U.S. patent application number 11/739284 was filed with the patent office on 2008-10-30 for field-assemblable bow-spring casing centralizer and method of making a centralizer.
This patent application is currently assigned to FRANK'S INTERNATIONAL, INC.. Invention is credited to Jean Buytaert, Eugene Edward Miller.
Application Number | 20080264629 11/739284 |
Document ID | / |
Family ID | 39670923 |
Filed Date | 2008-10-30 |
United States Patent
Application |
20080264629 |
Kind Code |
A1 |
Buytaert; Jean ; et
al. |
October 30, 2008 |
Field-Assemblable Bow-Spring Casing Centralizer and Method of
Making A Centralizer
Abstract
A casing centralizer is provided that may be shipped unassembled
and is then assemblable at a well site. According to one
embodiment, first and second collars each have a plurality of
circumferentially spaced aligning slots and a corresponding
plurality of threaded, extruded through-holes. A plurality of
bow-springs each have a foot at each end. Each bow-spring axially
extends between the first and second collars. The foot at one end
of each bow-spring is disposed in one of the aligning slots of the
first collar, and the foot at the other end is disposed in one of
the aligning slots on the second collar. A plurality of threaded
fasteners corresponding in number to the threaded extruded
through-holes secure the ends of the bow-springs to the threaded
extruded through-holes. The extruded through-holes have a flange
height greater than a collar thickness adjacent to the extruded
through-holes. The increased flange height allows more threads to
be formed within the extruded holes, resulting in a stronger
threaded connection with the threaded fasteners, and a
correspondingly stronger, more durable centralizer. The foot is
retained within the aligning slot to reinforce the coupling between
the bow-spring and the collar. A method of manufacturing the casing
centralizer is also provided.
Inventors: |
Buytaert; Jean; (Mineral
Wells, TX) ; Miller; Eugene Edward; (Weatherford,
TX) |
Correspondence
Address: |
STREETS & STEELE
13831 NORTHWEST FREEWAY, SUITE 355
HOUSTON
TX
77040
US
|
Assignee: |
FRANK'S INTERNATIONAL, INC.
Houston
TX
|
Family ID: |
39670923 |
Appl. No.: |
11/739284 |
Filed: |
April 24, 2007 |
Current U.S.
Class: |
166/241.7 |
Current CPC
Class: |
E21B 17/1028
20130101 |
Class at
Publication: |
166/241.7 |
International
Class: |
E21B 17/10 20060101
E21B017/10 |
Claims
1. A method of manufacturing a casing centralizer, comprising:
forming a plurality of bow-springs, each having a first end and a
second end; and each having a foot at each end; forming a first
collar and a second collar, each having a plurality of
circumferentially spaced bow-spring aligning slots, each bow-spring
aligning slot configured for receiving a foot on the end of a
bow-spring; forming at least one extruded through-hole in each
collar and adjacent to each aligning slot by positioning each
collar on a supporting back-up member having an opening aligned
with a punch, and by driving the punch through the collar wall and
into the opening, wherein the diameter of the punch is less than
about 80% of a diameter of the opening on the supporting member;
and tapping each extruded through-hole to threadedly receive a
fastener.
2. The method of claim 1, wherein forming the aligning slots
comprises driving a second punch through the collar into a second
opening in the supporting back-up member, wherein a width of the
second punch is smaller a width of the second opening on the
supporting back-up member.
3. The method of claim 1, further comprising: fastening a first end
of each bow-spring to the first collar using a fastener threadedly
engaged with one of the threaded extruded through-holes in the
first collar; and fastening a second end of each bow-spring to the
second collar using a second fastener threadedly engaged with one
of the threaded collar through-holes in the second collar.
4. The method of claim 3, further comprising securing each
bow-spring to a radially outwardly disposed surface of each
collar.
5. The method of claim 1, wherein the step of forming each extruded
through-hole in a collar comprises forming an extruded through-hole
having a height of at least about 1.5 times the material thickness
of the collar.
6. The method of claim 1, wherein the step of forming each extruded
through-hole comprises forming an extruded through-hole having a
flange height of between about 2.0 to 3.0 times the material
thickness of the collar.
7. The method of claim 1, wherein each of the aligning slots in the
circumferential all of the collar have a generally
circumferentially-extending slot length and a generally axially
extending slot width of substantially less than the slot
length.
8. The method of claim 1, further comprising forming the feet of
each bow-spring by inwardly bending the ends of the bow-springs to
create an angled portion at each end of the bow spring.
