Note: Descriptions are shown in the official language in which they were submitted.
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A LOW FRICTION CENTRALIZER
STATEMENT REGARDING FEDERALLY SPONSORED
RESEARCH OR DEVELOPMENT
[00011 Not applicable.
BACKGROUND
[00021 The disclosure relates to centralizers for downhole tubulars, such as
casing strings. More
particularly, the disclosure relates to a centralizer having roller balls that
facilitate movement of
the centralizer and a casing string coupled thereto relative to a surrounding
formation or another
casing string.
[0003] Centralizers are commonly used during completions operations in a
wellbore, such as to
cement a casing string within the wellbore. Prior to installation of the
casing string within the
wellbore, a centralizer is positioned within or about the casing string. The
casing string with the
centralizer coupled thereto is then lowered into the wellbore. As the casing
string is lowered, the
centralizer contacts the surrounding formation. Contact between the
centralizer and formation
impedes movement of the casing string and thus its installation. After the
casing string is
positioned within the wellbore, the centralizers maintain the casing string at
the wellbore center,
allowing cement to be uniformly distributed throughout an annulus formed by
the casing string
and surrounding formation.
[00041 To reduce frictional loads resulting from contact between the
centralizer and formation
during installation of the casing string, the centralizer typically has
structural features that
facilitate relative movement " between the centralizer and formation. For
instance, some
conventional centralizers have raised vanes that enable sliding contact
between the centralizer
and formation over a limited area. Even so, slidingly engagement between the
vanes and
formation can generate significant friction loads. Other conventional
centralizers have
cylindrical rollers that rotatably engage the formation, resulting in
comparatively lower frictional
loads. However, movement of the centralizer is facilitated only in a single
direction dependent
upon the orientation of the rotational axis of the roller relative to the
axial centerline of the
centralizer. Movement of the centralizer in another direction causes the
roller to slide against the
formation, increasing frictional loads therebetween. Furthermore, the sliding
engagement and
associated frictional loads cannot be eliminated by the addition of other
rollers having differently
orientated rotational axes because at least one of the rollers will always
slidingly engage the
formation no matter what direction the centralizer moves.
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[0005] Accordingly, there is a need for a centralizer that facilitates
movement between the
centralizer and casing string coupled thereto relative to the formation, or
another casing string,
in any direction with reduced associated frictional loads.
SUMMARY OF THE DISCLOSURE
[0006] A centralizer for a downhole system, including but not limited to a
casing system, is
disclosed. In some embodiments, the centralizer has a tubular body and a
plurality of roller ball
assemblies circumferentially spaced about the tubular body. Each roller ball
assembly includes
a plurality of rotatable balls adapted to engage a surface radially offset
from the centralizer and
rotate relative to the surface in any direction.
[0007] In some embodiments, the system includes a tubular positioned in a
wellbore and a
centralizer supported by the tubular. The centralizer has a roller ball
assembly with a plurality
of balls engaging a surface radially offset from the centralizer and rotatable
over the surface in
any direction.
[00081 In some embodiments, the system includes two concentric tubulars
positioned in a
wellbore, the two concentric tubulars comprising an inner tubular and an outer
tubular, and a
centralizer disposed therebetween. The centralizer includes a plurality of
balls engaging the
tubulars and rotatable in any direction. Rotation of the balls enables
relative movement of the
tubulars.
