CEMENT SET ACTIVATORS FOR SET-DELAYED CEMENT
COMPOSITIONS AND ASSOCIATED METHODS
AC GR
[0001] "The p invention relates to subterranean cementing operations and, more
particularly in certain embodiments, to set-delayed cement compositions and methods of
using set-delayed cement compositions in subterranean -fo rmations
[0002] Cement compositions may be used in variety of subterranean operations.
For example, in subterranean well construction, a p pe string (e.g., casing, liners, expandable
iubuiars, etc.) may be run into a well bore and cemented in place. The process of cementing
the pipe string in place is commonl referred to as "primary cementing." In a typical
primary cementing method, a cement composition may be pumped into an annulus between
the walls of the well bore and the exterior surface of the pipe siring disposed therein. The
cement composition may set in the annular space, thereby forming an annular sheath of
hardened, substantially impermeable cement (i.e., a cement sheath) thai may support and
position the pipe string in the wel bore and may bond th exterior surface of the pipe string
to the subterranean formation. Among other things, the cement sheath surrounding the pipe
string functions to prevent the migration of fluids in the annulus, as well as protecting the
pipe string from conrosion. Cement compositions also ma be used in remedial cementing
methods, for example, to seal cracks or holes in pipe strings or cement sheaths, to seal highly
permeable formation zones or fractures, to place a cement plug, and the like.
[0003] A broad variety of cement compositions have been used in subterranean
cementing operations. n some instances, set-delayed cement compositions have been used.
Set-delayed cement compositions are characterized by remaining in a pumpable fluid state
for an extended period of time (e.g., at least about day to about 2 weeks or more). When
desired for use the set-delayed cement compositions should be capable of being activated
whereby reasonable compressive strengths are developed. For example, cement set
activator may be added to a set-delayed cement composition whereby the composition sets
into a hardened mass. Among other things, the set-delayed cement composition may be
suitable for use in well bare applications, for example, where it is desired to prepare the
cement composition in advance. This may allow, for example, the cement composition to be
stored prior to its use. In addition, this may allow, for example, the cement composition to be
prepared at a convenient location and then transported to the job site. Accordingly, capital
expenditures may be reduced due to a reduction in the need for on-site bulk storage and
I
mixing equipment. This may be particularly useful for offshore cementing operations where
space onboard the vessels may be limited.
[0004] While set-delayed cement compositions have been developed heretofore,
challenges exist with their successful use in subterranean cementing operations. For
example, set-delayed cement composiiions prepared with Portland cement may have
undesired gelation issues which can limit their use and effectiveness i cementing
operations. Other set-delayed compositions that have been developed, for example, those
comprising hydrated lime and quartz, may e effective n some operations but may have
limited use at lower temperatures as the may not develop sufficient compressive strength
when used in subterranean formations having lower bottom hole static temperatures. n
addition, it may be problematic to activate some set-delayed cement compositions while
maintaining acceptable thickening times and compressive strength development.
SUMMARY
[0005] A embodiment discloses a method of cementing in a subterranean
formation, comprising: providing a set-delayed cement composition comprising water, -pumice,
hydrated lime, and a set retarder; activating the set-delayed cement composition with a cement
5set activator, wherein the cement set activator comprises at least one activator selected from the
group consisting of nanosihca, a polyphosphate, and combinations thereof; introducing the setdelayed
cement composition i fo a subterranean formation; and allowing the set-delayed cement
composition to set i the subterranean formation.
[0006] Another embodiment discloses a method or activating a set-delayed cement
lOcomposition comprising: providing a set-delayed cement composition comprising pumice,
hydrated lime in an amount of about . % to about 30% by weight of the pumice, a set retarder in
an amount of about 1% to about 5% by weight of the pumice, and water in an amount of about
35% to about 70% by weight of the pumice; storing the set-delayed cement composition for a
period of at least about I day; activating th set-delayed cement composition with a cement set
1 a tiva or wherein the cement set activator comprises a polyphosphate and an additive selected
from the group consisting of osiliea and a monovalent salt; introducing the set-delayed
cement composition into an a ul s between a conduit disposed in a well bore and a wait of the
wel bore or another conduit; and allowing the set-delayed cement composition to set in the
ann i s
20 [0007] Yet another embodiment discloses an activated set-delayed cement
composition comprising: water; pumice; hydrated lime; a set retarder; and &cement set activator,
wherein the cement set activator comprises at least one activator selected from the group
consisting of nanosihca, a polyphosphate, and combinations thereof.
[0008] Yet another embodiment discloses a cementing system comprising mixing
25equipment for mixing an activated set-delayed cement composition, the activated set-delayed
cement composition comprising water, pumice, hydrated lime, a set retarder, and, a cement se
activator, wherein the cement set activator comprises at least one activator selected from the
group consisting of nanosilica, a polyphosphate, and combinations thereof. The cementing
system ay further comprise pumping equipment for delivering the set-delayed cement
30composition into a well bore,
[0009] The features and advantages of the present invention wi be readil apparent
to those skilled in the art. While numerous changes may be made by those skilled in the art,
such changes are within the spirit of the invention.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0 0 The present invention relates to subterranean cementing operations and ore
psriieularfy, in certain embodiments, to set-delayed cement compositions and methods of
using set-delayed cement compositions in subterranean formations. n particular
embodiments, the present invention provides improved cement se activators for activation
of .set-delayed cement compositions. Embodiments of he cement set activators ma be use
to activate a set-delayed cement composition while achieving desirable thickening times and
compressive strength development.
[0 ί J Embodiments of the set-delayed cement compositions of the present
invention may generally comprise water, pumice, hydrated lime, an a set retarder.
Optionally, the set-delayed cement compositions may further comprise a dispersant.
Advantageously, embodiments of the set-delayed cement compositions may be capable o
remaining in pumpab!e fluid state for an extended period of time. Fo example, the setdelayed
cement compositions may remain i a pumpable fluid state for at least about 1 day
or longer. Advantageously, the set-delayed cement compositions may develop reasonable
compress e strengths after activation at relatively low temperatures.
[0012] The water used in embodiments of the set-delayed cement compositions of
the present invention may be from any source provided that t does not contain an excess of
compounds that ay undesirably affect othe components in the set-delayed cement
compositions. For example, a set-delayed cement composition may comprise fresh water or
salt water. Salt water generally may include one or more dissolved salts therein and may be
saturated or unsaturated as desired for a particular application. Seawater or brines may be
suitable for use in embodiments of the present invention. Further, th water may be present
in an amount sufficient to form a pumpable slurry, certain embodiments, the water ay be
present in the set-delayed cement composition in an amount in the range of from abou 33%
to about 200% by weight of the pumice in certain embodiments, the water may be present in
the set-delayed cement compositions in an amount i the range of from about 35% to about
70% by weight of the pumice. One of ordinary skill in the art with the benefit of this
disclosure will recognize the appropriate amount of water for a chosen application
[00 3] Embodiments of the set-delayed cement compositions may comprise pumice.