9. A casing centralizer, comprising: first and second collars each
having a plurality of circumferentially spaced aligning slots and a
corresponding plurality of threaded, extruded through-holes,
wherein the extruded throughholes have a flange height greater than
the collar thickness adjacent to the extruded throughholes; a
plurality of bow-springs, each having an aperture and a foot at
each end, each bow spring extending between the first and second
collars, with the foot at one end of each bow spring disposed in
one of the aligning slots of the first collar to align the adjacent
aperture on the end of the bow-spring with an extruded through-hole
of the first collar, and the foot at the other, opposite end of the
bow-spring disposed in one of the aligning slots on the second
collar to align the adjacent aperture on the end of the bow-spring
with an extruded through-hole of the second collar; and a plurality
of threaded fasteners corresponding in number and pitch of threads
to the threaded extruded through-holes for securing one end of each
of the bow springs to each of the first and second collars by
inserting a fastener through each aperture aligned with an extruded
through-hole and by threading the fastener into the threaded and
extruded through-holes.
10. The casing centralizer of claim 9, wherein the bow-springs are
disposed on outwardly facing surfaces of each collar.
11. The casing centralizer of claim 9, wherein the flange height of
each extruded throughhole is at least 1.5 times the collar
thickness.
12. The casing centralizer of claim 9, wherein the flange height of
each extruded throughhole is between about 2.0 to 3.0 times the
collar thickness.
13. The casing centralizer of claim 9, wherein the feet comprise
inwardly bent portions on the ends of the bow-springs.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates primarily to centralizers and
methods for centering a casing string downhole within the borehole
of a well. More particularly, the present invention relates to a
centralizer that may be shipped more efficiently and is easily
assemblable in the field.
[0003] 2. Description of the Related Art
[0004] Centralizers are commonly secured at intervals along a
casing string to radially offset the casing string from the wall of
a borehole in which the casing string is subsequently positioned.
The centralizers generally include evenly-spaced ribs that project
radially outwardly from the casing string to provide the desired
offset. Centralizers ideally center the casing string within the
borehole to provide a generally continuous annulus between the
casing string and the interior wall of the borehole. This
positioning of the casing string within a borehole promotes uniform
and continuous distribution of cement slurry around the casing
string during the subsequent step of cementing the casing string in
a portion of the borehole. Uniform cement slurry distribution
results in a cement liner that reinforces the casing string,
isolates the casing from corrosive formation fluids, and prevents
unwanted fluid flow between penetrated geologic formations.
[0005] A bow-spring centralizer is a common type of centralizer
that employs flexible bow-springs as the ribs. Bow-spring
centralizers typically include a pair of axially-spaced and
generally aligned collars that are coupled by multiple bow-springs.
The bow-springs bow outwardly from the axis of the centralizer to
engage the borehole to center a pipe received axially through the
generally aligned bores of the collars. Configured in this manner,
the bow-springs provide stand-off from the borehole, and flex
inwardly as they encounter borehole obstructions, such as tight
spots or protrusions into the borehole, as the casing string is
installed into the borehole. Elasticity allows the bow-springs to
spring back to substantially their original shape after passing an
obstruction to maintain the desired stand-off between the casing
string and the borehole.
[0006] Centralizers are usually assembled at a manufacturing
facility and then shipped to the well site for installation on a
casing string. The centralizers, or subassemblies thereof, may be
assembled by welding or by other means such as displacing a
bendable and/or deformable tab or coupon into an aperture to
restrain movement of the end of a bow-spring relative to a collar.
Other centralizers may be assembled into their final configuration
by riveting the ends of a bow-spring to a pair of spaced-apart and
opposed collars. The partially or fully assembled centralizers may
then be shipped in trucks or by other transportation to the well
site.
[0007] Pre-assembly of the centralizers reduces the amount of labor
and tooling required at the well site, but partially or fully
assembling the centralizers at a manufacturing facility greatly
increases shipping costs due to a dramatically decreased shipping
density since, due to the structure and the intended function of
centralizers, assembled centralizers take up a very large amount of
cargo space for relatively little weight. For example, a single
casing string may require many truckloads of centralizers to be
transported over very long distances and to remote locations, and
the inefficiency of shipping pre-assembled centralizers adds
substantially to the cost of completing a well.
[0008] Another factor that increases the costs of centralizers is
the cost of assembly. Welding the end of each bow-spring to two
opposed and spaced-apart collars is time-consuming and tedious. A
typical bow-spring centralizer requires 12 or more welds by
highly-skilled welder using specialized welding equipment, rods,
and a special power supply. Furthermore, welding a bow-spring to a
centralizer collar creates an undesirable heat-affected zone (HAZ)
in the bow-spring and in the collar around each weld, and this HAZ
can possibly weaken the material and render the centralizer more
subject to mechanical failure.
