U.S. patent application number 11/779737 was filed with the patent office on 2009-01-22 for downhole shock absorber for torsional and axial loads.
This patent application is currently assigned to Diamond Back - Quantum Drilling Motors, L.L.C.. Invention is credited to William C. Koger.
Application Number | 20090023502 11/779737 |
Document ID | / |
Family ID | 40265293 |
Filed Date | 2009-01-22 |
United States Patent
Application |
20090023502 |
Kind Code |
A1 |
Koger; William C. |
January 22, 2009 |
DOWNHOLE SHOCK ABSORBER FOR TORSIONAL AND AXIAL LOADS
Abstract
A shock-absorber subassembly for a subsurface drilling assembly
is disclosed. The shock-absorber subassembly comprises a mandrel, a
body assembly, and at least one torsional spring assembly. The
mandrel has a bore extending therethrough and has one end
connectable to a portion of the subsurface drilling assembly. The
body assembly has a bore extending therethrough and one end
connectable to another portion of the subsurface drilling assembly.
The body assembly is coupled to the mandrel to establish fluid
communication between the bore of the mandrel and the bore of the
body assembly and to permit planar rotational movement of the
mandrel relative to the body assembly. The at least one torsional
spring assembly engages the mandrel and the body assembly to absorb
torsional shocks and vibrations between the mandrel and the body
assembly and to limit the degree of planar rotation between the
mandrel and the body assembly. In a second embodiment, the body
assembly is coupled to the mandrel to permit axial movement as well
as planar rotational movement. In this second embodiment, the
shock-absorber subassembly further comprises at least one axial
spring assembly engaging the mandrel and the body assembly to
absorb axial shocks and vibrations between the mandrel and the body
assembly.
Inventors: |
Koger; William C.; (Edmond,
OK) |
Correspondence
Address: |
DUNLAP CODDING, P.C.
PO BOX 16370
OKLAHOMA CITY
OK
73113
US
|
Assignee: |
Diamond Back - Quantum Drilling
Motors, L.L.C.
|
Family ID: |
40265293 |
Appl. No.: |
11/779737 |
Filed: |
July 18, 2007 |
Current U.S.
Class: |
464/20 ;
175/57 |
Current CPC
Class: |
E21B 17/07 20130101 |
Class at
Publication: |
464/20 ;
175/57 |
International
Class: |
E21B 17/20 20060101
E21B017/20; E21B 7/00 20060101 E21B007/00 |
Claims
1. A shock-absorber subassembly for a subsurface drilling assembly,
the shock-absorber subassembly comprising: a mandrel having a bore
extending therethrough and having one end connectable to a portion
of the subsurface drilling assembly; a body assembly having a bore
extending therethrough and one end connectable to another portion
of the subsurface drilling assembly, the body assembly coupled to
the mandrel to establish fluid communication between the bore of
the mandrel and the bore of the body assembly and to permit planar
rotational movement of the mandrel relative to the body assembly;
and at least one torsional spring assembly engaging the mandrel and
the body assembly to absorb torsional shocks and vibrations between
the mandrel and the body assembly and to limit the degree of planar
rotation between the mandrel and the body assembly.
2. The shock-absorber subassembly of claim 1, wherein the torsional
spring assembly comprises: a rigid drive key; and at least one
spring engaging the drive key.
3. The shock-absorber subassembly of claim 2, wherein the at least
one spring comprises two springs engaging the drive key and each
spring opposingly-disposed on opposite sides of the drive key.
4. The shock-absorber subassembly of claim 3, wherein each spring
is a flat spring having at least one arcuate portion.
5. The shock-absorber subassembly of claim 1, wherein an outer
surface of the mandrel has at least one spring recess defined
therein, and wherein an inner surface of the body assembly has at
least one spring recess defined therein, the at least one spring
recess of the mandrel and the at least one spring recess of the
body assembly cooperating to form at least one spring chamber
therebetween, the torsional spring assembly positioned in the
spring chamber.
6. The shock-absorber subassembly of claim 5, wherein the torsional
spring assembly comprises: a rigid drive key; and at least one
spring engaging the drive key and at least one of the mandrel or
the body assembly.
7. The shock-absorber subassembly of claim 6, wherein the at least
one spring comprises two springs engaging the drive key and each
spring opposingly-disposed on opposite sides of the drive key.
