WO2026020103A1 - Acid degradable geopolymers - Google Patents

Abstract

Geopolymer precursors are presented that are useful for subterranean wells. The precursors contain an aluminosilicate source, an alkali activator, an acid responsive solid component, and an aqueous medium. The acid responsive solid additive allows the geopolymer system obtained from hardening the geopolymer precursor to be altered by treatment using acid.

Description

ACID DEGRADABLE GEOPOLYMERS

RELATED APPLICATIONS

This application claims the benefit of US Provisional Application Serial No. 63/673,493 filed on July 19, 2024, which bears the same title and is incorporated by reference.

FIELD

[0001] The present disclosure relates to cement-like materials. This patent application is about geopolymer formulations that result in geopolymer systems that can be degraded by acid.

BACKGROUND

[0002] Geopolymers are a class of materials that are formed by chemical reaction of various aluminosilicates, oxides, and silicates to form an amorphous three- dimensional framework cement-like structure. The term geopolymer was proposed and first used by J. Davidovits. His work is described in Davidovits, J: “Synthesis of New High-Temperature GeoPolymers for Reinforced Plastics/Composites.' Society of Plastics Engineers, IUPAC International Symposium on Macromolecules, Stockholm (1976). Other terms have been used to describe materials synthesized utilizing a similar chemistry, such as alkali-activated cement, geocement, alkali- bonded ceramic, inorganic polymer, hydroceramic. In the following description, the term geopolymer will be used.

[0003] Geopolymer systems have been investigated for use in several applications, including as concrete systems within the construction industry, as refractory materials and as encapsulants for hazardous and radioactive waste streams. Geopolymer precursors are also recognized as being rapid setting and hardening materials. The resulting geopolymer systems exhibit superior hardness and chemical stability. The preparation of geopolymer systems generally involves mixing a blend of reactive solid materials and activating the polymerization reaction by adding an alkaline solution. Typically, the slurry mixture is then applied and allowed to harden in place. In construction, faster hardening is usually valued.

[0004] In the hydrocarbon industry, cement-like materials are used to line wells to provide isolation and structural support within the well. Use of cement-like materials in hydrocarbon wells presents unique challenges. The slurry mixture precursor is typically pumped over long distances to the location where the mixture is to set, so the mixture must be pumpable without undue burden on equipment. Additionally, ambient conditions encountered in a typical hydrocarbon well are much more extreme than those encountered in a typical construction application. Further, the large vertical extent of hydrocarbon well applications present challenges of density, temperature, and pressure not faced in the construction industry. Other applications, like plugs, squeeze, and injector wells for water or carbon dioxide, also require a cementitious precursor to be pumped to an application site, so geopolymer compositions find broad use where pumping is required.

[0005] In some applications, the cementitious material may be applied temporarily. For example, in some uses of cementitious material in hydrocarbon wells, the material may be deployed for temporary isolation of a certain zone. As geopolymer systems become increasingly used in place of conventional cement materials, there is a need for geopolymer systems that can be deployed temporarily and then removed. In other cases, a geopolymer precursor may flow into portions of a subterranean formation from a well during deployment of the precursor mixture. When the geopolymer precursor sets to form a geopolymer system, it can obstruct flow paths from the formation into the well. There is a need for geopolymer formulations that make geopolymer systems with removable or degradable components such that permeability of the geopolymer system can be changed after the system is set.

SUMMARY

[0006] Embodiments described herein provide a method, comprising obtaining a geopolymer precursor comprising an aluminosilicate source, an alkali activator, an acid responsive solid additive, and an aqueous material; pumping the geopolymer precursor into a subterranean well; causing the geopolymer precursor to harden and set within the subterranean well to form a geopolymer system; and treating the geopolymer using an acid to remove a portion of the geopolymer system.

[0007] Other embodiments described herein provide a method, comprising forming a geopolymer system in a subterranean well using a pumpable precursor comprising an aluminosilicate source, an alkali activator, an acid responsive solid additive comprising an alkaline earth metal carbonate, and an aqueous material; and treating the geopolymer system using an acid to remove a portion of the geopolymer system.

[0008] Other embodiments described herein provide a method, comprising in a subterranean well, treating a geopolymer system having an acid responsive solid additive using an organic acid, an inorganic acid, or both to degrade the geopolymer system.

[0009] Other embodiments described herein provide a geopolymer precursor comprising an aluminosilicate source, an alkali activator, a polymeric acid responsive solid additive, and an aqueous material.

[0010] Other embodiments described herein provide a dry geopolymer precursor mixture, comprising an aluminosilicate source, an alkali activator, and an inorganic mineral acid responsive solid additive.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figs. 1-4 are graphs showing mass loss of geopolymer systems made from precursor formulations according to embodiments described herein, and one comparative formulation, when exposed to various acid solutions.

