SETTABLE DRILLING FLUIDS COMPRISING CEMENT KELN DUST AND

METHODS OF USING THEM

BACKGROUND

The present invention relates to subterranean operations and, more particularly, to settable drilling fluids that comprise an aqueous-based drilling fluid and cement kiln dust ("CKD"), and associated methods of use in subterranean operations.

During the drilling of a well bore in a subterranean formation, a drilling fluid may be used to, among other things, cool the drill bit, lubricate the rotating drill string to prevent it from sticking to the walls of the well bore, prevent blowouts by serving as a hydrostatic head to counteract the sudden entrance into the well bore of high pressure formation fluids, and remove drill cuttings from the well bore. A drilling fluid may be circulated downwardly through a drill pipe and drill bit and then upwardly through the well bore to the surface. A variety of drilling fluids may be used during the drilling of well bores into a subterranean formation. For instance, the drilling fluid used may be any number of fluids (gaseous or liquid) and mixtures of fluids and solids (such as solid suspensions, mixtures, and emulsions).

Once the well bore has been drilled to a desired depth, the drill string and drill bit may be removed from the well bore and the drilling fluid may be left in the well bore to provide hydrostatic pressure on the formation penetrated by the well bore, e.g., to prevent the flow of formation fluids into the well bore. Next, a pipe string (e.g., casing, liners, etc.) may be introduced into the well bore. Depending on the depth of the well bore and whether or not any problems are encountered in introducing the pipe string into the well bore, the drilling fluid may remain relatively static in the well bore for a relatively long time period, for example, up to 24 hours or longer. While drilling fluids are not settable (e.g., they generally do not to form a hardened mass over time), drilling fluids may increase in gel strength over time. As referred to herein, "gel strength" is the measure of the ability of a colloidal dispersion to form a gel and is based upon its resistance to shear. Accordingly, during the time period that the drilling fluid is static in the well bore, portions of the drilling fluid may increase in gel strength so that displacement of the drilling fluid from within the well bore may become more difficult.

After the pipe string has been introduced into the well bore, the pipe string may be cemented in the well bore by pumping a cement composition into an annular space

between the walls of the well bore and the pipe string disposed therein, thereby displacing the drilling fluid in the annulus. However, if the drilling fluid has developed sufficient gel strength due to remaining static in the well bore, portions of the drilling fluid in the annulus may not be displaced. Since the drilling fluid generally is not settable, this may be problematic. For example, because the drilling fluid may remain on the surfaces of the subterranean formation and on the surfaces of the pipe string, a suitable bond between the cement composition and the surfaces may not result. This may lead to the loss of zonal isolation, which can result in formation fluids continuing to enter and flow in the well bore.

In order to solve the above-described problem, settable drilling fluids have been used heretofore. Generally, a settable drilling fluid should be formulated so that it is compatible with drilling fluid (if any) remaining in the well bore. In some instances, the settable drilling may be formulated using at least a portion of the drilling fluid that was used in the drilling of the well bore. Because the settable drilling fluid should be compatible with any fluids remaining in the well bore, use of a settable drilling fluid in subsequent cement operations (e.g., primary cementing) may reduce the problems associated with incompatibility between a cement composition and the drilling fluid remaining in the well bore. Additionally, use of a settable drilling fluid may alleviate problems associated with disposal of the used drilling fluid.

During the manufacture of cement, a waste material commonly referred to as "CKD" is generated. "CKD," as that term is used herein, refers to a partially calcined kiln feed that is typically removed from the gas stream and collected during the manufacture of cement. Usually, large quantities of CKD are collected in the production of cement, and they 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 SiO2, Al2O3, Fe2O3, CaO, MgO, SO3, Na2O, and

SUMMARY

The present invention relates to subterranean operations and, more particularly, to settable drilling fluids comprising an aqueous-based drilling fluid and CKD, and associated methods of use in subterranean operations.

According to one aspect of the invention there is provided a settable drilling fluid that comprises an aqueous-based drilling fluid and cement kiln dust.

According to another aspect of the invention there is provided a settable drilling fluid that comprises an aqueous-based drilling fluid, cement kiln dust, silica fume, and calcium hydroxide.

According to another aspect of the invention there is provided a settable drilling fluid that comprises an aqueous-based drilling fluid, cement kiln dust, a hydraulic cement, silica fume, vitrified shale, and calcium hydroxide.

