Spacer fluid additive for compressive strength regression improvement

Abstract

Well spacer materials containing geopolymer adjuvants that polymerize under alkaline conditions are used to precede pumping geopolymer precursors into a well. Use of geopolymer adjuvant in the spacer material reduces hardening loss in the geopolymer at the interface with the spacer material. The geopolymer adjuvant can partially or entirely replace conventional weighting materials used in spacer compositions.

Description

SPACER FLUID ADDITIVE FOR COMPRESSIVE STRENGTH REGRESSION IMPROVEMENTFIELD

[0001] This patent application relates to compositions and methods for completing subterranean wells. Specifically, compositions to be used with cementitious materials for forming cement well walls are described herein.BACKGROUND

[0002] Wells are commonly drilled to access subterranean formation fluids or for injection of fluids. During the drilling operation, a drilling fluid is used to facilitate drilling by lubricating the interface between the drill bit and the geologic structures being drilled. The drilling fluid is also circulated within the lengthening well to fluidize and remove solids generated by the drill bit. The drilling fluid, often called “mud” also contains weighting materials to create a pressure within the well to counteract pressure within the geologic structure that would tend to collapse the well walls and close the drilled well around the drill bit.

[0003] When drilling is complete, in many cases the well is prepared for completion by casing and cementing. The well is lined with a cementitious material which maintains integrity of the well against pressure within the geologic formations, and which provides isolation of materials at different depths within the geologic formations. To form the lining, a hollow cylindrical member is typically lowered into the well, either during drilling or after drilling is complete. For example, when drilling is complete the drill bit can be removed from the well, which is left full of drilling fluid, and the hollow cylindrical member, often called a “casing,” is lowered into the well. The casing is typically somewhat smaller in diameter than the well itself to provide an annular space around the casing between the casing and the well wall. A cap or seal is emplaced at the surface to seal the well and to form a seal with the casing, resulting in a flow pathway in the interior of the casing and a flow pathway between the casingand the well wall. These flow pathways will be used to remove the drilling fluid from the well and to deploy a slurry precursor of the cementitious material.

[0004] Recently, materials known as geopolymer materials have been used increasingly as cementitious materials for well lining. Such materials include aluminosilicate precursors that polymerize in high pH environments, unlike conventional cements that hydrate in water, but the precursors are generally powdered materials with smaller particle sizes than conventional cement precursors and more selective compositions to provide a wider range of selectable properties. A geopolymer slurry is prepared by adding water to a geopolymer precursor. High pH activators can be added to the water, to the geopolymer precursor, or both to start the polymerization reaction that yields a hardened geopolymer. A number of additives can be used in geopolymer precursors to adjust hardening time, density, pumpability, and other properties. The precursor is pumped down the center of the casing, forcing drilling fluid to flow downward to the bottom of the casing and up the outside, between the outer surface of the casing and the well wall.

[0005] To avoid mixing between the geopolymer precursor and the drilling fluid, which can contaminate both the precursor and the drilling fluid, a spacer material is pumped into the well before pumping the geopolymer precursor. The precursor is then pumped after the spacer material. During pumping, the spacer material can mix with the geopolymer precursor at the interface between the two materials. The spacer material typically has water, various natural and / or synthetic polymers, and density selection materials to provide fluid properties that facilitate pumping the spacer material and displacing the drilling fluids already in the well. Spacer materials are also used in subterranean cementing applications that do not involve drilling fluids.

[0006] When a geopolymer precursor is pumped after a spacer, materials from the spacer can mix with the precursor and dilute the polymerizable materials of the precursor. When the precursor hardens, there is often a portion of the hardened material that has reduced strength due to dilution from the spacer materials. Because geopolymer precursors are often highly engineered for specific properties, effects ofsuch dilution on geopolymer precursors can mean significant portions of the hardened geopolymer depart widely from the desired properties, particularly compressive strength. There is a need for methods and compositions that prevent such regression of compressive strength in geopolymer precursors used following spacer compositions.SUMMARY

[0007] Embodiments described herein provide a method, comprising pumping a spacer material into a well, the spacer material comprising a geopolymer adjuvant; and pumping a geopolymer precursor into the well following the spacer material, and in contact with the spacer material.

