NO20140725A1 - Stiffenable compositions comprising cement kiln dust and rice husk as well as process using the same - Google Patents

Abstract

Embodiments of the present invention describe processes and compositions which include cement kiln dust and rice husk. An embodiment comprises a method of cementing extensively to place a stiffenable mixture in an underground formation, the stiffenable composition comprising cement kiln dust, rice husk and water, as well as giving the stiffenable mixture the opportunity to harden.

Description

Hardenable mixtures comprising cement kiln dust and rice husk ash and methods for using the same.

BACKGROUND

[0001] The present invention relates to cementing operations, and more particularly, in certain embodiments, to methods and mixtures comprising cement kiln dust ("CKD") and rice husk ash.

[0002] In cementing methods, such as well construction and remedial cementing, hardenable mixtures are usually used. As used herein, the term "hardenable mixture" refers to mixture(s) that set hydraulically or otherwise develop compressive strength. Hardenable mixtures can be used in primary cementing operations whereby pipe strings such as casing and extension pipes are cemented in wellbores. When carrying out primary cementing, a hardenable mixture can be pumped into an annulus between an underground formation and the pipe string placed in the underground formation. The hardenable mixture must solidify in the annulus, thereby forming an annular casing of hardened cement (like a cement casing) which will support and position the pipe string in the wellbore and bind the outer surface of the pipe string to the walls of the wellbore. Hardenable mixtures can also be used in remedial cementing methods, such as placement of cement plugs, and in pressure cementing to seal voids in a pipe string, cement casing, gravel packing, formation and the like.

[0003] Hardenable mixtures used heretofore generally comprise Portland cement. Portland cement is generally an important component of the cost of the hardenable mixtures. To reduce the cost of such hardenable mixtures, other components may be included in the hardenable mixture in addition to or instead of Portland cement. Such components may include fly ash, slag cement, shale, metakaolin, microfine cement and the like. "Fly ash", as the term is used here, refers to residues from the combustion of pulverized or ground coal, as the fly ash carried by the flue gases can be recovered, for example by electrostatic precipitation. "Slag", as the term is used herein, refers to a granulated blast furnace by-product formed in the production of cast iron and generally includes the oxidized impurities found in iron ore. Slag cement generally comprises slag and a base, for example, such as sodium hydroxide, sodium bicarbonate, sodium carbonate or lime, to produce a hardenable mixture capable of solidifying into a hard mass when combined with water.

Summary

[0004] The present invention relates to cementing operations and more specifically, in certain embodiments, methods and mixtures comprising CKD and rice husk ash.

[0005] One embodiment provides a method for cementing, comprising: placing a solidifiable mixture in an underground formation, the solidifiable mixture comprising cement kiln dust, rice husk ash and water, and allowing the solidifiable mixture to solidify.

[0006] Another embodiment provides a method for cementing, comprising: placing a hardenable mixture in an underground formation, the hardenable mixture comprising cement kiln dust, rice husk ash, Portland cement and water, and allowing the hardenable mixture to harden.

[0007] Another embodiment provides a method of cementing, comprising: placing a hardenable mixture in an underground formation, the hardenable mixture comprising: cement kiln dust, rice husk ash and water, the cement kiln dust being present in an amount ranging from about 50 to about 80% by weight of the cement kiln dust and rice husk slag, the rice husk slag being present in an amount ranging from about 20 to about 50% by weight of the cement kiln dust and rice husk slag, the water being present in an amount ranging from about 40 to about 200% by weight of the cement kiln dust and rice husk ash, the hardenable mixture being essentially free of Portland cement, as well as giving the hardenable mixture an opportunity to harden.

[0008] Another embodiment provides a solidifiable mixture comprising: cement kiln dust, rice husk ash and water.

[0009] The features and advantages of the present invention will be obvious to those skilled in the art. While many changes may be made by those skilled in the art, such changes are within the scope of the invention.

