Note: Descriptions are shown in the official language in which they were submitted.
CA 02717484 2015-08-26
Wellbore Drilling Accelerator
Field
The present invention relates to down hole tools and, in particular, a
wellbore drilling
accelerator for applying an axially directed percussive effect to a drill bit
and a tubular
connection.
Background
If one could add a percussive force to the drill bit while drilling a
wellbore, it is believed
that the rate of drilling penetration could be significantly increased, the
required weight
on bit could be significantly reduced and torque required to turn the drill
bit could be
significantly reduced. A "percussionized" drill bit should be an efficient
drilling tool.
Many previous attempts at developing percussion adapters have focused on
hydraulically driven devices. These devices use the flow of drilling fluid to
drive pistons
with a percussion adapter to create an axially directed percussive effect at
the drill bit.
A common problem experienced in down hole operations relates to the effect of
torque
on tubular connections. This problem may be exaggerated when torque is
generated in
the operation of a tool down hole.
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Summary
In accordance with a broad aspect of the present invention, there is provided
a method
for accelerating the drilling penetration of a rotary driven drill bit, the
method comprising:
providing a positive displacement motor including a motor housing, a fluid
discharge and
a rotor powered by fluid pressure; providing a drill bit; providing a drilling
accelerator
including a housing and a drive connection to mechanically convert rotational
drive to
axially directed percussive motion; connecting the drilling accelerator below
the motor
including connecting the housing to move with the motor housing, connecting
the drive
connection to be driven rotationally by the rotor and bringing the fluid
passage into
communication with the fluid discharge; connecting the drill bit below the
drilling
accelerator with the drive connection in drive communication with the drill
bit; pumping
fluid through the motor to drive the rotor and the drive connection to rotate
and to
generate axial percussive motion which is communicated from the drive
connection to
the drill bit and; discharging fluid from the fluid discharge to pass through
the drilling
accelerator and the drill bit.
In accordance with another broad aspect of the present invention, there is
provided
drilling accelerator comprising: a housing including an upper end and a lower
end; a
drive connection including an upper axially rotatable drive shaft for
receiving an input of
rotational motion, a rotational to axial mechanical drive converter in
communication with
the upper axially rotatable drive shaft for converting the input of rotational
motion to an
axial sliding motion; a lower longitudinally moveable drive shaft in
communication with
the rotational to axial mechanical drive converter to receive the axial
sliding motion from
the rotational to axial mechanical drive converter and a lower drill bit
installation site
connected to the lower longitudinally moveable drive shaft for receiving the
axial sliding
motion and capable of conveying axial percussive motion there through, the
lower drill
bit installation site telescopically mounted adjacent the lower end of the
housing and
slidably moveable relative thereto.
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In accordance with another broad aspect of the present invention there is
provided a
wellbore string tubular connection comprising: a first tubular including a
first threaded
pin end with a right hand thread form and a protrusion extending from its pin
end face to
create a stepped region thereon, a second tubular including a second threaded
pin end
with a left hand thread form and a recess on its pin end face forming a
shoulder sized to
accept the stepped region of the first pin end seated thereagainst, and a
collar including
a first threaded box with a first selected thread form selected to threadedly
engage the
right hand thread form of the first threaded pin end and a second threaded box
with a
second thread form selected to threadedly engage the left hand thread form of
the
second threaded pin end.
In accordance with a broad aspect of another invention, there is provided a
method for
making up a wellbore connection, the method comprising: providing a first
wellbore
tubular with a threaded pin end and an tooth extending from a pin end face
thereof, a
second tubular with a threaded pin end and recess in a pin end face thereof,
the recess
sized to accept the tooth of the first wellbore tubular and a collar including
a first
threaded box end and an opposite threaded box end; aligning the first wellbore
tubular
and the second wellbore tubular to be threaded into the box ends of the collar
and with
the tooth aligned with the recess and rotating the collar about its long axis
to engage the
threaded pin ends of the first wellbore tubular and the second wellbore
tubular and draw
the threaded pin ends into the collar.
It is to be understood that other aspects of the present invention will become
readily
apparent to those skilled in the art from the following detailed description,
wherein
various embodiments of the invention are shown and described by way of
illustration.
