NO20160246A1 - Two-Part Set-Delayed Cement Compositions - Google Patents

Description

TWO-PART SET-DELAYED CEMENT COMPOSITIONS

RACKGROUND

[0001] The present embodiments retaté to subterranean cementing operations and, in eertain 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 exåmple, in subterranean well constructton, a pipe string (e.g., eaising, finers, expandable tubulars, etc.) may be run itito a wcllborc and cemented in place. The process of cementing the pipe siring in place is commønly referred to as ''primary cementing/<t>In a typieai primary cementing method, a cement composition may be pumped intø an annulus between the walls of the weitbore and the exterior surface of the pipe string disposed therein. the cement composition may set in the annular space, thereby tonning an annular sheath of hardened, substantially impermeabie cement (Le., a cement sheath) that may support and positkm the pipe string i ti the weitbore and may botid the exterior surface of the pipe string to the subterranean formation. Among other things, the cement sheath surrounding the pipe string prevents the røigration of fluids in the annulus and proteets the pipe string from corrosion. Cement compositions may also be used in remedial cementing methods to séai cracks or holes in pipe strings or cement sheaths, to seal highly perrøeable formation zones or tmetures, or to place a cement plug and the like.

[0003] A broad variety of cement compositions have been used in subterranean cementing operations. In some instances, set-delayed cement compositions have been used. Set-delayed cement compositions arecharacterized byremaining in a pumpable fluid state for at least about one day (e.g., about 7 days, about 2 weeks, about 2 years or more) at room temperaiure (e.g., about 80° F) in quiescent storage. When desired for use, the set-delayed cement compositions should be capable of activation and consequently develop reasonable compressive strengths. For example, a cement set activator may be added to a set-delayed cement composition to induce the composition to set intø a hardened mass, Among other thitt<gs>, set-delayed cement compositions may be suitable for use in wellhore applications such as applications where it is desirable to prepare the cement composition in advance. This may allow (he cement composition to be stored prior to use. ln addition, this may al lo w the cement composition to be prepared at a convenient location before tramportatkm to the job site. Accordingly, capita! expenditures may be reduced due to a reduction in the need for onsite bulk storage and mixing equipment. This may be particularly usefui tor offshore cementing operations where space onboard the vessels may be limited.

[0004] While set-delayed cement compositions have been deveioped heretofore, challenges exiist with their successiul use in subterranean cementing operations. For example, set-delayed cement compositions prepared with Portland cement may have undesired gelation issues which can limit their usse and effectiveness in cementing operations. Other set-delayed eompositiom that have been deveioped, for example, those comprising hydrated lime and quartz, may be effective in some operations but may have limited use at Iower temperatures as they may not develop sufticient compressive strength whcn used in subterranean formations håving Iower bottom hole static tempenuures. In addition, it may be problematic to activate some set-delayed cement compositions while maintainvng acceptable thickening times and compressive strength development.

BRIEF DESCR1PTION OF THE DRAWIN43S

[0001] These dra whigs illustrate cértam åspeets of stirae of the embodiments of the present method. Md should not be used to limit or define the method.

[0002] FIG. i illustrates a system for preparation and delivery of a set-delayed Scemenl composition to a wellbore in accordance with cerlain ernbodiments.

[0003] FIG. 2A illustrates surface equipment that may be used in piacement of a set-delayed cement composition in å wellbore in accordance with certain ernbodiments.

[0004] FIG. 2B iitustrates piacement of a set-delayed cement composition inio a wellbore annulus m accordance with certain embodirøents.

DESCRIPTION OF PREFERRED EMBOMMENTS

[0005] The example enrbodiments relate to subterranean cementing operations and, more partieuiarly, in certain ernbodiments, to set-delayed cement eornpositiøns and methods of using set-delayed cement compositions in subterranean fonnations.

[0006] Ernbodiments of the set-delayed cement compositions may generally comprise water, a pozzolan, and hydrated lime. Optionally, the cement compositions may further comprise a dispersant and/or a cement set retarder. Alternat i vely, ernbodiments of the set-delayed cement composition may comprise two-part set-delayed cement composition

■comprising separate component sl urries with one component slurry comprising a pozzolan and the other component slurry comprising lime. Ernbodiments of the two-part set-delayed cement compositions are discussed in detail below. Advantageously, ernbodiments 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 or longer. Advantageously, the set-delayed cement compositidns may develop reasonable compressive strengths after activation at reiativeiy low temperatures. While the set-delayed cement compositions may be suitable for a number of subterranean cementing operations, they may be partieuiarly suitable for use in subterranean formations håving reiativeiy low bottom hole static temperatures, e.g„ temperatures less than about 200° F or ranging from about 10QS F to about 200* F. ln alternative embodimentSjthe set-delayed cement compositions may be used in subterranean fonnations håving bottom hole static temperatures up to 450° F orhigher.

[0007] The water used in ernbodiments may be from any source provided that it dpes not eontain an excess of compounds that. may undesirabiy affect other eomponents in the set-delayed cement compositions. For example, a cement composition may comprise fresh water or salt water. Salt water generally may inciude one or more dissolved salts therein and may be saturated or unsaturated as desired for a particular application. Sea water or brines may be suitable for use in ernbodiments. Further, the water may be present in an amount sufficient to form a pumpabie slurry. ln certain ernbodiments, the water may be present in the set-delayed cement compositions in an amount in the range of from about 33% to about 200% by weight of the pozzolan. ln certain ernbodiments, the water may be present in the set-delayed cement compositions in m amount ln the range of from about 35% to about 70% by weight of the pozzolan. With the benefit of this disclosure one of ordinary skill in the art wUi recognfee the appropriate amount of water for a chosen application.

[0008] Ernbodiments of the set-delayed cement compositions may comprise a pozzolan. Any pozzolan Is suitable lor use in ernbodiments. Example ernbodiments comprising a pozzolan may comprise fly ash, si Hea fume, metakaoHn, a natura! pozzolan (e.g., pumice), or combinations thereof.

[0000] Ernbodiments of the pozzolan may comprise fly ash. Å variety of fly asnes may be suitable, ineluding fly ash classified as Class C and Class F fly ash according to American Petroleum Institute, API Spccifleation lor Materials and Testing for Wcll Cements, API Speeifleation 10, Fifth Ed., .fuly 1, 1990. Class C fly ash comprises both siiica and lime*so It may set to form a hardened mass upon mixing with water. Class F fly ash generally does not eontain a sufflcient amount of lime to induce a eementUious reaction, therefore, an additionai source of calcium ions is necessary for a set-delayed cement composition comprising Class F fly ash. In some ernbodiments, lime may be mixed with Class F fly ash in an amount in the range of about 0.1% to about 100% by weight of the fly ash. ln some irtstanees, the lime may be hydrated lime, Suitable examples of Hy ash includé, btit are not limited to, POZMIX* A cement additive, commercially available from Halliburton Bnergy Services, Inc., Houston, Texas. [001.0] Ernbodiments of the pozzolan may comprise metakaoHn. Generally, metakaolin is a white pozzolan that may be prepared by heating kaolin clay, tor example, to temperatures in the range of about 600° C to about 800° C.

[0011] Ernbodiments of the pozzolan may comprise a natura! pozzolan. Natura! pozzolans are generally present on the BaruYs surface and set and harden in the presence of hydrated lime and water. Ernbodiments comprising a natural pozzolan may comprise pumice, diatomaceous earth, volcanic ash, opaline shak, tuff, and combinations thereof. The natural pozzolans may be ground or unground. Generally, the natural pozzolans may have any partiele size distribution as désired for a particular application. In certain embodimérits, the natural pozzolans may have a mean partiele size in a range of from about i micron to about 200 microns. The mean partiele size corresponds to d50 values as measured by partiele size analyzers such as those manufactured by Mal vern fnsimmenis, Worcestershire, United Kingdom. In specifk ernbodiments, the natural pozzolans may have a mean partiele size in a range of from about 1 micron to about 200 micron, from about 5 microns to about 100 microns, or from about 10 micrøn to about 50 microns. In one particular embodiment the natura! pozzolans may have a mean partiele size of less than about 15 microns. An example of a suitable commerctal natura! pozzolan is pumice available from Hess Pumice Products, Inc., Mal ad, Idaho, as DS-325 Ught weight aggregate, which has a partiele size of less than about 15 microns. It should be appreciated that partiele sizes too small may have mixability problems while partiele sizes too large may not be effectively suspended in the compositions and may be less reactive due to their decreased surface area. One of ordinary skill in the art, with the benefit of this disclosure, should bé able to select a partiele size for the natura! pozzolans suitable for use for a chosen application.

