WO2015035281A1

WO2015035281A1 - Cement set activators for set-delayed cement compositions and associated methods

Info

Publication number: WO2015035281A1
Application number: PCT/US2014/054497
Authority: WO
Inventors: Peter James Boul; Thomas Jason Pisklak; Samuel J. Lewis; Kyriacos Agapiou; Lance Everett Brothers; Pauline Akinyi Otieno; Ronnie Glen Morgan; Baya Adams; Cody Glenn Harris
Original assignee: Halliburton Energy Services, Inc.
Priority date: 2013-09-09
Filing date: 2014-09-08
Publication date: 2015-03-12
Also published as: BR112016001687A2; CA2920783C; AU2014317924A1; RU2637347C2; RU2016102673A; NO20160085A1; GB2534036B; AU2016266033A1; AU2014317924B2; NO347526B1; GB2534036A; AU2016266033B2; MX2016001053A; GB201600810D0; CA2920783A1; MY174792A

Abstract

Disclosed herein are cement compositions and methods of using set-delayed cement compositions in subterranean formations. In one embodiment, a method of cementing in a subterranean formation is described. The method may comprise providing a set-delayed cement composition comprising water, pumice, hydrated lime, and a set retarder; activating the set-delayed cement composition with a liquid additive to produce an activated cement composition, wherein the liquid additive comprises a monovalent salt, a polyphosphate, a dispersant, and water; and allowing the activated cement composition to set.

Description

CEMENT SET ACTIVATORS FOR SET-DELAYED CEMENT

COMPOSITIONS AND ASSOCIATED METHODS

BACKGROUND

[0001] Embodiments relate to subterranean cementing operations and, in certain embodiments, to set-delayed cement compositions and methods of using set-delayed cement compositions in subterranean formations,

[0002] Cement compositions may be used in a variety of subterranean operations. For example, in subterranean well construction, a pipe string {e.g., casing, liners, expandable tubulars, etc.) may be run. into a we^'ll bore and cemented ^'in place. The process of cementing the pipe string in place is commonly referred to as "primary cementing." In a typical primary cementing method, a cement composition may be pumped into an anmilus between the walls of the weII.bo.re and the exterior surface of the pipe string 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) that may support, and position the pipe string in the wellbore and may bond the 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 corrosion. Cement compositions also may 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, hi some instances, set-delayed cement composition have been used. Set-delayed cement compositions are characterized by remaining in a pumpabie fluid state for at. least about one day (e.g., a least about 7 days, abou 2 weeks, about 2 years or more) at room temperature (e.g.-, about 80* F) in quiescent storage. When desired for use, the .set- delayed cement compositions should be capable of being activated whereby reasonable compressive strengths are developed. For example, a cement set accelerator 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 wellbore 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. hi 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 mixing equipment, This i 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 i subterranean cementing operations. For example, set-delayed cement compositions prepared with Portland cement may have undesired gelation issues which can limit their use and effectiveness in cementing operations. Other set-delayed compositions that have been developed, for example, those comprising hydrated lime and quartz, may be effective in 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.

BRIEF DESCRIPTION OF THE DRAWINGS

[0001 ] These drawings illustrate certain aspects of some of the embodiments of the present method, and should not be used to limit or define the method.

[0002] FICJ. I illustrates a system for the preparation and delivery of a set-delayedee.ment composition to a wellborn in accordance with certain embodiments.

[0003] PIG. 2A illustrates surface equipment that ma be used in the placement of a set-delayed cement composition in a wei!bore in accordance with certain embodiments,

[0004] FIG. 2B il lustrates the placement of a set-delayed cement composition into a wellbore annulos in accordance with certain embodiments.

[Ό005] FIG. 3 is a graph of the dispersant amount vs. the thickening time of set- delayed cement compositions activated with a liquid additive comprising a monovalent salt and polyphosphate acti vator combination.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0006] Embodiments relate to subterranean cementing operations and. in certain embodiments, to set-delayed cement compositions and methods of using set-delayed cement compositions in subterranean formations, in particular embodiments, improved cement set activators used for the activation of set-delayed cement compositions may be provided. Embodiments of the cement set activators may be used to activate a set-delayed cement composition while also achieving desirable thickening times and compressive strength development.

[0007] Embodiments of the set-delayed cement compositions may generally comprise water, pumice, hydrated lime, and a set retarder. Optionally, the set-delayed cement compositions may further comprise a dispersant. Embodiments of the set-delayed cement compositions may be foamed. Advantageously, embodiments of the set-delayed cement compositions may be capable of remaining in a pumpabie fluid state for an extended period of time. For example, the set-delayed cement compositions may remain in a pumpabie fluid state for at least about 1 day, about 2 weeks, about 2 years, or longer. Advantageously, the set-delayed cement compositions may develop reasonable compressive strengths after activation at relatively low temperatures. While the set-delayed cement compositions may be suitable for a number of subterranean cementing operations, they may be particularly suitable for use in subterranean formations having relatively low bottom hole static temperatures, e.g., temperatures less than about 200^':'F or ranging from about i00°F to about 200"F. In alternative embodiments, the set-delayed cement compositions may be used in subterranean formations having bottom hole static temperatures up to 450°F or higher,.

[0008] The water used in embodimen ts of the set-delayed cement compositions may be from any source provided that, it does not contain an excess of compounds that may undesirably affect other 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 brine may be suitable for use in embodiments. Further, the water may be present in an amount, sufficient to form a pumpabie slurry. In certain embodiments, the water may be present in the set-delayed cement composition in an amount in. the range of from about 33% to about 200% by weight of the pumice. In certain, embodimenis, the water may be present in the set-delayed cement compositions in an amoun in 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.