[0009] Thus, embodiments described herein comprise a combination of features
and
characteristics intended to address various shortcomings associated with
conventional
centralizers. The various characteristics described above, as well as other
features, will be
readily apparent to those skilled in the art upon reading the following
detailed description of the
preferred embodiments, and by referring to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] For a detailed description of the disclosed embodiments, reference will
now be made to
the accompanying drawings in which:
[0011] FIG. 1 is schematic representation a low friction centralizer in
accordance with the
principles disclosed herein positioned in a casing string suspended in a
wellbore;
[0012] FIG. 2 is a perspective view of the centralizer of FIG. 1;
[0013] FIGS. 3A and 3B are axial and radial cross-sectional views,
respectively, of the tubular
body of FIG. 2;
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[0014] FIGS. 4A and 4B are axial cross-sectional and top views, respectively,
of the retainer
plate of FIG. 2;
[0015] FIG. 5 is schematic representation of another embodiment of a low
friction centralizer in
accordance with the principles disclosed herein disposed about a casing string
suspended in a
wellbore;
[0016] FIG. 6 is a perspective view of the centralizer of FIG. 5;
[0017] FIG. 7 is a perspective view of the tubular body of FIG. 6;
[0018] FIG. 8 is a perspective view of the centralizer of FIG. 6 in partial
cross-section;
[0019] FIGS. 9A and 9B are axial and radial cross-sectional views,
respectively, of the ball
socket block of FIG. 6;
[0020] FIGS. 10A and 10B are axial and radial cross-sectional views,
respectively, of the
retainer plate of FIG. 6;
[0021] FIG. 11 is schematic representation of yet another embodiment of a low
friction
centralizer in accordance with the principles disclosed herein rotatably
disposed between two
concentric casing strings;
[0022] FIG. 12 is a perspective view of the centralizer of FIG. 11;
[0023] FIG. 13 is a perspective view of the tubular body of FIG. 12;
[0024] FIG. 14 is a perspective view of the centralizer of FIG. 12 in partial
cross-section;
[0025] FIGS. 15A and 15B are axial and radial cross-sectional views,
respectively, of the ball
socket block of FIG. 12; and
[0026] FIGS. 16A and 16B are axial and radial cross-sectional views,
respectively, of the
retainer plate of FIG. 12.
DETAILED DESCRIPTION OF THE DISCLOSED EMBODIMENTS
[0038] The following description is directed to exemplary embodiments of a
modular reinforce
pipeline fabrication system and associated methods. The embodiments disclosed
should not be
interpreted, or otherwise used, as limiting the scope of the disclosure,
including the claims.
One skilled in the art will understand that the following description has
broad application, and
that the discussion is meant only to be exemplary of the described embodiment,
and not
intended to suggest that the scope of the disclosure, including the claims, is
limited to that
embodiment.
[0039] Certain terms are used throughout the following description and the
claims to refer to
particular features or components. As one skilled in the art will appreciate,
different persons
may refer to the same feature or component by different names. This document
does not intend
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to distinguish between components or features that differ in name but not
function. Moreover,
the drawing figures are not necessarily to scale. Certain features and
components described
herein may be shown exaggerated in scale or in somewhat schematic form, and
some details of
conventional elements may not be shown in interest of clarity and conciseness.
[0027] In the following discussion and in the claims, the terms "including"
and "comprising"
are used in an open-ended fashion, and thus should be interpreted to mean
"including, but not
limited to... ." Also, the term "couple" or "couples" is intended to mean
either an indirect or
direct connection. Thus, if a first device couples to a second device, that
connection may be
through a direct connection, or through an indirect connection via other
devices and
connections. Further, the terms "axial" and "axially" generally mean along or
parallel to a
central or longitudinal axis, while the terms "radial" and "radially"
generally mean
perpendicular to the central or longitudinal axis.
[0028] Referring now to FIG. 1, a schematic representation of a casing system
100, including
a low friction centralizer 105 in accordance with the principles disclosed
herein, is shown.
Casing system 100 further includes an outer casing 110 installed within a
wellbore 115 and
an inner casing 120 suspended therein. As illustrated, outer casing 110 is
secured in position
by cement 130 disposed in an annulus 135 between outer casing 110 and a
formation 140
surrounding wellbore 115. Inner casing 120 includes two casing pipe segments,
or joints,
125 with centralizer 105 coupled therebetween. Centralizer 105 maintains inner
casing 120 in
a central position within outer casing 110 and enables movement of inner
casing 120 relative to
outer casing string 110, as will be described.
[0029] Turning next to FIG. 2, a perspective view of one centralizer 105 is
shown. Centralizer
105 includes a tubular body 155 having a first end 160, a second end 165, and
a flowbore 170
extending therethrough. At first end 160, centralizer 105 has external threads
175 that enable
centralizer 105 to be threaded into a joint 125 (FIG. 1) of inner casing 120.
