Note: Descriptions are shown in the official language in which they were submitted.
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EASY DRILL SLIP WITH DEGRADABLE MATERIALS
CROSS REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of U.S. Application No. 14/189214, filed
on
February 25, 2014, which is incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
[0001] The invention relates generally to the design of slip elements that are
used in
gripping systems for downhole tools.
2. Description of the Related Art
[0002] Numerous downhole tools incorporate gripping systems that use one or
more
slips. The slips are moved radially outwardly against a surrounding tubular
member in order
to resist axial or torsional forces, or both. In many instances, slips are set
to securely anchor a
downhole tool in place within a surrounding tubular member. In other cases,
such as with
drag blocks, a slip may be set to merely resist axial or torsional movement.
Downhole tools
that incorporate gripping systems that use slips include, but are not limited
to, packers,
anchors, plugs, setting tools, bridge plugs, locks and fishing tools. Plugs,
for example, have a
plug body with slip elements that can be selectively moved radially outwardly
to bitingly
engage a surrounding tubular member. One type of plug is described in U.S.
Patent No.
6,167,963 issued to McMahan et al. That patent is owned by the assignee of the
present
application and is incorporated herein by reference.
[0003] Often, a downhole tool will need to be removed after it has been set,
and this
is usually done by milling through the tool. Unfortunately, milling through
most conventional
tool designs is costly and leaves large pieces which may be difficult to
circulate out of the
flowbore.
SUMMARY OF THE INVENTION
[0004] The present invention provides a design for a downhole tool wherein the
slip
elements of the gripping system include an inner body portion that is
substantially formed of a
material that is degradable by dissolution in response to a dissolving fluid
and a hardened,
resilient, radially outer contact portion. In described embodiments, the outer
contact portion
is substantially formed of a hardened material, such as cast iron, that is
shaped to provide for
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biting into a surrounding tubular member. In described embodiments, the outer
contact
portion extends from the upper end of the slip element to the lower end of the
slip element.
Also in described embodiments, the outer contact portion includes a plurality
of openings that
function as stress risers.
[0005] In described embodiments, the inner body portion is substantially
formed of a
material that is dissolvable in response to a dissolving agent. In one current
embodiment, the
dissolvable material forming the inner body portion comprises magnesium-based
composite
powder compact. When the dissolvable material is magnesium-based powder
compact, the
dissolving agent may be potassium chloride (kcl). In preferred embodiments,
the outer contact
portion is formed of a material that either does not dissolve away in response
to the dissolving
agent or which dissolves at a significantly slower dissolution rate than that
of the inner body
portions.
[0006] As described, the slip inserts are cast within a surrounding molding to
create
a slip ring which can then be disposed onto the setting cone of the downhole
tool. In
described embodiments, the molding is a phenolic material which provides a
laminate covering
for the slip elements that protects the dissolvable material against premature
dissolution.
[0007] In operation, the downhole tool is disposed into a flowbore and then
set.
When it is desired to remove the tool from the flowbore, a dissolving agent is
used to dissolve
away the inner body portions of the slip elements, thereby destroying the
integrity of the
gripping system of the tool. In some embodiments, a milling device is used to
expose the
dissolvable inner body portions to the dissolving agent. During removal of the
tool by milling,
the molding of the slip ring is ruptured by the mill, which exposes the
dissolvable material
forming the inner body portions to wellbore fluid which contains the
dissolving agent. The
dissolving agent dissolves away the inner body portions, leaving the outer
contact portions of
the slip elements. The presence of openings disposed through the outer contact
portions
assists in disintegration of the outer contact portions into smaller component
parts via
operation of the milling device. The outer contact portions, or portions
thereof, and other
components of the downhole tool may be circulated out of the wellbore via
fluid returns.
[0008] According to other embodiments, removal of a slip member, including the
outer contact portion and the inner body portions is done through degradation
and dissolution
when the slip member comes into contact with a dissolving agent. According to
these
embodiments, no milling is required. Dissolving agent is introduced into the
wellbore and is
brought into contact with the inner body portions. In these embodiments, the
inner body
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portions are either not covered by a laminate or have openings disposed
through the laminate
that permits the dissolving agent to contact the inner body portions.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] For a thorough understanding of the present invention, reference is
made to
the following detailed description of the preferred embodiments, taken in
conjunction with the
accompanying drawings, wherein like reference numerals designate like or
similar elements
throughout the several figures of the drawings and wherein:
[0010] Figure 1 is an isometric view of an exemplary downhole tool constructed
in
accordance with the present invention.