According to another aspect of the invention there is provided a method of cementing that comprises providing a settable drilling fluid comprising an aqueous-based drilling fluid and cement kiln dust, introducing the settable drilling fluid into a subterranean formation, and allowing the settable drilling fluid to set in the subterranean formation.

According to another aspect of the invention there is provided a method of converting an aqueous-based drilling fluid to a settable drilling fluid that comprises providing the aqueous-based drilling fluid, and adding cement kiln dust to the aqueous-based drilling fluid to form the settable drilling fluid.

According to another aspect of the invention there is provided a method of drilling a well bore and cementing a well bore that comprises drilling a well bore, circulating an aqueous-based drilling fluid in the well bore during the step of drilling the well bore, adding cement kiln dust to the aqueous-based drilling fluid to form a settable drilling fluid, and allowing the settable drilling fluid to set in the well bore.

The features and advantages of the present invention will be 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.

DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention relates to subterranean operations and, more particularly, to settable drilling fluids comprising an aqueous-based drilling fluid and CKD, and associated methods of use in subterranean operations.

I. Example Settable Drilling Fluids of the Present Invention

The present invention provides a settable drilling fluid comprising an aqueous- based drilling fluid and CKD. These settable drilling fluids should be suitable for use in a variety of subterranean cementing operations, including, but not limited to, primary cementing. Generally, the settable drilling fluids of the present invention may be formulated so that it is compatible with the drilling fluid, if any, that remains in the well bore from the drilling operations previously performed in the well bore.

Generally, any aqueous-based drilling fluid suitable for use in drilling operations may be used, provided the drilling fluid, or any components thereof, does not adversely interact with the other components of the settable drilling fluids of the present invention. In some embodiments, the drilling fluid may included at least a portion of the drilling fluid that was used in drilling the well bore. Suitable aqueous-based drilling fluids include any number of fluids that may be used for drilling a well bore. An example of a suitable aqueous drilling fluid comprises an aqueous gel. For viscosif?cation, in some embodiments, suitable aqueous gels may comprise a viscosifier, such as clays (e.g, bentonite, attapulgite, sepeolite, etc.) and polymeric viscosif?ers. In some embodiments, suitable aqueous gels may comprise a weighting material (e.g., barium sulfate). In some embodiments, suitable aqueous gels may comprise calcium oxide (e.g., lime muds) and/or partially hydrolyzed polyacrylamide ("PHPA") (e.g., PHPA muds). Additionally, suitable aqueous drilling fluids further may comprise any of a variety of suitable additives, including, but not limited to, thinners, filtration control agents, polymeric viscosif?ers, caustic soda, salts (e.g,, sodium chloride), and combinations thereof.

In some embodiments, the aqueous-based drilling fluid may be present in the settable drilling fluids of the present invention in an amount in the range of from about 5% to about 80% by weight of the settable drilling fluid. In some embodiments, the drilling fluid may be present in the settable drilling fluids of the present invention in an amount in the range of from about 5% to about 40% by weight of the settable drilling fluid. In some embodiments, the drilling fluid may be present in the settable drilling fluids of the present invention in an amount in the range of from about 10% to about 30% by weight of the settable drilling fluid. One of ordinary skill in the art will be able to determine, with the benefit of this disclosure, the appropriate amount of the drilling fluid present in the settable drilling fluids of the present invention based on a number of factors, including the desired

compressive strength, downhole temperature, formation permeability, formation porosity, setting of the mud filter cake, and rheology of the fluid.

The CKD should be included in the settable drilling fluid of the present invention in an amount sufficient, among other things, to provide the desired compressive strength for a particular application. In some embodiments, the CKD may be present in the settable drilling fluids of the present invention in an amount in the range of from about 5% to 30% by weight of the settable drilling fluid. In some embodiments, the CKD may be present in the settable drilling fluids of the present invention in an amount in the range of from about 5% to 20% by weight of the settable drilling fluid. In some embodiments, the CKD may be present in the settable drilling fluids of the present invention in an amount in the range of from about 5% to 15% by weight of the settable drilling fluid. hi some embodiments, the settable drilling fluids of the present invention optionally further may comprise additional water. The additional water included in the settable drilling fluids of the present invention may include 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 it does not contain an excess of compounds that may adversely affect other components in the settable composition. In some embodiments, the additional water may be included in the settable drilling fluids of the present invention in an amount in the range of from about 5% to about 40% by weight of the settable drilling fluid. In some embodiments, the additional water may be included in the settable drilling fluids of the present invention in an amount in the range of from about 15% to about 35% by weight of the settable drilling fluid.

