Note: Descriptions are shown in the official language in which they were submitted.
ISOLATION DEVICE CONTAINING A DISSOLVABLE ANODE AND ELECTROLYTIC
COMPOUND
Technical Field
[0001] Isolation devices can be used to restrict fluid
flow between intervals of a wellbore. An isolation device can
be removed from a wellbore after use. Methods of removing an
isolation device using galvanic corrosion are provided.
Summary
[0001a] In one aspect, there is provided a method of
removing a wellbore isolation device comprising: placing the
wellbore isolation device into the wellbore, wherein the
isolation device comprises: (A) a first material, wherein the
first material: (i) is a metal or a metal alloy; and (ii)
partially dissolves when an electrically conductive path exists
between the first material and a second material and at least a
portion of the first and second materials are in contact with an
electrolyte; and (B) an electrolytic compound, wherein the
electrolytic compound dissolves in a fluid located within the
wellbore to form free ions that are electrically conductive,
wherein the second material coats the electrolytic compound, and
wherein the first material coats the second material; and
allowing at least a portion of the first material to dissolve.
[0001b] In another aspect, there is provided a wellbore
isolation device comprising: a first material, wherein the first
material: (A) is a metal or a metal alloy; and (B) partially
dissolves when an electrically conductive path exists between
the first material and a second material and at least a portion
of the first and second materials are in contact with an
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electrolyte; and an electrolytic compound, wherein the
electrolytic compound dissolves in a fluid located within the
wellbore to form free ions that are electrically conductive,
wherein the second material coats the electrolytic compound, and
wherein the first material coats the second material
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 is a schematic illustration of a well
system containing more than one isolation device.
[0004] Figs. 2 - 4 are schematic illustrations of an
isolation device according to different embodiments.
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.
[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, layers, etc., as the case may be, and does not
indicate any particular orientation or sequence. Furthermore,
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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 the wellbore 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
surrounding the wellbore. As used herein, a "well" also
includes the near-wellbore region. The near-wellbore region is
generally considered the region within approximately 100 feet
radially of the wellbore. As used herein, 'into a well" means
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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. An isolation device can be used for zonal
Isolation and 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 into the zones
located below the isolation device and isolates the zone of
Interest. As used herein, the relative term "below" means at a
location further away from a wellhead and "above" means at a
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location closer to the wellhead compared to a reference object.
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, a plug, a bridge plug, a wiper plug, and a
packer. 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, for example, via a ball and seat by
dropping 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 zones downstream of the ball and seat.
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 zone. Generally, the inner
diameter (1.D.) of the ball seats are different for each zone.
For example, the I.D. of the ball seats sequentially decrease 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
zone that is the farthest downstream; that zone is treated; a
slightly larger ball is then dropped into another zone that is
located upstream of the first zone; that zone is then treated;
and the process continues in this fashion - moving 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
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caused to block fluid flow into downstream zones. 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 zones.
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
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] Galvanic corrosion can be used to dissolve
materials making up an isolation device. Galvanic corrosion
occurs when two different metals or metal alloys are in
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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
example of a metal and metal alloy is bronze, comprising the
metallic elements copper and tin.
[0017] 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
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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.
[0018] 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
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.
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[0019] 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
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
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[0020] 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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[0021] 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. 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.
[0022] In order for galvanic corrosion to occur, the
anode and cathode metals must be in contact with an 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.
An 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
(HCC13-).
[0023] The number of free ions in the electrolyte will
decrease as the galvanic reaction occurs because the free ions
in the electrolyte enable the electrochemical reaction to occur
between the metals by donating its free ions. At some point,
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the electrolyte may be depleted of free ions if there are any
remaining anode and cathode metals that have not reacted. If
this occurs, the galvanic corrosion that causes the anode to
dissolve will stop. Moreover, an electrolyte may not be present
in the wellbore to enable the galvanic reaction to proceed.
Examples of this can include water- or steam-injection wells in
which freshwater is needed to prevent salt or scale buildup
within the pores of the subterranean formation.