[0009] Embodiments of the set-delayed cement compositions may comprise pumice. Generally, pumice is a volcanic rock thai can exhibit cementitious properties in thai it may set and ^'harden in the presence of hydrated lime and water. The pumice may also be ground. Generally, the pumice may have any particle size distribution as desired for a particular application, in certain embodiments, the pumice may ^'have a mean particle ske in a range of from about I micron to about 200 microns. The mea particle size corresponds to d50 values as measured by particle size analyzers such a those manufactured by Malvern instruments, Worcestershire, United Kingdom. In specific embodiments, the pumice may have a mean particle size in a range of from about I niicron to about 200 microns, from about 5 micron to about 1 0 microns, or from about 10 microns to about 50 microns, in. one 'particular embodiment the pumice may have a mean particle size of less than about 15 microns. An example of a suitable pumice is available from Hess Pumice Products, Inc., Maiad, Idaho, as DS-325 lightweight aggregate, having a particle size of less than about 15 microns. It should be appreciated that particle sizes 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 able to select a particle size for the pumice suitable for a chosen application,

[0010] 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, .in some embodiments, the hydrated lime may be provided as quicklime (calcium oxide) which hydrates when mixed with water to form the hydrated lime. 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 pumice-to-hydrated-lime weight ratio of about 10: 1 to about 1 : 1 or 3: 1 to about 5: 1 , Where present the hydrated lime may be included, in the set-delayed cement compositions in an amount in. the range of .from about 10% to about 100% b weight of the pumice, for example. In some embodiments, the hydrated lime may be present in an. amount ranging between any of and/or including any o about 1 %, about 20%, about 40%, about 60%, about: 80%, or about 100% by weight of the pumice, in 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 in the presence of water. One of ordinary skill in the art, with the benefit of this disclosure, will recognize the appropriate amount of the hydrated lime io i nclude for a chosen application.

[001 1] 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. For example, the set retarder ma comprise phosphonic acids, such as ethyienediamine tetra(methylene phosphonic acid), diethyl enetriamine penta(rneihylene phosphonic acid), etc.; lignosulfonates, such as sodium lignosulfonate, calcium Hgnosiu'fon.aie, etc.; salts such as stannous sulfate, lead acetate, monobasic calcium phosphate, organic acids, such as citric acid, tartaric acid, etc.; cellulose derivatives such as hydroxy! ethyl cellulose (HEC) and earboxymeihyi hydroxyethyl cellulose (CMHEC); synthetic co- or ter-polymers comprising sulfonate and carboxylic acid groups such as sulfonate-firactkmaiked acrylaroidc-acrylic acid copolymers; borate compounds such as alkali borates, sodium roetaborate, sodium tetraborate, potassium peotaborate; derivatives thereof, or mixtures thereof, Examples of suitable set retarders include, among others, phosphonic acid derivatives. One example of a suitable set retarder is Micro Matrix* cement retarder, available from Halliburton Energy Services, Inc. Generally, the set retarder may be present in the set-delayed cement compositions in an amount sufficient to delay the setting for a desired time, in some embodiments, the set retarder may he present in the set-delayed cement compositions in an amount in the range of from about 0.01% to about 10% by weight of the pumice, i specific embodiments, the set retarder may be present in an amount ranging between any of and/or including any of about 0.01%, about 0.1%, about 1 %, about 2%, about 4%, about 6%, about 8%, or about 1 % by weight of the pumice. One of ordinary skill in. the art, with die benefit of this disclosure, will recognize the appropriate amount of the set retarder to include for a chosen application.

[0012] As previously mentioned, embodiments of the set-delayed cement compositions may optionally comprise a dispersant Examples of suitable dispersants include, without limitation, sulfonated- formaldehyde-based dispersants (e.g.. sulfonated acetone formaldehyde, condensate), examples of which may include Daxad*^' 19 dispersant available from Geo Specialty Chemicals, Ambler, Pennsylvania. Other suitable dispersants may be polycarboxylated ether dispersants such as Liqiti.menf* 558 IP and IJquimeni* 5141., dispersants available from BASF Corporation Houston, Texas; or Eihacryi'^'''* G dispersant available from Coatex, Genay, France. An additional, example of a suitable commercially available dispersant is CFR.'^M-3 dispersant, available from Halliburton Energy Services, Inc, Houston, Texas. The Liquimenf* 514L dispersant ma comprise 36% by weight of the polycarboxylated ether in water. While a variety of dispersants ma be used in accordance with embodiments, poiycarboxyiated ether dispersants may be particularly suitable for use in some embodiments. Without being limited b theory, it is believed that poiycarboxyiated ether dispersants may synergisticalfy interact with other components of the set-deiayed cement composition. For example, it is believed that the poiycarboxyiated ether dispersants ma react with certain set retarders (e.g., phosphorite acid derivatives) resulting in formation of a gel that suspends the pumice and hydrated lime in the composition for an extended period of time.

[0013] in some embodiments, the dispersant may be inciuded in the set-delayed cement compositions in an amount in the range of from about 0.01 % to about 5% by weight of the pumice. In 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 for a chosen application.

1001 Other additives suitable for use in subterranean, cementing operations also may be included in embodiments of the set-delayed ceraent compositions. Examples of such additives include, but are not limited to: weighting- agents, lightweight additives, gas- generating additives, mechanical-property-en^'hancing additives, lost-circulation materials, filt ation-controi additives, fmid-loss-control additives, defoaming agents, foaming agents, ihixotropic additives, and combinations thereof. In embodiments, one or more of these additives may be added to the set-delayed cement compositions after storing but prior to the placement of a 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.

[0015] Those of ordinary skill in the art will appreciate that embodiments of the set- delayed ceraent compositions generally 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 from about 4 pounds per gallon. fib gaT) to about 20 lb/gal. In certain embodiments, the set-delayed cement compositions may have a density in the range of from about 8 Ib gal to about 17 Ib/gal, Embodiments of the set-delayed cement compositions may be foamed or un foamed or may comprise other means to reduce their densities, such as hollow microspheres, low-density elastic beads, or other density-reducing additives known in the art. in embodiments, the density may be reduced after storing the composition, bu prior to placement in a subterranean formation. Those of ordinary skill in the art, with the benefit of this disclosure, will recognize the appropriate density for a particular application.

[0016] As previously mentioned, the set-delayed cement compositions may have a delayed set in that they remain in a pumpable fluid state for at least one day (e.g., at least about I day, about 2 weeks, about 2 years or more) at room temperature (e.g., about. SO* F) in quiescent storage. For example, the set-delayed cement compositions may remain in a pumpable fluid state for a period of time from about i day to about 7 days or more, in some embodiments, the set-delayed cement compositions may remai n in a pumpable fl u id state tor 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 where the fluid has a consistency of less than 70 Bearden units of consistency ("Be"), as measured on a pressurized consistoraeter in accordance with the procedure for determining cement thickening times set forth in API RP Practice 10B-2, Recommended Practice for ^'Testing Weil Cements, First Edition, July 2005.

10017] When, desired for use, embodiments of the set-delayed cement compositions may be activated (e.g., by combination with an activator) to 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, heavily retarded, or other cement, composition. By way of example, embodiments of the set-delayed cement compositions may be activated to form a hardened mass in a time period in the range of from about I hour to about 12 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/o inc luding any of about 1 day, about 2 days, about 4 days, about. 6 days, about 8 days, about 10 days, or about 12 days.