8. The shock-absorber subassembly of claim 7, wherein each spring
is a flat spring having at least one arcuate portion.
9. A shock-absorber subassembly for a subsurface drilling assembly,
the shock-absorber subassembly comprising: a mandrel having a bore
extending therethrough and having one end connectable to a portion
of the subsurface drilling assembly; a body assembly having a bore
extending therethrough and one end connectable to another portion
of the subsurface drilling assembly, the body assembly coupled to
the mandrel to establish fluid communication between the bore of
the mandrel and the bore of the body assembly and to permit planar
rotational movement and axial movement of the mandrel relative to
the body assembly; at least one torsional spring assembly engaging
the mandrel and the body assembly to absorb torsional shocks and
vibrations between the mandrel and the body assembly and to limit
the degree of planar rotation between the mandrel and the body
assembly; and, at least one axial spring assembly engaging the
mandrel and the body assembly to absorb axial shocks and vibrations
between the mandrel and the body assembly.
10. The shock-absorber subassembly of claim 9, wherein the
torsional spring assembly comprises: a rigid drive key; and at
least one spring engaging the drive key.
11. The shock-absorber subassembly of claim 10, wherein the at
least one spring comprises two springs engaging the drive key and
each spring opposingly-disposed on opposite sides of the drive
key.
12. The shock-absorber subassembly of claim 11, wherein each spring
is a flat spring having at least one arcuate portion.
13. The shock-absorber subassembly of claim 12, wherein an outer
surface of the mandrel has at least one spring recess defined
therein, and wherein an inner surface of the body assembly has at
least one spring recess defined therein, the at least one spring
recess of the mandrel and the at least one spring recess of the
body assembly cooperating to form at least one spring chamber
therebetween, the torsional spring assembly positioned in the
spring chamber.
14. The shock-absorber subassembly of claim 13, wherein the spring
recesses in the mandrel and the body assembly have a length greater
than the length of the torsional spring assembly to permit axial
movement of the torsional spring assembly within the spring chamber
during axial movement of the body assembly relative to the
mandrel.
15. The shock-absorber subassembly of claim 14, wherein the
torsional spring assembly comprises: a rigid drive key; and at
least one spring engaging the drive key and at least one of the
mandrel or the body assembly.
16. The shock-absorber subassembly of claim 15, wherein the at
least one spring comprises two springs engaging the drive key and
each spring opposingly-disposed on opposite sides of the drive
key.
17. The shock-absorber subassembly of claim 16, wherein each spring
is a flat spring having at least one arcuate portion.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates generally to a
vibration-dampening and shock-absorbing device, and more
particularly, but not by way of limitation, to a shock-absorber
subassembly adapted to engage a subsurface drilling assembly above
the drill bit, the shock-absorber subassembly provided with at
least one resilient shock absorber for absorbing torsional
vibrations, shocks, and impact loads to prevent and reduce wear on
drilling components.
[0003] 2. Brief Description of Related Art
[0004] During the drilling of an oil or gas well, a drill string is
rotated from the surface causing a drill bit to cut and crush rock
formations with the weight of drill collars assisting in driving
the drill bit downward into contact with the underlying rock. Drill
collars also act as conduits for the drilling fluids or "mud" used
to lubricate the drill bit and carry cuttings back to the surface.
Mud motors and turbines are sometimes employed down-hole to aid the
drill bit rotation.
[0005] The drilling of oil and gas wells often takes place in rock
formations. These rock formations are often porous and have layers
of varying hardness. In drilling through such formations, the drill
bit may generate significant vibrations, shocks, and impact loads.
If transmitted to the drill string, the vibrations, shocks, and
impact loads will eventually cause metal fatigue which could result
in cracking and ultimate failure of joints between drill string
segments, as well as entire drill string components. The direct
transfer of these loads from the drill bit to the drill string
reduces the useful life of the drill bit. Additionally, the
efficiency may be reduced because the shocks and impact loads may
cause the drill bit to "jump" or lose contact with the surface
being drilled.
