U.S. patent number 3,575,245 [Application Number 04/796,778] was granted by the patent office on 1971-04-20 for apparatus for expanding holes.
This patent grant is currently assigned to The Servco Company. Invention is credited to Paul J. Arnerich, Bruce J. Cordary.
United States Patent |
3,575,245 |
Cordary , et al. |
April 20, 1971 |
APPARATUS FOR EXPANDING HOLES
Abstract
A hole expander for use in conjunction with well bore drill
strings which has a tool body defining a cylinder, an axially
movable piston disposed in the cylinder, and a skirt portion
secured to the piston. A plurality of radially arranged arms have
one end secured to the tool body and another end adapted to receive
cutting tools such as rotary cone cutters or abrasive cutters that
are pivotal about axes transverse to an axis of the cylinder and
are movable in an axial direction over a predetermined distance.
Sides of the arms adjacent the skirt portion have a configuration
to engage the skirt portion. When the piston moves axially in
response to pressure being applied to the cylinder, the arms pivot
outwardly relative to the axis of the cylinders. An intermediate
skirt engaging surface of the sides of the arms is angularly
inclined relative to the axis of the cylinder and engages an end of
the skirt portion. When the arms are farthest removed from the
cylinder in an axial direction the intermediate skirt-engaging
surfaces of the arms are disposed adjacent the free ends of the
skirt portion of the cylinder and bias the skirt portion, together
with the piston, in a direction towards the cylinder. When the
cylinder is fully extended a skirt-engaging surface of the arms
engages a periphery of the skirt and locks the arms in an outwardly
projecting position.
Inventors: |
Cordary; Bruce J. (Los
Alamitos, CA), Arnerich; Paul J. (Fountain Valley, CA) |
Assignee: |
The Servco Company (Long Beach,
CA)
|
Family
ID: |
25169037 |
Appl.
No.: |
04/796,778 |
Filed: |
February 5, 1969 |
Current U.S.
Class: |
175/268 |
Current CPC
Class: |
E21B
10/345 (20130101) |
Current International
Class: |
E21B
10/26 (20060101); E21B 10/34 (20060101); E21b
043/16 () |
Field of
Search: |
;175/263,267,168 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Brown; David H.
Claims
We claim:
1. Apparatus for enlarging the diameter of subsurface holes
comprising:
a tool body adapted to be secured to a drill string;
walls defining a bore in the tool body having an open end and
another end in flow communication with a fluid carrying portion of
the drill string;
a piston axially movable in the bore and provided with a skirt
portion;
means for limiting the axial movement of the piston in the
bore;
a plurality of radially spaced arms adapted to mount cutting tools
adjacent one end of the arms for engaging a portion of the hole to
be enlarged and disposed exteriorly of the bore, means for mounting
the arms for free movement parallel to an axis of the bore over a
predetermined distance, and pivotable about axes transverse to the
axis of the bore adjacent another end of the arms proximate to the
piston, means on the arms for engaging the skirt portion when the
piston moves towards the open end of the bore for pivoting the ends
of the arms outwardly relative to the axis of the bore in
opposition to a pivotal force from the weight of the arms and for
biasing the skirt and the piston axially away from the open end of
the bore when the cutting tools are disengaged from a portion of
the subsurface hole; and
stop means for limiting the outward pivotal movement of the
arms.
2. Apparatus according to claim 1 including a member secured to the
tool body and projecting through an axial center bore in the piston
to a region in fluid communication with the exterior of the body, a
fluid passage in the end of the member projecting through the
piston; the member having a sufficient length that the bore in the
tool body fluidly communicates with the exterior of the body when
the arms are fully pivoted outwardly.
3. Apparatus according to claim 1 wherein the tool body includes a
flange adjacent each side of each arm, each pair of flanges
adjacent each arm having aligned slots engaging shaft means secured
to each arm such that the arms are pivotal about axes of said shaft
means and are movable in a direction parallel to the axis of the
bore within the confines of the slot.
