Cement compositions including a compressive strength additive, and related cement slurries and methods

Abstract

A cement composition for a subterranean wellbore includes at least one cement binder, at least one compressive strength additive, and a density reducing material. The at least one compressive strength additive constitutes between about 0.1 weight percent and about 20 weight percent of the cement composition and the density reducing material constitutes between about 1 weight percent and about 40 weight percent of a density reducing material. Related cement slurry compositions and methods are also disclosed.

Description

TITLECEMENT COMPOSITIONS INCLUDING A COMPRESSIVE STRENGTH ADDITIVE, AND RELATED CEMENT SLURRIES AND METHODSCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to and the benefit of U.S. Provisional Patent Application No. 63 / 582,274, filed September 13, 2023, and entitled “CEMENT COMPOSITIONS INCLUDING A COMPRESSIVE STRENGTH ADDITIVE, AND RELATED CEMENT SLURRIES AND METHODS,” which is incorporated by reference in its entirety.BACKGROUND OF THE DISCLOSURE

[0002] Wellbore drilling operations includes drilling a bore in a formation to access reservoirs of hydrocarbons and other subsurface resources. After a drilling operation, a casing string may be run through the wellbore and cemented into place. The cement may facilitate isolating a section of the formation from other portions of the formation. Cementing may be performed in a single-stage where the cement is pumped into the casing, down a cement shoe, and then up into an annulus between the casing and the formation. In other cases, such as where the casing string is long or the formation cannot support the hydrostatic pressure of a column of the cement, the cementing may be performed in a multistage operation. For example, the wellbore may include a conductor casing proximate the surface, a surface casing extending beyond (e.g., below) the conductor casing, an intermediate casing beyond the surface casing, and a production line beyond the intermediate casing. Cement may be located between the formation and each of the casings and the formation, as well as between the neighboring casing sections.

[0003] Achieving cost effective solutions that achieve the desired specifications for cement in downhole applications has been challenging. To reduce the cost associated with cementing a wellbore, relatively low-cost cement slurries may be used, such as a mixture of Class C / fly ash cement. It is desired for the resulting set cement to exhibit a compressive strength (hereinafter “CS”) able to withstand formation pressures, drilling stresses, or other forms of compression or tension stresses during the life of the wellbore. Unfortunately, many conventional, low cost, cements do not exhibit desired properties, such as a suitable CS for downhole applications.

[0004] Some additives for improving the CS and the compressive strength development (hereinafter “CSD”) of the cement as cement hydration occurs are commercially available. However, conventional additives for increasing the CS and CSD of cement are expensive and undesirably affect other properties of the cement, such as increasing the setting time of the cement slurry, reducing the thickening time, or negatively affecting one or more other properties.SUMMARY

[0005] In some embodiments, a cement composition includes at least one cement binder, between about 0.1 weight percent and about 20 weight percent of a compressive strength additive, and between about 1 weight percent and about 40 weight percent of a density reducing material.

[0006] In some embodiments, a cement slurry includes water, and a cement composition mixed with the water. The cement composition includes at least one cement binder, between about 0.1 weight percent and about 20 weight percent of a compressive strength additive, and between about 1 weight percent and about 40 weight percent of a density reducing material.

[0007] In some embodiments, a method of cementing a subterranean borehole includes mixing water with a cement composition to form a cement slurry and pumping the cement slurry into an annular space between a casing and a subterranean formation defining the subterranean borehole. The cement composition comprises at least one cement binder, between about 0.1 weight percent and about 20 weight percent of a compressive strength additive, and between about 1 weight percent and about 40 weight percent of a density reducing material.

[0008] This summary is provided to introduce a selection of concepts that are further described in the detailed description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of the claimed subject matter. Additional features and aspects of embodiments of the disclosure will be set forth herein, and in part will be obvious from the description, or may be learned by the practice of such embodiments.BRIEF DESCRIPTION OF THE DRAWINGS

[0009] In order to describe the manner in which the above-recited and other features of the disclosure can be obtained, a more particular description will be rendered by referenceto specific embodiments thereof which are illustrated in the appended drawings. For better understanding, the like elements have been designated by like reference numbers throughout the various accompanying figures. While some of the drawings may be schematic or exaggerated representations of concepts, at least some of the drawings may be drawn to scale. Understanding that the drawings depict some example embodiments, the embodiments will be described and explained with additional specificity and detail through the use of the accompanying drawings in which:

[0010] FIG. l is a representation of a drilling system for drilling an earth formation to form a wellbore, according to at least one embodiment of the present disclosure;

[0011] FIG. 2 is a simplified, partial cross-sectional view illustrating a portion a downhole system, according to at least one embodiment of the present disclosure;

[0012] FIG. 3 is a simplified, partial cross-sectional view of a particle of a density reducing material, according to at least one embodiment of the present disclosure;

[0013] FIG. 4 is a graph illustrating a particle size distribution of two different compressive strength additives, according to at least one embodiment of the present disclosure;

[0014] FIG. 5 is a graph illustrating a compressive strength and a compressive strength development of a cement slurry including a cement composition including a compressive strength additive and a cement slurry not including the cement strength additive; and

[0015] FIG. 6 is a graph illustrating a compressive strength and a compressive strength development of different cement slurries including different amounts of a compressive strength additive and not including density reducing materials.DETAILED DESCRIPTION

[0016] As used herein, “cement composition” means and includes a mixture (blend) of one or more binder materials to which water may be added to form a slurry, referred to herein as a “cement slurry.” In addition to the binder materials, the cement composition may include one or more filler materials and / or one or more additives. The binder materials may include one or more cementitious materials, cement binders, or combinations thereof. The cement binders of the cement composition may be an inorganic binder, which may be a cement powder, commonly known as Ordinary Portland Cement, or simply “cement”. Portland cement is produced by pulverizing clinker. Clinker may include one or more of tricalcium silicate, dicalcium silicate, tricalcium aluminate, or tetracalcium ferroaluminate and may include the calcined (burned) material that exits the rotary kiln in a cement plant.Upon hydrating and setting, the cement slurry forms a hardened water saturated material, which may be referred to herein as “set cement,” a “hardened cement,” or a “hydrated cement.”

[0017] As used herein, “geopolymer composition” means and includes a mixture (blend) of one or more materials to which water may be added to form a slurry, referred to herein as a “geopolymer slurry.” During hardening (also referred to as “setting”), the geopolymer slurry undergoes polycondensation wherein the composition included in the slurry (e.g., aluminosilicate) polymerizes and forms a crosslinked network, which may be referred to herein as a “geopolymer,” a “set geopolymer,” a “hardened geopolymer,” or a “geopolymer cement.” Geopolymers are a class of amorphous materials that are formed by chemical reaction (e.g., chemical dissolution and subsequent recondensation) of various aluminosilicate oxides and silicates to form an amorphous three-dimensional framework structure. Geopolymers include a three-dimensional aluminosilicate mineral polymer. The preparation of geopolymers generally involves mixing a blend of reactive solid materials and activating the polymerization reaction by adding an alkaline solution. The slurry mixture may then be applied and allowed to harden in place. Geopolymers have been employed as alternatives for wellbore cement.

[0018] This disclosure generally relates to devices, systems, and methods for cement compositions and cement slurries including one or more cement binders, one or more compressive strength additives, and one or more density reducing materials including a gaseous phase. The compressive strength additives may be formulated for increasing the CS of cement formed from the cement compositions. In some embodiments, the compressive strength additive comprises one or more pozzolanic materials, such as metakaolin. The cement composition may further include one or more density reducing materials, which may be dispersed in a cement slurry formed from the cement composition. The density reducing materials may include at least one of glass bubbles or cenospheres in the cement composition; a gas phase dispersed through the cement slurry and directly contacting an interface between the liquid phase and the solid phase; or both.

[0019] The cement composition may form a pumpable cement slurry when mixed with water or an aqueous material and / or may be configured for use during cementing operations and / or during operation of one or more subterranean wellbores. The combination of the compressive strength additive and the density reducing materials in the cement slurry may increase the CS of the cement and the rate of compressive strength development (hereinafter “CSD”) of the cement as it sets. It is believed that the combination of thedensity reducing materials with the compressive strength additive synergistically improves the CS and the CSD of the cement slurry and the hydrated cement more than either of the density reducing materials and the compressive strength additive alone. The combination of the density reducing materials with the compressive strength additive may facilitate increasing the CS and CSD of the cement slurry and set cement while also maintaining a relatively low solid volume fraction (SVF). In addition, reducing the density of the cement slurry and the set cement may facilitate increasing the concentration of the compressive strength additive in the cement composition, increasing the ratio of the compressive strength additive to the cement (the cement binder), increasing the CS and CSD of the cement slurry and set cement compared to conventional cement compositions. A higher rate of CSD may reduce the idle time duration between the cementing operation and one or more additional wellbore operations, such as additional drilling, completion, production, or other operations (Wait On Cement, WOC).