At second end 165,
centralizer 105 has internal threads 180 (FIG. 3A) that enable another joint
125 (FIG. 1) to be
threaded into centralizer 105. When centralizer 105 is coupled between joints
125, as shown in
FIG. 1, flowbore 170 enables conveyance of cement through centralizer 105
during cementing
operations.
[0030] Centralizer 105 further includes a plurality of raised vanes 185
disposed
circumferentially about tubular body 155. Each vane 185 has a length extending
substantially
in the longitudinal or axial direction and a height extending radially from
the outer surface 190
of tubular body 155, thereby creating a valley 195 disposed between adjacent
vanes 185.
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Referring now to FIGS. 3A and 3B, which depict axial and radial cross-
sectional views,
respectively, of tubular body 155, each vane 185 has a recess 200 therein.
Recess 200 is
bounded by radially extending surfaces 205 and an axially extending surface
210 therebetween.
As best viewed in FIG. 3A, a plurality of ball receptacles 215 and fastener
bores 220 are
disposed in surface 210. Each ball receptacle 215 is defined by a spherical
surface 225,
whereas each fastener bore 220 is configured to receive a fastener, as will be
described.
[0031] Returning briefly to FIG. 2, centralizer 105 further includes a roller
ball assembly 230
coupled within recess 200 of each raised vane 185. Each roller ball assembly
230 includes a
plurality of spherical balls 235, a plurality of fasteners 240, and a retainer
plate 245. Each ball
235 is disposed within a ball receptacle 215 (FIG. 3A) of vane 185. Further,
ball 235 is
rotatable within ball receptacle 215 relative to vane 185 and thus tubular
body 155 of
centralizer 105 in all directions.
[0032] Turning to FIGS. 4A and 4B, top and axial cross-sectional views,
respectively, of
retainer plate 245 are shown. Retainer plate 245 includes a plurality of
fastener throughbores
250 and a plurality of ball receptacles 255. Each fastener throughbore 250 is
configured to
receive a fastener 240 (FIG. 2) therethrough. Each ball receptacles 255 is
bounded by a surface
260 configured to receive a ball 235 (FIG. 2). Surface 260 extends between a
circular opening
265 in the inner surface 270 of retainer plate 245 and a circular opening 275
in the outer surface
280 of retainer plate 245. Opening 275 is defined by a diameter that is
smaller than a diameter
of each ball 235 (FIG. 2), whereas opening 265 is defined by a diameter that
is at least that of
the ball diameter.
[0033] To couple roller ball assembly 230 with tubular body 155 of centralizer
105, a ball 235
is disposed within each ball receptacle 215 of vane 185. Retainer plate 245 is
then positioned
over recess 200 of vane 185 such that ball receptacles 255 of retainer plate
245 align with and
receive balls 235. Fasteners 240 are inserted through fastener throughbores
250 of retainer
plate 245 and secured within fastener bores 220 of vane 185. In some
embodiments, a lubricant
is injected within ball receptacles 215 of vanes 185 and/or ball receptacles
255 of retainer plate
245 prior to coupling of retainer plate 245 to vane 185 to promote rotation of
balls 235 relative
to vanes 185 and retainer plate 245 for extended periods of time.
[0034] When retainer plate 245 is coupled to vane 185, as described, balls 235
are retained by
retainer plate 245 within recess 200 because openings 275 have diameters
smaller than those of
balls 235. The height of recess 200 and the depths of ball receptacles 215,
255, each dimension
measured in the radial direction, are selected such that a portion of each
ball 235 extends
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radially through its respective opening 275 in retainer plate 245 and beyond
outer surface 280
of retainer plate 245. As such, balls 235 engage outer casing 110 (FIG. 1).
[0035] When inner casing 120 is disposed within outer casing 110, such as
during installation
of inner casing 120, contact between balls 235 and outer casing 110 causes
rotation of balls 235
within ball receptacles 215 of vanes 185. Thus, balls 235 of centralizer 105
rotatably engage
outer casing 110. Because balls 235 may freely rotate in any direction,
friction loads associated
with such contact are greatly reduced in comparison to those associated with
conventional
centralizers, including those previously described. In other words,
centralizers 105 facilitate
low friction, or near unimpeded, movement of inner casing 120 relative to
outer casing 110
regardless of its direction of movement.