4. Apparatus according to claim 3 including at least two
pluralities of arms, ends of each plurality of arms projecting
outwardly from the axis of the hole a distance different from the
other pluralities of arms when the arms are fully pivoted
outwardly.
5. Apparatus for enlarging the diameter of subsurface holes
comprising:
a tool body adapted to be secured to a drill string and including
hydraulic actuating means having an axially extending skirt
portion;
a plurality of radially arranged arms disposed adjacent the skirt
portion and adapted to mount cutting tools adjacent an end of the
arms remote from the actuating means;
means for mounting the arms for pivotal movement about axes
substantially transverse to an axis of the skirt portion, and for
movement parallel to the axis of the skirt portion over a
predetermined distance;
a first skirt engaging surface on each arm for positioning the end
of the arm adjacent the axis of the skirt portion;
a second surface on each arm for engaging a free end of the skirt
portion and pivoting the end of the arm in a direction away from
the axis of the tool body in response to actuation of the actuating
means;
a third skirt engaging portion for positioning the ends of the arms
remote from said axis;
the predetermined distance being sufficient that the second skirt
engaging portion is disposed adjacent the free end of the skirt
portion after the hydraulic means have been actuated and the arms
are at one end of their axial movement;
means for securing the arms to the tool body such that they are
pivotable and axially movable over the predetermined distance;
stop means for limiting the pivotal movement of the arms in a
direction away from the axis of the skirt portion; and
means for limiting the axial movement of the skirt portion in
response to actuation of the actuating means.
6. Apparatus according to claim 5 wherein the means for mounting
the arms includes laterally spaced flanges secured to the tool body
adjacent sides of the arms and shafts connected with the
flanges.
7. Apparatus according to claim 6 wherein the body defines a
cylinder and the actuating means include a piston disposed in the
cylinder and secured to the skirt portion, the cylinder being in
flow communication with a fluid carrying portion of the drill
string and provided with an opening adjacent the piston to fluidly
communicate an interior space of the cylinder with the exterior of
the tool body when the free end of the skirt portion is adjacent
the third engaging surface and the arms moved axially over the
predetermined distance in a direction opposite to a direction the
piston moves when pressure is applied to the interior space.
8. Apparatus for enlarging the diameter of sub-surface holes, the
apparatus comprising:
a. a tool body having:
i. an end flange adapted to secure one end of the tool body to a
drill string;
ii. a cylinder having an axis, the cylinder being adapted to be in
fluid communication with a fluid carrying portion of the drill
string and having one end secured to the flange and another end
open; and
iii. a plurality of pairs of laterally spaced elongated flanges
adjacent a periphery of the cylinder extending axially away from
the end flange;
b. an axially movable piston disposed in the cylinder and including
a skirt portion projecting past the open end;
c. an arm disposed intermediate a pair of flanges having a free end
adapted to mount a cutting tool and another end adjacent the open
end of the cylinder pivotally and axially movably secured to the
flanges, the axial movement being limited to a predetermined
amount, the arms having a first, second and third skirt-engaging
portion progressively engageable by the skirt portion when the
piston moves away from the end flange in response to a fluid
pressure being applied to the cylinder such that the arm is pivoted
outwardly in response to such movements of the skirt portion while
a free end of the skirt portion is in engagement with the second
surface;
d. means for relieving the pressure in the cylinder in response to
a free end of the skirt portion being positioned adjacent the third
engaging surface of the arm and the arm is axially farthest removed
from the end flange;
e. stop means for limiting the pivotal movement of the arm in a
direction away from an axis of the cylinder;
f. means for pivotally and axially movably securing the other end
of the arm to the flanges; and
g. means connected with ends of the flanges remote from the end
flange for connecting another end of the tool body to a drill
string.
9. Apparatus according to claim 8 wherein the means for securing
comprises a shaft disposed intermediate each pair of flanges and
the arm disposed between such flanges, and a slot in each flange,
the shaft being axially movable in the slot to pivotally and
axially movably secure the arm to the pair of flanges.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to rotary well bore tools and more
particularly to rotary well bore tools for enlarging diameters of
intermediate portions of the well bore.