[0020] In addition to increasing the CS and CSD of cement and cement slurries, the combination of the compressive strength additives and the density reducing materials may increase the CS and CSD of geopolymers and geopolymer slurries. For example, the compressive strength additives and density reducing materials may be provided to a geopolymer composition including one or more aluminosilicate sources. The geopolymer composition may include one or more aluminosilicate materials, one or more compressive strength additives, and one or more density reducing materials including a gaseous phase. The one or more compressive strength additives and the one or more density reducing materials may be the same as described above and may be configured to synergistically increase the CS and CSD of the geopolymer and the geopolymer slurry.

[0021] FIG. 1 shows one example of a drilling system 100 for drilling an earth formation 101 to form a wellbore 102 during a drilling operation. The drilling system 100 includes a drill rig 103 used to turn a drilling tool assembly 104 which extends downward into the wellbore 102. The drilling tool assembly 104 may include a drill string 105, a bottomhole assembly (“BHA”) 106, and a bit 110, attached to the downhole end of drill string 105.

[0022] The drill string 105 may include several joints of drill pipe 108 connected end- to-end through tool joints 109. The drill string 105 transmits drilling fluid through a central bore and transmits rotational power from the drill rig 103 to the BHA 106. In some embodiments, the drill string 105 may further include additional components such as subs, pup joints, etc. The drill pipe 108 provides a hydraulic passage through which drilling fluidis pumped from the surface. The drilling fluid discharges through selected-size nozzles, jets, or other orifices in the bit 110 for the purposes of cooling the bit 110 and cutting structures thereon, and for lifting cuttings out of the wellbore 102 as it is being drilled.

[0023] After a section of the wellbore 102 has been drilled, the drill string 105 may be tripped (removed from the wellbore 102) and at least a portion of the earth formation 101 may be lined with a casing 107. After placing the casing 107, a cement operation may be performed during which cement is pumped through the casing 107, through the bottom of the casing, and out of the annulus between the casing 107 and the earth formation 101. After the cement sets, additional wellbore operations (e.g., additional drilling, completion) may be performed.

[0024] FIG. 2 is a simplified, partial cross-sectional view illustrating a portion a downhole system 200 including the earth formation 101 after one or more cementing operations have been performed in the wellbore 102 (FIG. 1), in accordance with embodiments of the disclosure. The downhole system 200 may include multiple sections of casing, each extending from the surface (at the drill rig 103 (FIG. 1)) through a portion of the earth formation 101 and progressively extending farther into the earth formation 101. For example, the casing may include a conductor casing 202 extending from the surface through a portion of the earth formation 101, a surface casing 204 extending from the surface beyond the conductor casing 202, an intermediate casing 206 extending beyond the surface casing 204, and a production casing 208 (also referred to as a “production liner”) extending from the surface beyond the intermediate casing 206. The conductor casing 202 may be configured to protect shallow portions of the earth formation 101 from contamination, such as by drilling fluids. The surface casing 204 may facilitate maintaining integrity of the wellbore 102 (FIG. 1) and / or prevent (substantially prevent) contamination of groundwater by hydrocarbons, subterranean brines, and drilling fluids. The intermediate casing 206 may be configured to isolate hydrocarbon-bearing portions of the earth formation 101 and fractured and lost circulation zones. The production casing 208 may be configured to isolate zones of the earth formation 101 above and within a production zone.

[0025] The sections of casing may individually be isolated from the earth formation 101 by cement 210, which may also be referred to as a “set cement,” a “hydrated cement,” or a “hardened cement.” The cement 210 may be located in the annular space between the earth formation 101 and each of the conductor casing 202, the surface casing 204, the intermediate casing 206, and the production casing 208. In some embodiments, the cement 210 may be located in the annular space between neighboring sections of the casing, suchas between the conductor casing 202 and the surface casing 204, between the surface casing 204 and the intermediate casing 206, and between the intermediate casing 206 and the production casing 208.

[0026] The cement 210 and the cement slurry from which the cement 210 forms may exhibit a greater CS and a relatively lower density than conventional cements and cement slurries used during wellbore construction. According to embodiments described herein, the cement 210 may be formed by mixing a cement composition with water or an aqueous solution to form a cement slurry (also referred to as a “slurry composition”). The cement slurry may be pumped through the sections of casing and into the annulus between the individual casing sections and the earth formation 101. The cement slurry may exhibit a relatively shorter CSD compared to conventional cement slurries, facilitating continuing wellbore operations faster than when using cement slurries exhibiting a relatively longer CSD. In other words, the wait on cement time may be reduced due to the faster CSD of the cement slurry, facilitating faster cementing operations and return to drilling operations compared to when conventional cement slurries are used to form the cement 210. Although FIG. 2 has been described as including cement 210, the disclosure is not so limited. In other embodiments, and as described in additional detail herein, the sections of casing may be placed with a geopolymer, which may include the one or more compressive strength additives and the density reducing materials described herein.

[0027] As described above, the cement 210 may be formed from a cement slurry comprising a cement composition mixed with water or an aqueous solution. The cement composition may include a base composition, one or more compressive strength additives, and one or more density reducing materials. In some embodiments, the cement composition further includes one or more additional additives, such as one or more of a filler material, metal silicate, an activator, a retardant (also referred to as a retarder), an accelerator, a dispersant, a surfactant, a binder, a viscosifier (e.g., xanthan gum), a fluid loss agent (e.g., cellulose, latex, and / or 2-acrylamido-2-methylpropane sulfonic acid (AMPS), an acrylamide copolymer), an extender (e.g., sodium metasilicate QS^SiCh), perlite), a defoamer (an antifoam additive, an antifoam agent), silica, an expanding agent, a flexible additive, a latex or latex-based additive, a dispersant (e.g., a sodium polynaphthalene sulfonate-based material), or combinations thereof.

[0028] The base composition may include one or more cement binders (also referred to as a “binder” or “cement particles”). In some embodiments, the base composition incudes a cement binder, such as one or more of portland cement, fly ash extended portland cement,slag extended portland cement, or pozzolan extended portland cement. The base composition may include a settable composition formulated and configured to harden and develop compressive strength during setting.

[0029] The one or more cement binders may include portland cement, fly ash extended portland cement, slag extended portland cement, or pozzolan extended portland cement. The one or more cement binders may include one or more of portland cement, a low density cementitious cement clinker blend, fly ash (siliceous fly ash, calcareous fly ash), slag (a by-product of smelting metal ores and including a mixture of metal oxides and silicon dioxide), tricalcium silicate (3CaO SiCh; CasSiOs) (alite), dicalcium silicate (2CaO SiCh; Ca2SiO4) (belite), tricalcium aluminate (3CaO AI2O3; CasAhOe), calcium aluminoferrite (4CaO AI2O3 Fe20s; Ca2(Al,Fe)20s) (brownmillerite), silica fume, at least one pozzolan material (a material including at least one siliceous or siliceous and aluminous material), diatomaceous earth, pumice, biomass ashes, ground granulated blast furnace slag (hereinafter “GGBS”), and one or more pozzolanic additives. Portland cement may be obtained by pulverizing clinker comprising or consisting of hydraulic calcium silicates. The portland cement may include gray or white portland cement. The pozzolanic additives may include one or more of fly ash, D-Dust, glass powder pozzolan, zeolite, rice husk ash, micro-slag, and calcinated clay. In some embodiments, the cement binder may include a geopolymer material and / or an alkali activated material (e.g., potassium hydroxide (KOH), calcium hydroxide (Ca(OH)2), magnesium hydroxide (Mg(OH)2), sodium metasilicate (Na2SiOs), a potassium silicate (e.g., potassium metasilicate ( ^SiOs)), calcium silicate (Ca2SiO4), calcium metasilicate (CaSiOs), or sodium carbonate QSfeCCh), and the like).