[0024] Thus, there is a need for being able to control
the rate of a galvanic reaction using the electrolyte. There is
also a need for efficiently providing an electrolyte in wellbore
operations that utilize a non-electrolyte fluid.
[0025] According to an embodiment, a wellbore isolation
device comprises: a first material, wherein the first material:
(A) is a metal or a metal alloy; and (B) partially dissolves
when an electrically conductive path exists between the first
material and a second material and at least a portion of the
first and second materials are in contact with an electrolyte;
and an electrolytic compound, wherein the electrolytic compound
dissolves in a fluid located within the wellbore to form free
ions that are electrically conductive.
[0026] According to another embodiment, a method of
removing a wellbore isolation device comprises: placing the
wellbore isolation device into the wellbore; and allowing at
least a portion of the first material to dissolve.
[0027] 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 apparatus and method embodiments.
[0028] 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.
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The subterranean formation 20 can be a portion of a reservoir or
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 first section of tubing string 15 can be
Installed in the wellbore 11. A second section of tubing string
16 (as well as multiple other sections of tubing string, not
shown) can be installed in the wellbore 11. The well system 10
can comprise at least a first zone 13 and a second zone 14. The
well system 10 can also Include more than two zones, for
example, the well system 10 can further include a third zone, a
fourth zone, and so on. 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 isolate each zone of the wellbore 11.
The isolation device can be the packers 18. The packers 18 can
be used to prevent fluid flow between one or more zones (e.g.,
between the first zone 13 and the second zone 14) via an annulus
19. The tubing string 15/16 can also include one or more ports
17. One or more ports 17 can be located in each section of the
tubing string. Moreover, not every section of the tubing string
needs to include one or more ports 17. For example, the first
section of tubing string 15 can include one or more ports 17,
while the second section of tubing string 16 does not contain a
port. In this manner, fluid flow into the annulus 19 for a
particular section can be selected based on the specific oil or
gas operation.
[0029] 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
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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.
[0030] According to an embodiment, the isolation device
is capable of restricting or preventing fluid flow between a
first zone 13 and a second zone 14. The first zone 13 can be
located upstream or downstream of the second zone 14. In this
manner, depending on the oil or gas operation, fluid is
restricted or prevented from flowing downstream or upstream into
the second zone 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, and a packer.
[0031] Referring to Figs. 2 - 4, the isolation device
comprises at least a first material 51, wherein the first
material is capable of at least partially dissolving 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 of the metal alloy can be selected from the group
consisting of, lithium, sodium, potassium, rubidium, cesium,
beryllium, magnesium, calcium, strontium, barium, radium,
aluminum, gallium, indium, tin, thallium, lead, bismuth,
scandium, titanium, vanadium, chromium, manganese, iron, cobalt,
nickel, copper, zinc, yttrium, zirconium, niobium, molybdenum,
ruthenium, rhodium, palladium, silver, cadmium, lanthanum,
hafnium, tantalum, tungsten, rhenium, osmium, iridium, platinum,
gold, graphite, and combinations thereof. Preferably, the metal
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or metal of the metal alloy is selected from the group
consisting of beryllium, tin, iron, nickel, copper, zinc, and
combinations thereof. According to an embodiment, the metal is
neither radioactive, unstable, nor theoretical.
[0032] 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 nickel and the
second material 52 can be gold. 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 second material 52 has a greater anodic index than the first
material 51. Stated another way, the second material 52 is
listed higher on a galvanic series than the first material 51.
According to another embodiment, the second material 52 is more
noble than the first material 51. In this manner, the first
material 51 acts as an anode and the second material 52 acts as
a cathode. Moreover, in this manner, the first material 51
(acting as the anode) at least partially dissolves when in
electrical connectivity with the second material 52 and when the
first and second materials are in contact with an electrolyte.
[0033] The methods include the step of allowing at least
a portion of the first material to dissolve. 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. 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
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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.
[0034] 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.