2. State of the Prior Art
In the drilling of wells such as oil wells, portions of the bore
below the surface must often be enlarged for various reasons, such
as to enable the packing of the bore with gravel. Frequently the
upper portions of the bore are provided with steel casing through
which any expanding hole drill apparatus must be lowered. It is
therefore necessary to retract the drilling apparatus to a diameter
less than the diameter of the upper portion of the well bore or the
inner diameter of the well casing. Upon arrival of the hole
enlarging apparatus at the desired depth, it is expanded to the
desired diameter and the enlarging or underreaming operation can
commence.
In the past, underreaming tools of various configurations have been
extensively used. All include pivotal arms which are retracted into
a tool body while the apparatus is being raised or lowered through
the narrow portions of the drill bore and which can be pivoted
outwardly relative to an axis of the apparatus. Because of the
relatively large forces required to expand the drill arms,
hydraulic actuators are usually coupled with the arms by means of
linkages. Alternatively, the arms have been provided with inclined
surfaces which project into a path of the hydraulic actuator and
are engaged by it upon its actuation. This engagement pivotally
forces the arms outwardly to the larger diameter.
Upon termination of the drilling operation, the arms must be
retracted. To enable the retraction, an axial force must be applied
to the piston of the hydraulic actuator to return it to its
original position.
In the prior art, the pistons were returned to their original
position in one of two ways. First, the apparatus was provided with
helical compression springs which acted against the piston and
biased it into an original position against the force to which the
hydraulic pressure subjected it. Upon release of the pressure, the
spring moved the piston axially into its original position. The
second class of underreamers is provided with double-acting pistons
which are subjected to a pressure forcing the pistons into their
original position upon termination of the drilling operation. This
embodiment is frequently employed in conjunction with relatively
large size underreamers.
SUMMARY OF THE INVENTION
The present invention provides apparatus for enlarging subsurface
holes, such as well holes. Briefly, it includes a tool body adapted
to be secured to a drill string and defining a cylindrical bore
having an open end. Another end of the bore is closed and in flow
communication with a fluid carrying portion of the drill string. A
piston is axially movable in the bore and includes a skirt portion
extending past the open end of the bore. Means are provided for
communicating an interior space of the cylinder confined by the
piston with the exterior of the tool body. A plurality of radially
spaced arms are adapted to mount cutting tools adjacent one end of
the arms for engaging a portion of the hole to be enlarged. The
arms are disposed exteriorly of the bore and are freely movable
parallel to an axis of the bore over a predetermined distance.
Furthermore, they are pivotal about an axis transverse to the axis
of the bore adjacent another end of the arms proximate to the
piston. The arms have a configuration to engage the skirt portion
when the piston moves towards the open end of the bore such that
the ends of the arms are pivoted outwardly relative to the axis of
the bore in opposition to a pivotal force from their weight. When
the cutting tools are disengaged from the portion of the hole being
enlarged, they engage an end of the skirt remote from the piston
and bias the skirt and the piston axially away from the open end of
the bore. Stop means limit the outward pivotal movement of the
arms.
Preferably, the tool body includes an elongated flange adjacent
each side of the arms and a shaft for pivotally and axially movably
mounting the arms in a slot of the flanges.
The underreaming apparatus of this invention eliminates the need
for a helical compression spring or a double-acting piston to
return the piston to its original position. Instead, the piston is
biased into its original position by the outwardly extending arms.
The arms include first, second and third skirt-engaging surfaces
which respectively position the arms adjacent the axis of the
cylinder when the piston is in its original position; pivot the
arms outwardly relative to the axis about the shaft; and position
the arms in an extended position so that the ends adapted to
receive the cutting tools are remote from the axis of the cylinder.