[0012] Ernbodiments of the set-delayed cement compositions may comprise hydrated lime. As used herein, the term "hydrated lime" will be understood to mean eafeiurø hydroxide. in some ernbodiments, 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 inciuded in ernbodiments, for example, to form a hydrauiic composition with the pozzolan. For example, the hydrated lime may be inciuded in a pozzolan-to-hydrated-lirøe weight ratio of about 10:1 to about 1:1 or a ratio of about 3:1 to about 5:1. Where present, the hydrated lime may be inciuded in the set-delayed cement compositions in an amount in the range of from about 10% to about 100% by weight of the pozzolan, for example, ln some ernbodiments, the hydrated l ime may be present in an amount ranging between any of and/or ineluding any of about 10%, about 20%, about 40%, about 60%, about 80%, or about 100% by weight of the pozzolan. ln some ernbodiments, the cementitious components present in the set-delayed cement composition may consist essentially of the pozzolan and the hydrated lime. For example, the cementitious components may primarily comprise the pozzolan and the hydrated lime without any additlpna! cementitious components (e.g., Portland cement) that hydraulieally set in the presence of water. One of ordinary skil! in the art, with the benefit of this disclosure, wii! recognize the appropriate amount of hydrated lime to include for a chosen application.

[0013] Ernbodiments of the set-delayed cement compositions may comprise a cement set retarder. A broad variety of cement set retarders may be suitable for use iti the set-delayed cement compositions. For example, the cement set retarder may comprise phosphonic acids, such as ethylenediamine tetra(methylene phosphonic acid), diethylenetriamine penta(methylene phosphonic acid), etc; lignosulfønales, such as sodiurn lignosultbnate, calcium iignosulfonate, ete.; salts such as stannous sulfate, lead acetate, monobasie calcium phosphate, organie acids, such as citric acid, tartaric acid, etc; cellulose derivatives such as hydroxyl ethyt cellulose (MEC) and carboxymethyl hydroxyethyl cellulose (GMHEC); synthetic co- or ter-poiytners comprising sulfonate and carboxylic acid groups such as sulfonate-functionalized acrylamide-acrylic acid co-polymers; borate compounds such as alkali borates, sodium metaborate, sodtum tetraborate, potassium pentaborate; derivatives thereof, or mixtures thereof. Examples of suitable cement set retarders include, among others, phosphonic acid derivatives. One example of a suitable cement set retarder is Micro Matrix* cement retarder, available from Halliburton Energy Services, Inc. Generally, the cement set retarder may be present in the set-delayed cement compositions in ah amount sufficient to delay the setting for a desired time. In sonte ernbodiments, the cement sét retarder may be present in the set-dela<y>ed cement compositions in an amount in the range of from about 0.01% to about 10% by weight of the pozzolan. ln specific ernbodiments. the cement set retarder may be present in an amount ranging between any of and/or ineluding any of about 0.01%, about 0.1%, about 1%, about 2%, about 4%, about 6%, about 8%, or about 10% by weight of the pozzolan. One of ordi nary skill in the art, with the benefit of this disclosure, will recognize the appropriaié amount of the cement set retarder to include for a chosen application.

[0014] As previously mentioned, enrbodiments of the set-delayed cement compositions may optionally comprise a dispersant. Examples of suitable dispersants include, without limitation, su I fbnated-fbrmaldehyde-based dispersants (e.g., suitonated aeetone tbrmaldehyde eondensate), 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 Liquiment* 5581F and Liquintenf*514L dispersants available Irbm BASF Corporation Houston, Texas; or Ethaeryl™ G dispersant available from Coatéx, Genay, France. An additional example of a suitable commercialiy avaiiable dispersant is CFRv*'-3 dispersant, available from Halliburton Energy Services, Inc, Houston, Texas. The Liquimenf* 514L dispersant may comprise 36% by weight of the polycarboxylated ether in water. While a variety of dispersants may be used in accordance with ernbodiments, polycarboxylated ether dispersants may be partieuiarly suitable for use in some ernbodiments. Without being limited by theory, it is beliéved that polycarboxylated ether dispersants may synergistically interact with other componentsbf the set-delayed cement composition. For example, it is believed that the polycarboxylated ether dispersants may react with certain cement: set retarders (e.g., phosphonic acid derivatives) resulting in formation of a gel that suspends the pozzolan and hydrated lime in the composition for an extended period of time.

[0015] In some ernbodiments, the dispersant may be inciuded in the set-delayed cement compositions In an amount in the range of trom about 0.01% io about 5% by weight of the pozzolan. lii speeiflc ernbodiments, the dispersant may be present in an amount ranging between any of and/or ineluding 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 pozzolan. 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.

[0016] Some ernbodiments of the set-delayed cement compositions may comprise siliea sources in addition to the pozzolan; for example, erystalline silica and/or amorphous silica. Crystalline si Hea is a powder that may be inciuded in ernbodiments of the set-delayed cemeni compositions, før example, to prevent cement compressive strength reirogressioh. Amorphous silica is a powder that may be inciuded in ernbodiments of the set-delayed cement compositions as a lightweight filler and/or to inerease cement compressive strength. Amorphous silica Is generally a byproduct of a férrosilicon production process, wherein the amorphous silica may be formed by oxidation and condensation of gaseous silicon suboxide, SiO, which is formed as an intermediate during the process. An example of a suitable source bf amorphous silica is Siliealite'* cement additive available from Halliburton Energy Services, Inc., Houston, Texas. Ernbodiments comprising additional silica sources may utilize the additional silica source as needed to enhance compressive strength or set times.

[0017] Other additives suitable for use in subterranean cementing operations also may be inciuded in ernbodiments of the set-delayed cement compositions. Examples of such additives include, but are not limited to; weighting agents, lightweight additives, gas-generating additives, mechanical-property-enhancing additives, lost-circulation materials, fiitration-contrøl additives, fjuid-ioss-eonirol additives, defoaming agents, foaming agents, thixotropic additives, and combinations thereof. In ernbodiments, one or more of these additives may be added to the set-delayed cement compositions after storing but prior to the piacement of a set-delayed cement composition intø a subterranean formation. A person håving ordinary skil! in the art, with the benefit of this disclosure, should réadily be able to determine the type and amount of additive useful for a particular application and desired result.

[0018] Those of ordinary skill in the art will appreciate that ernbodiments of the set-delayed cement compositions generally should have a dénsity suitable for a particular application. By way of example. the cement compositions may have a density in the range of trom about 4 pounds per gallon ("Ib/gaV) to about 20 lb/gal. In certain ernbodiments, the cement compositions may have a density in the rangebf from about 8 lb/gal to about 17 Ib/gal. Ernbodiments of the set-delayed cement compositions may be foamed or unlbamed or may comprise other means to reduee their densities, such as hollow microspheres, low-density elastic beads, or other density-reducing additives known in the art. ln ernbodiments, the density may be reduced after storage, but prior to piacement in a subterranean formation, ln ernbodiments, weighting additives may be used to Inerease the density of the set-delayed cement compositions. Examples of suitable weighting additives may include barite, hematite, hausmannite, calcium carbonate, sideriie, ilmenite, or combinations thereof. In particular ernbodiments, the weighting additives may have a specific gravity of 3 or greater. Those of ordinary skill in the art, With the benefit of this disclosure, will recognize the appropriate density for a particular application.

[0019] As previously mentioned, the set-delayed cement compositions may have a delayed set in that they remain in a pumpabie fluid state for at least one dav (e.g., about 1 day, about 2 weeks, about 2 years or more) at room temperature (e.g., about BO<*>F) in quiescent storage. For example, the set-delayed cement compositions may remain in a pumpabie fluid state for a period of time from about 1 day to about 7 days or more. ln some ernbodiments, tise set-delayed cement compositions may remain in a pumpabie 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 eonsidered to be in a pumpabie fluid state where the fluid has a consistency of less than 70 Bearden units of consistency ("Be"), as measured on a préssurized consistbmeter in accordance with the proeedure for determining cement thickening times set forth in API RF Practice 10B-2, Reeommended Practice for festing Weli Cemenis, First Edition, My 2005.

