Methods of cementing in subterranean formations using cement kiln cement kiln dust in compositions having reduced Portland cement content

This application is a continuation in part of U.S. application Ser. No. 12/420,630, entitled “Cement Compositions Having Cement Kiln Dust and/or Pumicite and Methods of Use,” filed on Apr. 8, 2009, which is a continuation in part of U.S. application Ser. No. 12/349,676, entitled “Extended Settable Compositions Comprising Cement Kiln Dust and Associated Methods,” filed on Jan. 7, 2009, which is a divisional of U.S. application Ser. No. 12/034,886 entitled “Extended Settable Compositions Comprising Cement Kiln Dust and Associated Methods, filed on Feb. 21, 2008, which is a continuation in part of U.S. application Ser. No. 11/223,669 entitled “Settable Compositions Comprising Cement Kiln Dust and Additive(s),” filed Sep. 9, 2005, the entire disclosures of which are incorporated herein by reference.

The present invention relates to cementing operations and, more particularly, in certain embodiments, to methods of cementing in subterranean formations using cement kiln dust (“CKD”) in compositions having reduced Portland cement content.

In cementing methods, such as well construction and remedial cementing, sealant compositions are commonly utilized. As used herein, the term “sealant composition” refers to a composition(s) that hydraulically sets or otherwise develops compressive strength suitable for use in subterranean applications. While a hydraulic composition is one type of sealant composition that may be used in cementing methods, other non-hydraulic sealant compositions also may be employed. By way of example, polymeric sealant compositions also may be used.

Sealant compositions may be used in primary cementing operations whereby pipe strings, such as casing and liners, are cemented in well bores. In performing primary cementing, a sealant composition may be pumped into an annulus between a subterranean formation and the pipe string disposed in the subterranean formation. The sealant composition should set in the annulus, thereby forming an annular sheath of hardened cement (e.g., a cement sheath) that supports and positions the pipe string in the well bore and bonds the exterior surface of the pipe string to the walls of the well bore.

Sealant compositions also may be used in remedial cementing operations, such as sealing voids in a pipe string or a cement sheath. As used herein the term “void” refers to any type of space, including fractures, holes, cracks, channels, spaces, and the like. Such voids may include: holes or cracks in the pipe strings; holes, cracks, spaces, or channels in the cement sheath; and very small spaces (commonly referred to as “microannuli”) between the cement sheath and the exterior surface of the well casing or formation. Sealing such voids may prevent the undesired flow of fluids (e.g., oil, gas, water, etc.) and/or fine solids into, or from, the well bore. The sealing of such voids, whether or not made deliberately, has been attempted by introducing a sealant composition into the void and permitting it to remain therein to seal the void. If the substance does not fit into the void, a bridge, patch, or sheath may be formed over the void to possibly produce a termination of the undesired fluid flow. Hydraulic pressure may be employed to force the sealant composition into the void. Once placed into the void, the sealant composition may be permitted to harden.

Remedial cementing operations also may be used to seal portions of subterranean formations or portions of gravel packs. The portions of the subterranean formation may include permeable portions of a formation, fractures (natural or otherwise) in the formation, and other portions of the formation that may allow the undesired flow of fluid into, or from, the well bore. The portions of the gravel pack include those portions of the gravel pack, wherein it is desired to prevent the undesired flow of fluids into, or from, the well bore. A “gravel pack” is a term commonly used to refer to a volume of particulate materials (such as sand) placed into a well bore to at least partially reduce the migration of unconsolidated formation particulates into the well bore. While screenless gravel packing operations are becoming more common, gravel packing operations commonly involve placing a gravel pack screen in the well bore neighboring a desired portion of the subterranean formation and packing the surrounding annulus between the screen and the well bore with particulate materials that are sized to prevent and inhibit the passage of formation solids through the gravel pack with produced fluids. Among other things, this method may allow sealing of the portion of the gravel pack to prevent the undesired flow of fluids without requiring the gravel pack's removal.