[0009] Conventional fasteners, such as rivets and bendable tabs
received within slots or apertures, may also be used to join a
bow-spring to collars in a non-welded centralizer, but conventional
fasteners such as these may present protrusions that may hang up
during installation of the pipe string into the borehole thereby
making installation of the centralizers and pipe string more
difficult and time-consuming. Also, riveting and bending tabs into
slots requires special equipment, such as mechanical presses and
special tools, that is difficult to power, use, and maintain in the
field.
[0010] U.S. Pat. No. 6,871,706 discloses a centralizer that
requires a step of bending a retaining portion of the collar
material into a plurality of aligned openings, each to receive one
end of each bow-spring. This step requires that the coupling
operation needs to be performed in a manufacturing facility using a
press. As shown in FIG. 1, the collars of the prior art centralizer
are cut with a large recess adjacent to each set of aligned
openings to accommodate passage of the bow spring that is secured
to the interior wall of the collar. The recess substantially
decreases the mechanical integrity of the collar due to the removal
of a large portion of the collar wall to accommodate the
bow-springs. The collars of the casing centralizer disclosed in the
'706 patent also require several additional manufacturing steps,
including the formation of both internal and external (alternating)
upsets in each collar to form the aligned openings for receiving
and securing bow-springs, a time-consuming process that further
decreases the mechanical integrity of the collar.
[0011] Improved centralizers and methods continue to be sought,
particularly in view of the limitations of the prior art and the
need for better or stronger centralizers. Considerations for the
development of new centralizers and of new methods of assembling
the centralizers include manufacturing costs, shipping costs, the
costs associated with installing the centralizers onto pipe strings
and the ease of running the pipe string into the well.
SUMMARY OF THE PRESENT INVENTION
[0012] A field-assemblable casing centralizer and method are
disclosed. One embodiment provides a method of manufacturing a
casing centralizer. A plurality of bow-springs are formed, each
having two opposed ends, each end having an aperture adjacent to a
foot for being received in an aligning slot in a collar to position
the bow spring for coupling to the collar at the aperture. A first
collar and a second collar are also formed, each collar having a
plurality of circumferentially spaced aligning slots, each slot for
receiving a foot at the end of a bow-spring. A plurality of collar
through-holes are formed in the collar, in positions to align with
apertures in the ends of a plurality of bow-springs. Each collar
through-hole is formed adjacent to an aligning slot by positioning
the collar on a supporting back-up member having an opening for
receiving an aligned punch, and by then forcibly driving the punch
through the wall of the collar and into the opening in the
supporting back-up member to extrude a portion of the collar wall
material into the opening. The preferred width of the punch is less
than about 80% of the width of the opening in the supporting
back-up member, or an amount sufficient to draw a portion of the
collar wall material onto the annular space between the received
punch and the interior wall of the opening to form an extruded
through-hole. Each collar through-hole is then threaded using a
tap.
[0013] Another embodiment provides a bow-spring centralizer that
may be field-assembled. First and second collars comprise a
plurality of circumferentially-distributed, extruded through-holes
that are threaded for receiving a fastener. The extruded and
threaded through-holes have a protruding flange height resulting
from the extrusion by the punch that is greater than the thickness
of the collar wall adjacent to the extruded through-holes. A
plurality of bow-springs each have a foot at protruding from each
end adjacent to an aperture for receiving a fastener. The foot at
one end of each of the plurality of bow-springs is disposed in an
aligning slot of the first collar and secured in place by a
threaded fastener installed through the aperture of the end of the
bow-spring and threaded into an extruded through-hole. The foot at
the other end of each bow-spring of each of the plurality of
bow-springs is disposed in an aligning slot of the second collar
and secured in place in the same manner. In this manner, only two
fasteners, and no other structures, are required to secure each
bow-spring to the pair of opposed and spaced-apart collars, and
only one relatively portable tool may be required to assemble the
centralizer in the field. Also, the foot and the aligning slot
serve a dual purpose. The first, as discussed above, is that of
aligning the aperture in the end of the bow-spring with an extruded
through-hole in the collar for receiving a fastener. The second
purpose is to reinforce the shear resistance of the mechanical
coupling between the bow-spring and the collar. The foot is
strategically placed in alignment with the anticipated direction of
the shearing force applied to the coupling when the centralizer is
secured to a tubular string and installed in a borehole. The
aligning slots may conveniently be punched in the collar and
adjacent to the extruded through-holes at the same time that the
through-holes are punched and extruded.
[0014] Other embodiments, aspects, and advantages of the invention
will be apparent from the following description and the appended
claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a perspective view of a prior art centralizer
described in U.S. Pat. No. 6,871,706.