[0018] In 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 axiaiiy directed pushing forces.. The compressive strength may be measured at a 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 destructive or non-destructive methods. 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 and is reported in units of pound-force per square inch (psi). Non-destructive methods may employ a UCA'^*' ultrasonic cement analyzer, available from Farm Instrument Company. Houston, TX. Compressive strength values may be determined in accordance with API RP 108-2, Recommended Practice for Testing Well Cements, First Edition, July 2005.

[0019] By way of example, the set-delayed cement compositions may develop a 24- hour compressi ve strength in the range of from about 50 psi to about 5000 psi, alternatively, from about 100 psi to about 4500 psi, or alternatively from about 500 psi to about 4000 psi. In some embodiments, the set-delayed cement compositions may develop a compressive strength in 24 hours of at least about 50 psi, at least about 100 psi, at least about 500 psi, or more. In some embodiments, the compressive strength values may he determined using destructive or non-destructive methods at a temperature ranging from 100°F to 200^fT,

[0020] In some embodiments, the set-delayed cement compositions may have desirable thickening times after activation. Thickening time typically refers to the time a fluid, such as a set-delayed cement composition, remains in a fluid state capable of being pumped. A number of different laboratory techniques may be used to measure thickening time. A pressurized consistonieter, operated in .accordance with the procedure set forth in the aforementioned API IIP ^'Practice I0B~2, may be used to measur whether a fluid is in a pumpable fluid state. The thickening time may be the time for the treatment fluid to reach 70 Be and may be reported as the time to reach 70 Be. in some embodiments, the cement compositions may have a thickening time of greater than about 1 hour, alternatively, greater than about 2 hours, alternatively greater than about 5 hours at 3,000 psi and temperatures in a range of from about 50°F to about 400^C'F, alternatively, in a range of from about 8Q°P to about 250°F, and alternatively at a temperature of about I 0°F.

[0021] Embodiments ma include the addition of a cement set activator to the set- delayed cement compositions. Examples of suitable cement set activators include, but are not limited to: zeolites, amines such as triethanolamine, diethanolamine; silicates such as sodium silicate; zinc formate; calcium, acetate; Groups IA and ISA hydroxide such as soclium hydroxide, magnesium hydroxide, and calcium hydroxide; monovalent salts such a sodium chloride; divalent salts such as calcium chloride; anosilica ( i.e., silica having a particle size of less than or equal to about 100 nanometers); polyphosphates; and combinations thereof, in some embodiments, a combination of the polyphosphate and a monovalent salt may be used, for activation. The monovalent salt 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, and sodium sulfate. A variety of different polyphosphates may be used in combination with the monovalent salt for activation of the set-delayed cement compositions, including polymeric metaphosphate salts. phosphate salts, and combinations thereof. Specific examples of polymeric metaphosphate salts that may be used include sodium hexametaphosphate, -sodium trimetaphosphaie. sodium tetrametaphosphate, sodium peniametaphosphate, sodi urn heptametaphosphafe, sodium octametaphosphate, and combinations thereof. A. specific example of a suitable cement set activator comprises a combination of sodium, sulfate and sodium hexametaphosphate. In particular embodiments, the activator may be provided and added to the set-delayed cement composition, as a liquid additive, for example, a liquid additive comprising a monovalent salt, a polyphosphate, and optionally a dispersant.

[0022] Some embodiments may include a cement set activator comprising nanosiliea. A used herein, the terra "nanosiliea" refers to si lica having a particle size of less than or equal to about 100 nanometers ("nm"). The size of the nanosiliea may be measured using an suitable technique. It should be understood that the measured size of the nanosiliea may vary based on measurement technique, sample preparation, and sample conditions such as temperature, concentration, etc. One technique for measuring the particle size of the nanosiliea is Transmission Electron Microscopy (TE ), An example of a commercially available product based on laser diffraction is the ZETASSZB Nano ZS particle size analyzer supplied by Mai vera Instruments, Worcestershire, UK, In some embodiments, the nanosiliea ma comprise colloidal nanosiliea. The nanosiliea may be stabilized using any suitable technique, in some embodiments, the nanosiliea ma be stabilized with a metal oxide, such as lithium oxide, sodium oxide, potassium oxide, and/or a combination thereof. Additionally the -nanosiliea may be stabilized with an amine and/or a metal oxide as mentioned above, Embodiments of the nanosilicas have an additional advantage in that they have been known to fill in pore space hi cements which can result in superior mechanical properties in the cement after it has set.

[00.23] Some embodiments ma include a cement set activator comprising a combination of a monovalent salt and a polyphosphate. The monovalent 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 may be an salt that dissociates to form a monovalent cation, such as sodium, and potassium salts. Specific examples of suitable monovalent salt include potassium sul fate and sod ium sul fate, A variety of different polyphosphates may be used in combination with the monovalent salt for activation of the set-delayed cement compositions, including polymeric metaphosphate salts, phosphate salts, and combinations thereof, for example. Specific examples of polymeric metaphosphate salts that ma be used include sodium hexametaphosphate, sodium trimetaphosphate, sodium tetrametaphosphate, sodium pentametaphosphate, sodium heptametaphosphate, sodium octametaphosphate, and combinations thereof. 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 of Portland cements. Because of the unique chemistry of polyphosphates, polyphosphates may be used as cement set activator for embodiments of the set-delayed cement compositions disclosed herein. The ratio of the monovalent salt to the polyphosphate may range, for example, from about 5:1 to about 1 :25 or from about 1: to about i : 10. Embodiments of the cement set activator may comprise the monovalent salt and the polyphosphate salt in a ratio {monovalent salt to polyphosphate) ranging betwee any of and/or including any of about 5: 1 , 2:1, about 1 : 1. about 1 :2» about 1 :5, about 1 : 10, about 1 :20, or about S. :25.

[0024] hi some embodiments, the combination of the monovalent salt and the polyphosphate may be mixed with a dispersant and water to form a liquid additive for activation of a set-delayed cement composition. Examples of suitable dispersants include, without limitation, the previousl described dispersants, such as suJf naied-formaldehyde- based dispersants and polyearboxylated ether dispersants, One example of a suitable sulfpnated-formaldehyde-based dispersant is a sulfonated acetone -formaldehyde condensate, available from Halliburton Energy Services, Inc., as CF -3"' dispersant. One example of a suitable polyearboxylated ether dispersant is Liquiment* 514L or 558 I F dispersants, available from BASF Corporation, Houston, Texas.