Sealant compositions also may be used during the drilling of the well bore in a subterranean formation. For example, in the drilling of a well bore, it may be desirable, in some instances, to change the direction of the well bore. In some instances, sealant compositions may be used to facilitate this change of direction, for example, by drilling a pilot hole in a hardened mass of cement, commonly referred to as a “kickoff plug,” placed in the well bore. Certain formations may cause the drill bit to drill in a particular direction. For example, in a vertical well, this may result in an undesirable well bore deviation from vertical. In a directional well (which is drilled at an angle from vertical), after drilling an initial portion of the well bore vertically, the direction induced by the formation may make following the desired path difficult. In those and other instances, special directional drilling tools may be used, such as a whipstock, a bent sub-downhole motorized drill combination, and the like. Generally, the directional drilling tool or tools used may be orientated so that a pilot hole is produced at the desired angle to the previous well bore in a desired direction. When the pilot hole has been drilled for a short distance, the special tool or tools are removed, if required, and drilling along the new path may be resumed. To help ensure that the subsequent drilling follows the pilot hole, it may be necessary to drill the pilot hole in a kickoff plug, placed in the well bore. In those instances, prior to drilling the pilot hole, a sealant composition may be introduced into the well bore and allowed to set to form a kickoff plug therein. The pilot hole then may be drilled in the kickoff plug, and the high strength of the kickoff plug helps ensure that the subsequent drilling proceeds in the direction of the pilot hole.

Sealant compositions (e.g., hydraulic compositions) used heretofore may comprise Portland cement. Portland cement generally is a major component of the cost for the sealant compositions. To reduce the cost of such sealant compositions, other components may be included in the sealant composition in addition to, or in place of, the Portland cement. Such components may include fly ash, slag cement, shale, metakaolin, zeolite, and the like. “Fly ash,” as that term is used herein, refers to the residue from the combustion of powdered or ground coal, wherein the fly ash carried by the flue gases may be recovered, for example, by electrostatic precipitation. “Slag,” as that term is used herein, refers to a granulated, blast furnace by-product formed in the production of cast iron and generally comprises 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 hydraulic composition that, when combined with water, may set to form a hardened mass.

During the manufacture of cement, a waste material commonly referred to as cement kiln dust (“CKD”) is generated. CKD, as that term is used herein, refers to a partially calcined kiln feed which is removed from the gas stream and collected, for example, in a dust collector during the manufacture of cement. Usually, large quantities of CKD are collected in the production of cement that are commonly disposed of as waste. Disposal of the waste CKD can add undesirable costs to the manufacture of the cement, as well as the environmental concerns associated with its disposal. The chemical analysis of CKD from various cement manufactures varies depending on a number of factors, including the particular kiln feed, the efficiencies of the cement production operation, and the associated dust collection systems. CKD generally may comprise a variety of oxides, such as SiO 2 , Al 2 O 3 , Fe 2 O 3 , CaO, MgO, SO 3 , Na 2 O, and K 2 O.

The present invention relates to cementing operations and, more particularly, in certain embodiments, to methods of cementing in subterranean formations using CKD in compositions having reduced Portland cement content.

An embodiment of the present invention includes a method that comprises placing a sealant composition that comprises CKD and is essentially free of Portland cement in a subterranean formation; and allowing the sealant composition to set.

Another embodiment of the present invention includes a method that comprises placing a hydraulic sealant composition that comprises CKD and water and is essentially free of Portland cement in a subterranean formation; and allowing the hydraulic sealant composition to set.

Another embodiment of the present invention includes a method that comprises placing a hydraulic sealant composition in a subterranean formation, wherein the hydraulic sealant composition consists essentially of: pumicite, lime, CKD, water, and an additive selected from the group consisting of a strength-retrogression additive, a set accelerator, a set retarder, a weighting agent, a lightweight additive, a gas-generating additive, a mechanical property enhancing additive, a lost-circulation material, a filtration-control additive, a dispersant, a fluid loss control additive, a defoaming agent, a foaming agent, an oil-swellable particle, a water-swellable particle, a thixotropic additive, a gas, and any combination thereof, and allowing the hydraulic cement composition to set.

The features and advantages of the present invention will be readily apparent to those skilled in the art. While numerous changes may be made by those skilled in the art, such changes are within the spirit of the invention.

The present invention relates to cementing operations and, more particularly, in certain embodiments, to methods of cementing in subterranean formations using CKD in compositions having reduced Portland cement content. There may be several potential advantages to the methods and compositions of the present invention, only some of which may be alluded to herein. One of the many potential advantages of the methods and compositions of the present invention is that the inclusion of the CKD and/or natural pozzolan in the sealant composition may reduce the amount of, or potentially eliminate, a higher cost additive, such as Portland cement, resulting in a more economical sealant composition.