[0036] In the above-described embodiment, centralizer 105 is coupled between
joints 125 of
inner casing 120, and thus is integral to inner casing 120. In other
embodiments, the low
friction centralizers are not integral to a casing but are instead "slipped
on" and coupled to its
exterior surface. FIGS. 5-8 illustrate an embodiment of a low friction, slip-
on centralizer.
[0037] Beginning with FIG. 5, a schematic representation of a casing system
300, including a
low friction centralizer 305 in accordance with the principles disclosed
herein, is shown.
Casing system 300 further includes an outer casing 310 installed within a
wellbore 315 and
an inner casing 320 suspended therein. Outer casing 310 is secured in position
by cement
330 disposed in an annulus 335 between outer casing 310 and a formation 340
surrounding
wellbore 315. Inner casing 320 includes two casing pipe segments, or joints,
325 threaded
end-to-end. Centralizer 305 is installed about inner casing 320 to maintain
inner casing 320 in
a central position within outer casing 310 and to enable movement of inner
casing 320 relative
to outer casing string 310, as will be described.
[0038] Turning to FIG. 6, a perspective view of one centralizer 305 is shown.
Centralizer 305
includes a tubular body 325 and a plurality of roller ball assemblies 330
disposed
circumferentially thereabout. Tubular body 325 has a first end 335, a second
end 340, a
throughbore 345 extending therethrough, and a plurality of circumferentially
spaced bores 355
proximal ends 335, 340. Throughbore 345 enables centralizer 305 to be
positioned about, or
"slipped on," inner casing 320, as illustrated in FIG. 5. Each bore 355 is
configured to receive
a fastener 360 to enable coupling of centralizer 305 about inner casing 320.
When secured to
inner casing 320 via fasteners 360, centralizer 305 does not move appreciably
relative to inner
casing 320. For this reason, centralizer 305 may be referred to as a "fixed,
slip-on centralizer."
Tubular body 325 further includes a plurality of circumferentially spaced
cutouts 350, best
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viewed in FIG. 7. Each cutout 350 is configured to receive a roller ball
assembly 330 therein,
as will be described.
[00391 Referring now to FIG. 8, a perspective view of centralizer 305 is shown
in partial cross-
section to better illustrate features of a roller ball assembly 330. As shown,
roller ball assembly
330, depicted in cross-section, is positioned within a cutout 350 of tubular
body 325. Roller
ball assembly 330 includes a ball socket block 365, a retainer plate 370, and
a plurality of
spherical balls 375 and fasteners 380 extending therebetween.
[00401 Turning to FIGS. 9A and 9B, top and axial cross-sectional views,
respectively, of ball
socket block 365 are shown. Ball socket block 365 has an outer surface 385
with a plurality of
ball receptacles 390 and fastener bores 395 disposed therein. Each fastener
bore 395 is
configured to receive a fastener 380 (FIG. 8) to enable coupling of retainer
plate 370 thereto.
Each ball receptacle 390 is defined by a spherical surface 400 configured to
receive a ball 375
(FIG. 8). As such, ball socket block 365 effectively performs the same
function as vanes 185
of centralizer 105, previously described.
[0041] FIGS. 10A and 10B are similar views of retainer plate 370. As shown,
retainer plate
370 includes a plurality of fastener throughbores 400 and a plurality of ball
receptacles 405.
Each fastener throughbore 400 is configured to receive a fastener 380 (FIG. 8)
therethrough.
Each ball receptacle 405 is bounded by a surface 410 extending between a
circular opening 415
in the inner surface 420 of retainer plate 370 and a circular opening 425 in
the outer surface 430
of retainer plate 370. Opening 425 is defined by a diameter that is smaller
than a diameter of
each ball 375 (FIG. 8), whereas opening 415 is defined by a diameter that is
at least that of the
ball diameter.
[00421 To couple roller ball assembly 330 with tubular body 325 of centralizer
305, ball socket
block 365 is disposed within cutout 350 of tubular body 325, as shown in FIG.
