U.S. patent application number 09/731675 was filed with the patent office on 2001-05-03 for bit torque limiting device.
Invention is credited to Tibbitts, Gordon A..
Application Number | 20010000591 09/731675 |
Document ID | / |
Family ID | 25233474 |
Filed Date | 2001-05-03 |
United States Patent
Application |
20010000591 |
Kind Code |
A1 |
Tibbitts, Gordon A. |
May 3, 2001 |
Bit torque limiting device
Abstract
A torque limiting device that allows a drill string to rotate
relative to the cutting structure of the bit when a predetermined
torque is applied between the cutting structure of the drill bit
and the drill string. The torque limiting device utilizes a
retaining member which restricts rotational movement of a first
component of the torque limiting device relative to a second
component. When a sufficient torque load is placed on the cutting
structure of the drill bit, the retaining member allows rotational
movement of the first component relative to the second component
and allows the drill string to continue to rotate relative to the
cutting structure of the bit until the torque is sufficiently
reduced. The torque limiting device may be an integral part of a
drill bit, may be a separate device attached between the drill
string and the drill bit or between the drill string and a downhole
motor, or may be part of a near-bit sub or incorporated in a
downhole motor.
Inventors: |
Tibbitts, Gordon A.; (Salt
Lake City, UT) |
Correspondence
Address: |
TRASK BRITT
P.O. BOX 2550
SALT LAKE CITY
UT
84110
US
|
Family ID: |
25233474 |
Appl. No.: |
09/731675 |
Filed: |
December 6, 2000 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09731675 |
Dec 6, 2000 |
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09172509 |
Oct 14, 1998 |
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6182774 |
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09172509 |
Oct 14, 1998 |
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08821465 |
Mar 21, 1997 |
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5947214 |
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Current U.S.
Class: |
175/57 ;
175/276 |
Current CPC
Class: |
E21B 17/04 20130101;
E21B 17/073 20130101; Y10T 29/4987 20150115; E21B 17/076 20130101;
Y10T 29/49899 20150115; E21B 44/04 20130101 |
Class at
Publication: |
175/57 ;
175/276 |
International
Class: |
E21B 007/00; E21B
010/60 |
Claims
What is claimed is:
1. A method of drilling a subterranean formation, comprising:
providing a drill bit including a crown; providing a torque
limiting device; attaching the drill bit and the torque limiting
device to a drill string with the torque limiting device located to
limit an application of torque upon the crown of the drill bit;
lowering the drill bit and torque limiting device attached to the
drill string into a bore hole; rotating the crown of the drill bit
while applying weight-on-bit and flowing drilling fluid through the
drill bit; and modifying at least one drilling parameter selected
from modifying weight-on-bit, modifying drilling fluid flow,
modifying drilling fluid pressure, and modifying rotational speed
of the drill bit in response to cessation of rotation of the crown
of the drill bit.
2. The method of claim 1, further comprising sensing when the crown
of the bit stops rotating by detecting vibration.
3. The method of claim 1, further comprising sensing when the crown
stops rotating by detecting shock waves.
4. The method of claim 1, further comprising sensing when the crown
stops rotating by detecting a reduction in rate-of-penetration of
the bit into the subterranean formation.
5. The method of claim 1, further comprising sensing at least one
of rotational speed of the drill string, torque-on-bit, flow of
drilling fluid, pressure of drilling fluid, and rate-of-penetration
of the drill bit into the subterranean formation.
6. The method of claim 1, further comprising continuing to modify
the at least one drilling parameter while monitoring at least one
of rate-of-penetration, flow of the drilling fluid, pressure of the
drilling fluid, torque-on-bit, the presence of shock waves, and the
presence of vibration.
7. The method of claim 1, wherein attaching the drill bit and the
torque limiting device to the drill string comprises locating the
torque limiting device longitudinally between the drill bit and the
drill string.
8. The method of claim 7, wherein attaching the drill bit and the
torque limiting device to the end of the drill string comprises
attaching a first threaded end of the torque limiting device to the
drill bit and attaching a second threaded end of the torque
limiting device to an end of the drill-string.
9. The method of claim 7, further comprising providing and
attaching a downhole motor to the drill string and wherein
attaching the drill bit and the torque limiting device to the drill
string and locating the torque limiting device longitudinally
between the drill bit and the drill string comprises locating the
torque limiting device longitudinally between the drill bit and the
downhole motor.
10. The method of claim 7, further comprising providing and
attaching a downhole motor to the drill string and wherein
attaching the drill bit and the torque limiting device to the drill
string and locating the torque limiting device longitudinally
between the drill bit and the drill string comprises locating the
torque limiting device longitudinally between the downhole motor
and the drill string.
11. The method of claim 1, further comprising providing and
attaching a downhole motor to the drill string and wherein
attaching the drill bit and the torque limiting device to the drill
string and locating the torque limiting device longitudinally
between the drill bit and the drill string comprises disposing the
torque limiting device within a downhole motor positioned
longitudinally intermediate the drill bit and the drill string.
12. The method of claim 11, wherein disposing the torque limiting
device within a downhole motor comprises disposing the torque
limiting device within a bearing housing positioned longitudinally
between the drill bit and a rotor/stator section of the downhole
motor.
13. The method of claim 1, wherein providing a drill bit comprises
providing a fixed cutter drag bit.
14. The method of claim 1, wherein providing a drill bit comprises
providing a roller cone bit.
15. The method of claim 1, wherein providing a drill bit comprises
providing a coring bit.