Generally, pumice is a volcanic rock that can exhibit cementitious properties, in that it may
se and ha rde in the presence of by rat d lime and water. The pumice may also be ground,
for example. Generally, the pumice may have an particle size distribution as desired for a
particular application. In certain embodiments, the pumice may have a mean panicle size in a
range of from about 1 micron to about 200 microns. The mean particle size corresponds to
d5 values as measured by particle siz analyzers such as. those manu factured by Malvern
Instruments, Worcestershire,, United Kingdom, specific embodiments, the pumice may
have a mean particle size i a range of from about I micron to about 200 micron, from about
5 microns to about 100 microns, or from about 10 micron to about 50 micro ns n one
particular embodiment, the pumice may have a mean particle of less than about
microns. An example of a suitable pumice is available from Hess Pumice Products, inc.,
Malad, Idaho, as DS-325 lightweight aggregate, havi g a particle size of less than about
microns t should be appreciated that particle i too small may have mixability problems
while particle sizes too targe may not be effectively suspended in the compositions. One of
ordinary skill in the art, with the benefit of this disclosure, should be ab e to select a particle
size for the pumice suitable for use for a chosen application.
[00 4] Embodiments of the set-delayed cement compositions may comprise
hydrated lime. As used herein, the term "hydrated lime" will be understood to mean calcium
hydroxide. The hydrated lime may be included in embodiments of the set-delayed cement
compositions, for example, to form a hydraulic composition with the pumice. For example,
the hydrated lime may be included in a pu ice o-hydra d- i e weight ratio of about 0 : 1
to about 1: or a ratio of about 3 to about 5:1. Where present, the hydrated lime ma be
included in the set-delayed cement compositions an amount i n the range of from about
10% to about 100% by weight of the pumice, for example. In so embodiments, the
hydrated lime may be present in an amount rangin betwee any of and/or including an of
about 10%, about 20%, about 40%. about 60%, about 80%, or about 100% by weight of the
pumice, ! n some embodiments, the cementitious components present in the set-delayed
cement composition may consist essentially of the pumice and the hydrated lime. For
example, the cementitious components may primarily comprise the pumice and the hydrated
lime without any additional components (e.g., Portland cement, fly ash, slag cement) that
hydraulically set n the presence of water. One of ordinary skill in the art, with the benefit o
this disclosure, will recognize the appropriate amount of the hydrated lime to include for a
chosen application:.
[00 5] Embodiments of the set-delayed cement compositions may comprise a set
retarder, A broad variety of set retarders may be suitable for use in the set-delayed cement
compositions useful i the present invention. For example, the set retarder may comprise a
phosphates, a phosphonic acid, phosphonic acid derivatives, phosphdnates, lignos onates,
salts, organic acids, carboxy methy Sated hydroxyethylated celluloses, synthetic co- or terpolymers
comprising sulfonate and carboxylic acid groups borate compounds, derivatives
thereof, or mixtures thereof. n certain embodiments, the set retarders used in the set-delayed
e compositions useful m the present invention are phosphonic ac d derivatives, such as
methylene phosphonic acid derivatives as described in U.S. Pat. No. 4,676,832, the
disclosure of which s incorporated herein by reference. Examples of suitable se retarders
include, amo g others, methylene pho ph ates such as Micro Matrix* cement retarder
MC available from Halliburton Energy Services, Inc., of Duncan, Oklahoma, as),
Dequesf* 2006 additive, and e ues 2066 additive. Dequesf* 2006 additive, and Dequest*
2066 additive are both available from Thermphos, North America / Sal a ch Chemicals,
Dequesf*"' 2066 additive is pH neutralized diethyieneiriamincpeniamethy!enephosphonaie.
Dequesf* 2006 additive miriloirismeihylenetriphosphonate. Dequest* 2066 additive m
be the stronger of the two Dequest additives in certain systems n some embodiments,
methylene phosphonates and/or methylene phosphonic aci derivatives ay foe used to retard
the pumice-containing compositions disclosed herein for extended periods of time. One of
the anv advantages of the embodiments of the present invention is that these stronger
cement retarders may be successfully used with the cement set activators discussed later.
Generally, the set retarder may be present in set-delayed cement composition used in the
present invention in an amount sufficient to delay the setting for a desired time. In so e
embodiments, the set retarder may be present in the set-delayed cement compositions n an
amount in the range of from about 0.01% o about 10% by weight of the pumice. In specific
embodiments, the set .retarder may be present in an amou t ranging between any of and/or
including any of about 0.01%, about 0.1%, about %, about 2%, about 4%. about 6%, about
8%, or about % by weight of the pumice. One of ordinary skill in the art, with the benefit
of this disclosure, will recognize the appropriate amount of the set retarder to include for a
chosen application.
[0016] As previously mentioned, embodiments of the set-delayed cement
compositions may optionally comprise a dispersant. Examples of suitable dispersants
include, without limitation, i ated formaidehyde based dispersants and
polycarboxylated ether dispersants. One example of a suitable suifonated-formaldehydebased
dispersant tha ma be suitable is a sulfonated acetone formaldehyde condensate,
available from Halliburton Energy Services, Inc., as C '-3 dispersant Examples of
suitable polycarboxylated ether dispersants include Liq imenf 4L and 55 F dispersants
(available f om BASF Corporation, Houston, Texas) and Coatex dispersants (available from
Coatex Inc.). While a variety of dispersants may be used in accordance with embodiments of
the present invention, polycarboxylated ether dispersants ay be particularly suitable for us
in some embodiments. W hout being limited by theory, it is believed that polycarboxylated
ether dispersants may synergistieally interact with other components of the set-delayed
e ent composition. For example, it is believed that he po yearbo i ed ether dispersants
may react with certain set retarders (e.g., phosphonic acid derivatives) resulting in formation
of a gel tha suspends the pumice a d hydrated .lime n the composition tor a extended
period of ti e
[00 ] in .some embodiments, the dispersaiit may be included in the set-delayed
cement compositions i an amount in the range of from about 0. % to about 5% by weight
of the pumice. n specific embodiments, the dispersant may be present in an amount ranging
between any of and/or including any of about 0.01%. about 0.1%, about 0.5%, about 1%,
about 2%, about 3%, about 4%, or about 5% by weight of the pumice. One of ordinary skill
in the art, with the benefit of this disclosure, will recognize the appropriate amount of the
dispersant to include fo a chosen application.
[00 18 Other additives suitable for use in subterranean cementing operations also
may be included in embodiments of the set-delayed cement compositions. Examples of such
additives include, bu are not limited to, weighting agents, lightweight additives, gasgenerating
additives, mechanical-property-enhancing additives, lost-circulation materials,
filtration-control additives, u d oss con ro additives, defoa ng agents, foaming agents,
thixotropic additives, and combinations thereof In embodiments, one or more of these
additives ma be added to the set-delayed cement composition after storing but prior to
placement of the set-delayed cement composition into a subterranean formation. A person
having ordinary skill in the art. with the benefit of this disclosure, should readily be able to
determine the type and amount of additive useful for a particular application and desired
result.