Optionally, in some embodiments, the settable drilling fluids of the present invention further may comprise silica fume. Generally, the silica fume may be included in the settable drilling fluids of the present invention in an amount sufficient to provide the desired compressive strength. In some embodiments, the silica fume may be present in the settable drilling fluids of the present invention in an amount in the range of from about 5% to 20% by weight of the settable drilling fluid. In some embodiments, the silica fume may be present in the settable drilling fluids of the present invention in an amount in the range of from about 8% to 15% by weight of the settable drilling fluid.

Optionally, in some embodiments, the settable drilling fluids of the present invention further may comprise a hydraulic cement. A variety of hydraulic cements may be utilized in accordance with the present invention, including, but not limited to, those comprising calcium, aluminum, silicon, oxygen, iron, and/or sulfur, which set and harden by reaction with water. Suitable hydraulic cements include, but are not limited to, Portland cements, pozzolana cements, gypsum cements, high alumina content cements, slag cements, silica cements, and combinations thereof. In certain embodiments, the hydraulic cement may comprise a Portland cement. In some embodiments, the Portland cements that are suited for use in the present invention are classified as Classes A, C, H, and G cements according to American Petroleum Institute, API Specification for Materials and Testing for Well Cements, API Specification 10, Fifth Ed., July 1, 1990.

Where present, the hydraulic cement generally may be included in the settable drilling fluids in an amount sufficient to provide the desired compressive strength, density, and/or cost. In some embodiments, the hydraulic cement may be present in the settable drilling fluids of the present invention in an amount up to about 10% by weight of the settable drilling fluid. In some embodiments, the hydraulic cement may be present in the settable drilling fluids of the present invention in an amount in the range of from 3% to about 7% by weight of the settable drilling fluid.

Optionally, in some embodiments, the settable drilling fluids of the present invention further may comprise vitrified shale. Among other things, the vitrified shale included in the settable compositions may react with excess lime to form a suitable cementing material, for example, calcium silicate hydrate. A variety of vitrified shales are suitable, including those comprising silicon, aluminum, calcium, and/or magnesium. 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, Texas. Generally, the vitrified shale may have any particle size distribution as desired for a particular application. In certain embodiments, the vitrified shale may have a particle size distribution in the range of from about 37 micrometers to about 4,750 micrometers.

Where present, the vitrified shale generally may be included in the settable drilling fluids in an amount sufficient to provide the desired compressive strength, density, and/or cost. In some embodiments, the vitrified shale may be present in the settable drilling

fluids of the present invention in an amount up to about 12% by weight of the settable drilling fluid. In some embodiments, the vitrified shale may be present in the settable drilling fluids of the present invention in an amount in the range of from 1% to about 10% by weight of the settable drilling fluid.

Optionally, in some embodiments, the settable drilling fluids of the present invention further may comprise calcium hydroxide (commonly referred to as "hydrated lime"). In some embodiments, the calcium hydroxide may be present in the settable drilling fluids of the present invention in an amount in the range of from about 10% to about 30% by weight of the settable drilling fluid.

Optionally, in some embodiments, the settable drilling fluids of the present invention further may comprise a dispersant. While a variety of dispersants known to those skilled in the art may be used in accordance with the present invention, a suitable dispersant comprises a water-soluble polymer prepared by the condensation of formaldehyde with acetone and sodium bisulfite. Such a dispersant is commercially available as CFR™-3 dispersant from Halliburton Energy Services, Inc., Duncan, Oklahoma. Another suitable dispersant comprises a sodium salt of naphthalene sulfonic acid condensed with formaldehyde, an example of which is commercially available as CFR™-2 dispersant also from Halliburton Energy Services, Inc., Duncan, Oklahoma. Another suitable dispersant comprises gluconic acid, an example of which is commercially available as CFR™-1 dispersant also from Halliburton Energy Services, Inc., Duncan, Oklahoma. In some embodiments, the dispersant may be present in the settable drilling fluids of the present invention in an amount in the range of from about 0.1% to about 5% by weight of the settable drilling fluid.