DETAILED DESCRIPTION

[0012] In the following description, numerous details are set forth to provide an understanding of the technology described. However, it may be understood by those skilled in the art that the methods described here may be practiced, in some cases, without some of the details, or in other combinations, and that numerous variations or modifications from the described examples may be possible.

[0013] In the development of any embodiments of the technology described herein, numerous implementation-specific decisions are made to achieve specific goals, such as compliance with system- and business-related constraints, which will vary from one implementation to another. Moreover, such a development effort might be complex and time consuming but would nevertheless be a routine undertaking for those of ordinary skill in the art implementing this technology. In addition, the compositions used/disclosed herein can include components other than those specifically mentioned. In the summary above and this detailed description, any numerical values should be understood as approximate, as for example modified by the term "about" (unless already expressly so modified), due to variation that can come from measurement and formulation variance, among other sources. The term “about” can be understood as any amount or range within 10% of the recited amount or range (for example, a range from about 1 to about 10 encompasses a range from 0.9 to 11 ). Also, in the summary and this detailed description, it should be understood that a concentration range listed or described as being useful, suitable, or the like, is intended to communicate that any concentration within the range, including the end points, is to be considered as usable and disclosed. For example, “a range of from 1 to 10” is to be read as indicating each possible number along the continuum between about 1 and about 10 can be used and is disclosed. Furthermore, one or more of the data points in the present examples may be combined together, or may be combined with one of the data points in the specification to create a range, and thus include each possible value or number within this range. Thus, even if specific data points within the range, or even no data points within the range, are explicitly identified or refer to a few specific, it is to be understood that inventors appreciate and understand that any data points within the range are to be considered to have been specified, and that inventors possessed knowledge of the entire range and the points within the range.

[0014] As used herein, “embodiments” refers to nonlimiting examples disclosed herein, whether claimed or not, which may be employed or present alone or in any combination or permutation with one or more other embodiments. Each embodiment disclosed herein should be regarded both as an added feature to be used with one or more other embodiments, as well as an alternative to be used separately or in lieu of one or more other embodiments. It should be understood that no limitation of the scope of the claimed subject matter is thereby intended, any alterations and further modifications in the illustrated embodiments, and any further applications of the principles of the application as illustrated therein as would normally occur to one skilled in the art to which the disclosure relates are contemplated herein.

[0015] The geopolymer formulations described herein use acid responsive solid additives in sufficient quantity to allow the eventual geopolymer system to be degraded and removed by acid treatment. The acid responsive solid additives generally react, dissolve, degrade, or otherwise change when exposed to an acid environment in a way that allows a set cementitious material formed from a geopolymer precursor described herein to be degraded, deconstructed, and/or easily removed. The acid responsive solid additives may be inorganic (i.e. , mineral) acid responsive solid additives or organic acid responsive solid additives. The acid responsive solid additives can be a filler material within the geopolymer precursor, and within the resulting geopolymer system that, upon exposure to an acid environment, changes in a way that weakens the geopolymer system, enabling easy removal. The filler material occupies space within, and contributes mechanical strength to, the geopolymer matrix that forms from reactive materials of the geopolymer precursor, and upon exposure to the acidic environment, the filler material is dissolved, degraded, or otherwise changed in a way that reduces its contribution to the mechanical strength of the geopolymer system to a point that the system can be collapsed, degraded, and/or removed. Removal of the acid responsive material from the geopolymer system may increase porosity of the geopolymer system in some cases. The solid additives can be added to the dry mixture from which the geopolymer precursor is made by adding water or an aqueous mixture or material, or the solid additives can be added to the aqueous component from which the geopolymer precursor is made. In some cases, all dry components can be mixed together to make a dry mixture to which only water is added to make a geopolymer precursor that can harden into a geopolymer system. [0016] The geopolymer precursors described herein involve the use of an aluminosilicate source and an alkali activator in an aqueous medium, along with the acid responsive additives mentioned above. The materials can be added or mixed in any order, and the acid responsive additive can be a single material or a mixture of acid responsive additives can be used. The acid responsive solid additives can be present in the geopolymer precursor, or in the dry mixture to which aqueous material is added to make a geopolymer precursor, in an amount that is not more than 300%, such as 10%-300%, for example 50%-300%, or not more than 250%, such as 10%- 250%, for example 50%-250%, by weight of the amount of aluminosilicate source. Any amount below that amount can be used, but typically a quantity is used that results in reasonable reaction rate between an acid and the acid responsive solid additives. .