[0006] Vibrations, shocks, and impact loads may also have an
adverse affect on sensors and electronics located within the drill
string. At various points during the drilling process, specialized
measurement and telemetry tools can also be employed to assess
downhole conditions. Methods known in the art include
measurement-while-drilling (MWD) and logging-while-drilling (LWD);
such methods employ a diverse and evolving range of sensors. These
sensors are usually located in the drill string near the drill bit
and measure data such as resistivity, gravity, magnetic and nuclear
magnetic resonance. The sensors then store the data in down-hole
memory or transmit the data to the surface.
[0007] While such sensors provide highly useful information about
the down-hole drilling environment, vibration due to the drilling
process can damage the sensors. An axial load is applied to the
drill bit during drilling into underlying formations, and this
produces vibrations in the overlying drill string, and vibration
can occur due to drill string rotation in a deviated or directional
well bore. While most of these sensors are sufficiently robust to
address the vibrations of normal drilling conditions, extended
vibrations, and especially heavy shocks or impact loads may have
adverse affects on the data measured by the sensors, and may
eventually lead to sensor damage and failure.
[0008] A number of attempts have been made in the prior art to
provide a shock absorber between the drill bit and the rest of the
drill string so as to reduce the vibrations and shocks that are
transmitted to the drill string. Several attempts have been made in
the prior art to reduce axial loads with shock absorbers that rely
on helical springs, Belleville springs, and wire mesh springs. In
addition, several attempts have been made in the prior art to
reduce both axial and torsional loads with shock absorbers that
rely on helical springs or helical grooves. The use of helical
geometry to reduce both axial and torsional loads makes the
reduction of one of the axial or torsional loads interdependent on
the other. That is, if the shock absorbing structure fails, neither
axial nor torsional loads will be reduced. Additionally, the
interdependence of the geometry may reduce the effectiveness of the
shock absorber with respect to both axial and torsional loads.
[0009] To this end, a need exists for an improved shock absorber
with independent means for reducing the transmission of axial loads
and independent means for reducing the transmission of torsional
loads. In addition, due to the current use of shock absorbers that
are directed solely to reducing the transmission of axial loads, a
need exists for an improved torsional shock-absorber that may be
implemented in conjunction with an axial shock-absorber. It is to
such an apparatus that the present invention is directed.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0010] FIG. 1 is a schematic view of a drilling assembly.
[0011] FIG. 2 is an exploded perspective view of a shock-absorber
subassembly constructed in accordance with the present
invention.
[0012] FIG. 3 is a cross-sectional view of the shock-absorber
subassembly.
[0013] FIG. 4 is an enlarged cross-sectional view of the
shock-absorber subassembly illustrating a torsional spring assembly
constructed in accordance with the present invention.
[0014] FIG. 5 is a perspective view of the torsional spring
assembly constructed in accordance with the present invention.
[0015] FIG. 6 is a cross-sectional view of one embodiment of the
shock-absorber subassembly taken along line 6-6 of FIG. 4.
DETAILED DESCRIPTION OF THE INVENTION
[0016] Referring to the drawings, and more particularly to FIG. 1,
a subsurface drilling assembly is depicted as an example of one
context for the use of the present invention. The depiction is
purely illustrative and exemplary, and is not intended to be
limiting in any way. Specifically, a drill string 10 is shown
suspended in a wellbore 14 and supported at the surface 18 by a
drilling rig 22. The drill string 10 includes multiple joints of
drill pipe 26 coupled to a downhole tool assembly 30. The downhole
tool assembly 30 includes multiple drill collars 34, an
instrumented drill pipe 38, a mud motor 42, and a drill bit 46. The
drill string 10 also preferably comprises a shock-absorber
subassembly 50. The shock-absorber subassembly is most preferably
disposed immediately above the mud motor 42, but may also be
disposed between the mud motor 42 and the drill bit 46, or
otherwise disposed further up the drill string 10 from the mud
motor 42.
[0017] The drill bit 46 is rotated by the mud motor 42 which
responds to the flow of drilling fluid, or mud, which is pumped
from a mud tank (not shown) through a central passageway or mud
channel through the drill pipe 26, drill collars 34, the
instrumented drill pipe 38, the shock-absorber subassembly 50, and
then to the mud motor 42. The pumped drilling fluid jets out of the
drill bit 46 and flows back to the surface through an annulus
formed between the drill string 10 and the wellbore 14. The
drilling fluid carries debris away from the drill bit 46 as the
drilling fluid flows back to the surface. The drill collars 34
provide a means to provide weight on the drill bit 46 while
maintaining the drill pipe 26 in tension, enabling the drill bit 46
to crush and cut the formations as the mud motor 42 rotates the
drill bit 46.