Embodiments of the sealant compositions of the present invention may comprise CKD and be essentially free of Portland cement. While a variety of different sealant compositions capable of gaining sufficient compressive strength for use in subterranean applications may be suitable for use, one example of a particularly suitable sealant composition is a hydraulic composition. By way of example, a suitable sealant composition is a hydraulic composition that may comprise CKD, a natural pozzolan (e.g., pumicite), lime, and water and also be essentially free of a Portland cement. Other optional additives may also be included in embodiments of the sealant compositions of the present invention as desired, including, but not limited to, fly ash, slag cement, metakaolin, shale, zeolite, combinations thereof, and the like. As described in more detail herein, embodiments of the sealant compositions of the present invention may be foamed and/or extended as desired by those of ordinary skill in the art.

The sealant compositions of the present invention should have a density suitable for a particular application as desired by those of ordinary skill in the art, with the benefit of this disclosure. In some embodiments, the sealant compositions of the present invention may have a density in the range of about 8 pounds per gallon (“ppg”) to about 16 ppg. In the foamed embodiments, the foamed sealant compositions of the present invention may have a density in the range of about 8 ppg to about 13 ppg.

It should be understood that the sealant compositions may be essentially free of Portland cement in accordance with embodiments of the present invention. As used herein, the term “essentially free” means less than about 1% by weight of cementitious components. Cementitious components include those components or combinations of components of the sealant compositions that hydraulically set, or otherwise harden, to develop compressive strength, including, for example, CKD, fly ash, natural pozzolans (e.g., pumicite), slag, lime, resins, shale, and the like. In certain embodiments, the sealant composition may contain Portland cement in an amount less than about 0.1% by weight of cementitious components and, alternatively, less than about 0.01% by weight of cementitious components. By way of example, the sealant composition, in certain embodiments, may be free of Portland cement, in that the sealant composition contains no Portland cement. In certain embodiments, the sealant compositions may be essentially free of Portland cements classified as Classes A, C, G, and H cements according to American Petroleum Institute, API Specification for Materials and Testing for Well Cements, API Specification 10, Fifth Ed., Jul. 1, 1990. By way of further example, the sealant compositions may be essentially free of Portland cements classified as ASTM Type I, II, or III.

Embodiments of the sealant compositions generally may comprise CKD. The CKD generally may exhibit cementitious properties, in that it may set and harden in the presence of water. The CKD may be used, among other things, to replace higher cost cementitious components, such as Portland cement, in embodiments of the sealant compositions, resulting in more economical sealant compositions. The CKD may be included in the sealant compositions in an amount sufficient to provide the desired compressive strength, density, and/or cost reduction. In some embodiments, the CKD may be present in the sealant compositions of the present invention in an amount in the range of about 1% to about 99% by weight of cementitious components. In some embodiments, the CKD may be present in the sealant compositions of the present invention in an amount in the range of about 5% to about 99% by weight of cementitious components. In some embodiments, the CKD may be present in an amount in the range of about 5% to about 80% by weight of cementitious components. In some embodiments, the CKD may be present in an amount in the range of about 10% to about 50% by weight of cementitious components. One of ordinary skill in the art, with the benefit of this disclosure, will recognize the appropriate amount of CKD to include for a chosen application.

Embodiments of the sealant compositions further may comprise a natural pozzolan. Natural pozzolans are generally present on the Earth's surface and set and harden in the presence of hydrated lime and water. Examples of natural pozzolans include pumicite, diatomaceous earth, volcanic ash, opaline shale, tuff, and combinations thereof. Generally, pumicite is a volcanic rock that exhibits cementitious properties, in that it may set and harden in the presence of hydrated lime and water. Hydrated lime may be used in combination with the pumicite, for example, to provide sufficient calcium ions for pumicite to set. The natural pozzolan may be used, among other things, to replace higher cost cementitious components, such as Portland cement, in embodiments of the sealant compositions, resulting in more economical sealant compositions. Where present, the natural pozzolan may be included in an amount in the range of from about 0.1% to about 50% by weight of cementitious components, for example. In some embodiments, the natural pozzolan may be present in an amount in the range of from about 25% to about 50% by weight of cementitious components. One of ordinary skill in the art, with the benefit of this disclosure, will recognize the appropriate amount of the natural pozzolan to include for a chosen application.

