Note: Descriptions are shown in the official language in which they were submitted.
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DRAG BLOCK ASSEMBLY
FIELD
[0001] This disclosure relates to drag block assemblies for use with
downhole tools in
subterranean wells, such as packers or bridge plugs.
BACKGROUND
[0002] In the completion and the production of hydrocarbons from wells,
it is frequently
necessary to isolate a portion of the well using a well tool, such as a
packer, plug, tubing hanger
and the like, supported in the wellbore at a subterranean location. These
tools are lowered into
the well in a retracted state called the "run position"; and in a process
called "setting", the
gripping means and packing means are radially expanded to a "set position"
wherein the slips
means and packing means engage the wellbore. A variety of types of gripping
means are well
known in the art, such as a slip means with wedge-shaped slip elements.
Typically, packing
means have resilient annular members mounted on the tool to move axially to
pack off or seal
the annulus around the tool. Such packing means can comprise one or more
resilient annular
packing elements which, depending on the use environment, may also comprise
back up and/or
anti-extrusion rings. When these packing elements are axially compressed, they
expand radially
from the mandrel into contact with the wellbore. To hold these tools in place
in the wellbore
against movement, slip means typically are mounted on the tool. These slip
means, like the
packing means, expand radially to grip the wellbore when forced to compress
axially.
[0003] Axially directed forces are used to axially compress the packing
elements and slip
assemblies. Such forces are typically generated by moving the tubing string,
initiating an
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explosive charge, or applying pressure to the tool. Examples of tools that are
set by manipulating
the tubing string include weight down and tension packers. A weight down
packer is one in
which force generated by the weight of the tubing string above the tool is
used to set (expand)
the packing and slip element and to hold the tool in set condition. In a
tension packer, the tubing
string is placed in tension and that tension force is used to set and hold the
tool in the set
condition.
[0004] Weight down and tension packers typically comprise a hollow
tubular mandrel
which is connected to the tubing string. Mounted on the mandrel are the
axially compressible
packing elements adjacent to the slip assembly. An annular tool element called
a "drag block
assembly" is located on the mandrel, adjacent the slip assembly on the
opposite side from the
packing elements. In weight down tools, the drag block is located below the
slip means. In a
tension packer, the drag block is located above the slip means.
[0005] Drag block assemblies typically frictionally engage the wellbore.
Drag block
assemblies are mounted to slide axially on the mandrel. Drag block assemblies
are used to center
the tool in the middle of the casing and to provide a resistant force or
frictional force, which aids
in the rotating, setting and unsetting of downhole tools. This frictional
force is also referred to as
"drag friction".
[0006] Conventional prior art packers use drag block having leaf, bow or
compression
springs to provide a resistant force pushing the drag block against the
interior surface of the
casing thus creating friction between the drag block and the casing.
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BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 is a perspective view of a drag block assembly in
accordance with an
embodiment.
[0008] FIG. 2 is a perspective view of a drag block element usable in the
drag block
assembly of FIG. 1.
[0009] FIG. 3 is a schematic cross-sectional view of a drag block mounted
in the sleeve
of the drag block assembly of FIG. 1.
DETAILED DESCRIPTION
[0010] Referring now to the drawings, wherein like reference numbers are
used herein to
designate like elements throughout the various views, various embodiments are
illustrated and
described. The figures are not necessarily drawn to scale; and in some
instances, the drawings
have been exaggerated and/or simplified in places for illustrative purposes
only. In the following
description, the terms "upper," "upward," "lower," "below," "downhole" and the
like, as used
herein, shall mean: in relation to the bottom or furthest extent of the
surrounding wellbore even
though the well or portions of it may be deviated or horizontal. The terms
"inwardly" and
"outwardly" are directions toward and away from, respectively, the geometric
center of a
referenced object. Where components of relatively well-known designs are
employed, their
structure and operation will not be described in detail. One of ordinary skill
in the art will
appreciate the many possible applications and variations of the present
invention based on the
following description.
[0011] Turning now to FIG. 1, a drag block assembly 10 in accordance with
one
embodiment can be seen. Drag block assembly 10 comprises a generally
cylindrically shaped
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sleeve 20 and a block element 40. Sleeve 20 can be suitable for being received
on a mandrel 12.
Mandrel 12 can be attached to a downhole tool at upper end 14 and/or lower end
16, or
mandrel 12 can be part of a mandrel of a downhole tool. Mandrel 12 has a
longitudinal central
axis or longitudinal axial centerline 18. Also, as referred to herein, the
term "radially" will refer
to a radial direction perpendicular to the longitudinal axial centerline 18
and "longitudinal" or
"axial" will refer to a direction parallel to the longitudinal axial
centerline 18.