0 Those of ordinary skill in the art w ll appreciate that embodiments of the setdelayed
cement compositions of the present invention genes-ally should have a density
suitable for a particular application. By way of example, the set-delayed cement
compositions may have a density in the range of fr about 4 pounds per gallon ( b/ga ') to
about 20 lb gal. In certain embodiments, the set-delayed cement compositions may have a
density in the range of from about 8 lb/gal to abou 17 lb/gal. Embodiments of the setdelayed
cement compositions may be foamed or un amed or may comprise other means to
reduce their densities, suc as hollow microspheres, low-density elastic beads or other
density-reducing additives known in the art. in embodiments the density may be reduced
after staring the composition, but prior to placement in a subterranean formation. Those of
ordinary skill in the art. with the benefi of this disclosure, will recognize the appropriate
density for particular application.
[0020] As previously mentioned, the set-delayed cement compositions may have a
delayed set in that they remain in a pumpable fluid state for an extended period of time. For
example, the set-delayed cement compositions may remain in a pumpable fluid state for a
period of ti e from about \ day to about 7 days or ore in some embodiments, the setdelayed
cement compositions may remain in a pumpable fluid state for at least about 1 day,
about 7 days, about 10 days, about 20 days, about 30 days, about 40 days, about 50 days,
about 60 days, or longer A fluid is considered to be in a pumpable fluid state w re the fluid
has a consistency of less than 70 Bearden units of consistency ("8c"), as measured on a
high-temperature high-pressure consistometer at .room temperature (e.g., about 80°F) in
accordance with the procedure for determining cement thickening times set forth i API P
Practice -2, mm Practice/or Testing Well C First Edition, July 2005.
As set forth in Example 4 below, an example composition was prepared that comprised
pumice, 20% hydrated lime, 1.4% dispersant ( q iment* I4 ), 1.26% set retarder (Micro
Matrix* cement retarder), and 62% water (all % b weight o pumice), After 45 days of
storage at ambient conditions, the example composition was mixed with 6% calcium
chloride by weight of the pumice. At 140°F, the example composition had a thickening time
(time to 70 Be) of 2 hours and 36 minutes and developed 50 psi compressive strength in 9
hours and 6 minutes as measured on an Ultrasonic Cement Analyzer ( CA , available
from Farm Instrument Company, Houston, TX, while maintained at 3000 psi. After 48 hours,
the sample was crushed and had a compressive strength of 2,240 psi.
[0021] When desired for use, embodiments of the set-delayed cement compositions
may b activated (e.g., by combination with a cement set activator) to thereby set into a
hardened mass. The term "cement set activator" or "activator", as used herein, refers to an
additive that activates a set-delayed or heavily retarded cement composition and may also
accelerate the setting of the set-delayed or heavily retarded cement. By way of example,
embodiments of the set-delayed cement compositions may e activated to set to form a
hardened mass in a time period in the range of from about 2 hours to about hours. For
example, embodiments of the set-delayed cement compositions may set to form a hardened
mass in a time period ranging between any of and/or including any of about 2 days, about 4
days, about 6 days, about 8 days, about 10 days, or about 1 days.
[0022] n some embodiments, the set-delayed cement compositions may set to have
a desirable compressive strength after activation. Compressive strength is generally the
capacity of a material or structure to withstand axia y directed pushing forces. The
compressive strength may be measured at specified time after the set-delayed cement
composition has been activated and the resultant composition is maintained under specified
temperature and pressure conditions. Compressive strength can be measured by either a
destructive method or non-destructive method. The destructive method physically tests the
strength of treatment fluid samples at various points in time by crushing the samples in a
compression-testing machine. The compressive strength is calculated from the failure load
divided by the cross-sectional area resisting the load an is reported in units of pound-force
per square inch (psi). Non-destructive methods typically ay employ an Ultrasonic Cement
Analyzer ("UCA"), available from Fann instrument. Company, Houston, TX. Compressive
strengths may be determined in accordance with AP P 10B-2, Recommended Practice for
Testing We l Cements, First Edition, July 2005.
[00231 By way of example, the set-delayed cement composition, may develop a 24-
hour compressi v strength in the range of from about 50 psi to about 5000 psi alternatively,
f o about 100 psi to about 4500 psi, or alternatively f om about 500 psi to about 4000 psi.
In so e embodiments, the set-delayed cement composition may develop a compressive
strength i 24 hours of at least about 50 psi, at least about 1 0 ps at least about 500 psi, or
more n some embodiments, the compressive strength values ma b determined using a
UCA at temperature ranging from F to 200°F while maintained at 3000 psi.
[0024] In some embodiments, the set-delayed cement composition may have a
desirable thickening time after activation. Thickening time typically refers to the time a fluid,
such as a cement composition, remains in a fluid state capable of being pumped. A number
of different laboratory techniques may be used to measure thickening time to give an
indication of the amount of time a treatment fluid will remain pumpable in we l An
example technique for determining whether a treatment fluid is in a pumpable fluid state may
use a high-temperature high-pressure consistometer at speciiled pressure and temperature
conditions, in accordance with the procedure for determining cement thickening times set
forth in the afore-mentioned API RP Practice 10R-2. The thickening time may be the t me
for the treatment fluid to reach 70 Bearden units of consistency ("Be") and may be reported
in time to reach 70 B . n some embodiments, the set-delayed cement compositions may
have a thickening time of greater than about hour, alternatively, greater than about 2 hours,
alternatively greater than about 5 hours at 3,000 psi and temperatures in a range of fro
about 50 F to about 400 ' F, alternatively, in a range of from about 0 F to about 250° ί and
alternatively at a temperaiure of about }.40 F
[0025] Embodiments of the present invention ma include addition of a cement set
activator to the set-delayed cement compositions. Examples of suitable cement set activators
include, but are not limited to, calcium chloride, triethanolamine, sodium silicate, zinc
formate, calcium acetate, sodium hydroxide, sodium sulfate, and combinations thereof An
additional example of a suitable cement set activator includes nanosilica. Yet another
example of a suitable cement activator includes a polyphosphate, ft has been found tha the
combination of the nanosilica and the polyphosphate ma be used to activate embodiments
of the set-delayed cement compositions. Additionally , the combination of the polyphosphate
and a monovalent sa l has proven to be a particularly effective cement set: activator in
accordance with embodiments of the present invention . Advantageously, set-delayed cement
compositions activated with the nanosilica, polyphosphate, the combination of a nanosilica
and a polyphosphate, o the combination of a polyphosphate a d a mono valent sa t may have
acceptable thickening times and/or compressive strength development. Moreover the
activators or combinations of activators of the preceding sentence may exhibit better results,
as compared to other activators such a calcium chloride, in compositions comprising
heavily retarded cement compositions such as compositions using methylene phosphonates
and/or methylene phosphonie acid derivatives as discussed above.