[0025] The liquid additive may function as a cement set activator. As discussed above, a cement set activator may also accelerate the setting of the set-delayed or heavily retarded cement. The use of a liquid additive to accelerate a set-delayed or heavily retarded cement is dependent upon the compositional makeup of the liquid additive as well as the compositional makeup of the set-delayed or heavily retarded cement. With the benefit of this disclosure, one of ordinary skill in the art should be able to formulate a liquid additive to activate and/or accelerate a set-delayed or heavily retarded cement composition,

[0026] The formulation of the liquid additive is a delicate balance that correlates with the specific compositional makeup of the set-delayed cement composition. The amount of the monovalent salt and the polyphosphate must be carefull balanced in relation to the dispersant. A liquid additive with an irregular mixture of components may lead to a set- delayed cement composition: with less than optimal theology, in some embodiments, the liquid additive may be added to the set-delayed cement composition in an amount of from about 1% to about 20% by weight of the set-delayed cement composition and, alternatively, from about 1% to about 0% by weight of the set-delayed cement composition. [0027] The monovalent salt may be present in the liquid additiv in an amount of about 0. % to about 30% by weight of the liquid additive. In specific embodiments, the polyphosphate may be present in an amount ranging between any of and/or including an of about 0.1 %, about ί .0%, about 10%, or about 30% by weight of the liquid additive. With the benefit of this disclosure, one of ordinary skill in the art should be able to formulate a liquid additive with a .sufficient amount of polyphosphate for a .specific application.

[0028] The polyphosphate may ^'be present in the liquid additive in an amount of about 0.1 % to about 30% by weight of the liquid additive. In specific embodiments, the polyphosphate may be present to an amount ranging between any of and/or including any of about 0.1 %, about 1.0%, about 10%, or about 30% by weight of the liquid additive. With the benefit of this disclosure, one of ordinary skill in the art should be able to formulate a liquid additive with a sufficient amount of polyphosphate for a specific application.

[0029] The dispersant may be present in the liquid additive in an amount of about 0.1 % to about 90% by weight of the liquid additive. In specific embodiments, the dispersant mav be present in an amount r nging between anv of and/or including anv of about 0.1 %, about ! %, about 50%, or about 90% by weight of the liquid additive. With the benefit of this disclosure, one of ordinary skill in. the art should be able to formulate a liquid additive with a sufficient amount of dispersant for a specific application.

[0030] The water may be present m the liquid additive in an amount of about 50% to about 90% by weight of the liquid additive. In specific embodiments, the water may be present in an amount ranging between any of and/or including any of about 50%, about 60%, about 75%, or about 90% by weight of the liquid additive. With the benefit of this disclosure, one of ordinary skill in the art should be able to formulate a liquid additi ve with a sufficient amount of water for a speci fic application.

[0031 ] in accordance with embodiments, the component ratio of the liquid additive may be relati ve to the makeup of the set-delayed cement composition. Whereby the amounts of the monovalent salt, polyphosphate, and the dispersant are therefore a function, of the amounts of the lime, pumice, and sum total of the water (i.e. the water in the set-delayed cement composition and any water in the liquid additive) used in the activated cement composition.

[0032] Without being limited by theory, the main limitations in the formulation of the liquid additive are the solubility limits of the monovalent salt and the polyphosphate; and the amount of di persant necessary to provide the cement with an acceptable rheokigy. The solubility limit is innate to the chosen monovalent salt and polyphosphate and therefore not alterable; however, the amount of dispersant is linked to the amounts of the monovalent salt and polyphosphate. The amounts of the monovalent salt polyphosphate and the dispersant are m a psendo direct relationship, whereb in a balanced formulation increasing the amount of one requires an increase in the amount of the other to maintain a balanced composition. For example, if the monovalent salt and the polyphosphate amounts are increased, the dispersant must also be increased or the cement composition will be too thick to pump. On the contrary, if the dispersant amount is increased, the cement composition will be too thin and the solid particulates may settle out of solution unless the amounts of the monovalent sail and the polyphosphate are also increased.

[0033] In some embodiments, the liquid additive should provide for a thickening time at wellborn conditions of greater than about 1 hour, alternatively, greater than about 2 hours, alternatively greater than about 5 hours, in some embodiments, the liquid additive may provide a thickening time at welihore conditions of about four to about six hours. As described above, thickening time typically refers to the time a fluid, such as a cement composition, remains in a fluid state capable of being pumped. The liquid additi ve affects the rheology of the cement composition. Therefore, a liquid additive .may affect the pump time of a cement. If cement rheology is not optimal the activated cement. composition may be too thick, or too thin, and therefore would be unsuitable for the desired pump time.

[0034] in some embodiments, the liquid additive may provide a set-delayed or heavily retarded cement, with desirable 24-hour mechanical properties. Desirable, mechanical properties include 24 hour compressive strength that i greater than 250 psi, a uniform density (i.e. no settling), and the absence of any free fluid.

[0035] Without being limited b theory, a description of a mechanism for activation of a lime and pumice set-delayed cement composition using a set-delayed cement activator comprising a combination of sodium sulfate and sodium hexametaphosphate is provided. It is believed that the sodium sulfate produces sodium hydroxide upon reaction with the lime. This reaction causes a resul ting rise in the pH of the slurry and consequently an increase in the rate of dissolution of silicon dioxide. Cement hydration rate has a direct relationship with the proportion of free silicates and/or aluminosilicates. Sodium he_.xametaphosphate chelates and increases the dissolution rate of calcium hydroxide. The combination of sodium sulfate and. sodium hexametaphosphate creates a synergy in various compositions of set-delayed cement compositions that provides better results than the singular use of either cement set activator.

[0(136] The cement set activator may be added to embodiments of the set-delayed cement composition in an amount sufficient to induce the set-delayed cement composition to set into a hardened mass, in certain embodiments_* the cemen set activator may be added to the set-delayed cement composition in an amount in the range of about 0,1% to about 20% by weight of the pumice, in .specific embodiments, the cement set acti vator ma be present in an. amount ranging between any of and/or including any of about 0.1%, abo u t }.%, abou t 5%, about 10%, about 15%, or about 20 by weight of the pumice. One of ordinary skill in the art, with the benefit of this disclosure, will recognize the appropriate amount of cement set activator to include tor a chosen application,

[0037] As will be appreciated by those of ordinary skill in the art, embodiments of the set-delayed cement compositions may be used in a variety of subterranean operations, including primar and remedial cementing. In 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 introduced into a 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 welibore drilled into the subterranean formation, into a near welibore region surrounding the welibore, or into both. Embodiments may further include activation of the set-delayed cement composition. The activation of the set-delayed cement composition may comprise, for example, the addition of a cement set activator to the set-delayed cement composition.