8, and welded,
or otherwise secured, to tubular body 325. Next, a ball 375 is disposed within
each ball
receptacle 390 of ball socket block 365. Ball 375 is freely rotatable within
ball receptacle 390
relative to ball socket block 365 in all directions. Retainer plate 370 is
then positioned over ball
socket block 365 such that ball receptacles 405 in retainer plate 370 align
with and receive balls
375. Lastly, fasteners 380 are inserted through fastener throughbores 400 of
retainer plate 370
and secured within aligned fastener bores 395 in ball socket block 365. In
some embodiments,
a lubricant is injected within ball receptacles 390 of ball socket block 365
and/or ball
receptacles 405 of retainer plate 370 prior to coupling of retainer plate 370
to ball socket block
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365 to promote rotation of balls 375 relative to ball socket block 365 and
retainer plate 370 for
extended periods of time.
[0043] When retainer plate 370 is coupled to ball socket block 365, as
described, balls 375 are
retained therebetween because openings 425 of retainer plate 370 have
diameters smaller than
those of balls 375. The depths of ball receptacles 390, 405, each dimension
measured in the
radial direction, are selected such a portion of each ball 375 extends
radially through its
respective opening 425 in retainer plate 370 and beyond outer surface 430 of
retainer plate 370.
As such, balls 375 engage outer casing 310 (FIG. 5).
[00441 When inner casing string 320 moves within outer casing 310, such as
during installation
of inner casing 320, contact between balls 375 and outer casing 310 causes
rotation of balls 375
within roller ball assembly 330. Thus, balls 375 of centralizer 305 rotatably
engage outer
casing 310. Because balls 375 may freely rotate in any direction, friction
loads associated with
such contact are greatly reduced in comparison to those associated with
conventional
centralizers, including those previously described. In other words,
centralizer 305 facilitates
low friction, or near unimpeded, movement of inner casing 320 relative to
outer casing 310
regardless of its direction of movement.
[0045] In the previously described embodiment, fixed, slip-on centralizer 305
does not move
relative to inner casing 320. Even so, there may be instances where relative
movement between
centralizer 305 and inner casing 320 is desirable. FIGS. 11-16 illustrate an
embodiment of a
low friction, slip-on centralizer that permits such movement.
[0046] Beginning with FIG. 11, a schematic representation of a casing system
600, including
a low friction centralizer 605 in accordance with the principles disclosed
herein, is shown.
Casing system 600 further includes an outer casing 610 installed within a
wellbore 615 and
an inner casing 620 suspended therein. Outer casing 610 is secured in position
by cement
630 disposed in an annulus 635 between outer casing 610 and a formation 640
surrounding
wellbore 615. Inner casing 620 includes two casing pipe segments, or joints,
625 threaded
end-to-end.
[0047] Centralizer 605 is installed about inner casing 620 to maintain inner
casing 620 in a
central position within outer casing 610. Further, centralizer 605 is moveable
relative to outer
casing 610 and to inner casing 620. To maintain the axial position of
centralizer 605 relative to
inner casing 620, casing system 600 further includes two locking collars 645
coupled to inner
casing 620 above and below centralizer 605. Locking collars 645 do not move
relative to inner
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casing 620 and thereby limit movement of centralizer 605 in the axial
direction relative to inner
casing 620.
[0048] Referring to FIG. 12, a perspective view of one centralizer 605 is
shown. Centralizer
605 includes a tubular body 610 and a plurality of roller ball assemblies 615
disposed
circumferentially thereabout. Tubular body 610 has a first end 620, a second
end 625, and a
throughbore 630 extending therethrough. Throughbore 630 enables centralizer
605 to be
positioned about, or "slipped on," inner casing 620, as illustrated in FIG.
11. Unlike centralizer
305, previously described, tubular body 610 is not fastened to inner casing
620, but rather is
enabled by roller ball assemblies 615 to move relative to inner casing 620.
Thus, tubular body
610 does not include fastening means, such as fastener bores proximal ends
620, 625. Because
centralizer 605 is moveable relative inner casing 620 but restricted by
locking collars 645 (FIG.