[0016] FIG. 2 is a perspective view of one embodiment of a
bow-spring centralizer according to the present invention.
[0017] FIG. 3 is a perspective view of one of the bow-springs of
the centralizer of FIG. 2.
[0018] FIG. 4 is a side elevation view of a portion of the collar
of the centralizer of FIG. 2.
[0019] FIG. 5 is a cross-sectional view of the collar supported on
a supporting back-up member prior to forming the aligning slot and
the extruded through-hole in the collar.
[0020] FIG. 6A is a cross-sectional view of the collar supported on
the supporting back-up member, illustrating the step of forming an
aligning slot and an extruded through-hole in the collar.
[0021] FIG. 6B is a detail view of the extruded through-hole taken
along the portion encircled in FIG. 6A.
[0022] FIG. 7 is a cross-sectional view of the collar supported on
the supporting back-up member, illustrating the step of threading
the extruded through-hole formed in FIG. 6A.
[0023] FIG. 8 is a cross-sectional view of the collar supported on
the supporting back-up member, showing the threads formed within
the extruded through-hole in FIG. 7.
[0024] FIG. 9 is an interior perspective view of a portion of the
collar after forming the aligning slot and threading the extruded
through-hole, and after then receiving the foot from the end of a
bow-spring and a threaded fastener, respectively.
DETAILED DESCRIPTION OF THE PRESENT INVENTION
[0025] The present invention provides an improved centralizer that
can be quickly and inexpensively assembled in the field. The few
components that make up the centralizer may be shipped unassembled
and efficiently packed to a well site to maximize shipping density
and minimize shipping costs. Once at the well site, centralizers of
the present invention may be quickly and inexpensively assembled
using basic tools and with minimal skilled labor. A centralizer
according to the invention requires no welding and is not subject
to complications from HAZ's.
[0026] In one embodiment of the centralizer of the present
invention, a first collar and a second collar each have a plurality
of circumferentially spaced aligning slots and a corresponding
plurality of threaded, extruded through-holes. A plurality of
bow-springs each have a foot at each end and an aperture generally
adjacent to the foot. Each bow-spring is axially extendable between
the first and second collars when the collars are generally aligned
and spaced one from the other to receive a bow-spring. The foot at
one end of each bow-spring is disposed in one of the aligning slots
of the first collar and fastened to the first collar with a
threaded fastener. The foot at the other end of that bow-spring is
disposed in one of the retaining slots on the second collar and
fastened to the second collar with a threaded fastener. A threaded
fastener is inserted through each aperture at each end of the
bow-spring and then threaded into an extruded through-hole in a
collar to secure the ends of each bow-spring to the two opposed
collars at opposed and corresponding through-holes to form a
centralizer.
[0027] To maximize the ease and speed of assembly and/or
disassembly of the centralizer, the bow-springs may be secured to a
radially outward, exterior surface of each collar. This positioning
of the bow-springs is, in contrast to that of conventional
bow-springs on prior-art centralizers that typically retain the
ends bow-springs inside a collar, allows each bow spring in the
centralizer to be easily and independently installed, removed or
replaced without necessarily removing any of the other bow-springs
from the centralizer.
[0028] A method of manufacturing the casing centralizer is also
provided, which includes the steps of extruding and threading holes
in each collar, each for threadedly receiving a threaded fastener.
The extruded through-holes have a radially-inwardly extruded flange
height greater than the collar thickness immediately adjacent to
the extruded through-holes. Preferably, the extruded flange height
is at least 1.5 times a material thickness of the wall of the
collar, and more preferably, the extruded height is between 2.0 and
3.0 times the material thickness of the wall of the collar. The
increased extruded height allows more threads to be formed within
the extruded holes, resulting in a much stronger threaded
connection with the threaded fasteners and a correspondingly
stronger and more durable centralizer.
[0029] FIG. 2 is a perspective view of one embodiment of a
bow-spring centralizer 10 according to the invention. The
centralizer 10 includes two generally cylindrical collars, a first
collar 12, and a second collar 14, substantially aligned one with
the other about a common centralizer axis 15. The collars 12, 14
may include two or more generally arcuate segments 38 coupled using
hinged connections 17 to facilitate installation of the centralizer
on long tubular strings. The collars 12, 14 are axially spaced one
from the other. Six bow-springs 18 for extending between and
flexibly positioning the two collars 12, 14 in a generally aligned
and spaced-apart relationship are secured at their opposed ends to
the two collars 12, 14 in the manner described herein. Other
embodiments of a centralizer according to the present invention may
have any number of bow-springs, but will typically include between
6 and 8 bow-springs.