[0038] in 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, for example, in a vessel or other suitable container. The set-deiayed 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 1 day or longer. For example, the set-delayed cement composition may remain in storage for a time period of about 1 day, about .2 days, about 5 days, about 7 days, about 10 days, about 20 days, about 30 days, about 40 days, about 50 days, about 60 days, or longer, in some embodiments, the set-delayed cement composition may remain in storage for a time period hi 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.

[0039] in primary cementing embodiments, for example, embodiments of the set- deiayed. cement composition may be introduced into an annular space between a conduit located in a welibore and the walls of a welibore (and/or a larger conduit in the welibore), wherein the welibore penetrates the subterranean formation. The set-delayed cement composition may be allowed to set in the annular space to form an annular sheath of hardened cement. The set-delayed cement composition may form a barrier that prevents the migration of fluids in the wellbore. The set-delayed cement composition may also, for example, support the conduit in. the wellbore.

[0040] In remedial cementing embodiments, a set-delayed cement composition may be used, for example, in squeeze-cementing operations or i the placement of cement plugs. By way of example, the set-delayed composition may be placed in a well^'bpre to plug an opening (e.g., a void or crack) in the formation, in a gravel pack, in the conduit, in the cement sheath, and/or between the cement sheath and the conduit (e.g., a microannulus).

[004.1 ] An embodiment comprises a method of cementing comprising: providing a set-delayed cement composition comprising water, pumice, bydrated Si me, and a set retarder; activating the set-delayed cement composition with a liquid additive to produce an activated cement composition, wherein the liquid additive comprises a monovalent salt, a polyphosphate, a dispersant, and water; and allowing the activated cement composition to set

[0042] An embodiment comprises an activated cement composition comprising: water; pumice; bydrated lime; a set retarder; monovalent salt; and a polyphosphate.

[0043] An embodiment comprises a cementing system comprising: a set-delayed cement composition comprising; water, pumice, hydra ted lime, and a set retarder; and a liquid additive for -activation of the set-delayed cement composition comprising: water, a monovalent salt, a polyphosphate, and a. dispersant.

[0044] Referring now to FIG. I , the preparation of a set-delayed cement composition in accordance with example embodiments will now be described, FIG. 1 illustrates a system 2 for the preparation of a set-delayed cement composition and subsequent delivery of the composition to a wellbore in accordance with certain embodiments. As shown, the set-delayed cement composition may be mixed in mixing equipment 4, such as a jet mixer, re-circulating mixer, or a batch, mixer, for example, and then pumped via pumping equipment 6 to the wellbore. In some embodiments, the mixing equipment 4 and the pumping equipment 6 may be disposed on one or more cement tracks a will be apparent to those of ordinary skill in the art In some embodiments, a jet mixer may be used, for example, to continuously mix the !ime/settable material with the water as it is being pumped to the wellbore. In set-delayed embodiments, a re-circulating mixer and/or a batch mixer may be used to mix the set-delayed cement composition, and the activator may be added to the mixer as a powder prior to pumping the cement composition downhole. Additionally, batch mixer type units for the slurry may be plumbed in line with separate tank containing

I S a cement set activator. The cement set activator may then be fed in-line with the slurry as it is pumped out of the mixing unit.

[0045] An example technique for placing a set-delayed cement composition into a subterranean formation will now be described with reference to FIGS. 2A and 2B. FIG. 2A illustrates surface equipment 10 that may be used in placement of a set-delayed cement composition in accordance with certain embodiments, li should be noted that while FIG. 2A generally depicts a land-based operation, those skilled in the art will readily reeognke that the principles described herein are equally applicable to subsea operations that employ ^•floating or sea-based platforms and rigs, without departing from the scope of the disclosure. As illustrated by FIG. 2 A, the surface equipment 10 may include a cementing unit 12, which may include one or more cement trucks. The cementing unit 12 may include mixing equipment 4 and pumping equipment 6 (e.g., FIG. 1) as will be apparent to those of ordinary skill in the art. The cementing unit 12 may pump a set-delayed cement composition 14 through a feed pipe 16 and to a cementing head 18 which conveys the set-delayed cement composition 14 downho!e.

[0046] Turning now to FIG. 2B, the set-delayed cement composition 14 may be placed into a subterranean formation 20 in accordance with example embodiments. As illustrated, a wellbore 22 may be drilled into the subterranean formation 20. While wellbore 22 is shown extending generally vertically into the subterranean formation 20, the principles described herein are also applicable to weilbores that extend at aft angle through the subterranean formation 20, such as horizontal and slanted weilbores. As illustrated, the wellbore 22 comprises walls 24. in the illustrated embodiment, a surface casing 26 has been inserted into the wellbore 22. The surface casing 26 may be cemented to the walls 24 of the wellbore 22 b cement sheath 28, in the illustrated embodiment, one or more additional conduits (e.g., intermediate easing, production casing, liners, etc.), shown here as casing 30 may also be disposed in the wellbore 22. As illustrated, there is a wellbore annulus 32 formed between the casing 30 and. the walls 24 of the wellbore 22 and/or the surface casing 26. One or more centrahzers 34 may be attached to the easing 30, for example, to centralize the casing 30 in the wellbore 22 prior to and during the cementing operation.