[0017] Examples of aluminosilicate sources from which geopolymer systems may be formed include (but are not limited to) ASTM type C fly ash, ASTM type F fly ash, ground blast furnace slag, ground granulated blast furnace slag (GGBS), calcined clays, partially calcined clays (such as metakaolin), aluminum-containing silica fume, natural aluminosilicate, synthetic aluminosilicate glass powder, zeolite, scoria, allophone, bentonite, red mud, calcined red mud and pumice. These materials contain a significant proportion of an amorphous aluminosilicate phase, which reacts in strong alkaline solutions. The more common aluminosilicates are fly ash, metakaolin and blast furnace slag. Mixtures of two or more aluminosilicate sources may also be used if desired. 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 comprises a first aluminosilicate binder and optionally one or more secondary binder components which may include ground granulated blast furnace slag, Portland cement, kaolin, metakaolin or silica fume. The aluminosilicate source may have a calcium oxide content that is at least 18% by weight.

[0018] In some cases, aluminosilicate sources for geopolymer systems have particle sizes, and particle size distributions, that are smaller than traditional cement materials. GGBS materials, for example, often have D90 particle size that is less than 50 pm, for example less than 40 pm. The D50 particle size of GGBS materials can be less than 20 m, and in some cases less than 15 pm, and the D10 particle size can be less than 3 pm, in some cases less than 2 pm. Fly ash Type C materials often have D90 particle size that is less than 150 pm, for example less than 100 pm. The D50 particle size of fly ash Type C materials can be less than 50 pm, and in some cases less than 20 pm, and the D10 particle size can be less than 10 pm, in some cases less than 5 pm.

[0019] The alkali activator may be an alkali metal, an alkaline-earth metal hydroxide, or combinations thereof. Alkali metal hydroxides may be sodium or potassium hydroxide. Alkaline-earth metal hydroxides may include calcium or barium hydroxide. The metal hydroxide may be in the form of a solid or an aqueous mixture. Other activators that do not contain hydroxide can also be used. For example, alkali metal silicates, silicate hydrates, metasilicates, orthosilicates, and pyrosilicates can be used as activators, solid or in aqueous solution. Such activators generally have the formula M2xSi_yO2y+x where x is 1 , 2, or 3 and y is 1 or 2 and M can be Li, Na, K, Rb, or Cs, or combination thereof. Alkali metal carbonates can also be used as activators, as solids or in aqueous solution.

[0020] 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 can be generated in situ by reaction of calcium hydroxide with sodium carbonate. The alkali activator may be present in the composition at a concentration between about 1 M to 10M or between 3M and 6M.

[0021] Calcium carbonate particles can be used as the acid responsive solid additive. Such particles do not dissolve in high pH solutions, so the particles become a solid component of the hardened geopolymer system. Other acid responsive particles, for example alkali metal and alkaline earth metal carbonates, phosphates, and oxides, for example calcium phosphate and magnesium oxide, can be used as acid responsive additives, alone or in mixtures. Metal particles, for example powdered metal, can also be used. Some materials that can be used as acid responsive solid additives can dissolve in water at neutral pH, so such materials are typically used along with other activation components that result in high pH of the geopolymer precursor so that the acid responsive solid additives do not dissolve. For example, sodium carbonate can be used as a water soluble activator in geopolymer precursor formulations, but sodium carbonate is practically insoluble in 50% sodium hydroxide solution. Thus, where sodium hydroxide solution is used as activator for a geopolymer precursor, sodium carbonate particles can be used as an acid responsive solid particle additive. Other alkali metal carbonates, such as lithium, potassium, rubidium, and cesium are similar. Other alkaline earth metal carbonates that can be used as acid responsive solid additives include magnesium carbonate, barium carbonate, and strontium carbonate. Metals such as iron, tin, zinc, nickel, and copper can be used as particulate additives for acid reactivity. Other salts, such as hydroxides can be used as acid responsive solid additives where the geopolymer precursor has sufficiently high pH to avoid dissolving the hydroxides. Thus, where 50% sodium hydroxide is used as activator for the geopolymer precursor, solids such as calcium hydroxide (or magnesium or barium or strontium hydroxide) can be used as acid responsive solid additives.

[0022] Other organic and inorganic materials can be used as the acid responsive solid additives. These are materials that degrade when exposed to a suitable acid environment commonly found in subterranean locations. Polymers that degrade or change, for example by hydrolyzing, including polyglycolic acid, polylactic acid, polyester, poly(a-hydroxybutyric acid), poly(hydroxyvaleric acid), poly(caprolactone), and combinations, copolymers, and multi-polymers thereof, can be used. Inorganic materials that dissolve, degrade, or change when exposed to an acidic environment include acid responsive clays such as kaolinite, chlorite, which can be iron rich or magnesium rich, or both, and smectite, feldspars such as albite, plagioclase, sodium feldspar, calcium feldspar, potassium feldspar, and combinations thereof, any of which can be natural mineral materials or synthetic materials, can also be used. Combinations of the above organic and inorganic materials can also be used, such as a combination of degradable polymers and degradable inorganic materials. Where organic materials might react prior to setting the geopolymer system, such materials can be encapsulated in a suitable material to slow any interaction of the acid responsive solid component such that the geopolymer system can set and harden with the solid component dispersed therein.