[0012] Referring now to FIGS. 1 and 3, sleeve 20 has an outer surface 22,
an array of
longitudinally disposed slots 24 disposed around outer surface 22, and an
inner surface 26 at the
bottom of each slot 24. A wall 28 extends from inner surface 26 to outer
surface 22 in each slot
24. A first magnet 30 is mounted in inner surface 26; thus, there are a
plurality of magnets
disposed about sleeve 20 in the bottom of slots 24. First magnet 30 can be
embedded within a
channel 34 in inner surface 26 such that the outer surface 32 of first magnet
30 lies flush with
inner surface 26. Typically, first magnet 30 will be an elongated magnet
having a length at least
50% of the length of slot 24 and can be at least 70 percent of the length of
slot 24. The width of
first magnet 30 will generally be from 80% to 100% of the width of slot 24.
Alternatively, first
magnet 30 can be a set of smaller magnets embedded into inner surface 26, as
long as they align
with the magnets in the block element to create a repulsive effect, as further
described below.
[0013] Referring now to FIGS. 1, 2 and 3, a block element 40 is mounted
to sleeve 20
such that it can radially slide. Block element 40 comprises an elongated block-
like body 42 with
a casing-wall-contacting outer surface 44 and a bottom surface 46. Further, a
second magnet 48
is mounted in bottom surface 46. Typically, there are a plurality of block
elements 40, such that
each slot 24 has one of block elements 40 mounted in it with casing-wall-
contacting outer
surface 44 protruding through the slot and bottom surface 46 facing inner
surface 26 of sleeve
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20. Second magnet 48 is generally mounted flush in bottom surface 46.
Typically, second
magnet 48 is approximately the same size and shape as first magnet 30 and is
positioned such
that when block element 40 is mounted in slot 24, first magnet 30 and second
magnet 48 will be
aligned so as to generate a magnetic repulsion between the two magnets. Second
magnet 48 can
be mounted in a channel 49 in bottom surface 46 such that it is flush with
bottom surface 46.
Alternatively, both slot 24 and block element 40 can have several smaller
magnets dispersed
about inner surface 26 and bottom surface 46, as long as their positioning and
magnetization
generate a repelling force between the inner surface 26 and bottom surface 46.
Also, while
described in terms of magnets, other electromagnetic elements are within the
scope of the
invention as long as they produce a repelling electromagnetic force between
inner surface 26 and
bottom surface 46, such that casing-wall-contacting outer surface 44 of block
element 40 is
radially outwardly biased from sleeve 20 by the electromagnetic elements. If
magnets are used,
typically the first magnet and the second magnet can have a magnetization
sufficient to provide a
spring-like action to the block element and generate a drag force between the
block element and
a casing of a wellbore when the drag block assembly is introduce into the
casing.
[0014] Block element 40 has a first lateral end 50 and a second lateral
end 52, which
extend laterally as opposed to axially or longitudinally. Block element 40
also has first
longitudinal side 54 and second longitudinal side 56, which extend axially or
longitudinally. A
first flange 58 extends lengthwise from first lateral end 50 and a second end
flange 60 extends
lengthwise from second lateral end 52. Accordingly, block element 40 can be
mounted within
slot 24 by retaining members on sleeve 20 that interact with flanges 58 and 60
so as to prevent
block element 40 from moving out of slot 24. Thus, first flange 58 can be
retained by a retaining
tab 38 connected to sleeve 20, and second flange 60 can be retained by a
retaining ring 36
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circumferentially disposed about outer surface 22 of sleeve 20. When so
mounted, block element
40 will be pushed outward from inner surface 26 by magnetic forces so as to
form a gap 62
between inner surface 26 and bottom surface 46. Gap 62 allows block element 40
to move
inward towards inner surface 26 when there is an exterior force on outer
surface 44 great enough
to overcome the magnetic force. Moreover, as bottom surface 46 nears inner
surface 26, the
magnetic force repelling the two surfaces will increase requiring greater
exterior force to
overcome it. When the exterior force lessens, block element 40 will move
outwardly so as to
have a spring-like action.
[0015] For example, a drag block assembly, having a gap 62 of 1 inch when
block
element 40 is in its outer most position in slot 24, might use two opposing
grade N52 magnets
having a length of 6 inches, a width of 1 inch and a depth of 1 inch. The
magnets for this drag
block assembly will exert approximately 110 lbs with a 1 inch gap with the
magnetic field
between magnets being about 1,107 gauss and the permeance coefficient being
1.6. As the
distance between the magnets is compressed and approaches contact between the
magnet, the
force can increase to approximately 300-4001bs.
[0016] Drag block 40 can have an elastic member extending around its
periphery, such as
0-ring 64. When drag block 40 is mounted in slot 24, 0-ring 64 contacts wall
28 to block debris
from entering into gap 62. 0-ring 64 is formed from an elastomeric material,
such as Nitrile
Butadiene Rubber (NBR). Mandrel 12 and sleeve 20 typically can be formed from
a drillable
material such as brass or composite materials such as engineered plastics.
Specific plastics
include nylon, phenolic materials and epoxy resins. Drag block element 40 can
also be formed
from a composite material or can be molded from an elastomeric material.