The third surface is in engagement with the skirt portion during
the drilling or underreaming operation when an axial force moves
the arms to a position closest to the interior space defined by the
bore. Upon termination of the underreaming, the apparatus is lifted
whereby the arms move axially in an opposing direction away from
the interior space under their weight. This axial movement is
sufficient to place the free end of the skirt portion adjacent the
angularly inclined second skirt-engaging surface of the arms. An
axial component force, resulting from the pivotal bias of the arms
under their own weight about the shaft securing it to the flanges
of the tool body, biases the skirt and the piston in a direction
towards their original position until the arms are positioned
adjacent the axis of the cylinder.
Although an underreamer constructed according to the present
invention can be constructed for underreaming any size hole, it is
particularly well adapted for use in conjunction with large
diameter drill holes which require large underreamed sections. The
relatively heavy arms subject the piston to a large axial force
biasing it towards its original position.
The reduction in the number of parts required to construct the
underreaming apparatus makes it substantially more economical to
manufacture than prior art underreamers. Its simple operating
mechanism assures trouble free operation of the apparatus and
substantially enhances its service life.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a fragmentary elevational view, in section, of a hole
expanding apparatus constructed in accordance with the present
invention and showing arms mounting cutting tools in an expanded
operating position in phantom lines;
FIG. 2 is a fragmentary front elevational view, in section, similar
to FIG. 1 wherein the arms are shown in an intermediary
position;
FIG. 3 is a fragmentary side elevational view of the apparatus
shown in FIG. 1; and
FIG. 4 is an illustration like FIG. 1 of a hole expanding apparatus
having a modified fluid flow path.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Initially referring to FIG. 1, there is shown a well bore 10 (in
phantom lines) and an apparatus 12 for enlarging a portion 14 of
the well bore. The apparatus is secured to a drill string (not
shown) lowered through an upper portion (not shown) of the
bore.
The apparatus 12 is described in conjunction with its application
for enlarging or underreaming intermediate portions of a
subterranean bore such as an oil well bore. However, it is obvious
that this apparatus can be used for cutting and milling tubular
conduits, such as oil well casing, by interchanging cutting tools
secured to the apparatus. The apparatus of the present invention is
therefore not intended to, and is not limited to the underreaming
of subterranean drill holes. Rather it is adapted for use in
conjunction with all rotatory drilling, boring, cutting, milling,
etc. tools which require an apparatus capable of expanding its
working surfaces from a lesser to a greater diameter.
The underreaming apparatus 12 includes a tool body 16 adapted to be
secured to an upper drill string (not shown). It defines a cylinder
18 having an open end 20, an axially movable piston 22 disposed
within the cylinder, and a plurality of pivotally mounted arms 24
and 24'. An end 26 of the arms farthest removed from cylinder 18 is
adapted to receive a conventional cutting tool which may be a
conventional rotary cone cutter 28, a cutter provided with an
abrasive surface (not shown) for cutting through tubular conduits,
or cutter adapted for other applications. The cutting tools are not
further described herein since they do not form a part of this
invention.
In the presently preferred embodiment, the tool body 16 is defined
by a circular end flange 30 which is coaxially secured to the
cylinder 18 and projects past a periphery 32 of the cylinder. A
face 34 of the end flange opposite face 36 adjacent the cylinder,
mounts a tubular member 38 which is provided with a suitable thread
engaging portion (not shown) adjacent its end (not shown) remote
from the end flange for securing the apparatus 12 to a lower end of
a drill string (not shown).
Preferably, a tubular core 40 is secured to face 34 of the end
flange and projects through a hole 42 in the flange past side 36
into a space defined by the cylinder 18. An end of the core remote
from the end flange includes radial projections 44 and a plurality
of relief slots 46 which extend from that end toward the end flange
a distance which is slightly greater than the thickness of the
piston. The core further includes a recessed hole 48 adjacent the
end provided with the radial projections 44 and, disposed in that
hole, an axially-movable generally cone-shaped plug 50 provided
with seal ring 52 on a cylindrical portion of the plug. An upper
end of the plug includes a spearhead 54 connected with a pull cable
56 extending upwardly past the tubular member 38 and the upper
drill string (not shown) to the surface of the bore.