[0026] Embodiments of the present invention may include a cement set activator
comprising nanosilica. As used herein, the term "nanosilica" refers to silica having a particle
size of less than or equal to about 1 0 nanometers ( m") The size of the nanosilica may be
measured using any suitable technique. It should be und stood th the measured size of the
nanosilica may vary based on measurement technique,, sample preparation, and sample
conditions s ch as temperature, concentration, etc. One technique for measuring particle e
of the nanosilica is Transmission Electron Microscope (TEM) observation. An example of a
suitable commercially available technique based on laser diffraction technique may use a
Zetaslzer a o ZS supplied by Malvern Instruments. Worcestershire, UK. n some
embodiments, the nanosilica may comprise colloidal nanosilica. Th nanosilica may also be
stabilized using any suitable technique. n some embodiments, the nanosilica y be
stabi lized with metal oxide, such as lithium oxide, sodium oxide, potassium oxide, and/or a
combination thereof. Additionally the nanosilica may be stabilized with an amine and/or a
metal oxide as mentioned above. Embodiments of the nanosiiieas have an additional
advantage in that they have been known to fill in pore space in cements which can result in
superior mechanical properties in the cement after the cement has set.
[0027] .Embodiments o the present invention may include a cement set activator
comprising a combination of a monovalent salt and a polyphosphate. The monova lent salt
and the polyphosphate may be combined prior to addition to the set-delayed cement
composition or may be separately added to the set-delayed cement composition. The
monovalent salt used may be any salt that dissociates to form a monovalent cation, such as
sodium and potassium salts,. Specific examples of suitable monovalent salts include
potassium sulfate, calcium chloride, and sodium sulfate. A variety of different
polyphosphates may be used i combination w th the monovalent sail for activation of the
set-delayed cement compositions, including polymeric eiaph sp ate salts, phosphate salts,
and combinations thereof, for example. Speci fic examples of polymeric mefaphosphate salts
that may be used include sodium hexametaphosphate, sodium metapho pha e, sodium:
tetranietaphosphate, sodium pentametaphosphate, sodium hepiametaphosphaie, sodium
octameiaphosphate, a d combinations thereo A specific example of a suitable cement set
activator comprises a combination of sodium sulfate and sodium hexametaphosphate.
interestingly, sodium hexametaphosphate is also known in the art to be a strong retarder o
Portland cements. Because of th unique chemistry of polyphosphates, polyphosphates may
he used as a cement set activator for embodiments of th set-delayed cement compositions
disclosed herein. The ratio of the monovalent salt to the polyphosphate may range, for
example, from about 2: to about :25 or from about 1: to about : 0. Embodiments of the
cement set activator may comprise the monovalent salt and the polyphosphate salt in a ratio
(monovalent salt to polyphosphate) rangin between an of and/or including a y of about
5: , 2:1 about 1:1, about 1 2, about :5 aboui : , about :20, or about . :25.
0028] n some embodiments, e combination of the monovalent salt and the
polyphosphate ma be provided as a liquid additive tha ma be used for activation of a setdelayed
cement composition. The iq uid additive may comprise water, the monovalent salt
the polyphosphate and a dispersant. Examples of suitable dispersants include, without
limitation, sulfonatcd-fornialdehyde-based dispersants and poiycarboxyiated ether
dispersants. On example of a suitable suiibnated-iornialdehyde-based dispersant is a
sulfonated acetone formaldehyde condensate, available from Halliburton Energy Services,
Inc., as C R, -3 dispersant One example of a suitable poiycarboxyiated ether dispersant is
Liqniment* 4 , or 558 F dispersants, available from BASF Corporation, Houston, Texas.
The dispersant may be included in the liquid additive in an amount from about 0.2% to 8%
about by weight of the liquid additive. The water may be included in the liquid additive i an
amount from about 90% to about 99.9% by weight of the liquid additi ve. The combination of
the monovalent salt and the polyphosphate ma range from about 0.1% to about 2.5% by
weight of the liquid additive.
[0029] Without being limited by theory, a description of a mechanism for activation
of a lime and pozzolan set-delayed cement composition using a set-delayed cement activator
comprising a combination of sodium sulfate and sodium hexaraetaphosphate is provided, t
is believed that the sodium sulfate produces sodium hydroxide upon reaction with the lime.
This reaction causes a resulting rise i the H of the slurry and consequently an increase in
the rate of dissolution of silicon diox ide. Cement hydration rate has a direct relationship with
the proportion of tree silicates and/or al inosilic tes. Sodium hex me-taphosphate chelates
and increases the dissolution ate of calcium hydroxide. The combination of sodium sulfate
and sodium hexametaphosphaie creates a synergy in various compositions of set-delayed
cement compositions that provides better results than the singular use of either cement se
activator,
0030 The ceme t set activator should be added to embodiments of the set-delayed
cement composition in a amount sufficient to activate the extended settable composition to
set into a hardened mass. In certain embodiments, the cement set activator may be adde to
the set-delayed cement composition in an amount in the range of about 0.1% to about 20%
by weight of the pu ice in specific embodiments, the cement set activator may be present in
an amount ranging between any of a d or including any of about 0. about 1 , about 5%,
about %, about 5%, or about 20% by weight of the pumice. One of ordinary skill i the
art, with the benefit of this disclosure, will recognize the appropriate amount of the cement
set activator to include for chosen application.
[0 As wil be appreciated by those of ordinary skill in the art, embodiments of
the set-delayed cement compositions of the present invention may be used in a variety of
subterranean operations, including primary and remedial cementing. n some embodiments, a
set-delayed cement composition may be provided that comprises water, pumice, hydrated
lime, a set retarder, a d optionally a dispersant The set-delayed cement composition may be
introduced into subterranean formation and allowed to set therein. As used herein,
introducing the set-delayed cement composition into a subterranean formation includes
introduction into any portion of the subterranean formation, including, without limitation,
into a well bore drilled into the subterranean formation, into a near well bore region
surrounding the well bore, or into both. Embodiments of the present invention may further
include activation of the set-delayed cement composition. The activation of the set-delayed
cement corn-position may comprise, for example, addition of a cement se activator to the setdelayed
cement composition. The cement set activator may be added to the set-delayed
cement composition prior to introduction nto the subterranean formation.
[0032] n some embodiments, a set-delayed cement composition may be provided
that comprises water, pumice, hydrated lime, a set retarder, and optionally a dispersant. The
set-delayed cement composition may be stored, or example, in a vessel or other suitable
container. The set-delayed cement composition may be permitted to remain in storage for a
desired time period. For example, the set-delayed cement composition may remain in storage
for a time period of about day or longer. For example, the set-delayed cement composition
ma remain in storage for a time period of about 1 day, about 2 days, about 5 days, about 7
days, about days, about 20 days, about 30 days, about 40 days, about 50 days, about 60
days, or longer. some embodiments, the set-delayed cement composition may remain in
storage for a time period n a range of from about 1 day to about 7 days or longer. Thereafter.
the set-delayed cement composition may be activated, for example, by addition of a cement
set activator, introduced into a subterranean formation, and allowed to set therein.