[0020] VVhen desired for use, ernbodiments of the set-delayed cement compositions may be aetivated (e.g., by combination with a cement set activator) lo set into a hardened mass. the term "cement set activator" or "activator", as used herein, reiers to an additive that activates a set-delayed or heavily retarded cement composition and may aiso accelerate the setting of the set-delayed, heavily retarded, or other cement composition. By way of example, ernbodiments of the sét-deiayed cement compositions may be aetivated to form a hardened mass in a time period in the range of from about 1 hour to about 12 hours. For example, ernbodiments of the set-delayed cement rømpositions may set to form a hardened mass in a time period ranging between any of and/or ineluding any of about 1 day, about 2 days, about 4 days, about 6 days, about 8 days, about 10 days, or about 12 days.

[0021] ln some ernbodiments, the set-delayed cement compositions may set. to have a desirable compressive strength after aetivation. Compressive strength is generally the eapacity of a material or structure to withstand axialiy directed pushing fbrces. The compressive strength may be measured at a specified time after the set-delayed cement composition has been aetivated and the resultant composition is maintained under specified temperature and pressure conditions. Compressive strength can be measured by eifhér destructive or non-destructive methods. The destmctive meth<p>d physically tests the strength of treatment fluid samples at various points in time by crushing the samples in a compression-testing mach ine. The compressive strength is calculated from the fat lure' load divided by the cross-sectional area resisting the load and is reported in units of pound-force per square meh (psi). Non-destructive methods may eraploy a UCA Ultrasonie Cement Analyzer, available troni Fann Instrument Company, Houston, TX> Compressive strength values may be determined in accordance with API RP 108-2, Reeommended Practice for 7' estiftg WeU Cements, First Edition, July 2005,

[0022] By way of example, the set-delayed cement compositions may devefop a 24-hour compressive 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. |n some ernbodi ments, the set-delayed cement composi tions may devel op a compressive strength in 24 hours of at least about 50 psi, at least about i 00 psi, at least about 500 psi, or more. in some ernbodiments, the compressive strength values may be determined using destructive or non-destructive methods at a temperature ranging from 100° F to 200<*>F.

[0023] ln some ernbodiments, the set-delayed cement compositions may have desirable thickening times after activation. Thickening time typicaily 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 iaboratory techniques may be used to measure thickening time. A pressurtzed consistometer, operated in accordance with the procedure set førth in the afbrementioned API RP Practice 10B-2, may be used to measure whether a fluid is in a pum<p>abie fluid state. The thickening time may be the time for the treatment lfuid to reach 70 Sc and may he reported as the time to reach ?0 Bc. ln some ernbodiments, 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 ai 3,000 psi and temperatures in a range of from about 50<*>F to about 400° F, alternatively, in a range of from about 80° F to about 250° F, and alternatively at a temperature of about 140° F.

[0024] Ernbodiments may include the addition of a cement set activatør to the set-delayed cement compositions. Examples of suitable cement set activators include, but are not limited tø: æeolites, amines such as triethanolamine, diefhanplamine; silicates such as sodium siticate; zinc formåte; calcium acetate; Groups IA and 11A hydroxides such as sodium hydroxide, magnesium hydroxide, and calcium hydroxide; monovalent salts such as sodium chloride; divalent salts such as calcium chloride; nanosilica {i.e., silica håving a partiele size of less than or equal to about 100 nanometers); polyphosphates; and combinations thereof! ln some ernbodiments, a combination of the poiyphosphate 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, ineluding polymeric metaphosphate salts, phosphate salts, and combinations thereof. Specific examples of polymeric metaphosphate salis that may be used include sodium hexametaphosphate, sodium trimeta<p>hosphate, sodium tetrametaphosphate, sodium pentametaphosphate, sodium heptametaphosphate, sodium octametaphosphate, and combinations thereof. A specific example of a suitable cement set activator eomprises a combination of sodium sulfate and sodium hexametaphosphate. In particular ernbodiments, the cement set 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.

[0025] The cement set activator should be added to ernbodiments of the set-delayed cement composition in an amount sufllcient to induce the set-delayed composition to set intø a hardened mass. In certain ernbodiments, the cement set activator may be added to the cement composition in an amount in the range of about 0.1% to about 20% by weight of the pozzolan. In specific enrbodiments, the cement set activator may be present in an amount ranging between any of and/or ineluding any of about 0,1%, about 1%, about 5%, about 10%y about 15%, or about 20% by weight of the pozæolan. One of ordinary skil l in the art, with the benefit of this disclosure, will recognize the appropriate amount of the cement set activator to include for a chosen application.

[0026] Ernbodiments of the set-delayed cement compositions may comprise the use oftwo separate component slurries that are combined to form a two-part set-delayed cement eompbsition. Ernbodiments of the two-part set-delayed cement may comprise providing a pozzolan slurry and a lime slurry whieh are kept separate in lieu of adding cement set retarders. The two-part set-delayed cement composition may utilize two individual slurries in a manner such that neither slurry is able to hydrate and méreføre sét independently. Therefore, each individual slurry of the two-part set-delayed cement composition should remain in a set-delayed state (Te. remaining in a pumpabie fluid state for at least about one day [e.g., at least about I day, about 2 weeks, about 2 years or more] at room temperature in quiescent. storage). Ernbodiments of the two-part set-delayed cement composition may comprise two component slurries. One component slurry eomprises a pozzolan and water. The other component slurry eomprises lime and water. In ernbodiments, each slurry may be stored at a well site or other storage site until needed. When needed, the two component slurries may be mixed together prior to or while pumping downhole. The combined slurry may then thicken and set within a desired period of time.

[0027] Advantageously, the use of a two-part set-delayed cement composition may allow for quicker setting at Iower temperatures (é.g. temperatures less than 140° F). Furthermore, because the reactive components of the two-part set-delayed cement composition are kept separate, additional additives or higher conceotrations of additives (e.g. additional silica sources, see ahøve) may be added to the two-part set-dela<y>ed cement composition without risk of premature setting or gelation.

[0028] Ernbodiments of the two-part set-delayed cement compositions may generally comprise two component slurries,. a pozzolan slurry and a lime slurry. Botn component slurries comprise water. Optionally, either component slurry may further comprise a dispersant and/or a cement set retarder. Advantageously, embodi ments of the two-part set-delayed cement compositions may be capable of remaining in a pumpabie fluid state for an extended period of time. For example, the two-part set-delayed cement compositions may remain in a pumpabie fluid state for at least about 1 day or longer. Advantageously, the iwo-paft set-delayed cement compositions may develop reasonable compressive strengths after activating (e.g. by niixing the two component slurries) at reiativeiy low temperatures. While the two-part set-delayed cement compositions may bø suitable for a number of subterranean cementing operations, they may be partieuiarly suitable for use ih subterranean formations håving reiativeiy low bottom hole static temperatures, e.g., temperatures less than about 20<0>° F or ranging from about 100° F to about 200° F. In alternative embodiments, the set-delayed cement compositions may be used in subterranean formations håving bottom hole static tempeKrtiires up to 450° F or higher.

[0029] Embodiments of the pozzolan slurry comprise a pozzolan. Any pozzolan is suitable for tise in embodiments. Example embodiments comprising a pozzolan may comprise fly ash, silica fume, metakaoHn, diatomaceous earth, a natura! pozzolan (e.g., pumice), or combinations thereof. In a two-part set-delayed cement composition embodiment, the pozzolan may be a non-hydraulic pozzolan, i.é. a pozzolan that will not react when mixed with water in the absence of hydrated lime to form a cementitious material. By way of example, some types of Glass C fly ash may not be suitable for use in a two-part set-delayed cement composition embodiment, because Class C fly ash may comprise lime and will theretbre react when mixed with water to become cementitious.

[0030] Embodiments of the pozzolan slurry may comprise fly ash. A variety of fly ashes may be suitable, ineluding fly ash classified as Class F fly ash according to American Petroleum Institute, AP! Specification for Materials and Testing for Wéll Cements, API Specification 10, Fifth Ed., July 1, 1990. Class C fly ash eomprises both silica and lime, so it may set to form a hardened mass upon mixing with water and may thus be unsuitable for use in the pozzolan slurry as it may undesirably sét when mixed with the water. Class F fly ash generally does not eontain a sufficient amount of time to induce a cementitious reaction, therefore, should remain in a pumpabie fluid state when mixed with water. Suitable examples of fly ash include, but are not limited to, POZMIX<*>A cement additive, eommerciaiiy availabie from ffallihurtøn Energy Services, Inc,, Houston,Texas.