[0023] The particles can have, or can be processed to have, a particle size distribution that supports reaction with acid at a useful rate but maintains pumpability of the geopolymer precursor for downhole deployment. Large particles facilitate mixing and pumping, while small particles react more quickly. The amount of acid responsive additives in a geopolymer precursor can be up to about 60% by weight of the geopolymer precursor to yield a geopolymer system with compressive strength suitable for some applications. The particle size distribution of the acid responsive particles typically includes some large particles, such as particles having dimension of at least 1 mm, for example particles having dimension of 1 to 3 mm, and some small particles, for example particles having dimension less than 0.1 mm, for example 10 pm to 50 pm. A larger quantity of large particles improves mixing and pumping of the geopolymer precursor, but the large particles react more slowly with acid after the geopolymer system is set. Smaller particles react more quickly with acid due to the large surface area provided by the smaller particles. Where more acid reactivity is desired, mixing and pumping can be facilitated by adding larger particles of other components to provide an overall particle size distribution of the solids in the geopolymer precursor for a desired mixing and pumping performance.

[0024] Table 1 shows the composition of example geopolymer formulations containing acid responsive solid additives and one comparative formulation without such additives. Quantities in the table are in grams.

Table 1 - Geopolymer Formulations

The geopolymer formulations shown in Table 1 were hardened at 85°C for 24 hours. Formulation 1 developed a crush strength of 2,034 psi. Formulation 2 developed a crush strength of 190 psi. The comparative formulation developed a crush strength of 2,200 psi. After breaking the hardened geopolymer system during the crush strength test, a piece of each geopolymer system was introduced into various HCI solutions and mass loss of each solid sample was evaluated after several durations at 60°C. The results are shown in Table 2.

Table 2 - Percentage Mass Loss of Geopolymer System Samples

The mass loss results in Table 2 indicate the functionality available from using acid responsive additives in a geopolymer system. It should also be noted that the geopolymer systems resulting from Formulation 1 and Formulation 2 showed significant mass loss, relative to the Comparative Formulation, when exposed to a 10% citric acid solution. Figs. 1 , 2, and 3 are graphs showing the mass loss evolution with time for samples based on the three formulations exposed to the HCI solutions in Table 2. Fig. 1 shows mass loss using the 5% HCI solution, Fig. 2 shows mass loss using the 10% HCI solution, and Fig. 3 shows mass loss using the 15% HCI solution. Fig. 4 shows mass loss for the sample using 10% citric acid in water. Formulations like Formulation 1 and Formulation 2 can be used in applications where a temporary, degradable, or removable, cementitious material is desired. [0025] Polysialate systems, which include a polysialate matrix (a polymer of silicon, oxygen, and aluminum), include geopolymers and other materials polymerized in alkaline solution. In addition to raw materials derived from other industrial processes, as described herein, raw materials can be synthesized for use in making polysialate systems. Such raw materials are generally synthesized from materials containing aluminum, silicon, and/or oxygen using application of energy to render the raw material alkaline-reactive. Synthetic raw materials can be made from mixtures containing aluminum, silicon, and oxygen by heating (e.g. by combustion), application of electrical or mechanical energy, or any combination thereof, to transform the mixture at the atomic level into an aluminum, silicon, oxygen material suitable for polymerization in alkaline solution. Elemental aluminum and silicon can be processed in the presence of oxygen to make such materials. Oxides of aluminum and silicon, and generic aluminosilicate materials, whether alkaline-reactive or not, can also be used to make alkaline-reactive raw materials. The combination of materials can be tailored to provide a desired elemental composition, for example silicon to aluminum ratio, and the processing of the materials can be tailored to provide a polysialate precursor having desired physical and chemical properties such as particle size distribution, particle morphology (e.g. shape, roundness, aspect ratio, etc.), particle specific gravity, compositional homogeneity, alkaline reactivity, and crystallinity.

[0026] In general, polysialate raw materials, synthetic or otherwise, may contain elements other than silicon, oxygen, and aluminum provided that silicon, oxygen, and aluminum are present in sufficient quantity, and proper atomic arrangement, to be reactive in alkaline solution to form a polysialate matrix or system. Materials that can be used to form synthetic polysialate raw materials may thus include other elements such as alkali metals (e.g. Li, Na, K, Rb, Cs), alkaline earth metals (e.g. Be, Mg, Ca, Sr, Ba), transition metals, which may be common metals such as Fe, Co, Ni, V, Zr, Cu, Cr, Zn, and Ti, noble metals, rare earth metals, and/or lanthanoid metals, and elements of Groups 5-9 of the periodic table, including metalloids and nonmetals such as B, Al, Ga, In, TI, C, Si, Ge, Sn, Pb, N, P, As, Sb, Bi, S, Se, Te, F, Cl, Br, and I, and actinides such as U and Th. These additional elements may be dopants (e.g. purposely added) or naturally occurring elements, and may occupy positions in the crystal lattice of a material before processing to make the material polysialation- reactive, or after such processing. Such elements may be present in any reasonable quantity, so long as the material, before or after processing, has enough silicon, oxygen, and aluminum to form an alkaline-reactive material that can participate in a polysialation reaction.