Optionally, in some embodiments, the settable compositions of the present invention further may comprise a set retarder. As used herein, the term "set retarder" refers to an additive that retards the setting of the settable drilling fluids 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, hydroxycarboxy acids, copolymers of 2-acrylamido-2-methylpropane sulfonic acid salt and 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 Um''ted States Patent 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 tradenames HR* 4, HR® 5, HR* 7, HR® 12, HR® 15, HR® 25, SCR™ 100, and SCR™ 500. Generally, where used, the set retarding additive may be included in the settable 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 an amount in the range of from about 0.1% to about 2% by weight of the settable drilling.

Additionally, those of ordinary skill in the art will recognize a variety of additional additives suitable for inclusion in the settable drilling fluids of the present invention for a particular application. Such additives may include, but are not limited to, accelerators, lost circulation materials, fluid loss control additives, and combinations thereof. p. Example Methods of the Present Invention

The settable drilling fluids of the present invention may be used in any of a variety of subterranean cementing operations. For example, a settable composition of the present invention that comprises a portion of the drilling fluid used in drilling a well bore may be used in cementing operations in the well bore. While the compositions of the present invention may be used in a variety of cementing operations, they may be particularly suitable for primary cementing operations because the settable drilling fluids of the present invention generally should be compatible with the drilling fluid, if any, remaining in the well bore.

An example of such a cementing operation using the settable drilling fluids of the present invention may comprise providing an aqueous-based drilling fluid, adding CKD to the aqueous-based drilling fluid to form a settable drilling fluid, introducing the settable drilling fluid into a subterranean formation, and allowing the settable drilling fluid to set in the subterranean formation. As will be understood by those of ordinary skill in the art, with the benefit of this disclosure, additional additives, such as those described above, may be added to the settable drilling fluid to impart desired properties thereto. In some embodiments, the settable drilling fluids of the present invention may be used in primary cementing, in that, the cementing embodiments further may comprise introducing a casing into a well bore penetrated by the well bore, wherein the settable drilling fluid sets in an annulus formed between the casing and a wall of the well bore.

In some embodiments, the methods of the present invention further may comprise drilling a well bore while the aqueous-based drilling fluid is circulated in the well

bore. At a desired time during the drilling operation (for example, when the well bore, or that portion of the well bore, has been drilled to the desired depth), the aqueous-based drilling fluid may be converted into a settable drilling fluid of the present invention. Converting the aqueous-based drilling fluid into a settable drilling fluid of the present invention generally comprises added CKD to the drilling fluid. In some embodiments, the CKD may be mixed with water to form a settable composition, prior to their addition to the aqueous-based drilling fluid. As will be understood by those of ordinary skill in the art, with the benefit of this disclosure, additional additives, such as those described above, may be added to the aqueous-based drilling fluid to impart desired properties thereto. This settable drilling fluid may then be used in any suitable cementing operation.

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.

EXAMPLE l

Three aqueous-based drilling fluids having a density of 10 pounds per gallon were prepared. The first drilling fluid was a bentonite mud. The second drilling fluid was a PHPA mud. The third drilling fluid was a lime mud. The formulation of each drilling fluid is provided in Table 1 below. After preparation, each drilling fluid was stirred on a dispersator for at least 60 minutes. Each of these drilling fluids was mixed with CKD and tested as provided in Examples 2-4.

Table 1: Drilling Fluid Formulations

Ground Bentonite available as AQUAGEL Viscosifier from Halliburton Energy Services, Inc., Duncan, Oklahoma.

2 A ferrochrome lignosulfonate available as QUIK-THIN® Thinner from Halliburton Energy Services, Inc., Duncan, Oklahoma.

3 A granular synthetic polymer containing PHPA copolymer available as EZ MUD DP® Borehole Stabilizer from Halliburton Energy Services, Inc., Duncan, Oklahoma.

4 PAC-L® Modifier Natural Cellulosic Polymer available from Halliburton Energy Services, Inc., Duncan, Oklahoma.

5 BARAZAN D PLUS® Viscosifier available from Halliburton Energy Services, Inc., Duncan, Oklahoma.

6 A ground barium sulfate available as Bariod® Weighting Material from Halliburton Energy Services, Inc., Duncan, Oklahoma.

