Note: Descriptions are shown in the official language in which they were submitted.
CA 02405261 2002-09-25
1 "HOLE-OPENER FOR ENLARGING PILOT HOLE"
2 FIELD OF THE INVENTION
3 The present invention relates to a hole-opener for enlarging the diameter of
an
4 underground pilot hole. More particularly it relates to a hole-opener that
can easily be
disassembled to replace the rotary cutting elements.
6
7 BACKGROUND OF THE INVENTION
8 In connection with laying cables or installing a flowline it is periodically
9 necessary to bore a generally horizontal, underground borehole extending
between
one surface location and another. This might be done, for example, to provide
a
11 borehole at a crossing beneath a river.
12 In such an operation, a relatively small diameter pilot hole is drilled by
a rig.
13 This is done using a string of drill pipe having, at the drilling end, a
fluid-driven
14 motor rotating a drill bit. Once the pilot hole is formed, the bit is
replaced with a tool
referred to as a hole-opener The drill string is then rotated and pulled to
draw the
16 hole-opener back along the pilot hole to enlarge its diameter. This
procedure may be
17 repeated more than once with progressively larger hole-openers, to
gradually increase
18 the pilot tube diameter to achieve a borehole of the desired size.
19 A typical prior art hole-opener is shown in Figure 1. It comprises:
~ a one-piece tubular body forming a through bore and having threaded
21 connections at the front and rear ends of the tool;
22 ~ 'arms' or bars are welded or bolted to the exterior surface of the body -
23 they extend longitudinally thereof in parallel, circumferentially spaced
24 apart relationship;
{ ET076988. DOC;1 )
CA 02405261 2002-09-25
2
1 ~ each arm has at its front end a rotary cutting element, such as a toothed
2 cone mounted on a support pin extending between the arm and the body;
3 ~ jet ports are provided, extending through the side wall of the body at the
4 cones, for jetting drilling fluid into the annulus formed between the tool
and drill string and the pilot hole wall to clean the cones and remove drill
6 cuttings; and
7 ~ a threaded plug is provided for closing the through bore at the body's
rear
8 end.
9 There are shortcomings associated with these commonly used tools. These
shortcomings appear to have simply been tolerated for many years without a
useful
11 remedy, as far as I am aware.
12 More particularly, the cones wear out in use and need to be removed and
13 replaced. However, it is not practical to make this change-out in the field
with the
14 prior art solid tools.
In addition, it is therefore necessary to maintain at the site an inventory of
16 complete tools having progressively larger diameters, if the pilot hole is
to be
17 enlarged in stages.
18 It is the objective of the present invention to provide a tool or hole-
opener
19 which is improved with respect to these shortcomings.
( ET076988. DOC;1 ~
CA 02405261 2002-09-25
3
1 SUMMARY OF THE INVENTION
2 In accordance with the invention, a hole-opener is provided which
3 incorporates a removable sleeve mounted on a tubular body (referred to as a
drive
4 sub). Arms and cutting elements are affixed to the sleeve. Means are
provided for
locking the drive sub and sleeve together so that they rotate as a unit. Means
are also
6 provided for locking the sleeve axially in a pre-determined position on the
drive sub.
7 And finally, means are provided for transmitting the pulling force of the
drill string
8 and attached drive sub to the sleeve and its cutting elements.
9 In one preferred embodiment, the hole-opener has front and rear ends and
comprises:
11 ~ a tubular drive sub having a longitudinal bore and threaded connections
at
12 each end, more preferably a box at the front end and a pin at the second
13 end;
14 ~ a tubular sleeve which slides onto the rear end of the drive sub. The
sleeve
has a plurality of radially protruding arms attached to its front end surface
16 at spaced positions about its circumference. A cutting element, preferably
17 a toothed cone, is rotatably mounted to the front end of each arm;
18 ~ means for engaging the drive sub and sleeve so that they rotate together.
19 More preferably such means comprise outwardly protruding,
circumferentially spaced apart stabilizer bars affixed to the external
21 surface of the drive sub and extending longitudinally thereof. These
22 stabilizer bars engage corresponding slots formed in the front end of the
23 sleeve. The bars and slot walls combine to transfer rotational force from
24 the drive sub to the sleeve. The bars also function as a stop, to limit the
ET076988.DOC:I )
CA 02405261 2002-09-25
4
1 axial travel of the sleeve along the drive sub and lock the tatter's front
end
2 at a pre-determined position; and
3 ~ a retainer sub, which has a threaded connection at its front end for
4 engaging the rear connection of the drive sub. The retainer sub also has a
radial shoulder which abuts the rear end face of the sleeve and locks the
6 sleeve at its rear in the pre-determined position. The retainer sub also
7 functions to transmit the axial pull force from the drill string and drive
sub
8 to the sleeve and its cutting elements;
9 ~ the drive sub forming ports extending through its side wall which, when
the tool has been assembled, are positioned adjacent the cutting elements
11 and serve to jet drilling fluid so as to clean the cones and remove
cuttings
12 through the annulus.