16. The method of claim 1, wherein providing a drill bit comprises
providing a drill bit having cutters thereon selected from the
group consisting of cutters comprising polycrystalline diamond
compact, cutters comprising thermally stable product, and cutters
comprising natural diamonds.
17. The method of claim 1, wherein providing a torque limiting
device with the torque limiting device disposed above a crown of
the drill bit comprises providing a torque limiting device integral
to the drill bit.
18. The method of claim 1, further comprising passing a drilling
fluid through the drill string, through a plenum provided in the
torque limiting device, and discharging the drilling fluid from the
crown of the drill bit.
19. The method of claim 18, wherein discharging the drilling fluid
from the crown of the drill bit comprises discharging the drilling
fluid from a plurality of nozzle ports.
20. The method of claim 1, further comprises drilling a
subterranean formation while conducting at least one
measurement-while-drilling operation when modifying the at least
one drilling parameter.
21. A method of drilling a subterranean formation, comprising:
providing a drill bit including a crown and a shank, the shank
including a structure for connecting with a drill string; disposing
a torque limiting device between the crown of the drill bit and the
shank of the drill bit; attaching the drill bit and the torque
limiting device to a drill string with the torque limiting device
located to limit an application of torque upon the crown of the
drill bit; lowering the drill bit and the torque limiting device
into a bore hole; rotating the crown of the drill bit while
applying weight-on-bit and flowing drilling fluid through the drill
bit; and modifying at least one drilling parameter selected from
modifying weight-on-bit, modifying drilling fluid flow, modifying
drilling fluid pressure, and modifying rotational speed of the
drill bit in response to cessation of rotation of the crown of the
bit.
22. The method of claim 21, wherein disposing a torque limiting
device between the shank and the crown of the drill bit comprises
configuring a torque limiting device to comprise at least one
recess in the shank, at least one cooperating recess in the crown,
at least one biasing member, and at least one retaining member and
wherein the at least one retaining member is biased by the at least
one biasing member at least partially into one of the at least one
recess in the shank and the at least one cooperating recess in the
crown with the at least one biasing member being at least partially
retained by the other of the at least one recess in the shank and
the at least one cooperating recess in the crown.
23. The method of claim 22, wherein configuring a torque limiting
device to comprise at least one recess in the shank, at least one
cooperating recess in the crown, at least one biasing member, and
at least one retaining member comprises configuring a torque
limiting device to comprise a plurality of recesses in the shank, a
plurality of cooperating recesses in the crown, a plurality of
biasing members, and a plurality of retaining members.
24. The method of claim 22, wherein configuring a torque limiting
device to comprise at least one recess in the shank, at least one
cooperating recess in the crown, at least one biasing member, and
at least one retaining member comprises configuring the at least
one retaining member to exhibit a shape selected from the group
consisting of a substantially cylindrical shape, a substantially
wedge shape, and a substantially spherical shape.
25. The method of claim 23, wherein disposing a torque limiting
device between the shank and the crown of the drill bit comprises
interposing a generally cylindrical insert between the crown and
the shank.
26. The method of claim 22, wherein disposing a torque limiting
device between the shank and the crown of the drill bit comprises
disposing a fluidic seal between the shank and the crown.
27. The method of claim 26, further comprising passing a drilling
fluid through the drill string, the torque limiting device, and
discharging the drilling fluid from the crown of the drill bit.
28. The method of claim 21, wherein disposing a torque limiting
device between the shank and the crown of the drill bit comprises
configuring the torque limiting device to comprise a friction band
interposed between the shank and the crown.
29. The method of claim 21, wherein disposing a torque limiting
device between the shank and the crown of the drill bit comprises
disposing a torque limiting device configured to comprise a
resilient, elastomer band fitted around a plurality of protrusions
radially extending from an outer surface of the shank, the
resilient, elastomer band including a layer of wear resistant
material provided on an outer surface of the band and wherein the
layer of wear resistant material configured to matingly match an
inner surface of the crown.
30. The method of claim 21, wherein disposing providing a torque
limiting device between the shank and the crown of the drill bit
comprises disposing a torque limiting device configured to include
a plurality of rotatable clutch elements held in fixed relation to
the shank and rotatable along an inner surface of the crown.
31. The method of claim 21, wherein providing a drill bit comprises
selecting a drill bit from the group consisting of a fixed cutter
drag bit and a roller cone bit.
32. The method of claim 21, wherein providing a drill comprises
providing a drill bit having cutters thereon selected from the
group consisting of cutters comprising polycrystalline diamond
compact, cutters comprising thermally stable product, and cutters
comprising natural diamond.
33. The method of claim 21, further comprising sensing when the
crown of the bit stops rotating by detecting vibration.
34. The method of claim 21, further comprising sensing when the
crown stops rotating by detecting shock waves.
35. The method of claim 21, further comprising sensing when the
crown stops rotating by detecting a reduction in
rate-of-penetration of the bit into the subterranean formation.
36. The method of claim 21, further comprising sensing at least one
of rotational speed of the drill string, torque-on-bit, drilling
fluid flow, drilling fluid pressure, and rate-of-penetration of the
drill bit into the subterranean formation.
37. The method of claim 21, further comprising continuing to modify
the at least one drilling parameter while monitoring at least one
of rate-of-penetration, drilling fluid flow, drilling fluid
pressure, torque-on-bit, the presence of shock waves, and the
presence of vibration.
Description
1. This application is a divisional of application Ser. No.
09/172,509, filed Oct. 14, 1998, which is a divisional of
application Ser. No. 08/821,465, filed Mar. 21, 1997, now U.S. Pat.