[0030] The bow-springs 18 are angularly spaced one from the others
along the collars 12, 14 and about the centralizer axis 15, and are
typically evenly spaced, i.e. with substantially the same angular
spacing between each pair of adjacent bow-springs 18.
[0031] As shown in FIG. 2, the bow-springs 18 bow radially
outwardly from the axis 15 at their middle or contact portions 19
intermediate the collars 12, 14. The bow springs 18 may be formed
of flexible and resilient materials that provide sufficient
stand-off to center a heavy casing string within the borehole, but
that also provide an appreciable resiliency to allow the
bow-springs 18 to flex radially inwardly to accommodate borehole
obstructions and irregularities as needed as the casing string is
installed in a borehole.
[0032] A first end 20 of each bow-spring 18 comprises a foot 28 for
being disposed in an aligning slot 21 of a collar, which as shown
in the embodiment illustrated in FIG. 2, is one of a plurality of
aligning slots 21 in the first collar 12. Similarly, a second end
22 of each bow-spring 18 is disposed in an aligning slot 21 in the
second collar 14. Each of the collars 12, 14 have a plurality of
aligning slots 21 corresponding to the number of bow-springs 18 on
the centralizer 10. These aligning slots 21 may alternatively be
referred to as retaining slots 21 for retaining the ends of the
bow-springs 18 in a position to be coupled to the collar, and also
for maintaining the bow-springs 18 in a generally aligned
orientation with respect to the centralizer axis 15. In the
embodiment illustrated in FIG. 2, the aligning slots 21 extend all
the way through the thickness of the wall of the collar 12. In
other embodiments, an aligning slot may only extend partially
through a collar (e.g., into a recess or indentation in the wall of
the collar).
[0033] Each bow-spring 18 is further secured at its first end 20 to
the first collar 12 using a threaded fastener 24 inserted through
an aperture (not shown in FIG. 2) in the first end 20 of a
bow-spring 18, and secured at its second end 22 to the second
collar 14 using a threaded fastener 24 inserted through an aperture
in the second end 22 of the bow-spring 18. The bow-springs 18 may,
therefore, be quickly and easily coupled to the first and second
collars 12, 14, and the threaded members 24 may be easily threaded
into to the collars 12, 14 using ordinary tools such as a hex
wrench, socket wrench, or other type of wrench, depending on the
type of fastener head selected for the fastener. Further
description of the structure and the method of forming the collars
12, 14, and of attaching the bow-springs 18 to the collars 12, 14,
is provided below.
[0034] To maximize the ease and speed of assembly and/or
disassembly of the centralizer 10, the bow-springs 18 have been
configured so that they may be secured as shown to the radially
outward, exterior wall 25 of each collar 12, 14. This positioning
of the ends 20, 22 of the bow-springs 18 on the radially outward,
exterior wall 25 is in contrast to that of conventional bow-springs
of prior-art centralizers that typically secure each end of each
bow-spring inside a collar, i.e. between the interior wall of the
collar and the exterior wall of the casing string to be installed
within the bore of the centralizer along its axis 15. Thus, unlike
with prior art centralizers, any of the bow-springs 18 in the
centralizer 10 of the present invention may be independently
installed or removed without removing the centralizer 10 from the
casing and without removing any of the other bow-springs 18 from
the centralizer. This feature increases the speed and reduces the
costs of assembling the centralizer 20. Also, being
field-assemblable allows for two or more types of bow-springs to be
usable with the same type of centralizer collars. A user can
maintain a smaller inventory, but still select the specific type of
bow-spring centralizer according to the length, shape, material and
strength needed to serve a particular application and have
bow-springs of that type delivered to the well site for assembly
with a single, or "universal," type of collars for that given
diameter of tubular string.
[0035] FIG. 3 is a perspective view of one of the bow-springs 18
included with the centralizer 10 shown in FIG. 2. The bow-spring 18
includes feet 28, 30 on the respective ends 20, 22, respectively.
The feet 28, 30 in this embodiment are inwardly bent ends of the
bow-springs 18. Alternative types of feet may include upset
portions of the bow-springs or short, stub-like threaded posts
threadedly secured to the ends of the bow-spring. Adjacent to each
foot 28, 30 are respective apertures 32, 34, which may
alternatively be referred to as bow-spring through-holes 32, 34 to
distinguish them from the extruded through-holes 36 in the first
and second collars 12, 14. The feet 28, 30 are adapted for being
received in the aligning slots 21 on the respective collars 12, 14
(FIG. 2). A threaded fastener 24 (FIG. 2) may be inserted through
each bow-spring through-hole 32 or 34 and subsequently threaded
into the threads of an extruded through-hole 36 in the collar 12 or
14 (discussed below in relation to FIG. 4).