[0008] Other embodiments described herein provide a method, comprising displacing a fluid in a well by pumping a spacer material into the well, the spacer material comprising an aluminosilicate material; and pumping a geopolymer precursor into the well following the spacer material, and in contact with the spacer material.

[0009] Other embodiments described herein provide a method, comprising pumping a spacer material comprising water, a polymeric material, a densifier, and an aluminosilicate material into a well; pumping a geopolymer precursor into the well following the spacer material, and in contact with the spacer material; disposing the geopolymer precursor at a target location within the well; and hardening the geopolymer precursor to form a geopolymer.DETAILED DESCRIPTION

[0010] Compositions and methods are described herein for spacer materials to be used with geopolymer precursors in cementing wells. The spacer materials described herein generally comprise a geopolymer adjuvant to counteract the effect of any mixing of material from the spacer with a geopolymer precursor pumped into a well following the spacer. Including a geopolymer adjuvant in the spacer material that is reactive with the other materials in the geopolymer precursor can counteract the dilution effect on hardening of the geopolymer precursor at or near the interface with the spacer material.

[0011] Geopolymer precursors generally contain aluminum, silicon, and oxygen, which can be in the form of aluminosilicate source materials, or alternately mixtures of alumina and silica. Such materials can polymerize under aqueous conditions of high pH, such as 12 or higher, generally in the presence of high concentrations of hydroxyl ions. The resulting polymers are generally referred to as poly(sialate)s and have the general structure (-Si-O-AI-O-)n, where n is the degree of polymerization. The sialate network comprises S iC and AIC tetrahedra linked alternately by sharing all the oxygens, with Al3+and Si4+in IV-fold coordination with oxygen. Positive ions (Na+, K+, Li+, Ca2+... ) may be present in the framework cavities to balance the negative charge of Al3+in IV-fold coordination. The empirical formula of polysialates is: Mm {-(SiO2)z-AIO2}n, w H2O, wherein M is a cation such as potassium, sodium or calcium, n is a degree of polymerization and z is the Si / AI atomic ratio that may be 1 , 2, 3 or more.

[0012] The aluminosilicate source can be selected from the group of materials consisting of fly ash, for example ASTM type C, type F fly ash, or another fly ash, volcanic ash, ground blast furnace slag, calcined clays, which may be partially or fully calcined clays (metakaolin is a partially calcined clay), aluminum-containing silica fume, natural aluminosilicate, synthetic aluminosilicate glass powder, zeolite, scoria, allophone, bentonite, red mud, which may be calcined, pumice, and combinations thereof. These materials contain a significant proportion of an amorphous aluminosilicate phase, which reacts in strong alkaline solutions. The more common aluminosilicate sources are fly ash, metakaolin and blast furnace slag. In addition, alumina and silica may be added separately, for example as a blend of bauxite and silica fume. In another embodiment, the aluminosilicate component of a geopolymer precursor comprises a first aluminosilicate source and optionally one or more secondary aluminosilicate sources which may include ground granulated blast furnace slag, portland cement, kaolin, metakaolin or silica fume.

[0013] Formation of the set geopolymer also involves using an alkali activator. Thus, a geopolymer precursor can contain an alkali activator or a material that forms an alkali activator in-situ when the geopolymer precursor is placed at a target location for forming a geopolymer. The alkali activator may be an alkali metal hydroxide, analkaline-earth metal hydroxide, or combinations thereof. Alkali metal hydroxides may be sodium, lithium, or potassium hydroxide. Alkaline-earth metal hydroxides may include calcium, barium, or magnesium hydroxide. The alkali activator and the geopolymer precursor material is generally contacted in aqueous solution, for example by adding the alkali activator to water to form an activator solution and then adding the activator solution to the geopolymer precursor material, or by adding the alkali activator to the geopolymer precursor material and then adding water to the resulting mixture. The alkali activator may be generated in-situ by including in the geopolymer precursor a material that reacts with pre-existing materials at the target location to form the alkali activator.

