Note: Descriptions are shown in the official language in which they were submitted.
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METHODS OF ADJUSTING THE RATE OF GALVANIC CORROSION OF A
WELLBORE ISOLATION DEVICE
Technical Field
[0001] An isolation device and methods of removing the
isolation device are provided. The isolation device includes at
least a first material that is capable of dissolving via
galvanic corrosion when an electrically conductive path exists
between the first material and a different metal or metal alloy
in the presence of an electrolyte. According to an embodiment,
the isolation device is used in an oil or gas well operation.
Several factors can be adjusted to control the rate of
dissolution of the first material in a desired amount of time.
Brief Description of the Figures
[0002] The features and advantages of certain
embodiments will be more readily appreciated when considered in
conjunction with the accompanying figures. The figures are not
to be construed as limiting any of the preferred embodiments.
[0003] Fig. 1 depicts a well system containing more than
one isolation device.
[0004] Fig. 2 depicts an isolation device according to
an embodiment.
Detailed Description
[0005] As used herein, the words "comprise," "have,"
"include," and all grammatical variations thereof are each
intended to have an open, non-limiting meaning that does not
exclude additional elements or steps.
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[0006] It should be understood that, as used herein,
'first," 'second," "third," etc., are arbitrarily assigned and
are merely intended to differentiate between two or more
materials, isolation devices, wellbore intervals, etc., as the
case may be, and does not indicate any particular orientation or
sequence. Furthermore, it is to be understood that the mere use
of the term "first" does not require that there be any 'second,"
and the mere use of the term "second" does not require that
there be any 'third," etc.
[0007] As used herein, a "fluid" is a substance having a
continuous phase that tends to flow and to conform to the
outline of its container when the substance is tested at a
temperature of 71 F (22 C) and a pressure of one atmosphere
"atm" (0.1 megapascals "MPa"). A fluid can be a liquid or gas.
[0008] Oil and gas hydrocarbons are naturally occurring
in some subterranean formations. In the oil and gas industry, a
subterranean formation containing oil or gas is referred to as a
reservoir. A reservoir may be located under land or off shore.
Reservoirs are typically located in the range of a few hundred
feet (shallow reservoirs) to a few tens of thousands of feet
(ultra-deep reservoirs). In order to produce oil or gas, a
wellbore is drilled into a reservoir or adjacent to a reservoir.
The oil, gas, or water produced from a reservoir is called a
reservoir fluid.
[0009] A well can include, without limitation, an oil,
gas, or water production well, or an injection well. As used
herein, a 'well" includes at least one wellbore. A wellbore can
include vertical, inclined, and horizontal portions, and it can
be straight, curved, or branched. As used herein, the term
"wellbore" includes any cased, and any uncased, open-hole
portion of the wellbore. A near-wellbore region is the
subterranean material and rock of the subterranean formation
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surrounding the wellbore. As used herein, a "well" also
includes the near-wellbore region. The near-wellbore region is
generally considered to be the region within approximately 100
feet radially of the wellbore. As used herein, into a well"
means and includes into any portion of the well, including into
the wellbore or into the near-wellbore region via the wellbore.
[0010] A portion of a wellbore may be an open hole or
cased hole. In an open-hole wellbore portion, a tubing string
may be placed into the wellbore. The tubing string allows
fluids to be Introduced into or flowed from a remote portion of
the wellbore. In a cased-hole wellbore portion, a casing is
placed into the wellbore that can also contain a tubing string.
A wellbore can contain an annulus. Examples of an annulus
Include, but are not limited to: the space between the wellbore
and the outside of a tubing string in an open-hole wellbore; the
space between the wellbore and the outside of a casing in a
cased-hole wellbore; and the space between the inside of a
casing and the outside of a tubing string in a cased-hole
wellbore.
[0011] It is not uncommon for a wellbore to extend
several hundreds of feet or several thousands of feet into a
subterranean formation. The subterranean formation can have
different zones. A zone is an interval of rock differentiated
from surrounding rocks on the basis of its fossil content or
other features, such as faults or fractures. For example, one
zone can have a higher permeability compared to another zone.
It is often desirable to treat one or more locations within
multiples zones of a formation. One or more zones of the
formation can be Isolated within the wellbore via the use of an
isolation device to create multiple wellbore intervals. At
least one wellbore interval corresponds to a formation zone.
The isolation device can be used for zonal isolation and
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functions to block fluid flow within a tubular, such as a tubing
string, or within an annulus. The blockage of fluid flow
prevents the fluid from flowing across the isolation device in
any direction and isolates the zone of interest. In this
manner, treatment techniques can be performed within the zone of
interest.
[0012] Common isolation devices include, but are not
limited to, a ball and a seat, a bridge plug, a packer, a plug,
and wiper plug. It is to be understood that reference to a
"ball" is not meant to limit the geometric shape of the ball to
spherical, but rather is meant to include any device that is
capable of engaging with a seat. A "ball" can be spherical in
shape, but can also be a dart, a bar, or any other shape. Zonal
isolation can be accomplished via a ball and seat by dropping or
flowing the ball from the wellhead onto the seat that is located
within the wellbore. The ball engages with the seat, and the
seal created by this engagement prevents fluid communication
into other wellbore intervals downstream of the ball and seat.
As used herein, the relative term "downstream" means at a
location further away from a wellhead. In order to treat more
than one zone using a ball and seat, the wellbore can contain
more than one ball seat. For example, a seat can be located
within each wellbore interval. Generally, the inner diameter
(I.D.) of the ball seats is different for each zone. For
example, the I.D. of the ball seats sequentially decreases at
each zone, moving from the wellhead to the bottom of the well.