EXAMPLE 2

Sample settable compositions (Fluid Nos. 1-2) were prepared. The sample settable compositions comprised water, CKD, silica fume, a dispersant, a set retarder, and calcium hydroxide as shown below in Table 2.

Table 2: Sample Settable Composition Comprising CKD

CFR™-3L Dispersant from Halliburton Energy Services, Inc. 2 HR™-4L Retarder from Halliburton Energy Services, Inc.

After preparation of the sample settable compositions, to prepare sample settable drilling fluids, the sample settable compositions were mixed with the sample drilling fluids from Example 1 in a volume ratio of sample settable composition to drilling fluid of about 80:20, as shown below in Table 3. Thereafter, the resultant foamed sample compositions were subjected to 72-hour compressive strength tests at the temperature indicated in accordance with API Specification 10. The results of the compressive strength tests are set forth in the table below.

Table 3: Compressive Strength of Sample Settable Drilling Fluids

EXAMPLE 3

A sample settable composition (Fluid No. 3) was prepared. Fluid No. 3 comprised water, CKD, silica fume, class H Portland cement, a dispersant, a set retarder, and calcium hydroxide as shown below in Table 4.

Table 4: Sample Settable Composition Comprising CKD and Portland Cement

2 HR™-4L Retarder from Halliburton Energy Services, Inc. After preparation, to prepare sample settable drilling fluids, Fluid No. 3 was mixed with the sample drilling fluids from Example 1 in a volume ratio of Fluid No. 3 to drilling fluid of about 80:20. Thereafter, the resultant settable drilling fluids were subjected to thickening time and 72-hour compressive strength tests at the temperature indicated in accordance with API Specification 10. The results of the compressive strength tests are set forth in the table below.

Table 5: Compressive Strength/Thickening Time of Sample Settable Drilling Fluids

EXAMPLE 4

A sample settable composition (Fluid No. 4) was prepared. Fluid No. 4 comprised water, CKD, silica fume, vitrified shale, class H Portland cement, a dispersant, a set retarder, and calcium hydroxide as shown below in Table 6.

Table 6: Sample Settable Composition Comprising CKD, Portland Cement, and Vitrified Shale

CFR™-3L Dispersant from Halliburton Energy Services, Inc.

2 HR™-4L Retarder from Halliburton Energy Services, Inc.

After preparation, to prepare sample settable drilling fluids, Fluid No. 4 was mixed with the sample drilling fluids from Example 1 in a volume ratio of Fluid No. 4 to drilling fluid of about 80:20. Thereafter, the resultant settable drilling fluids were subjected to 72 -hour compressive strength tests at the temperature indicated in accordance with API Specification 10. The results of the compressive strength tests are set forth in the table below.

Table 7: Compressive Strengths of Sample Settable Drilling Fluid

These examples thus indicate that settable drilling fluids comprising a drilling fluid and CKD may have suitable thickening times and/or compressive strengths for a particular application.

Therefore, the present invention is well adapted to attain the ends and advantages mentioned as well as those that are inherent therein. The particular embodiments disclosed above are illustrative only, as the present invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular illustrative embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the present invention. In particular, every range of values (of the form, "from about a to about c," or, equivalently, "from approximately a to c," or, equivalently, "from approximately a-c") disclosed herein is to be understood as referring to the power set (the set of all subsets) of the respective range of values, and set forth every range encompassed within the broader range of values. Also, the terms in the claims have their plain, ordinary meaning unless otherwise explicitly and clearly defined by the patentee.

CLAIMS:

1. A settable drilling fluid comprising: an aqueous-based drilling fluid; and cement kiln dust.

2. The settable drilling fluid of claim 1 wherein the aqueous-based drilling fluid comprises water and the settable drilling fluid comprises additional water.

3. The settable drilling fluid of claim 1 wherein the cement kiln dust is present in the settable drilling fluid in an amount in the range of from about 1% to about 25% by weight of the settable drilling fluid.

4. The settable drilling fluid of claim 1 wherein the aqueous-based drilling fluid is a bentonite mud, a lime mud, a partially hydrolyzed polyacrylamide mud, or combinations thereof.