[0030] In some embodiments, the one or more cement binders include first binder particles and second binder particles having a relatively smaller size than the first binder particles. In some embodiments, the second binder particles include so-called “micro fine cement” including microfine particles. The second binder particles may have a specific surface area greater than about 800 m2 / g, such as greater than about 850 m2 / g, or greater than about 900 m2 / g. The second binder particles may include one or more of the materials described above with reference to the binder materials. In some embodiments, the second binder particles include blast furnace slag. A median particle size of the second binder particles may be less than about 3.0 pm, such as less than about 2.5 pm, or less than about 2.0 pm. In some embodiments, the second binder particles exhibit a higher compressive strength than the first binder particles and increases the rate of development of compressivestrength as a binder slurry including the second binder particles sets. In some embodiments, the cement binder includes only one of the first particles or the second particles.

[0031] The one or more cement binders may constitute from about 10.0 weight percent to about 99.5 weight percent of the cement composition (by weight of blend; BWOB), such as from about 10.0 weight percent to about 20.0 weight percent, from about 20.0 weight percent to about 30.0 weight percent, from about 30.0 weight percent to about 40.0 weight percent, from about 40.0 weight percent to about 50.0 weight percent, from about 50.0 weight percent to about 60.0 weight percent, from about 60.0 weight percent to about 70.0 weight percent, from about 70.0 weight percent to about 80.0 weight percent, from about 80.0 weight percent to about 90.0 weight percent, from about 90.0 weight percent to about 95.0 weight percent, from about 95.0 weight percent to about 97.0 weight percent, from about 97.0 weight percent to about 98.0 weight percent, from about 98.0 weight percent to about 99.0 weight percent, from about 99.0 weight percent to about 99.5 weight percent of the cement composition. However, the disclosure is not so limited, and the one or more cement binders may be present in the cement composition at different amounts than that described.

[0032] As used herein, by weight of blend (BWOB) when referring to a component of the cement composition means and includes the weight percent of the particular component when considering the entire cement composition (the entire blend) including the cement binder, the one or more compressive strength additives, the density reducing materials, any fillers, and any other additives in the cement blend. For example, a particular component present in the cement composition at 10 percent BWOB includes 10 grams of the particular component for every 100 grams of the cement composition. On the other hand, when referring to by weight of cement (BWOC) of a particular component, means and includes the weight percent of a particular component the weight percent of the particular component with reference to the cement binder. For example, for a cement composition that includes 50 grams of cement binder and 50 grams of the particular component, the particular component is present in the cement composition at 100 percent BWOC (and 50 percent BWOB when the cement composition includes only the cement binder and the particular component). Stated another way, the BWOB of a particular component refers to the percentage of the particular component in the total amount of the cement composition (blend). As used herein, when referring to by volume of cement (BVOC) with respect to a particular component in the cement composition means and includes the volume of particular component relative to the volume of the cement binder. Similarly, as used herein,when referring to by volume of blend (BVOB) with respect to a particular component in the cement composition means and includes the volume of particular component relative to the volume of the entire cement composition (the entire blend). Those skilled in the art of formulating cement blends and slurries will easily be able to calculate additive and solids concentrations when provided with the reference as used, and some additive specific data such as the specific gravity of cement, and other blend solids.

[0033] The base composition comprises, consists essentially of, or consists of the binder material. In some embodiments, the base composition is present in the cement composition at about 100 percent BWOC.

[0034] As described above, the cement composition may further include one or more compressive strength additives and one or more density reducing materials. The density reducing materials may include glass bubbles (hollow spheres formed from silica, silicon dioxide, glass, fibrous glass, glass wool, oxide glass, non-crystalline silica and the like, and filled with air or an internal gas), cenospheres (hollow spheres formed from silica and alumina and filled with air or an internal gas), or a combination thereof. FIG. 3 is a simplified, partial cross-sectional view of a particle (e.g., piece) 300 of the density reducing material, in accordance with embodiments of the disclosure.

[0035] The particle 300 includes a shell 302 surrounding a cavity 304 defined by inner surfaces of the shell 302. The shell may include one or more of silica, alumina, aluminosilicate (a material including aluminum, silicon, and oxygen and including one or more Si-O-Al bonds), zirconium oxide, borosilicate glass, and titanium oxide. In some embodiments, the shell 302 further includes calcium oxide and / or iron oxide.

[0036] The cavity 304 may be filled with a gas, such as air or nitrogen. In some embodiments, the cavity 304 is filled with air. In some embodiments, each of the particles 300 include the same gas in the cavity 304. In other embodiments, at least some of the particles 300 include a cavity filled with a first gas and at least other particles 300 include a cavity 304 filled with a second gas different than the first gas.

[0037] A concentration of the density reducing materials in the cement composition may be within a range of from about 1 BWOB percent to about 40 percent BWOB, such as from about 1 percent BWOB to about 3 weight percent, from about 3 weight percent to about 10 percent BWOB, from about 10 percent BWOB to about 20 percent BWOB, from about 20 percent BWOB to about 30 percent BWOB, or from about 30 percent BWOB to about 40 percent BWOB. In some embodiments, the concentration of the density reducing materials in the cement composition is within a range of from about 7 percent BWOB toabout 30 percent BWOB, or from about 10 percent BWOB to about 20 percent BWOB. The concentration of the density reducing material may be within a range of from about 5 percent to about 60 percent BWOC, such as from about 8 percent BWOC to about 50 percent BWOC, or from about 12 percent BWOC to about 40 percent BWOC. A cement slurry formed from the cement composition may, accordingly, include from about 1 weight percent to about 40 weight percent of the density reducing materials; and the cement 210 may include from about 1 weight percent to about 40 weight percent of the density reducing materials exclusive of water.

[0038] The particle 300 may have a diameter D within a range of from about 50 pm to about 200 pm, such as from about 50 pm to about 100 pm, from about 100 pm to about 150 pm, or from about 150 pm to about 200 pm. In some embodiments, the particles 300 of the density reducing material may be less than about 150 pm (e.g., less than 100 mesh such that less than about 1 percent of the particles are larger than 150 pm). In some embodiments, the particles 300 may be greater than 400 mesh (e.g., less than about 5 percent of the particles 300 have a diameter D less than about 37 pm). In some embodiments, the median diameter D of the particles 300 is about 120 pm. In other embodiments, the median diameter D of the particles 300 is about 100 pm. However, the disclosure is not so limited, and the diameter D may be different than those described. The shell 302 may have a wall thickness T within a range of from about 2 pm and about 20 pm, such as from about 4 pm to about 15 pm, or from about 6 pm to about 12 pm. However, the disclosure is not so limited, and the wall thickness T may be different than those described.

[0039] The density reducing materials may exhibit a substantially uniform distribution of particle sizes (diameter D) in the base composition. In some such embodiments, the base composition may exhibit a unimodal particle size distribution, such as a monodisperse particles size distribution, of the density reducing materials. In other embodiments, the base composition exhibits a multimodal particle size distribution, such as a polymodal size distribution, of the density reducing materials.

[0040] The thickness T of the shell 302 of particles of the density reducing materials in the base composition may be substantially uniform. In other embodiments, the base composition may exhibit a polymodal size distribution of the thickness T of the shell 302.

[0041] A specific gravity (SG) of the particles 300 may be within a range of from about250 kg / m3to about 990 kg / m3, such as from about 250 kg / m3to about 350 kg / m3, fromabout 350 kg / m3to about 500 kg / m3, from about 500 kg / m3to about 750 kg / m3, or from about 750 kg / m3to about 990 kg / m3.

[0042] In some embodiments, the density reducing materials include a foaming agent formulated and configured to form foamed cement including a foamed gas dispersed in the cement slurry and the cement 210 and reduce the density of the cement 210. The foaming agent may include one or more of a surface active or polymer organic compound, configured to facilitate reaction between the cement binder and another material (e.g., water) to create a foam. By way of non-limiting example, the foaming agent may include a foam stabilizing agent selected from, a protein-based foaming agent (e.g., egg-whites, gelatin, casein, soy proteins), polyvinyl alcohol (PVA)), and a surface active additive comprising at least one surface active additive based on alkyl ethoxylated alcohols, a surface active additive based on a salt of alkyl alcohol ethoxysulfate (such as sodium, potassium, ammonium salt, and the like ), a surface active additive based on betaine, a surface active additive based on sulfobetaine (zwitterionic compounds including an ammonium group (e.g., a positively charged ammonium group) and a sulfonic acid group (e.g., a negatively charged sulfonate group)), and the foamed cement may include a synthetic gas-producing foaming agent (e.g., azodi carbonamide, p-toluenesulfonyl hydrazide, sodium bicarbonate), and / or a gas phase comprising a gas selected from air, nitrogen gas, carbon dioxide, another material, or mixtures thereof.

