Note: Descriptions are shown in the official language in which they were submitted.
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RADIATION-INDUCED THICKENING FOR SET-ON-COMMAND SEALANT
COMPOSITIONS AND METHODS OF USE
FIELD OF THE INVENTION
[0001] The
present invention generally relates to hydrocarbon exploration and production
operations, and more particularly to compositions and methods that allow for
greater control
over the thickening of fluids or slurries, such as cement during and after
subterranean
cementing operations.
BACKGROUND OF THE INVENTION
[0002]
Natural resources such as oil and gas located in a subterranean formation can
be
recovered by drilling a wellbore down to the subterranean formation, typically
while
circulating a drilling fluid in the wellbore. After the wellbore is drilled, a
string of pipe, e.g.,
casing, is run in the wellbore. The drilling fluid is then usually circulated
downwardly
through the interior of the pipe and upwardly through the annulus between the
exterior of the
pipe and the walls of the wellbore, although other methodologies are known in
the art.
[0003]
Fluids and slurries such as hydraulic cement compositions are commonly
employed in the drilling, completion and repair of oil and gas wells. For
example, hydraulic
cement compositions are utilized in primary cementing operations whereby
strings of pipe
such as casing or liners are cemented into wellbores. In performing primary
cementing, a
hydraulic cement composition is pumped into the annular space between the
walls of a
wellbore and the exterior surfaces of a pipe string disposed therein. The
cement composition
is allowed to set in the annular space, thus forming an annular sheath of
hardened
substantially impermeable cement. This cement sheath physically supports and
positions the
pipe string relative to the walls of the wellbore and bonds the exterior
surfaces of the pipe
string to the walls of the wellbore. The cement sheath prevents the unwanted
migration of
fluids between zones or formations penetrated by the wellbore. Hydraulic
cement
compositions are also commonly used to plug lost circulation and other
undesirable fluid
inflow and outflow zones in wells, to plug cracks and holes in pipe strings
cemented therein
and to accomplish other required remedial well operations. After the cement is
placed within
the wellbore a period of time is needed for the cement to cure and obtain
enough mechanical
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strength for drilling operations to resume. This down time is often referred
to as "waiting-on-
cement", or WOC. If operations are resumed prior to the cement obtaining
sufficient
mechanical strength, the structural integrity of the cement can be
compromised.
[0004] Two
common pumping methods have been used to place the cement composition
in the annulus. The cement composition may be pumped down the inner diameter
of the
casing and up through the annulus to its desired location. This is referred to
as a
conventional-circulation direction method. Alternately, the cement composition
may be
pumped directly down the annulus so as to displace well fluids present in the
annulus by
pushing them up into the inner diameter of the casing. This is referred to as
a reverse-
circulation direction method. Cement can also be used within the wellbore in
other ways,
such as by placing cement within the wellbore at a desired location and
lowering a casing
string into the cement. The latter method may be used, for example, when there
is not the
ability to circulate well fluids due to fluid loss into a formation penetrated
by the wellbore.
[0005] In
carrying out primary cementing as well as remedial cementing operations in
wellbores, the cement compositions are often subjected to high temperatures,
particularly
when the cementing is carried out in deep subterranean zones. These high
temperatures can
shorten the thickening times of the cement compositions, meaning the setting
of the cement
takes place before the cement is adequately pumped into the annular space.
Therefore, the
use of set retarding additives in the cement compositions has been required.
These additives
extend the setting times of the compositions so that adequate pumping time is
provided in
which to place the cement into the desired location.
[0006]
While a variety of cement set retarding additives have been developed and
utilized, known additives, such as sugars or sugar acids, can produce
unpredictable results.
Hydroxy carboxylic acids, such as tartaric acid, gluconic acid and
glucoheptonic acid are
commonly used in oil well cementing as cement retarders. However, if an excess
of hydroxy
carboxylic acid, or any other retarder, is used it can over-retard the set of
the cement slurry
and thereby causing it to remain fluid for an extended period of time. This
over-retardation
can result in extended waiting time prior to resuming drilling and may allow
gas to invade the
slurry thereby causing unwanted gas migration. The extended waiting time
results in delays
in subsequent drilling or completion activities.
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[0007] In a number of cementing applications, aqueous salt has been
utilized as an
additive in cement compositions. The salt, generally sodium chloride,
functions as a
dispersant in cement slurry, causing the slurry to expand upon setting whereby
the attainment
of a good bond between the wellbore and casing upon setting of the slurry is
enhanced.
However, salt saturated slurries can cause problems to bordering formations,
and in certain
situations salt can be leached out of the cement slurry, which could cause
cement failure.
Also, certain salts, such as calcium salts, can act as accelerating agents,
which reduce the
setting time of the cement composition. However, the presence of a set and
strength
accelerating agent, such as calcium salt, in the cement composition increases
the risk that the
cement composition may thicken or set before placement. Given the complexity
of the
cement chemistry and the large temperature and pressure gradients that can be
present in the
well bore and the difficulty in predicting the exact downhole temperatures
during the
placement and setting of a cement it can be difficult to control the retarding
additive and
accelerating to get the desired setting behavior. Systems generally are over-
engineered to
have very long setting (or thickening) times in order to ensure that the mix
remains fluid until
all of the cementitious material is in place.
[0008] Therefore, there is a need for improved set control methods, which
bring about
predictable fluid and slurry thickening times in subterranean environments
encountered in
wells. In particular, it is desirable to develop methods for rapidly
thickening of such fluids,
such as cement-based systems, whereby the timing of the fluid thickening is
under the control
of engineers in the field.
SUMMARY OF THE INVENTION
[0009] According to one aspect of the present invention, there is provided
a method for
use in a wellbore comprising: placing a composition comprising a polymeric
additive into a
subterranean formation after drilling of the wellbore therein; and subjecting
the composition
to ionizing radiation after placement into the wellbore.
[0010] In another aspect, there is provided a composition for use in
subterranean
formation, comprising a polymeric additive capable of thickening the
composition upon
exposure to ionizing radiation.
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[0011] In a further aspect, the invention provides a method of isolating a
portion of a
wellbore comprising: placing a sealant composition comprising a polymeric
additive into a
subterranean formation after drilling of the wellbore therein; and subjecting
the sealant
composition to ionizing radiation.
[0012] In
a further aspect, the invention provides a method of cementing a wellbore
comprising: placing a cement composition comprising a polymeric additive into
a
subterranean formation after drilling of the wellbore therein; and subjecting
the cement
composition to ionizing radiation after placement into the wellbore.
[0013] In
another aspect, the invention provides a wellbore sealant composition
comprising: a wellbore treatment fluid; and said polymeric additive: wherein
the sealant
composition is capable of thickening upon exposure to ionizing radiation.
[0014] In
a further aspect, there is provided a cement composition for use in a
subterranean formation comprising: hydraulic cement; water; and a polymeric
additive
capable of thickening the cement composition upon exposure to ionizing
radiation.