As will be realized, the invention is capable for other and different
embodiments and its
several details are capable of modification in various other respects.
Accordingly the
drawings
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and detailed description are to be regarded as illustrative in nature and not
as
restrictive.
Brief Description of the Drawings
Referring to the drawings, several aspects of the present invention are
illustrated by way
of example, and not by way of limitation, in detail in the figures, wherein:
Figure 1 is a schematic sectional view along a portion of a drill string.
Figure 2 is an axial sectional view along one embodiment of a drilling
accelerator.
Figure 3 is an axial sectional view along another drilling accelerator.
Figure 3A is an elevation, partly in section, of a drive shaft useful in a
drilling
accelerator.
Figure 4 is an axial sectional view along another drilling accelerator.
Figure 4A is perspective view of a cam-type drive converter useful in the
present
invention.
Figure 4B is an axial section through a cam-type converter useful in the
present
invention.
Figure 4C is an axial section through a roller-type cam insert useful in the
present
invention.
Figure 4D is a front elevation of the insert of Figure 4C.
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Figure 5A is an exploded, axial section through a tubular connection useful in
the
present invention.
Figure 5B is an assembled, axial section through a tubular connection useful
in the
present invention.
Figure 5C is a section along line Hof a pin end of Figure 5A.
Description of Various Embodiments
The detailed description set forth below in connection with the appended
drawings is
intended as a description of various embodiments of the present invention and
is not
intended to represent the only embodiments contemplated by the inventor. The
detailed
description includes specific details for the purpose of providing a
comprehensive
understanding of the present invention. However, it will be apparent to those
skilled in
the art that the present invention may be practiced without these specific
details.
A drilling accelerator can be installed in a drill string to facilitate
wellbore drilling
operations. Drilling accelerators are sometimes alternately called percussive
adapters,
drilling hammers, and fluid hammers. A drilling accelerator creates a
percussive effect
applied to the drilling bit that alone or with rotary drive of the bit causes
the drill bit to drill
into a formation.
With reference to Figure 1, the lower end of a drill string is shown. A
drilling accelerator
can include a drive converter connection that accepts rotational drive about
axis x
from a torque generating device 12 above and converts that rotational drive to
an axially
directed percussive force that is output to a bit box sub 14 positioned below
the drilling
accelerator. When such a drill string is in use with a drill bit 16 installed
in the bit box
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and the drill bit being rotationally driven, arrow R, the axially directed
percussive force,
arrow P, applied to the bit box sub is conveyed to the drill bit and can
facilitate drilling at
the drill bit.
One embodiment of drilling accelerator 10 is shown in Figure 2. Drilling
accelerator 10
may include an outer housing 18 including an upper end 18a and a lower end
18b.
Outer housing 18 is rugged, being exposed on its external surface 18c to the
wellbore
annulus and houses therewithin the drive components for generating a
percussive force.
To facilitate construction of the drilling accelerator, as will be
appreciated, the housing
can be formed in sections and connected together by various means such as by
welding, interlocks or threaded engagement, as shown at connections 21.
Upper end 18a of the housing is formed for connection into a drill string,
such as by
forming as a threaded connection. Lower end 18b of the housing is formed for
connection, shown herein directly but may be indirect, to a bit box sub 14.
Bit box sub
14 has formed therein a site, such as, for example, threaded bit box 20, for
accepting
connection of a drill bit.
Bit box sub 14 is connected for rotational movement with housing 18 through a
splined
connection 22. However, connection 22 permits axial sliding motion of the bit
box sub
within housing 18, such axial sliding motion being generated by a connection
to the
drive connection of drilling accelerator 10, the drive connection is intended
to drive the
bit box sub axially to apply a percussive force at any drill bit connected
into the bit box
during drilling. Seals may be provided, such as 0-rings and wiper seals 24 to
resist fluid
passage between the housing and the bit box sub, etc.
In one embodiment, the drive connection includes an axial shaft 30 supported
in
bearings 32 to convey rotational drive from an input end 30a to an output end
30b which
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carries a bevel gear 34. This bevel gear 34 meshes with a second bevel gear 36
mounted on transverse shaft 38 which is rotatably supported in the housing.
Transverse shaft 38 includes an eccentric 40 thereon which drives a drive
shaft 42.
