Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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METHODS OF PREPARING SETTABLE FLUIDS COMPRISING PARTICLE-SIZE
DISTRIBUTION-ADJUSTING AGENTS, AND ASSOCIATED METHODS
BACKGROUND
The present invention relates to settable fluid compositions, and more
particularly, to
settable fluid compositions that comprise particle-size distribution-adjusting
agents, and
associated methods.
Hydraulic cement compositions are commonly utilized in subterranean
operations,
particularly in subterranean well completion and remedial operations. For
example, hydraulic
cement compositions are used in primary cementing operations whereby pipe
strings, such as
casings and liners, are cemented in well bores. In performing primary
cementing, hydraulic
cement compositions are pumped into the annular space between the walls of a
well bore and
the exterior surface of the pipe string disposed therein. The cement
composition is permitted
to set in the annular space, thereby forming an annular sheath of hardened
substantially
impermeable cement therein that substantially supports and positions the pipe
string in the
well bore and bonds the exterior surface of the pipe string to the walls of
the well bore.
Hydraulic cement compositions are also used in remedial cementing operations
such as
plugging highly permeable zones or fractures in well bores, plugging cracks
and holes in pipe
strings, and the like.
Set-delayed cement compositions are often utilized at a number of job sites in
circumstances where an operator finds it desirable to prepare a volume of a
cement
composition that remains in a pumpable state for a long period of time (e.g.,
for about two
weeks or more), and that can be selectively activated to set into a hard mass
at a desired time.
For example, in circumstances where large volumes of cement are utilized (such
as in
offshore platform grouting), the equipment required for mixing and pumping the
requisite
large volumes of cement composition may be very expensive, and may be
difficult to
assemble at the desired location. The storage of the requisite amount of dry
cement prior to
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use may be another problem. As another example, the use of a set-delayed
cement
composition may also be desirable in circumstances where a relatively small
volume of
cement composition is used, such as a small construction job, for example, or
a plugging and
squeezing operation performed in the petroleum industry, for instance.
In such circumstances, the cost to transport the cement composition to a job
site, and
to mix and pump it on location may be undesirable relative to the revenue
generated from
performing the cementing operation. A job site may include any location above-
ground or
below-ground for which a cement composition may be suitable as well as the
area
surrounding such locations. Set-delayed cement compositions may be useful in
such
circumstances, as they can be prepared at a convenient location, then
transported to and
stored at a job site until use. At a desired time, the set-delayed cement
composition may be
mixed with a set activating agent; the resulting mixture may then be placed
into a desired
location (e.g., into a subterranean formation) and permitted to set therein.
In some conventional formulations, an excessive amount of set-activating
agents have
been added to the set-delayed cement compositions, thereby "over-activating"
the cement
composition, after which a retarder is then added to the cement composition,
in an attempt to
fine-tune the eventual set time of the cement composition. This can be
difficult to manage.
Additionally, operations involving conventional set-delayed cement
compositions
may encounter a number of other difficulties. For example, the cement
composition may
thicken or gel with time, increasing the cement composition's viscosity, and
thus impairing
its pumpability. Another difficulty is that the activation process maybe quite
complicated, as
exemplified by operations wherein the cement composition's set-time is first
delayed until
shortly before use, after which the cement composition is over-activated and
again retarded.
Another problem that may occur with some conventional set-delayed cement
compositions is that the addition of set-activating agents may cause premature
localized
setting of the cement, e.g., localized regions within the bulk cement slurry
wherein the set-
activating agent becomes concentrated, thereby causing premature setting of a
portion of the
bulk cement. Such premature localized setting of the cement composition may be
likely to
occur, for instance, when the cement composition is inadequately mixed.
Premature
localized setting of the cement composition may lead to pumping problems
(e.g., hardened
cement particles may damage pump impellers), and may also cause problems such
as setting
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of the bulk cement while in storage tanks.
An additional difficulty posed by some conventional set-delayed cement
compositions
is that the performance of the set-activating agents commonly used to
selectively activate the
cement compositions may be unpredictable. This may cause premature setting of
the cement
before placement (e.g., where the activating agent imparts an unexpectedly
strong activating
effect), or delayed setting of the cement after placement (e.g., where the
activating agent
imparts an unexpectedly weak activating effect). Both are usually undesirable.