[0011] Figure 2 is an isometric view of an exemplary slip element which is
used with
the tool shown in Figure 1.
[0012] Figure 3 is an isometric view of the exemplary outer contact portion of
the
slip element of Figure 2.
[0013] Figure 4 is an isometric view of the exemplary inner body portion of
the slip
element of Figure 2.
[0014] Figure 5 is an isometric view of an exemplary alternative outer contact
portion of the slip element in accordance with the present invention.
[0015] Figure 6 is an isometric view of an exemplary slip ring which
incorporates slip
elements constructed in accordance with the present invention.
[0016] Figure 7 is a one-quarter side cross-sectional view depicting an
exemplary
downhole tool in accordance with the present invention secured within a
surrounding tubular.
[0017] Figure 8 is a one-quarter side cross-sectional view depicting removal
by
milling of an exemplary downhole tool from the surrounding tubular in
accordance with the
present invention.
[0018] Figure 9 is a chart illustrating exemplary dissolution rates of
different
compounds.
[0019] Figure 10 is cross-sectional schematic depiction of an integrally-
formed slip
element in accordance with the present invention.
[0020] Figure 11 is a side, cross-sectional view of an alternative exemplary
slip
element constructed in accordance with the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
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[0021] Figure 1 depicts an exemplary downhole tool 10 constructed in
accordance
with the present invention. The tool 10 can be any of a class of devices that
use radially
moveable slip elements within a gripping system that resists axial or
torsional forces. The
downhole tools may include packers, anchors, plugs, setting tools, bridge
plugs, locks and
fishing tools. The downhole tool 10 includes a setting cone 12 which is
generally cylindrical.
The outer radial surface 14 of the setting cone 12 includes a plurality of
angled ramps 16
which are separated by guides 18. A slip element 20, constructed in accordance
with the
present invention, is located upon each of the ramps 16.
[0022] In preferred embodiments, the slip elements 20 are cast within a
surrounding
molding 21, which is best seen in Figure 6. In particular embodiments, the
molding 21 is
formed of a phenolic resin and is cast in an annular ring shape having sheaths
23. The sheaths
23 each encase one of the slip elements 20. The molding 21 forms a slip ring
which, as Figure
1 illustrates, is disposed onto the setting cone 12.
[0023] The slip elements 20 are moveable upon the ramps 16 of the setting cone
12
between the retracted, unset position shown in Figure 1 and a set position,
wherein the slip
elements 20 are moved upon the ramps 16, in a manner known in the art,
radially outwardly
with respect to the setting cone 12. In the set position, the slip elements 20
of the downhole
tool 10 are brought into engagement with a surrounding tubular member.
[0024] The structure of the slip elements 20 is better appreciated with
reference to
Figures 2 and 3. As Figure 2 shows, the slip element 20 has a slip body which
includes a
radially inner body portion 22 and an outer contact portion 24. The inner body
portion 22 is
formed of a material that is substantially dissolvable in response to a
dissolving agent. In one
current embodiment, the inner body portion 22 is formed of magnesium-based
composite
powder compact. In other exemplary embodiments, the inner body portion 22 is
formed of an
aluminum-based or iron-based composite material. The magnesium, aluminum and
iron-based
composite materials may be a powder compact, a casting, a forging, an extruded
component,
or a laser additive 3D printed structure. Figure 4 illustrates the inner body
portion 22 apart
from other components. The inner body portion 22 is generally wedge shaped.
The inner body
portion 22 may be formed by high-pressure compression at high temperatures.
Thereafter, the
part is shaped by known mechanical processes.
