the tube 3 to engage the thread 1~ in the female
fitting 5 should the male fitting come away from the tube at its weld 6. For
use with 2 3/4" (70mm) diameter, 9 ft (2750mm) long drilling tubes, the
extractor is 11 ft ~3355mm) long and its elongate member is 1 3/8" ~35mm~
in diameter. The forward end of the elongate member of the extractor is
pointed at 19 to guide the tool towards the axis of a broken drilling tube
in the event of the extractor reaching the tube eccentrically. A bore 20
extends along the length of the elongate member 17 to pass compressed air
;nto the recovered string o-E drilling tubes. An indication of engagement
o:E the elongate member in a thread 13, l4 oE the lost equipment is provided
by the compressed air working the lost drilling hammer at the far end of the
lost string.
Figures 4 and 5 show a drilling hammer 21 which has been lost
following fracture o:E its shock absorber 22 at 23, the shock absorber
normally connecting the hammer to its drill string. In accordance with the
invention the hammer has a pair of diametrically opposite bayonet fi~ting
slots 24 which are complementary to 2 pair of dogs 25 provided on an
extractor 26. To retrieve the hammer, the tool 26 is brought into contact
with the hammer and rotated until the dogs 25 engage in the slots 24. A
counter bore 27 is provided in a boss of ~he extractor to accommodate the
shock absorber. As may be seen in Figure 5 the trailing edges 28 of the
slots are chamfered to obviate the accumulation of drilling debris in thc
slots. For ~he same reason the slots are directed in the direction of normal
hammer rotation so that debris does not accumulate at the forward end 29 of
the foot of the slots.