11) from moving appreciably in the axial direction relative to inner casing
620, centralizer 605
may be referred to as a "rotatable, slip-on centralizer." Tubular body 610
further includes a
plurality of circumferentially spaced cutouts 635, best viewed in FIG. 13.
Each cutout 635 is
configured to receive a roller ball assembly 615 therein, as will be
described.
[0049] Referring now to FIG. 14, a perspective view of centralizer 605 is
shown in partial
cross-section to illustrate features of a roller ball assembly 615. As shown,
roller ball assembly
615, depicted in cross-section, is positioned within a cutout 635 of tubular
body 610. Roller
ball assembly 615 includes a ball socket block 640, a retainer plate 645, and
a plurality of
spherical balls 650 and fasteners 655 extending therebetween. In contrast to
retainer plate 370
of centralizer 305, retainer plate 645 is disposed radially inward of ball
socket block 640 and
coupled thereto by fasteners 655 extending from the interior of centralizer
605. In the unlikely
event that.fasteners 655 were to loosen, inner casing 620 (FIG. 11) would
prevent them from
disengaging retainer plate 645.
[0050] Turning to FIGS. 15A and 15B, top and axial cross-sectional views,
respectively, of ball
socket block 640 are shown. Ball socket block 640 has an inner surface 660
with a plurality of
ball receptacles 665 and fastener bores 670 disposed therein. Each fastener
bore 670 is
configured to receive a fastener 655 (FIG. 14) therein. Each ball receptacle
665 is defined by a
spherical surface 675 configured to receive a ball 650 (FIG. 14). Surface 675
extends between
a circular opening 680 in inner surface 660 and a circular opening 685 in the
outer surface 690
of ball socket block 640. Opening 685 is defined by a diameter that is smaller
than a diameter
of each ball 650 (FIG. 8), whereas opening 680 is defined by a diameter that
is at least that of
the ball diameter.
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[0051] FIGS. 16A and 16B are similar views of retainer plate 645. As shown,
retainer plate
645 includes a plurality of fastener throughbores 695 and a plurality of ball
receptacles 700.
Each fastener throughbore 695 is configured to receive a fastener 655 (FIG. 8)
therethrough.
Each ball receptacle 700 is defined by a spherical surface 705 configured to
receive a ball 650
(FIG. 14). Surface 705 extends between a circular opening 710 in the inner
surface 715 of
retainer plate 645 and a circular opening 720 in the outer surface 725 of
retainer plate 645.
Opening 710 is defined by a diameter that is smaller than a diameter of each
ball 650 (FIG. 14),
whereas opening 720 is defined by a diameter that is at least that of the ball
diameter.
[00521 To couple roller ball assembly 615 with tubular body 610 of centralizer
605, a ball 650
is disposed within each ball receptacle 665 of ball socket block 640. Retainer
plate 645 is then
positioned over ball socket block 640 such that ball receptacles 700 of
retainer plate 645 align
with and receive balls 650. Fasteners 655 are inserted through fastener
throughbores 695 of
retainer plate 645 and secured within aligned fastener bores 670 in ball
socket block 640. In
some embodiments, a lubricant is injected within ball receptacles 665 and/or
ball receptacles
700 prior to coupling of retainer plate 645 to ball socket block 640 to
promote rotation of balls
650 relative to ball socket block 640 and retainer plate 645 for extended
periods of time.
Lastly, roller ball assembly 615 is disposed within cutout 635 of tubular body
610, as shown in
FIG. 14, and secured in position, such as by welding ball socket block 640 to
tubular body 610.
[0053] When retainer plate 645 is coupled to ball socket block 640, as
described, balls 650 are
retained therebetween because openings 710 of retainer plate 640 and openings
685 of ball
socket block 640 have diameters smaller than those of balls 650. At the same
time, balls 665
are freely rotatable within ball receptacles 665, 700 relative to ball socket
block 640 and
retainer plate 645 in all directions. The thickness of ball socket block 640
between surfaces
660, 690 and the thickness of retainer plate 640 between surfaces 715, 725 are
selected such
that a portion of each ball 650 extends radially through ball receptacle 700
in retainer plate 645
and beyond inner surface 715 of retainer plate 645. Similarly, a portion of
each ball 650
extends radially through ball receptacle 665 in ball socket block 640 and
beyond outer surface
690 of ball socket block 640. As such, balls 650 engage inner casing 620 and
outer casing 610
(FIG. 11).