[0014] Mixtures of alkali metal hydroxides, alkaline earth metal hydroxides, and mixtures of both alkali metal and alkaline earth metal hydroxides can be used. The metal hydroxide may be in the form of a solid or an aqueous mixture Also, the activator in another embodiment can be encapsulated. The activator when in solid and / or liquid state can be trapped in a capsule that will break when subjected to, for example, mechanical stress on the capsule, or coating degradation owing to temperature, chemical exposure or radiation exposure. Also, the activator when in solid and / or liquid state can be trapped in a capsule that will naturally degrade if made from a biodegradable or self-destructive material. Furthermore, the alkali activator when in liquid state may be adsorbed into a porous material and may be released after a certain time or due to a predefined event. The alkali activator may be present in the composition at a concentration between about 0.1 moles / L (M) to 10M or between 3M and 6M.

[0015] As noted above, the geopolymer precursor made by contacting geopolymer precursor materials with activator in an aqueous medium is pumped into a well following a spacer material to separate the geopolymer precursor from drilling fluids displaced by pumping the spacer and the geopolymer precursor into the well. The spacer prevents mixing of material from the drilling fluid with the geopolymer precursor. The spacer material typically includes water, polymeric materials, and density materials such as barite and / or calcium carbonate to provide a bulk density for the spacer material that will result in the spacer material moving downward in thewell against the drilling fluid and displacing the drilling fluid into the annular space between the casing and the well wall and flowing the drilling fluid upward, in the annular space, to the surface. Spacer materials can also contain antifoaming agents, viscosifiers, surfactants, mutual solvents, and cleaning agents such as fibers.

[0016] Herein, the spacer material also contains a geopolymer adjuvant. The geopolymer adjuvant is a material that is reactive with materials in the geopolymer precursor, such as those described above. A material that is reactive in a geopolymer reaction, such as an aluminosilicate source or alkali activator, is added to the spacer material, as geopolymer adjuvant, prior to deploying the spacer material into the well. Any of the geopolymer reactive materials mentioned above can be used, or any mixture thereof. In some cases, the geopolymer adjuvant added to the spacer can be a component of the geopolymer precursor that follows the spacer, such as a material used to activate or participate in the geopolymer reaction, in the geopolymer precursor. In other cases, a geopolymer adjuvant can be used that is not a component of the geopolymer precursor that follows the spacer. The quantity of geopolymer adjuvant added to the spacer material is typically about 10 percent by weight, or less, but can be up to 50%, based on the total weight of the spacer material. In many cases, a concentration of geopolymer adjuvant in the spacer material of 5 percent by weight can be used, for example 3 percent or 4 percent by weight.

[0017] In some cases, the geopolymer adjuvant can provide density modification or selection. A dense material that can react with other materials in a geopolymer precursor under alkaline conditions can be used in place of, or with conventional inert weighting material to provide both density modification and support for polymerization activity at the interface between the geopolymer precursor and the spacer material. Thus, a spacer material can be formulated that is free of inert densifiers such as barite, where a dense geopolymer adjuvant that can undergo a geopolymerization reaction under alkaline conditions is used as a densifier. Use of a dense geopolymer adjuvant as a weighting material can increase solid volume fraction of the spacer material, which will result in less fluid exchange between the spacer material and a geopolymer precursor at the interface.

[0018] A spacer composition typically contains water and weighting agents, and may contain other additives as described above. The weighting agent increases the density of the spacer composition to a level that will allow the spacer to flow downward within a well to displace drilling fluid within the well and to the surface in the annulus between the well casing and the well wall. A typical density for a spacer is at least about 11 Ib / gal, for example from about 11 Ib / gal to about 14 Ib / gal. The density of the spacer is typically selected to be less than the density of the geopolymer slurry to follow the spacer.

[0019] In some cases, the geopolymer adjuvant can itself be a geopolymer precursor. Such a geopolymer adjuvant can have the same composition as the geopolymer precursor to be pumped following the spacer material, or a different composition. In some cases, the geopolymer adjuvant can be a geopolymer precursor that is enhanced in one or more components, for example excess in aluminosilicate sources. In some cases, a low activation geopolymer precursor having alkali activator present at a concentration of 3M or less, such as 1 M or less, can be used as the geopolymer adjuvant added to the spacer material.