[0043] The compressive strength additives may include one or more of metakaolin (also referred to as calcined kaolin clay), a pozzolanic material (e.g., silicon dioxide, aluminum oxide), fly ash, D-Dust, glass powder pozzolan, zeolite, rice husk ash, microslag, calcinated clay, and diatomaceous earth. In some embodiments, the compressive strength additives consist of or consist essentially of metakaolin. As used herein, a “pozzolanic” material means and includes a material including at least one siliceous material and / or at least one aluminous material. Pozzolanic materials may themselves not exhibit cementitious properties, but when finely ground, and in the presence of water, may chemically react with calcium hydroxide to form compounds having cementitious properties.

[0044] The compressive strength additives may be present in the cement composition at a concentration within a range of from about 0.1 percent BWOB to about 50 percent BWOB, such as from about 0.1 percent BWOB to about 1.0 percent BWOB, from about 1.0 percent BWOB to about 5.0 percent BWOB, from about 5.0 percent BWOB to about 20 percent BWOB, from about 20 percent BWOB to about 40 percent BWOB, or fromabout 40 percent BWOB to about 50 percent BWOB. In some embodiments, the compressive strength additives are present in the cement composition at a concentration within a range of from about 0.1 percent BWOB to about 20 percent BWOB. In some embodiments, the compressive strength additives are present in the cement composition at a concentration within a range of from about 1 percent BWOB to about 15 percent BWOB, or from about 1.5 percent BWOB to about 7.0 percent BWOB. In some embodiments, a concentration of the compressive strength additive in the cement composition is within a range of from about 2.0 percent BWOB to about 3.0 percent BWOB, such as about 2.9 percent BWOB.

[0045] The compressive strength additive may include a first compressive strength additive. The compressive strength additive may further include a second compressive strength additive and / or a third compressive strength additive. Greater than about 50 percent, such as greater than about 75 percent, greater than about 90 percent, or greater than about 95 percent of the first compressive strength additive may be in an amorphous phase (e.g., may include an amorphous aluminosilicate material). In some embodiments, the first aluminosilicate material is present in the cement composition at a concentration within a range of from about 1 percent to about 30 percent BWOC, such as from about 1 percent to about 2 percent, from about 2 percent to about 5 percent, from about 5 percent to about 10 percent, from about 10 percent to about 20 percent, or from about 20 percent to about 30 percent BWOC.

[0046] The first aluminosilicate material may exhibit a weight ratio of silicon oxide (e.g., silica) to aluminum oxide within a range of from about 1.0: 1.0 to about 2.5: 1.0, such as from about 1.0: 1.0 to about 1.5: 1.0, from about 1.5: 1.0 to about 2.0: 1.0, or from about 2.0: 1.0 to about 2.5: 1.0. In other words, for every 1.0 part of aluminum oxide, the first aluminosilicate material may include from about 1.0 part to about 2.5 parts of silicon oxide. The first aluminosilicate material may include at one or more of at least one pozzolanic material, D-dust, glass powder pozzolan, zeolite, rice husk ash, fly-ash, micro-slag, metakaolin, calcined clay, diatomaceous earth, pumice, biomass ash, ground granulated blast furnace slag, or combinations thereof. In some embodiments, the first aluminosilicate material includes calcined clay.

[0047] In embodiments including the second compressive strength additive, the second compressive strength additive may include a second aluminosilicate material including one or more of D-dust, glass powder pozzolan, zeolite, fly-ash, micro-slag, metakaolin, calcined clay, diatomaceous earth, pumice, biomass ashes, ground granulated blast furnace slag, orcombinations thereof. In some embodiments, the second compressive strength additive includes fly-ash. The second compressive strength additive may be present in the cement composition at a concentration within a range of from about 10 percent BWOC to about 200 percent BWOC, such as from about 10 percent BWOC to about 50 percent BWOC, from about 50 percent BWOC to about 100 percent BWOC, from about 100 percent BWOC to about 150 percent BWOC, or from about 150 percent BWOC to about 200 percent BWOC.

[0048] The second aluminosilicate material may exhibit a weight ratio of silicon oxide to aluminum oxide within a range of from about 1.7: 1.0 to about 2.3: 1.0, such as from about 1.7: 1.0 to about 2.0: 1.0, from about 2.0: 1.0 to about 2.5: 1.0, or from about 2.5: 1.0 to about 3.0: 1.0. In other words, for every 1.0 part of aluminum oxide, the second aluminosilicate material may include from about 1.7 parts to about 3.0 parts of silicon oxide. In some embodiments, the second aluminosilicate material exhibits a higher weight ratio of silicon oxide to aluminum oxide than the first aluminosilicate material.

[0049] The third compressive strength additive may include a pozzolanic material and may include one or more of silica fume, D-dust, glass powder pozzolan, zeolite, rice husk ash, micro-slag, metakaolin, high-reactivity metakaolin, calcined clay, diatomaceous earth, pumice, biomass ash, ground granulated blast furnace slag, or combinations thereof. In some embodiments, the third compressive strength additive includes rice husk ash, silica fume, or both.

[0050] The third compressive strength may exhibit a weight ratio of silicon oxide to aluminum oxide greater than about 4.0: 1.0. In other words, for every 1.0 part of aluminum oxide, the third compressive strength additive may include from at least about 4.0 parts of silicon oxide. In some embodiments, the third compressive strength includes a greater weight ratio of silicon oxide to aluminum oxide than the first aluminosilicate material and the second aluminosilicate material.

[0051] A particle size of the compressive strength additives may be within a range of from about 0.5 pm to about 65 pm. In some embodiments, the compressive strength additive exhibits a volume averaged diameter within a range of from about 3.5 pm to about 6.0 pm. In some embodiments, the particle size distribution of the compressive strength additives is polydisperse. In some such embodiments, the compressive strength additives may exhibit at least a first group of particles having a relatively smaller average particle size and at least a second group of particles having a relatively larger average particle size. As described in further detail below, the first group of particles having the relatively smallerparticle size may facilitate an increase in a concentration of the compressive strength additive particles at an interface between a gas phase and a slurry phase of a cement slurry formed from the cement composition; and the second group of particles having the relatively larger average particle size may facilitate providing relatively larger volumes (domains) of high strength material within the cement formed from the cement composition. In some embodiments, the particle size of the compressive strength additive is less than the particle size of the cement binder.

[0052] In some embodiments, the compressive strength additive includes a first group of particles (e.g., the first compressive strength additive) having an average diameter within a range of from about 0.5 pm to about 3.0 pm; a second group of particles (e.g., the second compressive strength additive) having an average diameter within a range of from about 3.0 pm to about 6.5 pm; and a third group of particles (e.g., the third compressive strength additive) having an average diameter greater than about 10 pm. In some embodiments, the first group of particles constitutes from about 15% to about 50% by volume of the compressive strength additive and the third group of particles constitutes from about 10% to about 30% by volume of the compressive strength additive. In some embodiments, at least about 20% by volume of particles of the compressive strength additive have a diameter less than about 3.5 pm, at least about 35% by volume of the particles have a diameter less than about 5.0 pm, and at least about 50% by volume of the particles have a diameter less than about 8.0 pm.

[0053] The cement slurry and the cement 210 may exhibit a final or overall compressive strength greater than about 1,000 psi, such as greater than about 1,200 psi, greater than about 1,500 psi, greater than about 1,800 psi, greater than about 2,000 psi, greater than about 2,200 psi, greater than about 2,300 psi, greater than about 2,400 psi, or even greater than about 2,500 psi. The cement slurry and the cement 210 formed from the cement composition including the combination of the compressive strength additives and the density reducing materials described herein may exhibit a compressive strength greater than the compressive strength of cement slurries and cements formed from cement compositions including only one of compressive strength additives or density reducing materials. For example, a cement slurry including about 9.9 percent BWOB of glass bubbles and no compressive strength additive reached a compressive strength of about 1,000 psi after about 12 hours. By way of comparison, a similar cement composition including about 9.6 percent BWOB of glass bubbles and about 2.9 percent BWOB ofmetakaolin (a compressive strength additive) exhibited a compressive strength of about 1,000 psi after only about 4 hours.