In this manner, a smaller ball is first dropped into a first
wellbore interval that is the farthest downstream; the
corresponding zone is treated; a slightly larger ball is then
dropped into another wellbore Interval that is located upstream
of the first wellbore interval; that corresponding zone is then
treated; and the process continues in this fashion - moving
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upstream along the wellbore - until all the desired zones have
been treated. As used herein, the relative term "upstream"
means at a location closer to the wellhead.
[0013] A bridge plug is composed primarily of slips, a
plug mandrel, and a rubber sealing element. A bridge plug can
be Introduced into a wellbore and the sealing element can be
caused to block fluid flow into downstream intervals. A packer
generally consists of a sealing device, a holding or setting
device, and an inside passage for fluids. A packer can be used
to block fluid flow through the annulus located between the
outside of a tubular and the wall of the wellbore or inside of a
casing.
[0014] Isolation devices can be classified as permanent
or retrievable. While permanent isolation devices are generally
designed to remain in the wellbore after use, retrievable
devices are capable of being removed after use. It is often
desirable to use a retrievable isolation device in order to
restore fluid communication between one or more wellbore
Intervals. Traditionally, isolation devices are retrieved by
inserting a retrieval tool into the wellbore, wherein the
retrieval tool engages with the isolation device, attaches to
the isolation device, and the Isolation device is then removed
from the wellbore. Another way to remove an isolation device
from the wellbore is to mill at least a portion of the device or
the entire device. Yet, another way to remove an isolation
device is to contact the device with a solvent, such as an acid,
thus dissolving all or a portion of the device.
[0015] However, some of the disadvantages to using
traditional methods to remove a retrievable isolation device
include: it can be difficult and time consuming to use a
retrieval tool; milling can be time consuming and costly; and
premature dissolution of the isolation device can occur. For
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example, premature dissolution can occur if acidic fluids are
used in the well prior to the time at which it is desired to
dissolve the isolation device.
[0016] A novel method of removing an isolation device
includes using galvanic corrosion to dissolve at least a portion
of the isolation device. The rate of corrosion can be adjusted
by selecting the materials used, the electrolyte used, the
concentration of free ions available in the electrolyte, and the
distance between the two materials of the galvanic system.
[0017] Galvanic corrosion occurs when two different
metals or metal alloys are in electrical connectivity with each
other and both are in contact with an electrolyte. As used
herein, the phrase "electrical connectivity" means that the two
different metals or metal alloys are either touching or in close
enough proximity to each other such that when the two different
metals are in contact with an electrolyte, the electrolyte
becomes electrically conductive and ion migration occurs between
one of the metals and the other metal, and is not meant to
require an actual physical connection between the two different
metals, for example, via a metal wire. It is to be understood
that as used herein, the term "metal" is meant to include pure
metals and also metal alloys without the need to continually
specify that the metal can also be a metal alloy. Moreover, the
use of the phrase "metal or metal alloy" in one sentence or
paragraph does not mean that the mere use of the word "metal" in
another sentence or paragraph is meant to exclude a metal alloy.
As used herein, the term "metal alloy" means a mixture of two or
more elements, wherein at least one of the elements is a metal.
The other element(s) can be a non-metal or a different metal.
An example of a metal and non-metal alloy is steel, comprising
the metal element iron and the non-metal element carbon. An
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example of a metal and metal alloy is bronze, comprising the
metallic elements copper and tin.
[0018] The metal that is less noble, compared to the
other metal, will dissolve in the electrolyte. The less noble
metal is often referred to as the anode, and the more noble
metal is often referred to as the cathode. Galvanic corrosion
is an electrochemical process whereby free ions in the
electrolyte make the electrolyte electrically conductive,
thereby providing a means for ion migration from the anode to
the cathode - resulting in deposition formed on the cathode.
Metals can be arranged in a galvanic series. The galvanic
series lists metals in order of the most noble to the least
noble. An anodic index lists the electrochemical voltage (V)
that develops between a metal and a standard reference electrode
(gold (Au)) in a given electrolyte. The actual electrolyte used
can affect where a particular metal or metal alloy appears on
the galvanic series and can also affect the electrochemical
voltage. For example, the dissolved oxygen content in the
electrolyte can dictate where the metal or metal alloy appears
on the galvanic series and the metal's electrochemical voltage.
The anodic index of gold is -0 V; while the anodic index of
beryllium is -1.85 V. A metal that has an anodic index greater
than another metal is more noble than the other metal and will
function as the cathode. Conversely, the metal that has an
anodic index less than another metal is less noble and functions
as the anode. In order to determine the relative voltage
between two different metals, the anodic index of the lesser
noble metal is subtracted from the other metal's anodic index,
resulting in a positive value.
[0019] There are several factors that can affect the
rate of galvanic corrosion. One of the factors is the distance
separating the metals on the galvanic series chart or the
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difference between the anodic indices of the metals. For
example, beryllium is one of the last metals listed at the least
noble end of the galvanic series and platinum is one of the
first metals listed at the most noble end of the series. By
contrast, tin is listed directly above lead on the galvanic
series. Using the anodic index of metals, the difference
between the anodic index of gold and beryllium is 1.85 V;
whereas, the difference between tin and lead is 0.05 V. This
means that galvanic corrosion will occur at a much faster rate
for magnesium or beryllium and gold compared to lead and tin.
[0020] The following is a partial galvanic series chart
using a deoxygenated sodium chloride water solution as the
electrolyte. The metals are listed in descending order from the
most noble (cathodic) to the least noble (anodic). The
following list is not exhaustive, and one of ordinary skill in
the art is able to find where a specific metal or metal alloy is
listed on a galvanic series in a given electrolyte.