[00541 When inner casing 620 moves within outer casing 610, such as during
installation of
inner casing 620, contact between balls 650 and casings 610, 620 causes
rotation of balls 650
within roller ball assembly 615. Thus, balls 650 of centralizer 615 rotatably
engage outer
casing 610 and inner casing 620. Because balls 650 may freely rotate in any
direction, friction
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loads associated with such contacts are greatly reduced in comparison to those
associated with
conventional centralizers, including those previously described. In other
words, centralizer 605
facilitates low friction, or near unimpeded, movement of inner casing 620
relative to outer
casing 610 regardless of its direction of movement.
[00551 Furthermore, balls 650 facilitate low friction movement of centralizer
605 relative to
inner casing 620 in any direction. This may be particularly useful in other
embodiments
wherein outer casing 610 is not fixed, but is moveable like inner casing 620.
In the illustrated
embodiment, however, locking collars 645 (FIG. 11) limit axial movement of
centralizer 605
relative to inner casing 620.
[00561 As described, centralizer 305 has a tubular body 325 with a plurality
of cutouts 350,
each cutout 350 receiving a ball socket block 365, which is coupled to tubular
body 325, such
as by welding. Similarly, centralizer 605 has a tubular body 610 with a
plurality of cutouts 635,
each cutout 635 receiving a ball socket block 640, which is coupled to tubular
body 610, such
as by welding. One of ordinary skill in the art will readily appreciate that
tubular body 325,
610 and ball socket block 365, 640, respectively, may be formed integrally as
a single
component, rather than as separate components subsequently joined in some
manner. For
example, tubular body 325 and ball socket block 365 may be formed as a single
component
through casting or forging. During assembly of centralizer 305, balls 375
would then be seated
in ball receptacles 390 of the integral tubular body and ball socket block and
retainer plate 370
coupled thereto. Likewise, tubular body 610 and ball socket block 640 may be
formed as a
single component through casting or forging. During assembly of centralizer
605, balls 650
would then be seated in ball receptacles 665 of the integral tubular body and
ball socket block
and retainer plate 645 coupled thereto.
[00571 A centralizer in accordance with the principles disclosed herein,
including the
embodiments described above, enables low friction movement of the centralizer
relative to a
downhole tubular, such as a casing string, or a surrounding formation.
Movement of the
centralizer relative to the casing string, or surrounding formation, is
facilitated by a plurality of
balls which engage the casing string, or formation, and rotate freely in any
direction. Thus, the
centralizer is moveable in any direction relative to the casing string or
formation. The friction
forces associated with such movement are no greater in one direction than any
other, in contrast
to many conventional centralizers. Moreover, the friction forces are
significantly less than
those associated with many conventional centralizers, in particular those
which enable sliding
engagement, as previously described.
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100581 While various embodiments have been shown and described, modifications
thereof can
be made by one skilled in the art without departing from the spirit and
teachings herein. The
embodiments herein are exemplary only, and are not limiting. Many variations
and
modifications of the apparatus disclosed herein are possible and within the
scope of the
invention. For example, centralizers 105, 305, 605 are depicted and described
as facilitating
movement of an inner casing 120, 320, 620 within a fixed outer casing 110,
310, 610,
respectively. Centralizers 105, 305, 605 would function identically as
described were they to
instead engage a surrounding formation 140, 340, 640 in the absence of outer
casing 110, 310,
610. Furthermore, the embodiments of the low friction centralizers disclosed
herein are
described in the context of being integral with or coupled to a casing string
for the purpose of
centralizing the casing string and facilitating movement of the casing string
relative to another
casing string. One having ordinary skill in the art will readily appreciate
that the low friction
centralizers are equally applicable to other types of tubulars or tubular
strings, such as but not
limited to drill strings, which require centralization and/or movement
relative to a formation or
another tubular string. Accordingly, the scope of protection is not limited by
the description set
out above, but is only limited by the claims which follow, that scope
including all equivalents of
the subject matter of the claims.
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