[0027] Formation of a geopolymer or polysialate system may also involve a metal silicate that is not an activator (for example where a stronger base material is used as activator) but participates in a polymerization reaction. The metal silicate may be an alkali metal silicate such as sodium silicate, sodium metasilicate or potassium silicate. The sodium metasilicate may be present at a concentration between 0.02 kg/L and 0.2 kg/L, or between 0.05 kg/L and 0.1 kg/L. The SiO2/Na2O molar ratio may be less than or equal to 3.2. The SiO2/K2O molar ratio may be less than or equal to or less than 3.2. The metal silicate may be present in the composition at a concentration between about 0.1 M and 5M, or between 0.5M and 2M. The metal silicates may be dry blended with the aluminosilicate source. Also, the metal silicate in another embodiment may be encapsulated.

[0028] Thickening time of the geopolymer precursors described herein can be adjusted or selected by adding retarders and/or accelerators. Several retarders may delay the setting and hardening of geopolymer systems to allow time for the geopolymer precursor to be placed at a target location before setting. Retarders such as sodium pentaborate decahydrate, borax, sucrose, boric acid, lignosulphonates, sodium glucoheptonate, tartaric acid, citric acid, or phosphorus containing compounds such as phosphoric acid, salts thereof, or mixtures thereof can be added to the geopolymer precursor particulate mixture in amounts of 0.01 to 5 part per hundred by weight of the total particulate precursor mixture. The amount of retardation of the polymerization reaction, and the setting of the slurry, depends on the type of raw materials used for the slurry and the type and relative quantity of retarder used. Adding too much retarder reagent to a geopolymer precursor can cause the slurry to remain unhardened by interfering with the polymerization reaction so the geopolymer precursor does not set. In other embodiments a retarder solution can be added to the carrier fluid or to the geopolymer precursor, or both. By this means, the same geopolymer precursor could be pumped into different sections of a well and setting time of geopolymer precursor in the different sections can be controlled through addition of a different amount of the retarder solution.

[0029] Accelerators can also be added to the geopolymer precursor in amounts up to about 0.01-10, such as 1-5, parts per hundred weight of the geopolymer precursor. The amount of acceleration of the polymerization reaction, and the setting of the precursor, depends on the type of raw materials used and the type and relative quantity of accelerating reagent used. Adding too much accelerator to a geopolymer precursor can cause the precursor to thicken too quickly making it difficult to deploy the precursor to a target location. It should be noted that the retarders and accelerants described herein can be included as particulate materials in the dry mixture to which an aqueous material is added to form a geopolymer precursor, or such reagents can be added to the aqueous material before the aqueous material is added to a geopolymer precursor composition described herein.

[0030] The aqueous material referred to herein can be pure water, alone. The aqueous material can also be a type of water that is not pure water, such as sea water or ground water. The aqueous material can be nonactivating (i.e., pH below about 10), or the aqueous material can contain an activator such as a hydroxide or metal silicate, as described above, which can be dissolved or dispersed in the aqueous material. The aqueous material can also contain nonaqueous miscible liquids, which can be solvents or carrier fluids for other components to be included in the aqueous material. Thus, as such, the aqueous material can be a water-based mixture of organic and inorganic materials, which can be dissolved or dispersed in the aqueous material. Any of the ingredients described herein can be included in, or added to, the aqueous material before it is mixed with aluminosilicate reactants to start the geopolymerization reaction.

[0031] Geopolymer precursors for use in well lining applications typically have a slurry density range from 0.84 g/cm³ (7 Ibm/gal) to 2.87 g/cm³ (24 Ibm/gal), such as 1.32 g/cm³ (11 Ibm/gal) to 2.4 g/cm³ (20 Ibm/gal) or 1.32 g/cm³ (11 Ibm/gal) to 2.16 g/cm³ (18 Ibm/gal), for example 1.36 g/cm³ (11.3 Ibm/gal) to 1.90 g/cm³ (15.8 Ibm/gal). The slurry density can be less than 12 Ibm/gal, less than 15 Ibm/gal, or less than 18 Ibm/gal. The slurry density can be influenced by quantity of water added and/or by adding density modifiers. Water typically makes up from about 20% by weight to about 60% by weight of a geopolymer precursor.