[0018] As drilling progresses, it is desirable to monitor a variety
of downhole conditions. To accomplish this, an elongated portion of
instrumented drill pipe 38 is used to measure downhole parameters
and formation characteristics. The data can be transmitted in real
time utilizing mud pulse and electromagnetic telemetry or recorded
in downhole memory and retrieved after the tool returns to the
surface.
[0019] Similarly, to help ensure consistent and efficient drilling,
it is desirable to have one or more shock-absorber assemblies 50
disposed above the drill bit 46 in the drill string 10. The
shock-absorber subassembly 50 preferably reduces the transfer of
torsional and/or axial shocks and vibrations between the drill bit
and the drill string 10. The present invention is directed to
several embodiments of an improved version of a shock-absorber
subassembly 50.
[0020] Referring now to FIG. 2, an exploded perspective view of one
embodiment of shock-absorber subassembly 50 is shown.
Shock-absorber subassemblies have been used for some time in the
art and thus not all elements will be described in as much detail.
The present invention is particularly directed to the incorporation
of a torsional shock absorbing element into a shock-absorber
subassembly 50. Thus, the torsional shock-absorber elements are
described in the most detail, while other elements are described
with enough particularity that one skilled in the art will
understand the context within which the torsional shock-absorber
elements may be implemented. Thus, it should be understood that the
disclosure will enable one skilled in the art to implement the
torsional shock-absorber elements described herein either alone or
in a variety of shock-absorber subassembly configurations.
Similarly, the materials used in such subassemblies are well known
in the art and any suitable materials may be used for a given
application. For example, when the shock-absorber subassembly 50 is
disposed near the instrumented drill pipe 38 (FIG. 1), it may be
desirable to construct the shock-absorber subassembly 50 out of
non-magnetic alloys. Similarly, seal and spring materials are well
known in the art, and may be constructed from natural or synthetic
rubber, polyurethane, or other suitable polymers.
[0021] In one embodiment, the shock-absorber subassembly 50
comprises a mandrel assembly 54 and a body assembly 58 rotatably
mounted about the mandrel assembly 54. For simplicity and clarity,
the mandrel assembly 54 may also be referred to as the mandrel
herein and in the attached claims. The mandrel assembly 54
preferably comprises a mandrel body 62, a washpipe 66, and a sleeve
70. Additionally, the mandrel assembly 54 is provided with bore 72
extending through the mandrel body 62 and the washpipe 66, and, as
necessary for other embodiments, the sleeve 70. The mandrel body 62
is preferably cylindrically-shaped and is formed with a base
portion 74, a compression portion 78, a spindle portion 82, and a
connection portion 86. The base portion 74 is adapted to engage one
of the drill bit 46 (FIG. 1) or another portion of the drill string
10 (FIG. 1). As will be appreciated by those skilled in the art,
the base portion 74 can be either internally or externally
threaded, that is, provided with male or female threads, to permit
the mandrel 50 to be connected to one of the drill bit 46 (FIG. 1)
or another portion of the drill string 10 (FIG. 1).
[0022] The compression portion 78 is preferably formed with a
smaller diameter than that of the base portion 74 so as to form a
shoulder 94 between the compression portion 78 and the base portion
74. The spindle portion 82 is formed with a smaller diameter than
that of the compression portion 78 so as to form a seal shoulder 98
between the spindle portion 82 and the compression portion 78. The
spindle portion 82 is also formed with at least one torsional
spring recess 102 sized to receive a torsional spring assembly 106.
More preferably, the spindle portion 108 is provided with a
plurality of spring recesses 102 equally spaced about the
circumference of the spindle portion 82. As shown, the connection
portion 86 is preferably formed with internal, or female, threads
for receiving the washpipe 66, and with external, or male, threads
for engaging the sleeve 70.