Detailed description

[0010] The present invention relates to cementing operations and more specifically, in certain embodiments, methods and mixtures comprising CKD and rice husk ash. There may be several potential advantages to the methods and compositions of the present invention, while only some of these will be elaborated upon here. One of the many potential advantages of embodiments of the present invention is that the inclusion of rice husk ash in hardenable mixtures comprising CKD can improve the mechanical properties of the CKD-containing hardenable mixtures. As an example, the inclusion of rice husk ash can provide increased compressive strength for hardenable mixtures comprising CKD. Another potential advantage of embodiments of the present invention is that CKD and/or rice husk ash can be used to reduce the costs of the hardenable mixtures. For example, using waste CKD and/or rice husk ash to replace a more expensive component, such as Portland cement, will result in a more economical, hardenable mixture.

[0011] Embodiments of the solidifiable mixtures according to the present invention may comprise CKD, rice husk ash and water. Other optional additives may, if desired, also be included in embodiments of the hardenable mixtures, including, but not limited to, unexpanded perlite, pumicite, fly ash, slag cement, metakaolin, shale, zeolite, combinations thereof, and the like. Embodiments of the curable mixtures may also be foamed and/or expanded as desired by those skilled in the art. The curable mixtures according to the present invention should have a density which is suitable for a specific application as desired by a person skilled in the art, with support in this description. In some embodiments, the curable compositions may have a density in the range of about 0.95 to about 1.90 kg/l (8-16 pounds/gallon). In other embodiments, the settable mixtures may be foamed to a density in the range of about 0.95 to about 1.56 kg/l (8-13 pounds/gallon).

[0012] Embodiments of the curable mixtures may generally include CKD. As used herein, the term "CKD" refers to a partially calcined kiln feed that is removed from the gas stream and collected, for example, in a dust collector during the manufacture of the cement. Usually, large quantities of CKD are collected during the production of cement, which is often thrown away as waste. Disposal of waste CKD can add unwanted costs to the production of cement, as well as environmental concerns related to the disposal. The chemical analysis of CKD from different cement manufacturers varies depending on a number of factors, including the particular kiln feed, the efficiency of cement production and the associated dust collection systems. CKD can generally include a variety of oxides, such as SiO2, Al2O3, Fe2O3, CaO, MgO, SO3, Na2O, and K2O.

[0013] CKD in general can exhibit cement properties, in that it can set and become hard in the presence of water. In accordance with embodiments of the present invention, CKD can be used, among other things, to replace more expensive cementitious components, such as Portland cement, resulting in more economical hardenable mixtures. In addition, replacing Portland cement with CKD can result in a hardenable mix with a reduced carbon footprint.

[0014] CKD can be included in the hardenable mixtures in an amount sufficient to provide the desired compressive strength, density, cost reduction, and/or reduced carbon footprint. In some embodiments, CKD may be present in the hardenable mixtures of the present invention in an amount ranging from about 0.1 to about 99% by weight of cementitious components. Cementitious components include such components or combinations of components of the hardenable mixtures which harden hydraulically or otherwise harden to develop compressive strength, including, for example, CKD, rice husk ash, unexpanded perlite, fly ash, pumicite, slag, lime, shale and the like. CKD may be present, in certain embodiments, in an amount varying between any of and/or including any of about 0.1%, about 1%, about 5%, about 10%, about 15%, about 20 %, about 25%, about 30%, about 35%, about 40%, about 45%, about 50%, about 55%, about 60%, about 65%, about 70%, about 75%, about 80%, about 90%, about 95%, or about 99%. In one embodiment, CKD may be present in the hardenable mixtures in an amount ranging from about 5 to about 95% by weight of cementitious components. In another embodiment, the CKD may be present in an amount ranging from about 50% to about 95% by weight of cementitious components. In yet another embodiment, the CKD may be present in an amount ranging from about 50 to about 80% by weight of the cementitious components. One of ordinary skill in the art, with the aid of this disclosure, will recognize the proper amount of CKD to include for a selected application.

[0015] Embodiments of the solidifiable mixtures may generally comprise rice husk ash. As used herein, the term "rice husk" refers to the hard protective coatings on grains of rice that are separated from rice during production. Rice husks are also often referred to as rice husks or rice husks. Large quantities of rice husks, which are usually thrown away as waste, are usually formed during the production of rice. However, disposal of rice husks in landfills can be problematic as landfill space can be limited. Rice husk typically contains a significant amount of silica and which when burned produces an ash, referred to herein as "rice husk ash", which is rich in amorphous silica. In some embodiments, the ash obtained from burning rice husks can be processed further by dry grinding the ash into powder form.