No. 5,947,214, issued Sep. 7, 1999.
BACKGROUND OF THE INVENTION
2. 1. Field of the Invention
3. This invention relates generally to rotary drill bits used in
drilling subterranean wells and, more specifically, to rotary drill
bits employing a torque limiting device allowing the drill string
to rotate relative to the crown of the bit when a predetermined
reactive torque is experienced by the crown of the drill bit.
4. 2. State of the Art
5. The equipment used in drilling operations is well known in the
art and generally comprises a drill bit attached to a drill string,
including drill pipe and drill collars. A rotary table or other
device such as a top drive may be employed to rotate the drill
string, resulting in a corresponding rotation of the drill bit. The
drill collars, which are heavier and stiffer than drill pipe, are
normally used on the bottom part of the drill string to add weight
to the drill bit. The weight of these drill collars assists in
stabilizing the drill bit against the formation at the bottom of
the borehole, causing it to drill when rotated. Too much weight on
bit (WOB), however, may cause the drill bit to stall.
6. Downhole motors may also be employed to rotate the drill bit and
include two basic components: a rotor, which is a steel shaft
shaped in the form of a spiral or helix, and a stator, which is a
molded rubber sleeve in a rigid tubular housing, that forms a
spiral passageway to accommodate the rotor. When the rotor is
fitted inside the stator, the difference in geometry between the
two components creates a series of cavities through which drilling
fluid is pumped. In doing so, the fluid displaces the rotor,
forcing it to rotate as the fluid continues to flow between the
rotor and the stator. An output shaft connected to the rotor
transmits its rotation to the bit.
7. A typical rotary drill bit includes a bit body secured to a
steel shank having a threaded pin connection for attaching the bit
body to the drill string or the output shaft of a downhole motor
and a crown comprising that part of the bit fitted with cutting
structures for cutting into an earth formation. Generally, if the
bit is a fixed-cutter or so-called "drag" bit, the cutting
structure includes a series of cutting elements made of a
superabrasive substance, such as polycrystalline diamond, oriented
on the bit face at an angle to the surface being cut. On the other
hand, if the bit has rotating cutters such as on a tri-cone bit,
each cone independently rotates relative to the body of the bit and
includes a series of protruding teeth, which may be integral with
the cone or comprise separately-formed inserts.
8. The bit body of a drag bit is generally formed of steel or a
matrix of hard particulate material such as tungsten carbide
infiltrated with a binder, generally of copper-based alloy. In the
case of steel body bits, the bit body is usually machined from
round stock to the shape desired, usually with internal
watercourses for delivery of drilling fluid to the bit face.
Topographical features are then defined at precise locations on the
bit face by machining, typically using a computer-controlled,
five-axis machine tool. For a steel body bit, hardfacing may be
applied to the bit face and to other critical areas of the bit
exterior, and cutting elements are secured to the bit face,
generally by inserting the proximal ends of studs on which the
cutting elements are mounted into apertures bored in the bit face.
The end of the bit body opposite the face is then threaded, made up
and welded to the bit shank.
9. In the case of a matrix-type drag bit body, it is conventional
to employ a preformed so-called bit "blank" of steel or other
suitable material for internal reinforcement of the bit body
matrix. The blank may be merely cylindrical and tubular, or may be
fairly complex in configuration and include protrusions
corresponding to blades, wings or other features on the bit face.
Other preform elements comprised of sand, or in some instances
tungsten carbide particles, in a flexible polymeric binder may also
be employed to define internal watercourses and passages for
delivery of drilling fluid to the bit face, as well as cutting
element sockets, ridges, lands, nozzle displacements, junk slots
and other external topographic features of the bit. The blank and
other preforms are placed at appropriate locations in the mold used
to cast the bit body before the mold is filled with tungsten
carbide. The blank is bonded to and within the matrix upon cooling
of the bit body after infiltration of the tungsten carbide with the
binder in a furnace, and the other preforms are removed once the
matrix has cooled. The threaded shank is then welded to the bit
blank. The cutting elements (typically diamond, and most often a
synthetic polycrystalline diamond compact, or PDC) may be bonded to
the bit face by the solidified binder subsequent to furnacing of
the bit body. Thermally stable PDCs, commonly termed "TSPs", may be
bonded to the bit face by the furnacing process or may be
subsequently bonded thereto, as by brazing, adhesive bonding, or
mechanical affixation.
10. In order for the cutting elements to properly cut the formation
during a drilling operation, considerable torque is required to
generate the necessary rotational force between the cutting
elements and the formation under a WOB substantial enough to ensure
an adequate depth of cut. The resultant or reactive torque on the
bit from formation contact is translated through the drill string
and must be overcome by the means used to rotate the drill string,
such as a rotary table, top drive, or downhole motor. In some
instances, such as drilling through harder formations, the
resultant torque may result in the winding up and sudden release of
the drill string under torque, manifested as so-called "slaps" of
the drill string at the rotary table. In other instances, torque
may be sufficient to actually stop the bit from rotating. The
rotary table may continue to rotate the drill string for some time,
in effect "twisting" the drill string and placing the bit under
very high torque loads before an operator realizes that the bit is
no longer rotating. This problem is of particular concern with drag
bits, due to direct engagement of the formation by the fixed PDC
cutters, but also manifests itself with rock bits. If such a
condition occurs and the rotary table continues to rotate, the
drill string, the bit and/or components thereof may be damaged, or
the drill string may even part under the torque load. If failure of
the drill string occurs, the portion of the drill string above the
break must be removed from the wellbore. A "fishing" assembly
inserted into the wellbore is then normally employed in an attempt
to retrieve the remainder of the drill string. If retrieval is
impractical or unsuccessful, a new drilling assembly must be
deflected, "sidetracked," or steered around the "fish." Any such
scenario adds to the cost of production and results in down-time of
the drilling operation while the remainder of the broken drill
string is "tripped" from the wellbore and replaced with other
bottom hole assemblies.