13 Broadly stated, the invention is concerned with a hole-opener for enlarging
the
14 diameter of a pilot hole, the hole-opener having front and rear ends and
comprising: a
tubular drive sub having an external surface, a longitudinal bore and threaded
16 connections at its front and rear ends; a tubular sleeve for sliding
axially over the rear
17 end of the drive sub; means for locking the sleeve and drive sub together
for rotation
18 as a unit; means, carned by the drive sub, for engaging the front end of
the sleeve to
19 stop its axial movement along the drive sub at a pre-determined position; a
retainer
sub for threadably engaging the rear end connection of the drive sub and
bearing
21 against the rear end of the sleeve to lock the sleeve in the pre-determined
position; the
22 sleeve carrying at least one rotary cutting element assembly at its front
end; the drive
23 sub forming ports for jetting drilling fluid contiguous to the cutting
elements when the
24 sleeve is locked in the pre-determined position.
(ET076988.DOC:1 E
CA 02405261 2002-09-25
1 DESCRIPTION OF THE DRAWINGS
2 Figure 1 is a perspective sectional side view of a hole-opener in accordance
3 with the prior art;
4 Figure 2 is a partly sectional side view of an assembled hole-opener in
5 accordance with the present invention;
6 Figure 3 is a sectional side view of the drive sub;
7 Figure 4 is a sectional side view of the retainer sub; and
8 Figure 5 is a sectional side view of the sleeve showing a slot, the arms and
9 rotary cones.
11 DESCRIPTION OF THE PREFERRED EMBODIMENT
12 The tool or hole-opener 1 comprises a drive sub 2, a sleeve 3 and a
retainer
13 sub 4
14 'Subs' are used because they are heavy steel tubulars equipped with
threaded
pins and boxes adapted to connect with the connections of drill pipe commonly
used
16 in this service. The subs are adapted to be 'made up' and 'broken' by the
rig
17 equipment. However the subs have been modified in certain respects, as
described
18 below, to prepare them for use in this tool.
19 More particularly, the drive sub 2 has a box connection 5 at its front end
6 and
a pin connection 7 at its rear end 8. Stabilizer bars 9 are welded to the
drive sub's
21 external surface 10. These stabilizer bars 9 extend longitudinally of the
drive sub 2 at
22 spaced positions around its circumference. The stabilizer bars 9 are
designed to
23 centralize the tool in the pilot hole (not shown). They also function to
act as stops
24 limiting axial advance of the sleeve 3 along the drive sub 2 and as part of
the rotary
f ET076988.DpC:I }
CA 02405261 2002-09-25
6
1 drive connection between the drive sub 2 and sleeve 3. The drive sub side
wall 11
2 also forms ports I2, between the stabilizer bars 9, for jetting drilling
fluid into the
3 annulus formed between the tool and the borehole wall.
4 The sleeve 3 is formed with slots 13 in its forward end 14, for receiving
the
stabilizer bars 9. The side walls 15 of the slots 13 and the bars 9 combine to
lock the
6 sleeve 3 and drive sub 2 together for rotation as a unit. The sleeve 3 also
carnes a
7 plurality of outwardly protruding arms 16 affixed to the front end of the
sleeve's outer
8 surface I7. The arms I6 extend longitudinally of the sleeve 3 in spaced
apart
9 arrangement. Each arm 16 carnes a rotatably mounted, toothed cone 18 at its
front
end 19. The cones 18 are positioned adjacent the jet ports 12.
11 The retainer sub 4 has a box connection 20 at its front end, sized to be
slidably
12 received in the rear end of the bore 21 of the sleeve 3. The box connection
20 is
13 connected with the pin connection 7 of the drive sub 2. The retainer sub 4
also has a
14 radial shoulder 22 which abuts the rear end face 23 of the sleeve 2 when
the tool is
assembled. The retainer sub 4, being threadably engaged with the drive sub 2,
16 therefore functions to transmit axial pull from the drill string 24 to the
sleeve 3 and its
17 rotary cones 18. In addition, the retainer sub shoulder 22 combines with
the stabilizer
18 bars 9 to lock the sleeve 3 in a pre-determined position with the cones 18
positioned
19 opposite the jet ports 12.
A plug sub 25 is threaded onto the rear pin connection 26 of the retainer sub
4,
21 to close off its bore 27.
22 The resultant tool can be disassembled by backing off and removing the
23 retainer sub 4 and removing and replacing the sleeve 3. This is done when
the cones
24 18 are worn or are to be replaced to cut a larger diameter borehole.
~ ET076988.DOC:1 }
CA 02405261 2002-09-25
7
1 It is contemplated that variants of the described tool can be implemented by
2 those skilled in the art without changing the substance of the tool. For
example,
3 splines can be used to lock the drive sub and sleeve for rotation together.
In addition,
4 the tubular retainer sub can be replaced with a plug - the term 'retainer
sub' is
intended to be interpreted to include a plug.
~ ET076988. DOC; I E