PLATINUM
GOLD
ZIRCONIUM
GRAPHITE
SILVER
CHROME IRON
SILVER SOLDER
COPPER - NICKEL ALLOY 80-20
COPPER - NICKEL ALLOY 90-10
MANGANESE BRONZE (CA 675), TIN BRONZE (CA903, 905)
COPPER (CA102)
BRASSES
NICKEL (ACTIVE)
TIN
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LEAD
ALUMINUM BRONZE
STAINLESS STEEL
CHROME IRON
MILD STEEL (1018), WROUGHT IRON
ALUMINUM 2117, 2017, 2024
CADMIUM
ALUMINUM 5052, 3004, 3003, 1100, 6053
ZINC
MAGNESIUM
BERYLLIUM
[0021] The
following is a partial anodic index listing
the voltage of a listed metal against a standard reference
electrode (gold) using a deoxygenated sodium chloride water
solution as the electrolyte. The metals are listed in
descending order from the greatest voltage (most cathodic) to
the least voltage (most anodic). The following list is not
exhaustive, and one of ordinary skill in the art is able to find
the anodic index of a specific metal or metal alloy in a given
electrolyte.
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Anodic index
Metal Index
(V)
Gold, solid and plated, Gold-platinum alloy -0.00
Rhodium plated on silver-plated copper -0.05
Silver, solid or plated; monel metal. High nickel- -0.15
copper alloys
Nickel, solid or plated, titanium an s alloys, Monel -0.30
Copper, solid or plated; low brasses or bronzes; -0.35
silver solder; German silvery high copper-nickel
alloys; nickel-chromium alloys
Brass and bronzes -0.40
High brasses and bronzes -0.45
18% chromium type corrosion-resistant steels -0.50
Chromium plated; tin plated; 12 chromium type -0.60
corrosion-resistant steels
Tin-plate; tin-lead solder -0.65
Lead, solid or plated; high lead alloys -0.70
2000 series wrought aluminum -0.75
Iron, wrought, gray or malleable, plain carbon and -0.85
low alloy steels
Aluminum, wrought alloys other than 2000 series -0.90
aluminum, cast alloys of the silicon type
Aluminum, cast alloys other than silicon type, -0.95
cadmium, plated and chromate
Hot-dip-zinc plate; galvanized steel -1.20
Zinc, wrought; zinc-base die-casting alloys; zinc -1.25
plated
Magnesium & magnesium-base alloys, cast or wrought -1.75
Beryllium -1.85
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[0022] Another factor that can affect the rate of
galvanic corrosion is the temperature and concentration of the
electrolyte. The higher the temperature and concentration of
the electrolyte, the faster the rate of corrosion. Yet another
factor that can affect the rate of galvanic corrosion is the
total amount of surface area of the least noble (anodic metal).
The greater the surface area of the anode that can come in
contact with the electrolyte, the faster the rate of corrosion.
The cross-sectional size of the anodic metal pieces can be
decreased in order to increase the total amount of surface area
per total volume of the material. The anodic metal or metal
alloy can also be a matrix in which pieces of cathode material
is embedded in the anode matrix. Yet another factor that can
affect the rate of galvanic corrosion is the ambient pressure.
Depending on the electrolyte chemistry and the two metals, the
corrosion rate can be slower at higher pressures than at lower
pressures if gaseous components are generated. Yet another
factor that can affect the rate of galvanic corrosion is the
physical distance between the two different metal and/or metal
alloys of the galvanic system.
[0023] According to an embodiment, a method of removing
a wellbore isolation device comprises: contacting or allowing
the wellbore isolation device to come in contact with an
electrolyte, wherein at least a portion of the wellbore
isolation device comprises a first material and pieces of a
second material, wherein the first material: (A) is a metal or a
metal alloy; (B) forms a matrix of the portion of the wellbore
isolation device; and (C) partially or wholly dissolves when an
electrically conductive path exists between the first material
and the second material and at least a portion of the first and
second materials are in contact with the electrolyte, wherein
the pieces of the second material: (A) are a metal or metal
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alloy; and (B) are embedded within the matrix of the first
material; wherein the first material and the second material
form a galvanic couple and wherein the first material is the
anode and the second material is the cathode of the couple; and
allowing at least a portion of the first material to dissolve.
[0024] According to another embodiment, a method of
removing a wellbore isolation device comprises: contacting or
allowing the wellbore isolation device to come in contact with
an electrolyte, wherein at least a portion of the wellbore
isolation device comprises pieces of a first material, pieces of
a second material, and a third material, wherein the first
material: (A) is a metal or a metal alloy; and (B) partially or
wholly dissolves when an electrically conductive path exists
between the first material and the second material and at least
a portion of the first and second materials are in contact with
the electrolyte, wherein the second material is a metal or metal
alloy, wherein the first material and the second material form a
galvanic couple and wherein the first material is the anode and
the second material is the cathode of the couple, and wherein
the third material physically separates at least a portion of a
surface of one or more pieces of the first material from at
least a portion of a surface of one or more pieces of the second
material; and allowing at least some of the pieces of the first
material to dissolve.
[0025] Any discussion of the embodiments regarding the
isolation device or any component related to the isolation
device (e.g., the electrolyte) is intended to apply to all of
the method embodiments.
[0026] Turning to the Figures, Fig. 1 depicts a well
system 10. The well system 10 can include at least one wellbore
11. The wellbore 11 can penetrate a subterranean formation 20.
The subterranean formation 20 can be a portion of a reservoir or
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adjacent to a reservoir. The wellbore 11 can Include a casing
12. The wellbore 11 can Include only a generally vertical
wellbore section or can include only a generally horizontal
wellbore section. A tubing string 15 can be installed in the
wellbore 11. The well system 10 can comprise at least a first
wellbore Interval 13 and a second wellbore interval 14. The
well system 10 can also Include more than two wellbore
intervals, for example, the well system 10 can further include a
third wellbore interval, a fourth wellbore interval, and so on.