[0047] With continued reference to FIG. 2B, the set-delayed cement composition 14 may be pumped down the interior of the casing 30. The set-delayed cement composition 14 may be allowed to flow down the interior of the casing 30 through the casing shoe 42 at the bottom of the casing 30 and up around the casing 30 into the wellbore annulus 32. The set- delayed cement composition 14 may be allowed to set in the wellbore annulus 32, for example, to form a cement sheath thai supports and positions the casing 30 in the wellbore 22. While not illustrated, other techniques may also be utilized for introduction of the set- delayed cement composition 1 , By way of example, re verse circulation techniques may be used that include introducing the set-delayed cement composition 14 into the subterranean formation 20 by way of the wellbore annulus 32 instead of through the casing 30,

[0048] As it is introduced, the set-delayed cement composition 14 may displace other fluids 36, such as drilling fluids and/or spacer fluids that may be present in the interior of the casing 30 and/or the wellbore annulus 32. At least a portion of the displaced fluids 36 may exit the wellbore annulus 32 via a flow Sine 38 and be deposited, for example, in one or more retention pits 40 (e.g., a mud pit), as shown on FIG. 2.A. Referring again to FIG. 2B, a bottom plug 44 may be introduced into the wellbore 22 ahead of the set-delayed cement composition 1 , for example, to separate the set-delayed cement composition 14 from the fluids 36 thai may be inside the easing 30 prior to cementing. After the bottom plug 44 reaches the landing collar 46, a diaphragm: or other suitable device should rupture t allow the set-delayed cement^' composition 14 through the bottom plug 44, In FIG, 26, the bottom plug 44 is shown on the landing collar 46. In the illustrated embodiment, a top plug 48 ma be introduced into the wellbore 22 behind the set-delayed cement composition 14. The top plug 48 may separate the set-delayed cement composition 1 from a displacement fluid 50 and al o push the set-delayed cement composition 14 through the bottom plug 44.

[0049] The exemplary set-delayed cement compositions disclosed herein may directly or indirectly affect one or more components or pieces of equipment associated with 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 units, composition separators, heat exchangers, sensors, gauges, pumps, compressors, and the like used generate, store, monitor, regulate, and/or recondition the exemplary set-delayed cement compositions. The disclosed set-delayed cement compositions may also directly or indirectl 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 compositional ly move the set-delayed cement compositions from one location to another, any pomps, 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 flow rate of the set-delayed cement compositions, and any sensors (i.e., pressure and temperature), gauges, and/or combinations thereof, and the like. The disclosed set-delayed 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, sliekhne, wireline, drill pipe, drill collars, mud motors, downhole motors and/or pumps, cement pumps, surface-mounted motors and/or pumps, centralism, turbolixers, scratches, floats (e.g., shoes, collars, valves, etc.), logging tools and related telemetry equipment, actuators (e.g., electromechanical devices, hydrcmiechanfcal devices, etc.), sliding sleeves, production sleeves, plugs, screens, filters, flow control devices (e.g., inflow control devices, autonomous inflow control devices, outflow control devices, etc.), couplings (e.g., electro-hydraulic 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.

[0050] To facilitate a better understanding of the present embodiments, the following examples of certain aspects of some embodiments are given, in no way should the following examples be read to limit, or define, the entire scope of the embodiments.

EXAMPLES

Example 1

[0051 ] The following example describes an. example liquid additive composition, for use with an example set-delayed cement composition. For this example, the liquid additive was added to the set delayed cement composition in the amount of 8% of the total mass of the combined bydrated lime and pumice. After activation, the activated set-delayed cement composition had a thickening time of 5.5 hours at 100T. The thickening time was measuring using a pressurized consistometer at ί 00 F in accordance with the procedure for determining cement thickening tiroes set forth in. API RP Practice I OB-2, Recommended Practice fi)r Testing Weil Cements, First Edition, July 2005. As discussed above, varyin ihe concentration, of the dispemnt without adjusting the monovalent salt and polyphosphate to compensate may produce an activated slurry with less than optimal rbeology and may alter the thickening time.

[0052] The example set-delayed cement composition comprised water; DS-325 lightweight aggregate pumice, available from Hess Pumice Products, inc., Malad, Idaho; hydrated lime; Liquiment 558 IF* dispersant, available from BASF Corporation, Houston, Texas; and Micro Matrix* cement retarder (M.MCR), available from Halliburton Energy Services, Inc., Duncan, Oklahoma. The compositional makeup is presented in Table 1 below. The amounts listed in Table 1 are .shown as a percentage by weight of the pumice.

Table 1

Example Set-De!ayed Cement Composition

j Component % by weight of pumice

Water j 60

Pumice j 100

tiydrated Lime j 20

J Dispersant j 0.7

I Retarder 1 1.26 [0053] Hie example liquid additive comprised water, a monovalent (sodium sulfate), a polyphosphate, (sodium hexametaphosphate), and Liquiment 5583 dispersant. The compositional makeup is presented in Table 2 below. The amounts listed are shown as a percentage of the total composition of the liquid additive.

Table 2

Example Liquid Additive

Example 2

[0054] In this example, a series of six liquid additive samples were prepared for use with an example set-delayed cement composition. The composition for the set-delayed cement composition is presented in Table 3 below. In Table 3, "%bwP" stands for "percentage by weight of pumice" and "gal/sk" stands for "gallons per sack 46 lb. sack of pumice," The liquid additive comprised water, a monovalent salt (sodium sulfate), a polyphosphate (sodium hexametaphosphate), and Liquiment 558 I F* dispersant The water, monovalent salt, and polyphosphate amounts were held constant as shown in Table 4 below. The dispersant concentration was varied each of the six samples as shown in Table 5 below. The liquid additive from Table 4 was added to the set-delayed cement composition from Table 3 such that the liquid additive comprised 10% of the combined weight of the set- delayed cement composition and the liquid additive- Table 3

Example Set-Delay d Cement Composition

Table 4

Example Liquid Additive

[0055] The dispersant amounts varied from, a rang of 0.00% to 4.3%, The rheoiogy of the slurries also varied based on the amount of dispersant present since the monovalent salt and polyphosphate amounts were held constant. To reiterate, the dispersant amount is a percentage of the total activated composition. After preparation, the rheological properties of the samples were determined using a Model 35 A Farm Viscometer and a No. 2 spring with a Fann Yield Stress Adapter, in accordance with the procedure set forth in API RP Practice 108-2, Recommended Practice- for Testing Well Cements, The data is presented in Table 5 below. The theological data shown in Table 5 are apparent viscosity values measured at a hear rate of 100 f I /sec). Table 5

Dfepersant Amount vs. Rheo!ogy

[0056] Example 2 illustrates that varying the dispersam amount,, without compensating by adjusting the monovalent salt and the polyphosphate amounts, may create slurries with less than optimal theologies.

[0057] Slurry Sample I from Table 5 was unworkable and was not poumble. Archimedes tests were performed for the remaining 5 slurries. In order to do the Archimedes tests, each of the samples was poured into 2" x 4" cylinders and left to set at i40^i>F lor 24 hours. The set samples were then cut into three equally spaced parts along the length of the cylinders. Using the Archimedes principle of density and displacement, the densities of the samples were determined and recorded in unite of lb/gal. The results are presented in Table 6 below.