0033 n primary cementing embodiments, or example, embodiments of the setdelayed
cement composition may be activated and introduced into a space between a conduit
(e.g., pipe strings, liners) located in the well bore an a wall of the well bore (or another
conduit), the wel bore penetrating the subterranean formation. The set-delayed cement
composition ay be allowed to set to form an annular sheath o hardened cement in the
space between the conduit and the well bore wall (or the other conduit). Among other things,
the set cement composition may form a barrier, preventing the migration of fluids in the well
bore, The set cement composition also may, for example, support the conduit in the well
bore.
[0 34] n remedial cementing embodiments, a set-delayed cement composition may
be used, for example, in squeeze-cementing operations or n the placement of cement plugs.
By way of example, the set-delayed composition may be activated and placed in a well bore
to plug an opening, such as a void or crack, in the formation, in a gravel pack, in the conduit,
in the cement sheath, and/or a microannulus between the cement sheath and the conduit.
[0035] The exemplary set-delayed cement compositions disclosed herein may
directly or indirectly affect one or more components or pieces of equipment associated w h the
preparation, delivery, recapture, recycling, reuse, and/or disposal of the disclosed set-delayed
cement compositions. For example, the disclosed set-delayed cement compositions may directly
or indirectly affect one or more mixers, related mixing equipment, mud pits, storage facilities or
uni ts composition separators, heat exchangers, sensors, gauges, pumps, compressors, and th
like used generate, store, monitor, regulate, arid or recondition the exemplary set-delayed cement
compositions. The disclosed set-delayed cement compositions may also directly or indirectly
affect any transport or delivery equipment used to convey the set-delayed cement compositions
to a well site or downhole such as, for example, any transport vessels, conduits, pipelines, trucks,
tubulars, and/or pipes used to compositionally move the set-delayed cement compositions from
one location t another, any pumps, compressors, or motors (e.g., topside or downhole) used to
drive the set-delayed cement compositions into motion, any valves or related joints used to
regulate the pressure or How rate of the set-delayed ceme compositions, and any sensors (i.e.,
press t and temperature), gauges, and/or combinations thereof, and the like. The disclosed seidelayed
cement compositions may also directly or indirectly affect the various downhole
equipment and tools that may come into contact with the set-delayed cement compositions such
as, but not limited to, wellbore casing, wellbore liner, completion string, insert strings, drill
string, coiled tubing, s ekl ne, wireline, drill pipe, drill collars, d motors, downhole motors
5and/or pumps, cement pumps, surface-mounted motors and or pumps, cenlralizers, turbolizers,
scratchefs, floats (e.g., shoes, collars, valves, etc.), logging tools and related telemetry
equipment, actuators (e.g., electromechanical devices, hydromechanics! devices, etc.), sliding
sleeves, production sleeves, plugs, screens, fillers, f ow control devices (e.g., inflow control
devices, autonomous inflow control devices, outflow control devices, etc.), couplings (e.g.,
iOelectro-hydraulie wet connect, dry connect, inductive coupler, etc.), control lines (e.g., electrical,
fiber optic, hydraulic, etc.), surveillance lines, drill bits and reamers, sensors or distributed
sensors, downhole heat exchangers, valves and corresponding actuation devices, tool seals,
packers, cement plugs, bridge plugs, and other wellbore isolation devices, or components, and
the like.
15 [0036] To facilitate a better understanding of th present invention, the following
examples o f certain aspects of some embodiments are g iven n no wa should the following
examples be read to limit, or define, the entire scope of the invention.
EXAMPLE 1
[0037] The following series of tests was performed to evaluate the force resistance
20 properties of comparative cement compositions comprising pumice and hydrated lime. Three
different comparative sample settable compositions, designated Samples 1-3, were prepared
using pumice (DS-325 lightweight aggregate), hydrated lime, Liq ment* 5141... dlspersant,
and water, as indicated i the table below. After preparation, the samples were placed in an
UCA and cured at 140°F an 3,000 ps for 24 hours. The cured cement was then removed
25 from the UCA and crushed to yield the compressive strength values provided in Table
below.
TABLE
Compressive Strength Tests
Lime 4 0 3 0
Dispersant g 12 4 13
Water 6 87 220
24-ff r Crash Strength psi 2,240 00 60
[0038] Example .1 thus indicates that ce e t compositions that comprise pumice and
ime in a weight ratio ranging from 3 : 1 to 5 : may develop compressive strengths suitable
for particular applications.
EXAMPLE 2
[0039] A sample set-delayed cement composition, designated Sample 4, having a
density of .3 lb/gal was prepared that comprised 500 grams of pumice (DS-325
lightweight aggregate), 0 grams of hydrated l me. 1 grams o Li imen * 5 4 ,
dispersant, 24 gram of Micro Malm* cement r arder, and 300 grams of water. The
theological properties of the sample were measured after storing at room temperature and
pressure for periods of 1 da and 6 days. After preparation, the theological properties of the
sample were determined at roo temperature (e.g.. about P) using a Model 35A Faun
Viscometer and a No. 2 spring, in accordance with the procedure set forth i API P Practice
i B~2 Recommended Practicefor Testing Well Cemems. The results of this test are set forth
in the table below.
[0040] Example 2 thus indicates that set-delayed cement compositions that comprise
pumice, hydrated lime, a dispersant. a set retarder. and water can remain fluid after days.
EXAMPLE 3
[0041] A sample set-delayed cement composition, designated Sample 5, having a
density of 3.4 lb/gal was prepared thai comprised 500 grams of pumice (DS-325
lightweight aggregate), 0 grams of hydrated lime, 7 grams of i uiment*' 4 1, dis ersan
6.3 grant of Micro Matrix* cement retarder, and 304 gra s o f water. The fheologicaS
properties of the sample were measured after storing at room temperature arid pressure for
pe riod of from 1 day to . days. The rheo ogica properties were measured at room
temperature (e.g., about 8 ='F) using a Model 35A Farm Viscometer a d a No. 2 spring, in
accordance with the procedure set forth in AP I P Practice 10B-2, Recommended Practice
or Testing Well Cements. The results of this test are set fo rt h in the table below.
Table 3
Viscosity Tests
[0042] After 7 days, calcium chloride in the amount indicated in Table 4 below was
added to a separately prepared sample of the same formulation as above. The sample was
then placed in an and the initial setting time, which i the time for the composition to
reach a . compressive strength of 50 psi while maintained at 3,000 psi was determined h
accordance with A P . RP Prac tice B 2, Recommended Practice for Testing Well Cements,
The initial setting time of the sample was also determined without: addition of the calcium
chloride. The samples with and without the calcium chloride were heated to a temperature of
1 0*F in 30 minutes and then maintained at that temperature throughout the test.
TABLE 4
Compressive Strength Tests
[0043] Example 3 thus indicates that the set-delayed cement compositions that
comprise pumice, hydraled ime, a dispersaut, a set retarder, and water will ot set for a
period of at least days at ambient temperature and over 4 days at !40 F. Example 3
further indicates tha sample set-delayed cement compositions be activated at a desired
time by addition of a suitable activator.