At least one wellbore interval can correspond to a zone of the
subterranean formation 20. The well system 10 can further
include one or more packers 18. The packers 18 can be used in
addition to the isolation device to create the wellbore interval
and isolate each zone of the subterranean formation 20. The
Isolation device can be the packers 18. The packers 18 can be
used to prevent fluid flow between one or more wellbore
intervals (e.g., between the first wellbore interval 13 and the
second wellbore interval 14) via an annulus 19. The tubing
string 15 can also include one or more ports 17. One or more
ports 17 can be located in each wellbore interval. Moreover,
not every wellbore interval needs to Include one or more ports
17. For example, the first wellbore interval 13 can include one
or more ports 17, while the second wellbore interval 14 does not
contain a port. In this manner, fluid flow into the annulus 19
for a particular wellbore interval can be selected based on the
specific oil or gas operation.
[0027] It should be noted that the well system 10 is
Illustrated in the drawings and is described herein as merely
one example of a wide variety of well systems in which the
principles of this disclosure can be utilized. It should be
clearly understood that the principles of this disclosure are
not limited to any of the details of the well system 10, or
13
components thereof, depicted in the drawings or described
herein. Furthermore, the well system 10 can include other
components not depicted in the drawing. For example, the well
system 10 can further include a well screen. By way of another
example, cement may be used instead of packers 18 to aid the
isolation device in providing zonal isolation. Cement may also
be used in addition to packers 18.
[0028]
According to an embodiment, the isolation device
is capable of restricting or preventing fluid flow between a
first wellbore interval 13 and a second wellbore interval 14.
The first wellbore interval 13 can be located upstream or
downstream of the second wellbore interval 14. In this manner,
depending on the oil or gas operation, fluid is restricted or
prevented from flowing downstream or upstream into the second
wellbore interval 14. Examples of isolation devices capable of
restricting or preventing fluid flow between zones include, but
are not limited to, a ball and seat, a plug, a bridge plug, a
wiper plug, a packer, and a plug in a base pipe. A detailed
discussion of using a plug in a base pipe can be found in US
patent 7,699,101 issued to Michael L. Fripp, Haoyue Zhang, Luke
W. Holderman, Deborah Fripp, Ashok K. Santra, Anindya Ghosh on
Apr. 20, 2010. If there is any conflict in the usage of a word
or phrase herein and any paper incorporated by reference, the
definitions contained herein control. The portion of the
isolation device that includes at least the first material and
the second material can be the mandrel of a packer or plug, a
spacer ring, a slip, a wedge, a retainer ring, an extrusion
limiter or backup shoe, a mule shoe, a ball, a flapper, a ball
seat, a sleeve, or any other downhole tool or component of a
downhole tool used for zonal isolation.
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[0029] As depicted in the drawings, the isolation device
can be a ball 30 (e.g., a first ball 31 or a second ball 32) and
a seat 40 (e.g., a first seat 41 or a second seat 42). The ball
30 can engage the seat 40. The seat 40 can be located on the
inside of a tubing string 15. The inner diameter (I.D.) of the
first seat 41 can be less than the I.D. of the second seat 42.
In this manner, a first ball 31 can be dropped or flowed into
wellbore. The first ball 31 can have a smaller outer diameter
(0.D.) than the second ball 32. The first ball 31 can engage
the first seat 41. Fluid can now be temporarily restricted or
prevented from flowing into any wellbore intervals located
downstream of the first wellbore interval 13. In the event it
is desirable to temporarily restrict or prevent fluid flow into
any wellbore Intervals located downstream of the second wellbore
interval 14, then the second ball 32 can be dropped or flowed
into the wellbore and will be prevented from falling past the
second seat 42 because the second ball 32 has a larger O.D. than
the I.D. of the second seat 42. The second ball 32 can engage
the second seat 42. The ball (whether it be a first ball 31 or
a second ball 32) can engage a sliding sleeve 16 during
placement. This engagement with the sliding sleeve 16 can cause
the sliding sleeve to move; thus, opening a port 17 located
adjacent to the seat. The port 17 can also be opened via a
variety of other mechanisms instead of a ball. The use of other
mechanisms may be advantageous when the isolation device is not
a ball. After placement of the isolation device, fluid can be
flowed from, or into, the subterranean formation 20 via one or
more opened ports 17 located within a particular wellbore
Interval. As such, a fluid can be produced from the
subterranean formation 20 or injected into the formation.
[0030] Referring to Figs. 2 - 3, the isolation device
comprises at least a first material 51, wherein the first
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material partially or wholly dissolves when an electrically
conductive path exists between the first material 51 and a
second material 52. The first material 51 and the second
material 52 are metals or metal alloys. The metal or metal
alloy can be selected from the group consisting of, lithium,
sodium, potassium, rubidium, cesium, beryllium, calcium,
strontium, barium, radium, aluminum, gallium, indium, tin,
thallium, lead, bismuth, scandium, titanium, vanadium, chromium,
manganese, thorium, iron, cobalt, nickel, copper, zinc, yttrium,
zirconium, niobium, molybdenum, ruthenium, rhodium, palladium,
praseodymium, silver, cadmium, lanthanum, hafnium, tantalum,
tungsten, terbium, rhenium, osmium, iridium, platinum, gold,
neodymium, gadolinium, erbium, oxides of any of the foregoing,
graphite, carbon, silicon, boron nitride, and any combinations
thereof. Preferably, the metal or metal alloy is selected from
the group consisting of magnesium, aluminum, zinc, beryllium,
tin, iron, nickel, copper, oxides of any of the foregoing, and
combinations thereof. According to an embodiment, the metal is
neither radioactive, nor unstable.