[0054] FIG. 4 is a graph illustrating a particle size distribution of two different compressive strength additives (labeled as “Material 1” and “Material 2” in FIG. 4. As shown in FIG. 4, greater than about 70 volume percent of the compressive strength additive may have a particle size smaller (e.g., less) than about 10 pm. In some embodiments, an average particle size of the compressive strength additives may be smaller (e.g., less) than an average particle size of the density reducing materials.

[0055] In some embodiments, the cement composition further includes one or more additional additives. The one or more additional additives may be selected from the group consisting of one or more of filler materials, metal silicate, an activator, an extender, a retardant, an accelerator, a surfactant, a binder, a viscosifier, a fluid-loss agent, a weighting agent, a lost circulation additive, a defoamer, silica, a swelling additive, an expanding agent, a flexible additive, a foamer, a latex or latex -based additive, a dispersant, and / or one or more fibers. In some embodiments, the additional additives may be included in the cement composition to control, change, or adjust one or more characteristics, properties, and / or features of the resulting cement and / or cement slurry. The one or more characteristics, properties, and / or features may comprise density, setting time, strength, flow, fluid loss, rheology, expansion, one or more mechanical properties, self-healing, or a combination thereof, wherein the one or more mechanical properties may comprise at least one selected from CS, Young’s modulus, Poisson ratio, tensile strength, or at least one combination thereof. The additional additives may be present at a concentration range of at least about 0.01% BWOC, about 0.05% BWOC, or about 0.1% BWOC and no greater than about 25% BWOC, about 35% BWOC, or about 45% BWOC.

[0056] The filler materials may include one or more of glass bubbles, sand (e.g., silicon dioxide (SiO?), also referred to as silica), gravel (aggregate), barite (BaSO4), and / or one or more pozzolanic materials (e.g., a siliceous material or a siliceous material and an aluminous material).

[0057] The activator may be present when the binder material includes at least one aluminosilicate source. The activator may include one or more of an alkali activator or an alkali activator precursor. The alkali activator may be an alkali metal hydroxide, an alkaline-earth metal hydroxide, an alkaline earth metal oxide, an alkaline earth metal peroxide, at least one alkali salt, or combinations thereof. Alkali metal hydroxides may include lithium hydroxide, sodium hydroxide, or potassium hydroxide. Alkaline earthmetal hydroxides may include calcium hydroxide, magnesium hydroxide, strontium hydroxide, or barium hydroxide. The alkaline earth metal oxides may be calcium oxide (e.g., lime), magnesium oxide, strontium oxide, barium oxide, or combinations thereof. The alkaline earth metal peroxide may be calcium peroxide or magnesium peroxide. The at least one alkali salt may be a metal carbonate (e.g., M2CO3, such as sodium carbonate), a metal sulfate (e.g., M2SO4), a metal sulfite (e.g., M2SO3), a metal phosphate (e.g., M3PO4), a metal oxalate (e.g., M2C2O4), a metal silicate (e.g., M2XSiyO(2y+x), wherein x is 1, 2, or 3, and y is 1 or 2), a metal fluoride (e.g., MF), a metal hexafluoride (e.g., M2SiFe), a metal iodate (e.g., MIO3), a metal molybdate (e.g., M2MOO4), wherein M is a metal such as lithium, sodium, potassium, rubidium, and / or cesium in each of the above examples. The alkali activator may be added as a solid, an aqueous mixture, or an encapsulated liquid or solid material. In an encapsulated embodiment, the solid or liquid activator can be trapped in a capsule that will break when subjected to, for example, mechanical stress on the capsule, or coating degradation from temperature, radiation, and / or chemical exposure. The capsule can also naturally degrade if made from a biodegradable or self-destructive material. Furthermore, the alkali activator when in liquid state may be adsorbed into a porous material and may be released after a certain time or due to a predefined event. The alkali activator may be added to the geopolymer slurry at a concentration within a range of from about 1 M to about 10M, such as from about 3M to about 6M.

[0058] In some embodiments, the activator includes a metal silicate, such as an alkali metal silicate, such as sodium silicate, sodium metasilicate (ISfeSiCh), potassium silicate (e.g., potassium metasilicate (K^SiCh)), calcium silicate (Ca2SiO4), calcium metasilicate (CaSiCh), sodium carbonate (ISfeCCh), or combinations thereof. The activator may include silicates of lithium, sodium, potassium, rubidium, cesium, or combinations thereof.

[0059] The extender may include sodium metal silicate (e.g., sodium metasilicate) (Na2SiO3)), perlite, another material, or combinations thereof. The defoamer may include one or more of a propylene glycol, such as polypropylene glycol, a polyglycol ether, a silicone, or another material. The defoamer may be present in the binder composition at a weight percent from about 0.01 weight percent to about 0.50 weight percent by weight of blend, such as from about 0.01 weight percent to about 0.05 weight percent, from about 0.05 weight percent to about 0.10 weight percent, from about 0.10 weight percent to about 0.20 weight percent, from about 0.20 weight percent to about 0.30 weight percent, from about 0.30 weight percent to about 0.40 weight percent, or from about 0.40 weight percent to about 0.50 weight percent by weight of the blend.

[0060] The retardant may include one or more of ferric sulfate (F 62(804)3), sodium lignosulfonate (C2oH24Na20ioS2), sodium pentaborate decahydrate, borax, boric acid, lignosulphonates, sodium glucoheptonate tartaric acid, citric acid, sucrose, or phosphorus containing compounds such as phosphoric acid, salts thereof, or mixtures thereof. In some embodiments, the retarder includes ferric sulfate. In some embodiments, the retarder may also act as a coagulant, such as, for instance, when the retarder comprises iron sulfate (e.g., ferric sulfate). A concentration of the retardant in the binder composition may be within a range of from about 0.5 weight percent to about 3.0 weight percent, such as from about 0.5 weight percent to about 1.0 weight percent, from about 1.0 weight percent to about 1.5 weight percent, from about 1.5 weight percent to about 2.0 weight percent, from about 2.0 weight percent to about 2.5 weight percent, or from about 2.5 weight percent to about 3.0 weight percent by weight of aluminosilicate. In some embodiments, the retardant is present in the binder composition at a concentration within a range of from about 1.1 weight percent to about 2.3 weight percent.

[0061] The accelerator may include lithium salts such as, for example, lithium chloride, lithium hydroxide, or a mixture thereof. The accelerator may be present in the binder composition at a concentration within a range of from about 0.5 weight percent to about 3.0 weight percent, such as from about 0.5 weight percent to about 1.0 weight percent, from about 1.0 weight percent to about 1.5 weight percent, from about 1.5 weight percent to about 2.0 weight percent, from about 2.0 weight percent to about 2.5 weight percent, or from about 2.5 weight percent to about 3.0 weight percent of the binder composition.

[0062] The viscosifier may include one or more of a polysaccharide (e.g., xanthan gum, diutan gum, welan gum), polyanionic cellulose (PAC), a carboxymethylcellulose (CMC), or another material. In some embodiments, the viscosifier includes diutan gum having a molecular weight higher than about 1 x 106. The viscosifier may be present in the cement slurry at a concentration between 0.14 g / L and 1.4 g / L (0.05 Ib / bbl and 0.5 Ib / bbl). The molecular weight of the polysaccharides, which may be biopolymers, may be between 100,000 g / mol and 1,000,000 g / mol.

[0063] The fluid-loss agent may include a styrene butadiene latex material. In some embodiments, the additional fluid loss control material includes an alkali-swellable latex. In some embodiments, the additional fluid loss control material includes a crosslinked polymer and bridging materials. The bridging materials may include particles of at least one of calcium carbonate, zinc carbonate, barium carbonate, a coated metal oxide (e.g., hemalite, ilmenite, magnesium oxide), dolomite (calcium magnesium carbonate),colemanite, ulexite, analcite, apatite, bauxite, brucite, gibbsite, hydrotalcite, galena, hematite, magnetite, iron oxides, siderite, celestite, magnesium citrate, calcium citrate, calcium succinate, calcium maleate, calcium tartrate, magnesium tartrate, bismuth citrate, other suspended salts, mica, nutshells, or fibers.

[0064] The defoamer may be present in the binder composition at a weight percent from about 0.01 weight percent to about 0.50 weight percent by weight of blend, such as from about 0.01 weight percent to about 0.05 weight percent, from about 0.05 weight percent to about 0.10 weight percent, from about 0.10 weight percent to about 0.20 weight percent, from about 0.20 weight percent to about 0.30 weight percent, from about 0.30 weight percent to about 0.40 weight percent, or from about 0.40 weight percent to about 0.50 weight percent by weight of the blend.