Drive shaft 42 includes a strap 44 with a bearing 46 therein in which
eccentric 40
rotates. Drive shaft 42 at its opposite end includes an eye 48 through which
the drive
shaft is pinned via pin 50 to a percussion adapter 52 secured to bit box sub
14 for a drill
bit.
Rotation in shaft 30 through reduction gears 34, 36 will impart on the
percussive adapter
52 an axially directed reciprocation determined by the throw of eccentric 40.
This axially
directed reciprocation is then conveyed directly to any bit secured in the bit
box 20 of
the bit box sub.
The input torque may be generated by a mud motor. For example, axial shaft 30
may
be connected to a rotor of a mud motor such that any rotation of the rotor, by
flow of
drilling fluid through the motor, may be conveyed to the drive connection. In
one
embodiment, the mud motor may include a positive displacement-type motor
(PDM),
which uses pressure and flow of the drilling fluid to turn a rotor within a
stator. Shaft 30
can be connected directly or indirectly to the rotor, as through threaded
connection 60.
Where a bent sub is positioned between the motor and the drilling accelerator,
a
universal connector may be positioned therebetween to convey rotation from the
rotor to
the axial shaft.
The fluid that drives the motor can continue down through the accelerator and
to the bit.
As such, the accelerator may include drilling fluid passages 54 that can be
connected in
communication with the motor discharge and that extends from end 18a, about
the drive
connection components, to passages 62 through adapter 52 into a bore 56 of bit
box
sub 14. Passages 54 may be formed, as by milling, etc. through outer housing
18 and
can be directed by ports, seals, etc. from the discharge of the pump to
passages 62 into
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the inner bore of the bit box. In some embodiments, outer housing 18 may
require
thickening or laminate/telescopic construction to accommodate the passages.
Gears 34, 36 and other moving parts may be grease packed for lubrication
thereof. A
compensator may be provided, for example, in end 30a to accommodate or
alleviate
pressure differentials which may occur during down hole operations.
The embodiment of Figure 2 operates to drill a borehole by applying a
percussive force
through the drill bit to the formation, with or without rotating the drill
string from surface.
In another embodiment shown in Figure 3, the drilling accelerator may include
a drive
system for conveying rotational drive from the motor to the drill bit in
addition to the
percussive forces generated thereby.
Referring, therefore to Figures 3, a drilling accelerator is shown including
an outer
housing 118 including a lower end 118b, an axial shaft 130 (shown in part) to
convey
rotational drive from an input to a gear transmission, a shaft 138 including
an eccentric
140 for driving a drive shaft 142 and a percussion adapter 152 formed integral
with a bit
box sub 114 for a drill bit.
In this embodiment, the gear transmission includes gears to convey both
rotational and
axially reciprocal motion to the bit box sub. As illustrated, for example,
gear
transmission includes a first gear 135 that accepts input from bevel gear 134
and
meshes with a gear 136 that drives shaft 138. Gear 136 also meshes with a
second
bevel gear 139 that drives the rotation of an inner housing 166. Inner housing
166
extends and rotates within outer housing 118. Inner housing 166 is connected
at its
lower end for rotational transmission to bit box sub 114. In particular, as
shown, bit box
sub 114 is connected for rotational movement with housing 166 through a
splined
connection 122 such that any bit installed in the bit box can be driven to
rotate by
rotation conveyed from shaft 130.
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Connection 122 also permits axial sliding motion of the bit box sub within
housing 166,
such axial sliding motion being generated by a connection to shaft 138 of the
drilling
accelerator, the shaft intended to drive the bit box sub axially to apply a
percussive force
at any drill bit connected into the bit box during drilling, while gear 139
and housing 166
drive rotation of the bit box sub. Seals may be provided, such as 0-rings and
wiper
seals 124 to resist fluid passage between the housing and the bit box sub,
etc. Outer
housing 118 can extend down to protect the inner housing. Bearings 168 and
seals
124a may be provided to facilitate rotation and seal against fluid and debris
migration
between the parts.