Moreover, conventional set-delayed cement compositions often may be prepared
in
batch and stored at a central location, rather than being prepared at a job
site shortly before
use. Typically, if there is a need for density modifications to the slurry at
a job site prior to
pumping, addition of dry density modifying additives to achieve a desired
density would be
required, which may be inconvenient and would require additional equipment for
the addition
and the mixing stages. Furthermore, if multiple job sites needing slurries
with different
densities are to be supplied cement slurries from a single slurry stored in a
central location,
current technology requires that density adjustment at each job site be
accomplished by
addition of different levels and types of dry density modifying additives,
which would lower
the benefits of using a single storable slurry for multiple cementing jobs.
Thus, conventional
set-delayed cement compositions may lack the ability or flexibility to tune
the density as
needed from a single set-delayed slurry used in different wells or in a single
wellbore at
different depths or a single well with varying fracture gradients. Thus,
presently the use of
conventional set-delayed cement compositions is limited only to those
subterranean
formations for which the design density of the set-delayed cement composition
matches the
required slurry density at a job site. There is a need to increase the
flexibility of on-the-fly
density modification to enable use of a single cement slurry to service
multiple wells or
multiple depths in a single well.
SUMMARY OF THE INVENTION
The present invention relates to settable fluid compositions, and more
particularly, to
settable fluid compositions that comprise particle-size distribution-adjusting
agents, and
associated methods.
In one embodiment, the present invention provides a method of cementing in a
subterranean formation, comprising: providing a base cement composition
comprising water,
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a hydraulic cement, a set retarder, and a particle-size distribution-adjusting
agent, the base
cement composition having a density; adjusting the density of the base cement
composition
on-the-fly with a density, modifying agent to provide a density-adjusted
cement; activating the
density-adjusted cement composition; placing the density-adjusted cement
composition in a
subterranean formation; and permitting the density-adjusted cement composition
to set in the
subterranean formation.
In one embodiment, the present invention provides a method of customizing the
density of a settable composition for use at a job site comprising: providing
a base cement
composition comprising water, a hydraulic cement, a set retarder, and a
particle-size
distribution-adjusting agent, the base cement composition having a density;
and adjusting the
density of the base cement composition at the job site by variably injecting a
density modifier
into the base cement composition.
The features and advantages of the present invention will be readily apparent
to those
skilled in the art upon a reading of the description of exemplary embodiments,
which follows.
DETAILED DESCRIPTION
The present invention relates to settable fluid compositions, and more
particularly, to
settable fluid compositions that comprise particle-size distribution-adjusting
agents, and
associated methods. The settable fluid compositions of the present invention
are density-
adjusted cement compositions wherein a base cement composition (that comprises
a particle
size distribution agent) is or has been treated with a density modifying
agent. These settlable
fluid compositions can be used in any application requiring a settable fluid.
One of the many
advantages of the present invention is that the base cement composition
comprising particle-
size distribution-adjusting agents may be prepared in batch with a standard
density, and then
customized to obtain a cement composition with a density appropriate for a
particular
application. Moreover, this can be done on-the-fly, which is desirable in many
instances.
In some embodiments, the present invention provides methods of cementing in a
subterranean formation. An example of such embodiments is a method of
cementing in a
subterranean formation, comprising: providing a base cement composition
comprising water,
a hydraulic cement, a set retarder, and a particle-size distribution-adjusting
agent, the base
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cement composition having a density; adjusting the density of the base cement
composition
on-the-fly with a density modifying agent to provide a density-adjusted cement
composition;
activating the density-adjusted cement composition with an activator
composition; placing
the density-adjusted cement composition in a subterranean formation; and
permitting the
density-adjusted cement composition to set in the subterranean formation. A
"base cement
composition", as that term is used herein, refers to a cement composition of
the present
invention prior to some density adjustment.