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[0017] In operation, a plurality of block elements 40 are mounted in
slots 24 spaced
about the periphery of sleeve 20. Drag block elements 40 are outwardly biased
within the slots
by an electromagnetic element, such as magnet pairs 30 and 48. The resulting
drag block
assembly is mounted on a mandrel of a downhole tool. Next, the downhole tool
is placed into a
casing in a wellbore such that casing-wall-contacting outer surface 44 of each
block element 40
presses outward on the casing, thus centering the downhole tool in the casing
and creating drag
friction. To provide additional drag force and to limit damage to block
element 40, wear
members 66 in the form of buttons or inserts can be mounted on or in casing-
wall-contacting
outer surface 44. The wear members can be formed from tough wear resistant
materials, such as
composite materials (hard rubber, resins and the like), metallic materials
(steel, carbide and the
like), and ceramic materials.
[0018] In accordance with the above description, there is provided in one
embodiment a
drag block assembly for a downhole tool. The drag block assembly comprises a
generally
cylindrical shaped sleeve and a block element. The block element is mounted to
the sleeve such
that it can radially slide. The block element is outwardly biased from the
sleeve by an
electromagnetic element. The electromagnetic element can comprise a first
magnetic member
mounted to the sleeve and a second magnetic member mounted to the block
element. The first
magnetic member and second magnetic member have magnetization aligned such
that they repel
each other. The first magnetic member and the second magnetic member can have
a
magnetization sufficient to provide a spring-like action to the block element
and generate a drag
force between the block element and a casing of a wellbore when the drag block
assembly is
introduce into the casing.
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[0019] In a further aspect, the sleeve can have an outer surface, an
array of longitudinally
disposed slots disposed around the outer surface, and an inner surface at the
bottom of each slot.
The block element can have an elongated block-like body with a casing-wall-
contacting outer
surface and a bottom surface. There can be a plurality of the block elements,
and each slot has
one of the block elements mounted in it such that the casing-wall-contacting
outer surface
protrudes through the slot and the bottom surface faces the inner surface of
the sleeve. The drag
block can be radially moveable in the slot.
[0020] Further, the sleeve can comprise a wall extending from the inner
surface to the
outer surface in each slot. The block can have an elastic member extending
around its periphery,
such that the elastic member contacts the wall to block debris from entering
into a space between
the inner surface and the bottom surface.
[0021] Additionally, the electromagnetic element comprises a plurality of
first magnetic
members and second magnetic members. Each slot has one of said first magnetic
members
mounted to the inner surface thereof. Each block element has one of said
second magnetic
members mounted to the bottom surface thereof. The first magnetic member and
the second
magnetic member have magnetization aligned such that they repel each other to
thus outwardly
bias the drag block element in the slot.
[0022] In another aspect, the block element can have a first lateral end
having a first
flange extending lengthwise therefrom and a second lateral end having a second
flange extending
lengthwise therefrom. The first flange can be retained by a retaining ring
disposed about the
outer surface of the sleeve, and the second flange can be retained by a tab
connected to the
sleeve. The block is thus mounted in and retained from moving out of the slot.
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[0023] In another embodiment, there is provided a method of centering a
downhole tool
with drag friction. The method comprises:
(a) connecting a drag block assembly to the downhole tool, the drag block
assembly having a generally cylindrically shaped sleeve and a plurality of
block elements mounted to the sleeve such that they can radially slide;
(b) biasing each block element outwardly from the sleeve by an electromagnetic
element; and
(c) placing the downhole tool into a casing in a wellbore such that a casing-
wall-
contacting outer surface of each block elements presses outward on the
casing, thus centering the downhole tool in the casing and creating drag
friction.
[0024] In the method, the block elements are radially moveable. The
electromagnetic
element can comprise a plurality of first magnetic members mounted to the
sleeve and a plurality
of second magnetic members. Each block element has one of the second magnetic
members
mounted to it. The first magnetic member and second magnetic member have
magnetization
aligned such that they repel each other. Also, the sleeve can comprise an
outer surface, an array
of longitudinally disposed slots disposed around the outer surface, and an
inner surface at the
bottom of each slot. Each block element can comprise an elongated block-like
body with a
casing-wall-contacting outer surface and a bottom surface. Each slot can have
one of the block
elements mounted in it such that the casing-wall-contacting outer surface
protrudes through the
slot, and the bottom surface faces the inner surface of the sleeve. The sleeve
can further comprise
a wall extending from the inner surface to the outer surface in each slot.
Each block can have an
elastic member extending around its periphery, such that the elastic member
contacts the wall to
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block debris from entering into a space between the inner surface and the
bottom surface. The
drag block can be radially moveable within the slot.
[0025] While various embodiments of the invention have been shown and
described
herein, modifications may be made by one skilled in the art without departing
from the spirit and
the teachings of the invention. The embodiments described here are exemplary
only and are not
intended to be limiting. Many variations, combinations, and modifications of
the invention
disclosed herein are possible and are within the scope of the invention.
Accordingly, the scope of
protection is not limited by the description set out above, but is defined by
the claims which
follow. The scope includes all equivalents of the subject matter of the
claims.