In this embodiment, drive shaft 142 experiences differential rotation
therealong: where
upper portion 142a is not rotatably driven, but lower portion 142b is pinned
to
percussion adapter and is rotatably driven. In order to accommodate
differential rotation
along shaft 142, a bearing 170 can be provided along its length. Bearing 170
allows
rotational motion therein of part 142b about its long axis relative to part
142a, but resists
axial sliding motion such that axial percussive movement generated by the
throw of
eccentric 140 is conveyed along the shaft rather than being absorbed.
The input torque may be generated by a mud motor. For example, axial shaft 130
may
be connected to a rotor of a mud motor such that any rotation of the rotor, by
flow of
drilling fluid through the motor, may be conveyed to the drive connection.
It is to be understood that a cam and cam follower can be used to replace an
eccentric
and connected drive shaft (i.e. items 40, 42 of Figure 2). When using cams, it
may be
useful to use weight on bit to maintain the contact between the cam parts.
For example, as shown in Figures 4, another drilling accelerator 210 may
include an
outer housing 218 including an upper end 218a and a lower end 218b. Outer
housing
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218 is rugged, being exposed on its external surface 218c to the wellbore
annulus and
houses therewithin the drive components for generating a percussive force to
be applied
to a bit connected therebelow.
To facilitate construction of the drilling accelerator, as will be
appreciated, the housing
can be formed in sections and connected together by various means such as by
welding, interlocks or threaded connections 280.
Upper end 218a of the housing is formed for connection at the distal end of a
drill string.
Lower end 218b of the housing accommodates a bit box sub 214, which
telescopically
extends from lower end 218b.
Bit box sub 214 has formed therein a site, such as, for example, threaded bit
box 220,
for accepting connection of a drill bit (not shown). A bushing and safety
catch 224 acts
between housing 218 and sub 214 to allow rotation of the sub within the
housing and
may secure the sub against fully passing out of the housing lower end 218b.
Safety
catch 224 allows some axial sliding motion of sub 214 within the housing, such
axial
motion, for example, resulting from moving the sub between a lower position
(as shown)
and an upper, weight on bit position and being that as a result of the
percussive force.
In one embodiment, safety catch 224 may be eliminated with the safety
provisions
thereof instead taken up entirely by interacting shoulders 225a, 225b on the
parts. This
allows housing end 218b to be thicker along its length.
Bit box sub 214 is connected to an axial shaft 230, the combination of sub 214
and shaft
230 acting to transmit drive energy from an input end 230a of the shaft to a
drill bit
installed in box 220. Bit box sub 214 and axial shaft 230 may be connected by
a
telescoping splined connection 222 that ensures continuous rotational drive
conveyance
while permitting axial sliding motion of the bit box sub relative to shaft
230.
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The input torque applied to end 230 may be generated by a mud motor. For
example,
axial shaft 230 may be connected to a rotor of a mud motor such that any
rotation of the
rotor, as by flow of drilling fluid through the motor, may be conveyed to the
bit box sub.
In one embodiment, the mud motor may include a positive displacement-type
motor
(PDM), which uses pressure and flow of the drilling fluid to turn a rotor
within a stator.
Shaft 230 can be connected directly or indirectly to the rotor, as through
threaded
connection 260. Where a bent sub is positioned between the motor and the
drilling
accelerator, a universal connector may be positioned therebetween to convey
rotation
from the rotor to the axial shaft.
The fluid that drives the motor can continue down through the axial shaft and
sub 214
and to the bit. As such, these parts may include drilling fluid passages such
as axial
bores 254 passing therethrough that can be connected in communication with the
motor
discharge.
Bearings 268, 268a and bushings 268b may be positioned between the axial shaft
and
the housing to accommodate radial and on bottom and off bottom thrust loads. A
safety
catch may also be provided between these parts.
Drilling accelerator 210 further includes a drive converter intended to
convert the
rotational drive from the motor to an axial, reciprocating motion to drive the
bit box sub
axially to apply a percussive force at any drill bit connected into the bit
box during
drilling.
In the illustrated embodiment, the drive converter includes a pair of cam
surfaces 270a,
270b. The first cam surface 270a is installed in the housing and the second
cam
surface 270b is installed to move with bit box sub 214. Cam surfaces 270a,
270b are
positioned to be separated by a gap 272 when the bit box is in its lower
position, as
shown, but can come together when weight is placed on bit. In other words, gap
272
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closes when bit box sub is moved into its upper, weight on bit position.