[0015] The
present invention generally relates to methods of using wellbore fluid and/or
slurry compositions that allow for greater control over the setting of such
compositions in a
wellbore.
[0016]
Disclosed herein is a method of isolating a portion of a wellbore by preparing
a
sealant composition comprising a fluid component and a polymeric additive
component,
placing the sealant composition into a wellbore and subjecting the sealant
composition to
ionizing radiation. The ionizing radiation can cause bonding between polymeric
additive
components and creates a polymer matrix within the sealant composition that
increases the
mechanical strength of the sealant composition. The ionizing radiation can
cause the
destruction of at least a portion of the polymeric additive molecules,
resulting in an increase
in the mechanical strength of the sealant composition.
[0017] The
sealant composition can contain chemical retarders used to inhibit sealant
composition setting and the ionizing radiation can cause the destruction of at
least a portion
of the chemical retarders, thereby reducing fluidity in the sealant
composition and increasing
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the mechanical strength of the sealant composition. The sealant composition
can include one
or more components selected from the group consisting of sealants, resins,
cements, settable
drilling muds, conformance fluids, and combinations thereof The polymeric
additive can be
a water-soluble crosslinkable polymer, or a comb polymer. The sealant
composition can
further include at least one scintillator material capable of emitting
secondary ionizing
radiation, or non-ionizing radiation, upon exposure to the ionizing radiation.
[0018] The
polymeric additive can be a homopolymer, copolymer, terpolymer,
hyperbranched or dendritic polymer. In embodiments the polymeric additive can
be selected
from polyalkyleneoxide, poly(vinyl pyrrolidone), poly(vinyl alcohol),
polyacrylamide,
polyacrylate, poly(vinyl methyl ether), and combinations thereof.
[0019]
Embodiments of the present invention also generally relate to wellbore
cementing
compositions and methods, which allow for greater control over the setting of
cement in a
wellbore.
[0020] An
embodiment of the invention is a method of cementing a wellbore that
includes preparing a cement composition having a polymeric additive, placing
the cement
composition into the wellbore and subjecting the placed cement to ionizing
radiation. The
ionizing radiation can induce crosslinlcing between the polymer chains, thus
creating a
polymer matrix anchored to two or more particles to increase the mechanical
strength of the
composite, sufficient to enable resumption of drilling. The ionizing radiation
can include
neutron radiation, which can be referred to as ionization inducing or
indirectly ionizing. The
polymeric additive can be a monomer, prepolymer, or polymer. In an embodiment
at least a
portion of the polymeric additive contains at least one functional group that
can bond to the
surface of the cement particles and at least a portion of the polymeric
additive contains at
least one functional group that is water-soluble and can form crosslinks when
exposed to the
ionizing radiation.
[0021] The
ionizing radiation can cause the destruction of at least a portion of the
polymeric additive molecules, resulting in an increase in the mechanical
strength of the
slurry.
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[0022] The
slurry can also contain chemical retarders used to inhibit slurry setting and
the
ionizing radiation can cause the destruction of at least a portion of the
chemical retarders,
thereby reducing fluidity in the cement phase and enhancing the increase in
mechanical
strength of the slurry.
[0023] The
slurry can further include bridging agents capable of reacting with the
polymeric additive. The bridging agents can be selected from the group
comprising ethylene
glycol, propylene glycol, diethylene glycol, poly vinyl pyrrolidone, poly
vinyl alcohol, poly
vinyl methyl ether, poly acrylamide, polyols (alcohols containing multiple
hydroxyl
functional groups), polyacrylates and combinations thereof. The slurry can
further include at
least one scintillator material capable of emitting secondary ionizing
radiation, or non-
ionizing radiation, upon exposure to the ionizing radiation.
[0024]
Also disclosed herein is a cement composition comprising cement particles,
water
and a polymeric additive. At least a portion of the polymeric additive can
have at least one
functional group that can bond to the surface of the cement particles and at
least a portion of
the polymeric additive can have at least one functional group that is water-
soluble and can
form crosslinks when exposed to ionizing radiation. The polymeric additive can
be a comb
polymer that can include polycarboxylic acid (PCA) backbones that are adsorbed
onto the
surface of the cement particles and polyalkyleneoxide (PAO) chains that extend
into the
aqueous phase of the cement composition. The polyalkyleneoxide chains can be
capable of
crosslinking when subjected to the ionizing radiation to create a polymer
matrix within the
cement composition to increase the mechanical strength of the composite prior
to normal
hydration setting of the cement. The PAO chains can be polyethyleneoxide
chains. The
cement composition can further include at least one scintillator material
capable of emitting
secondary ionizing, or non-ionizing, radiation upon exposure to the ionizing
radiation.
[0025]
Additionally disclosed herein is a method of cementing a wellbore that
includes
preparing a cement composition containing a comb polymer that has cement
anchoring
groups and pendant ionizable dispersing groups. The method includes placing
the cement
composition into the wellbore, and subjecting the placed cement composition
mixed with the
comb polymer to ionizing radiation, wherein the ionizing radiation creates
erosslinks between
the polymer chains. The cement anchoring groups can be polycarboxylic acid
backbones of
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the comb polymer that are absorbed onto the surface of the cement particles.
The ionizable
dispersing groups can be polyalkyleneoxide chains that extend into the aqueous
phase of the
cement composition that can ionize and bond with adjacent ionized
polyalkyleneoxide chains
to form a polymer matrix within the cement composition to increase the
mechanical strength
of the composite prior to normal hydration setting of the cement. The cement
composition
can further include at least one scintillator material capable of emitting
secondary radiation
upon exposure to the ionizing radiation.
[0026]
Further disclosed herein is a method of cementing a wellbore that includes
placing
a cement composition that includes monomer, prepolymer, or polymer into the
wellbore and
subjecting the placed cement composition to ionizing radiation. The ionizing
radiation
initiates polymerization of the monomers or prepolymers and/or crosslinking
between the
polymer chains of the ionized cement composition resulting from the ionizing
radiation,
wherein the emitting of the ionizing radiation is subject to the control of
technicians in the
field. The cement composition can further include at least one scintillator
material capable of
emitting secondary radiation upon exposure to the ionizing radiation.
[0027] The
present invention also relates to wellbore fluid and/or slurry compositions
that
allow for greater control over the setting of such compositions in a wellbore.
[0028]
Disclosed herein is a sealant composition comprising a wellbore treatment
fluid
and a polymeric additive component that can be placed into a wellbore and
subjected to
ionizing radiation. The polymeric additive can be a polymer that crosslinks
when exposed to
the ionizing radiation. The ionizing radiation can cause bonding between
polymeric additive
components and create a polymer matrix within the sealant composition that
increases the
mechanical strength of the sealant composition. The ionizing radiation can
cause the
destruction of at least a portion of the polymeric additive molecules,
resulting in an increase
in the mechanical strength of the sealant composition.