[0023] The washpipe 66 is formed with an elongated, cylindrical
shape and has a threaded end 110 sized to engage the female threads
of the connection portion 86 of the mandrel body 62. The sleeve 70
is preferably formed with a hollow, cylindrical extension portion
114 and a flange portion 118. The extension portion is sized to fit
snugly about the washpipe 66 and the flange portion 118 is provided
with internal threads sized to engage the external threads of the
connection portion 86 of the mandrel body 54.
[0024] The body assembly 58 includes a top packing sub 200, a seal
assembly 204, an axial spring assembly 208, an axial spring sub
212, a torsional spring sub 216, and a bottom packing sub 220. The
body assembly 58 is provided with a bore 238 extending through the
top packing sub 200, and, as necessary for other embodiments, the
axial spring sub 212, torsional spring sub 216, and lower packing
sub 220. When the shock-absorber subassembly 50 is assembled, as
described below, the bore 238 through the body assembly 58 axially
aligns with the bore 72 through the mandrel assembly 54 such that
the bores 238 and 72 are in fluid communication and cooperate to
form a mud channel through the entire shock-absorber subassembly
50.
[0025] The top packing sub 200 is preferably cylindrically-shaped
and is formed with a distal end 224. The distal end 224 is adapted
to engage one of the drill bit 46 (FIG. 1) or another portion of
the drill string 10 (FIG. 1). As will be appreciated by those
skilled in the art, the distal end 224 can be either internally or
externally threaded, that is, provided with male or female threads,
to permit the mandrel body assembly 58 to be connected to one of
the drill bit 46 (FIG. 1) or another portion of the drill string 10
(FIG. 1). Each of the top packing sub 200, axial spring sub 212,
torsional spring sub 216, and bottom packing sub 220 are formed
with correspondingly-threaded ends 228 such that they can be
sequentially connected as shown. The threaded ends 228 may be
formed as male or female threads in any suitable size or thread
pitch, so long as adjacent ends of adjacent pieces correspond to on
another, i.e., can be threaded together as shown to form a firm
connection. The torsional spring sub 216 is provided with at least
one spring recess 232 (FIG. 3) to correspond to each spring recess
106 in the spindle portion 82 of the mandrel body 62. The bottom
packing sub 220 is further formed with an internally-smooth distal
end 236 such that relative axial displacement may be permitted
between the body assembly 58 and the mandrel assembly 54 during
assembled operation.
[0026] The body assembly 58 further includes a number of set screws
240, filler plugs 244, o-rings 248, and relief valves 252. The uses
of such elements are well known in the art and no further
description thereof is deemed necessary to enable one skilled in
the art to implement the present invention. Similarly, the position
of these elements is exemplary, and may be adjusted as necessary
for different configurations of shock-absorber subassemblies 50.
The shock-absorber subassembly 50 further comprises a wear bushing
256, a floating seal 260, and a seal stop 264; all of which are
formed with an internal radius such that they will fit closely over
the spindle portion 82 of the mandrel body 62. The respective
functions of the wear bushing 256, floating seal 260, and seal stop
264 will be described in more detail below with reference to FIG.
3.
[0027] In one embodiment, assembly of the shock-absorber
subassembly 50 may be achieved by the following steps. The seal
stop 264 and the floating seal 260 are first sequentially placed
over the spindle portion 82 of the mandrel body 62 such that the
seal stop 264 is adjacent to the seal shoulder 98. The bottom
packing sub 220 is then placed over the spindle portion 82 and the
wear bushing 256 is inserted between the spindle portion 82 and the
bottom packing sub 220. The torsional spring assemblies 206 (FIG.
3) are then placed within the spring recesses 102 and the torsional
spring sub 216 is placed over the spindle portion 82 such that the
spring recesses 232 of the torsional spring sub 216 align with the
spring recesses 102 of the mandrel body 62 and the torsional spring
assemblies 106 (FIG. 3) are within the spring recesses 102 and 232.
The correspondingly-threaded portions 228 of the torsional spring
sub 216 and the bottom packing sub 220 are then screwed together to
connect the two pieces.
[0028] Next, the threaded end 110 of the washpipe 66 is threaded
into the internal threads of the connection portion 86 of mandrel
body 62. The sleeve 70 is then placed over the washpipe 66,
inserted within torsional spring sub 216, and the flange 118 can be
threaded onto the external threads of the connection portion 86 of
the mandrel body 62. The axial spring sub 212 is then placed over
the extension portion 114 of the sleeve 70 and the threaded end 228
of the axial spring sub 212 screwed into the threaded end 228 of
the torsional spring sub 216. The axial spring assembly 208 is then
placed over the washpipe 66 within the axial spring sub 212.