[0016] Addition of rice husk ash to hardenable mixtures comprising CKD has been shown to give an increase in compressive strength. In accordance with the present embodiments, rice husk ash can be included in CKD-containing hardenable mixtures to increase the compressive strength thereof. As an example, inclusion of rice husk ash in a hardenable mixture comprising CKD can, in one embodiment increase compressive strength in an amount greater than or equal to about 10%, in another embodiment greater than or equal to about 25%, in another embodiment greater than or equal to about 50%, in another embodiment greater than or equal to about 75%, compared to the same hardenable composition that does not contain the latex strength enhancer. As used here, "compressive strength" is measured at a specific point in time after the mixture has been mixed and the mixture is maintained under given temperature and pressure conditions. For example, compressive strength may be measured at a time ranging from about 24 to about 48 hours after the mixture is mixed and the mixture is maintained at a temperature of 71°C (160F) and atmospheric pressure. Compressive strength can be measured by either a destructive method or a non-destructive method. The destructive method physically tests the strength of samples of the hardenable mixture at different times by crushing the samples in a compressive strength testing machine. The compressive strength is calculated from the failure load divided by the cross-sectional area resisting the load and is reported in units of bar (alternatively pound-force per square inch (psi). Non-destructive methods can usually utilize an Ultrasonic Cement Analyzer ("UCA"), available from Fann Instrument Company , Houston, TX.

[0017] In some embodiments, rice husk ash may be present in the hardenable compositions of the present invention in an amount in the range of from about 0.1 to about 99% by weight of cementitious components. The rice husk husk may in certain embodiments be present in an amount varying between any of and/or including any of about 0.1%, about 1%, about 5%, about 10%, about 15%, about 20% , about 25%, about 30%, about 35%, about 40%, about 45%, about 50%, about 55%, about 60%, about 65%, about 70%, about 75%, about 80%, about 90%, about 95%, or about 99%. In one embodiment, the rice husk husk may be present in the hardenable mixture in an amount ranging from about 5 to about 95% by weight of cementitious components. In another embodiment, rice husk ash may be present in an amount ranging from about 5 to about 50% by weight of cementitious components. In yet another embodiment, the rice husk ash may be present in an amount ranging from about 20 to about 50% by weight of cementitious components. One skilled in the art with the aid of this disclosure will recognize the proper amount of rice husk ash to include in a selected application.

[0018] The water that can be used in embodiments of the solidifiable mixtures includes, for example, fresh water, salt water (for example, water containing one or more dissolved salts), brine (for example, saturated salt water produced from underground formations), sea water, or combinations of those mentioned. In general, the water may be from any source, provided that the water does not contain an excess of compounds which may adversely affect other components of the curable mixture. In some embodiments, the water may be included in an amount sufficient to form a pumpable slurry. In some embodiments, the water can be included in the hardenable mixtures according to the present invention in an amount in the range from about 40 to about 200% by weight of cementitious components. In some embodiments, the water may be included in an amount ranging from about 40 to about 150% by weight of the cementitious components. A person skilled in the art will, with the help of this description, recognize the correct amount of water to include in a selected application.

[0019] In some embodiments, the hardenable mixtures can further comprise a hydraulic cement. A number of hydraulic cements may be used in accordance with the present invention, including, but not limited to, those comprising calcium, aluminium, silicon, oxygen, iron and/or sulphur, which harden upon reaction with water. Suitable hydraulic cements include, but are not limited to, Portland cements, pozzolanic cements, gypsum cements, high aluminum cements, silica cements, and any combination thereof. In certain embodiments, the hydraulic cement may comprise a Portland cement. In some embodiments, Portland cements suitable for use in the present invention are classified as Class A, C, H, and G cements according to the American Petroleum Institute, API Specification for Materials and Testing for Well Cements, API Specification 10, 5th ed. ., July 1, 1990.1 In addition, cements suitable for use in the present invention may, in some embodiments, include cements classified as ASTM Type I, II, or III.