The piston 22 disposed within cylinder 18 has a coaxial center bore
58 engaging a periphery of the tubular core 40. A suitable seal
ring 60 seals an interior space 62 defined by end flange 30,
cylinder 18, and piston 22 from the exterior of the tool body. One
or more holes 63 communicate the interior space with the tubular
member 38. The cylinder includes a preferably annular protrusion 64
adjacent the center bore 58 to space a face 66 of the piston from
face 36 of the end flange 30 when the piston is in an original
position adjacent the end flange. A seal ring 68 is disposed about
a periphery of the piston adjacent walls of cylinder 18 and further
seals the interior space 62 from the exterior of the tool body.
An end of the piston remote from the end flange includes a
preferably cylindrical skirt portion 70 which extends from the
piston past the open end 20 of the cylinder. A free end 72 of the
skirt portion is provided with a taper 74 for purposes to be
described hereinafter.
A pair of laterally-spaced elongated flanges 76 are disposed on
each side of each arm 24 or 24' and are suitably secured to face 36
of the end flange 30 and the periphery 32 of cylinder 18. The
flanges extend from adjacent the end flange past the free end 72 of
the skirt and have opposite ends 78 secured to a disc 80 such that
the pairs of flanges are substantially rigid. The cylindrical disc
suitably connects a tubular protrusion 82 which is coaxial with the
disc and an axis of the cylinder. A free end of the protrusion is
provided with a threaded end 84 for engaging the apparatus 12 with
a lower portion of the drill string (not shown).
Each pair of flanges 76 include a pair of slots 86 which are
aligned with each other to slidably receive a shaft 88 secured to
ends 90 of the arms 24 or 24'. The arms are thereby pivotal about
the axis of the shaft. They can also move in an axial direction
parallel to the axis of the cylinder from a lowermost position
(shown in FIG. 1) which is farthest removed from end flange 30 to
an uppermost position (shown in FIG. 1 in phantom lines) which is
proximate to the end flange.
Each arm includes a first skirt-engaging surface 92 immediately
adjacent end 90 of the arm on the side of the arm facing towards
the skirt portion 70. The first engaging surface is arranged to
position an outer side 94 of the arm within an axial projection of
end flange 30 to prevent interference between the narrow drill hole
10 and the arms when the apparatus 12 is axially moved through the
drill bore. The first engaging surface 92 is substantially parallel
to a periphery of the skirt portion 70 when the arm is pivoted
about the axis of shaft 88 and positioned within the axial
projection of end flange 30.
A second skirt-engaging surface 96 or 96' is joined with the first
engaging surface by a preferably arcuate transitional portion 98
and extends from the first surface toward the end 26 of the arm.
The second engaging surface is angularly inclined relative to the
first surface and projects inwardly towards the axis of the
cylinder 18. Immediately adjacent the second engaging surface is a
third skirt-engaging surface 100 or 100' which is shorter than
either the first or the second engaging surface and which has an
angular inclination relative to the first surface which is less
than the inclination of the second surface 96 or 96'. The exact
angular inclination is a function of both the length and the
angular inclination of the second engaging surface 96 or 96' and is
such that when the piston, together with skirt portion 70, is
axially moved towards disc 80, and the arms have pivoted outwardly
relative to the axis of the cylinder, the third skirt-engaging
surface 100 or 100' is parallel to the periphery of the cylindrical
skirt portion 70 when the piston is adjacent the radial projections
44 of the core 40, as shown in phantom lines in FIG. 1.
Joined to the third engaging surface 100 or 100' is an inner side
102 of the arm which defines the outline of the arm intermediate
the end of the third surface and the end 26 of the arm 24 or 24'.
This inner side has a configuration to position the cutting tool 28
adjacent the tubular protrusion 82, as shown in FIG. 1.