[0029] An
embodiment of the invention is a cement composition having a polymeric
additive that can be placed into the wellbore and subjected to the ionizing
radiation. The
ionizing radiation can induce polymerization of at least a portion of the
polymeric additive
and can create crosslinks between the polymer chains, thus creating a polymer
matrix
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anchored to two or more particles to increase the mechanical strength of the
composite,
sufficient to enable resumption of drilling. The ionizing radiation can
include neutron
radiation, which can be referred to as ionization inducing or indirectly
ionizing. The
polymeric additive can be a monomer, prepolymer, or polymer. In an embodiment
at least a
portion of the polymeric additive contains at least one functional group that
can bond to the
surface of the cement particles and at least a portion of the polymeric
additive contains at
least one functional group that is water-soluble and can form crosslinks when
exposed to the
ionizing radiation.
[0030]
Additionally disclosed herein is a cement composition containing a comb
polymer
that has cement anchoring groups and pendant ionizable dispersing groups. The
cement
composition can be placed into the wellbore and subjected to ionizing
radiation, wherein the
ionizing radiation creates crosslinks between the polymer chains. The cement
anchoring
groups can be polycarboxylic acid backbones of the comb polymer that are
absorbed onto the
surface of the cement particles. The ionizable dispersing groups can be
polyalkyleneoxide
chains that extend into the aqueous phase of the cement composition that can
ionize and bond
with adjacent ionized polyalkyleneoxide chains to form a polymer matrix within
the cement
composition to increase the mechanical strength of the composite prior to
normal hydration
setting of the cement. The cement composition can further include at least one
scintillator
material capable of emitting secondary ionizing radiation upon exposure to the
ionizing
radiation.
[0031] Further
disclosed herein is a cement composition that includes monomer,
prepolymer, or polymer that can be placed into the wellbore and subjected to
the ionizing
radiation. The ionizing radiation initiates polymerization of the monomers or
prepolymers
and/or crosslinking between the polymer chains of the ionized cement
composition resulting
from the ionizing radiation, wherein the emitting of the ionizing radiation is
subject to the
control of technicians in the field. The cement composition can further
include at least one
scintillator material capable of emitting secondary ionizing radiation upon
exposure to the
ionizing radiation.
[0032] The
preceding has outlined rather broadly the features and technical advantages of
the present invention in order that the detailed description of the invention
may be more fully
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understood. The features and technical advantages of the present invention
will be readily
apparent to those skilled in the art upon a reading of the detailed
description of the
embodiments of the invention, which follows.
BRIEF DESCRIPTION OF DRAWINGS
[0033] Figure 1 illustrates a cross sectional side view of a well bore.
[0034] Figure 2 is a graph of results from a radiation dose study.
[0035] Figure 3 is a graph of Storage Modulus values from a radiation dose
study.
[0036] Figure 4 is a graph of Loss Modulus values from a radiation dose
study.
DETAILED DESCRIPTION
[0037] The present invention relates to generally to wellbore operations
involving fluids
or slurries, and more particularly, to fluids or slurries that contain polymer
or polymer
precursors that can be reacted on command to provide thickening to the fluid
or slurry. The
fluids or slurries referred to herein can be any suitable for wellbore
operations, drilling,
completion, workover or production operations such as cements, drilling muds,
lost
circulation fluids, fracturing fluids, conformance fluids, sealants, resins,
etc.
[0038] In embodiments the fluid or slurry is a cementitious composition
generally
comprising water and a cement component such as hydraulic cement, which can
include
calcium, aluminum, silicon, oxygen, and/or sulfur, which sets and hardens by
reaction with
the water.
[0039] Referring to FIG. 1, a cross sectional side view of an embodiment of
a wellbore 2
is illustrated. Surface casing 4, having a wellhead 6 attached, is installed
in the wellbore 2.
Casing 8 is suspended from the wellhead 6 to the bottom of the wellbore 2. An
annulus 10 is
defined between casing 8 and the wellbore 2. Annulus flow line 12 fluidly
communicates
with annulus 10 through the wellhead 6 and/or surfacing casing 4 with an
annulus valve 14.
Flow line 16 is connected to the wellhead 6 to allow fluid communication with
the inner
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diameter of casing 8 and a casing valve 18. At the lower most end of casing 8
the casing is
open to the wellbore 2 or has circulation ports in the walls of casing 8 (not
shown) to allow
fluid communication between the annulus 10 and the inner diameter of casing 8.
[0040] A
cement composition can be pumped down the =casing 8 and circulated up the
annulus 10 while fluid returns are taken from the annulus 10 out flow line 12,
in a typical
circulation direction. Alternately the cement composition can be pumped into
the annulus 10
from annulus flow line 12 while fluid returns are taken from the inner
diameter of casing 8
through flow line 16. Thus, fluid flows through wellbore 2 in a reverse
circulation direction.
[0041] In
an alternate method a fluid composition, such as a cement slurry, can be
placed
within the wellbore 2 and a sealed or filled tubular, such as casing 8, can be
lowered into the
wellbore 2 such that the fluid composition is displaced into the annulus 10
area, thereby
placing the fluid composition within the annulus 10 without pumping the fluid
composition
into the annulus 10. The above method can be referred to as puddle cementing.
The fluid
composition can be a drilling fluid placed within the wellbore after drilling
operations are
complete.
[0042] Any
cement suitable for use in subterranean applications may be suitable for use
in the present invention. In certain embodiments, the cement compositions used
in the
present invention comprise a hydraulic cement. Examples of hydraulic cements
include but
are not limited to Portland cements (e.g., Classes A, C, G, and H Portland
cements),
pozzolana cements, gypsum cements, phosphate cements, high alumina content
cements,
silica cements, high alkalinity cements, and combinations thereof. Cements
comprising
shale, cement kiln dust or blast furnace slag also may be suitable for use in
the present
invention. In certain embodiments, the shale may comprise vitrified shale; in
certain other
embodiments, the shale may comprise raw shale (e.g., unfired shale), or a
mixture of raw
shale and vitrified shale.
[0043] The
cementitious compositions used in the present invention generally comprise a
base fluid. A wide variety of base fluids may be suitable for use with the
present invention,
including, inter alia, an aqueous-based base fluid, a nonaqueous-based base
fluid, and
mixtures thereof. Where the base fluid is aqueous-based, it may comprise water
that may be
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from any source, provided that the water does not contain an excess of
compounds (e.g.,
dissolved organics, such as tannins) that may adversely affect other compounds
in the cement
compositions. For example, a cement composition useful with the present
invention can
comprise fresh water, salt water (e.g., water containing one or more salts
dissolved therein),
brine (e.g., saturated salt water), or seawater. Where the base fluid is
nonaqueous-based, the
base fluid may comprise any number of organic liquids. Examples of suitable
organic liquids
include, but are not limited to, mineral oils, synthetic oils, esters, and the
like. In certain
embodiments of the present invention wherein primary cementing is performed,
an aqueous-
based base-fluid may be used. The base fluid may be present in an amount
sufficient to form
a pumpable slurry. More particularly, in certain embodiments wherein the base
fluid is
water, the base fluid may be present in the cement compositions used in the
present invention
in an amount in the range of from about 25% to about 150% by weight of cement
("bwoc").