Table 6

Sample Density Measurements

[0058] Samples 2-5 had no significant settling issues. Sample 6 did display settling. In general, the more dispe.rsa.nt that is added, the less viscous the cement slurry will be. Sample 5 possessed the best slurry characteristics and would be the optimal choice compared to the other 5 samples on this measure alone. The other slurries could potentially be optimal when such factors as cost and early mechanical strength development are taken, int account. Exam le 3

[0059] The slurry composition presented in Table 3 above was used as an example set-delayed cement composition. The example liquid additive formulation, however, is different from the one presented in Table 4. Table 7 lists a new liquid additive formulation specific to this example.

Table 7

Example Liquid Additive

Component | Wt% of total sum of the watt it, 1

monovalent salt, and the ji

polyphosphate

Water | 87.5 |

Monovalent Salt | 6.25

Polyphosphate | 6.25

Dispersant | X | [0060] Table 8 depicts the different values for the dispersant described in Table 7.

Four different dispersant amounts were used. The dispersant concentration is a percentage of the total weight of the activated slurry. The dispersant amount ranged, from 0.0% to 4.3%, After preparation, the rheo!ogical properties of the samples were determined using a Model 35A Farm Viscometer and a No, 2 spring with a Fatm Yield Stress Adapter, in accordance with, the procedure set forth in API R.P Practice 10B~2, Recommended Practice for Testing Well Cements, The data is presented in Table 8 below. The rheologicai data shown in Table 8 are apparent viscosity vaiites measured at a shear rate of 100 (I /sec).

Table 8

Dispersant Amount vs. Rheology

Archimedes tests, each of the samples was cut into three equally spaced parts. Using the 7 Archimedes principle of density and displacement, the densities of the samples were determined and recorded in units of lb/gal. The results are presented, in Table 9 below.

Table 9

Densities of Samples Described in Table 8

0062] Significant settling occurred in Samples 9 and 1 0, representing 0.68% and. 4.3% dispersant respectively. In comparison with Example 2, this indicates that .reducing the amount of liquid additive added to the sample may also cause the optimum liquid additive dispersant concentration to change. Here the optimum concentration was 0.45% dispersant, whereas in the previous example the optimum concentration was 2.4%.

Example 4

[0063] in this example, the slurr described in Table 3 was used for the base composition. The liquid additive formulation is described in Table 10 below. The monovalent salt was sodium sulfate. The polyphosphate was sodium hexametaphosphate. The dispersant was Coatex 1.702, available from Coa.tex inc., Chester, South Carolina. As illustrated in Table 1 1 , the dispersant concentration varied from 0,45% to 8,33%,

Table 1Θ

Example Liquid Additive

Table ϊ Ϊ

Dispersant Concentration per Sample

[0064] in order to determine the effect of varying the dispersant concentration on the compressive strength of set samples, the compressive strength of each sample was measured after five days. The destructive compressive strength was measured by allowing the samples to core in a 2" by 4" plastic cylinder that was placed in a water bath at I 0°F to form set cylinders. Immediately after removal from the water bath, destructive compressive strengths were determined using a mechanical press in accordance with API P 10B-2, Recommended Practice for Testing Well Cements. The results of mis test are set forth below in Table 12, in units of psl The reported compressive strengths are an average for two cylinders, of each sample.

Table 12

Compressive Strength Tests

[0065] Varying the dispersant concentration had a direct impact on the compressive strength of the samples. This effect was stronger than the settling effect of adding dispersant. It therefore stands to reason that the dispersant can have an antagonistic effect on the sodium hexametaphosphate activation of the extended, life slurry when retarded, with the phosphonate, nitri!otrismediylenetriphosphonic acid.

[0066] Archimedes tests were performed for Samples 1 -5. Each of the samples was poured into 2" x 4" cylinders and left to set at 140T for five days. Th set samples were then cut into three equally spaced parts alon the length of the cylinders. Using, the Archimedes principle of density and displacement, the densities of the samples were determined and recorded. The results are presented in Tables 13-17 below, where PPG is the symbol for units of lb/gal.

Table 13

Sample I Archimedes Test

Volume (mL) Weight (g) Density (g/mL) Density (PPG)

Top 65.96 99.18 1 .5036 12.5

Middle j 60.55 1.12 1 .5049 12.5

Bottom j 64,29 96.45 .1 .5002 12.5

Table 14

Sample 2 Archimedes Test

j Volume (ml..} Weight (g) j Density (g mL) Density (PPG)

Top 54.31 81.58 1.5021 1 2.5

M iddle 67.38 100.97 1 .4985 12.5

Bottom j 54 J 8 81 ,53 j 1.5048 12.5

Table 15

Sample 3 Archimedes Test

Volume (mL) Weight (g) Density (g mL) Density (PPG)

Top j 60.56 90.98 j 1 .5023 12,5

Middle 57.44 85.84 j 1 .4944 12.4

Bottom 61.3 91.8 1 .4976 12.5

Table 16

St iiijple 4 Archimedes Test

Volume (mL) Weight (g) Density (g/mL) Density (PPG) j

Top 60,63 89.53 1 .4767 12.3

Middle | 58.83 87.83 ^r i .492 1 2.4

Bottom 62.12 93.05 1 .4979 12,5 Table 17

Sample 5 Archimedes Test

Volume (mh) Weight (g) ί Density (g/niL) Density (PPG) fop 1 64.04 94.09 j 1 .4692 j "'

Middle | 56.47 82.6 1 1.4627 j ( 2.2

Boitom. 1 59.5 87.91 ί 1 .4775 12.3

[0067] Samples 4 and 5 di splayed slight settling behavior.

Example 5

0068] In this example, ten sample liquid additives were prepared for use with, a set- delayed cement composition. The compositional makeup of the set-delayed cement composition is presented hi Table 18 below. The liquid additive comprised water, a monovalent salt in the form of sodium, sulfate, a polyphosphate in the form of sodium hexametaphosphate, and Liquiment 558 I F* dispersant. it should be noted that the percentages of the monovalent sail and the polyphosphate were held constant throughout the experiment while the dispersant concentration was varied. The compositio of the liquid additive is illustrated below in Tabic 1.9. All of the listed amounts are shown as a percentage of the total composition of the liquid additive. The liquid additive rom Table .1 was added to the set-delayed cement composition described in Table 18 such that the monovalent salt and polyphosphate were present, in the combined, amount of 1.25 % bwP or 1.00% bwP.