EXAMPLE 4
[0044] A sample set-delayed cement composition, designated Sample 6, having a
density of .4 lb/gal was prepared that comprised pumice (DS-325 lightweight aggregate),
20% hydrated lime, 1.4% Li i ef 5 14 1. dispersant, 1.26% Micro Matrix* cement
retarder, and 62% of water (all by weight of pumice, referred o in the table below as
bwop"). After 45 days in storage at ambient conditions, the sample was mixed with 6%
calcium chloride. At 40 F, the sample ha a thickening time (time to 0 Be) of 2 hours and
36 minutes and an initial setting time (time to 5 psi) of 9 hours and 6 minutes as measured
using an UGA while maintained at. 3000 ps . After 48 hours, th sample was crushed with a
mechanical press which gave a compressive stre ngth of 2.240 psi. The thickening time and
initial setting time were both determined in accordance with API RP Practice -2,
Recommended Practice for Testing Well Cements. The results of this test are set forth in the
table below.
TABLE 5
Ϊ 4 J Example 4 thus indicates that the set-delayed cement compositions that
comprise pumice, ydrat lime, a dispersant, a set retarder, and water will no set for &
period of at least 45 days a ambient temperature. Example 4 further indicates that sample
set-delayed cement compositions may be activated at desired time by addition of a suitable
activator.
EXAMPLE 5
046 This example was performed to evaluate the ability of sodium hydroxide and
sodium sulfate to activate a set-delayed cement composition that comprised pumice (DS-32S
lightweight aggregate), hydrated lime, Li imen * 5 14 dispersant. Micro Matrix* cement
retarder, and water. Four sample set-delayed cement compositions, designated Samples - ,
were prepared having concentrations of components a indicated in the table below. The
samples were monitored via an UCA. After the samples were placed in the UCA, the
pressure was increased to 3,000 psi and th temperature was increased to !00 F over a -
minute time period and held for the duration of th test. A portion of the slurry was retained
and poured nto a plastic cylinder to monitor the slorry behavior at room temperature and
pressure, These procedures wer repeated for a S samples,
[0047] Sa ple 7 was monitored for 72 hours over which time no strength was
developed and the slurry was still pounible when removed from the UCA The portion kept
at room temperature an pressure was likewise still pot ble after 72 hours,
[0048] Sample 8 was prepared using the same slurry design as Sample 7 except that
sodium hydroxide was added as an activator. The sodium hydroxide was added in solid form
directly to the mixing jar that contained the prepared sample. As can be seen from Table 6,
Sample 8, reached 50 psi of compressive strength at 16 hours and 3 minutes. The strength
continued to build, reaching a maximum of 1,300 psi, when the test was stopped at 72 hours.
The cured cement was removed from the UCA and crushed with a mechanical press which
gave a compressive strength of 969 psi. The portion kept at room temperature and pressure
was crushed after 7 days resulting in a compressive strength of 143 psi.
[ 49] Sample 9 was prepared using th same slurry desig as Sample 8 except that
sodium sulfate was added as an activator. The sodium sulfate was added in solid form
directly to th mixing jar that contained the prepared slurry. Sample 9 reached 50 psi of
compressive strength at 67 hours a d 29 minutes, The strength continued to build, slowly,
reaching a maximum of 78 psi, when the test was stopped at 72 hours. The cured cement was
removed from the CA and crushed with a mechanical press which gave a compressive
strength of 68.9 psi. The portion kepi at room temperature and pressure was still too soft to
be crushed after 7 days.
[0050] Sample 10 was prepared using the same slurry design as Sample 8 except
that equal amounts of sodium hydroxide and sodium sulfate were added as an activator. The
sodium hydroxide and sodium sul fate were added i solid form directly to the mixing jar that
contained the prepared slurry. Sample. 10 reached 50 psi of compressive strength at 22 hours
and 40 minutes. The strength continued to build, reaching a maximum of 900 psi. when the
test was stopped at 72 hours. The cured cement wa removed from the UCA and crushed
with a mechanical press which gave a compressive strength of 786 psi. The portion kept at
room temperature and pressure was crushed after 7 days resulting in a compressive strength
of 47.9 psi.
[005 The results of these tests a set forth in the table below. The abbreviation *
bwop" refers to the percent of the component by weight of the pumice. The abbreviation
gal s , refers to gallons of the component per 46-pound sack of the pumice. The
abbreviation "RTF" refers to room temperature and pressure.
TABLE 6
Sample 7 8 9
Density ib/ga! 3 .3 8 13.38 133$ 1.3,38
Water % bwop j 6 ,97 63.60 64,62 64,1 1
miee % bwop 0 0 0 0
ydr ted Lime % bwop j 20 20 20 20
isp rsar ga / k j 0.07 0.07 0 0? 0.07
Set Retarder % bwop 0,06 0.06 0.06 0,06
Sodium Hydroxide %bwop j 4 ί
Sodium Sulfate % bwop — - 4 ■
7-Day Crush Strength (RTF) | psi j 143.20 0 00 1 47.90
[0052] Example 5 thus indicates that sodium hydroxide. sodium sulfate, and
combinations of the two ca activate the set-delayed cement compositions, but to varying
degrees. The testing showed that both sodium hydroxide and combinations of sodium
hydroxide with sodium sulfate activated the cement compositions to an acceptable level.
When compared to the non-activated composition, sodium sulfate activated the cement
compositions, but much less so than the sodium hydroxide or combination of sodium
hydroxide and sodium sulfate.
EXAMPLE
[0053] T is example was performed to evaluate the effect of sodium sulfate and
sodium hexametaphospate on the setting time of a set-delayed cement composition having a
density of 13 5 lb/gal that comprised pumice (DS-325 lightweight aggregate), hydrated lime,
Liquiment* 558 F dispersant, Micro Matrix* cement retarder, and water. Micro Matrix *
cement retarder (MMCR) is a phosphonate cement retarder. Four sample set-delayed cement
compositions, designated Samples - 14, were prepared having concentrations of
components as indicated in the table below, based o the percentage of the component by
weight of the pumice ( bwop). The samples were cast in 2 x4 cylinders and cured for 24
hours in a water bath. One set of samples (samples , 2 ,· and } we e cured at 0 F and
another set of samples (samples 14, , and ) were cured at 11 F. Uniaxial compression
tests we performed on all samples after the 24 hour period.
[0054] Samples 11 a d 14 were activated using sodium hexametaphosphate.