[0031] Embodiments of the pozzolan slurry may comprise metakaolin. Generally, metakaolin is a white pozzolan that may be prepared by heating kaolin clay, for example, to temperatures in the range of about 600" C to about 800" C.

[0032] Embodiments of the pozzolan slurry may comprise a natural pozzolan. Natural pozzolans are generally present: on the Earth's surface and set and harden in the presence of hydrated lime and water. Embodiments comprising a natural pozzolan may comprise pumice, diatomaceous earth, volcanic ash, opaline shale, tuff, and combinations thereof. The natural pozzolans may be ground or ungrøund. Generally, the natural pozzolans may have any partiele size distribution as desired før a particular application, ln certain embodiments, the natural pozzolans may have a mean partiele size in a range of from about 1 micron to about 200 microns. The mean partiele size corresponds to d50 values as measured by partiele size analyzers such as those manufactured by Mal vern Instruments, Worcestershire, United Kingdom, ln specific embodiments, the natural pozzolans may have a mean partiele size in a range of from about 1 micron to about 200 micron, from about 5 microns to about 100 microns, or from about 10 micron to about 50 microns. In one particular embodiment, the natural pozzolans may have a mean partiele size of less than about 15 microns. An example of a suitable commercial natural pozzolan is pumice available from Mess Pumice Products, Inc., Malad, Idaho, as DS-325 lightweight aggregafe, which has a partiele size of less than about 15 microns. It should be appreciated that partiele sizes too small may have mixability problems white partiele sizes too large may not be effeetively suspended in the compositions and may be less reactive due to their decreased surface area. One of ordinary skill in the art, with the benefit of this disclosure, should be able to select a partiele size for the natural pozzolans suitable før use før a chosen application.

[0033] Embodiments of the pozzolan slurry comprise water. The water used In embodiments of the pozzolan slurry may be from any source provided that it does not eontain an exeess of compounds that may undesirably affect other components in the pozzolan slurry. For example, the pozzolan slurry may comprise fresh water or salt water. Salt water generally may include øne or more dissølved salts therein and may be saturated or unsaturated as desired for a particular application. Seawater or brines may be suitable for use in embodiments. Further, the water may be present in an amount sutfkient to form a pumpabie slurry. In certain embodiments, the water may be individually present in the pozzolan slurry in an amount in the range of from about 33% to about 200% by weight of the pozzolan. ln certain embodiments, the water may be present in the pozzolan slurry in an amount in the range of from about 35% to about 85% by weight of the pozzolan. With the benefit of this disclosure one of ordinary skill in the firt wiil recognize the appropriate amount of water for a chosen application. Embodiments of the pozzolan slurry may comprise additives suitable for use in subterranean cementing operations. Any additive, ineluding additional silica sources, may be added to the pozzolan slurry. Examples of additives include, but are not limited to: weighting additives, lightweight additives, gas-generating additives, meehanical-prøperty-enhancing additives, lost-cireulation materials, filtraiion-control additives, fluid-loss-control additives, detbaming agents, foaming agents, thixotrøpic additives, dispersants, cement. set activatOiTs/accelerators, cement set retarders, and combinations thereof. ln embodiments of the pozzolan slurry, one or more of these additives may be added to the pozzolan slurry before or after storing. Additional ly one or more offhese additives may be added io the pozzolan slurry before or after mixing the pozzolan slurry with the lime slurry. A person håving ordinary skill in the art, with the benefit of this disclosure, shouid readily be able to determine the type and amount of additive use ful tor a particular application and desired result.

[0034] Embodiments of the lime slurry comprise hydrated lime. As used herein, the term "hydrated lime" wiil be understood to mean ealeium hydroxide. ln some embodiments, the hydrated lime may be provided as quicklime (calcium oxide) which hydraies when mixed with water to form the hydrated lime. The hydrated lime may be inciuded in embodiments of the lime slurry to form a hydraulie composition with the pozzolan. For example, the hydrated lime may be inciuded in a pozzolan-to-hydrated-lime weight ratio of about 10:1 to about I; I or a ratio of about 3:1 to about 5:1, based on the combined mix of both component slurries. Where present, the lime slurry may comprise an amount of hydratet! lime between about 10% to about 100% by weight of the pozzolan present in the pozzolan slurry. ln some embodiments, the hydrated lime may be present in the lime slurry in an amount ranging between any of and/or ineluding any of about 10%, about 20%, about 40%, about 60%, about 80%, or about 100% by weight of the pozzolan in the pozzolan slurry. ln some embodiments, the cementitious components present in the two-part set-delayed cement cømposltion may consist essentially of the pozzolan and the hydrated lime. For example, the cementitious components may primarily comprise the pozzolan (e.g,, pumice) and the hydrated lime without any additional cementitious components (e.g., Portland cement) that hydraulically set in the presence of water. One of ordinary skill in the art, with the benefit of this disclosure, wiil recognize the appropriate amount of hydrated lime to include for a chosen application.

[0035] Embodiments of the lime slurry comprise water. The water used in embodiments of the l ime slurry may be trom any source provided that it does not eontain an excess of compøunds that may undesirably afTect other components in the lime slurr<y>. For example, the lime slurry may comprise Iresh water or salt water, Salt water generally may include one or more dissølved salts therein and may be satufated or unsaturated as desired for a particular application. Seawater or brines may be suitable for use in embodiments. Further, the water may be present in an amount sufficient to fonn a pumpabie slurry. ln certain embodiments, the water may be individually present in the lime slurry in an amount in the range of from about 33% to about 200% by weight of the lime. ln certain embodiments, the water may be present in the lime slurry in an amount in the range of from about 35% to about 70% by weight of the lime. With the benefit of this disclosure one of ordinary skill in the art wiil recognize the appropriate amount of water for a chosen application,

[0036] Embodiments of the lime slurry may comprise additives suitable for use in subterranean cementing operations. Any additive, ineluding additional silica sourees, may be added to the lime slurry. Examples of such additives include, but are not limited to: weighting additives, lightweight additives, gas-generating additives, mechanical-prøperty-enhancing additives, lost-eirculation materials, illtratiøn-cøntrol additives, fluid-loss-control additives, defoaming agents, foaming agents, ihixotropie additives, dispersants, cement set activators^accéleratørs, cement set retarders, and combinations thereof. ln embodiments of the lime slurry, one or more ofthese additives may be added to the lime slurry before or after storing, Additionally one or more of these additives may be added to the lime slurry before or after mixing the lime slurry with the pozzolan slurry. A person håving ordinary skill in the art, with the benefit of this disclosure, should readiiy be able to determine the type and amount of additi ve useful for a particular application and desired result.

[0037] Embodiments of the two-part set-delayed cement compositions may comprise a cement set retarder as described above. Any cement set retarder described in embodiments of the set-delayed cement compøsitions above may also be suitable for embodiments of the two-part set-delayed cement compositions. Cement set retarders may bé added to one or both component slurries or may be added to the combined slurry, Amongst other reasons. cement set retarders may be added to inerease thickening time. In some embodiments, the cement set retarder may be present in the component slurries (esther individually or in both) ør in the combined slurry of the two-part set-delayed cement compositions in an amount in the range of from about 0,01% to about 10% by weight of the pt>zzoIan. ln specific embodiments, the cement set retarder may be present in an amount ranging between any of and/or ineluding any of about 0.01%, about 0.1%, about 1%, about 2%, about 4%, about 6%, about 8%, or about 10% by weight of the pozzolan for the pozzolan slurry or by weight of the lime tor the lime slurry, One of ordinary ski il in the art, with the benefit of this disclosure, wiil recognize the appropriaie amount of the cement set retarder to include for a chosen application. (0038] As previously mentioned, embodiments of the two-part set-delayed cement compositions may optionally comprise a dispersant as described above. Any dispersant described in embodiments of the set-delayed cement compositions may also be suitable tor embodiments of the two-part set-delayed cement compositions. in some embodiments, the dispersant may be inciuded in one or both of the component slurries or in the combined slurry of the two-part set-delayed cement compositions in an amount in the range of from about 0.01% to about 5% by weight of the pozzolan or the hydrated lime. In specific embodiments, the dispersant may be present ih an amount ranging between any of and/or ineluding 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 pozzolan or the hydrated lime. One of ordinary skill in the art. with the benefit of this disclosure, wiil recognize the appropriate amount of the dispersant to include for a chosen application.