Because the
housing and shaft/bit box sub 230/214 rotate at different speeds, the cam
surfaces act
to ride over each other. Generally, rotation of sub 214 within and at a faster
rate than
any rotation of the housing causes cam surface 270b to ride over cam surface
270a and
cam surface 270a effectively becomes the cam follower. Cam surfaces 270a, 270b
include one or more cam protrusions 274a, 274b that are oriented and
configured to act
with consideration of the direction of relative rotation therebetween such
that the cam
surfaces ride up over each other and drop down thereby generating an axial
percussive
force to be applied to the bit box sub 214. Cam protrusions 274a, 274b have a
ramped
approach side, a peak and an exit side. The ramped approach side inclines
upwardly to
allow the cam protrusions to ride easily up over each other toward the peak.
The exit
side of the protrusions can be ramped down away from the peak, but a more
significant
percussive effect may be provided by forming the exit side as shown with an
abrupt
height change forming a drop off such that the forces (i.e. weight on bit)
that drive the
cam surfaces together force the parts to abruptly close any gap between them,
the gap
formed when the protrusions exit off each other. The gap closing develops an
abrupt,
hammering vibration as the surfaces again come together. While one or more cam
protrusions can be provided, it may be useful to position the cam protrusions
in a
balanced fashion about surfaces 270a, 270b, for example, by positioning the
protrusions
each equally spaced about the circumference of the cam surface such that all
protrusions are on the approach side at the same time. As shown, for example,
protrusions 274a, 274b can be in pairs on each surface with a first protrusion
of the pair
diametrically opposed from the second protrusion of the pair on their cam
surface. This
may reduce adverse lateral forces in the accelerator.
Cam surfaces 270a, 270b may be formed from materials that accommodate
considerable wear without rapid break down.
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In another embodiment, one or both of the cam surfaces may be include bearings
to
facilitate movement of the surfaces over one another and reduce detrimental
wear to
increase tool longevity. For example, in one embodiment, as shown in Figures
4C and
4D, the cam protrusions on one of the cam surfaces, for example, surface 270a
of
Figure 4 may be replaced by a cam insert 275a carrying rollers 279 on the cam
surface
270c. Rollers 279 are installed to ride up over the cam protrusions 274b of
the opposite
surface (i.e. surface 270b) and drop down the exit side of the protrusions to
create a
vibratory effect. In one embodiment, the rollers may be ball bearing type
rollers carried
in the selected cam surface. Alternately, the rollers may be cylindrical
rollers, as shown,
or conical type rollers held to rotate along an axis extending radially from
the tool long
axis x.
Rotation in shaft 230 and bit box sub 214 relative to housing 218 will impart
on sub 214
axially directed reciprocation determined by the throw of cam protrusions
274a, 274b of
surfaces 270a, 270b. This axially directed reciprocation is then conveyed as a
vibratory
effect to any bit secured in, directly or indirectly, the bit box 220 of the
bit box sub.