[0065] The expanding agent may include calcium sulfate hemihydrate, metal oxides such as calcium oxide (CaO), magnesium oxide (MgO), or combinations thereof. The expanding agent may constitute from about 0.01 weight percent to about 1.0 weight percent of the binder composition, such as from about 0.01 weight percent to about 0.10 weight percent, from about 0.10 weight percent to about 0.30 weight percent, from about 0.30 weight percent to about 0.50 weight percent, from about 0.50 weight percent to about 0.75 weight percent, or from about 0.75 weight percent to about 1.0 weight percent of the binder composition.

[0066] The dispersant may include a sodium polynaphthalene sulfonate-based, carboxylic acids including gluconic acid and soluble salts thereof, glucoheptonic acid and soluble salts thereof, tartaric acid and soluble salts thereof, citric acid and soluble salts thereof, glycolic acid and soluble salts thereof, lactic acid and soluble salts thereof, formic acid and soluble salts thereof, acetic acid and soluble salts thereof, proprionic acid and soluble salts thereof, oxalic acid and soluble salts thereof, malonic acid and soluble salts thereof, succinic acid and soluble salts thereof, adipic acid and soluble salts thereof, malic acid and soluble salts thereof, nicotinic acid and soluble salts thereof, benzoic acid and soluble salts thereof, ethylenediamine tetraacetic acid (EDTA) and soluble salts thereof, phosphoric acid, or combinations thereof. The dispersant may be present in the binder composition at a weight percent from about 0.01 weight percent to about 0.50 weight percent by weight of blend, such as from about 0.01 weight percent to about 0.05 weight percent, from about 0.05 weight percent to about 0.10 weight percent, from about 0.10 weight percent to about 0.20 weight percent, from about 0.20 weight percent to about 0.30weight percent, from about 0.30 weight percent to about 0.40 weight percent, or from about 0.40 weight percent to about 0.50 weight percent by weight of the blend.

[0067] The cement composition may be mixed with water or another aqueous material to form a cement slurry comprising the cement composition and the water. The cement slurry may be a pumpable composition. In use and operation, the cement slurry may be pumped into the annular space between one or more sections of casing 202, 204, 206, 208 (FIG. 2) and the earth formation 101 (FIG. 2) and / or between neighboring sections of casing 202, 204, 206, 208. After setting, the cement slurry may form the cement 210, which may be hydrated and set.

[0068] In some embodiments, a density of the slurry composition may be within a range of from about 1,000 kg / m3(about 8.33 pounds per gallon (ppg)) to about 1,500 kg / m3(about 12.5 ppg). However, the disclosure is not so limited, and the density of the slurry composition may be different than that described. A viscosity of the cement slurry may be less than about 400 centipoise (hereinafter “cP”), less than about 350 cP, or less than about 300 cP.

[0069] A solid volume fraction (SVF) (defined as the volumetric fraction of the cement slurry comprised of solid particles) of the cement slurry may be within a range of from about 25% to about 60%, such as from about 40% to about 55%. A dispersed material volume fraction (DMVF) may be defined as the solids and gases dispersed in the liquid phase (e.g., the water, brine, or aqueous phase) in which the cement composition is dispersed. In some cases, the DMVF is identical to the SVF, such as when the dispersed material comprises the density reducing materials including entrapped gas (e.g., the particles 300), but no additional dispersed gas phase. In other embodiments, the DMVF may be higher than the SVF, such as when the dispersed material comprises a foamed gas. Water, brine, or another aqueous liquid (in which the solid materials are dissolved) may constitute from about 20% to about 85% by volume of the cement slurry or from about 40% to about 70% by volume of the cement slurry and may be referred to as a liquid volume fraction (LVF). In some embodiments, such as where the cement slurry includes a dispersed gas phase (and not the particles 300 of the density reducing material), the sum of the DMVF and the LVF may be equal to 1 (e.g., DMVF+LVF = 1), but the sum of the SVF and the LVF may be lower than 1 (e.g., SVF+LVF < 1). In embodiments where the cement slurry includes a cement composition including the density reducing material as particles 300, but no additional dispersed gas phase the sum of the DMF and the LVF is equal to 1 (e.g., DMF+LVF=1), as is the sum of the SVF and the LVF (e.g., SVF+LVF = 1).

[0070] In some embodiments, due to the presence of the density reducing materials in the cement slurry, a gas fraction of the cement slurry may be within a range of from about 1 volume percent to about 60 volume percent of the cement slurry, such as from about 10 volume percent to about 55 volume percent, or from about 10 volume percent to about 40 volume percent of the cement slurry (e.g., at downhole pressure and temperature conditions).

[0071] In some embodiments, the cement composition may be mixed with water and a gaseous material to form the cement slurry to form a foamed cement slurry, which upon set is considered a foamed cement. The foamed cement slurry may be formed with a foaming agent, which may include one or more of the materials described above. In some such embodiments, the slurry composition may include a gas phase including the gaseous material dispersed in the cement slurry. The gaseous material may include, for example, nitrogen (N2) or air. In some embodiments, the gaseous material includes nitrogen. In some embodiments, the cement composition does not include the density reducing material. In other embodiments, the cement composition includes the density reducing material and the cement slurry further includes a gaseous material in addition to the density reducing material. In some embodiments, a foamer is included to facilitate a stable foam.

[0072] In some embodiments, the gas fraction of the cement slurry may be within a range of from about 1% by volume to about 80% by volume of the cement slurry, such as from about 5% to about 65%, such as from about 7.5% to about 55%, or from about 10% to about 40% by volume of the cement slurry (e.g., at downhole pressure and temperature conditions).

[0073] After setting, a density of the set cement formed from the cement composition may be within a range of from about 800 kg / m3(about 6.68 ppg) to about 1,500 kg / m3(about 12.5 ppg), however the disclosure is not so limited, and the density of the cement may be different than those described.

[0074] Without being bound by any particular theory, it is believed that the gas phase dispersed in the cement slurry (due to density reducing materials including the particles 300 and / or the foaming agent) facilitates an improved effectiveness of the compressive strength additive in the cement composition. In other words, it is believed that the combination of the compressive strength additive and the gas phase caused by the density reducing materials facilitates an increase in the CS and the CSD of the cement slurry during setting thereof to form the cement. It is believed that the gas phase (whether in the form of the particles 300 or as a separate phase directly contacting the cement slurry) enhances theaccumulation of the compressive strength additive at interfaces between the gaseous phase and other phases (e.g., a liquid phase, a solid phase) in the cement slurry and the resulting cement. The increased concentration of the compressive strength additive at the interfaces increases the CS and the CSD of the cement.

[0075] Including the combination of the compressive strength additive(s) and the density reducing materials in the cement composition may increase the CS of the cement slurry and the cement 210 compared to either the compressive strength additives or the density reducing materials alone or the sum of the increase caused by each of the compressive strength additives and the density reducing materials when included in the cement composition without the other of the compressive strength additives or the density reducing materials.

[0076] Without being bound by any particular theory, it is believed that including the combination of the compressive strength additive and the density reducing materials facilitates increasing the weight ratio of the compressive strength additive relative to the binder material. For example, forming the cement composition to include a relatively large volume fraction of the density reducing materials (and the gas phase encapsulated therein and / or of the foamed gas) may increase the concentration of the compressive strength additive (e.g., metakaolin) per gram of the cement binder at the interfaces (e.g., between the density reducing materials and the solid phase of the cement binder). In addition, enhancing the concentration of the compressive strength additive (e.g., metakaolin) per gram of the cement binder will result in a large increase of the compressive strength of the set material surrounding the density reducing materials, and foam that, in turn, will increase the adhesion between these gas containing fillers and the cement matrix resulting in overall higher compressive strength for the set cement material.

[0077] In some embodiments, the combination of the compressive strength additive and the density reducing materials facilitate forming a cement slurry and / or cement 210 exhibiting a relatively higher CS and CSD at relatively lower concentrations of the compressive strength additives. Accordingly, the combination of the density reducing materials with the compressive strength additives may facilitate reducing the concentration of the compressive strength additives in the cement composition without reducing the CS and CSD of the cement slurry and cement 210.

[0078] In some embodiments, the faster CSD of the cement slurry facilitates a faster completion of wellbore operations after cementing operations utilizing the cementcompositions described herein. Accordingly, the cement compositions may improve an efficiency of the cementing operations and improve a profitability of wellbore operations.