[0020] It should be understood that the use of hydraulic cement in embodiments of the hardenable mixtures, in addition to CKD and/or rice husk ash, can be reduced or eliminated to provide, for example, the desired cost savings and/or reduced carbon footprint. Accordingly, embodiments of the hardenable mixtures according to the present invention may comprise hydraulic cement in an amount from 0% to about 75%. For example, in certain embodiments, the hydraulic cement may be present in an amount varying between any of and/or including any of about 1%, about 5%, about 10%, about 15%, about 20%, about 24%, about 25%, about 30%, about 35%, about 40%, about 50%, about 55%, about 60%, about 65%, about 70%, or about 75%. In one embodiment, the hydraulic cement may be present in an amount ranging from about 0% to about 20%. In another embodiment, the hydraulic cement may be present in an amount ranging from about 0% to about 10%. In yet another embodiment, the hardenable mixtures may be substantially free of hydraulic cement. As used here, the expression "substantially free of" means that hydraulic cement is not present, or possibly that trace amounts of hydraulic cement are present in an amount that is less than approximately 1% by weight of cement components. In certain embodiments, the hardenable mixture may contain hydraulic cement in an amount less than 0.1% by weight of cementitious components and optionally less than about 0.01% by weight of cementitious components. By way of example, in certain embodiments, the hardenable mixture may be free of hydraulic cement, in that the hardenable mixture contains no hydraulic cement.

[0021] Embodiments of the solidifiable mixtures may further comprise a solidification-delaying additive. As used here, the term "hardening retarding additive" refers to an additive which delays the hardening of the hardenable mixtures according to the present invention. Examples of suitable setting retarding additives include, but are not limited to, ammonium, alkali metals, alkaline earth metals, metal salts of sulfoalkylated lignins, organic acids (eg, hydroxycarboxylic acids), copolymers comprising acrylic acid or maleic acid, and combinations thereof. One example of a suitable sulfoalkylated lignin includes a sulfomethylated lignin. Suitable setting retarding additives are described in greater detail in US Patent No. Re. 31190, as the entire description of this is incorporated here by reference. Suitable retarding additives are commercially available from Halliburton Energy Services, Inc. under the trademarks HR<*>4, HR<*>5, HR<*>7, HR<*>12, HR<*>15, HR<*>25 , HR<*>601, SCR ™ 100, and SCR ™ 500 retarders. In general, when used, set retarding additives may be included in the settable compositions of the present invention in an amount sufficient to provide the desired setting delay. In some embodiments, set retarding additive may be present in the setable mixtures of the present invention in an amount ranging from about 0.1 to about 5% by weight of cementitious components. A person skilled in the art will, with the help of this description, recognize the correct amount of additive to include for a selected application.

[0022] Optionally, other additional additives can be added to the hardenable mixtures according to the present invention, if deemed appropriate by a person skilled in the field with support in this description. Examples of such additives include, but are not limited to, strength reducing additives, setting accelerators, weight increasing additives, lightweight additives, gas developing additives, mechanical property promoting additives, circulation loss additives, filtration control additives, dispersants, fluid loss control additives, antifoam additives, foam forming additives , oil-swellable particles, water-swellable particles, thixotropic additives, and combinations thereof. Specific examples of these and other additives include unexpanded perlite, pumicite, fly ash, slag cement, metakaolin, shale, zeolite, crystalline silica, amorphous silica, highly dispersed silica, salts, fibers, hydratable clays, microspheres, elastomers, elastomeric particles, resins, latex, combinations of the aforementioned, and the like. A person of ordinary skill in the art, with the aid of this description, will easily be able to determine the type and amount of additive useful for a particular application and desired result.

[0023] In some embodiments, CKD and rice husk ash can be combined to form a cement component. In addition to the CKD and the rice husk shell, additional components may also be included in the cement component, as a filler or for other purposes that will be obvious to a person of ordinary skill in the art, with the support of this description. For example, other components that can set and harden in the presence of water may also be included in that cement component. In some embodiments, the cement component may further comprise unexpanded perlite, pumicite, fly ash, slag cement, metakaolin, shale, zeolite, or combinations thereof. In some embodiments, the cement component may be placed in a sack or other suitable container for storage and/or delivery to a well site. In one embodiment, the cement component can then be combined with water to create a hardenable mixture.