The arms 24 and 24' further include stop pins 104 which preferably
protrude from each face 106 of the arms and engage suitable cutouts
108 in flanges 76 for limiting the pivotal movement of the arms
about shaft 88 in a direction away from the axis of the cylinder
18.
Turning now to the operation of the underreaming apparatus 12, it
is first secured to a drill string (not shown) and lowered into a
drill hole 10. After it has reached the depth where the diameter of
the hole is to be enlarged, the downward movement of the apparatus
is halted. The drill string is filled with fluid drilling mud which
enters the tubular member 38 and, through holes 63 in the end
flange 30, the interior space 62 of the tool body 12. Thereafter
the drill string and the apparatus 12 are rotated by a suitable
rotatory table (not shown) on the surface of the well bore 10. The
piston 22 is disposed in its original position, the shafts 88 of
the arms are disposed at the lowermost position farthest removed
from end flange 30, and the arms, by virtue of their weight, are
pivoted inwardly to a position where ends 26 are closest adjacent
the axis of the cylinder 18.
The drilling mud is pressurized through the drill string to actuate
the piston 22 and move it axially away from end flange 30. When the
end 72 of the skirt portion 70 arrives at the transitional portion
98 intermediate the first and second skirt-engaging surfaces 92 and
96 or 96', respectively, the arms are pivoted outwardly away from
the axis of the cylinder. The free end of the skirt and
particularly the taper 74 of the free end, slides along the second
engaging surface 96 or 96'. This imparts a pivotal force onto the
arms which opposes the pivotal force imparted upon them by their
weight. The movement of the arms continues until the periphery of
the skirt portion 70 is disposed adjacent the third engaging
surface 100 or 100', as shown in phantom lines in FIG. 1.
Simultaneously with the pivotal movement of the arms, the cutting
tools 28 disposed adjacent ends 26 of the arms, begin to engage the
formation and commence their underreaming action. To effectively
drill and expand the hole, weight is applied to the drill string
from the surface to impart an axial force onto the cutting tools.
This axial force is transmitted to the cutting tool through flanges
78 and shaft 88. It causes the arms 24 and 24' and the shaft 88 to
move relative to the flanges 76 within the confines of slot 86
until the shafts are in their uppermost position adjacent the ends
of the slots proximate the end flange 30.
The downward movement of the piston 22 continues and the skirt
portion 70 is given a length such that when the shafts 88 are
disposed proximate to the end flange, the third engaging surface
100 or 100' is disposed on the periphery of the skirt portion.
Additionally, the cutouts 108 of the flanges are arranged to engage
the stop pins and prevent a further pivotal, outward movement of
the arms when surface 100 or 100' abuts skirt portion 70. In this
position, the arms extend outwardly a maximum distance.
The radial projections 44 on the tubular core 40 are arranged to
engage the piston 22 when the free end 72 of the skirt portion 70
is disposed just beyond the end of the third engaging surface 100
or 100' and the arms are proximate to the end flange 30. The relief
slots 46 in the tubular core now permit unrestricted circulation of
drilling mud from the interior space 62 to the exterior of the tool
body 16. Pressure in the interior space 62 is thereby relieved. No
additional axial forces are imparted upon the piston which remains
in the position adjacent the radial projections during the drilling
or underreaming operation.
The resulting pressure drop in the interior space 62 as well as in
the drill string is sensed at the surface. It simultaneously
communicates to the operator that the piston has reached its
lowermost position and that, by necessity, the arms are fully
extended. Moreover, as long as the drilling operation continues and
no pressure builds up in the interior space and the drill string
the operator knows that the arms are in a locked position and
prevented from collapsing inwardly. The operator is assured that
the hole is underreamed to the desired diameter.