[0039] Embodiments may include the addition of a cement set activator to the two-part set-delayed cement compositions as described above. The cement set activator may be inciuded to accelérate setting times, amongst other reasons. Any cement set activator described in embodiments of the set-delayed cement compositions may also be suitable for embodiments of the two-part set-delayed cement compositions. Any cement set activator may be added to either one or both of the component slurries as weii as tb the combined slurry in an amount sufficient to accelérate the setting of the combined two-part set-delayed composition (if added to only a component slurry, the acceleration of the set time should happen when the component slurries are mixed). In embodiments, the cement set activator may be added to the component slurries (either individually or both) or to the combined slurry of the two-part set-delayed cement composition in an amount in the range of about 0.1% to about 20?/b by weight of the pozzolan. In specific embodiments, the cement set activator may be present in the component slurries (either individually or in both) or in the combined slurry of the two-part set-delayed cement composition in an amount ranging between any of and/or ineluding any of about 0,1%, about 1%, about 5%, about 10%, about 15%, or about 20% by weight of the pozzolan. One of ordinary skill in the art, with the benefit of this disclosure, wiil recognize the appropriate amount of the cement set activator to include for a chosen application.

[0040] Those of ordinary skill in the art wiil appreeiate that embodiments of the two-part set-delayed cement compositions generally should have a density suitable for a particular application. By way of example, the combined two-part set-delayed cement compositions may have a density in the range of from about 4 pounds per gallon ("Ib/gaP') to about 20 lb/gal. ln certain embodiments, the combined two-part set-delayed cement compositions may have a density in the range of from about 8 lb/gal to about 17 Ib/gal. Embodiments of the two-part set-delayed cement cwmposjtions may be foamed or unfbamed or may comprise other means to rcduce their dcnsities, such as holiow microspheres, iow-density elastic beads, or other density-reducing additives known in the art. In embodiments, the density may be reduced after storage, but prior to piacement in a subterranean formation. In embodiments, weighting additives may be used to inerease the density of the two-part set-delayed cement compositions, Examples of suitable weighting additives may include barhe, hematite, hausmannite, calcium carbonate, siderite, iimenite, or combinations thereof. In particular embodiments, the weighting additives may have a specific gravity of 3 or greater. Thosé: of ordinary skill in the art, with the benefit of this disclosure, wiil recognize the appropriate density for a particular application.

[0041] As previously mentioned, the component slurries of the two-part set-delayed cement compositions may have a delayed set in that they remain in a pumpabie fluid state for at least one day (e.g., about i day, about 2 weeks, about 2 years or more) at room temperature (é.g., about 80* F) in quiescent storage. For example, the component slurries of the two-part set-delayed cement compositions may remain in a pumpabie fluid state for a period of time from about 1 day to about 7 days or more. In some embodiments, the component slurries of the two-part set-delayed cement compositions may remain in a pumpabie 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 pumpabie fluid state where the fluid has a consistency of less than 70 Bearden units of consistency ("Bc"), as measured on a pressurized consistometer in accordance with the procedure for determining cement thickening times set forth in API RP Practice 10B-2, Rééomnwmted Pmciiwfaf Testing WéU C& ment*% First Edition, July 2005.

[0042] When desired for use, embodiments df the two-part set-delayed éemént compositions may be aetivated (e.g., by combining the pozzolan and lime slurries) to set into a hardened mass. By way of example, embodiments of the two-part set-delayed cement compositions may be aetivated 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 two-part set-delayed cement eomppsiiions may set to form a hardened mass in a time period ranging between any øf and/or ineluding any of about 1 day, about 2 days, about 4 days, about 6 days, about 8 days, about 10 days. or about 12 days.

[0043] ln some embodiments, the two-part set-delayed cement compositions may set to have a desirable compressive strength after activation, Compressive strength is generally the capacity of a material ør struoture to withstand axially directed pushing tørces. The compressive strength may be measured at a specified time after the two-part set-delayed cement composition has been aetivated 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 ai various points in time by crushing the samples in a compressiøn-tesfing machine. The compressive strength is calculated from the failure load divided by the cross-séctional area resisting the load ånd is reported in units of pound-ibrce per square inch (pst). Non-destructive methods may employ a UCA™ Uitrasonic Cement Analyzer, available from Fann Instrument Company, Houston, TX. Compressive strength values may be determined in accordance with API RP 10B-2, Recommended Praelice fb? Testing WeU CemétUs, First Edition* My 2005.

[0044] By way of example, the two-part set-delayed cement compositions may develop a 24-hour compressive 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. lii some embodiments, the two-part 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 søme embodiments, the compressi ve strength values may be determined using destructive ør non-destructive methods at a temperature ranging from 100° F to 2<)0" F.

[0045] ln some embodiments, the two-part 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 rtumber of different laboratory techniques may be used to measure thickening time. A pressurized consistometer, øperated in accordance with the procedue rset forth in the aforementioned API RP Practice 10B-2, may be used tø measure whether a fluid is in a pumpabie fluid state. The thickening time may be the time før the treatment fluid to reach 70 Bc and may be reported as the time to reach 70 Bc, In some embodiments, the two-part set-delayed 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 between about 1,000 psi to about 20,000 psi and temperatuers in a range of from about 50° F to about 400° F, alternatively, in a range of from about SG* F to about 250° F, and alternatively at a temperature bfabout 140° F.

[0046] Embodiments of the two-part set-delayed cement comrxisition may be used to dispiace a prior placed fluid (i.e. embodiments of the two-part set-delayed cement composition may be used as a spacer fluid). The pozzolan slurry of the two-part set-delayed cement composition, comprising a pozzolan and water, may be sim i lar in composition to conventionai spacer fluids. Because of this sirøilarily, the pozzolan slurry may be used as a spacer fluid in embodiments. The pozzolan slurry may be used to dispiace a drilling mud, separate cement from a drilling mud, dispiace another treatment fluid, separate the drilling mud from a treatment fluid, and/or separate eement from a treatment fluid. Advatttageousiy, the use of the pozzolan slurry as a spacer fluid may condition the subterranean formation With part of the same composition that ultimately may be used as the annular sealant Therefore, the risk of incompatibilities between sealant and spacer fluid may be reduced,

[0047] In embodiments wherein the pozzolan component slurry of the two-part set-delayed eement composition may be used as a spacer fluid, the density of the pozzolan slurry may be adjusted by the addition of water and/or a viscosifier. The water and viscosifiers may be added in any amount to achieve the appropriate density to provide a suitable rheological hierarchy for a given application. An example of a suitable viscosifier is SA-l0i$™ suspending agent available from: Halliburton Energy Services, Houston, TX. Additional ly, weighting agents may be added to adjust tlie density as may be appropriate to maintain a suitable rheological hierarchy. One of ordinary skill in the art, with the benefit of this disclosure, wiil recognize the appropriate density and method of density adjustment necéssary for a chosen application.

[0048] Moreover, in embodiments wherein the pozzolan slurry may be used as a spacer fluid, the spacer fluid may be foamed with a foaming additive and/or a gas. the spacer fluid may be foamed, for example, to provide a spacer fluid with a reduced density. The gas used for foaming the composition may be any suitable gas for foaming, ineluding, but not limited to: air, nitrogen, or combinations thereof Generally, the gas should be present in an amount sufficient to form the desired amount or quality of foam. Foaming additives may be inciuded in embodiments to, for example, facilitate foaming andror stabilize the resultant foam formed therewith. Examples of suitable foaming additives include, but are not limited to: mixtures of an ammonium salt of an alkyl ether sulfate, a cocoamidopropyl betaine suriaetant, a cocoamidopropyl dimelhylamine oxide suriactant, sodium chloride, aud water; mixtures of an ammonium salt of an alkyl ether sulfate suriactant, a cocoamidopropyl hydroxysultaine suriactant, a cocoamidopropyl dimethylamine oxkle surfactant, sodium chloride, and water; hydrolyzed keratin; mixtures of an ethoxylated alcohol ether sulfate surfactant, an alkyl or alkene amidopropyl betaine surfactant and an alkyl or alkene dimethylamine oxide surfactant; aqueous solutiøns of an alpha-ølefmic sulfønate surfactant and a betaine surfactant; and combinations thereof. An example of a suitable foaming additive is ZONESEALANT™ 2000 agent, available from Halliburton Energy Services, Houston, TX.