[0024] In some embodiments, the components of the curable mixtures can be combined in any order as will be understood by one skilled in the art. In one embodiment, CKD and rice husk ash can be combined with water to create a settable mixture. As will be appreciated, one or more additional components as described above, for example, may also be included in the curable mixture. The components of the curable mixture can be combined using any mixing device compatible with the mixture, as known to a person of ordinary skill in the art, for example a bulk mixer.

[0025] As will be understood by one skilled in the art, embodiments of the hardenable mixtures can be used in a variety of different underground applications, including primary and remedial cementing. Embodiments of the solidifiable compositions may be introduced into an underground formation to solidify therein. For example, the hardenable mixture can be placed in a cavity between an underground formation, and a pipe located in the underground formation. As used herein, introducing the solidifiable composition into a subterranean formation includes introducing the composition into any part of the subterranean formation, including, without limitation, into a well bore drilled into the subterranean formation, into an area near the wellbore and surrounding the wellbore, or both.

[0026] In embodiments of primary cementing, for example, a solidifiable mixture can be introduced into a space outside a pipeline (eg pipe strings, extension pipes) located in the underground formation. The pipe may be located in a wellbore drilled into the underground formation. The hardenable mixture can be allowed to harden and form an annular sheath of hardened cement in the space outside the line. Among other things, the solidified, solidifiable mixture can form a barrier that prevents the migration of fluids in the wellbore. The solidified, solidifiable mixture can, for example, also support the pipe in the borehole.

[0027] In embodiments of remedial cementing, a hardenable mixture can be used, for example in pressure cementing operations, or when placing cement plugs. As an example, the hardenable mixture can be placed in a wellbore to plug a cavity or fracture in the formation, in a gravel pack, in the pipe, in the cement casing, and/or a microannulus between the cement casing and the pipe.

[0028] In support of a better understanding of the present invention, the following example of certain aspects of some embodiments is provided. In no way should the following example be read to limit or define the scope of the invention.

Example

[0029] A series of samples of hardenable mixtures were prepared and tested to analyze force resistance properties of hardenable mixtures comprising CKD and rice husk ash. The test mixtures were allowed to solidify in a water bath at 71 °C (160 F) for 24 hours at ambient pressure. Immediately after removal from the water bath, crushing strengths (destructive compressive strength) were determined using a Tinius Olsen tester. The results of crushing strength tests are given in the table below.

[0030] Ten different tests were carried out, designated Test No. 1-10, using the indicated amounts of water, CKD, rice husk ash, hydrated lime and cement dispersant. The quantities of these components are indicated in the table below as a percentage by weight ("wt-%") which indicates the percentage of the component in relation to the weight of cement and rice husk ash. The amount of rice husk ash was varied in an amount from 0 to 50% by weight. Tests 1 and 5 were comparison tests that did not include any rice husk ash. Dispersant used was CFR-3™ cement friction reducer, from Halliburton Energy Services, Inc., Duncan, Oklahoma. CKD used was supplied by Holcem (US) Inc., of Ada, Oklahoma. Rice husk ash used was supplied by Riceland Foods, Inc., Stuttgart, Arkansas, and had particles ranging from about 1 micron to about 10 microns.

[0031] This example thus indicates that inclusion of rice husk ash provides strength improvement to CKD-containing mixtures. In fact, an increase in compressive strength of 50% or more was obtained for Tests No. 6-10 with a density of 1.50 kg/l (12.5 ppg) and containing rice husk ash in an amount varying from 20 to 50% by weight, compared to Test No. 5 which did not contain any rice husk ash.

[0032] It should be understood that while the compositions and methods are described as "comprising", "containing" or "including" various components or steps, the compositions and methods may also "mainly consist of" or "consist of" the various components and steps .