In some embodiments, the present invention provides methods of customizing the
density of a settable fluid for use at a job site. An example of such a method
comprises:
providing a base cement composition comprising water, a hydraulic cement, a
set retarder,
and a particle-size distribution-adjusting agent, the base cement composition
having a
density; and adjusting the density of the base cement composition at the job
site by variably
injecting a density modifier into the base cement composition.
The base cement compositions used in conjunction with the present invention
generally comprise water, a cement, a set retarder, and a particle-size
distribution-adjusting
agent. Density modifying agents with specific gravities in the range of from
about 0.1 to
about 10 may be added into the fluid stream while carrying out a pumping
operation (e.g. on-
the-fly) to adjust the density of the base cement composition, if desired.
Optionally, other
additives suitable for use in a settable fluid may be added. Density modifying
additives may
be included in aqueous suspensions or other solutions for improved rheology
(e.g., mixability
and pumpability).
Generally, the density-adjusted cement compositions of the present invention
may
have a density in the range of from about 4 to about 25 pounds per gallon.
Higher or lower
densities may be appropriate depending on the application. In certain
exemplary
embodiments, the density-adjusted cement compositions of the present invention
may have a
density in the range of from about 10 to about 25 pounds per gallon.
In certain exemplary embodiments of the present invention, the base cement
composition provided may be formulated as a "densified" base cement
composition (e.g.,
formulated with a significantly higher density than that which is calculated
to be necessary
for its intended use) before the addition of the density modifying agent and
activator
composition. Such a densified base cement composition may be provided in a
variety of
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ways, such as through the addition of high-density particles, or by
formulating the base
cement composition with less water than necessary for its intended use. Among
other
benefits, the employment of a densified base cement composition will
facilitate the addition
of an activator composition in the form of a dilute solution. For example, if
a cement
composition having a 16.4 pounds per gallon density is required, a densified
base cement
composition having a density of, for example, 17 pounds per gallon or higher
may be
provided and activated with an activator composition diluted with sufficient
water to
ultimately provide the desired 16.4 pounds per gallon slurry. Among other
benefits, the
addition of the activator composition in a dilute solution to a densified base
cement
composition may minimize the possibility of developing localized zones having
excessive
activator concentration due to inadequate mixing. Examples of suitable density
modifying
agents that may be added for the purpose of reducing the density of the
provided densified
base cement composition of the present invention include, but are not limited
to, density
reducers such as water, gas, low bulk density inorganic materials containing
entrapped air
such as expanded mica and expanded vermiculite, and microspheres. In some
embodiments,
the density reducer may have specific gravities in the range of from about 0.1
to about 3Ø
In certain exemplary embodiments, where the density of the provided base
cement
compositions is to be reduced, microspheres may be directly added to the
densified base
cement composition. Suitable microspheres that may be utilized in accordance
with the
present invention include hollow, solid, and porous microspheres. The
microspheres may be
present in the settable compositions of the present invention in an amount in
the range of
from about 1% to about 90% by weight of base cement composition. The size of
the
microspheres present in the base cement composition is in the range of from
about 5 microns
to about 1000 microns, and can be present in a variety of sizes or in a
uniform size. The
microspheres may utilize a variety of materials in accordance with the present
invention,
including, but not limited to, glass, soda lime borosilicate glass, silica,
gold, silver, palladium,
platinum, polymethylmethacrylate, poly(L-lactic acid), polyacrylic acid,
latex, alumina,
titania, melamine, dextran, fly ashes as mined or expanded, ceramic, other
polymeric
materials for example, thermoplastics such as polyethylene, polypropylene,
polystyrene, and
elastomers such styrene-butadiene random or block polymers, ethylene-propylene-
dienemonomer (EPDM), and mixtures thereof. In some embodiments of the settable
compositions of the present invention, the microspheres utilized are hollow
microspheres.
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The microspheres may be obtained from any suitable source. Examples of
suitable
microspheres are fly ash hollow beads commercially available from Halliburton
under the
tradename SPHERELITE , hollow synthetic glass beads commercially available
from 3M
Corporation under the tradename SCOTCHLITE , elastomeric hollow beads
comprising
organic fluids under the tradename EXPANCEL , and expandable polystyrene (EPS
grade)
beads available from Huntsman Corporation.