[0032] Density modifiers for geopolymer precursors can be solid or liquid, and can be soluble or nonsoluble in the aqueous medium of the geopolymer precursor. The nonsoluble density modifiers can be included as large particles, small particles, or a mix of large and small particles. Dense particles can be added to the dry mixture into which an aqueous medium is mixed to form the geopolymer precursor, or dense particles can be added to the aqueous medium prior to mixing with the dry mixture, or dense particles can be added to the geopolymer precursor. Soluble density modifiers can be added to the aqueous medium prior to mixing with the dry mixture, added to the geopolymer precursor after mixing, or prior dissolved or dispersed in a carrier fluid that is then mixed with the aqueous medium or the geopolymer precursor. In some cases, ultra-high densities can be achieved in a pumpable geopolymer precursor by pairing a density modified carrier fluid with solid insoluble density modifiers. The heavy particles typically may have densities exceeding 2 g/cm³, or more than 3 g/cm³. Examples include hematite, barite, ilmenite, silica and also manganese tetroxide commercially available under the trade names of MicroMax™ and MicroMax FF™. Mixtures of density modifiers can be used to target a particular slurry density or density profile. Thus, a geopolymer precursor as described herein can also include a nonsoluble density modifier selected from the group consisting, hematite, barite, ilmenite, silica, manganese tetroxide, and combinations thereof. Such density modifiers can all be used with the acid responsive materials described herein.

[0033] The methods presented herein are applicable to the oilfield, for example during completion of the wellbore of oil or gas wells. To be used in oilfield applications, a pumpable precursor is formed or obtained where the geopolymer precursor is provided with a carrier fluid. Various additives may be added to, or included in, the precursor, including acid responsive solid additives, and the precursor may then be pumped into the wellbore. A geopolymer precursor may be considered pumpable where the geopolymer precursor has a slurry consistency lower than about 70 Be as measured by a high-temperature, high-pressure Consistometer. A geopolymer precursor may also be considered pumpable where the geopolymer precursor has a viscosity less than about 300 cPs at ambient conditions, as measured using a direct-indicating viscometer in R1 B1 F1 configuration operating at 300 rpm (i.e., a reading, using such an instrument, of less than about 511 sec^-1). The yield value (Ty) of a pumpable geopolymer precursor may be lower than about 60 lbf/100ft². The precursor is then caused, or allowed, to set and harden in the well to provide zonal isolation in the wellbore. In other contexts, a geopolymer precursor can be prepared, placed at a target location, by pumping or any other suitable means, and caused, or allowed, to set and harden to provide the advantages of a geopolymer system in any suitable application. The geopolymer system resulting from a precursor containing acid responsive solid additives can be treated with acid, organic acid, inorganic acid, or both, to remove some of the acid responsive solids. Such treatment can increase the porosity of the geopolymer system.

[0034] Such acid treatment can be pursued in connection with acid treatment of a formation. For example, a subterranean well that has a geopolymer system installed therein can be used as part of an acid treatment of the formation adjacent to the well, and the acid treatment can also remove acid responsive solid additives of the geopolymer system to remove or degrade the acid responsive solid additives.

[0035] The geopolymer precursors described herein may have a multimodal particle-size distribution. For example, various solid materials that may be included in the geopolymer precursor, such as aluminosilicate materials, other silicate materials, and additives, can have different particle size distributions that may overlap to varying degrees to form a multimodal particle-size distribution.