In certain embodiments wherein the base fluid is water, the base fluid may be
present in the
cement compositions in the range of from about 30% to about 75% bwoc. In still
other
embodiments wherein the base fluid is water, the base fluid may be present in
the cement
compositions in the range of from about 40% to about 60% bwoc. In still other
embodiments
wherein the base fluid is water, the base fluid may be present in the cement
compositions in
the range of from about 35% to about 50% bwoc. The cement composition may
include a
sufficient amount of water to form a pumpable cementitious slurry. The water
may be fresh
water or salt water, e.g., an unsaturated aqueous salt solution or a saturated
aqueous salt
solution such as brine or seawater.
[0044] The cementitious compositions used in the present invention can
further comprise
a set retarder. A broad variety of set retarders may be suitable for use in
the cement
compositions used in the present invention. For example, the set retarder may
comprise, inter
alia, phosphonic acid, phosphonic acid derivatives, lignosulfonates, salts,
sugars,
carbohydrate compounds, organic acids, carboxymethylated hydroxyethylated
celluloses,
synthetic co- or ter-polymers comprising sulfonate and carboxylic acid groups,
and/or borate
compounds. In certain embodiments, the set retarders used in the present
invention are
phosphonic acid derivatives, such as those described in U.S. Pat. No.
4,676,832..
Examples of suitable borate compounds include, but are not limited to, sodium
tetraborate and
potassium pentaborate. Examples of _________________________________
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suitable organic acids include, inter alia, gluconic acid and tartaric acid.
Generally, the set
retarder is present in the cement compositions used in the present invention
in an amount
sufficient to delay the setting of the cement composition in a subterranean
formation for a
desired time. More particularly, the set retarder may be present in the cement
compositions
used in the present invention in an amount in the range of from about 0.1% to
about 10%
bwoc. In certain embodiments, the set retarder is present in the cement
compositions used in
the present invention in an amount in the range of from about 0.5% to about 4%
bwoc. In an
embodiment of the present invention the imposition of ionizing radiation
results in the
alteration or destruction of a set retarder additive. As the set retarder is
altered by the
exposure to the ionizing radiation the effect of the set retarder on the
slurry is reduced and the
slurry can set sooner than it would in the absence of the ionizing radiation.
[0045] The
set retarders of the current invention may include a sensitizer-containing
retarder, such as a boron-containing retarder. The sensitizer can be made from
a material
having a strong radiation absorption property. The sensitizer can also be a
scintillator
material. The sensitizer can be any material that increases the capture
efficiency of the
ionizing radiation within the slurry. This sensitizer-containing retarder,
also referred to as a
sensitized retarder, can be a boron-containing retarder, also referred to as a
boronated
retarder, may include a wide variety of set retarders, including the set
retarders disclosed
herein, wherein the selected set retarder, or combination or set retarders,
additionally includes
at least one boron atom. As discussed in the immediately preceding paragraph,
sugars and/or
carbohydrates can be used as a retarder in the setting of a cement
composition. In an
embodiment, the retarder is a sensitized sugar or carbohydrate. In a more
specific
embodiment, the sensitized retarder is boronated glucose. In an even more
specific
embodiment, the boronated glucose is represented by 3-0-(o-Carborany-1-
ylmethyl)-D-
glucose, as presented in U.S. Patent No. 5,466,679, to Soloway et al.
[0046]
Optionally, the cementitious compositions used in the present invention may
comprise a fluid loss control additive. A variety of fluid loss control
additives may be
suitable for use with the present invention, including, inter alia, fibers,
flakes, particulates,
modified guars, latexes, and acrylamide methyl sulfonic acid copolymers such
as those that
are further described in U.S. Pat. Nos. 4,015,991; 4,515,635; 4,555,269;
4,676,31'7;
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4,703,801; 5,339,903; and 6,268,406. Generally, the fluid loss control
additive is present in the cement
compositions used in the present invention in an amount sufficient to provide
a desired
degree of fluid loss control. More particularly, the fluid loss control
additive may be present
in the cement compositions used in the present invention in an amount in the
range of from
about 0.1% to about 10% bwoc. In certain embodiments, the fluid loss control
additive is
present in the cement compositions used in the present invention in an amount
in the range of
from about 0.2% to about 3% bwoc.
[0047] Optionally, the cementitious compositions used in the present
invention also may
include a mechanical-property modifier. Examples of suitable mechanical-
property modifiers
may include, inter alia, gases that are added at the surface (e.g., nitrogen),
gas-generating
additives that may generate a gas in situ at a desired time (e.g., aluminum
powder or
azodicarbonamide), hollow microspheres, elastomers (e.g., elastic particles
comprising a
styrene/divinylbenzene copolymer), high aspect ratio materials (including,
inter alia, fibers),
resilient graphitic materials, vapor/fluid-filled beads, matrix-sorbable
materials having time-
dependent sorption (initiated by, e.g., degradation), mixtures thereof (e.g.,
mixtures of
microspheres and gases), or the like. In certain embodiments of the present
invention, the
optional mechanical-property modifier may include a latex.
[0048] In certain optional embodiments wherein microspheres are added to
the cement
compositions useful with the present invention, the microspheres may be
present in the
cement compositions in an amount in the range of from about 5% to about 75%
bwoc. In
certain embodiments of the present invention, the inclusion of microspheres in
the cement
compositions useful with the present invention may reduce the density of the
cement
composition.
[0049] In certain optional embodiments wherein one or more gas-generating
additives are
used as mechanical property modifiers in the cementitious compositions used in
the present
invention, the one or more gas-generating additives may comprise, inter alia,
aluminum
powder that may generate hydrogen gas in situ, or they may comprise
azodicarbonamide that
may generate nitrogen gas in situ. Other gases and/or gas-generating additives
also may be
suitable for inclusion in the cementitious compositions used in the present
invention. Where
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included, a gas-generating additive may be present in the cement compositions
used in the
present invention in an amount in the range of from about 0.1% to about 5%
bwoc. In certain
embodiments where the gas-generating additive is aluminum powder, the aluminum
powder
may be present in the cement compositions used in the present invention in an
amount in the
range of from about 0.1% to about 1% bwoc. In certain embodiments where the
gas-
generating additive is an azodicarbonamide, the azodicarbonamide may be
present in the
cement compositions used in the present invention in an amount in the range of
from about
0.5% to about 5% bwoc.
[0050]
Optionally, the cementitious compositions used in the present invention also
may
include additional suitable additives, including defoaming agents,
dispersants, density-
reducing additives, surfactants, weighting materials, viscosifiers, fly ash,
silica, free water
control agents, and the like. Any suitable additive may be incorporated within
the cement
compositions used in the present invention.
[0051] In
an embodiment of the present invention, the fluid or slurry includes a monomer
additive. The monomer additive may be a synthetic or natural monomer. Examples
of
synthetic monomers include hydrocarbons such as ethylene, propylene or styrene
monomers.