Samples 12 and 1 were activated usi g a combination of sodium hexametaphospbale and
sodium sulfate. Samples 13 and 6 were activated with calcium chloride. The additive was
added directly to the mixing jar tha contained the prepared sample. As can be see fro
'fable , samples containing the combination of sodium sulfate d sodium
hexametaphosphate achieved higher 24-hour compressive strengths than those samples set at
the sa e temperature w th only sodium sulfate. This increas i strengt observed whe
sodium sulfate is added, highlights the synergy between sodium sulfate and sodium
hexametaphosphate in activating the setting o f the extended ife cement slurry. Furthermore,
when calcium chloride was used to acti ate the cement there was no compressive strength
observed either at 00 F or 0 °F. The cement d ot set in either ease. This highlights the
activating power of sodium hexametaphosphate a d the sodium hexametaphosphate a d
sodium sulfate combination with regards to calcium chloride.
TABLE 7
[0055] Example 6 thus indicates tha sodium hexametaphosphate, sodium sulfate,
and combinations of the two can activate the set-delayed cement compositions, but. to
varying degrees. Th testing showed that the combination of sodium sulfate and sodium
hexametaphosphate activated the cement compositions unde conditions were calcium
chloride would not effectively activate the cement to set.
EXAMPLE 7
[0056 This example performed to further evaluate the ability of sodium sulfate
and sodium hexametaphospate to activate a set-delayed cement composition having a densit
of .5 lb/gal that comprised pumice (DS-325 lightweight aggregate), hydratecl lime,
Liquhnenf* 558 F dispersant, Micro Matrix'* cement retarder, and water. Micro Matrix*"
cement retarder (MMCR) is a phosphonate cement retarder. Five sampie set-delayed cement
compositions, designated Samples 17-21, were prepared having concentrations of
co po ents as indicated i the table below. The thickening times of the samples were both
determined in accordance with AP RP Practice 0B-2 Recommended Practice fi r Testing
Well Cements, The results of this test are set forth i the table below,
[0057] Samples 1 , 19, and 20 were activated using a combination of sodium
hesametaphos hate and sodium sulfate as a liquid additive. The liquid additive was added
directly to the mixing jar that contained the prepared sample. The liquid additive comprised
sodium hexmetaphosphate 10 g) sodium sulfate ( . g), Liquiment* 558 dispersant (2.5
g), and water (50 g). Samples 18 and 2 1 were activated with calcium chloride. As can b
seen trora Table 8, Sample 1 reached 00 B after 5.5 hours whereas Sample (with
calcium chloride did not set after 00 hours). Samples 19 and 20 were set at 40 F These
samples had compositions with 2.6 an 5.2% MMCR ( bwop), respectively. They were
activated with the sodium sulfate and sodium h xame aph phat and they gave thickening
times of i hour and 5.5 hours respectively. The thickening times of the activated samples
was determined at !40°F in accordance with API RP Practice 10B-2, Recommended Practice
for Testing Well Cements. The results of this test are set forth n the table below.
S i exaxne p p a e % bwop 2
Sodium Sulfate % bwop •1
Calciu Chloride % bwop — ~
Thickening Time to 00 B 5.5 > 0 5.5
h n ) hours hours 1 hour hours
[0058] Example . , , and 20 thus indicate that sodium hexametaphosphate,
sodium sulfate, and combinations of the two can activate the set-delayed cement
compositions where activation with calcium chloride is inadequate for a phosphonale set
retarder such asM R was used.
EXAMPLE 8
[0059] This example was performed to evaluate the ability of nanosilica to activate
set-delayed cement compositions composition having a density of .5 lb/gal that comprised
pumice (DS-325 lightweight aggregate), 20% hydrated lime in an amount of, .2%
Lkjuimeut* 558 F dispersant, .3% Micro Matrix'* cement retarder, and 60% water (all by
weight of pumice). Samples 2 -26 were activated with nanosilica stabilized with lithium
oxide. The nanosilica stabilised with lithium oxide was a colloidal nanosilica that was
approximately 20% active. Samples -26 were stabilized with nanosilica stabilized with
lithium oxide (LSS-35 from Nissan Chemical), referred t in the table below as Nanosilica
A. The nanosilica stabilized with lithium oxide was a colloidal nanosilica that was
approximately 20% active. The nanosilica was added directly to the mixing jar containing
the prepared sample for each sample. After activation, the thickening times were measured at
various temperatures after the addition o varying amounts of lithium stabilized activators.
The thickening time was determined in accordance with API RF Practice B-2,
Recommended Practicefo Testing Well Cements. The results of this test are set forth i the
table below.
TABLE 9
22 8 Nanosilica A 8 00:35 00:35
23 80 Nanosilica A 04:00 04:30
24 80 Nanosilica A 5,5 04:40 06:00
25 80 Nanosilica A 4 14:00 22:00
26 H O Nanosilica A 6.9 00:25 00:35
[0060] Example 8 thus indicates that decreasing the amount of the nanosilica
stabilized w t lithium oxide added to the slurry leads to increased thickening times.
EXAM PLE 9
006 3] This Example describes an additional combination of activators with a
synergetic effect similar to th effect described in Samples 17, 19, and 20. Sample setdelayed
cement compositions, designated Samples 27-30, with densities as shown in Table
0, were prepared comprising pumice (DS-325 lightweight aggregate), 20% hydrated lime,
1.2 %Liquiment* 558 F dispersant, 2 6% Micro Matrix* cement retarded and 76% of water
(a l by weight of pumice). Samples 2.1-24 all demonstrate synergies between dissimilar
activators. Sample 27 uses the activator combination of sodium sulfate and sodium
hexameiaphosphaie (as in Samples 17, 19, a d 20). At a set temperature of 140 , the 24-
hour compressive strength of the sample was determined to be 800 psi L8S-75 is used in
sample 28 as a synergetic component to sodium hexametaphosphate {replacing sodium
sulfate's role in sample 27). f LSS-75 was added in place of sodium sulfate, the compressive
strength is even higher, at 950 psi. LSS-75 is referred to in the table below as Nanosilica B
and is a nanosilica stabilized by lithium oxide sold by Nissan Chemical Ltd The Sample 29
uses a different nanosilica additive supplied by Nissan Chemical. This additive is
SNOWTEX-PS-M, referred to in the table below as Nanosilica C. The 24-hour compressive
strength of the cement cured in sample 24 cured a 0 T is 962 psi. Sample 30 illustrates
the use of nanosilica as a synergetic additive to sodium hexametaphosphate at lower
temperature ( 1 !0°F).
j Strength p S 800 962 208
EXAMPLE 10
[0062 This example describes; the use of different phosphonate retarders and their
effects on the 24-hour compressive strength of the activa ted cement compositions. Pequest
2006 and Dequest 2066 additives are in the same phosphonate .family of retarders as
M C . Samples 3 1 a d 32 are described n Table 1 Sample 3 1 i the sample with
Dequest*' 2066 additive, whereas Sample 32 is that with eq est* 2066 a f vi . They have
24-hour compressive strengths of 452 and 5 4. This example demonstrates the utility of the
combination of sodium hexametaphosphate and sodium sulfate as an activator with other
retarders of the phosphonate type.