[0036] The geopolymer precursors described herein may include other functional materials. For example, a geopolymer precursor may include a metal silicate such as sodium silicate, sodium, metasilicate, sodium disilicate, potassium silicate, or other alkali metal silicate, for example using alkali metals lithium, cesium, and/or rubidium. Alkali metal silicate may be present in the composition at a concentration between about 0.05M and 5M, or between 1 M and 4M. The metal silicates may be dry blended with the aluminosilicate source. Also, the metal silicate may be encapsulated. [0037] Other additives can be included in the geopolymer precursors described herein. Such additives may include activators, antifoam agents, defoamers, silica, fluid-loss control additives, viscosifiers, dispersants, surfactants, expanding agents, anti-settling additives or combinations thereof. The fluid-loss control agent may comprise one or more of a water-soluble polymer, a polymer particle dispersion, a dispersant, and a particle additive. In some cases, the fluid-loss control agent may comprise, or may be, a latex. The latex may be an alkali-swellable latex. The latex may be present in the geopolymer precursor compositions at a concentration between 0.02 L/L and 0.3 L/L (1 gal/bbl and 10 gal/bbl), or between 0.05 L/L and 0.15 L/L. Polymers that can be used as fluid loss control agents include polyvinyl alcohol, polyvinyl amine, polysaccharide and other carbohydrates, and esters thereof, poly(meth)acrylic acid, polyethylene imine, polyethylene glycol, polyether, polymaleic acid, acrylamidomethylpropane sulfonic acid/acrylamide copolymer, vinyl acetal polymer, vinylamide/vinylsulfonated copolymer, starch, and combinations and derivatives thereof, any of which can be used as a dispersion or solution in water, or as a latex. Starch derivatives such as starch styrene butadiene and starch flotrol can be used. Latexes such as polystyrene latex and polystyrene-butadiene latex can also be used. The aforementioned polymers can be used as oligomers in most cases. Polynaphthalene sulfonate, polymelamine sulfonate, polycarboxylate, and sulfonated polyamide dispersants can be used. Bentonite, wood cellulose, ground walnut shells, calcium carbonate, mica, and polyester synthetic fibers can be used as particle additives. Viscosifiers may comprise diutan gum having a molecular weight higher than about 1 x 10⁶. The diutan gum may be present at a concentration between 0.14 g/L and 1.4 g/L (0.05 Ibm/bbl and 0.5 Ibm/bbl). Other viscosifiers may comprise polysaccharide materials, which may be biopolymers. Suitable polysaccharide biopolymers can include polyanionic cellulose (PAC), welan gum, and/or carboxymethylcellulose (CMC). Polysaccharide materials can be present in a geopolymer precursor at a concentration between 0.14 g/L and 1 .4 g/L (0.05 Ibm/bbl and 0.5 Ibm/bbl). The molecular weight of the polysaccharide materials may be between 100,000 and 1 ,000,000. Mixtures of any of these viscosifiers can also be used. Expanding agents may comprise calcium sulfate hemihydrate, metal oxides such as MgO or combinations thereof. The expanding agents may be present in the geopolymer precursor at concentrations between 0.01 kg/L and 0.2 kg/L of slurry, or between 0.05 and 0.1 kg/L.

[0038] Carboxylic acids including glucoheptonic acid, tartaric acid, citric acid, glycolic acid, lactic acid, formic acid, acetic acid, proprionic acid, oxalic acid, malonic acid, succinic acid, adipic acid, malic acid, nicotinic acid, benzoic acid and ethylenediamine tetraacetic acid (EDTA) may be included in the geopolymer precursor compositions as retarders or dispersants or both. Phosphoric acids may be present for the same purpose. Soluble carboxylate salts of these acids may also be employed. These materials may be present in the compositions at concentrations between 0.2 g/L and 20 g/L, such as between 0.5 g/L and 10 g/L, for example between 1 g/L and 5 g/L. Mixtures of these acids, salts, and acids with salts, can be used and can also be mixed with other retarders and dispersants described herein. Low molecular weight saccharides, such as glucose and sucrose, can also be used as retarders.

[0039] When various components are used with or within the geopolymer precursor, the particle sizes of the components may be selected and the respective proportions of particle fractions may be optimized in order to have a high Packing Volume Fraction (PVF) solids, and a mixable and pumpable precursor with a minimum amount of carrier fluid. As a result, the Solid Volume Fraction (SVF) of the resulting precursor may be 35-75%, or 50-60%.

[0040] The geopolymer precursor may be, or may include, a “trimodal” combination of particles: “large” particles (e.g., sand or crushed wastes with an average dimension between 100 and 1000 pm), “medium” particles, and “fines” (e.g., micromaterials such as micro fly ashes or micro slags with an average dimension between 0.2 and 10 pm). The geopolymer precursor may also be, or may include, a “tetramodal” combination of particles: “large” particles (average dimension between about 200 and 350 pm), “medium” particles (average dimension between about 10 and 20 pm), “fine” particles (average dimension of about 1 pm) and “very fine” particles (average dimension between about 0.1 and 0.15 pm). The geopolymer precursor may also include “very large” particles (e.g., glassmaker sand or crushed wastes with an average dimension larger than 1 mm). The “very fine” particles may be, or may include, latexes, pigments, or polymer microgels whose particle sizes may be between about 0.05 and 0.5 |j.m. The geopolymer precursor may also include “ultra fine” particles, which may include colloidal silica or alumina with average particle sizes between about 7 and 50 nm. Geopolymer precursor compositions can include these particle size distributions.