Where the base cement compositions of the present invention are to be foamed
(e.g.,
to reduce the density of the base cement composition, or to improve its
mechanical
properties), the base cement composition may be foamed by direct addition of
the gas into the
base cement composition. For instance, where the base cement composition is
foamed by the
direct injection of gas into the composition, the gas utilized can be air or
any suitable inert
gas, such as nitrogen, or even a mixture of such gases. In certain exemplary
embodiments,
nitrogen is used. Where foaming is achieved by direct injection of gas, the
gas may be present
in the composition in an amount sufficient to foam the composition, generally
in an amount in
the range of from about 0.01% to about 60% by volume of the composition under
downhole
conditions. The base cement composition may also be foamed by gas generated by
a reaction
between the cement slurry and an expanding additive present in the base cement
composition
in particulate form. For example, the composition may be foamed by hydrogen
gas generated
in situ as the product of a reaction between the slurry and fine aluminum
powder present in
the base cement composition. To stabilize the foam, surfactants optionally may
be added to
the base cement composition. Surfactant compositions suitable for use in the
present
invention are described in U.S. Pat. Nos. 6,063,738 and 6,367,550.
In certain exemplary embodiments of the present invention, the base cement
composition provided may be formulated as a "lightened" base cement
composition (e.g.,
formulated with a significantly lower density than that which is calculated to
be necessary for
its intended use) before the addition of the density modifying agent, for
example a densifying
agent, and activator composition. Such a lightened base cement composition may
be provided
in a variety of ways, such as by formulating the base cement composition with
more water
than necessary for its intended use. Suitable density modifying agents for the
purpose of
increasing the density of the provided base cement composition of the present
invention are
densifiers such as iron oxides, manganese oxides, zinc oxide, zirconium oxide,
iron
* Trademark
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carbonate or aqueous solutions of soluble salts such as sodium chloride,
calcium chloride,
cesium chloride, cesium formate and the like. In some embodiments, the
densifiers have
specific gravities in the range of from about 3.5 to about 10. Examples of
suitable densifying
agents are HI-DENSE 3 commercially available from Halliburton, HI-DENSE 4 from
Halliburton, and MicroMaxTM FF from Halliburton. Densifying agents may be
included in
the cement compositions of the present invention in an amount up to 100% by
weight of dry
cement.
The water present in the base cement compositions of the present invention may
be
from any source provided that it does not contain an excess of compounds that
adversely
affect other compounds in the base cement composition. For example, a base
cement
compositions of 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.
The water may be present in an amount sufficient to produce a pumpable slurry.
Generally,
the water may be present in the base cement compositions of the present
invention in an
amount in the range of from about 25% to about 150% by weight of cement
("bwoc") therein.
In certain exemplary embodiments, the water may be present in the base cement
compositions
of the present invention in an amount in the range of from about 40% to about
55% bwoc
therein.
Any cements suitable for use in subterranean applications are suitable for use
in the
present invention. Furthermore, any cements suitable for use in surface
applications, e.g.,
construction cements, are suitable for use in the present invention. In
certain exemplary
embodiments, the improved cement compositions of the present invention
comprise a
hydraulic cement. A variety of hydraulic cements are suitable for use
including those
comprised of calcium, aluminum, silicon, oxygen, and/or sulfur, which set and
harden by
reaction with water. Such hydraulic cements include, but are not limited to,
Portland cements,
pozzolana cements, gypsum cements, high alumina content cements, silica
cements, and high
alkalinity cements.
The base cement compositions of the present invention may further comprise a
set
retarder. Generally, any set retarder may be used with the base cement
compositions of the
present invention. In certain exemplary embodiments, the set retarders used in
the present
invention comprise phosphonic acid derivatives, such as those that are
described in U.S.