[0036] FIG. 4 is a side elevation view of a portion of a typical
collar 12 or 14 of FIG. 2. The aligning slot 21 and the threaded,
extruded through-hole 36 are positioned one adjacent to the other
on the collar 12. The extruded through-hole 36 includes internal
threads 37 into which the threaded fastener 24 (FIG. 2) may be
threaded to secure an end 20 or 22 of the bow-spring 18 to the
collar 12. The collar 12 may include a radially inwardly rimmed
portion 23 that approaches or contacts an outer wall of a casing
segment (not shown) received within the bore of the collar 12 along
the axis 15 (FIG. 2), and a radially outward portion 26 that
provides a generally annular gap between the interior wall of the
radially outward portion 26 of the collar 12 and the exterior wall
of the casing received into the bores of the generally aligned
collars 12, 14. This structure provides enhanced rigidity and
strength to the collar. Also, the annular gap provides sufficient
clearance between each of the collars 12, 14 and the casing segment
received therethrough so that the casing does not interfere with
either insertion of the foot 28 (FIG. 3) into the aligning slot 21
or the threading of the fastener 24 into the threaded, extruded
through-hole 36. Thus, the feet 28 on the ends 20, 22 of the
bow-springs 18, and the ends of the fasteners 24, may extend
inwardly beyond a thickness of the collar 12 or 14 without
substantially interfering with the outer wall of the casing. This
feature prevents the fasteners 24 and the feet 28 from catching or
hanging up on an obstruction within the borehole, and enables the
casing string to be installed more quickly and easily in the
borehole.
[0037] FIGS. 5-8 are cross-sectional views of an exemplary first
collar 12 supported on a supporting member 40, schematically
illustrating one method of forming the aligning slot 21 (see FIG.
4) and the threaded, extruded through-hole 36 (see FIG. 4) into the
collar 12 according to one embodiment of the present invention. For
simplicity, the first collar 12 is illustrated in FIGS. 5-8 as a
basic circular ring, excluding certain reinforcing features such as
the radially inward rimmed portion 23 and the radially outward
portions 26 that are shown in the perspective view of FIG. 4.
[0038] FIG. 5 is a cross-sectional view of the wall of the first
collar 12 hanging or otherwise supported on a supporting back-up
member 40 prior to forming the aligning slot 21 and the extruded
through-hole 36 (see FIG. 4) in the wall of the first collar 12.
The supporting back-up member 40 may be, for example, a worktable
or a mandrel designed specifically for use in making the first
collar 12, and is not part of the centralizer 10. The supporting
back-up member 40 includes adjacent openings 52, 54. A pair of
reciprocating (relative to the openings) punches 42 and 44 are
positioned adjacent the openings 52 and 54 in the supporting
back-up member 40 and aligned with the openings 52 and 54,
respectively, for forming an aligning slot 21 and an extruded
through-hole 36. The punches 42, 44 of this embodiment are
schematically illustrated as having radially-moveable (relative to
the axis of the collar blank 12) heads 46, 48 to which the punches
51, 53 are secured, respectively. The punches 51, 53 may be, for
example, made of a hardened material, and the punches may be
removable from the heads.
[0039] The punches may have selected dimensions favorable for
perforating the specific thickness and grade of sheet metal or
other relatively thin-walled workpieces such as the collar 12. The
heads 42, 44 may be powered to deliver sufficient punching forces
to the punches 51, 53. For example, the heads 42, 44 may operated
together or independently, and they may be hydraulically and/or
pneumatically powered, or the may be driven with a pair of
rotatable threaded guide axles (not shown). Alternatively, the
heads 42, 44 may be either automatically or manually driven by a
weighted assembly, or driven manually by an operator using a
leveraged actuator (not shown). Other ways of driving the heads 42,
44 or otherwise imposing sufficient penetrating forces to the
punches 51, 53 to perforate the collar 12 may be devised according
to the present invention.
[0040] FIG. 6A is a cross-sectional view of the first collar 12
supported on the supporting back-up member 40 illustrating the
step(s) of forming an aligning slot 21 and an extruded through-hole
36 in the first collar 12. Although shown together in this figure,
the aligning slot 21 and (not yet extruded) through-hole 36 may be
independently formed in separate steps. The slot for making the
aligning slot, or the "slot" punch, 51 and the corresponding
opening 52 in the supporting back-up member 40 cooperate to form
the aligning slot 21 in the first collar 12 for receiving the foot
of a bow-spring. In particular, the slot punch 51 has a dimension
d1 and the cooperating opening 52 on the supporting member 40 has a
dimension d2 that is at least greater than d1. The dimension d1 of
the slot punch 51 and the dimension d2 of the opening 52 are
substantially similar, so that the slot punch 51 fits very closely
within the corresponding opening 52. In particular, the dimension
d1 of the punch 51 may be at least 90% of the dimension d2 of the
opening 52. Thus, as the head 42 is driven downwardly toward the
first collar 12, the slot punch 51 shears a coupon 55 (see FIG. 5A)
from the collar 12, thereby creating the aligning slot 21 (FIG. 4).