[0049] li is to be understood, that any additive, component, or embodiment disciosed herein may additionally be used or combined with embodiments of the two-part set-delayed cement composition. For example, previousiy described additives such as weighting agents, lightweight additives, gas-generating additives, meehanieai-property-enhancing additives, lost-circulation materials, filtration-control additives, fluid-loss-control additives, defbaming agents, foaming agents, thixotropk additives,, dispersants, cement set retarders, cement set activators/aceelerators, additional silica sources, and the like, and combinations thereof may all be used with embodiments of the pozzolan slurry, lime slurry, and the combined slurry of the two-part set-delayed cement compositions in the same manner as previousiy described. The two-part set-delayed cement composition embodiment is therefore inclusive of every additive, component, ør øther embodiment that may be used in combination: ineluding the use of cement set activators and cement set retarders. For example, the two-part set-delayed cement composition may comprise a cement set activator to accelérate setting time and enhance early strength, additionally or alternatively, the two-part set-delayed cement composition may comprise a cement set retarder to delay thickening time. Any additive, component, or embodiment disciosed herein may be added to one or both of the component slurries or to the combined slurry of the two-part set-delayed cement compositions. Moreover, any additive, component, or embodiment disciosed herein that is used with the pozzolan slurry, the lime slurry, or the combined slurry may also be used with embodiments of the two-part set-delayed cement composition that comprise a spacer fluid.

[0050] As wiil be appreciated by those of ordinary skill in the art, embodiments of the set-delayed cement compositions ineluding the two-part set-delayed cement compositions may be used in a variety of subterranean operations, ineluding primary and remedia! cementing. In some embodiments, a set-delayed cement composition (in the two-part set-delayed cement composition embodiments, this may be a combined two-part set-delayed cement composition) may be provided that eomprises water, a pozzolan, hydrated lime, a cement set retarder, and optionally å dispersant. The set-delayed cement composition may be introduced into a subterranean formation and aliowed to set therein. As used herein, introducing the set-delayed cement composition into a subterranean formation includes introduetion into any portion of the subterranean formation, ineluding, without iimitation, into a welibore drilled into the subterranean formalion, into a near wellbore region surrøunding the wellbore, 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, addition of a cement set acceierator to the set-delayed cement composition or the mixing of the two component slurries of the two-part set-delayed cement composition.

[0051] ln some embodiments, a set-delayed cement composition may be provided that eomprises water, a pozzolan, hydrated lime, a cement set retarder, and opiionaliy a dispersant. The set-delayed cement composition may be stored, for example, in a vessel or other suitable container. In alternative embodiments a two-part set-delayed cement composition may be provided that eomprises a first part comprising a pozzolan and water component slurry and a second part comprising a hydrated lime and water component slurry. The first and second parts may individually stored and combined prior to or while pumping downhoie. The set-delayed cement compositions may be perrøitted to remain in storage for a desired time period. For example, the set-delayed cement compositions may remain in storage for a time period of about i day, about 2 weeks, about 2 years, or longer. For example, the set-delayed cement compositions 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, ør up to about 2 years. In søme embodiments, the set-delayed cement composition may remain in storage for a time period in a range of from about 1 day to about 2 years or longer, Thereaftei\the set-delayed cement eompGsition may be aetivated, for example, by mixing the two-component slurries together, introdueed into a subterranean formation, and allowed to set therein.

[0052] In primary cementing embodiments, for example, embodiments of the set-delayed cement composition may be introdueed intø an annular space between a conduit iocated in a wellbore and the walis of a wellbore (and/ør a larger conduit in the wellbore), 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 rølgration of fluids in the wellbore. The set-delayed cement composition may also, for example, support the conduit in the wellbore.

[0053] In remedia! cementing embodiments, a set-delayed cement composition may be used, for example, in squeeze-eementing operations or in the piacement of cement plugs. By way of example, the set-delayed composition may be placed in a wellbore tø plug an open ing (e.g,, a void ør craek) in thé formation, in a gravel pack, in thé conduit, in the cement sheath. and/<p>r between the cement sheath and the conduit (e.g., a microannulus).

[0054] An embodiment eomprises a method of cementing comprising: providing a pozzolan slurry comprising a pozzolan and waten providing a lime slurry comprising hydrated lime and water; allowing the pozzolan slurry and the lime slurry to remain separate for about one day or longer; mixing the pozzolan slurry and the lime slurry to form a cement composition; and allowing the cement composition to set.

[0055] An embodiment eomprises a method of displacing a fluid in a subterranean formation comprising: providing a pozzolan slurry comprising a pozzolan and water; providing a lime slurry comprisin<g>hydrated lime and water; introducing at least a portion of the pozzolan slurry into a wellbore that penetraies a subterranean formation such that thé pozzolan slurry displac.es at least one fluid from the wellbore; activating the set-delayed cement composition by mixing at least a portion of the pozzolan slurry and at least a portion of the lime slurry to form a cement composition; introducing the cement composition into a subterranean formation; and allowing the cement composition to set in the subterranean formation,

[0056] An embodiment eomprises a system for cementing comprising: a pozzolan slurry comprising a pozzolan and water; a lime slurry for combination with the pozzolan slurry to form a cement composition comprising hydrated lime and water,

[0057] Referring riow to FIG. i, preparation of a set-delayed cement composition in accordance with example embodiments wiil now be described. FIG. 1 illustrates a system 2 før preparation of-a set-delayed cement composition and deiivery 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, før 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 ør more cement trucks as wiil be apparent to those of ordinary skill in the art. In some embodiments, a jet mixer may be used, for example, to eøntinuously mix the lime/seltahle material with the water as it ts being pumped to the welibore. ln two-part set-delayed embodiments, mixing equipment (e.g., a jet mixer, re-circulating mixer, and/or a batch mixer) may be used to mix the combined two-part set-delayed cement composition slurry,

[0058] An example technique for placing a set-delayed cement composition into a subterranean formation wiil now be described with reference to FIGS. 2A and 28. FIG, 2A illustrates surface equipment 10 that may be used in piacement of a set-delayed cement composition in accordance with certain embodiments. It should be noted that while FIG. 2A generally depicts a land-based operation, those skilled in the art wiil readily récognke that the prineiples described herein are equaliy applicabie to subsea operations that employ floating or sea-based platfbrms and rigs, without departing from the scope of the disclosure. As illustrated by FIG. 2Å, 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 wtll 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 downhole.

[0059] 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 verticaliy into the subterranean formation 20, the prineiples described herein are also applicabie to wellbores that extend at an angle through the subterranean formation 20, such as hortzohtal and slanted wellbores. As illustrated, the wellbore 22 eomprises 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 by cement sheaih 28, In the illustrated embodiment, one or more additional conduits (e.g., intermediate casing, production casing, liners, etc,), shown here as casing 30 may also be disposed in the wellbore 22. As iilustratéd, 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 centralizers 34 may be attached to the casing 30, for example, to centralize the casing 30 in the wellbore 22 prior to and during the cementing operatien.

[0060] 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 øf the casing 30 and up arøund 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 that supports and positions the casing 30 in the welibore 22. While not illustrated, other techniques may also be utilized for introduction of the set-delayed cement composition 14. By way of example, reverse circuiation techniques may be used that include introducing the set-delayed cement composition 14 into the subterranean formation 20 by way of the welibore annulus 32 instead of through the casing 30.

[006.1] As it is introdueed, the set-delayed cement composition 14 may dispiace 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 welibore annulus 32. At least a portion of the displaced fluids 36 may exit the welibore annulus 32 via a flow line 38 and be deposited, tor example. in one or more retention pits 40 {e.g., a mud pit), as shown on FIG. 2A. Referring again to FIG. 2B, a bottom plug 44 may be introdueed into the wellbore 22 ahead of the set-delayed cement composition 14, for example, to separate the set-delayed cement composition 14 from the fluids 36 that may be inside the casing 30 prior to cementing. After the bottom plug 44 reaches the landing coilar 46, a diaphragm or other suitable de vice should rupture to allow the set-delayed cement composition 14 through the bottom plug 44. ln FIG. 2B, the bottom plug 44 is shown on the landing coilar 46. In the illustrated embodiment, afop plug 48 may be introdueed into the wellbore 22 behind the set-delayed cement composition 14. The top plug 48 may separate the set-delayed cement composition 14 from a displacement fluid 50 and also push the set-delayed cement composition 14 through the bottom plug 44.