11. When a downhole motor is being used to rotate the drill bit, a
sudden rise in surface pressure of the drilling fluid may indicate
that the motor has stalled. While other conditions may cause a rise
in fluid pressure, such as a clogged motor or plugged nozzles, if
the motor stalls because the bit is no longer rotating due to
excessive torque on the bit and is maintained in a stalled
condition, the elastomeric stator lining may be damaged, preventing
a proper interface between the stator and the rotor, thus requiring
the motor to be tripped out of the wellbore and replaced. At the
least, the bottomhole assembly, including the motor, must be pulled
off-bottom and drilling and circulation recommenced to start the
motor before the formation is re-engaged by the bit.
12. In addition to damage to drill strings and bits, directional
drilling presents its own set of problems when excessive torque is
applied to the drill bit. A directional well must intersect a
target that may be several miles below the surface location of the
drilling rig, and laterally offset therefrom. In order to reach the
target, the wellbore must be directed or steered along a
predetermined trajectory. The trajectory of the bit is typically
determined by the tool face orientation (TFO), which must be
maintained during drilling in order to maintain the trajectory of
the wellbore toward the desired target. If the TFO shifts due to a
stalled drill bit, the drilling must stop and a new TFO set as a
reference point for the direction of drilling. While a shift in TFO
is quickly manifested to the operator due to the essentially
real-time nature of the MWD (measurement while drilling) mud-pulse
transmissions, nonetheless, loss of TFO and resetting thereof
results in considerable reduction in the overall rate of
penetration (ROP) of the drilling assembly.
13. It would thus be advantageous to provide a drill bit assembly
that includes a torque limiting device that is either an integral
part of the bit construction or is attached near the bit between
the drill bit and the drill string, or is positioned between the
downhole motor and the drill bit.
BRIEF SUMMARY OF THE INVENTION
14. According to the present invention, a torque limiting device is
provided that allows the drill string to rotate relative to the
cutting structure of the bit at a predetermined torque placed on
the cutting structure of the bit. The torque limiting device may be
incorporated into the structure of the bit itself, be a separate
structure attached to a drill bit, or be near-bit positioned
between the drill string and the bit. In any case, the torque
limiting device prevents movement of the cutting structure relative
to the drill string during normal operation. When a predetermined
torque is applied to the cutting structure of the bit, the torque
limiter allows the drill string to rotate relative to the
stationary cutting structure until the torque is decreased below
the predetermined level, typically by backing off the drill string
to decrease the WOB.
15. In a preferred embodiment having the torque limiting device as
an integral part of a drill bit, the fixed-cutter bit is comprised
of a crown for providing a cutting face to which a plurality of
cutting elements may be attached and a shank for supporting the
crown and attaching the crown to a drill string. The crown has a
substantially cylindrical internal chamber sized and shaped to mate
with and effectively cap the proximal end of the shank, which also
has a generally cylindrical configuration. The shank and the crown
fit together in a snug arrangement without inhibiting rotational
movement between the crown and the shank.
16. In one preferred embodiment, around the perimeter of the shank
are a number of recesses positioned to match corresponding recesses
formed in the wall of the internal chamber of the crown. A biasing
member comprised of a resilient material or a spring is placed in
each recess formed in the shank. A retaining member, preferably
made of a hard material such as steel, is subsequently placed on
top of (radially outboard of) each of the biasing members. When the
shank and crown are assembled together longitudinally, the
retaining member compresses the biasing member and is forced by the
wall of the internal chamber of the crown into the recess formed in
the shank. The lower portion of the retaining member may be tapered
to facilitate assembly of the torque limiting device. When the
shank and crown are completely engaged, the biasing member forces
the retaining member into the recess in the internal chamber
wall.
17. If sufficient torque is applied to the crown of the bit, the
retaining member is forced against the biasing member out of the
recess in the internal chamber wall of the crown. The shank can
then rotate relative to the crown. If a single retaining member and
recess are utilized as part of the torque limiting device, the
shank will make a complete revolution before the retaining member
can reengage the recess. If the torque is still sufficient, the
shank will continue to rotate until the torque is sufficiently
decreased and the retaining member is realigned with the recess.
Preferably, there is more than one retaining member and more than
one recess spaced around the perimeter of the shank. Thus, the
retaining member or members may reengage with other recesses,
depending on when the torque is sufficiently lowered. In addition,
the retaining member may be longitudinally oriented or oriented at
some angle relative to the bit axis. Engagement or disengagement of
the retaining member or members with the recesses manifests itself
as vibrations on the rig floor, alerting the driller to reduce
WOB.
18. In another preferred embodiment where the torque limiting
device is part of the drill bit itself, the crown is securely
attached to a substantially cylindrical bit blank. The blank and
the shank are then attached in a manner similar to the
aforementioned embodiment, including the torque limiting feature.
Such a configuration may be necessary if the crown is comprised of
a relatively brittle material, such as tungsten carbide, where
forming recesses therein and engaging and reengaging a retaining
member may cause the crown to crack. Thus, the blank is preferably
formed of a more ductile material and the crown of a more abrasion
resistant material, with the recesses necessary for engagement of
the retaining member formed in the blank.