Although the axial spring assembly 208 is shown as a stack of
Belleville washers, alternate embodiments may use any suitable
springs. For example, the axial spring assembly 208 may comprise
helical springs, solid springs of rubber or other elastomeric
materials, or the like.
[0029] The seal assembly 204 is then placed over the washpipe 66
and the top packing sub 200 placed over the seal assembly 204 and
the washpipe 66. As shown, the threaded end 228 of the top packing
sub 200 is then threaded into the threaded end 228 of the axial
spring sub 212 so as to form a firm connection therebetween. The
assembled shock-absorber subassembly 50 is depicted in FIG. 3 and
the internal features and functions will be described in more
detail with reference thereto.
[0030] Referring now to FIG. 3, a cross-sectional view of an
assembled shock-absorber subassembly 50 is shown. As mentioned
above, and best depicted here, the body assembly 58 comprises the
top packing sub 200, the seal assembly 204, the axial spring
assembly 208, the axial spring sub 212, the torsional spring sub
216, and the bottom packing sub 220. The mandrel assembly 54
comprises the mandrel body 62, the washpipe 66, and the sleeve 70.
When the shock-absorber subassembly 50 is assembled, the body
assembly 58 and mandrel assembly 54 are permitted to move both
axially and rotationally, relative to one another and within a
predetermined range. As will be appreciated, the axial spring
assembly 208 absorbs some of the energy imparted by axial loads to
reduce the transfer of axial shocks and vibrations between the body
assembly 58 and the mandrel assembly 58, and the torsional spring
assembly 106 absorbs some of the energy imparted by torsional loads
to reduce the transfer of torsional shocks and vibrations between
the body assembly 58 and the mandrel assembly 54.
[0031] Several interior features of the various parts contribute to
this functionality and should be specifically noted here. The
floating seal 260 maintains a seal between the bottom packing sub
and the spindle portion 82 of the mandrel body 62. The seal stop
264 abuts the seal shoulder 98 of the mandrel body 64 so as to
prevent the floating seal 260 from being pushed over the seal
shoulder 98 as the body assembly 58 moves axially relative to the
mandrel assembly 54. As will also be appreciated from the drawing,
the shoulder 94 of the mandrel body 62 provides an absolute limit
to the amount of axial travel permitted. Specifically, because the
base portion 74 of the mandrel body 62 is larger than the bottom
packing sub 220, the distal end 236 of the bottom packing sub 220
cannot travel beyond the shoulder 94 of the mandrel body 62.
[0032] The bottom packing sub 220 is also further provided with an
internal tab 300 to maintain the wear bushing 256 in a fixed
position relative to the bottom packing sub 220. Additionally, to
facilitate the relative axial travel between body assembly 58 and
the mandrel assembly 54, the spring recesses 102 and 132 are
preferably longer than the torsional spring assembly 106 such that
the torsional spring assembly is permitted to slide within the
spring recesses 102 and 132.
[0033] As shown, the axial spring sub 212 is provided with an
enlarged spring chamber 304 to receive the axial spring assembly
208. The axial spring assembly 208 is preferably formed with a
central opening large enough about the washpipe 66, but small
enough so as not to fit about the extension portion 114 of the
sleeve 70. This permits the extension portion 114 of the sleeve 70
to contact, and thereby transmit axial loads to, the axial spring
assembly 208.
[0034] The torsional spring sub 216 is provided with sufficient
length to form an open space 308 to permit axial motion between the
body assembly 58 and the mandrel assembly 54. Similarly, the top
packing sub 200 is provided with a seal shoulder 312 and an
enlarged chamber 316. The seal shoulder 312 maintains the seal
assembly 204 in a fixed position relative to the top packing sub
200 so as to permit the washpipe 66 to slide through the seal
assembly 204 and into the enlarged chamber 316 as the body assembly
58 travels axially relative to the mandrel assembly 54.