[0079] As described herein, it is believed that due to the presence of a gaseous material in the cement slurry (e.g., in the cement composition inside glass bubbles or cenospheres) and / or as a gas phase dispersed through the cement slurry (e.g., such as in foamed cements), the cement slurry includes a multiphase system with at least a solid phase, a liquid phase, and a gaseous phase. The addition of a gaseous phase dispersed in the cement slurry encompasses the formation of an interface between the cement slurry and the dispersed gaseous phase. For example, the interface may be between the gaseous phase and each of the solid phase and the liquid phase of the cement slurry. The presence of the interface between the gaseous phase and the cement slurry may surprisingly improve the CS of the cement during setting and increase the rate at which the CS develops, even at relatively low concentrations of a compressive strength additive. Further, as the cement hydrates, the liquid phase may become entrapped in water saturated cement.

[0080] The cement may be useful in earth formations exhibiting a relatively low fracturing pressure, such as in wellbores having issues with circulating heavy (e.g., high density) fluids, such as pumping a slurry of a known density at an excessive rate so as to exceed the maximum equivalent circulating density (ECD). The cement slurries described herein may facilitate reducing the slurry density and / or the pumping rate. In some such embodiments, reducing the density of the cement slurry with one or more density reducing materials (e.g., the particles 300, the dissolved gas phase in the cement slurry) is desirable.

[0081] While the cement composition, the cement slurry, and the cement 210 have been described as being formed with cement binders, the disclosure is not so limited. In some embodiments, the binder material of the base composition includes a geopolymer composition including at least one aluminosilicate source (at least one aluminosilicate material).

[0082] The at least one aluminosilicate source may be in the form of a solid or an aqueous solution of metal silicate. The at least one aluminosilicate source may include, but is not limited to, fly ashes such as ASTM type C fly ash, ASTM type F fly ash, and fly ashes not classified by ASTM, volcanic ash, volcanic glass, slag, ferrous slag, ferroalloy slag, non-ferrous slag (e.g., copper slag, nickel slag, tin slag, zinc slag), blast furnace slag, basic oxygen furnace slag, electric arc furnace slag, ground blast furnace slag (GGBS), diatomaceous earths, pumice, calcined or partially calcined clays (such as metakaolin), aluminum-containing silica fume, natural aluminosilicate, feldspars (which may bedehydrated), alumina and silica sols, synthetic aluminosilicate glass powder, zeolite, scoria, allophone, bentonite, red mud, which may be calcined, and pumice. Such materials may include a significant proportion of an amorphous aluminosilicate phase, which reacts in strong alkaline solutions. In embodiments from which the at least one aluminosilicate source is formed from a clay such as bentonite or metakaolin, the at least one aluminosilicate source may be amorphous silicon. For example, the bentonite or metakaolin may be calcined to convert the material from a crystalline state to an amorphous material.

[0083] In some embodiments, the at least one aluminosilicate source includes at least one of fly ash, metakaolin, or blast furnace slag. In some embodiments, the at least one aluminosilicate source includes fly ash, such as ASTM type C fly ash. In some embodiments, the at least one aluminosilicate source includes a mixture of two or more aluminosilicate sources. In addition, alumina and silica sources may be added separately, for example, as a blend of bauxite and silica fume. Other amorphous silica sources can also be used, which may include soda-lime glass dust, borosilicate glass dust, microsilica, fumed silica, precipitated silica, nanosilica, rice husk ash, or a combination thereof. It should be noted that some of the aluminosilicate sources mentioned above, such as GGBS and ASTM Class C fly ash, also contain calcium oxide, so these materials can also be considered activator sources. Suitable aluminosilicate sources for purposes herein can have at least 2%, at least 7%, at least 12%, at least 18%, at least 25%, at least 30%, at least 35%, at least 40%, at least 45%, or at least 50% by weight calcium oxide. These aluminosilicate sources become reactive when placed in strongly alkaline environments, typically at pH greater than 11. The aluminosilicate sources described above react under such conditions to form geopolymers and other materials derived from alkali active materials.

[0084] The at least one aluminosilicate source may be amorphous. In some embodiments, the at least one aluminosilicate source is substantially free of crystalline aluminosilicate. For example, in some embodiments, the at least one aluminosilicate source may be subjected to a calcination process such that the aluminosilicate is amorphous.

[0085] The at least one aluminosilicate source may be present in the geopolymer composition at a weight percent within a range of from about 50 weight percent to about 99 weight percent, such as from about 50 weight percent to about 60 weight percent, from about 60 weight percent to about 70 weight percent, from about 70 weight percent to about 80 weight percent, from about 80 weight percent to about 90 weight percent, from about 90 weight percent to about 95 weight percent, from about 95 weight percent to about 97 weight percent, or from about 97 weight percent to about 99 weight percent, based on theweight of the blend (BWOB), wherein the weight of the blend includes the weight of the geopolymer composition (including the aluminosilicate source and other materials in the geopolymer composition). However, the disclosure is not so limited, and the weight percent of the at least one aluminosilicate source in the geopolymer composition may be different than that described.

[0086] The geopolymer slurry and the geopolymer formed from the geopolymer composition may exhibit improved CS and CSD due to the presence of the compressive strength additives and the density reducing materials, as described above with reference to the cement slurry and the cement 210.EXAMPLESExample 1

[0087] The CS and CSD of cement slurries formed from a cement composition including the density reducing material including glass bubbles and not including a compressive strength additive (metakaolin) (“Sample 1”); and a cement composition including the density reducing material and the compressive strength additive (“Sample 2”) were compared. Sample 1 was a first cement composition including a mixture of about 78.9% BWOB of a low density cementitious clinker blend with a standard particle size diameter, about 9.9% BWOB of a low density and finer grade cementitious clinker blend, about 9.9% BWOB of glass bubbles, about 0.8% BWOB of a sodium lignosulfonate based retarder, about 0.2% BWOB of a sodium metasilicate based extender, and about 0.3% BWOB of a sodium polynaphthalene based dispersant. Water was added to the cement composition to form a cement slurry. The cement slurry exhibited a SVF of about 45% and a density of about 11.54 ppg (about 1,382.8 g / L).

[0088] Sample 2 was substantially the same as Sample 1 and included metakaolin. Sample 2 included about 76.6% BWOB of the low density cementitious clinker blend with a standard particle size diameter, about 9.6% BWOB of the low density and finer grade cementitious clinker blend, about 9.6% BWOB of glass bubbles, about 0.8% BWOB of the sodium lignosulfonate based retarder, about 0.2% BWOB of the sodium metasilicate based extender, about 0.3% BWOB of a sodium polynaphthalene based dispersant, and about 2.9% BWOB of the metakaolin.

[0089] Water was added to each of the first cement composition and the second cement composition to form respective cement slurries. The CS and the CSD of each cement slurry was measured as the cement slurry set, according to American Petroleum InstituteRecommended Practice 10B-2 (API RP 10B-2). Each cement slurry was mixed and placed into a cylinder, inside the heating chamber of an ultrasonic cement analyzer (UCA) and the temperature was raised to a bottom hole circulatory temperature (“BHCT”) of about 64.4°C (about 148°F). After increasing the temperature to the desired BHCT, the CS and the CSD of the cement slurry was measured as the cement slurry set. Ultrasonic waves were passed through a column of the cement during setting thereof and the transit time through the cement was measured and recalculated to a compressive strength measurement, via UCA in psi by means of known industry correlations.

[0090] FIG. 5 is a graph illustrating the results of the CS and the CSD of each cement slurry. Curve 502 represents the test temperature of each cement slurry. Curve 504 is the compressive strength of the cement slurry of Sample 1 including glass bubbles and not including the metakaolin and curve 506 is the compressive strength of the cement slurry of Sample 2 including the glass bubbles and metakaolin. As seen in FIG. 5, the cement slurry including the metakaolin and the glass bubbles exhibited a higher compressive strength than the cement slurry not including the metakaolin at all times during a 24 hour period.

[0091] Surprisingly, the cement slurry of Sample 2 including the metakaolin and the glass bubbles exhibited significantly improved CS and CSD compared to the cement slurry of Sample 1 including the glass bubbles and not including the metakaolin. Further, compared to a cement slurry including the metakaolin and not include the glass bubbles, the cement slurry of Sample 2 exhibited a significantly higher CS and CSD, indicating that the combination of the density reducing material and the compressive strength additives substantially improves the CS and CSD of the cement and cement slurry.Example 2

[0092] Three cement compositions were prepared: a first cement composition not including a density reducing material or a compressive strength additive (a baseline cement composition), a second cement composition containing a compressive strength additive and not including a density reducing material, and third cement composition containing a different cement binder and a similar volume percent of the compressive strength additive and not including a density reducing material.