[0062] The exemplary set-delayed cement compositions disciosed herein may directly or indirectly affect one or more components or pieces of equipment associated with the preparation, delivery, recapture, recycling, reuse, and/or disposai of the disciosed set-delayed cement compositions. For example, the disciosed set-delayed cement compositions may directly or indirectly affect one or more mixers, related mixing equipment, mud pits, storage facilities or uiiits, composition separators, heat exehangers, sensors, gauges, pumps, compressors, and the like used generate, store, monitor, regulate, and/or recondition the exemplary set-delayed cement compositions. The disciosed 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. andror pipes used to compøstiionaliy move the set-delayed cement compositions from one location to 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 br 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 disciosed set-delayed cement compositions may also directly or indirectly affect the various downhole equipment and tobis that may come into contact with the set-delayed cement compositions such as, but not limited to, welibore casing, wellbore liner, completion string, insert strings, drill string, coiled tubing, slickline, wireline, drill pipe, drill collars, mud motors, downhole motors and/or pumps, cement pumps, surface-mounted motors and/or pumps, centralizers, turbolizers, scratchers, floats (e.g., shoes, eo!lars, valves, ete.), logging tools and related telemetry equipment, actuators (e.g., electromechanical deviees, hydromechanical dévicés. etc), sliding sieeves, production sieeves, plugs, screens, filters, flow control deviees (e.g., mftow contrøl deviees, autonomous Infipw control deviees, ouiflow control deviees, etc), cøuplings (e.*., eleclro-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, vai ves and corresponding actuation deviees, tooi seals, paekers, cement plugs, bridge pings, and other wellbore isolation deviees, or components, and the like.

EXAMPLES

[0063] To faciittate a hetter understanding of the present embodiments, the fbliowing examples of certain aspects of some embodiments are given, ln no way should the fbliowing examples be read tolimit, ør define, the entire scope of the embodiments.

Example 1

[0064] A two part set-deiayed cement composition was prepared which corøprised the fbliowing component slurries:

[0065] Slurry A was prepared in a Waring* blender by first adding water to the blender tøllowed by a dispersant, Liquiment* 5581F dispersant. The dispersant was allowed to fuliy disperse, then the pumice, silica (Siliealite™ cement additive), and a weight additive (MicroMax<*>FF weight additive) were added. After all of the components were added, Slurry A was blended at a speed of 6000 rpm for 40 seconds to fully hømogemze the sample. Slurry B was prepared in the same manner as Slurry A. The caiculated density of Slurry A was 13.33 pounds per gallon (ppg) and Slurry B was 12.75 ppg.

[0066] Immediateiy after preparation (designated Day 0) and periodically thereafter, the rheological properties of the samples were determined using a Model 35A Fann Viscometer and a No. 2 spring With a Fann Yield Stress Adapter (FYSA), in accordance with the procedure set forth in API RP Practice 108-2, Recommehded Praetæe for Tes ting Well Cements. Dispersant was added as needed to maintain adequate viscosity values,. % bwoP reiers to "percent by weight of the pumice," and % bwoI lL refers to "percent by weight of hydrated lime."

[0067] To form the settable combined slurry, 129.4 grams of Slurry B was added to 500.Q grams of Slurry A. This was performed by adding Slurry A to a Waring* blender set to 4000 rpm and slowly pouring in Slurry B to form Slurry AB with a final slurry composition of:

[0068] The calculated density of Slurry AB was 13.23 ppg. A portion of Slurry AB was accelerated with 10% bwoP CaC!> by mixing 200.0 grams of Slurry AB with 21.92 grams of 43% CaCijsolution. This sample is shown in table 5 as accelerated. Immediateiy after preparation, the rheology of the sample was measured using a Mode! 35A Fann Viscometer and a-No* 2 spring with a Fann Yield Stress Adapter (FYSA), in accordance with the procedure set forth in API RP Practice t0B-2, Recommended Practice for Testing WeU Cemenfs.

[0069] After mixing the two com<p>onent slurries to aetivate the set-delayed cement composition, the combined slurry was cured in a 2" by 4" plastic éylinder that was placed in a water batn at between about 90* F to about 150° F to form set evl inders. Then the destructive compressive strength (C.S.) was measured using a mechaniea! press in accordance with API RP Practice 10B-2, Recommended Practice for Testing Wdl Cements. The results of this test are set forti» in Table 6 beiow. The reported compressi ve strengths are an average for two cylinders of each sample. Compressive strength measuremehts were tåken at 24 hours.

[0070] For comparison, a non-two part set-delayed slurry was prepared by combining 350 grams water, 500 grams pumice, 100 grams hydrated lime, 20 grams Mieromax<*>weight additive, 6.25 grams Micro Matrix*' cement retarder, and 3.5 grams Liquiment<*>5581F dispersant. This slurry (NC1) was aged 35 days prior to use, aetivated with 10% hwøP CaCI? solution, and cured in the water haths at the same time as Slurry AB.

[0071] As Example 1 shows, siurry AB is more active at Iower temperatures than NC1. Without being limited by theory, this eiTect may be due to the lack of cement retarders in slurry AB and/or the inclusion of a silica additive.

10 Example 2

[0072] ln the previous examples the pozzolan and lime slurries were mixed to give a hydrated lime content of 20.0% bwoP. The next example illustrates hpw it may be advantageous to mix the two parts in different ratios to produee slurries with varying Mme content. In this example, 258.8 grams of Slurry B was mixed with 500.0 grams of Siurry A to give a lime 15content of 40% bwoP:

[0073] After mixing, this sample was eured in a water bath at 90c F for 24 hours then crushed to obtain a compressive strength of 150 psi. The strength of this sample was about 33% greater than the sample with only 20% lime content (105 psi).

Example 3

[0074] A two part set-delayed cement composition was prepared which comprised the følløwing component slurries:

[0075] Slurry C was prepared in a Waring<*>blender by first adding water to the blender fblløwed by a dispersant, Liquiment* 5581F dispersant. The dispersant was allowed to fully disperse, then the pumice and a weight additive (MieroMax<*>FF weight additive) were added. After all of the components were added, Slurry C was blended at a speed of 6000 rprø for 40 seconds to fully homogenize the sample. Slurry D was prepared in the same manner as Slurry C. The caiculated density of Slurry C was 13.24 pounds per gallon (ppg) and Slurry B was 12.75 ppg.

[0076] Immediatel<y>after preparation (dcsignatéd Day 0) and pertodically thereafter, the rheological properties of the samples were determined using a Model 35A Fann Viscometer and a No. 2 spring with a Fann Vieldi Stress Adapter (FYSA), in accordance with the procedure set forth in API RP Practice 10B-2, Recommended Practice for Testing Well Cements. Dispersant was added as needed to maintain adequate viscosity values.

[0077] To form the settable combined slurry. 129.4 grams of Sl urry D was added to 500.0 grams of Siurry C. This was performed by adding Slurry C to a Waring<*>blender set to 4000 rpm and siowly pouring in Slurry D to form Slurry CD with a final slurry composition of:

[0078] The caleulated density of Slurry CD was 13,13 ppg, A portion of Slurry CD was accelerated with 50% bwoP CaCIjby mixing 200.0 grams of Slurry CD with 21.51 grams of 43% CaCljsolution. This sample is shown in table l i as accelerated. Immediately after preparation, the rheology of the sample was measured using a Mode! 35A Fann Viscometer and a No. 2 spring with a Fann Yiekl Stress Adapter (FYSA), in accordance with thé procedure sét forth in API RP Practice 10B-2, Recomméndéd Praetieejbr Testing Wdl Cements,

[0079] After mixing the two component slurries to activate the set-delayed cement composition, the combined slurry Was cured in a 2" by 4" piastic cylinder that was placed in a water bath at 190° F to form set cyl inders. Then the destructive compressive strength (C.S.) was measured using a mechanical press in accordance with API RP Practice 10B-2, ReCommended Practice for Testing Weli Cements, The results of this test are sét forth in Table 12 below. The reported compressive stren<g>ths are an average for two cyl inders of each sample. The samples and eontrols were eared at 1 attnosphere, between about 90° F to about 150* F; compressive strength measurements were tåken at 24 or 48 hours.