19. In either of the aforementioned embodiments, a standardized
shank could be manufactured to accommodate a variety of crown
and/or cutter sizes and configurations. In yet another embodiment,
the crown is configured to be inserted into the proximal end of the
shank with the proximal end of the shank having a substantially
cylindrical chamber formed therein to mate with the distal end of
the crown. The torque limiting device of the aforementioned
embodiments is utilized in a substantially similar manner to limit
the torque that may be applied to the bit crown.
20. In still another preferred embodiment where the torque limiting
device is part of the bit itself, a pair of bands is positioned
between the shank and the blank with one band attached to each. The
bands maintain relative position due to a frictional interference
fit but can slide relative to one another if a predetermined torque
is applied to the crown of the bit. In addition, the bands may have
various orientations including vertical, horizontal, or any angle
therebetween. Moreover, one or both of the bands may be comprised
of a resilient material, such as synthetic elastomers, and the band
material may be filled with particles or fibers of asbestos or
other brake-material compounds. The location of the bands may be
sealed from wellbore fluids, or the band materials may be selected
to operate in the wellbore environment. Such a torque limiting
device would act in a clutch-like manner where the bands remain in
stationary relationship, so long as the force between them caused
by torque on the crown does not exceed the static coefficient of
friction between the bands. Moreover, the torque limiting device
would have equal utility for tri-cone bits, as well as coring or
other bits used in rotational-type drilling.
21. In yet another preferred embodiment, the torque limiting device
includes a plurality of load-driven rollers (clutch rollers) that
allows rotational movement when a predetermined torque or load is
placed on the cutting structure of the bit.
22. In another preferred embodiment, a ratchet-type torque limiter
may be comprised of two substantially concentric rings of similar
or dissimilar materials, each having teeth or projections in
engaging contact with one another that disengage when a
predetermined torque is applied to the cutting structure of the
bit.
23. In an alternate embodiment where the torque limiting device of
the present invention is separate from the bit, the device couples
a typical drill bit to a drill string and/or downhole motor. The
torque limiting device includes connecting structures, such as
threads, at both ends, one for attaching the device to the bit and
one for attaching it to the drill string. The device may be formed
as part of a downhole motor, or as a near-bit sub. Similar to the
construction of the drill bit embodiments, the torque limiter may
be comprised of two connecting structures that are fitted together
in a male-female interconnection and held together by retaining
members engaged in recesses formed in the internal wall of one
connector. If sufficient torque is applied to the bit by the
formation, the torque limiting device will allow the drill string
to rotate relative to the bit.
24. As will be recognized, when the retaining members are
disengaged from their respective recesses, the two connecting
structures need not be axially mechanically attached to one another
except for frictional forces applied by the retaining members on
the internal wall of one connecting structure. Because the bit is
being forced into the bottom of the wellbore, however, the two
connecting structures are held together by the weight of the drill
string. Thus, the two connecting structures will not become
separated. The same is true for the embodiments where the torque
limiting device is part of the bit construction. However, as
required, additional structures as known in the art may be employed
to help the two connecting structures remain secured together
against longitudinal tensile forces encountered when tripping out
of the wellbore.
25. It will be recognized by those skilled in the art that in any
of the aforementioned embodiments, the configurations of the
retaining and biasing members may vary. For example, the retaining
member may simply be spherically shaped, cylindrically shaped,
wedge shaped or otherwise suitably shaped including combinations
thereof. Moreover, the retaining members may be biased by a segment
of resilient material, a coil-type spring, a leaf spring, a
belleville spring, or other means known in the art.
26. As noted above, a torque limiting device, in accordance with
the present invention, will reduce the possibility of bit damage
from excessive torque and will quickly signal the drilling operator
through vibrations or shock waves that excessive torque is being
applied to the drill bit.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
27. FIG. 1 is a partial sectional view of a drill bit including a
first embodiment of a torque limiting device in accordance with the
present invention;
28. FIG. 2 is a cross-sectional view of the embodiment shown in
FIG. 1;
29. FIG. 2A is a cross-sectional view of a second embodiment of a
torque limiting device in accordance with the present
invention;
30. FIG. 3 is a partial sectional view of a drill bit including a
third embodiment of a torque limiting device in accordance with the
present invention;
31. FIG. 4 is a cross-sectional view of the embodiment shown in
FIG. 3;
32. FIG. 5 is another cross-sectional view of the embodiment shown
in FIG. 3;
33. FIG. 6 is a partial sectional view of a drill bit including a
fourth embodiment of a torque limiting device in accordance with
the present invention;
34. FIG. 6A is a partial sectional view of a drill bit including a
fifth embodiment of a torque limiting device in accordance with the
present invention;
35. FIG. 7 is a sectional view of a sixth embodiment of a torque
limiting device in accordance with the present invention;
36. FIG. 7A is a cross-sectional view of a drill bit including a
seventh embodiment of a torque limiting device in accordance with
the present invention;
37. FIG. 8 is a partial cross-sectional view of an alternate
embodiment of a retaining member and its associated biasing member
positioned in a near-bit coupling device in accordance with the
present invention;
38. FIG. 9 is a partial sectional view of a drill bit including an
eighth embodiment of a torque limiting device in accordance with
the present invention;
39. FIG. 9A is a partial sectional view of a drill bit including a
ninth embodiment of a torque limiting device in accordance with the
present invention;
40. FIG. 10 is a cross-sectional view of a drill bit including a
tenth embodiment of a torque limiting device in accordance with the
present invention;
41. FIG. 11 is a cross-sectional view of a drill bit including an
eleventh embodiment of a torque limiting device in accordance with
the present invention;
42. FIG. 12 is a cross-sectional view of a drill bit including a
twelfth embodiment of a torque limiting device in accordance with
the present invention; and
43. FIG. 13 is a partial sectional view of a downhole motor
including a torque limiting device in accordance with the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
44. FIG. 1 shows an exemplary drill bit 10, in accordance with the
present invention, attached by threads 12 to an end 14 of a drill
string 16. The drill bit 10 comprises a crown 18 attached to a
shank 20 by the retaining members 22. The crown 18 may have a
typical rotary bit exterior configuration including a plurality of
cutting elements 24, nozzle exit ports 26, and gage pads 28. As
with other similarly configured bits known in the art, the shank 20
includes a plenum 21 longitudinally extending through the shank 20
that is in fluid communication with the drilling fluid supply 15 of
the drill string 16 and the nozzle exit ports 26 of the crown
18.