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[0035] As can be seen in Fig. 1, the first section of
tubing string 15 can be located within the first zone 13 and the
second section of tubing string 16 can be located within the
second zone 14. The wellbore Isolation device can be a ball, a
plug, a bridge plug, a wiper plug, or a packer. The wellbore
isolation device can restrict fluid flow past the device. The
wellbore isolation device may be a free falling device, may be a
pumped-down device, or it may be tethered to the surface. 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. When the first section of tubing string 15 is
located below the second section of tubing string 16, then 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 placed into the first section of tubing string 15. The first
ball 31 can have a smaller diameter than a second ball 32. The
first ball 31 can engage a first seat 41. Fluid can now be
temporarily restricted or prevented from flowing into any zones
located downstream of the first zone 13. In the event it is
desirable to temporarily restrict or prevent fluid flow into any
zones located downstream of the second zone 14, the second ball
32 can be placed into second section of tubing string 16 and
will be prevented from falling into the first section of tubing
string 15 via the second seat 42 or because the second ball 32
has a larger outer diameter (0.D.) than the I.D. of the first
seat 41. 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 50 during placement. This engagement
with the sliding sleeve 50 can cause the sliding sleeve to move;
thus, opening a port 17 located adjacent to the seat. The port
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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 zone. As such, a fluid can be
produced from the subterranean formation 20 or injected into the
formation.
[0036] Figs. 2 - 4 depict the Isolation device according
to certain embodiments. As can be seen in the drawings, the
Isolation device can be a ball 30. As depicted in Fig. 2, the
Isolation device can comprise the first material 51, the second
material 52, and the electrolytic compound 53. According to
this embodiment, the first and second materials 51/52 and the
electrolytic compound 53 can be nuggets of material or a powder.
Although this embodiment depicted in Fig. 2 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. The first
material 51, the second material 52, and the electrolytic
compound 53 can be bonded together in a variety of ways,
including but not limited to powder metallurgy, in order to form
the isolation device. At least a portion of the outside of the
nuggets of the first material 5]. can be in direct contact with
at least a portion of the outside of the nuggets of the second
material 52. By contrast, the outside of the nuggets of the
first material 51 do not have to be in direct contact with the
outside of the nuggets of the second material 52. For example,
the electrolytic compound 53 can be an intermediary substance
located between the outsides of the nuggets of the first and
second materials 51/52. In order for galvanic corrosion to
occur (and hence dissolution of at least a portion of the first
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material 51), both, the first and second materials 51/52 need to
be capable of being contacted by the electrolyte. If the
wellbore contains a fluid that is an electrolyte, then
preferably, at least a portion of one or more nugget 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 wellbore fluid.
In the event the wellbore fluid is not an electrolyte, then
preferably, the electrolytic compound 53 also forms the outside
of the isolation device. In this manner, the electrolytic
compound 53 can dissolve in a fluid located within the wellbore
to form free ions (e.g., an electrolyte).
[0037] The
size, shape and placement of the nuggets of
the first and second materials 51/52 can 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
nugget, 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 nugget of the first material 51 can be the same or
different, the cross-sectional area of each nugget of the second
material 52 can be the same or different, and the cross-
sectional area of the nuggets of the first material 51 and the
nuggets of the second material 52 can be the same or different.
Additionally, the cross-sectional area of the nuggets forming
the outer portion of the isolation device and the nuggets
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
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device, then the cross-sectional area of the individual nuggets
comprising the outer portion can be smaller compared to the
cross-sectional area of the nuggets comprising the inner
portion. The shape of the nuggets of the first and second
materials 51/52 can also be adjusted to allow for a greater or
smaller cross-sectional area. The proximity of the first
material 51 to the second material 52 can also be adjusted to
control the rate of dissolution of the first material 51.
According to an embodiment, the first and second materials 51/52
are within 2 inches, preferably less than 1 inch of each other.