Other synthetic monomers that can be used include the acrylic monomers such as
acrylic
acid, methyl methacrylate and acrylamide. In an embodiment, the monomer
additive is
present in amounts of from about 0.01% to about 10.0% bwoc, optionally from
about 0.05%
to about 7.5% bwoc, optionally from about 0.25% to about 2.5% bwoc.
[0052] In
an embodiment, the fluid or slurry includes a crosslinkable prepolymer
additive. The prepolymer additive can be a polymer intermediate, or a reactive
low-
molecular-weight macromolecule, or an oligomer, capable of being crosslinked
by further
polymerization. An example of a prepolymer is polyurethane prepolymer that is
commercially available and well known in the art. Prepolymers can include
crosslinkable
functional groups that are attached to an element or compound, such as a
crosslinkable
prepolymer functional group attached to a polymeric material. In an
embodiment, the
prepolymer additive is present in amounts of from about 0.01% to about 10.0%
bwoc,
optionally from about 0.05% to about 7.5% bwoc, optionally from about 0.25% to
about
2.5% bwoc.
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[0053] In an embodiment, the fluid or slurry includes a polymer additive.
Examples of
the polymer additive include a monomer, prepolymer, or polymer. The polym eric
additive
can be a homopolymer, copolymer, terpolyrner, hyperbranched or dendritic
polymer. In
embodiments the polymeric additive can be selected from polyalkyleneoxide,
poly(vinyl
pyrrolidone), poly(vinyl alcohol), polyacrylamide, polyacrylate, poly(vinyl
methyl ether), and
combinations thereof
100541 The polymeric additive can contain at least one functional group
that can bond to
the surface of the cement particles and at least one functional group that is
water-soluble and
can form crosslinks when exposed to the ionizing radiation. The polymeric
additive can be a
comb polymer. In an embodiment, the polymer additive is present in amounts of
from about
0.01% to about 10.0% bwoc, optionally from about 0.05% to about 7.5% bwoc,
optionally
from about 0.25% to about 2.5% bwoc.
[0055] In an embodiment the polymeric additive is a polycarboxylate polymer
superplasticizer (PCS). Superplasticizers can be useful in reducing the amount
of water
required to fluidify a cement mixture, and/or to impart thixotropic
properties. The PCS can
include one or more polymers, copolymers, terpolymers and polymeric additive
solutions
thereof. In an embodiment, the PCS is a comb type polymer. The comb polymer
can have a
polycarboxylic acid backbone and sidechains of polyalkyleneoxide (PAO) chains.
When
added to a slurry the polycarboxylic acid backbones can be absorbed onto a
particle surface.
For example with a cement slurry, the polycarboxylic acid backbones can be
absorbed onto a
cement particle surface, whereas the hydrophilic PAO chains extend into the
aqueous phase.
As the polycarboxylic acid backbones are absorbed onto the cement surface they
are
anchored to the cement surface and can resist forces to disassociate. The PAO
chains extend
from the polycarboxylic acid backbone into the aqueous phase. The PAO chains
can then be
ionized, such as through the imposition of the ionizing radiation, and can
react with ionized
PAO chains extending into the aqueous phase from an adjacent PCS polymer
attached to an
adjacent cement particle. The ionized PAO chains can bond with other ionized
PAO chains
forming a polymer lattice structure throughout the cement slurry. The polymer
lattice
structure can impart rigidity to the cement slurry prior to the setting of the
cement slurry
through the normal hydration setting process.
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100561 In an embodiment the polymeric additive is a polycarboxylate comb
polymer
superplasticizer having a backbone polymeric chain which serves as an
anchoring group and
having pendant non-ionized dispersing groups. The quantity of ionized particle
anchoring
groups and non-ionized dispersing groups and their relative ratio is not
limited within the
present invention. In an embodiment the ratio of the ionized particle
anchoring groups ranges
from about 1:100 to about 100:1 with respect to the non-ionized dispersing
groups.
Alternately the ratio of the ionized particle anchoring groups is about 1:50
to about 50:1,
optionally about 1:1 to about 25:1 with respect to the non-ionized dispersing
groups. The
ionized particle anchoring group can be absorbed onto a particle surface,
whereas the non-
ionized dispersing groups extend into the aqueous phase. The non-ionized
dispersing groups
can then be ionized, such as through the imposition of the ionizing radiation,
and can react
with each other forming a polymer lattice structure throughout the slurry that
thickens the
slurry. Further, polycarboxylate polymer molecules are available with multiple
lengths of
pendant polyalkylene oxide groups, wherein the selection of the correct ratio
can control both
workability retention and rate of crosslinking upon exposure to the ionizing
radiation.
Polycarboxylate polymer superplasticizers (PCS) that are suitable for use in
the current
invention are commercially available from companies such as BASF and W. R.
Grace, Sika,
Nippon Shokubai, Kao Soap, Nippon Oil and Fats, and others.
[0057] In an embodiment the polymeric additive is a polymer selected from a
group
comprising of polyalkyleneoxide (PAO), poly vinyl pyrrolidone (PVP), poly
vinyl alcohol
(PVA), poly vinyl methyl ether (PVME), poly acrylamide (PAAm). The polymeric
chains
can be dispersed within the aqueous phase of the fluid or slurry and can be
ionized, such as
through the imposition of the ionizing radiation, to react with adjacent
ionized polymeric
chains. The linking of adjacent ionized polymeric chains forms a polymer
lattice structure
throughout the fluid that imparts thickening to the aqueous phase. The polymer
lattice
structure can impart thickening to cement slurry prior to the setting of the
cement slurry
through the normal hydration setting process. In alternate embodiments the
polymer lattice
structure can impart thickening to other fluids such as a confomiance fluid
used to seal a
water-bearing zone or to a settable drilling fluid. The polymeric additive can
be a water-
soluble polymer that can be cross-linked upon exposure to the ionizing
radiation. The
polymeric additive can also be a comb polymer with at least two functional
groups, one that
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can be anchored, such as to a cement grain, and another that can be cross-
linked upon
exposure to the ionizing radiation.
[0058] In an embodiment of the present invention the imposition of the
ionizing radiation
results in the alteration or destruction of the polymeric additive. As the
polymeric additive is
altered by the exposure to the ionizing radiation, the resulting altered
polymeric additive can
result in a thickening of the slurry. In embodiments the slurry can thicken
sooner than it
would in the absence of the ionizing radiation.
[0059] The fluid or slurry compositions used in the present invention can
further include
a scintillator material. The scintillator material can act to increase capture
efficiency of the
ionizing radiation and/or can emit radiation upon exposure to the ionizing
radiation. A
scintillator material having the property of fluorescence can emit radiation,
which can be
referred to as secondary radiation, as the result of absorption of radiation
from another
source. For example a scintillator material may emit gamma rays, X-rays, or UV
radiation
upon exposure to neutrons or gamma rays. This secondary radiation can be used
to provide
radiation to promote the degradation of the polymer and/or the release of the
accelerator into
the fluid or slurry. If the secondary radiation includes photons or particles
with the same
wavelength as that of the absorbed radiation, it can be referred to as
resonance radiation.