Embodiments of the sealant compositions further may comprise lime. In certain embodiments, the lime may be hydrated lime. The lime may be included in embodiments of the sealant compositions, for example to, form a hydraulic composition with other components of the sealant compositions, such as the pumicite, fly ash, slag, and/or shale. Where present, the lime may be included in the sealant compositions in an amount in the range of from about 1% to about 40% by weight of cementitious components, for example. In some embodiments, the lime may be present in an amount in the range of from about 5% to about 20% by weight of cementitious components. One of ordinary skill in the art, with the benefit of this disclosure, will recognize the appropriate amount of the lime to include for a chosen application.

In an embodiment, sealant compositions of the present invention may comprise a natural pozzolan (e.g., pumicite) and CKD in a weight ratio of from about 1/99 to about 99/1 with lime present in an amount of about 5% to about 15% by the combined weight of the natural pozzolan and the CKD. In another embodiment, sealant compositions of the present invention may comprise a natural pozzolan (e.g., pumicite) and CKD in a weight ratio of from about 65/35 to about 80/20 with lime present in an amount of about 5% to about 15% by the combined weight of the natural pozzolan and the CKD. In general, it should be understood that as the amount of the CKD is decreased the amount of the natural pozzolan may be increased, in accordance with embodiments of the present invention.

Embodiments of the sealant compositions further may comprise fly ash. A variety of fly ashes may be suitable, including fly ash classified as Class C and Class F fly ash according to American Petroleum Institute, API Specification for Materials and Testing for Well Cements, API Specification 10, Fifth Ed., Jul. 1, 1990. Class C fly ash comprises both silica and lime so that, when mixed with water, it should set to form a hardened mass. Class F fly ash generally does not contain sufficient lime, so an additional source of calcium ions is required for the Class F fly ash to form a hydraulic composition. In some embodiments, lime may be mixed with Class F fly ash in an amount in the range of about 0.1% to about 25% by weight of the fly ash. In some instances, the lime may be hydrated lime. Suitable examples of fly ash include, but are not limited to, POZMIX® A cement additive, commercially available from Halliburton Energy Services, Inc., Duncan, Okla.

Where present, the fly ash generally may be included in the sealant compositions in an amount sufficient to provide the desired compressive strength, density, and/or cost. In some embodiments, the fly ash may be present in the sealant compositions of the present invention in an amount in the range of about 5% to about 75% by weight of cementitious components. In some embodiments, the fly ash may be present in an amount in the range of about 10% to about 60% by weight of cementitious components. One of ordinary skill in the art, with the benefit of this disclosure, will recognize the appropriate amount of the fly ash to include for a chosen application.

Embodiments of the sealant compositions further may comprise a slag cement. In some embodiments, a slag cement that may be suitable for use may comprise slag. Slag generally does not contain sufficient basic material, so slag cement further may comprise a base to produce a hydraulic composition that may react with water to set to form a hardened mass. Examples of suitable sources of bases include, but are not limited to, sodium hydroxide, sodium bicarbonate, sodium carbonate, lime, and combinations thereof.

Where present, the slag cement generally may be included in the sealant compositions in an amount sufficient to provide the desired compressive strength, density, and/or cost. In some embodiments, the slag cement may be present in the sealant compositions of the present invention in an amount in the range of about 0.1% to about 99% by weight of cementitious components. In some embodiments, the slag cement may be present in an amount in the range of about 5% to about 75% by weight of cementitious components. One of ordinary skill in the art, with the benefit of this disclosure, will recognize the appropriate amount of the slag cement to include for a chosen application.

Embodiments of the sealant compositions further may comprise metakaolin. Generally, metakaolin is a white pozzolan that may be prepared by heating kaolin clay, for example, to temperatures in the range of about 600° C. to about 800° C. In some embodiments, the metakaolin may be present in the sealant compositions of the present invention in an amount in the range of about 5% to about 95% by weight of cementitious components. In some embodiments, the metakaolin may be present in an amount in the range of about 10% to about 50% by weight of cementitious components. One of ordinary skill in the art, with the benefit of this disclosure, will recognize the appropriate amount of the metakaolin to include for a chosen application.