Drilling mud continues to be pumped down through the drill string,
the interior space 62, past the relief slots 46, and into the space
exterior of the tool body to facilitate the drilling operations and
remove loosened formation to the surface. The drilling mud rises in
the annular space intermediate the drill string and the well bore
10 or a casing (not shown) disposed therein. Upon termination of
the drilling operation, the drill string, together with the
apparatus 12, is lifted off the bottom of the underreamed hole to
disengage the cutting tools 28 therefrom. The weight of the arms 24
and 24' and the cutting tools now axially moves the arms and the
shafts 88 relative to the flanges 76 in slots 86 until the arms are
at the lowermost position. The length of this movement, and
therefore of slot 86, is sufficient to disengage the third engaging
surface 100 or 100' from the periphery of the skirt portion 70 and
engage the taper 74 of the free end 72 of the skirt with the second
engaging surface 96 or 96'. The weight of the arms 24 or 24',
together with the cutters, pivotally biases the arms about the axes
of shafts 88. An axial component force acting in a direction
towards the end flange 30 is thereby imparted on the taper 74 of
the skirt portion. This axial force moves the piston axially
towards the end flange until the first engaging surface 92 engages
the periphery of the skirt portion. In that position, the arms are
fully retracted to within the axial projection of the end flange
and the apparatus can be axially moved through the well bore 10 to
the surface. After the drilling operation is terminated, the cable
56 is pulled to remove plug 50 from the recessed hole 48 in the
tubular core 40. The drill mud in the drill string is thereby
drained, and the interior space 62 is communicated with the
exterior of the tool body 16 such that no resistance force is
exerted upon the piston during its axial movement towards the end
flange.
If the diameter of the enlarged portion 14 of the drill bore 10 is
substantially greater than the diameter of drill hole 10, the arms
24 and 24' are pivoted outwardly different amounts such that some
of the cutting tools 28 cut a diameter which is greater than the
diameter cut by the other cutting tools. In an apparatus having,
say, six cutting tools 28 and arms 24 and 24', three of them 24'
are provided with a second skirt-engaging surface 96' which is
substantially longer than that of the other three. Their engaging
surfaces 100' are therefore substantially closer to the axis of the
cylinder when they are in a collapsed position. Upon actuation of
the piston 22, the arms 24' provided with the longer second
skirt-engaging surface 96' pivot outwardly a substantially greater
amount than the other arms 24. The length and angular inclination
of the engaging surfaces are arranged such that when all arms are
in a fully extended position, the cutting tools make annular cuts
into the formation which have successively greater diameters to
cover the full width of the underreamed bore with a cutting tool.
The operation of the apparatus remains identical to that described
above.
FIG. 4 illustrates a hole opening apparatus adapted for use in
conjunction with drilling operations requiring reverse circulation
of the drilling mud. In reverse circulation, where the drilling mud
is brought down from the surface to the drill tool through a first
annular space 120 intermediate a first outer drill string 121 and a
second inner string 122 and is returned to the surface through the
second inner drill string, the tubular core 40 disposed in the end
flange is left open. The exterior of the tool body is in flow
communication with the interior of the inner string through the
tubular core 40. The relief slots 46 in the tubular core are
omitted such that no fluid communication between the interior space
62 and the exterior of the tool body is possible adjacent the
center bore 58 of the piston. The first outer drill string,
however, fluidly communicates with the interior space 62 through
holes 63.
Included are a plurality of holes 123 extending radially through
walls of cylinder 18 and positioned so that the interior space 62
communicates with the exterior of the tool body when the piston is
adjacent the radial projections 44 on tubular core 40. The holes
are connected with suitable conduits 124 (hidden by flange 76)
disposed substantially parallel to the flanges 76 which terminate
adjacent the circular disc 80. Drilling mud pumped down through the
annular space between the outer and inner drill strings is then
discharged adjacent the bottom of the enlarged portion 14 being
drilled and returns to the surface through the hole 42 in the
tubular core 40 and the inner drill string 122. The operation of
the apparatus, namely the pivotal and axial movements of the arms,
the axial movement of the cylinder and the axial return of the
cylinder to its original position by the weight of the arms,
remains identical to the above described operation.
* * * * *