45. The crown 18 has an internal chamber 30 defined by walls 32 and
34 and floor 36. The internal chamber 30 is substantially
cylindrically shaped and is sized to closely fit over the proximal
end 38 of the shank 20, which also has a substantially cylindrical
shape. The shank 20 and the crown 18 form a male-female
interconnection such that the shank 20 may rotate within the
internal chamber 30 of the crown 18.
46. As previously mentioned, the shank 20 is held in relative
position to the crown 18 by retaining members 22 that protrude into
recesses 40 formed in the wall 32 of the internal chamber 30. The
retaining members 22 may be formed of steel, bronze or any other
suitable material known in the art. The retaining members 22 are
radially biased by the biasing members 42 positioned in recesses 41
formed in the outer surface 44 of the shank 20 proximate its
proximal end 38. The biasing members 42 may be formed of a
resilient elastomeric material, such as natural or synthetic rubber
compounds, polyurethane or other materials known in the art and may
have varying durometer ratings, depending on the desired resiliency
to accommodate the design torque limit. In order to keep drilling
fluid from the plenum 21 or from outside the drill bit 10 from
entering between the shank 20 and the crown 18 and into the
recesses 40 and 41, O-rings or other sealing structures 45 and 47
may be utilized to rotationally seal the crown 18 to the shank
20.
47. As better shown in FIG. 2, the cross-section of the drill bit
10 illustrates the position of the junk slots 43 and the gage pads
28, relative to a plurality of retaining members 22 and biasing
members 42, which are shown equidistantly placed about the
perimeter 46 of the shank 20. The embodiment shown in FIG. 2
includes four torque limiting assemblies 48. As will be recognized
by those skilled in the art, the number of torque limiting
assemblies 48 is not critical and may include one or more. It is
advantageous, however, to place a plurality of the torque limiting
assemblies 48 equidistantly around the perimeter 46 of the shank 20
so that any one retaining member 22 may engage with any other
recess 40.
48. For example, as further illustrated in FIG. 2A, each torque
limiting assembly 70 may engage with a plurality of different
recesses 71. Moreover, while each retaining member 72, in the form
of a substantially spherical ball, is illustrated as being forced
into a recess 71 formed in the crown 73, those skilled in the art
will recognize that the recesses 71 may with equal utility be
formed in the shank 74 with each torque limiting assembly 70 fitted
within the crown 73.
49. When a sufficient amount of torque is placed on the crown 18 of
the drill bit 10 to load the retaining members 22 and force them
radially into the biasing members 42, a distance that allows the
retaining members 22 to clear the perimeter of interior wall 32 of
the crown 18, the shank 20 will rotate relative to the crown 18. In
every quarter turn of the shank 20 relative to the crown 18, the
retaining members 22 will reengage with the recesses 40. If the
torque applied to the crown 18 is still sufficient to overcome the
forces applied by the biasing members 42 on the retaining members
22, the shank 20 will continue to rotate. If not, the retaining
members 22 will reengage with the next closest recess 40, and the
crown 18 will then rotate along with the shank 20.
50. The retaining members 22 of the embodiment shown in FIGS. 1 and
2 have a substantially cylindrical cross-section with a flat side
50 used to provide uniform contact by the biasing member 42 along
the length and width of the retaining member 22. It should also be
noted that the rounded side 52 of the retaining member 22 must not
extend a distance into the crown 18 such that the retaining member
forms a mechanical lock between the crown 18 and the shank 20. That
is, the rounded side 52 must be able to slide out of the recess 40
when a predetermined torque is applied to the bit crown 18. In
addition, for assembly purposes, the retaining members 22 have a
tapered portion 56 to slidedly engage with the beveled edge 60 of
the crown 18. Thus, when the shank 20 and the crown 18 are slid
together during assembly of the drill bit 10, the tapered portion
56 is assisted into the recess 41 by the beveled edge 60.
51. Similar to the embodiment shown in FIG. 1, the drill bit 100,
depicted in FIG. 3, is attached to a drill string 102 by a threaded
portion 104. The drill bit 100, however, includes a substantially
cylindrical tubular blank or crown insert 106, longitudinally
extending along a length of the drill bit 100, positioned between
the crown 108 and the shank 110 proximate its proximal end 114. The
crown 108 is securely attached to the crown insert 106, which
attachment may be assisted by protrusions 112, to mechanically hold
the crown insert 106 relative to the crown 108.