Embodiments of the sealant compositions further may comprise shale. Among other things, shale included in the sealant compositions may react with excess lime to form a suitable cementing material, for example, calcium silicate hydrate. A variety of shales may be suitable, including those comprising silicon, aluminum, calcium, and/or magnesium. An example of a suitable shale comprises vitrified shale. Suitable examples of vitrified shale include, but are not limited to, PRESSUR-SEAL FINE LCM material and PRESSUR-SEAL COARSE LCM material, which are commercially available from TXI Energy Services, Inc., Houston, Tex. Generally, the shale may have any particle size distribution as desired for a particular application. In certain embodiments, the shale may have a particle size distribution in the range of about 37 micrometers to about 4,750 micrometers.

Where present, the shale may be included in the sealant compositions of the present invention in an amount sufficient to provide the desired compressive strength, density, and/or cost. In some embodiments, the shale may be present in the sealant compositions of the present invention in an amount in the range of about 5% to about 75% by weight of cementitious components. In some embodiments, the shale may be present in an amount in the range of about 10% to about 35% by weight of cementitious components. One of ordinary skill in the art, with the benefit of this disclosure, will recognize the appropriate amount of the shale to include for a chosen application.

Embodiments of the sealant compositions further may comprise zeolite. Zeolites generally are porous alumino-silicate minerals that may be either a natural or synthetic material. Synthetic zeolites are based on the same type of structural cell as natural zeolites, and may comprise aluminosilicate hydrates. As used herein, the term “zeolite” refers to all natural and synthetic forms of zeolite. Examples of suitable zeolites are described in more detail in U.S. Patent Publication No. 2007/10056475 A1. An example of a suitable source of zeolite is available from the C2C Zeolite Corporation of Calgary, Canada. In some embodiments, the zeolite may be present in the sealant compositions of the present invention in an amount in the range of about 5% to about 65% by weight of cementitious components. In certain embodiments, the zeolite may be present in an amount in the range of about 10% to about 40% by weight of cementitious components. One of ordinary skill in the art, with the benefit of this disclosure, will recognize the appropriate amount of the zeolite to include for a chosen application.

Embodiments of the sealant compositions further may comprise a set retarding additive. As used herein, the term “set retarding additive” refers to an additive that retards the setting of the sealant compositions of the present invention. Examples of suitable set retarding additives include, but are not limited to, ammonium, alkali metals, alkaline earth metals, metal salts of sulfoalkylated lignins, organic acids (e.g., hydroxycarboxy acids), copolymers that comprise acrylic acid or maleic acid, and combinations thereof. One example of a suitable sulfoalkylate lignin comprises a sulfomethylated lignin. Suitable set retarding additives are disclosed in more detail in U.S. Pat. No. Re. 31,190, the entire disclosure of which is incorporated herein by reference. Suitable set 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. Generally, where used, the set retarding additive may be included in the sealant compositions of the present invention in an amount sufficient to provide the desired set retardation. In some embodiments, the set retarding additive may be present in the sealant compositions of the present invention an amount in the range of about 0.1% to about 5% by weight of cementitious components. One of ordinary skill in the art, with the benefit of this disclosure, will recognize the appropriate amount of the set retarding additive to include for a chosen application.

Embodiments of the sealant compositions further may comprise water. The water used in embodiments of the sealant compositions may include, for example, freshwater, saltwater (e.g., water containing one or more salts dissolved therein), brine (e.g., saturated saltwater produced from subterranean formations), seawater, or combinations thereof. Generally, the water may be from any source, provided that the water does not contain an excess of compounds that may undesirably affect other components in the sealant composition. In some embodiments, the water may be included in an amount sufficient to form a pumpable slurry. In some embodiments, the water may be included in the sealant compositions of the present invention in an amount in the range of about 40% to about 200% by weight of dry components. In some embodiments, the water may be included in an amount in the range of about 40% to about 150% by weight of dry components. One of ordinary skill in the art, with the benefit of this disclosure, will recognize the appropriate amount of water to include for a chosen application.