[0020] In some cases, two spacer materials can be used to separate a geopolymer precursor from drilling fluids. A first spacer material, free of any geopolymer adjuvant, can be pumped, and then a second spacer material, containing geopolymer adjuvant, can be pumped. In this way, use of geopolymer adjuvant in the spacer material can be minimized.

[0021] Inclusion of a geopolymer adjuvant in the spacer material reduces or precludes regression of hardening in the geopolymer precursor due to mixing with spacer material components. Since a small amount of geopolymer adjuvant can be used, overall properties of the spacer fluid important to its function, such as rheology, pumpability, or ability to displace fluids and clean the well, can be unaffected by inclusion of the geopolymer adjuvant.

[0022] An example of the effect of adding a geopolymer adjuvant to a spacer material is shown in Table 1. To generate the data of Table 1 , a neat geopolymer precursor was made and allowed to harden. Additionally, the same geopolymerprecursor was mixed with a spacer material, 80 percent by volume geopolymer precursor with 20 percent by volume spacer material. In one case, the spacer material contained barite and was free of any geopolymer adjuvant, and in another case the spacer material had fly ash as a geopolymer adjuvant, in the quantity shown, with no barite.Table 1

[0023] The data in Table 1 show that a spacer material with a fly ash additive, when mixed with a geopolymer precursor, results in less compressive strength loss than a conventional spacer material. These results indicate that use of a spacer material containing a small amount of a geopolymer adjuvant can mitigate loss of geopolymer functionality in a well. The data in Table 1 also show that a spacermaterial can be formulated, using a dense geopolymer adjuvant that can polymerize under alkaline conditions with no other density modifier, to a similar density as a spacer material formulated using a conventional density modifier.

[0024] An example of a spacer material that uses a geopolymer adjuvant as a weighting material is shown in Table 2. Two spacer materials are shown in Table 2, a conventional spacer that uses barite as a weighting material and an example embodiment of the spacers described herein that uses fly ash, a geopolymer aluminosilicate source, as a weighting material and a geopolymer adjuvant.Table 2Spacer 1 was observed to have a solid volume fraction of 16.14%, and Spacer 2 was observed to have a solid volume fraction of 32 %. Each of Spacer 1 and Spacer 2 was blended to a density of 13 Ib / gal, demonstrating that a useful spacer composition can be formulated using a dense geopolymer adjuvant that can polymerize under alkaline conditions as a weighting material instead of conventional weighting materials. These spacers were tested for interaction with a geopolymer precursor. The components of the precursor are shown in Table 3. The composition of Table 3 had a density of 15.00 Ib / gal, a solid volume fraction of 44%, and a porosity of 56%.Table 3The geopolymer precursor of Table 3 was tested for thickening time, alone and in combination with the two spacers of Table 2, and the resulting geopolymers were tested for compression strength. Blend 1 was 90% Table 3 slurry and 10% Spacer 1 by weight. Blend 2 was 90% Table 3 slurry and 10% Spacer 2 by weight. For thickening time tests, each batch was mixed at 40 °C for 2.5 hours, and the time to achieve the indicated thickness (in Bearden consistency units) was measured. Forcompressive strength testing, each batch was mixed for 150 minutes at 40 °C and 15 psi, then conditioned for 120 minutes at 55 °C and 15 psi, then put into molds and placed in a curing chamber at 55 °C and 3,100 psi, then the ambient temperature in the curing chamber was ramped up to 100°C, at 3,100 psi constant pressure, over a duration of 2,160 minutes. UCS crush strength of the resulting geopolymers was then measured using 4 in2samples. Thickening time results are shown in Table 4 and compression strength results are shown in Table 5.Table 4Table 5

[0025] The data in Table 4 and Table 5 show that using spacer compositions that contain geopolymer adjuvants that polymerize in the presence of high pH can mitigate strength decline from mixing of the spacer composition with a geopolymer precursor. In particular, dilution of a geopolymer precursor with up to 10% by weight of a spacer composition that contains alkaline polymerizable materials, such as aluminosilicate sources, as geopolymer adjuvants can still yield geopolymer materials having crushstrength suitable for some applications, particular primary and remedial well cementing.