* Trademark
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Patent No. 4,676,832. Commercially available examples of a suitable set
retarder include
those available from Solutia Corporation of St. Louis, Missouri under the
tradename
"DEQUEST ." In certain exemplary embodiments of the present invention, a
sodium salt of a
phosphonic acid commercially available from Solutia Corporation of St. Louis,
Missouri
under the tradename "DEQUEST 2006"* is used. A suitable phosphonic acid based
retarder
is commercially available from Halliburton under the tradename "MMCR" ,
micromatrix
cement retarder. Generally, the set retarder is present in the base cement
compositions of the
present invention in an amount in the range of from about 0.1 % to about 5%
bwoc.
The particle-size distribution-adjusting agents suitable for use in the base
cement
compositions of the present invention may be any compound that desirably
affects the
particle-size distribution of the base cement composition by agglomerating
particles therein
such that the base cement composition's rheology remains desirably stable for
a chosen
period of time. Even though dispersants affect the particle size distribution
by
deagglomeration, it is believed that particle size adjusting agents which
effect the particle size
distribution by agglomeration of fine particles are more suitable in the
present invention.
Among other benefits, the presence of the particle-size distribution-adjusting
agent in the base
cement compositions may forestall the onset of gelation for a desired period
of time.
Accordingly, certain embodiments of the base cement compositions of the
present invention
are capable of remaining stable in a slurry state for several weeks or more
before being
activated by the addition of an activator composition. Among other benefits,
the presence of
the particle-size distribution-adjusting agent in the base cement composition
tends to cause
smaller particles in the base cement composition to agglomerate, thereby
tending to narrow
the distribution range of the size of the particles in the base cement
composition.
One example of a suitable particle-size distribution-adjusting agent is a
cationic
polymer. Examples of cationic polymers suitable for use with the present
invention include,
but are not limited to, cationic polyacrylamides, cationic hydroxyethyl
cellulose,
poly(dimethyldiallylammonium chloride), and cationic starches. In an exemplary
embodiment, the cationic polymer used in the base cement compositions of the
present
invention is a cationic starch. A commercially available example of a cationic
starch is
available under the tradename "REDIBOND 5330 A ," from National Starch Co. of
Bridgewater, Connecticut.
* Trademark
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Generally, the particle-size distribution-adjusting agent may be present in
the base
cement compositions in an amount sufficient to adjust the particle-size
distribution of the
base cement composition to a desired range. More particularly, the particle-
size distribution-
adjusting agent may be present in the base cement composition in an amount in
the range of
from about 0.01% to about 4% bwoc. Other amounts maybe suitable in some
applications.
Optionally, the base cement compositions of the present invention may further
comprise a yield stress reducing agent. The use of such yield stress reducing
agents may be
particularly beneficial in certain exemplary embodiments where a densified
base cement
compositions is used. Among other benefits, the use of a yield stress reducing
agent may
facilitate pumping of the densified base cement compositions, inter alia, by
reducing the force
required to move the densified base cement compositions from a static
position. While the
present invention is not limited by any particular theory, it is believed that
the yield stress
reducing agent, inter alia, increases the repulsive force between cement
particles, thereby
preventing them from approaching each other. An example of a suitable yield
stress reducing
agent is a sulfonated melamine formaldehyde condensate that is commercially
available under
the tradename "MELADYNE " from Handy Chemicals, Ltd., of Beachwood, Ohio.
Another
example of a suitable yield stress reducing agent is a sulfite adduct of an
acetone
formaldehyde condensate, commercially available from Halliburton Energy
Services, Inc., of
Duncan, Oklahoma, under the tradename "CFR-3 ." Another example of a suitable
yield
stress reducing agent is a sulfonated naphthalene condensate, commercially
available from
Halliburton Energy Services, Inc., of Duncan, Oklahoma, under the tradename
"CFR-6 ."
One of ordinary skill in the art, with the benefit of this disclosure, will be
able to identify a
suitable yield stress reducing agent for a particular application.
Optionally, the base cement compositions of the present invention may further
comprise an expanding additive. Where an expanding additive in particulate
form is used,
aluminum powder, gypsum blends, and deadburned magnesium oxide are preferred.