[0060] A
variety of neutron scintillators are known, a non-limiting list includes
LiF/ZnS:Ag, Li-glass, and LiI:Eu. LiF/ZnS:Ag is shown to produce a very large
neutron
multiplication factor and has been measured at 160,000 photons per neutron
absorbed with
the majority of the emission occurring below about 450 nm. Li-glasses
typically have an
emission maximum below about 400 nm.
[0061] A
variety of gamma ray scintillators are known, a non-limiting list includes
NaLT1+, Bi4Ge3012(GS0), Gd2Si05:Ce3+, ZnS:Ag.
Alkali halides include CsI and Nal.
Typical emission maxima observed for some scintillators are: Cs1 ¨ about
300nm; BaF2 ¨
about 190 to about 305 inn; CaF2:Eu ¨ about 410 run; GSO:Ce ¨ about 420 nm;
YA1:CaTiO3:Ce ¨ about 350 run.
[0062] The
scintillator may be used in a powder or crystal form or with a coating such as
a polymer. Advantages of incorporating scintillators into the fluid or slurry
of the present
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invention can include the local creation of secondary radiation that can
minimize the impact
from the well casing or other environmental influences. Potentially large
multiplication
factors are possible, for example some scintillators will emit more than
10,000 photons for
each absorbed ionizing radiation particle/photon. The photons produced by
scintillators can
be in the X-ray and UV spectral regions that can be highly absorbed by the
polymeric
component of the slurry. Since these photons are created locally by the
scintillation their
emission may increase the efficiency of the polymer encapsulation degradation.
More
photons above the threshold for radical generation from the polymer can
increase the rate of
either cross-linking or polymer degradation via chain scission, or both
simultaneously,
depending on polymer chemistry. This process can speed the thickening of the
cement slurry
and enhance the set-on-command behavior.
[0063] The
scintillator material may be added to the fluid or slurry. The scintillator
material may be incorporated into a polymeric additive or component.
[0064] As
used herein the term polymeric additive or polymer additive can include one or
more of a polymer or one or more of a polymer precursor such as a monomer or
prepolymer
intermediate, or combinations thereof.
[0065] In
an embodiment, the polymeric additive is added to a cement mixture before
water is added to the mixture. In another embodiment, the polymeric additive
is added to a
cement mixture after water has been added to the mixture. In yet another
embodiment, the
polymeric additive is added to water that is to be added to a cement mixture.
In yet another
embodiment, the polymeric additive is added during the mixing of a cement and
water. In
another embodiment, different polymeric additives are added at any of the
separate times as
described above during the preparation of the cement mixture.
[0066] In
an embodiment, once the cementitious composition containing the polymeric
additive is obtained, the mixture is then placed in the wellbore, such as in a
wellbore/casing
annulus. Upon the placement of the cement mixture containing the polymeric
component in
the wellbore, the cement particles would be in intimate contact with one
another and the
absorbed polymer chains of neighboring particles would be intermixed.
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[00671
According to embodiments of the invention, after the intermixed composition is
placed in the wellbore, ionizing radiation is introduced. Ionizing radiation
contains
subatomic particles or electromagnetic waves that are energetic enough to
detach electrons
from atoms or molecules, thereby ionizing them. The occurrence of ionization
depends on
the energy of the intruding individual particles or electromagnetic waves,
which must have
energies above the ionization threshold (i.e., photoelectric effect). In an
embodiment, the
amount of the ionizing radiation introduced into the wellbore is determined by
the amount of
ionizing radiation required to ionize the monomer, prepolymer or polymer
chains of the
polymeric additive. The ionizing radiation can be emitted from or in the form
of charged
particles.
[00681 In
an embodiment, the charged particles include alpha particles, beta particles,
or
gamma particles, or combinations thereof. In an optional embodiment, the
amount of
ionizing radiation required to ionize a polymeric additive component is
between about 1
KiloGray to about 500 KiloGray, optionally between about 1 KiloGray to about
100
KiloGray, optionally between about 4 KiloGray to about 40 KiloGray. The amount
of
ionizing radiation emitted is determined by the level of crosslinking desired
and the type of
polymer added to the cement mixture. The fluid or slurry can further include
at least one
scintillator material capable of emitting secondary radiation upon exposure to
the ionizing
radiation. In embodiments the scintillator material is capable of reducing the
ionizing
radiation required. In an embodiment the scintillator material is capable of
reducing the
ionizing radiation required to less than half that is required without the
scintillator material.
[0069] In
an embodiment, the ionizing radiation is introduced by an ionizing radiation
emitter located at a point within the wellbore. In another embodiment, an
ionizing radiation
emitter located at the surface introduces the ionizing radiation directed
downward into the
wellbore. In another embodiment, a radiation source is lowered into the
wellbore, such as on
a wireline, and the ionizing radiation is emitted. The radiation source can be
shielded to not
emit radiation other than when the shielding is removed. For example a
radiation source can
be shielded at the surface when personnel could otherwise be exposed. Once the
radiation
source is placed in the wellbore and the ionizing radiation can safely be
emitted, the shield
can be removed or opened, such as by an electronically activated signal
transmitted from the
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surface down the wireline to the shield. In an embodiment the radiation
emitter can emit
ionizing radiation as it is lowered down the wellbore and as it is pulled up
the length of the
wellbore. In a further embodiment, two or more radiation emitters are
separately lowered to
two or more depths, such that two or more depths of the wellbore may be
subject to the
ionizing radiation simultaneously.
[0070] In an embodiment, the ionizing radiation is introduced under the
control of a
technician in the field. The technician, engineer, or other on-site employee,
can have the
control over the emission of ionizing radiation by imputing a signal that
causes a release of
ionizing radiation from an emitter. In this embodiment, the ionizing radiation
is released on
demand from the technician in the field. The ionizing radiation can be
released by a control
system having parameters such as timer, flow meter, temperature sensor, or the
like. In
another embodiment, the lowering and/or emitting of the ionizing radiation
source is
triggered by a timing mechanism. In a further embodiment, the lowering and/or
emitting of
the ionizing radiation source is triggered by a flow meter that detects the
amount of the
intermixed composition delivered into the wellbore.
[0071] Upon the introduction of the ionizing radiation, a network of
crosslinks between
polymeric chains can be created. This can be a result of the ionizing
radiation on the
polymeric chain and from the effects of ionizing radiation on other compounds
present such
as water and solvents. Radiation, such as alpha radiation, can also initiate
the dissociation of
molecules, which can be referred to as radiolysis. In one embodiment the
radiolysis of water
can generate hydroxide radicals, which can abstract hydrogen from the
polymeric chains, and
thereby form a polymer radical. The polymer radicals can combine through
intermolecular
and/or intramolecular crosslinking and produce a gelled state. The radiolysis
of other
compounds such as solvents (solvent radiolysis) can generate intermediates
that also can react
with the polymeric chain. Such a network of crosslinks increases the
mechanical strength of
the intermixed composition, for example a cement composite prior to the
typical cement
hydration setting.