[0093] A first composition (“Sample 3”) was prepared including 100% BWOB of a commercial light weight cement with an SVF of 17.2%. A second composition (“Sample 4”) was prepared including 75% by volume of the blend (BVOB) of cement class C and 25% BVOB of metakaolin, the second composition having an SVF of 16.5%. A thirdcomposition (“Sample 5”) was prepared including 70% BVOB of cement class C, 30% BVOB of pozzolan (fly ash), and 20% BWOB of metakaolin, the third composition having an SVF of 17.2%. Each of the first composition, the second composition, and the third composition had a density of 11.0 ppg.

[0094] FIG. 6 is a graph illustrating the test temperature and the compressive strength development of each of Sample 3, Sample 4 and Sample 5. The compressive strength of Sample 3 corresponds to curve 602, the compressive strength of Sample 4 corresponds to curve 604, the compressive strength of Sample 5 corresponds to curve 606, and the temperature of the samples corresponds to curve 608. As shown in FIG. 6, the cement compositions including the metakaolin compressive strength additive (Sample 4 and Sample 5) exhibited an early increase in CS compared to Sample 3 not including the metakaolin. However, the CS of Sample 4 and Sample 5 only reached between about 600 psi and about 700 psi after about 70 hours. By way of comparison, the CS of Sample 2 of Example 1 (including both metakaolin and glass bubbles) reached about 2,400 psi after about 20 hours. Thus, the combination of the density reducing materials (the glass bubbles) and the compressive strength additive (the metakaolin) exhibits a synergistic effect on the CS and the CSD of the resulting cement slurry, even at relatively low concentrations of the compressive strength additive.

[0095] The embodiments of cement composition, the cement slurry, and the cement formed therefrom have been primarily described with reference to wellbore cementing operations; the cement composition, the cement slurry, and the cement formed therefrom described herein may be used in applications other than the cementing of a wellbore. In other embodiments, cement composition, the cement slurry, and the cement formed therefrom according to the present disclosure may be used outside a wellbore or other downhole environment used for the exploration or production of natural resources. For instance, cement composition, the cement slurry, and the cement formed therefrom of the present disclosure may be used in a borehole used for harvesting geothermal energy of fluids, for storage of fluids including gases, such as natural gas, or carbon dioxide, and or placement of utility lines. Accordingly, the terms “wellbore,” “borehole” and the like should not be interpreted to limit tools, systems, assemblies, or methods of the present disclosure to any particular industry, field, or environment.

[0096] One or more specific embodiments of the present disclosure are described herein. These described embodiments are examples of the presently disclosed techniques. Additionally, in an effort to provide a concise description of these embodiments, not allfeatures of an actual embodiment may be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous embodiment-specific decisions will be made to achieve the developers’ specific goals, such as compliance with system -related and business-related constraints, which may vary from one embodiment to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure.

[0097] Additionally, it should be understood that references to “one embodiment” or “an embodiment” of the present disclosure are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. For example, any element described in relation to an embodiment herein may be combinable with any element of any other embodiment described herein. Numbers, percentages, ratios, or other values stated herein are intended to include that value, and also other values that are “about” or “approximately” the stated value, as would be appreciated by one of ordinary skill in the art encompassed by embodiments of the present disclosure. A stated value should therefore be interpreted broadly enough to encompass values that are at least close enough to the stated value to perform a desired function or achieve a desired result. The stated values include at least the variation to be expected in a suitable manufacturing or production process, and may include values that are within 5%, within 1%, within 0.1%, or within 0.01% of a stated value.

[0098] A person having ordinary skill in the art should realize in view of the present disclosure that equivalent constructions do not depart from the spirit and scope of the present disclosure, and that various changes, substitutions, and alterations may be made to embodiments disclosed herein without departing from the spirit and scope of the present disclosure. Equivalent constructions, including functional “means-plus-function” clauses are intended to cover the structures described herein as performing the recited function, including both structural equivalents that operate in the same manner, and equivalent structures that provide the same function. It is the express intention of the applicant not to invoke means-plus-function or other functional claiming for any claim except for those in which the words ‘means for’ appear together with an associated function. Each addition, deletion, and modification to the embodiments that falls within the meaning and scope of the claims is to be embraced by the claims.

[0099] The terms “approximately,” “about,” and “substantially” as used herein represent an amount close to the stated amount that is within standard manufacturing or process tolerances, or which still performs a desired function or achieves a desired result. For example, the terms “approximately,” “about,” and “substantially” may refer to an amount that is within less than 5% of, within less than 1% of, within less than 0.1% of, and within less than 0.01% of a stated amount. Further, it should be understood that any directions or reference frames in the preceding description are merely relative directions or movements. For example, any references to “up” and “down” or “above” or “below” are merely descriptive of the relative position or movement of the related elements.

[0100] The present disclosure may be embodied in other specific forms without departing from its spirit or characteristics. The described embodiments are to be considered as illustrative and not restrictive. The scope of the disclosure is, therefore, indicated by the appended claims rather than by the foregoing description. Changes that come within the meaning and range of equivalency of the claims are to be embraced within their scope.

Claims

CLAIMSWhat is claimed is:

1. A cement composition, comprising: at least one cement binder; between about 0.1 weight percent and about 20 weight percent of a compressive strength additive; and between about 1 weight percent and about 40 weight percent of a density reducing material.

2. The cement composition of claim 1, wherein the density reducing material comprises at least one of glass bubbles, cenospheres, hollow spheres filled with a gas, or a foamed gas.

3. The cement composition of claim 1, wherein a wall thickness of the density reducing material is within a range of from about 2 pm and about 20 pm.

4. The cement composition of claim 1, wherein particles of the density reducing material have a diameter less than about 150 pm.

5. The cement composition of claim 1, wherein the compressive strength additive comprises metakaolin.

6. The cement composition of claim 1, wherein at least about 20 percent by volume of the compressive strength additive has a diameter less than about 3.5 pm.

7. The cement composition of claim 1, wherein at least about 50 percent by volume of the compressive strength additive has a diameter less than about 8.0 pm.

8. The cement composition of claim 1, wherein a particle size of the compressive strength additive is smaller than a particle size of the density reducing material.

9. The cement composition of claim 1, further comprising at least additive selected from the group consisting of a cement retarder, a cement extender, and a dispersant.

10. The cement composition of claim 1, wherein the compressive strength additive constitutes from about 1.5 percent to about 7.0 percent of the cement composition.

11. The cement composition of claim 1 , wherein a specific gravity of the density reducing material is within a range of from about 250 kg / m3to about 990 kg / m3.

12. A cement slurry, comprising: water; and a cement composition mixed with the water, the cement composition comprising: at least one cement binder; between about 0.1 weight percent and about 20 weight percent of a compressive strength additive; and between about 1 weight percent and about 40 weight percent of a density reducing material.

13. The cement slurry of claim 12, wherein the cement slurry comprises a gas phase dispersed throughout the cement slurry and constituting from about 1 percent by volume to about 80 percent by volume of the cement slurry.

14. The cement slurry of claim 13, wherein the gas phase comprises nitrogen.

15. The cement slurry of claim 13, wherein the gas phase is entrapped in at least one of glass bubbles and cenospheres.

16. The cement slurry of claim 12, wherein the cement slurry composition comprises a solid volume fraction with a range of from about 40 percent to about 55 percent.

17. The cement slurry of claim 12, wherein a density of the cement slurry composition is within a range of from about 1,000 kg / m3to about 1,500 kg / m3.

18. A method of cementing a subterranean borehole, the method comprising: mixing water with a cement composition to form a cement slurry, the cement composition comprising: at least one cement binder; between about 0.1 weight percent and about 20 weight percent of a compressive strength additive; and between about 1 weight percent and about 40 weight percent by of a density reducing material; and pumping the cement slurry into an annular space between a casing and a subterranean formation defining the subterranean borehole.

19. The method of claim 18, wherein mixing water with the cement composition to form a cement slurry comprises forming the cement slurry to have a solid volume fraction with a range of from about 40 percent to about 55 percent.

20. The method of claim 18, wherein mixing water with a cement composition to form a cement slurry comprises mixing water with a cement composition comprising metakaolin and at least one of glass bubbles and cenospheres.

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