Preferred
expanding additives comprising aluminum powder are commercially available
under the
tradenames "GAS-CHEK " and "SUPER CBL*" from Halliburton Energy Services,
Inc., of
Duncan, Oklahoma; a preferred expanding additive comprising a blend containing
gypsum is
*
commercially available under the tradename "MICROBOND " from Halliburton
Energy
Services, Inc., of Duncan, Oklahoma; and preferred expanding additives
comprising
deadburned magnesium oxide are commercially available under the tradenames
* Trademark
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"MicroBond M and "MicroBond HT*" from Halliburton Energy Services, Inc., of
Duncan,
Oklahoma. Such preferred expanding additives are described in commonly-owned
U.S. Pat.
Nos. 4,304,298; 4,340,427; 4,367,093; 4,450,010; and 4,565,578. One of
ordinary skill in the
art, with the benefit of this disclosure, will be able to determine the
appropriate amount of
expanding additive to include in the base cement compositions of the present
invention for a
particular application.
Additional additives may be added to the base cement compositions of the
present
invention as deemed appropriate by one skilled in the art with the benefit of
this disclosure.
Examples of such additives include, inter alia, fluid loss control additives,
salts, vitrified
shale, fly ash, fumed silica, bentonite, fixed-density weighting agents, and
the like. An
example of a suitable fluid loss control additive is commercially available
from Halliburton
Energy Services, Inc., of Duncan, Oklahoma, under the tradename "HALAD 9."
To prepare the base cement compositions of the present invention for use, an
activator
composition of the present invention may be added. The activator compositions
of the present
invention generally comprise a mixture of at least one alkali or alkaline
earth metal
hydroxide, and a trialkanolamine. A wide variety of alkali or alkaline earth
metal hydroxides
are suitable for use in the present invention. In certain exemplary
embodiments, the alkali or
alkaline earth metal hydroxide is selected from the group consisting of sodium
hydroxide and
potassium hydroxide. A wide variety of trialkanolamines are suitable for use
in the present
invention. In certain exemplary embodiments, the trialkanolamine is selected
from the group
consisting of: triethanolamine ("TEA"), tripropanolamine, and
triisopropanolamine. Such
combinations have been found to provide a synergistic effect, resulting in
cement
compositions that achieve desirably high compressive strengths at a faster
rate than would be
achieved had the TEA or alkali metal hydroxide been added individually. In
certain
exemplary embodiments, the alkali metal hydroxide is sodium hydroxide.
Generally, the
activator composition may be added to a base cement composition of the present
invention in
an amount sufficient to enable the cement composition to achieve a desired
compressive
strength and a desired thickening time. More particularly, the activator
composition may be
added to the base cement composition in an amount in the range of from about
0.1% to 5%
bwoc. Generally, the alkali or alkaline earth metal hydroxide may be present
in the activator
composition in an amount in the range of from about 50% to about 99.9% by
weight.
* Trademark
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Generally, the trialkanolamine may be present in the activator composition in
an amount in
the range of from about 0.1 % to about 50% by weight.
The activator composition may be added in a variety of ways. For example, the
activator composition may be added to the base cement composition while the
latter is still in
storage. In certain other exemplary embodiments, the activator composition may
be variably
injected into the base cement composition at the same time that the cement
composition is
injected into the subterranean formation. Among other benefits, the injection
of the activator
composition while the cement composition is injected into the formation may
assist in
minimizing the development within the cement composition of localized regions
having a
high activator concentration.
One example of injecting density modifying agents or other additives on-the-
fly into
flowing cement slurry includes connecting fluid suspensions to the suction
side of the
cementing pumping unit. Another example is to variably inject the suspension
or solution of
a density modifying additive into the flowing cement slurry stream under
pressure using a
separate pump. By variably controlling the rate of injection, the amount of
density modifying
material, and as a consequence the density of the slurry can be precisely
controlled. This is
particularly useful in cases where the formation penetrated by the well is
heterogeneous and
exhibits different fracture gradients and hence slurry density has to be
closely monitored so
that the hydrostatic pressure from the cement slurry does not exceed the
fracture gradient of
the formation resulting in loss circulation. In fact, the method of on-the-fly
density
modification allows for a quick response in cases where cement circulation
loss is
encountered during pumping, at which time the density can be variably adjusted
appropriately, for example by lowering the density of the slurry being pumped
by increasing
the amount of density reducing additive or decreasing the amount of density
increasing
additive being injected, to stop the loss circulation. The ability to control
the cement slurry
density by on-the-fly adjustment of slurry density is also important in
cementing long strings
of vertical casing where significant density variation may be needed from the
bottom of
casing (for example the shoe area) to the top of the cement column. Examples
of mixing
systems suitable for on-the-fly adjustment of slurry density include the RCM
II Mixing
System and RCM Ile Mixing System commercially available from Halliburton.