[0031] According to an embodiment, the first material 51
and the second material 52 are different metals or metal alloys.
By way of example, the first material 51 can be magnesium and
the second material 52 can be iron. Furthermore, the first
material 51 can be a metal and the second material 52 can be a
metal alloy. The first material 51 and the second material 52
can be a metal and the first and second material can be a metal
alloy. The first material and the second material form a
galvanic couple and wherein the first material is the anode and
the second material is the cathode of the couple. Stated
another way, the second material 52 is more noble than the first
material 51. In this manner, the first material 51 (acting as
the anode) partially or wholly dissolves when in electrical
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connectivity with the second material 52 and when the first and
second materials are in contact with the electrolyte.
[0032] The
methods include allowing at least a portion
of the first material or at least some of the pieces of the
first material to dissolve. The step of allowing can be
performed after the step of contacting or allowing the first
material to come in contact with the electrolyte. At least a
portion of the first material 51 can dissolve in a desired
amount of time. The desired amount of time can be pre-
determined, based in part, on the specific oil or gas well
operation to be performed. The desired amount of time can be in
the range from about 1 hour to about 2 months, preferably about
to about 10 days. There are several factors that can affect
the rate of dissolution of the first material 51. According to
an embodiment, the first material 51 and the second material 52
are selected such that the at least a portion of the first
material 51 dissolves in the desired amount of time. By way of
example, the greater the difference between the second
material's anodic index and the first material's anodic index,
the faster the rate of dissolution. By contrast, the less the
difference between the second material's anodic index and the
first material's anodic index, the slower the rate of
dissolution. By way of yet another example, the farther apart
the first material and the second material are from each other
in a galvanic series, the faster the rate of dissolution; and
the closer together the first and second material are to each
other in the galvanic series, the slower the rate of
dissolution. By evaluating the difference in the anodic index
of the first and second materials, or by evaluating the order in
a galvanic series, one of ordinary skill in the art will be able
to determine the rate of dissolution of the first material in a
given electrolyte.
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[0033] Another factor that can affect the rate of
dissolution of the first material 51 is the proximity of the
first material 51 to the second material 52. A more detailed
discussion regarding different embodiments of the proximity of
the first and second materials is presented below. Generally,
the closer the first material 51 is physically to the second
material 52, the faster the rate of dissolution of the first
material 51. By contrast, generally, the farther apart the
first and second materials are from one another, the slower the
rate of dissolution. It should be noted that the distance
between the first material 51 and the second material 52 should
not be so great that an electrically conductive path ceases to
exist between the first and second materials. According to an
embodiment, any distance between the first and second materials
51/52 is selected such that the at least a portion of the first
material 51 dissolves in the desired amount of time.
[0034] Another factor that can affect the rate of
dissolution of the first material 51 is the concentration of the
electrolyte and the temperature of the electrolyte. A more
detailed discussion of the electrolyte is presented below.
Generally, the higher the concentration of the electrolyte, the
faster the rate of dissolution of the first material 51, and the
lower the concentration of the electrolyte, the slower the rate
of dissolution. Moreover, the higher the temperature of the
electrolyte, the faster the rate of dissolution of the first
material 51, and the lower the temperature of the electrolyte,
the slower the rate of dissolution. One of ordinary skill in
the art can select: the exact metals and/or metal alloys, the
proximity of the first and second materials, and the
concentration of the electrolyte based on an anticipated
temperature in order for the at least a portion of the first
material 51 to dissolve in the desired amount of time.
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[0035] Fig. 2 depicts the isolation device 30 according
to certain embodiments. According to this embodiment, the first
material 51 forms a matrix of the portion of the wellbore device
that contains the first material 51 and the second material 52.
It is to be understood that the entire isolation device, for
example, when the isolation device is a ball or ball seat, can
be made of at least the first material and second material.
Moreover, only one or more portions of the isolation device can
be made from at least the first and second materials. As can be
seen in Fig. 2, the second material 52 can be in the form of
pieces, wherein the pieces of the second material are embedded
within the matrix of the first material 51. The exact number or
concentration of the pieces of the second material 52 can be
selected and adjusted to control the dissolution rate of the
first material 51 such that at least the portion of the first
material 51 dissolves in the desired amount of time. For
example, the higher the concentration of pieces of second
material 52 that are embedded within the matrix of the first
material 51, generally the faster the rate of dissolution.
Moreover, the pieces of the second material 52 can be uniformly
distributed throughout the matrix of the first material 51.
This embodiment can be useful when a constant rate of
dissolution of the first material is desired. The pieces of the
second material can also be non-uniformly distributed throughout
the matrix of the first material such that different
concentrations of the second material are located within
different areas of the matrix. By way of example, a higher
concentration of the pieces of the second material can be
distributed closer to the outside of the matrix for allowing an
initially faster rate of dissolution; whereas a lower
concentration of the pieces can be distributed in the middle and
inside of the matrix for allowing a slower rate of dissolution.
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By contrast, a higher concentration of the pieces of the second
material can be distributed in the middle and/ or inside of the
matrix for allowing a faster rate of dissolution at the end of
dissolution; whereas a lower concentration of the pieces can be
distributed closer to the outside of the matrix for allowing an
initially slower rate of dissolution. Of course the
concentration of pieces of the second material can be
distributed in a variety of ways to allow for differing rates of
dissolution of the first material matrix.
[0036]
According to an embodiment, a third material is
included in the portion of the isolation device (not shown in
Fig. 2). The third material can be a bonding agent for bonding
the pieces of the second material into the matrix of the first
material 51. This embodiment can be useful during the
manufacturing process to provide a suitable bond between the
matrix of the first material 51 and pieces of the second
material 52. Preferred manufacturing processes can include
casting, forging, hot- and/or cold-working, metal injection
molding, but would exclude powder compaction and sintering.