The vibratory effect may be created by axially reciprocating movement created
at the
interacting cam surfaces which causes a hammering effect when the two parts
impact
against one another. However, in one embodiment, the tool may be selected to
create
the vibratory effect by first generating axially reciprocating movement at the
interacting
cam surfaces that in turn cause a hammering effect at surfaces apart from the
cam
surfaces. In such an embodiment, the form of the cam surfaces may be preserved
by
reducing the detrimental wear caused by the parts striking against one
another. In
particular, while the reciprocating action is generated at the cam surfaces,
the impact
creating the hammering effect is generated elsewhere. Such an embodiment may
be
provided, for example, by provision of a two part mandrel, as provided by
axial shaft 230
and bit box sub 230, selected to take up and generate the hammering effect
caused by
the throw of the cam surfaces. In the illustrated embodiment, for example,
while the
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cam surfaces 270a, 270b create an axially reciprocating motion, the hammering
effect
generated by that motion occurs at the telescoping splined connection 222. The
axially
sliding motion that is created by the cam surfaces riding over one another
causes the
upper cam surface 270a, housing 218 and axial shaft 230 to be raised relative
to bit box
sub 214, as by axial movement between axial shaft 230 and bit box sub 214 at
the
telescoping splined connection 222. As the cam surfaces continue to ride over
one
another, the cam protrusions 274a, 274b (which may or may not include rollers)
will
drop off each other on their exit sides and this, in turn, causes upper cam
surface 270a,
housing 218 and axial shaft 230 to drop down. When this happens, end 230a of
shaft
230 will strike against upper end 214a of bit box sub 214 (inside connection
222)
creating a hammering effect that is conveyed to the bit in bit box 220. To
ensure that
the major striking force occurs at connection 222 between parts 214a and 230a,
any
operational gap between parts 214a, 230a, which is the maximum gap distance
achieved when there is weight on bit driving sub 214 up into the housing and
the cams
have driven parts 214a, 230a apart, should be at least slightly less than the
maximum,
unrestricted throw of cam surfaces, which is the maximum unrestricted distance
that
could be traveled by upper cam surface 270a as its cam protrusions 274 or
rollers drop
off the cam protrusions or rollers on lower cam surface 270b. If the gap
between parts
214a and 230a is more than the throw of the cam surfaces, the cam surfaces
will strike
each other before the axial shaft and bit box sub can come together. Although
this will
create a percussive effect, it does cause greater wear at the cam surfaces and
requires
the use of adequate thrust and radial bearings along the axial shaft. However,
by
selecting the gap distance between parts 214a, 230a to be less than the throw
of the
cam surfaces, the hammering is taken up and generated along the shaft, which
maintains the force in line, concentrated around the center axis x of the tool
and
between more rugged parts. In such an embodiment, the cam surfaces also are
protected from at least some wear, reducing their need for repair or
replacement.
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In one embodiment, the contact surfaces between parts, where the hammering
effect is
generated may be supplemented with percussion plates that have a greater wear
resistance than the other materials of these parts. In one embodiment, seals
or
structures may be provided to facilitate fluid flow through bore 254 past the
impact area
between parts 214a, 230a. For example, in one embodiment, a sleeve/nipple may
provided on one part 214a or 230a that inserts into an enlarged region of the
bore
formed on the other of the two parts and seals, such as o-rings may be
provided
therebetween to prevent fluid from passing from bore 254 into the impact
region
between the parts.
In the illustrated embodiment, first cam surface 270a is provided by a ring
275 installed
in housing 218. Ring 275 forms surface 270a annularly with protrusions 274a
downwardly facing. A bore 276 in the ring provides an opening through which a
portion
of shaft 230 (as illustrated) or bit box sub 214 extends. Second cam surface
270b, in
the illustrated embodiment, is provided by a ring 277 that includes threads
278 for
securing on an end of sub 214 such that surface 270b is facing upwardly to
position its
cam protrusions 274b for engagement against those on surface 270a.
Ring 275 and housing 218, at shoulder 218c, bear against each other such that
movement, such as upward movement caused by interaction of the cam surfaces,
is
transferred to the housing. In addition, ring 275 and housing, at shoulder
230c, also
may bear against each other such that upward movement caused by interaction of
the
cam surfaces is as well transferred to the shaft 230.
The embodiment of Figure 4 operates to drill a borehole by applying a
percussive force
through the drill bit to the formation when weight is applied on bit. When the
bit is lifted
off bottom, the bit box sub 214 is able to drop into its lower position which
separates the
cam surfaces and discontinues the percussive force.
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When weight on bit is resumed and axial shaft 230 is driven to rotate, cam
surfaces
270a, 270b will be rotated at different speeds such that their cam surfaces
will ride up
over one another and drop off the exit side causing housing 218 and axial
shaft to be
lifted away from bit box sub 214, as that sub and the bit it carries remains
on bottom,
and, thereafter, as the cam protrusions exit off one another, the housing and
the axial
shaft drop down. When the housing and axial shaft 230 drop down, a hammering
effect
is applied to bit box sub, as by surface 230a striking surface 214a.