[0038] Figs. 3 and 4 depict the isolation device
according to other embodiments. As can be seen in Fig. 3, the
Isolation device, such as a ball 30, can be made of the first
material 51. The electrolytic compound 53 can be a layer that
coats the outside of the first material 51. There can also be
multiple layers of the first material 51 and the electrolytic
compound 53, wherein the first material and the electrolytic
compound can be the same or different for each layer. As can be
seen in Fig. 4, the second material 52 can coat the electrolytic
compound 53 and the first material 51 can coat the second
material 52. This embodiment may be useful when the wellbore
fluid is an electrolyte. In this manner, the first material 51
and second material 52 can start to dissolve, thereby exposing
the electrolytic compound 53. The electrolytic compound 53 can
then dissolve in the wellbore fluid to increase the
concentration of free ions available in the electrolyte fluid.
At least a portion of a seat 40 can comprise the second material
52. According to this embodiment, at least a portion of the
first material 51 of the ball 30 can come in contact with at
least a portion of the second material 52 of the seat 40.
Although not shown in the drawings, according to another
embodiment, at least a portion of a tubing string can comprise
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the second material 52. This embodiment can be useful for a
ball, bridge plug, packer, etc. isolation device. Preferably,
the portion of the tubing string that comprises the second
material 52 is located adjacent to the isolation device
comprising the first material 51. More preferably, the portion
of the tubing string that comprises the second material 52 is
located adjacent to the isolation device comprising the first
material 51 after the isolation device is situated in the
desired location within the wellbore 11. The portion of the
tubing string that comprises the second material 52 is
preferably located within a maximum distance to the isolation
device comprising the first material 51. The maximum distance
can be a distance such that an electrically conductive path
exists between the first material 51 and the second material 52.
In this manner, once the isolation device is situated within the
wellbore 11 and the first and second materials 51/52 are in
contact with the electrolyte, at least a portion of the first
material 51 is capable of dissolving due to the electrical
connectivity between the materials.
[0039] According to an embodiment, at least the first
material 51 is capable of withstanding a specific pressure
differential (for example, the isolation device depicted in Fig.
3). 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 first
material 51 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
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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,
both, the first and second materials 51/52 are capable of
withstanding a specific pressure differential (for example, the
isolation device depicted in Fig. 2).
[0040] 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
material 51 includes one or more tracers (not shown). The
tracer(s) can be, without limitation, radioactive, chemical,
electronic, or acoustic. The second material 52 and/or the
electrolytic compound 53 can also Include one or more tracers.
As depicted in Fig. 2, each nugget of the first material 51 can
Include a tracer. At least one tracer can be located near the
outside of the isolation device and/or at least one tracer can
be located near the inside of the device. Moreover, at least
one tracer can be located in multiple layers of the device. 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.
[0041] The electrolytic compound 53 dissolves in a fluid
located within the wellbore (i.e., the wellbore fluid) to form
free ions that are electrically conductive. Prior to contact
with the wellbore fluid, the electrolytic compound 53 will be
inert and will not degrade the isolation device. According to
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an embodiment, the wellbore fluid is an electrolyte and the free
ions formed increase the concentration of the free ions in the
electrolyte. This embodiment is useful when the wellbore fluid
is a brine or seawater or otherwise already contains free ions
available to initiate the galvanic reaction between the first
material 51 and the second material 52. According to this
embodiment, the concentration of free ions available in the
electrolyte wellbore fluid can be reduced to such a low
concentration that the galvanic reaction stops or the reaction
slows to an undesirable rate. Therefore, the free ions formed
from the dissolution of the electrolytic compound 53 in the
wellbore fluid increases the concentration of free ions
available to either maintain the galvanic reaction or increase
the reaction rate.
[0042] According to another embodiment, the wellbore
fluid does not contain a sufficient amount of free ions to
initiate the galvanic reaction between the first material 51 and
the second material 52. According to this embodiment, the
electrolytic compound 53 dissolves in the wellbore fluid to form
an electrolyte. The free ions formed are now available to
initiate the galvanic reaction. Subsequent dissolution of the
electrolytic compound 53 can maintain the galvanic reaction or
increase the rate of the reaction.