[0035] Referring now to FIGS. 4, 5, and 6, the
torsional-shock-absorbing elements and function of the present
invention will be described in more detail. FIG. 4 depicts a
close-up cross-sectional view of the torsional shock-absorber
elements of the shock-absorber subassembly 50. FIG. 5 depicts a
perspective view of the torsional spring assembly 106 disposed
within the spring recess 102 of the spindle portion 82 of the
mandrel body 62. FIG. 6 depicts a cross-sectional view of the
torsional spring assembly 106, taken along the line 6-6 of FIG. 4.
As best shown in FIG. 5, the torsional spring assembly 106
preferably comprises a drive key 400 and a pair of springs 404, one
each on either side of the drive key 400. In some embodiments, the
springs 404 may be affixed to the drive key 400, such as by
adhesive, rivets, screws, or any other suitable fastening means.
The spring assembly 106 may also be provided with any suitable
number of springs, for example, three, four, or the like. The
springs 404 are preferably formed as flat springs, as shown, having
a at least two arcuate portions 408. In other embodiments, the
springs may have any suitable number of arcuate portions 408, for
example, one, three, four, or the like. In yet further embodiments,
the springs 404 may be formed in any suitable shape, for example,
helical springs disposed perpendicular to the drive key, solid
rubber or elastomeric springs, leaf springs, or any other suitable
spring type or shape.
[0036] As best shown in FIG. 6, the spring 404 absorbs a portion of
torsional loads imparted so as to reduce the transfer of torsional
shocks and vibration between the torsional spring sub 216 and the
spindle portion 82 of the mandrel body 62. The spring assembly 106
thereby reduces the transfer of torsional shocks and vibration
between the body assembly 58 and the mandrel assembly 54, while
still being capable of transferring rotary motion, and permitting
relative axial movement, between the body assembly 58 and the
mandrel assembly 54. Additionally, even in the event that the
springs 404 fail, the solid drive key 404 limits the relative
rotation permitted between the spindle portion 82 of the mandrel
body 62 and the torsional spring sub 216 to a predetermined range.
Additionally, because the torsional spring assembly 106 is
independent of the axial spring assembly 208, planar rotation of
the body assembly 58 is permitted relative to the mandrel assembly
54, without requiring any axial motion therebetween. Thus, each
spring assembly 106 and 208 can most efficiently absorb the loads,
torsional and axial respectively, they are designed to addressed.
It should also be appreciated that the size of the spring recesses
can be increased or decreased to increase the permitted range of
relative rotation between body assembly 58 and the mandrel assembly
54.
[0037] As best shown in FIG. 4, in one embodiment, the spring
recesses 102 and 232 are formed with a length greater than that of
the torsional spring assembly 106 so as to permit the body assembly
58 to move axially relative to the mandrel assembly 54, and
independently of any rotation. The wear bushing 256 cooperates with
the torsional spring sub 216 to define the spring recess 232. As
the body assembly 58 moves axially relative to the mandrel assembly
54, the torsional spring assembly 106 is permitted to move axially
within the spring recesses 102 and 232, which cooperate to limit
the travel of the torsional spring assembly 106. Thus, when an
axial shock is applied to one of the body assembly 58 or the
mandrel assembly 54, relative axial motion is permitted between the
body assembly 58 and the mandrel assembly 54, as the axial spring
assembly 204 absorbs a portion of the axial shock, without forcing
rotation between the body assembly 58 and the mandrel assembly
54.
[0038] It should be appreciated that the torsional shock absorbing
elements of the present invention may also be implemented alone in
a shock absorbing subassembly 50. For example, a shock absorbing
subassembly 50 may be constructed to include only torsional shock
absorbing elements. Such a configuration would be useful, for
example, in conjunction with axial shock absorbing subassemblies
already in use, to provide axial and torsional shock absorption
without having to replace a functional axial shock absorber.
Similarly, such a configuration would be useful, for example, when
axial displacement is undesirable, such as in softer rock
formations, or where more precision is desirable.
[0039] From the above description, it is clear that the present
invention is well adapted to carry out the objects and to attain
the advantages mentioned herein, as well as those inherent in the
invention. While presently preferred embodiments of the invention
have been described for purposes of this disclosure, it will be
understood that numerous changes may be made which will readily
suggest themselves to those skilled in the art and which are
accomplished within the spirit of the invention disclosed and as
defined in the appended claims.
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