52. The torque limiting assemblies 116 are located between the
shank 110 and the crown insert 106 and proximate the proximal end
114. In this embodiment, however, it is not critical that the
torque limiting assemblies 116 be located at or near the proximal
end 114, and could therefore be positioned at any point along the
interface 118 between the crown insert 106 and the shank 110. As in
the previous embodiment, each torque limiting assembly 116 includes
a retaining member 120 and a biasing member 122 (in this case a
coil spring). Moreover, the retaining member 120, which is held
into the recess 124 by the biasing member 122, has a tapered edge
126 at its proximal end 128. During the assembly process, when the
shank 110 is slid into the crown insert 106, this tapered edge 126
contacts the beveled recess 130 located on the inner distal edge
132 of the crown insert 106 and helps to force the retaining member
120 into the crown insert 106. As better shown in FIG. 5, a
cross-sectional view of the drill bit 100 taken through the
interface between the crown insert 106 and the drill string 102,
there are four such beveled recesses 130 positioned to correspond
to each torque limiting assembly 116.
53. Referring now to FIG. 4, depicting a cross-section of the drill
bit 100 through the torque limiting assemblies 116, the crown
insert 106 has a number of radially extending blades 150
corresponding to the external blades 152 of the crown 108. The
crown insert 106 provides structural support for the crown 108 so
that the crown 108 does not fracture during drilling. The retaining
members 120 have a wedge-shaped cross-section with a tapered edge
154 which, when positioned in the recess 124, extends into the
recess 156 to provide a sliding surface between the retaining
member 120 and the edge 157 of the recess 124 at the inner surface
158 of the insert crown 106. Again, there are four, equidistantly
spaced torque limiting assemblies 116. As one skilled in the art
will recognize, however, there may be as few as one torque limiting
assembly 116, or as many as will fit within the given space,
depending on their size and configuration.
54. As illustrated in FIG. 3, O-rings 134 and 136, or other seals
as known in the art, placed in races 138 and 140, respectively,
seal the torque limiting assemblies 116 from drilling fluid
contained in the plenum 142 and drilling fluid located outside the
drill bit 100. A top view of the O-ring race 140 is shown in FIG.
5.
55. FIG. 6 is a partial sectional view of an alternate preferred
embodiment of a drill bit 160, in accordance with the present
invention. In this embodiment, a portion 162 of the crown 164
actually fits in an internal chamber 166 defined by the proximal
end 168 of the shank 170 in a male-female interconnection.
Additionally, the torque limiting assembly 172 is comprised of a
substantially spherically shaped retaining member 174 and a
substantially cylindrical biasing member 176. Thus, the shank 170
can rotate relative to the crown 164 when a sufficient torque on
the crown 164 forces the retaining member 174 toward the biasing
member 176 enough that the retaining member 174 clears the wall 178
defining the internal chamber 166. O-rings 180 and 182 positioned
in O-ring races 184 and 186, respectively, substantially seal the
torque limiting assembly 172 from drilling fluid.
56. Likewise, in FIG. 6A, the torque limiting feature of the drill
bit 271 operates in a similar manner to that illustrated in FIG. 6.
The retaining member 270 and biasing member 272, however, are
vertically oriented between the crown 274 and the shank 276.
57. FIG. 7 illustrates that many modifications and/or combinations
of the aforementioned embodiments of the torque limiting assembly
200 can be made without departing from the spirit of this
invention. For example, the retaining member 202 may include a
semi-spherical or semi-cylindrical portion 204 at its proximal end
206 for engagement with an insert or crown 208, as the case may be,
and a guide rod or fin 210 to keep the portion 204 from rotating
during disengagement and reengagement from the recess 212. The
biasing member or coiled spring 214 sits in a first recess 216
formed in the shank 218. The first recess 216 is followed by a
second recess 220, which is smaller and sized and shaped to
accommodate the rod or fin 210 through its full range of motion.
Additionally, as illustrated in FIG. 7A, the retaining member and
biasing member may be a single integral retaining component, such
as spring 230. Such a spring 230 could hold the crown 231 relative
to the shank 232 while engaged with engagement portions 233 in the
outer surface 234 of the shank 232. As shown, the engagement
portions 233 are comprised of recesses in the outer surface 234,
but could just as well be flattened portions that would require
deflection of the spring 230 to allow rotation of the crown 231
relative to the shank 232.
58. While other preferred embodiments of the torque limiting
assembly, according to the present invention, have been illustrated
as including a biasing member and a retaining member, other devices
which provide releasability between two drilling related structures
are also contemplated. For example, as illustrated in FIGS. 9 and
9A, the torque limiting assembly 280 includes a pair of
circumferential bands 282 and 284, at least one of which is
comprised of an abrasion-resistant, yet resilient, material, the
bands 282 and 284 being frictionally held in relative relation and
adhesively or mechanically attached to the crown 286 and shank 288,
respectively. The bands 282 and 284 remain in one relative position
to one another so long as the force between the two bands 282 and
284 does not exceed the force holding the bands 282 and 284
together based on the coefficient of static friction between the
two bands. Once the force holding the bands 282 and 284 together is
exceeded, however, the bands will move relative to one another,
allowing the crown 286 to rotate relative to the shank 288. In
addition, the bands may be substantially vertically oriented as
illustrated in FIG. 9, substantially horizontally oriented, or
oriented at any angle thereinbetween, as further illustrated in
FIG. 9A.
59. As further illustrated in FIG. 10, the torque limiting assembly
may be comprised of a single friction band 290 interposed between
the crown 292 and the shank 294. The band 290 may be attached to
either the crown 292 or the shank 294, or not be attached at all.