Preferably, the portion of the isolation device is made via
casting. Preferably, the portion of the isolation device is
also modified with a heat treatment. In one embodiment, the
heat treatment involves precipitation heat treatment where the
alloy is heated to allow the precipitation of the constituent
ingredients that are held in a solid solution. The
precipitation heat treatment temperature can be in the range
from 300 F to 500 F (149 C to 260 C) for 1 to 16 hours. For
example, a forged metal alloy can be heated for 24 hours at 350
F (177 C). In another example, cast parts are heated for 1 to
2 hours at 400 F to 500 F (204 C to 260 C), followed by slow
cooling. The precipitation heat treatment could follow a
solution heat treatment. A solution heat treatment involves
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heating the metal alloy to a temperature at which certain
ingredients of the alloy go into solution, and then quenching so
as to hold these ingredients in solution during cooling. The
solution heat treatment temperature can be in the range from 650
F to 1050 F (343 C to 566 C) for 10 to 24 hours.
[0037] Examples of materials suitable for use as a
bonding third material include, but are not limited to, copper,
platinum, gold, silver, nickel, iron, chromium, molybdenum,
tungsten, stainless steel, zirconium, titanium, indium, and
oxides of any of the foregoing. Preferably, the third material
includes a metal and/or a non-metal that is different from the
metals making up the first and second materials 51/52. In one
example, the first material is aluminum, the second material is
iron, and the third material is iron oxide. In another example,
the first material is magnesium, the second material is carbon,
and the third material is iron oxide. It may be desirable to
use the oxide of the metal to create a better bond between the
first and second materials 51/52. The third material can be
coated onto the pieces of the second material 52. A layer of
the third material can be located between the surfaces of the
pieces of the second material and the matrix of the first
material with the surfaces of pieces of the second material
being physically separated from the matrix of the first material
via the layer of third material. The coating of third material
can form a metal or metal oxide interface with the surface of
each of the pieces of the second material 52 with the matrix of
the first material 51. Accordingly, after manufacture, there
will be a layer of the third material 53 located between the
surfaces of the pieces of the second material 52 and the matrix
of the first material 51. The thickness of the layer of the
third material can be selected to provide the desired bond
strength between the pieces of the second material 52 and matrix
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of the first material 51. For example, if the layer is too
thin, then there may be an insufficient amount of third material
to create a good bond, and if the layer is too thick, then the
layer may become mechanically weak and mechanical failure can
occur at the Interface between the third material 53 and the
first or second materials or failure could also occur within the
layer of third material. Preferably, the thickness of the layer
of third material is in the range of about 10 nanometers to
about 100 nanometers. In another embodiment, the thickness of
the third material is less than 10 nanometers. In another
embodiment, the thickness of the third material is 100
nanometers to 5,000 nanometers.
[0038] Fig. 3 depicts the Isolation device according to
certain other embodiments. As depicted in Fig. 3, the Isolation
device can comprise pieces of the first material 51, pieces of
the second material 52, and the third material 53. Although
this embodiment depicted in Fig. 3 illustrates the Isolation
device as a ball, it is to be understood that this embodiment
and discussion thereof is equally applicable to an Isolation
device that is a bridge plug, packer, etc. In order for
galvanic corrosion to occur (and hence dissolution of at least a
portion of the first material 51), both, the first and second
materials 51/52 need to be capable of being contacted by the
electrolyte. Preferably, at least a portion of one or more
pieces of the first material 51 and the second material 52 form
the outside of the isolation device, such as a ball 30. In this
manner, at least a portion of the first and second materials
51/52 are capable of being contacted with the electrolyte.
[0039] According to another embodiment, the third
material 53 physically separates at least a portion of a surface
of one or more pieces of the first material 51 from at least a
portion of a surface of one or more pieces of the second
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material 52. These embodiments can be useful when it is desired
to use the distance between the first and second materials 51/52
as a way to control the rate of dissolution of the first
material 51. The third material 53 may also limit the ionic
conductivity or the electrical conductivity between the first
and second materials 51/52. According to an embodiment, the
third material 53 is in the form of pieces. The third material
can be selected from the group consisting of metals, non-metals,
sand, plastics, ceramics, and polymers. Preferably, the third
material includes a metal and/or a non-metal that is different
from the metals making up the first and second materials 51/52.
The pieces of the third material 53 can be located between one
or more of the pieces of the first and second materials 51/52.
The size and shape of the pieces of the third material 53 can be
selected to provide a desired distance of the physical
separation of the first and second materials 51/52. By way of
example, the thicker the cross-sectional size of the piece of
third material 53, the greater the reduction of the ionic and/or
electrical conductivity between the pieces of the first material
51 and the pieces of the second material 52. Conversely, the
smaller the thickness of the third material, the smaller the
reduction of the ionic and/or electrical conductivity between
the pieces of the first and second materials 51/52. The pieces
of the third material 53 can also separate two or more pieces of
the first material 51 and/or two or more pieces of the second
material 52. The size of the pieces of the third material 53
can be the same or different. The pieces of third material
having different thicknesses can be distributed throughout the
portion of the isolation device in a variety of ways to provide
different rates of dissolution. For example, larger-sized
pieces can be located towards the outside of the portion of the
isolation device; whereas smaller-sized pieces can be located
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towards the middle and/or inside. This embodiment could provide
an initially slower rate of dissolution due to the initially
greater distance between the first and second materials 51/52
and a faster rate of dissolution later due to a decreased
distance between the first and second materials 51/52. Of
course, the distribution of different sized pieces of the third
material 53 can vary and be selected to provide the desired
rates of dissolution of at least some of the pieces of the first
material 51.