[0080] For com<p>arison, a non-two part set-delayed slurry was prepared by combining 350 grams water, 500 grams pumice, 100 grams hydrated lime, 20 grams Micromax<*>weight additive, 6.25 grams Micro Matrix<*>cement retarder, and 3,5 grams Liquimcnt<*>5581F dispersant. This slurry (NCi) was aged 35 days prior to use, aetivated with 10% bwøP CaClj solution, and etired tn the Water baths at the same time as Slurry AB.

Example 4

[0081] A two part set-delayed cement composition was prepared which comprised the fbliowing component slurries:

[0082] Slurry E was prepared in a Waring* blender by first adding water to the blender fbllowed by a dispersant, Li<q>uimcnf<*>5581F dispersant. The dispersant was allowed to fully di sperse, then the pumice was added. After all of the components were added, Siurry E was blended at a speed of6000 rpm for 40 seconds to fully homogenize the sample. Slurry F was prepared in the same manner as Slurry E. The caleulated density of Slurry E was 13,4 pounds per gallon (ppg) and Siurry F was 1.2.4 ppg. Siurry E and Slurry F were then stored for 48 hours. After 48 hours neither .slurry contained frée water. However, Slurry F was slightiy gei led and required mixing to måke it flowahle.

[0083] At 48 hours, 778.7 grams of Slurry E was added to 175.4 grams of Slurry F. This was performed by adding Siurry E to a Waring<*:>blender set to 4000 rpm and slowly pouring in Slurry F to form Slurry EF. When they were mixed a gel formed and 1.0 gram of dispersant (Liquimenf*' 5581F dispersant) was added to make the mixture flowahle.

[0084] The caleulated density of the final slurry was 13.2 ppg. 15.0 grams of CaCi? powder (2.5% bwoP+HL) was added to the final slurry before placing it in a consistometer. The thickening time was measured as 5:38 hours at 140° F and 3000 psi. The thickening time was measured using a high-tem<p>emture high-pressure consistometer in accordance with the procedure for determinin<g>cement thickening times set forth in API RP Practice 10B-2, Recammended Practice for Testing Weli Cements, First Edition, July 2005.

[0085] It should be understood that the compositions ånd methods are described in terms of "comprising," "containing," or "ineluding" vartous components or steps, the compositions and methods can also "consist essentiallybf pr "consist of the various components and steps. Moreover, the indefinite articles "a" or "an," as used in the claims, are defrned herein to mean one or more than one of the element that it introduces.

[0086] For the sake of brevity, only certain ranges are explicitly disciosed herein. However, ranges from any Iower limit may be combined with any upper limit to recite a range not explicitly reeited, as well as, ranges from any Iower limit may be combined with any other Iower limit to recite a range not explicitly reeited, in the same way, ranges from any upper limit may be combined With any other upper limit to recite a range not explicitly reeited. Additionally, whene<y>er a numerical range with a Iower limit and an upper limit is disciosed, any number and any inciuded range felling within the range are specifically disciosed. ln particular, every range of values (of the form, "from about a to about W or, equivalently, "from approximately a to b " or, equivalently, "from approximately a-b") disciosed herein is to be understood to set forth every number and range encompassed within the broader range of values even if not explicitly reeited. Thus, every point or individual vakte may serve as its own Iower or upper limit combined with any other point or individual vakte or any other Iower or upper limit, to recite a range not explicitly reeited.

[0087] Therefore, the present embodiments are well adapted to attain the ends and advantages mentioned as wel! as those that are inherent therein. The particular embodiments disciosed above are illustrative oniy, and may be modified and practieed iri different but equivalent manners apparent to those skilled in the art håving the benefit of the teachings herein. Although individual embodiments are discussed, the disclosure covers ali combinations of all of the embodiments. Purthcrmorc, no limitation* 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 uniess otherwise explicitly and clearly defined by the patentee. It is therefore evident that the particular illustrative embodiments disciosed above may be altered or modified and all such variatkms are considered within the scope and spirit of those embodiments. If there is any conflict in the usages of a word or term in this specification and one or more patent(s) or other documents that may be incorporated herein by reference, the deflnitlons that are consistent with this specification should be adopted.

Claims (18)

1. A meihod of cementing comprising: providing a pozzolan siurry comprising a pozzolan and water; providing a lime siurry comprising hydrated lime and water; allowing the pozzolan siurry and the lime slurry to remain separate for about one day or longer* mixing the pozzolan slurry and the lime slurry to form a cement composition; and allowing the cement composition to set.;

2. A method according to claim 1 wherein the cement composition is introdueed into a weilbore penetrating a subterranean formation and allowed to set within.;

3. A method according to claim I or 2 wherein the pozzolan is selected from the group consisting of fly ash, silica fume, metakaolin, pumice, and any combination thereof.;

4. A method according to any of claims 1 to 3 wherein at least one of the pozzolan slurry, the lime slurry, or the cement composition further eomprises a dispersant.;

5. A method according to claim 4 wherein the dispersant eomprises at least one dispersant selected from the group consisting of a sulfonated-fonnaldehyde-based dispersant, a polycarboxylated ether dispersant, and any combination thereof;

6. A method according to any of claims 1 to 5 wherein at least one of the pozzolan slurry, thé Hmé slurry, or the cement composition further eomprises a cement set retarder.;

7. A method according to claim 6 wherein the cement set retarder is selected trom the group consisting of a phosphonic acid, a phosphonic acid derivative, a lignøsulfonate, a salt, an organie acid. a carboxymethylated hydroxyelhylaled cellulose, a synthetic eo- or ter-polymer comprising sulfonate and carboxylic acid groups, a borate compound, and any combination thereof.;

8. A method according to any of claims I to 7 wherein at least one of the pozzolan slurry, the lime slurry, or thé cement composition further eomprises a cement set activator; wherein the cement set activator eomprises at least one cement set activator selected from the group consisting of an amine, a silicate, zinc formåte, calcium acetate, a Group IA hydroxide; a Group 11A hydroxide, a monovalent salt, a divalent salt nanosilica, a poiyphosphale, and any combination thereof.;

9. A meihod according io any of claims 1 to 8 further compirsing storing at least one of the pozzolan slurry or the lime slurry for a time period of about 7 days or longer prior to the step of mixing.;

10. A method according to any of claims 1 to 9 further comprising pumping the cement composition through å teed pipe and into a wellbore annulus thai is penetrating the subterranean formation,;

11. A method of displacing a fluid in a subterranean formation comprising: providing a pozzolan slurry eomprising a pozzolan and water; providing a lime siurry comprising hydrated lime and water; introducing at least a portion of the pozzolan siurry into a wellbore that penetrates a subterranean formation such that the pozzolan slurry dispiaces at least one fluid from the wellbore; activating the set-delayed cement composition by mixing at least a portion of the pozzolan slurry and at least a portion of the lime slurry to form a cement composition; introducing the cement composition into a subterranean formation; and allowing the cement composition to set in the subterranean formation.;

12. A method according to claim I I wherein the pozzolan is selected from the group consisting of fly ash, silica fume, metakaolin, pumice, and any combination thereof.;

13. A method according to claim 11 or 12 wherein the portion of the pozzolan slurry that dispiaces at least one fluid from the wellbore is foamed prior to displacing at least one fluid from the wellbore.;

14. A method according to any of claims 11 to 13 wherein at least one of the pozzolan slurry, the lime slurry, or the cement composition further eomprises a dispersant.;

15. A method according to any of claims 11 to 14 wherein at least one of the pozzolan slurry* the inne slurry, or the cement composition further eomprises a cement set retarder.

16. A method according to any of claims 11 to 15 wherein at least one of the pozzolan slurry, the lime siurry, or the cement composition éømprises a cement set activator.

17. A method according to any of claims 11 to 16 further comprising storing at least one of the pozzolan siurry or the lime siurry for a time period of about 7 days or longer prior to the step of m ixing.

18. A method according to any of claims 11 to 17 further comprising pumping the cement composition through a feed pipe and into a welibore annulus that is penetrating the subterranean formation.

19, A system for cementing comprising: a pozzolan slurry comprising a pozzolan and water; a time siurry for combination with the pozzolan slurry to forta a cement composition, wherein the lime slurry eomprises hydrated lime aud water.

20, The system of claim 19 further comprising mixing equipment for mixing the pozzolan siurry and the lime slurry to form the cement composition, and pumping equipment for delivering the cement composition into a wellbore.