5. The settable drilling fluid of claim 1 wherein the aqueous-based drilling fluid is an aqueous gel comprising a viscosifier selected from the group consisting of a clay, a polymeric viscosifier, and combinations thereof.

6. The settable drilling fluid of claim 1 wherein the aqueous-based drilling fluid is present in the settable drilling fluid in an amount in the range of from about 5% to about 40% by weight of the settable drilling fluid.

7. The settable drilling fluid of claim 1 wherein the settable drilling fluid comprises at least one additive selected from the group consisting of an accelerator, a lost circulation material, a fluid loss control additive, a dispersant, a set retarder, calcium hydroxide, silica fume, a hydraulic cement, vitrified shale, and combinations thereof.

8. The settable drilling fluid of claim 1 wherein the settable drilling fluid comprises silica fume in an amount in the range of from about 5% to about 20% by weight of the settable drilling fluid.

9. The settable drilling fluid of claim 1 wherein the settable drilling fluid comprises a hydraulic cement in an amount up to about 10% by weight of the settable drilling fluid.

10. The settable drilling fluid of claim 1 wherein the settable drilling fluid comprises vitrified shale in an amount up to about 10% by weight of the settable drilling fluid.

11. The settable drilling fluid of claim 1 wherein the settable drilling fluid comprises calcium hydroxide in an amount in the range of from about 10% to about 30% by weight of the settable drilling fluid.

12. A settable drilling fluid comprising: an aqueous-based drilling fluid; cement kiln dust; silica fume; and calcium hydroxide.

13. The settable drilling fluid of claim 12 wherein the cement kiln dust is present in the settable drilling fluid in an amount in the range of from about 1% to about 25% by weight of the settable drilling fluid.

14. The settable drilling fluid of claim 12 wherein the aqueous-based drilling fluid is a bentonite mud, a lime mud, a partially hydrolyzed polyacrylamide mud, or combinations thereof.

15. The settable drilling fluid of claim 12 wherein the aqueous-based drilling fluid is present in the settable drilling fluid in an amount in the range of from about 5% to about 40% by weight of the settable drilling fluid.

16. The settable drilling fluid of claim 12 wherein the settable drilling fluid comprises at least one additive selected from the group consisting of an accelerator, a lost circulation material, a fluid loss control additive, a dispersant, a set retarder, a hydraulic cement, vitrified shale, and combinations thereof.

17. The settable drilling fluid of claim 12 wherein: the silica fume is present in an amount in the range of from about 5% to about 20% by weight of the settable drilling fluid; and the calcium hydroxide is present in an amount in the range of from about 10% to about 30% by weight of the settable drilling fluid.

18. A settable drilling fluid comprising: an aqueous-based drilling fluid; cement kiln dust; a hydraulic cement; silica fume; vitrified shale; and calcium hydroxide.

19. The settable drilling fluid of claim 18 wherein the cement kiln dust is present in the settable drilling fluid in an amount in the range of from about 1% to about 25% by weight of the settable drilling fluid.

20. The settable drilling fluid of claim 18 wherein the aqueous-based drilling fluid is a bentonite mud, a lime mud, a partially hydrolyzed polyacrylamide mud, or combinations thereof.

21. The settable drilling fluid of claim 18 wherein the aqueous-based drilling fluid is present in the settable drilling fluid in an amount in the range of from about 5% to about 40% by weight of the settable drilling fluid.

22. The settable drilling fluid of claim 18 wherein the settable drilling fluid comprises at least one additive selected from the group consisting of an accelerator, a lost circulation material, a fluid loss control additive, a dispersant, a set retarder, and combinations thereof.

23. The settable drilling fluid of claim 18 wherein: the silica fume is present in an amount in the range of from about 5% to about 20% by weight of the settable drilling fluid; the hydraulic cement is present in an amount up to about 10% by weight of the settable drilling fluid; the vitrified shale is present in an amount up to about 10% by weight of the settable drilling fluid; and the calcium hydroxide is present in an amount in the range of from about 10% to about 30% by weight of the settable drilling fluid.

24. A method of cementing comprising: providing a settable drilling fluid comprising an aqueous-based drilling fluid and cement kiln dust; introducing the settable drilling fluid into a subterranean formation; and allowing the settable drilling fluid to set in the subterranean formation.