The use of a percussive adapter to apply a percussive, axially directed
reciprocation to
a drill bit may generate left hand torque in the drill string. Such torque may
adversely
effect standard threaded connections along the string, such as connections
280,
causing them to become loosened or to unthread completely. As such, with
reference
to Figures 5, a threaded connection can be used at connection 280 or in
connections in
other string components that can accommodate left hand torque substantially
without
weakening the connection. In one embodiment, such a connection includes a
collar 380
including a pair of threaded box ends 382, 384. Box end 382 includes a thread
form
extending in a direction opposite from the thread form of box end 384. For
example, if
box end 382 includes a left hand thread, box end 384 includes a right hand
thread. As
will be appreciated by persons skilled in the art of wellbore tubular strings,
a collar is the
term used to describe a substantially cylindrical connector that is formed to
accept
threaded engagement of a pair of tubulars, each with a threaded pin end. The
box ends
each have thread forms that start adjacent the collar end face 382a, 384a,
respectively,
and extend fully or partially toward a crest 385. Crest 385 may be threaded or
smooth,
depending on the type of collar.
The illustrated connection further includes a first wellbore tubular 386 and a
second
wellbore tubular 388, each formed with a pin end 386a, 388a, respectively.
Tubulars
386, 388 can by housing sections of a drilling accelerator, mud motor, or
other tubular
portions of a down hole assembly or drill string. Each pin end has a pin end
face 386b,
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388b, respectively. The pin ends each include a thread form selected to thread
into
their respective box end 382 or 384. Pin ends 386a, 388a further have
corresponding
stepped regions formed by axial extensions from their pin end faces such that
the pin
ends can engage each other to restrict or possibly eliminate relative
rotational
movement therebetween about their long axis xt, when they are held end face
adjacent
to end face in collar 380. The stepped regions are formed by varying the pin
end's
length from its pin base to its end face, creating an axially extending
stepped area along
the pin end face. For example, one pin end face 386b includes a stepped
extension
where the face has a length change creating a shoulder 389a while the other
pin end
face 388b includes a stepped recess along its circumference also creating a
shoulder
389b, the stepped recess is formed to correspond to and, for example, follow
in the
reverse, the stepped extension of the first pin end such that the two
shoulders can be
seated against each other, preventing the two pin ends from rotating relative
to each
other. To most effectively prevent relative rotation between the pin ends, the
stepped
regions may be formed of abrupt length changes creating sharper corners,
rather than
being curved undulations that could ride over each other. Also, to allow the
pin ends to
mesh, as by being advanced towards each other along their long axis, it will
be
appreciated that the stepped regions may form the shoulders along a line
substantially
aligned with the tubular's long axis. .
It will be appreciated that such shoulders formed by stepped regions and
recesses, form
at least one tooth 390a, 390b extending from each pin end face 386b, 388b,
each
formed so that the pin end faces can mesh and be prevented from rotating
relative to
each other.
The shoulders may be positioned to resist the relative rotation that is
adverse to the
threaded condition of the connection. For example, in one embodiment, the
shoulders
may be positioned to provide resistance to back off by left hand torque.
Alternately,
each pin end face may include at least one left hand facing shoulder and at
least one
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right hand facing shoulder such that the tubulars are substantially prevented
from
rotating in either direction relative to each other. In the illustrated
embodiment, the
tubulars each include a plurality of left and right hand facing shoulders
forming, in effect,
a plurality of teeth with gaps g therebetween. The teeth on the first wellbore
tubular are
formed to mesh closely between the teeth on the second wellbore tubular. In
particular,
the teeth 390a of the first tubular are formed to fit tightly between the
teeth 390b on the
second tubular such that, if the pins are brought together, end to end, the
teeth 390a fit
into the gaps between teeth 390b with the sides 390a' of teeth 390a positioned
closely
alongside the sides 390b' of teeth 390b. In this position, engagement between
the
shoulders 389a, 389b formed by the sides of the teeth prevents rotation of one
pin end
relative to the other, when they are held pin end to pin end in the collar.
Forces tending to urge the pin ends to rotate about their long axis to
unthread from the
connection are resisted by contact between the shoulders of the pin ends. As
such, it is
useful to provide a reasonable surface area for contact between the shoulders
of
opposite pin ends. In one embodiment, for example, corresponding shoulders may
have sides 390a', 390b' that are cut substantially radially, in other words
substantially
along a radial line extending out from the center axis of the tubular.