[0072] The modification of mechanical strength of the fluid, slurry or
composite depends
upon the level of crosslinking. Low crosslink densities can raise the
viscosity of the
composition to a gum-like consistency and high crosslink densities can cause
the composition
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to become rigid. In one embodiment, the ionizing radiation is introduced such
that a low
level of crosslinking is achieved, followed by another introduction of the
ionizing radiation
such that a higher level of crosslinking is ultimately achieved. The increase
in the
mechanical strength of a cement composite prior to the typical cement
hydration setting can
enable the resumption of activities at an earlier time as compared to having
to wait on the
cement hydration setting.
[0073] The fluid or slurry compositions used in the present invention can
further include
a scintillator material. The scintillator material can act to increase capture
efficiency of the
ionizing radiation and/or can emit radiation upon exposure to ionizing
radiation.
[0074] In an embodiment, wherein the polymer is a polycarboxylate
superplasticizer, the
ionizing radiation can be used to crosslink neighboring polymeric chains in
the aqueous
medium. In this embodiment, particles are separated by the steric hindrance
caused by
anchored polymeric chains, which results in very few crosslinics being
required to create a
continuous crosslinked network resulting in increased strength. This effect
can be further
enhanced by adding agents in the aqueous phase that can increase the density
of potential
reactants in the vicinity of the particles and improve the kinetics of the
radiation-enhanced
setting process of the current invention without otherwise affecting the
properties of the fluid,
slurry or composite such as a cement composition.
[0075] The ionizing radiation of the current invention can destroy
molecules in addition
to causing crosslinking. For example, the destruction of polymeric chains and
the chemical
retarders used to inhibit setting may also serve to reduce fluidity in the
cement phase and thus
enhance the increase in the mechanical strength of the process. Rather than
being
problematic, this result of the invention can serve to improve the performance
of the "set on
command" aspect of the current invention.
[0076] In an embodiment, the cementitious compositions disclosed herein can
also
contain a water-soluble crosslinking agent to facilitate the reaction between
two polymer
chains. In an embodiment, the water-soluble crosslinking agent is a lower
molecular weight
species having good mobility in the aqueous phase and high reactivity towards
the free
radicals that are created by the ionizing radiation of the polymeric additive.
In an
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embodiment, the water-soluble crosslinking agent is a water-soluble polymer.
In another
embodiment, the water-soluble crosslinking agent is a high molecular weight
water-soluble
polysaccharide. In an embodiment, the water-soluble crosslinking agent is
selected from the
group consisting of ethylene glycol, diethylene glycol, propylene glycol,
polyalkyleneoxides
such as polyethyleneoxide, polyvinyl alcohol, and polycarboxylic acids such as
polyacrylic
acid, citric acid, butanetetracarboxylic acid and the like.
[0077] As mentioned above, the ionizing radiation of the current invention
can be under
the control of technicians in the field. In an embodiment the ionizing
radiation emissions can
induce a preliminary increase in mechanical strength of the cement composite
prior to the
hydration setting of the cement. Therefore, the increase in mechanical
strength of the
concrete composition of the invention is under the control of technicians in
the field. Such
control can result in a decrease in the time needed to wait on cement (WOC) in
the drilling
and completion of a wellbore. In an embodiment, the WOC time of the cement
composition
of the invention containing an ionizing radiation reactive polymeric additive
is less than the
WOC time of a substantially similar cement composition not containing the
polymeric
additive. In embodiments the inventive cement composition reduces the WOC time
by at
least an hour, at least two hours, at least five hours, or at least 10 hours
as compared to a
substantially similar cement composition not containing the polymeric
additive.
EXAMPLES
[0078] Example 1
[0079] 800 grams of a Class H cement was mixed with 320 mL of water (to
give a water-
to-cement, w/c, ratio of 0.40) and 0.5% bwoc of a 900,000 MW PEO (polyethylene
oxide) to
form a sluny. The slurry also contained 0.50% bwoc maltrodextrin, a cement set
retarder.
The slurry was mixed for 45 seconds in a Waring blade mixer at high shear. The
slurry was
split into two samples. One sample was exposed to 4.3 Mrads of gamma radiation
exposure
from a Co-60 source while the other was kept as the control. The control
sample, that was
not irradiated was still fluid (yield point measured at 3.5 Pa) whereas the
gamma-irradiated
sample had cross-linked and was totally solid.
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[0080] Example 2
[0081] Several slurries were prepared using a Class H cement, water (to
give a water-to-
cement, w/c, ratio of 0.40) with two different PEOs (100,000 MW and 900,000
MW). Other
components in the slurries were a polycarboxylate ether (dispersant), Diutan
gum (viscosity
modifier) and maltodextrin (retarder). The mix-designs for the slurries are
given in Table 1.
10082] Table 1 - Mix designs for the slurries used in cross-linking
experiments.
Mix Design MIX #1 , MIX #2 MIX #3 MIX #4= #5 MIX #6
Cement ,grams 800 800 800 800- 800 800
water srams . 316,4 316.4 320-, 325- 320 , 320,
Retarder Naltodextrin) .9rams , 4 4 4, 4- 4
4,
_
Dispersant Name ADVA
575 ADVA 575 Melflux 1641 Melflux 1641 Melflux 2651 Melflux 2651
Disperant Total Solids 0.40 0.40 1.00 1.00 1.00 1.00
Dispersant , grams 6. 6 2.4 2.4- 2.4 2,4
VMA (Diutan Gum) grams 3.2 3.2 3,2 3.2 3.2- 3.2
-
-PEO MW 100,000 900,000 100,000 900,000-
100,000 ' 900,000 '
_
-PEO grams 4 4 Li- 4, 4- 4
100831 All
of the slurries were exposed to 4.3 Mrads of gamma radiation from a Co-60
source and were found to cross-link and gel on exposure to gamma radiation non-
radiated
controls were still fluid. The yield points for the controls were determined
using a FANN
35 viscometer and are shown in Table 2. No such measurements were possible on
the gelled
samples.
100841
Table 2 - Yield point measurements of the controls for the cross-linking
experiments.
Mix ID Yield Point (Pa) -
-
1 92
2 94
3 110
4 96
110 _
6 122
,
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[0085] Example 3
10086] 800 grams of a Class H cement was mixed with 320 mL of water
(w/c=0.40) and
0.5% bwoc of a 360,000 MW poly (vinyl pyrrolidone) to form a slurry. The
slurry also
contained 0.50% bwoc maltrodextrin, a cement set retarder. The slurry was
mixed for 45
seconds in a Waring blade mixer at high shear. The slurry was split into two
samples. One
sample was exposed to 4.3 Mrads of gamma radiation exposure from a Co-60
source while
the other was kept as the control. The control sample that was not irradiated
was still fluid,
with a yield point measured at 150 Pa, whereas the gamma-irradiated sample had
cross-linked
and was totally solid.