[0033] For simplicity, only certain areas are explicitly described. However, areas from any lower limit may be combined with any upper limit to indicate an area not explicitly stated, just as areas from any lower limit may be combined with any other lower limit to indicate an area which is not explicitly stated, and similarly areas from any upper limit may be combined with any other upper limit to state an area not explicitly stated. In addition, whenever a numerical range with a lower limit and an upper limit is described, any number, and any included range that falls within the range, is specifically described. In particular, any range of values (of the form "from about a to about b", or, equivalently, "from about a to b", or, equivalently, "from about a-b") described herein is to be understood as indicating any number and any range encompassed within the wider range of values, even if this is not explicitly stated. Thus, each point or single value may serve as its own lower or upper limit in combination with any other point or individual value or any other lower or upper limit, to indicate a range not explicitly stated.

[0034] Thus, the present invention is well adapted to achieve the purposes and advantages mentioned as well as those as other inherent advantages. The particular embodiments described above are illustrative only, as the present invention may be modified and practiced in different but equivalent ways apparent to those skilled in the art having the benefit of the teachings herein. Although individual embodiments are discussed, the invention encompasses all combinations of all these embodiments. Furthermore, no limitations are intended to be placed on the details of construction or design as shown here, other than those described in the requirements below. Furthermore, the designations in the patent claims have their usual, ordinary meaning unless otherwise explicitly and clearly defined by the patent holder. It is therefore clear that the specific illustrative embodiments described above may be changed or modified, and all such variations are considered to be within the scope and spirit of the present invention.

Claims (32)