[0025] In instances wherein the dissolvable material is magnesium-based,
aluminum-
based or iron-based composite-powder compact, the dissolving agent may
comprise various
brines or acids often used in an oil or gas well. The brines include, but are
not limited to,
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potassium chloride (kcl), sodium chloride (NaC1) and calcium chloride/calcium
bromine
(Ca2C1/CaBr2). The acids include, but are not limited to, hydrogen chloride,
acetic acid and
formic acid. In particular embodiments, the dissolving agent is a solution
that includes from
about 2% to about 5% potassium chloride. In a particularly preferred
embodiment, the
dissolving agent is a solution that includes about 3% potassium chloride.
[0026] Also in these embodiments, the inner body portions 22 are entirely
covered
by the phenolic material forming the molding 21. As Figure 1 illustrates, the
contact surfaces
26 of the outer contact portions 24 may extend radially outside of the sheaths
23. This
material acts as a laminate that separates the dissolvable material forming
the inner body
portion 22 from surrounding fluids which might contain one of more agents
capable of
dissolving the body portion 22.
[0027] Figure 3 depicts the outer contact portion 24 apart from the body
portion 22.
The contact surface 26 of the contact portion preferably includes stepped
wickers 28 formed
thereupon to create a biting engagement with a surrounding tubular member. The
outer
contact portion 24 is preferably formed of a hardened material that is
suitable for creating a
biting engagement into a surrounding tubular or proximate metallic surface. In
one preferred
embodiment, the outer contact portion 24 is formed of cast iron. Also
according to preferred
embodiments, the outer contact portion 24 is substantially non-dissolvable by
the dissolving
agent that is used to dissolve the inner body portions 22.
[0028] Alternatively, the outer contact portion 24 has a dissolution rate that
is
slower than that of the dissolvable material making up the inner body portion
22. In preferred
embodiments, the outer contact portion 24 has a dissolution rate that is
significantly slower
than that of the inner body portion 22. A significantly slower rate of
dissolution, as defined
herein, is a dissolution rate that is more than ten times slower. Figure 9
illustrates the
dissolution of coupons of various materials over time in response to a
dissolving agent.
Disintegration (dissolution) of the coupon (in inches) is plotted against time
in hours. Line 31
is representative of the dissolution rate of an aluminum-magnesium alloy. Line
33 is
representative of the dissolution rate of a magnesium-tungsten alloy. Line 35
is representative
of the dissolution rate of a magnesium-iron alloy. Line 37 represents the
dissolution rate of
magnesium-nickel alloy. It will be appreciated from reference to Figure 9 that
an aluminum-
magnesium alloy has a faster dissolution rate than that of magnesium-tungsten,
magnesium-
iron or magnesium-nickel. In accordance with particular embodiments of the
present
invention, the outer contact portion 24 can be formed of a material that has a
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dissolution rate than that of the material making up the inner body portion
22. Therefore, the
inner body portion 22 might be made up of, for example, magnesium-iron alloy
if the outer
body portion 24 is made up of magnesium-nickel alloy.
[0029] In certain embodiments, openings 30 are preferably formed through the
outer
contact portion 24. The openings 30 introduce points of weakness in the
structure of the
portion 24. Thus, they serve as stress risers which assist the outer contact
portion 24 in
disintegration during removal of the downhole tool 10 by drilling. Figure 6
depicts an
alternative embodiment for an outer contact portion 24' which has a similar
construction to
the outer contact portion 24. However, the openings 30' are in the form of
elongated slots.
[0030] The contact portion 24 (or 24') preferably extends from the upper end
32 to
the lower end 34 of the slip element 20. The outer contact portion 24 (or 24')
is preferably
affixed to the body portion 22 using a suitable adhesive.
[0031] According to alternative embodiments, the outer contact portion and the
inner body portion of a slip element are integrally formed. Figure 10 is a
schematic cross-
section of an exemplary slip element 20" that is made up of an inner body
portion 22" and an
outer contact portion 24". Because the slip element 20" is integrally formed,
the inner body
portion 22" and the outer contact portion 24" are interconnected by a
transition gradient zone
23. Layers 25a, 25b, 25c, 25d and 25e are overlayed upon each other.
Collectively, the
layers 25a, 25b, 25c, 25d and 25e make up a transition gradient zone 27 that
interconnects the
inner body portion 22" and the outer contact portion 24". The slip element 20"
may be
manufactured by use of 3-D laser printing systems of a type known in the art.