Table 1$

Example Set-Delayed Cement Composition

Table 19

Example Liquid Additive

Component j Wt% of total sum of the water, monovalent

salt and the polyphosphate

1 Water 81.59

1 Monovalent Salt [ 8.53

1 Polyphosphate [ 8,53

1 Dispersant j X

[0069] The dispersant amount varied from a range of 0.10% to 1.39%. The thickening time of the slurries varied based on the amount of dispersant, since the monovalent salt and polyphosphate were held constant.

[0070] The compressive; strength and thickening times of each sample were measured. The destructive compressive strength was measured by allowing the samples to cure in a 2^*' by 4" plastic cylinder that was placed in a water bath at 1 0°F to form set cylinders. Immediately after removal from the water bath, destructive compressive strengths were determined using a mechanical press in accordance with API RP 10B-2, Recommended Practice for Testing Well Cements. The results of this test are set forth in Table 20 below. The reported compressive strengths are an average for three cylinders of each sample.

TABLE 20

Pispersant Amount vs. Thickening l ime and Compressive Strength

[0071 ] Varying the dispersant concentration of the liquid additive allowed the thickening time of the set-delayed cement composition to be controlled. Thi added benefit was realized through the observation that the thickening time of the cement samples increased wiih increasing dispersant amount. For the liquid additive samples containing 1 ,25% bwP monovalent salt-polyphosphate, the relationshi is almost linear as shown in FIG. 3.

[0072] it should be understood thai the compositions and methods are described in terms of "comprising," "containing," or "including" various components or steps, the compositions and methods can also "consist essentially of or "consist of the various components and steps. oreover, the indefinite articles ⁱ⁴a" or "an." as used in the claims, are defined herein to mean one or more than one of the element that it introduces.

[0073] For the sake of brevity, only certain ranges are explicitly disclosed herein. However, ranges from any lower 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 lower limit to recite a range not explicitl recited, in the same way, ranges from 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 falling within the range are specifically disclosed. In particular, every range of values (of the form, "from about a to about b," or, equivalent^, "from approximatel a to b," or, eqiuvalentfy, "from approximately a-b") disclosed herein is to be understood to set forth ever number and range encompassed within the broader range of values even 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 lo wer or upper limit, to recite a range not explicitly recited.

[0074] Therefore, the present embodiments are 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 embodiments may be modified and practiced in different but equivalent manners apparent to those skilled in. the art having the benefit of the teachings herein. Although individual embodiments are discussed, all combinations of each embodiment are contemplated and covered by the disclosure. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. Also, the terms in the claims have their plain, ordinary meaning unless otherwise explicitly and clearly defined by the patentee, it is therefore evident that the particular illustrative embodiments disclosed above may be altered or modified and ail such variations are considered within the scope and spirit of the present disclosure. If there is any conflict in the usages of a word or term in this specification and one or more pateni(s) or other documents that ma be incorporated herein by reference, the definitions that are consistent with this specification should be adopted.

Claims

CLAIMS What is claimed is:

1. A method of cementing comprising:

providing a set-delayed cement composition comprising water, pumice, hydrated lime, and a set retarder;

activating the set-delayed cement composition with a liquid additive to produce an activated cement composition, wherein the liquid additive comprises a monovalent salt, a polyphosphate, a dispersant, and water; and

allowing the activated cement composition to set.

2. A method according to claim 1 wherein the liquid additive is added to the set-delayed cement composition in an amount of about 1% to about 20% by weight of the set-delayed cement composition,

3. A method according to claim I or 2 wherein the monovalent salt is present in the liquid additive in an amount of about 0.1% to about 30% by weight of the liquid additive, wherein the polyphosphate is present in the liquid additive in an amount of about 0.1 % to about 30% b weight of the liquid additive, wherein the dispersant is present in the liquid additive in an amount of about 0.1% to about 90% by weight of the liquid additive, and wherein the water is present in the liquid additive in an amount of about 50% io about 90% by weight of the hquid additive,

4. A method according to any of claims I to 3 wherein the polyphosphate comprises sodium hexametaphosphate,

5. A method according to any of claims 1 to 4 wherein the monovalent salt comprises sodium sulfate.

6. A method according to an of claims I to 5 wherein the dispersant comprises a. polycarboxylated ether.

7. A method according to any of claims 1 to 6 wherein the ratio of the monovalent salt to the polyphosphate is from about 5: 1 to a bom 1 :25.

8. A method according to an of claims 1 to 3 or 7 wherein the polyphosphate comprises sodium hexametaphosphate, the monovalent salt comprises sodium sulfate, and the dispersant comprises a polycarboxylated ether.

9. A method according to any of claim i to 8 wherein the set-delayed cement composition remains in a pumpable fluid state for a time period of about 4 hours to about 6 hours after acti vation.

10. A method accorditig to any of claims 1 to 9 further comprisin storing the set-delayed cement com position for a period of about 1 day or longer,

1 1. A method according to any of claims I to 10 further comprising introducing the activated cement composition into a subterranean formation.

12 , A method according to any of claims 1 to 1 1 further comprising pumping the activated cement composition through a conduit, through a casing shoe, and into a e!lbore annul us.

13, An activated cement composition comprising

water;

pumice;

hydrated !irae;

a set retarder;

a monovalent salt; and

a polyphosphate,

14. An activated cement composition according to claim 13 comprising one or more of the features defined in any one of claims 4 to 8.

15. A cementing system comprising:

a set-delayed cement ^'composition comprisi g:

water.

pumice,

hydrated lime, and

a sec retarder; and

a liquid additive for activation of the set-delayed cement composition comprising:

water,

a monovalent salt,

a polyphosphate, and

a dispersant.

16. A cementing system according to claim 15 wherein the ratio of the monovalent salt to the polyphosphate is from about 5: ί to about 1 :25,

17. A cementing system according to claim 15 or 16 wherein the polyphosphate comprises sodium hexametaphosphate.

1 8. A cementing system according to any of claims .15 to 17 wherein the monovalent salt comprises sodium sulfate, and wherein the dispersant comprises a polycarboxylated ether.

1 . A cementing system according to claim 15 or 16 wherein the polyphosphate comprises .sodium hexa.metaphosphate, the monovalent salt comprises sodium sulfate, and the dispersant comprises a po!ycarboxylated ether.

20. A cementing system accordi ng to any of claims 15 to 19 further comprising: mixing equipment for mixing the set-delayed cement composition and the liquid additive to produce an activated set-delayed cement composition; and

pumping equipment for delivering the activated set-delayed cement composition into a wellborn.