1. Method of cementing, comprising: placing a settable mixture in an underground formation, the settable mixture comprising cement kiln dust, rice husk ash and water, and allowing the settable mixture to set. 2. The method of claim 1, wherein the curable mixture has a density in the range of about 0.95 - 1.90 kg/l (8 - 16 pounds per gallon). 3. The method of claim 1, wherein cement kiln dust is present in an amount in a range of from about 0.1 to about 99% by weight of cementitious components, and wherein the rice husk ash is present in an amount in a range of from about 0, 1 to about 99% by weight of cementitious components. 4. Method according to claim 1, wherein cement kiln dust is present in an amount in a range from about 50 to about 95% by weight of cementitious components. 5. Method according to claim 1, wherein rice husk ash n is present in an amount in the range from about 5 to about 50% by weight of cementitious components. 6. A method according to claim 1, wherein rice husk ash n is included in the curable mixture in an amount sufficient to increase the 24-hour destructive compressive strength of the curable mixture at 71 °C (160 F) and atmospheric pressure in an amount equal to or greater than about 10%. 7. A method according to claim 1, wherein rice husk ash n is included in the curable mixture in an amount sufficient to increase the 24-hour destructive compressive strength of the curable mixture at 71 °C (160 °F) and atmospheric pressure in an amount equal to or greater than 75% by weight. 8. Method according to claim 1, wherein the water is present in an amount in a range from about 40 to about 200% by weight of cementitious components. 9. Method according to claim 1, in that the hardenable mixture is essentially free of hydraulic cement in addition to cement kiln dust. 10. Method according to claim 1, wherein the solidifiable mixture further comprises a solidification-delaying additive. 11. Method according to claim 1, wherein the solidifiable mixture further comprises at least one additive selected from the group consisting of unexpanded perlite, pumicite, lime, fly ash, slag cement, metakaolin, shale, zeolite, crystalline silica, amorphous silica, highly dispersed silica, salt, fiber, hydratable clay, microspheres, elastomers, elastomeric particles, resin, latex, and any combination of the foregoing. 12. Method according to claim 1, in that the curable mixture comprises at least one additive selected from the group consisting of a strength-reducing additive, a hardening accelerator, a weight-increasing additive, a lightweight additive, a gas-evolving additive, an additive that promotes a mechanical property, an agent against circulation loss , a filtration control additive, a dispersant, a fluid loss control additive, an antifoam additive, a foaming agent, an oil swellable particle, a water swellable particle, a thixotropic additive and any combination thereof. 13. Method according to claim 1, in that the solidifiable mixture is allowed to solidify in an annulus outside a pipe arranged in the underground formation. 14. Method according to claim 1, in that the hardenable mixture is used for primary cementation. 15. Method according to claim 1, in that the hardenable mixture is used in remedial cementation. 16. Method of cementing, comprising: placing a hardenable mixture in an underground formation, the hardenable mixture comprising cement kiln dust, rice husk ash, Portland cement, and water, and allowing the hardenable mixture to harden. 17. A cementitious component according to claim 16, wherein the cement kiln dust is present in an amount ranging from about 0.1 to about 99% by weight of cementitious components, and wherein the rice husk ash is present in an amount ranging from about 0.1 to approximately 99% by weight of cementitious components. 18. A cementitious component according to claim 16, wherein the cement kiln dust is present in an amount in a range of from about 0.1 to about 50% by weight of cementitious components, wherein the rice husk ash is present in an amount in a range of from about 0, l to about 50% by weight of cementitious components, and wherein Portland cement is present in an amount ranging from about 50 to about 99% by weight of cementitious components. 19. Method according to claim 16, wherein the solidifiable mixture further comprises at least one additive selected from the group consisting of unexpanded perlite, pumicite, lime, fly ash, slag cement, metakaolin, shale, zeolite, crystalline silica, amorphous silica, highly dispersed silica, salt, fiber, hydratable clay, microspheres, elastomer, elastomeric particles, resin, latex, and any combination thereof. 20. Method according to claim 16, wherein the solidifiable mixture further comprises at least one additive selected from the group consisting of a strength-reducing additive, a hardening accelerator, a weight-increasing agent, a lightweight additive, a gas-evolving additive, an additive that promotes a mechanical property, a circulation loss additive, a filtration control additive, a dispersant, a fluid loss control additive, an antifoam additive, a foaming agent, an oil swellable particle, a water swellable particle, a thixotropic additive and any combination thereof. 21. Method of cementing, comprising: placing a solidifiable mixture in an underground formation, the solidifiable mixture comprising: cement kiln dust, rice husk ash, and water, the cement kiln dust being present in an amount ranging from about 50 to about 80 wt. % of the cement kiln dust and rice husk slag, the rice husk slag being present in an amount ranging from about 20 to about 50 wt% of the cement kiln dust and rice husk slag, the water being present in an amount ranging from about 40 to about 200 wt. % of the cement kiln dust and rice husk ash, the hardenable mixture being essentially free of Portland cement, and giving the hardenable mixture an opportunity to harden. 22. The method of claim 21, wherein the curable mixture has a density in the range of about 0.95-1.90 kg/l (8-16 pounds per gallon). 23. The method of claim 21, wherein inclusion of rice husk ash in the curable mixture increases the 24-hour destructive compressive strength of the curable mixture at 71°C (160 F) and atmospheric pressure by an amount equal to or greater than about 10%. 24. The method of claim 21, wherein the inclusion of rice husk ash in the curable mixture increases the 24-hour destructive compressive strength of the curable mixture at 71°C (160 F) and atmospheric pressure by an amount equal to or greater than about 75%. 25. Method according to claim 21, wherein the solidifiable mixture further comprises a solidification delaying additive. 26. Method according to claim 21, wherein the solidifiable mixture further comprises at least one additive selected from the group consisting of unexpanded perlite, pumicite, lime, fly ash, slag cement, metakaolin, shale, zeolite, crystalline silica, amorphous silica, highly dispersed silica, salt, fiber, hydratable clay, microspheres, elastomer, elastomeric particles, resin, latex, and any combination thereof. 27. Method according to claim 21, wherein the setable mixture comprises at least one additive selected from the group consisting of a strength-reducing additive, a hardening accelerator, a weight-increasing agent, a lightweight additive, a gas-evolving additive, an additive that promotes a mechanical property, an additive against circulation loss, a filtration control additive, a dispersant, a fluid loss control additive, an antifoam additive, a foaming agent, an oil swellable particle, a water swellable particle, a thixotropic additive and any combination of the aforementioned 28. Method according to claim 21, wherein the solidifiable mixture is allowed to solidify in an annulus outside a pipe arranged in the underground formation. 29. Method according to claim 21, in that the hardenable mixture is used in primary cementation. 30. Method according to claim 21, in that the hardenable mixture is used in remedial cementation. 31. A curable mixture comprising: cement kiln dust, rice husk ash and water. 32. Hardenable mixture according to claim 31, wherein the cement kiln dust is present in an amount ranging from about 0.1 to about 99% by weight of cementitious components, and wherein the rice husk ash is present in an amount ranging from about 0.1 to about 99% by weight of cementitious components.