In the process of shearing the collar 12, the elongate coupon 55 of
collar material is punched from the collar 12.
[0041] Still referring to FIG. 6A, the punch 53 and the
corresponding opening 54 cooperate to form an extruded through-hole
36 in the first collar 12. The punch 53 has dimension d3 and the
cooperating opening 54 in the supporting member 40 has a dimension
d4 that is substantially greater than d3. While the punch 53 is
driven downwardly toward the first collar 12 by the head 48, the
punch 53 penetrates the collar 12 as it moves into the general
center of the opening 54. Due to the annular gap defined between
the exterior of the punch 53 (of dimension d3) and the cooperating
interior of the opening 54 (of dimension d4), the collar 12 wall
material is radially-inwardly plastically deformed (rather than
simply sheared) in proximity to the punch 53, drawing or extruding
a portion of the collar wall material (the "extruded portion") 56
between the punch 53 and the opening 54 prior to ultimate (shear)
material failure. Thus, the through-hole 36 in the first collar 12
is formed as an extruded through-hole 36.
[0042] It should be noted that the dimensions d1, d2, d3, and d4
are shown in the plane of the page, and do not necessarily indicate
the dimensions 51, 53 of the punches relative to the dimensions of
opening 52, 54. For example, the slot retainer 21 formed in FIG. 6A
typically includes both a slot width (shown in FIG. 5) and a slot
length (not shown, but may be substantially greater than the slot
width). Thus, the slot punch 51 and the cooperating opening 52 are
typically elongate, having respective widths d1 and d2 in the plane
of the page a length into the page that is greater than their
widths d1, d2. The punch 53 and opening 54 are generally circular,
however, so that the opening 54 may receive the punch 53 to form an
extruded and generally cylindrical through-hole that may
subsequently be threaded. Thus, the punch 53 and the cooperating
opening 54 are typically circular, having respective diameters d3,
d4, respectively.
[0043] Only one aligning slot 21 and one extruded through-hole 36
are shown in FIGS. 5 and 6A; the collar 12 may be subsequently
rotated about its axis 15 on the supporting back-up member 40 and
additional aligning slots 21 and extruded through-holes 36 may be
formed at any desired angular spacing about the circumference of
the first collar 12. Alternately, a collar 12 may be quickly made
using multiple punches positioned at different angles to the axis
and acting simultaneously.
[0044] FIG. 6B is a detail view of an exemplary extruded
through-hole 36 taken along the portion encircled in FIG. 6A. The
collar 12 has a material thickness, "t," and the extruded
through-hole 36 has a "flange height," h, defined as illustrated.
The diameter d3 of the punch 53 is preferably less than about 80%
of the diameter d4 of the opening 54, and more preferably between
about 65% and 75% of the diameter d4 of the opening 54. The ration
between the diameters of the punch and the opening may vary
depending on the diameter of the collar and the thickness and
material of the collar. The resulting flange height h of the
extruded through-hole is typically at least 1.5 times the
thickness, t, of the collar 12, and may be between about 2.0 and
3.0 times the thickness, t, of the collar 12. The increased flange
height, h, of the extruded portion 56, as compared with the
thickness, t, of the surrounding collar material, desirably
provides more surface area for threads to be formed within the
extruded through-hole 36, resulting in a much stronger threaded
connection for securing the bow-spring to the collar using a
fastener.
[0045] The movement of the heads 42, 44 and the punches 51, 53 may
be relatively rapid and "explosive," such as performed by a
stamping operation, or it may be slow and controlled, such as may
be performed by a controlled movement of the heads 42, 44. A number
of factors may be considered in selecting the speed of movement of
the heads 42, 44 and the punches 51, 53, such as the strength of
the collar material, the thickness, t, of the collar material, and
the mechanical properties of the punches collar material and of the
51, 53. For forming the slot 21 with the punch 51, the movement may
be rapid, such as to maximize manufacturing productivity when
forming multiple slots 21 in many collars 12. A quick movement of
the punch 51 may maximize the shearing effect, as well. By
contrast, the speed of movement of the punch 53 in forming the
extruded hole 36 may affect the flange height, h, of the extruded
hole 36. For example, slower, more controlled punch movement may
result in more plastic deformation (elongation) of the extruded
hole 36 prior to shear. The temperature of the collar 12 is also
likely to affect the extent of the elongation. If the collar 12 is
sufficiently heated, the collar material may allow a generally
longer extrusion. If the collar 12 is instead worked at or near
ambient temperature, the movement of the punch 53 may be relatively
slow to minimize the possibility of premature shear in the extruded
through-hole 36.