Pin end faces and shoulders may have close tolerances. If some flex is desired
at the
connection, such that the lateral rigidity at the connection is reduced,
tolerances may be
relaxed between pin end faces, such that the length of the shoulder extension
on one
tubular does not quite equal the depth of the shoulder on the opposite
tubular. In other
words, the length L of the teeth, measured from tip 392 to base 393 (Figure
5C) on one
tubular is more than the length of the teeth on the other tubular. The gap
formed
between the tips of one tubulars teeth and the bases of the other tubulars
teeth allows
some lateral flex at the connection. Another option to provide for more
lateral deflection
at the connection, in addition or alternately to the foregoing, may be to
indent the outer
surface of the teeth. This reduces the thickness t (Figure 5C) of the pin end
along the
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length of the teeth and may create a space between the tooth and the inner
surface of
the collar, when the pin is threaded into the collar. The surface indentation
can be
initiated at a tapering surface 391 adjacent the base 393 of the teeth to
provide more
landing space for lateral deflection.
The type of thread form, including for example, taper and pitch, used in the
connection
is not particularly important. In one embodiment, a modified Acme thread may
be used
to enhance seating and to deter fluid migration through the threaded
interfaces at the
connection, but other thread forms may be used, as desired.
Seals may be provided in the connection, such as for example o-rings 392 in
the collar
at the crest and/or at interfacing surfaces, for example surfaces 394a, 394b
with close
tolerances, to enhance the fluid sealing properties of the collar.
To make up the connection, the first and second wellbore tubulars are aligned
to be
threaded into their respective box ends of the collar and also, the tubulars
are aligned
with their teeth offset so that the teeth of each tubular are aligned to mesh
into the
openings between the teeth of the other tubular. In this way, the stepped
regions
formed by the teeth on one tubular may be set against the shoulders formed by
the
teeth on the other tubular. With the teeth alignment preserved, the first and
second
wellbore tubulars are then brought into a position such that their threads can
be
engaged by the threads of the collar and the collar is rotated about its long
axis to
engage the tubular pin ends and draw the pin ends into the collar. As the
tubulars are
drawn in by the collar, the teeth become meshed at the thread crest.
Once threaded together, the interlock provided by the intermeshed teeth act
against,
and may prevent completely, back off in the connection even where there is
considerable left hand torque. In addition, torque tends not to be transferred
through
the threads of the connection. Also, by allowing some tolerance between the
pin end
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faces, the connection can allow for lateral flexing, such that the connection
may not
become too stiff.
When using the connection, it may be useful to position the right hand
threaded pin end
on the uphole end of the connection. Generally in wellbore operations, torque
input
from surface is most often to the right. As such, placing the right hand
threaded pin end
on the upper end of the connection ensures that even if the connection itself
binds down
hole, the string will in its normal rotation continue to drive the pin end
into the
connection, rather than backing off. That being said, it is believed that such
a condition
would be rare. It is believed that with the pin to pin locking provided by the
teeth, the
only way the torque won't transition through the connection is if the collar
completely
binds down hole such that it cannot rotate, while the tubulars both have
opposite torque
applied thereto sufficient to overcome the interlock of the teeth.
Left hand torque is common and often problematic in mud motor applications
such as
the current motor driven drilling hammer. However, the connection may also be
useful
for other applications where left hand torque tends to act adversely on
tubular
connections such as in subs adjacent any rotationally driven drill bit.
To release the connection, the collar is reverse rotated about the
connection's axis xt,
again while the tubulars are held stationary.
The previous description of the disclosed embodiments is provided to enable
any
person skilled in the art to make or use the present invention. Various
modifications to
those embodiments will be readily apparent to those skilled in the art, and
the generic
principles defined herein may be applied to other embodiments. Thus, the
present
invention is not intended to be limited to the embodiments shown herein, but
is to be
accorded the full scope consistent with the claims, wherein reference to an
element in
the singular, such as by use of the
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article "a" or "an" is not intended to mean "one and only one" unless
specifically so
stated, but rather "one or more". All structural and functional equivalents to
the
elements of the various embodiments described throughout the disclosure that
are know
or later come to be known to those of ordinary skill in the art are intended
to be
encompassed by the elements of the claims. Moreover, nothing disclosed herein
is
intended to be dedicated to the public regardless of whether such disclosure
is explicitly
recited in the claims.
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