[0040] The
concentration and distribution patterns of
pieces of the third material 53 can also be selected to provide
the desired rate of dissolution of at least some of the pieces
of the first material 51 such that at least some of the pieces
of the first material dissolve in the desired amount of time.
For example, generally, the higher the concentration of the
third material, the slower the rate of dissolution, and the
lower the concentration of the third material, the faster the
rate of dissolution. Moreover, the pieces of the third material
53 can be uniformly distributed throughout the portion of the
isolation device containing the first, second, and third
materials. This embodiment (assuming a relatively uniform size
of the pieces of third material) can be used to provide a
relatively constant rate of dissolution of the pieces of the
first material 51. The pieces of the third material 53 can also
be non-uniformly distributed throughout the portion of the
isolation device. By way of example, a higher concentration of
the pieces of the third material can be distributed closer to
the outside of the portion of the isolation device for allowing
an initially slower rate of dissolution; whereas a lower
concentration of the pieces can be distributed in the middle and
inside for allowing a faster rate of dissolution. By contrast,
a higher concentration of the pieces of the third material can
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be distributed in the middle and/ or inside of the matrix for
allowing a slower rate of dissolution at the end of dissolution;
whereas a lower concentration of the pieces can be distributed
closer to the outside for allowing an initially faster rate of
dissolution.
[0041] The pieces of the first material 51 and the
pieces of the second material 52 can be bonded together via a
third material as described above with reference to Fig. 2. In
this manner, the pieces of first material and pieces of the
second material can be bonded together to form the portion of
the isolation device. The device of Fig. 3 can also be
manufactured and optionally subjected to the heat treatments
described above.
[0042] The size, shape and placement of the pieces of
the first and second materials 51/52 can also be adjusted to
control the rate of dissolution of the first material 51. By
way of example, generally the smaller the cross-sectional area
of each piece, the faster the rate of dissolution. The smaller
cross-sectional area increases the ratio of the surface area to
total volume of the material, thus allowing more of the material
to come in contact with the electrolyte. The cross-sectional
area of each piece of the first material 51 can be the same or
different, the cross-sectional area of each piece of the second
material 52 can be the same or different, and the cross-
sectional area of the pieces of the first material 51 and the
pieces of the second material 52 can be the same or different.
Additionally, the cross-sectional area of the pieces forming the
outer portion of the isolation device and the pieces forming the
inner portion of the isolation device can be the same or
different. By way of example, if it is desired for the outer
portion of the isolation device to proceed at a faster rate of
galvanic corrosion compared to the inner portion of the device,
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then the cross-sectional area of the individual pieces
comprising the outer portion can be smaller compared to the
cross-sectional area of the pieces comprising the inner portion.
The shape of the pieces of the first and second materials 51/52
can also be adjusted to allow for a greater or smaller cross-
sectional area.
[0043] According to an embodiment, at least the first
material 51 and second material 52 are capable of withstanding a
specific pressure differential for a desired amount of time. As
used herein, the term "withstanding" means that the substance
does not crack, break, or collapse. The pressure differential
can be the downhole pressure of the subterranean formation 20
across the device. As used herein, the term "downhole" means
the location of the wellbore where the portion of the isolation
device is located. Formation pressures can range from about
1,000 to about 30,000 pounds force per square inch (psi) (about
6.9 to about 206.8 megapascals "MPa"). The pressure
differential can also be created during oil or gas operations.
For example, a fluid, when introduced into the wellbore 11
upstream or downstream of the substance, can create a higher
pressure above or below, respectively, of the isolation device.
Pressure differentials can range from 100 to over 10,000 psi
(about 0.7 to over 68.9 MPa). According to another embodiment,
the isolation device is capable of withstanding the specific
pressure differential for the desired amount of time. The
desired amount of time can be at least 30 minutes. The desired
amount of time can also be in the range of about 30 minutes to
14 days, preferably 30 minutes to 2 days, more preferably 4
hours to 24 hours.
[0044] As discussed above, the rate of dissolution of
the first material 51 can be controlled using a variety of
factors. According to an embodiment, at least the first
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material 51 includes one or more tracers (not shown). The
tracer(s) can be, without limitation, radioactive, chemical,
electronic, or acoustic. As depicted in Fig. 3, each piece of
the first material 51 can include a tracer. A tracer can be
useful in determining real-time information on the rate of
dissolution of the first material 51. For example, a first
material 51 containing a tracer, upon dissolution can be flowed
through the wellbore 11 and towards the wellhead or into the
subterranean formation 20. By being able to monitor the
presence of the tracer, workers at the surface can make on-the-
fly decisions that can affect the rate of dissolution of the
remaining first material 51.
[0045] Such decisions might include to increase or
decrease the concentration of the electrolyte. As used herein,
an electrolyte is any substance containing free ions (i.e., a
positive- or negative-electrically charged atom or group of
atoms) that make the substance electrically conductive. The
electrolyte can be selected from the group consisting of,
solutions of an acid, a base, a salt, and combinations thereof.
A salt can be dissolved in water, for example, to create a salt
solution. Common free ions in an electrolyte include sodium
(Nat), potassium (K), calcium (Ca2-'), magnesium (Mg2+), chloride
(C1), hydrogen phosphate (HP042-), and hydrogen carbonate (HCO3-
). The concentration (i.e., the total number of free ions
available in the electrolyte) of the electrolyte can be adjusted
to control the rate of dissolution of the first material 51.