Accordingly, the crown 292 can rotate relative to the shank 294
when a torque placed on the crown 292 results in a force in excess
of the static frictional force between the crown 292 and band 290
or the shank 294 and the band 290. Materials employed in brake
linings and pads for motor vehicles may be especially suitable for
band 290.
60. In yet another preferred embodiment illustrated in FIG. 11, the
torque limiting assembly 300 includes a band 302 of resilient
material, such as an elastomer, that is mechanically attached to or
molded onto and fitted around a plurality of protrusions 304
radially extending from an outer surface 306 of the shank 308.
Accordingly, the band 302 is restricted from moving relative to the
shank 308. The band 302 includes a layer 310 of wear-resistant
material provided on its outer surface 312 that follows the contour
of the outer surface 312 of the band 302. The outer surface 312 of
the band 302, and more specifically the contour of the layer 310,
is configured to substantially matingly match with the contour of
the inner surface 314 of the crown 316. In this example, the inner
surface 314 of the crown 316 is comprised of a zig-zag or
corrugated, ribbed pattern that uniformly repeats around the inner
surface 314. Thus, when a sufficient torque is applied to the crown
316, the crown 316 can rotate relative to the shank 308 with the
layer 310 protecting the band 302 from being damaged or destroyed
by the inner surface 314 of the crown 316. It will also be
understood that while illustrated in a zig-zag configuration, the
interface between the band 302 and the crown 316 may be similar to
a sinusoidal wave, saw teeth, or any other desired pattern. Such an
arrangement may be formed using an elastomer of one durometer for
band 302 having molded thereon a second, higher-durometer layer
310. Polyurethanes are especially suitable for such an
arrangement.
61. Moreover, in FIG. 12, the torque limiting assembly 320 may
include one or more rotatable clutch elements 322 held in fixed
relation to the shank 324 but rotatable along an inner surface 326
of the crown 328 when sufficient torque is applied to the crown
328.
62. It is also contemplated that the torque limiting device of the
present invention may be incorporated into a near-bit coupling
device 250, as illustrated in FIG. 8, which incorporates a torque
limiting assembly 252, as previously described. The coupling device
250 is comprised of two interface structures or connectors 254 and
256. The first connector 254 would typically be attached to a drill
string as known in the art and the second connector 256 would be
attached to a typical drill bit. As with other embodiments
described herein, the torque limiting assemblies 252 are releasable
and allow rotational movement of the first interface structure or
connector 254 relative to the second interface structure or
connector 256. The coupling device 250 also includes a plenum 255
to allow passage of drilling fluid from a drill string to a drill
bit. O-ring 258 placed in race 260 and another O-ring placed in
race 262 could help seal the torque limiting assemblies 252 and the
coupling device 250 relative to a connected drill string and bit.
Such a coupling device 250, incorporating a torque limiting
assembly 252, would allow a typical bit to have torque limiting
abilities without modifying the bit itself or the manufacturing of
such a bit.
63. It will be appreciated by those of ordinary skill in the art
that use of the present invention facilitates the use of drag bits
having aggressive PDC cutters, such as those with minimal or no
back rake or even a forward (positive) rake of the cutting faces.
Prior art bits, in part, employ negatively-back raked cutters to
limit torque, but this also limits ROP, so runs take longer for a
given borehole interval in the interests of preserving the bit and
string against damage.
64. During a drilling operation utilizing a drill bit incorporating
a torque limiting device in accordance with the present invention,
if the crown of the bit ceases rotation, the vibrations generated
by the disengagement and reengagement of the torque limiting device
will quickly signal the operator that the crown is not rotating.
Drilling parameters can then be promptly adjusted to decrease the
WOB applied on the bit crown, or in the case of a downhole motor,
the drilling fluid flow as well as WOB.
65. It will be appreciated by those skilled in the art that many
modifications and combinations of the preferred embodiments can be
made without departing from the scope of the invention and
particularly the appended claims. More specifically, features of
the torque limiting device that have been illustrated as an
integral part of the drill bit could be incorporated into a
near-bit torque limiting device or anywhere between the drill
string and the drill bit. For example, as illustrated in FIG. 13, a
torque limiting device could be incorporated at a variety of
locations along a downhole motor 330. A torque limiting device,
according to the present invention, may have utility at point A
between a downhole motor 330 and drill bit 332, at point B between
motor 330 and drill string 334, or even at point C within downhole
motor 330 as, for example, within bearing housing 336 below the
rotor/stator section 338 and connecting rod assembly 340. In
addition, the torque limiting device, while being illustrated with
respect to a fixed-cutter bit, will have equal utility when used
with or as an integral part of a roller cone bit (also called
"tri-cone" or "rock" bit), as well as coring or other bits used in
rotational-type drilling. Moreover, those skilled in the art will
appreciate that configurations of the components could be
interchanged between embodiments, such as changing the type and/or
shape of the retaining member and/or the type and/or shape of the
biasing member. Further, the arrangement of torque limiting
assemblies may be reversed so that the retaining members are
radially inwardly biased by biasing members carried by the crown
(or blank) into cooperating recesses formed in the shank. Thus, it
is believed that the essence of the invention is to provide a
torque limiting device in a drill bit or between a drill string or
downhole motor, as is known in the art, and a bit so that the drill
string or motor drive shaft can continue to rotate while the crown
of the bit remains stationary once a predetermined torque is
exceeded by the drill bit.
* * * * *