[0026] The preceding description has been presented with reference to present embodiments. Persons skilled in the art and technology to which this disclosure pertains will appreciate that alterations and changes in the described structures and methods of operation can be practiced without meaningfully departing from the principle, and scope of this present disclosure. Accordingly, the foregoing description should not be read as pertaining only to the precise structures described and shown in the accompanying drawings, but rather should be read as consistent with and as support for the following claims, which are to have their fullest and fairest scope.

Claims

Claims1. A method, comprising: pumping a spacer material into a well, the spacer material comprising a geopolymer adjuvant; and pumping a geopolymer precursor into the well following the spacer material, and in contact with the spacer material.

2. The method of claim 1 , wherein a quantity of the geopolymer adjuvant in the spacer material is up to 50% by weight.

3. The method of claim 1 or 2, wherein the geopolymer adjuvant is a fly ash or metakaolin.

4. The method of any of claims 1 to 3, wherein the spacer material is a first spacer material, and prior to pumping the first spacer material, pumping a second spacer material that is free of geopolymer adjuvant.

5. The method of any of claims 1 , 2, or 4, wherein the geopolymer adjuvant is a geopolymer precursor.

6. The method of any of claims 1 to 5, wherein the spacer material is free of inert weighting materials.

7. The method of any of claims 1 to 6, wherein the geopolymer adjuvant is a weighting material.

8. The method of any of claims 1 to 7, wherein the spacer material further comprises an antifoaming agent, a viscosifier, a surfactant, a solvent, a cleaning agents, or a combination thereof.

9. A method, comprising: displacing a fluid in a well by pumping a spacer material into the well, the spacer material comprising an aluminosilicate material; andpumping a geopolymer precursor into the well following the spacer material, and in contact with the spacer material.

10. The method of claim 9, wherein the aluminosilicate material is selected from the group consisting of fly ash, volcanic ash, ground blast furnace slag, calcined clay, aluminum-containing silica fume, natural aluminosilicate, synthetic aluminosilicate glass powder, zeolite, scoria, allophone, bentonite, red mud, pumice, and combinations thereof.11 . The method of claim 9 or 10, wherein a quantity of the aluminosilicate material in the spacer material is up to 50% by weight.

12. The method of any of claims 9 to 11 , wherein the aluminosilicate material is a fly ash or metakaolin.

13. The method of any of claims 9 to 12, wherein the spacer material is a first spacer material, and prior to pumping the first spacer material, pumping a second spacer material that is free of geopolymer adjuvant.

14. The method of any of claims 9 to 13, wherein the spacer material further comprises an antifoaming agent, a viscosifier, a surfactant, a solvent, a cleaning agents, or a combination thereof.

15. The method of any of claims 9 to 14, wherein the aluminosilicate material is a component of a geopolymer precursor.

16. The method of any of claims 9 to 15, wherein the geopolymer precursor contains the aluminosilicate material.

17. A method, comprising: pumping a spacer material comprising water, a polymeric material, a densifier, and an aluminosilicate material into a well; pumping a geopolymer precursor into the well following the spacer material, and in contact with the spacer material; disposing the geopolymer precursor at a target location within the well; andhardening the geopolymer precursor to form a geopolymer.

18. The method of claim 17, wherein the aluminosilicate material is selected from the group consisting of fly ash, volcanic ash, ground blast furnace slag, calcined clay, aluminum-containing silica fume, natural aluminosilicate, synthetic aluminosilicate glass powder, zeolite, scoria, allophone, bentonite, red mud, pumice, and combinations thereof.

19. The method of claim 17 or 18, wherein the aluminosilicate material is a component of a geopolymer precursor.

20. The method of any of claims 17 to 19, wherein the geopolymer precursor contains the aluminosilicate material.

Images