Optionally, other additional additives may be added to the sealant compositions of the present invention as deemed appropriate by one skilled in the art, with the benefit of this disclosure. Examples of such additives include, but are not limited to, strength-retrogression additives, set accelerators, weighting agents, lightweight additives, gas-generating additives, mechanical property enhancing additives, lost-circulation materials, filtration-control additives, dispersants, fluid loss control additives, defoaming agents, foaming agents, oil-swellable particles, water-swellable particles, thixotropic additives, and combinations thereof. Specific examples of these, and other, additives include crystalline silica, amorphous silica, fumed silica, salts, fibers, hydratable clays, microspheres, rice husk ash, elastomers, elastomeric particles, resins, latex, combinations thereof, and the like. A person having ordinary skill in the art, with the benefit of this disclosure, will readily be able to determine the type and amount of additive useful for a particular application and desired result.

As mentioned above, the sealant compositions of the present invention may be foamed, for example, further comprising a gas and a surfactant, in accordance with embodiments of the present invention. A foamed sealant composition may be used, for example, where it is desired for the sealant composition to be lightweight. For example, a foamed sealant composition of the present invention may comprise CKD, a gas, a surfactant and water and be essentially free of Portland cement. By way of further example, a foamed sealant composition of the present invention may comprise CKD, a natural pozzolan, lime, a gas, a surfactant, and water and be essentially free of Portland cement. Other suitable additives, such as those discussed previously, also may be included in the foamed sealant compositions of the present invention as desired by those of ordinary skill in the art, with the benefit of this disclosure.

The gas used in the foamed sealant compositions of the present invention may be any gas suitable for foaming a sealant composition, including, but not limited to, air, nitrogen, or combinations thereof. Generally, the gas should be present in the foamed sealant compositions of the present invention in an amount sufficient to form the desired foam. In certain embodiments, the gas may be present in a foamed sealant composition of the present invention in an amount in the range of about 10% to about 80% by volume of the composition. One of ordinary skill in the art, with the benefit of this disclosure, will recognize the appropriate amount of gas to include for a chosen application.

Where foamed, embodiments of the sealant compositions of the present invention further comprise a surfactant. In some embodiments, the surfactant comprises a foaming and stabilizing surfactant composition. As used herein, a “foaming and stabilizing surfactant composition” refers to a composition that comprises one or more surfactants and, among other things, may be used to facilitate the foaming of a sealant composition and also may stabilize the resultant foamed sealant composition formed therewith. Any suitable foaming and stabilizing surfactant composition may be used in the sealant compositions of the present invention. Suitable foaming and stabilizing surfactant compositions may include, but are not limited to: mixtures of an ammonium salt of an alkyl ether sulfate, a cocoamidopropyl betaine surfactant, a cocoamidopropyl dimethylamine oxide surfactant, sodium chloride, and water; mixtures of an ammonium salt of an alkyl ether sulfate surfactant, a cocoamidopropyl hydroxysultaine surfactant, a cocoamidopropyl dimethylamine oxide surfactant, sodium chloride, and water; hydrolyzed keratin; mixtures of an ethoxylated alcohol ether sulfate surfactant, an alkyl or alkene amidopropyl betaine surfactant, and an alkyl or alkene dimethylamine oxide surfactant; aqueous solutions of an alpha-olefinic sulfonate surfactant and a betaine surfactant; and combinations thereof. In one certain embodiment, the foaming and stabilizing surfactant composition comprises a mixture of an ammonium salt of an alkyl ether sulfate, a cocoamidopropyl betaine surfactant, a cocoamidopropyl dimethylamine oxide surfactant, sodium chloride, and water. A suitable example of such a mixture is ZONESEAL® 2000 foaming additive, commercially available from Halliburton Energy Services, Inc. Suitable foaming and stabilizing surfactant compositions are described in U.S. Pat. Nos. 6,797,054, 6,547,871, 6,367,550, 6,063,738, and 5,897,699, the entire disclosures of which are incorporated herein by reference.

Generally, the surfactant may be present in the foamed sealant compositions of the present invention in an amount sufficient to provide a suitable foam. In some embodiments, the surfactant may be present in the foamed sealant compositions of the present invention an amount in the range of about 0.8% and about 5% by volume of the water (“bvow”). One of ordinary skill in the art, with the benefit of this disclosure, will recognize the appropriate amount of the surfactant to include for a chosen application.