[0046] FIG. 7 is a cross-sectional view of the collar 12 supported
on the supporting member 40, illustrating the step of threading the
extruded through-hole 36 that was formed in FIG. 6. The extruded
through-hole 36 may be tapped by a thread tapping tool ("thread
tap") 60. The thread tap 60 includes a shank 62 that may be gripped
and rotated by a chuck 64, such as may be provided on a drill press
or hand-held drill, or possibly on a hand-held tool for manually
tapping a thread. The thread tap 60 is aligned with the extruded
through-hole 36 and urged axially downward into the extruded
through-hole 36 while rotating to form threads in the extruded
through-hole 36. FIG. 8 is a cross-sectional view of the collar 12
supported on the supporting member 40, showing the threads 66
formed within the extruded through-hole 36 in FIG. 7.
[0047] FIG. 9 is an interior perspective view of a portion of the
collar 12 after forming the aligning slot 21 and forming and
tapping the extruded through-hole 36. The first end 20 of the
bow-spring 18 (which is mostly hidden in this view--see FIG. 3) is
secured to the collar 12. The foot 28 of the bow-spring 18 is
protruding through the aligning slot 21. The foot 28 fits closely
with the aligning slot 21 to substantially constrain movement of
the bow-spring 18 with respect to the collar 12 to maintain the
generally axially extending orientation of the bow-spring 18 with
respect to the centralizer axis 15 (see FIG. 2). The fastener 24 is
threadedly engaged with the threaded, extruded through-hole 36 to
securely fasten the bow-spring 18 to the collar 12. The other end
of the bow-spring 18 may be similarly attached to the second collar
14, as shown in FIG. 2. This attachment of the bow-springs 18 to
the collars 12, 14 is relatively simple and fast, yet provides a
robust, high-strength, and durable assemblage of the centralizer
10.
[0048] The invention, therefore, includes both the provision of a
field-assemblable casing centralizer and a method of manufacturing
the field-assemblable centralizer. The centralizer may be shipped
unassembled to increase shipping density and decrease associated
shipping costs. Once at the well site, the components of the
centralizer, such as the collars and the bow-springs, may be
assembled easily using minimal tools, skills, and labor. The
bow-springs are desirably secured to outer portions of the collars
and may therefore be quickly and easily removed or replaced without
having to remove the casing centralizer from the casing. The
extruded through-holes in the collar are extruded to increase the
number of threads that may be disposed within the through-holes,
which increases the strength of the threaded connection made up
using the threaded fasteners and improves the overall strength and
durability of the centralizer. While the invention has been
described with respect to a limited number of embodiments, those
skilled in the art, having benefit of this disclosure, will
appreciate that other embodiments can be devised which do not
depart from the scope of the invention as disclosed herein.
Accordingly, the scope of the invention should be limited only by
the attached claims.
[0049] There is a generally large number of combinations of
dimensions and materials that may be used to implement the present
invention, and there are no specific ratios or parameters that are
required to implement the present invention. Those skilled in the
art will recognize that the extruded hole can be obtained in the
manner disclosed herein for those materials having sufficient
ductility, but may not be obtained using materials having excessive
hardness, and that the material will often dictate the ratio of the
width of the punch to the width of the opening in the backing
member that will produce a satisfactory extruded hole that can be
successfully tapped and used to implement the present
invention.
[0050] The terms "comprising," "including," and "having," as used
in the claims and specification herein, shall be considered as
indicating an open group that may include other elements not
specified. The terms "a," "an," and the singular forms of words
shall be taken to include the plural form of the same words, such
that the terms mean that one or more of something is provided. The
term "one" or "single" may be used to indicate that one and only
one of something is intended. Similarly, other specific integer
values, such as "two," may be used when a specific number of things
is intended. The terms "preferably," "preferred," "prefer,"
"optionally," "may," and similar terms are used to indicate that an
item, condition or step being referred to is an optional (not
required) feature of the invention.
[0051] The term "pair" may be used to indicate two items that are
not identical in structure, size, shape and material, but are
substantially identical with respect to the properties or structure
related to the characteristic or quality being referred to in the
context of the disclosure using that term. An insubstantial change
that does not materially affect the use of the present invention
does not make one item not form a "pair" with the substantially
similar item.
* * * * *