TABLE 1 1
Sample 31 32
De sity j ib/gai j 13,29 13.23
Temperature 1 1 40 40
%b op 62 62
Pumice bwop 00 0
l y lr t Unite % bwop 20 20
Disper a % b op 7 7
Phosp nate Set Retarder;
Deques** 2(166 Additive bwop 0.64
ho p nate Set e rder
e esi* 2006 Additive % bwop 1.3
Sodium e a t e p sp te % bwop .9
d Sulfate % bwop .8
24-hour Compressive 514
Strength psi 452
[0063] t should be understood tha the compositions and methods are described in
terms of "comprising," "containing," or "including" various components or steps, the
compositions and methods can also "consist essentia y of or "consist of the various
components and steps. Moreover, the indefinite articles or "an," as used in the claims,
are defined herein to mean one or more tha one of the element that it introduces.
[0064] For the sake of brevity, only certain ranges are explicitly disclosed herein.
However, ranges ft any ower limit may be combined with any upper limit to recite a
range not explicitly recited, as well as, ranges from any lower limit may be combined with
any other ower imi to recite a range not explicitly recited, the same way, ranges trora
any upper limit may be combined with any other upper limit to recite a range not explicitly
recited. Additionally, whenever a numerical range with a lower limit and an upper limit is
disclosed, any number and any included range failing within the range are specifically
disclosed. n particular, every range of values (of the form, "from about a to about , or,
equ valent!) , "from approximately a to b," or, equivalency, "from approximately a-b")
disclosed herein is to be understood to set forth every number and. range encompassed within
the broader range of values eve if not explicitly recited. Thus, every point or individual
value may serve as its own lower or upper limit combined with any other point or individual
value or any other lower or upper limit, to recite a range ot explicitly recited.
[0065] 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 o
the teachings herein. Although individual embodiments are discussed, the invention covers
all combinations of all those embodiments. Furthermore, no limitations are intended to the
details of construction or desig herein shown, other than as described in the claims below.
A so, the terms in the claims have their plain, ordinary meaning unless otherwise explicitly
and clearly defined by the pate te e It is therefore evident that the particular illustrative
embodiments disclosed above may be altered or modified and a l such variations are
considered within the scope and spirit of the present invention. f there is any conf ict n the
usages of a word or term in this specification and one or more patent! ) or other documents
that may be incorporated herein by reference, the definitions that are consistent with this
specification should be adopted.

What is claimed is:
. A method of cementing i a subterranean formation, comprising;
providing a set-delayed cement composition comprising water, pumice,
hydrated .lime, and a set retarder;
activating the se -delayed cement composition with a cement set activator,
wherein the cement set activator comprises at least one activator selected from the group
consisting of nanosilica, a polyphosphate, and combinations thereof;
introducing the set-delayed cement composition into a subterranean
formation; and
allowing the set-delayed cement composition to set in the subterranean
formation,
2 The method of claim 1 wherein the cement set activator is added to the setdelayed
cement composition in an amount of abou t 0.1% to about 20% by weight of the setdelayed
cement composition.
3, The method of claim 1 wherein the cement set activator comprises the
combination of a monovalent salt and the polyphosphate.
4. The method of claim 3 wherein the polyphosphate comprises sodium
hexametaphosphate.
5. The method of claim 3 wherein the .monovalent salt comprises sodium
sulfate.
6. The method of claim 3 wherein the ratio of the monovalent salt to the
polyphosphate is from about 2:1 to about 1:25.
7. The method of claim wherein the set retarder comprises at least one
retarder selected fro the group consisting of a phosphate, a phosphonate, a phosphonic
acid, phosphonic acid derivative, a l gnos lr nate, a salt, an organic acid, a
carboxymethylated hydroxyethylated cellulose, a synthetic co- or ter-po e comprising
sulfonate and carhoxyiic acid groups, a borate compound, and any mixture thereof.
8. The method of claim 1 wherein the set-delayed cement composition further
comprises a hspersan
9 The method of claim 1 wherein the cement set activator comprises nanosilica
and wherein the nanosilica has been stabilized by at least one nanosilica stabilizer selected
from the group consisting of; sodium oxide, potassium oxide, lithium oxide, an amine, and
any co bi tion thereof,
10. The method of claim 1 wherein the set-delayed cement composition remains
a pumpab!e fluid state for a time period of at leas t about 7 clays prior to the activating.
, The method of claim .1 wherein the set-delayed cement composition is
introduced into a well bore penetrating the subterranean formation, the wel bore having a
bottom-hole sta tic temperature of less than about 2
The method of claim .1 wherein the set-delayed cement composition s
introduced into an an lus between a conduit disposed in a well bore and a wall of the well
bore or another conduit.
13 The method of clai 1 wherein the set retarder comprises at east one
retarder selected trom the group consisting of a methylene phosphonie acid derivative and a
methylene phosphonate, and wherein the set-delayed cement composition further comprises
a p Sy arboxySated ether dispersant.
A method for activating a set-delayed cement composition comprising:
providing a set-delayed cement composition comprising pumice, hydra d
lime in an amount of about % t about 30% by weight of the pumice, a set retarder in an
amount of about % to about 5% by weight of the pumice, and water in an amount of about
35% to about 70% by weight of the pumice;
storing the set-delayed cement composition for a period of at least about I
day;
activating the set-delayed cement composition with a cement set activator,
wherein the cement set activator comprises a polyphosphate and an additive selected fro
the group consisting of nanosilica and a monovalent salt;
introducing the set-delayed cemen composition into an annulus between a
conduit disposed in a well bore and a wall of th well bore or another conduit; and
allowing the set-delayed cement composition to set in the a ulus .
5 The method of claim 14, wherein the cement set activator s added in a
amount of abou t {). 1% to about 20% by weight of the set-delayed cement composition.
The method of claim 14 wherein the cement set activator comprises a
combination of the polyphosphate and the monovalent salt, wherein the polyphosphate
comprises sodium hexametaphosphate, and wherein the monovalent salt comprises sodium
sulfate.
17 The method of claim 14 wherein the cement set activator comprises a
combination of the polyphosphate and the nanosilica, wherein the polyphosphate comprises
sodium hexametaphosphate, an wherein nanosilica has been stabilized by at least one
nanosilica stabilizer selected from the group consisting of: sodium oxide, potassium oxide,
lithium oxide, an amine, and any combination thereof
8 An activated set-delayed cement composition comprising:
water;
pumice;
hydrated lime;
a e retarder; a d
a cement set activator, wherein the cement set activator comprises at least
one activator selected fro the group consisting of -nanosilica, a . polyphosphate, and
combinations thereof.
19 The composition of claim 8 wherein the cement set activator comprises a
combination of a monovalent salt and the polyphosphate.
20 A cementing system comprising:
mixing equipment for mixing an activated set-delayed cement
composition, the activated set-delayed cement composition comprising water, pumice,
hydrated lime, a set retarder; and, a cement set activator, wherein the cement set activator
comprises at ieast one activator selected from the group consisting of nanosilica, a
polyphosphate, a d combinations thereof; and
pumping equipment for delivering the set-delayed cement
composition nto a well bore.