According to an
exemplary method of manufacture, multiple layers of material are deposited
onto a substrate
that corresponds to the outer contact portion 24". The layers 25a, 25b, 25c,
25d and 25e
contain various proportions of the materials making up the outer body portion
and the inner
body portion. Figure 10 shows a layer 25a having a composition that is about
75% of the
material used to form the outer contact portion 24" and about 25% of the
material used to
form the inner body portion 22". Layer 25b has a composition that is about 60%
of the
material forming the outer contact portion 24" and about 40% of the material
forming the
inner body portion 22". Layer 25c has a composition that is about 50% of outer
contact
portion material and about 50% of inner body portion material. Layer 25d is
made up of
about 60% of inner body portion material and about 40% of outer contact
portion material.
Layer 25e is made up of about 75% inner body portion material and about 25% of
outer
contact portion material. There may be more or fewer than five layers within
the transition
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gradient zone 27, as desired. The transition gradient zone 27 serves to
transition the material
of the slip member 20" from one to the other in a graded manner. Figure 10 is
not to scale or
in proportion as it is for illustrative purposes only. According to particular
embodiments, the
transition gradient zone 27 may have an actual thickness that is from about 10
microns to
about 1000 microns.
[0032] In operation, the tool 10 is run into a flowbore and then moved from
its unset
position to a set position, in a manner known in the art. The outer contact
portions 24 (or
24') of the slip elements 20 engagingly contact the surrounding tubular
member.
[0033] When it is desired to remove the tool 10 from the flowbore, a drilling
or
milling device, of a type known in the art, contacts the tool 10 and begins to
destroy it by
grinding action. Figure 7 illustrates the tool 10 having been set within a
surrounding tubular
member 36 such that the wickers 28 of the slip elements 20 (one shown) are set
into the
interior surface 38 of the tubular member 36 in an engaging contact. A milling
device 40 is
disposed within the tubular member 36 and moved in the direction of arrow 42
through
flowbore 44 toward engagement with the upper end 46 of plug 10. As Figure 8
shows, the
milling device 40 then engages and begins to mill away or remove the upper end
46 of the
downhole tool 10. The setting cone 12 is abraded away. As the milling device
40 encounters
the slip elements 20, the phenolic material forming the slip ring molding 21
is milled through,
as depicted, thereby exposing the inner body portions 22 to fluid within the
flowbore 44.
Dissolving agent is present in the fluid within the flowbore 44 and acts to
dissolve the inner
body portions 22 within the wellbore fluid. It is noted that potassium
chloride in solution is
typically present in conventional drilling fluids. In addition, the milling
tool 40 will mill away
the outer contact portions 24, and rupture the outer contact portions 24 into
smaller
component pieces due to the pattern of openings 30 which are disposed through
the outer
contact portions 24. The design of the slip inserts 20 will permit the
downhole tool 10 to be
rapidly removed from the flowbore 44. In addition, a number of the components
of the tool
can be more easily circulated out of the flowbore 44.
[0034] An alternative embodiment of the invention, features a slip element (50
in
Figure 11) which does not require milling or physical abrasion of the slip
element in order to
destroy the slip element. Figure 11 illustrates the slip element 50 in a set
position within
tubular member 36. Except where indicated to the contrary, the slip element 50
is constructed
and operates in the same manner as the slip element 20 described earlier.
Openings 52 are
disposed through the molding 21 and allow for fluids in the flowbore 44 to be
in fluid
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communication with the inner body portion 22 of the slip member 50. In
alternative
embodiments, some or all of the molding 21 is removed from surrounding the
inner body
portion 22. In order to destroy the slip element 50, and thereby release a
downhole tool from
being set within the flowbore 44, a dissolving agent is circulated into the
flowbore 44
proximate the slip element 50 and will dissolve away the inner body portion
22. This will
destroy the integrity of the slip element 50 and permit a downhole tool
incorporating the slip
element 50 to be released from engagement from the surrounding tubular 36.
[0035] Those of skill in the art will recognize that numerous modifications
and
changes may be made to the exemplary designs and embodiments described herein
and that the
invention is limited only by the claims that follow and any equivalents
thereof
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