Using
conventional method of single density slurry could potentially may be
inadequate to prevent
loss of fluids in the deepest part of the cemented zone and sufficient to
exceed the fracture
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gradient near the top of the cement column.
To facilitate a better understanding of the present invention, the following
examples
of some exemplary embodiments are given. In no way should such examples be
read to limit
the scope of the invention.
EXAMPLES
The base cement composition provided in the following examples comprised Class
G
cement (100% bwoc), SSA-1 (35% bwoc), HALAD-9 (0.27% bwoc), CFR-6 (0.196%
bwoc),
FDP-C754-04 (1% bwoc), FDP-C662-02 (0.375% bwoc), and water (5.62 gal/sack);
with
density (16.2 pound per gallon) and yield (1.45 Cuft/sack). The density and
compressive
strength of the density-adjusted cement compositions described in the
following examples
were measured according to API Specification 10B, Twenty-Second Edition,
December,
1997.
EXAMPLE 1
Sample No. 1 comprised the provided base cement composition described above,
to
which 14% bwoc hollow beads were added. Sample No. 2 comprised the provided
base
cement composition, to which 60% bwoc MicromaxTM was added. Sample No. 3
comprised
the provided base cement composition, to which 32% by volume of slurry
nitrogen foamer
were added. The resulting densities of the density-adjusted cement
compositions are set forth
in the table below.
TABLE 1
Additive Density
(pounds per gallon)
Sample No. 1 Hollow beads 10.74
Sample No. 2 MicromaxTM 18.0
Sample No. 3 Foamer and nitrogen 11.0
Example 1 demonstrates, inter alia, that we can successfully vary the density
and
obtain reasonable compressive strength out of the set materials.
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14
EXAMPLE 2
Sample Nos. 1 and 2 described in the previous example were cured at autoclave
under
300 F and 3000 psi for 72 hours. The base slurry sample comprised Class G
cement (100%
bwoc), SSA-1 (35% bwoc), HALAD-9 (0.27% bwoc), CFR-6 (0.196% bwoc), FDP-C754-
04
(1% bwoc), FDP-C662-02 (0.375% bwoc), and water (5.62 gal/sack); with density
(16.2
pound per gallon) and yield (1.45 Cuft/sack). The compressive strengths were
measured
using standard Tinius Olsen equipment (model no. 398) and are set forth in the
table below.
TABLE 2
Density Compressive Strength
(pound per (psi)
gallon)
Base Slurry 16.2 9340
Sample No. 1 10.74 1709
Sample No. 2 18.0 7600
Example 2 demonstrates, inter alia, that the density-adjusted cement
compositions of
the present invention could be prepared from a base cement composition
successfully.
Therefore, the present invention is well adapted to attain the ends and
advantages
mentioned as well as those that are inherent therein. The particular
embodiments disclosed
above are illustrative only, as the present invention may be modified and
practiced in
different but equivalent manners apparent to those skilled in the art having
the benefit of the
teachings herein. Furthermore, no limitations are intended to the details of
construction or
design herein shown, other than as described in the claims below. It is
therefore evident that
the particular illustrative embodiments disclosed above may be altered or
modified and all
such variations are considered within the scope and spirit of the present
invention. 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 as referring to the power set (the set of all subsets) of the
respective range of
values, and set forth every range encompassed within the broader range of
values. Also, the
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terms in the claims have their plain, ordinary meaning unless otherwise
explicitly and clearly
defined by the patentee.