As mentioned above, the sealant compositions may be extended in accordance with embodiments of the present invention, in that the present invention provides extended sealant compositions that are capable of remaining in a pumpable fluid state for an extended period of time. For example, the extended sealant compositions may be capable of remaining in a pumpable fluid state for at least about 1 day or longer (e.g., at least about 5 days). When desired for use, the extended sealant composition may be activated (e.g., by addition of a cement set accelerator) to thereby set into a hardened mass. By way of example, the extended sealant composition, after activation, may set to a compressive strength (as determined using the procedure set forth in API Recommended Practice 10B) at 140° F. of at least 100 psi in 72 hours, alternatively at least 500 psi. Among other things, the extended sealant compositions of the present invention may be suitable for use in well bore applications, for example, where it is desired to prepare the cement composition in advance. By way of example, the extended sealant compositions may facilitate preparation of the sealant composition at a convenient location and then transport to the job site for use in the cementing operation.

An example of a suitable extended sealant composition of the present invention comprises CKD, a set retarding additive, and water and is essentially free of Portland cement. By way of further example, a suitable extended composition comprises CKD, a natural pozzolan, lime, a set retarding additive, and water and is essentially free of Portland cement. Optionally, a suspending agent may be included in the extended sealant composition as desired. Other suitable additives, such as those discussed previously, also may be included in the extended sealant compositions of the present invention as desired by those of ordinary skill in the art, with the benefit of this disclosure.

Set retarding additives are included in the extended sealant compositions of the present invention, in accordance with embodiments of the present invention. Examples of suitable set retarding additives for extending the sealant compositions include, but are not limited to, organic acids, lignosulfonates, synthetic retarders and combinations thereof. It has been discovered that certain set retarding additives, such as phosphonated compounds, may not be desirable in certain applications because the sealant composition may become over retarded such that the composition does not activate and develop reasonable compressive strength. Examples of organic acids that may be included in the extended sealant compositions of the present invention include, but are not limited to, tartaric acid, gluconic acid, carboxylic acids (e.g., citric acid), hydroxy carboxy acids, and combinations thereof. One example of a suitable tartaric acid is HR®-25 cement retarder available from Halliburton Energy Services, Inc. Examples of lignosulfonates that may be included in the extended sealant compositions of the present invention include, but are not limited to, a sulfomethylated lignin, calcium lignosulfonates, sodium lignosulfonates, and combinations thereof. Examples of suitable lignosulfonates include HR®-4, HR®-5, and HR®-7 cement retarders available from Halliburton Energy Services, Inc. Examples of synthetic retarders that may be included in the extended sealant compositions of the present invention include, but are not limited to, copolymers of acrylic acid and acrylamido-methylpropane sulfonate polymer and copolymers of maleic anhydride and acrylamido-methyl-propane sulfonate polymer. Examples of suitable synthetic retarders include SCR™-100 and SCR™-500 cement retarders available from Halliburton Energy Services, Inc. Examples of suitable synthetic retarders are described in U.S. Pat. Nos. 4,941,536, 5,049,288, 5,472,051, and 5,536,311, the disclosures of which are incorporated herein by reference.

The set retarding additive should be included in the extended sealant compositions of the present invention in an amount sufficient for the sealant composition to remain in a pumpable fluid state for an extended period of time (e.g., at least about 1 day). In certain embodiments, the set retarding additive may be included in the extended sealant compositions of the present invention in an amount in the range of about 0.1% to about 5% by weight of cementitious components. In certain embodiments, the set retarding additive may be included in an amount in the range of about 0.1% to about 1.5% by weight of cementitious components. Where the set retarding additive comprises tartaric acid, the tartaric acid may be included, for example, in the extended sealant composition in an amount in the range of about 0.2% to about 0.35% by weight of cementitious components, for example. Where the set retarding additive comprises a sulfomethylated lignin, the sulfomethylated lignin may be included, for example, in the extended sealant composition in an amount in the range of about 0.2% to about 1% by weight of cementitious components. Those of ordinary skill in the art, with the benefit of this disclosure, should be able to determine an appropriate set retarding additive and amount thereof for a particular application.