According to an embodiment, the concentration of the electrolyte
is selected such that the at least a portion of the first
material 51 dissolves in the desired amount of time. If more
than one electrolyte is used, then the concentration of the
electrolytes is selected such that the first material 51
dissolves in a desired amount of time. The concentration can be
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determined based on at least the specific metals or metal alloys
selected for the first and second materials 51/52 and the
bottomhole temperature of the well. Moreover, because the free
ions in the electrolyte enable the electrochemical reaction to
occur between the first and second materials 51/52 by donating
its free ions, the number of free ions will decrease as the
reaction occurs. At some point, the electrolyte may be depleted
of free ions if there is any remaining first and second
materials 51/52 that have not reacted. If this occurs, the
galvanic corrosion that causes the first material 51 to dissolve
will stop. In this example, it may be necessary to cause or
allow the first and second materials to come in contact with a
second, third, or fourth, and so on, electrolyte(s).
[0046] It may be desirable to delay contact of the first
and second materials 51/52 with the electrolyte. The isolation
device can further include a coating 60 on the outside of the
device. The coating can be a compound, such as a wax,
thermoplastic, sugar, salt, or a conducting polymer and can
include chromates, phosphates, and polyanilines. The coating
can be selected such that the coating dissolves in wellbore
fluids, melts at a certain temperatures, or cracks and falls
away. Upon dissolution or melting, at least the first material
51 of the isolation device is available to come in contact with
the electrolyte. The coating 60 can also be porous to allow the
electrolyte to come in contact with some of the surface of the
first and second materials 51/52.
[0047] It may also be desirable to selectively dissolve
certain portions of the first material 51 at different times or
at different rates. By way of example, it may be desirable to
dissolve the top portion of the isolation device first and then
dissolve the bottom portion at a later time. This can be
accomplished, for example, by introducing a first electrolyte
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into the wellbore to come in contact with the first and second
materials 51/52. There are many operations, such as stimulation
operations involving fracturing or acidizing techniques, or
tertiary recovery operations involving injection techniques, in
which this may be desirable. After the desired operation has
been performed, the bottom of the isolation device can be
contacted by produced formation fluids. The formation fluids
can contain a sufficient concentration of free ions to allow the
dissolution of the remaining first material 51.
[0048] The methods include the step of contacting or
allowing the wellbore isolation device to come in contact with
the electrolyte. The step of contacting can include introducing
the electrolyte into the wellbore 11. The step of allowing can
Include allowing the isolation device to come in contact with a
fluid, such as a reservoir fluid. The methods can Include
contacting or allowing the device to come in contact with two or
more electrolytes. If more than one electrolyte is used, the
free ions in each electrolyte can be the same or different. A
first electrolyte can be, for example, a stronger electrolyte
compared to a second electrolyte. Furthermore, the
concentration of each electrolyte can be the same or different.
It is to be understood that when discussing the concentration of
an electrolyte, it is meant to be a concentration prior to
contact with either the first and second materials 51/52, as the
concentration will decrease during the galvanic corrosion
reaction. Tracers can be used to help determine the necessary
concentration of the electrolyte to help control the rate and
finality of dissolution of the first material 51. For example,
if it is desired that the first material 51 dissolves to a point
to enable the isolation device to be flowed from the wellbore 11
within 5 days and information from a tracer indicates that the
rate of dissolution is too slow, then a more concentrated
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electrolyte can be introduced into the wellbore or allowed to
contact the first and second materials 51/52. By contrast, if
the rate of dissolution is occurring too quickly, then the first
electrolyte can be flushed from the wellbore and a less
concentrated electrolyte can then be introduced into the
wellbore.
[0049] The methods can further include the step of
placing the isolation device in a portion of the wellbore 11,
wherein the step of placing is performed prior to the step of
contacting or allowing the isolation device to come in contact
with the electrolyte. More than one isolation device can also
be placed in multiple portions of the wellbore. The methods can
further include the step of removing all or a portion of the
dissolved first material 51 and/or all or a portion of the
second material 52 or the substance 60, wherein the step of
removing is performed after the step of allowing the at least a
portion of the first material to dissolve. The step of removing
can include flowing the dissolved first material 51 and/or the
second material 52 or substance 60 from the wellbore 11.
According to an embodiment, a sufficient amount of the first
material 51 dissolves such that the isolation device is capable
of being flowed from the wellbore 11. According to this
embodiment, the isolation device should be capable of being
flowed from the wellbore via dissolution of the first material
51, without the use of a milling apparatus, retrieval apparatus,
or other such apparatus commonly used to remove isolation
devices. According to an embodiment, after dissolution of the
first material 51, the second material 52 or the substance 60
has a cross-sectional area less than 0.05 square inches,
preferably less than 0.01 square inches.
[0050] Therefore, the present invention is well adapted
to attain the ends and advantages mentioned as well as those
that are inherent therein. The particular embodiments disclosed
above are illustrative only, as the present invention may be
modified and practiced in different but equivalent manners
apparent to those skilled in the art having the benefit of the
teachings herein. Furthermore, no limitations are intended to
the details of construction or design herein shown, other than
as described in the claims below. It is, therefore, evident that
the particular illustrative embodiments disclosed above may be
altered or modified and all such variations are considered
within the scope and spirit of the present invention. While
compositions and methods are described in terms of "comprising,
" "containing," or "including" various components or steps, the
compositions and methods also can "consist essentially of" or
"consist of" the various components and steps. Whenever a
numerical range with a lower limit and an upper limit is
disclosed, any number and any included range falling within the
range is specifically disclosed. In particular, every range of
values (of the form, "from about a to about b, IT or,
equivalently, "from approximately a to b") disclosed herein is
to be understood to set forth every number and range encompassed
within the broader range of values. Also, the terms in the
claims have their plain, ordinary meaning unless otherwise
explicitly and clearly defined by the patentee. Moreover, the
indefinite articles "a" or "an," as used in the claims, are
defined herein to mean one or more than one of the element that
it introduces. If there is any conflict in the usages of a word
or term in this specification and one or more patent (s) or
other, the definitions that are consistent with this
specification should be adopted.
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