[0043] The electrolytic compound 53 is preferably
soluble in the fluid located within the wellbore. The wellbore
fluid can comprise, without limitation, freshwater, brackish
water, saltwater, and any combination thereof. As stated above,
the wellbore fluid can contain free ions in which the fluid is
an electrolyte or it may not contain a sufficient amount of free
ions to function as an electrolyte. According to an embodiment,
the electrolytic compound 53 is a water-soluble acid, base, or
salt. The water-soluble salt can be a neutral salt, an acid
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salt, a basic salt, or an alkali salt. As used herein, an "acid
salt" is a compound formed from the partial neutralization of a
diprotic or polyprotic acid, and a 'basic salt" and 'alkali
salt" are compounds formed from the neutralization of a strong
base and a weak acid, wherein the base of the alkali salt is an
alkali metal or alkali earth metal. Preferably, the water-
soluble salt is selected from the group consisting of sodium
chloride, sodium bromide, sodium acetate, sodium sulfide, sodium
hydrosulfide, sodium bisulfate, monosodium phosphate, disodium
phosphate, sodium bicarbonate, sodium percarbonate, calcium
chloride, calcium bromide, calcium bicarbonate, potassium
chloride, potassium bromide, potassium nitrate, potassium
metabisulphite, magnesium chloride, cesium formate, cesium
acetate, alkali metasilicate, and any combination thereof.
Common free ions in an electrolyte or formed from dissolution
include, but are not limited to, sodium (Na-'), potassium (K-'),
calcium (Ca2-'), magnesium (Me), chloride (C1-), hydrogen
phosphate (HP042-), and hydrogen carbonate (HCO3-). An acid salt,
basic salt, or alkali salt may be useful when it is desirable to
buffer the pH of the wellbore fluid. For example, during
galvanic corrosion, the wellbore fluid may become undesirably
acidic or basic. The electrolytic compound, once dissolved in
the wellbore fluid, can then bring the pH to a desirable value.
[0044] Another factor that can affect the rate of
dissolution of the first material 51 is the concentration of
free ions and the temperature of the electrolyte. Generally,
the higher the concentration of the free ions, the faster the
rate of dissolution of the first material 51, and the lower the
concentration of the free ions, the slower the rate of
dissolution. Moreover, the higher the temperature of the
electrolytic fluid, the faster the rate of dissolution of the
first material 51, and the lower the temperature of the
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electrolytic fluid, 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 electrolytic compound 53 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.
[0045] It may be desirable to control the rate of
dissolution of the first material 51 due to galvanic corrosion
using the electrolytic compound 53. According to an embodiment,
the concentration of the electrolytic compound 53 within the
Isolation device 30 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 type of electrolytic compound 53 is
used, then the exact electrolytic compound and the concentration
of each electrolytic compound are selected such that the first
material 51 dissolves in a desired amount of time. The
concentration can be 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. The
location of the electrolytic compound 53 within the isolation
device and concentration at each location can be adjusted to
control the rate of dissolution of the first material 51. By
way of example, with reference to Fig. 2, the nuggets of the
electrolytic compound 53 located closer to the perimeter of the
Isolation device 30 can be smaller (or larger depending on the
desired initial reaction rate) than the nuggets of electrolytic
compound 53 located closer to the center of the isolation device
30. In this manner, as the first material 51 dissolved due to
galvanic corrosion, different concentrations of electrolytic
compound are exposed to provide the desired reaction rate and
dissolution of the first material in the desired amount of time.
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Another example, with reference to Fig. 3, is the thickness of
the electrolytic compound 53 layer(s) can be selected to provide
the desired concentration of free ions once dissolved in the
wellbore fluid. 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.
[0046] The methods include placing the isolation device
into the wellbore 11. 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, 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
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 5]. and/or the second material
52 has a cross-sectional area less than 0.05 square inches,
preferably less than 0.01 square inches.
[0047] 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
26
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," 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
documents that may be herein referred to, the definitions that
are consistent with this specification should be adopted.
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