As previously mentioned, at a desired time for use, the extended sealant composition may be activated, for example, by addition of a cement set accelerator. Examples of suitable cement set accelerators include, but are not limited to, calcium chloride, triethanolamine, sodium silicate, zinc formate, calcium acetate, and combinations thereof. An example of a suitable sodium silicate is ECONOLITE™ additive, available from Halliburton Energy Services, Inc. The cement set accelerator should be added to the extended sealant composition in an amount sufficient to activate the extended sealant composition to set into a hardened mass. In certain embodiments, the cement set accelerator may be added to the extended sealant compositions of the present invention in an amount in the range of about 0.1% to about 4% by weight of cementitious components. One of ordinary skill in the art, with the benefit of this disclosure, will recognize the appropriate amount of the cement set accelerator to include for a chosen application.

As will be appreciated by those of ordinary skill in the art, embodiments of the sealant compositions of the present invention may be used for forming a seal in a variety of subterranean applications. By way of example, embodiments of the sealant compositions may be used in cementing methods, including primary and remedial cementing.

An example of a method of the present invention comprises placing a sealant composition in a subterranean formation, and allowing the sealant composition to set. In some embodiments, the sealant compositions of the present invention may be foamed. As desired by one of ordinary skill in the art, with the benefit of this disclosure, the sealant compositions of the present invention useful in this method may comprise any of the above-listed additives, as well any of a variety of other additives suitable for use in subterranean applications.

Another example of a method of the present invention includes a method of cementing a conduit (e.g., pipe string, casing, expandable casing, liners, etc.) disposed in a well bore. An example of such a method may comprise placing a sealant composition into the annulus between the conduit and the subterranean formation, allowing the sealant composition to set in the annulus. Generally, in most instances, the sealant composition should fix the conduit in the well bore. In some embodiments, the sealant compositions of the present invention may be foamed or extended. As desired by one of ordinary skill in the art, with the benefit of this disclosure, the sealant compositions of the present invention useful in this method may comprise any of the above-listed additives, as well any of a variety of other additives suitable for use in subterranean application.

Another example of a method of the present invention includes a method of sealing a portion of a gravel pack or a portion of a subterranean formation. An example of such a method may comprise placing a sealant composition into the portion of the gravel pack or the portion of the subterranean formation, and allowing the sealant composition to set. The portions of the subterranean formation may include, for example, permeable portions of the formation and fractures (natural or otherwise) in the formation and other portions of the formation that may allow the undesired flow of fluid into, or from, the well bore. The portions of the gravel pack may include, for example, those portions of the gravel pack, wherein it is desired to prevent the undesired flow of fluids into, or from, the well bore. Among other things, this method may allow the sealing of the portion of the gravel pack to prevent the undesired flow of fluids without requiring the gravel pack's removal. In some embodiments, the sealant compositions of the present invention may be foamed or extended. As desired by one of ordinary skill in the art, with the benefit of this disclosure, the sealant compositions of the present invention useful in this method may comprise any of the above-listed additives, as well any of a variety of other additives suitable for use in subterranean applications.

Another example of a method of the present invention includes a method of sealing voids located in a conduit (e.g., pipe string, casing, expandable casings, liners, etc.) or in a cement sheath. Generally, the conduit will be disposed in a well bore, and the cement sheath may be located in the annulus between the conduit disposed in the well bore and the subterranean formation. An example of such a method may comprise placing the sealant composition into the void, and allowing the sealant composition to set in the void. In some embodiments, the sealant compositions of the present invention may be foamed or extended. As desired by one of ordinary skill in the art, with the benefit of this disclosure, the sealant compositions of the present invention useful in this method may comprise any of the above-listed additives, as well any of a variety of other additives suitable for use in subterranean applications.

When sealing a void in a conduit, methods of the present invention, in some embodiments, further may comprise locating the void in the conduit, and isolating the void by defining a space within the conduit in communication with the void; wherein the sealant composition may be introduced into the void from the space. The void may be isolated using any suitable technique and/or apparatus, including bridge plugs, packers, and the like. The void in the conduit may be located using any suitable technique. When sealing a void in the cement sheath, the methods of the present invention, in some embodiments, further may comprise locating the void in the cement sheath, producing a perforation in the conduit that intersects the void, and isolating the void by defining a space within the conduit in communication with the void via the perforation, wherein the sealant composition is introduced into the void via the perforation. The void in the cement sheath may be located using any suitable technique. The perforation may be created in the conduit using any suitable technique, for example, perforating guns. The void may be isolated using any suitable technique and/or apparatus, including bridge plugs, packers, and the like.

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