[0087] Example 4
(0088] 800 grams of a Class H cement was mixed with 320 mL of water
(w/c=0.40) and
0.5% bwoc of a 900,000 MW PEO (polyethylene oxide) to form a slurry. The
slurry also
contained 0.50% bwoc maltrodextrin, a cement set retarder. The slurry was
mixed for 45
seconds in a Waring blade mixer at high shear. The slurries were exposed to
gamma
radiation dose ranging from 0.4 Mrad to 2.5 Mrad. All the slurry samples
exposed to gamma
radiation resulted in gelling of the samples whereas the control samples
remained fluid with a
yield point of 36 Pa.
[0089] Figure 2 illustrates the results of the dose response study in PEO
of differing
radiation exposure. Figures 3 and 4 illustrate the results of the dose
response study in PEO of
differing radiation exposure and the resulting effect on Storage Modulus and
Loss Modulus.
The modulus values increased with radiation dosage.
[0090] Example 5
[0091] Aqueous solutions of PEO and Polycarboxylates were irradiated with
4.3 Mrads
of gamma-radiation. The observations were as shown in Table 3.
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[0092] Table 3
Sample Sample Effect of Radiation
ID
1 2% solution of 100,000 MW PEO Cross-links
2 5% solution of 100,000 MW PEO Cross-links
3 2% solution of 900,000 MW PEO Cross-links
4 5% solution of 900,000 MW PEO Cross-links
5 10% solution of ADVA 575 No crosslinlcing
6 10% solution of Melflux 1641 No crosslinking
7 10% solution of Melflux 2651 No crosslinlcing
[0093] The fluid or slurry compositions used in the present invention can
further include
a sensitizer material. The sensitizer can be made from a material having a
strong radiation
absorption property. The sensitizer can also be a scintillator material. The
sensitizer can be
any material that increases the capture efficiency of the ionizing radiation
within the slurry.
[0094] Various elements can be utilized as a sensitized material. In
general, elements
having a greater absorption cross-section than the wellbore treatment fluid
composition can
be used to increase the capture efficiency of the ionizing radiation within
the composition.
Many wellbore treatment fluid compositions can comprise calcium, which has an
absorption
cross-section for 2200 m/s neutrons of about 0.43 barn. A non-limiting listing
of elements
having an absorption cross-section for 2200 m/s neutrons of 10 barn or greater
is shown
below in Table 4. A barn is defined as being 10-28 2,
m and corresponds to approximately the
cross sectional area of a uranium nucleus.
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26
10095] Table 4 Absorption cross section for 2200 m/s neutrons
Absorption cross section for 2200 m/s neutrons
Element
(barn)
Li 71
767
Cl 34
Sc 28
Mn 13
Co 37
Se 12
Kr 25
Tc 20
Rh 145
Ag 63
Cd 2,520
In 194
Xe 24
Pr 12
Nd 51
Pm 168
Sm 5,922
Eu 4,530
Gd 49,700
Tb 23
Dy 994
Ho 65
Er 159
Tin 100
Yb 35
Lu 74
Hf 104
Ta 21
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27
18
Re 90
Os 16
Ir 425
Pt 10
Au 99
Hg 372
[0096] As used herein, "comb polymers" means those polymers having a main
chain
backbone and linear side chain pendant groups.
[0097] As used herein, "polycarboxylate comb superplasticizers" means those
cement
dispersing polymers and copolymers having a polycarboxylate backbone and
polyalkylene
oxide groups pendant therefrom, such as polyethylene oxide, polypropylene
oxide, etc., and
mixtures of the same. Polyrners of these general types can be prepared by any
suitable
manner such as, for example, by copolymerizing unsaturated
(alkoxy)polyalkylene glycol
mono (meth)acrylic acid or ester type monomers with (meth) acrylic acid type
monomers
such as are described in U.S. Pat. No. 6,139,623 .
[0098] The term "cementitious composition" as may be used herein includes
pastes (or
slurries), mortars, and grouts, such as oil well cementing grouts, shotcrete,
and concrete
compositions comprising a hydraulic cement binder. The terms "paste", "mortar"
and
"concrete" are terms of art: pastes are mixtures composed of a hydratable (or
hydraulic)
cement binder (usually, but not exclusively, Portland cement, Masonry cement,
Mortar
cement, and/or gypsum, and may also include limestone, hydrated line, fly ash,
granulated
blast furnace slag, and silica fume or other materials commonly included in
such cements)
and water; "mortars" are pastes additionally including fine aggregate (e.g.,
sand), and
"concretes" are mortars additionally including coarse aggregate (e.g., crushed
rock or gravel).
The cement compositions described in this invention are formed by mixing
required amounts
of certain materials, e.g., a hydraulic cement, water, and fine and/or coarse
aggregate, as may
be required for making a particular cementitious composition.
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[0099] The
term "ionizing radiation" as may be used herein can be referred to as
ionization inducing or indirectly ionizing, that are able to detach electrons
from atoms or
molecules, and can include alpha rays, beta rays, gamma rays, proton rays,
neutron radiation,
UV and X-rays.
[00100] The term "polymeric additive" as may be used herein can include one or
more of a
polymer or polymer precursor, such as a monomer or a prepolymer intermediate,
that is
susceptible to ionizing radiation.
[001011 The term "set" as used herein refers to an increase in mechanical
strength of a
fluid or slurry sufficient to perform a desired result, such as to restrict
movement of an item
or impede fluid flow or pressure transfer through a fluid. A cement may be
referred to as set
when it can restrict the movement of a pipe, or impede fluid flow or pressure
transfer,
regardless of whether the cement has cured to a fully solid composition. A
fluid or slurry can
be referred to as set when it has thickened to a sufficient level that it
achieves the desired
result, such as the isolation of a particular zone or the restriction of fluid
flow or pressure
transfer, regardless of whether it has reached its final consistency.
[00102] Depending on the context, all references herein to the "invention" may
in some
cases refer to certain specific embodiments only. In other cases it may refer
to subject matter
recited in one or more, but not necessarily all, of the claims. While the
foregoing is directed
to embodiments, versions and examples of the present invention, which are
included to
enable a person of ordinary skill in the art to make and use the inventions
when the
information in this patent is combined with available information and
technology, the
inventions are not limited to only these particular embodiments, versions and
examples.
Other and further embodiments, versions and examples of the invention may be
devised
without departing from the basic scope thereof and the scope thereof is
determined by the
claims that follow.
[00103] While compositions and methods are described in terms of "comprising,"
"containing," or "including" various components or steps, the compositions and
methods can
also "consist essentially of' or "consist of' the various components and
steps. All numbers
and ranges disclosed above may vary by some amount. Whenever a numerical range
with a
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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," or,
equivalently, "from
approximately a-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.