25. The method of claim 24 wherein the aqueous-based drilling fluid comprises water and the settable drilling fluid comprises additional water.

26. The method of claim 24 wherein the cement kiln dust is added to the settable drilling fluid in an amount in the range of from about 1% to about 25% by weight of the settable drilling fluid.

27. The method of claim 24 wherein the aqueous-based drilling fluid is a bentonite mud, a lime mud, a partially hydrolyzed polyacrylamide mud, or combinations thereof.

28. The method of claim 24 wherein the aqueous-based drilling fluid is an aqueous gel comprising a viscosif?er selected from the group consisting of a clay, a polymeric viscosif?er, and combinations thereof.

29. The method of claim 24 wherein the aqueous-based drilling fluid is present in the settable drilling fluid in an amount in the range of from about 5% to about 40% by weight of the settable drilling fluid.

30. The method of claim 24 wherein the settable drilling fluid comprises at least one additive selected from the group consisting of an accelerator, a lost circulation material, a fluid loss control additive, a dispersant, a set retarder, calcium hydroxide, silica fume, a hydraulic cement, vitrified shale, and combinations thereof.

31. The method of claim 24 wherein the settable drilling fluid comprises silica fume in an amount in the range of from about 5% to about 20% by weight of the settable drilling fluid.

32. The method of claim 24 wherein the settable drilling fluid comprises a hydraulic cement in an amount up to about 10% by weight of the settable drilling fluid.

33. The method of claim 24 wherein the settable drilling fluid comprises vitrified shale in an amount up to about 10% by weight of the settable drilling fluid.

34. The method of claim 24 wherein the settable drilling fluid comprises calcium hydroxide in an amount in the range of from about 10% to about 30% by weight of the settable drilling fluid.

35. The method of claim 24 wherein the settable drilling fluid is allowed to set in an annulus between the subterranean formation and a pipe string located in the subterranean formation.

36. A method of converting an aqueous-based drilling fluid to a settable drilling fluid comprising: providing an aqueous-based drilling fluid; and adding cement kiln dust to the aqueous-based drilling fluid to form the settable drilling fluid.

37. The method of claim 36 further comprising the step of adding additional water to the aqueous-based drilling fluid.

38. The method of claim 36 wherein the aqueous-based drilling fluid is a bentonite mud, a lime mud, a partially hydrolyzed polyacrylamide mud, or combinations thereof.

39. The method of claim 36 wherein the cement kiln dust is added to the aqueous-based drilling fluid in an amount in the range of from about 1% to about 25% by weight of the settable drilling fluid.

40. The method of claim 36 wherein the aqueous-based drilling fluid is present in the settable drilling fluid in an amount in the range of from about 5% to about 40% by weight of the settable drilling fluid.

41. The method of claim 36 further comprising the step of adding at least one additive to the aqueous-based drilling fluid, the at least one additive selected from the group consisting of an accelerator, a lost circulation material, a fluid loss control additive, a dispersant, a set retarder, calcium hydroxide, silica fume, a hydraulic cement, vitrified shale, and combinations thereof.

42. A method of drilling a well bore and cementing a well bore comprising: drilling a well bore; circulating an aqueous-based drilling fluid in the well bore during the step of drilling the well bore; adding cement kiln dust to the aqueous-based drilling fluid to form a settable drilling fluid; and allowing the settable drilling fluid to set in the well bore.

43. The method of claim 42 further comprising the step of adding additional water to the aqueous-based drilling fluid.

44. The method of claim 42 wherein the aqueous-based drilling fluid is a bentonite mud, a lime mud, a partially hydrolyzed polyacrylamide mud, or combinations thereof.

45. The method of claim 42 wherein the cement kiln dust is added to the aqueous-based drilling fluid in an amount in the range of from about 1% to about 25% by weight of the settable drilling fluid.

46. The method of claim 42 wherein the aqueous-based drilling fluid is present in the settable drilling fluid in an amount in the range of from about 5% to about 40% by weight of the settable drilling fluid.

47. The method of claim 42 further comprising the step of adding at least one additive to the aqueous-based drilling fluid, the at least one additive selected from the group consisting of an accelerator, a lost circulation material, a fluid loss control additive, a dispersant, a set retarder, calcium hydroxide, silica fume, a hydraulic cement, vitrified shale, and combinations thereof.