[0041] The geopolymer precursor may further include one or more of the following materials: an aqueous inverse emulsion of polymer comprising a betaine group, poly- 2,2,1 -bicyclo heptane (polynorbonene), alkylstyrene, crosslinked substituted vinyl acrylate copolymers, diatomaceous earth, natural rubber, polyisoprene, vinyl acetate polymer, polychloroprene, acrylonitrile butadiene polymer, hydrogenated acrylonitrile butadiene polymer, EPDM polymer, ethylene propylene polymer, styrene butadiene polymer, styrene/propylene/diene polymer, brominated poly(isobutylene-co-4- methylstyrene), butyl polymer, chlorosulfonated polyethylenes, polyacrylate, polyurethane, silicone polymer, brominated butyl rubber, chlorinated butyl rubber, chlorinated polyethylene, epichlorohydrin ethylene oxide copolymer, ethylene acrylate polymer, sulfonated polyethylene, fluoro silicone rubbers, fluoroelastomers, substituted styrene acrylate copolymers and bivalent cationic compounds. Any copolymer or multipolymers described above may be a block or non-block (e.g., random) polymer.

[0042] The methods described herein can be useful in completing subterranean wells, including oil and/or gas wells, water wells, geothermal wells, acid gas wells, and carbon dioxide injection or production wells. Placement of a geopolymer precursor in the portion of the wellbore to be completed is accomplished by means that are well known in the art of well completion. The geopolymer precursor is typically placed in an annular region surrounding a casing to prevent vertical communication through the annulus between the casing and the wellbore or the casing and a larger casing. The geopolymer precursor may be placed in a wellbore by circulation down the inside of the casing, followed by a wiper plug and a nonsetting displacement fluid. The wiper plug is usually displaced to a collar, located near the bottom of the casing. The collar catches the wiper plug to prevent overdisplacement of the geopolymer precursor and also minimizes the amount of the geopolymer precursor left in the casing. The geopolymer precursor is circulated up the annulus surrounding the casing, where it is allowed to harden. The annulus could be between the casing and a larger casing or could be between the casing and the borehole wall. Operations that use a geopolymer precursor described herein may cover only a portion of the open hole, or more typically up to a point inside the next larger casing or sometimes up to the surface. This method has been described for completion between formation and a casing, but can be used in any type of completion, for example with a liner, a slotted liner, a perforated tubular, an expandable tubular, a permeable tube and/or tube or tubing. In the same way, the methods of the present invention are useful in completing subterranean wells by reverse circulation.

[0043] The geopolymer precursor can also be used in remedial applications including “squeeze cementing” and “plug cementing,” including plug and abandonment operations. During “squeeze cementing” the geopolymer precursor may be forced through perforations or openings in the casing, whether or not these perforations or openings are made intentionally, to the formation and wellbore surrounding the casing to be repaired. The geopolymer precursor can be placed in this manner to repair and seal poorly isolated wells, for example, when either the original cement or geopolymer system fails, or was not initially placed acceptably, or to shut off a producing interval. For “plug cementing,” the geopolymer precursor is placed inside the well by means that are well known in the art.

[0044] The geopolymer precursors described herein can also be used in surface applications, which can be new applications or remedial applications. The geopolymer precursor is generally mixed and placed at a target location, and then allowed to harden. Such applications can include construction applications.

[0045] The geopolymer systems described herein enable methods that use a temporary placement of a geopolymer system that is later removed. Such methods include obtaining a geopolymer precursor that includes one or more acid responsive solid components, deploying the geopolymer precursor at a target location, temporarily hardening the geopolymer precursor to form a geopolymer system, and later treating the geopolymer system with an acid to remove the geopolymer system. The acid can be any acid sufficiently strong to react with the acid responsive components in the geopolymer system. It is believed that reaction of the acid responsive components with acid dissolves, degrades, or otherwise changes the acid responsive components, or at least dislodges the acid responsive components such that the geopolymer matrix of the geopolymer system is disrupted, weakened, and ultimately unbonded to some extent such that the geopolymer system is disassembled and can be removed.

[0046] The acid can be a mineral acid (j.e. inorganic acid), such as HCI, HF, or H2SO4, or an organic acid, such as formic, acetic, methane sulfonic, or citric acid. The acid is typically dissolved in water, or an aqueous material, to form a treatment fluid with a target acid concentration. For solutions that use an organic acid, the solution can have any suitable concentration of organic acid, such as 1 % to 99% acid in water (or other aqueous material). For solutions that use an inorganic acid, the solution can have any suitable concentration of inorganic acid, such as 1 % to 35% acid in water (or other aqueous material). The treatment fluid can include any known reagent usable with acid treatment fluids to adjust properties of the acid treatment fluid for optimal function upon contact with the system. The treatment fluid is deployed to the location of the geopolymer system to contact and react with the geopolymer system such that the geopolymer system loses structural solidity and can be removed. The acid treatment may be applied to a well in which the geopolymer system is formed or to a formation to remove a geopolymer system from the formation. The acid treatment can be a formation acid treatment, for increasing fluid flow pathway volumes in the formation, that incidentally removes a geopolymer system as well as natural acid-reactive materials in the formation.

[0047] It should be noted that, where a metal carbonate material is used as the acid responsive solid component, a chelating agent can be used, in addition to or instead of an acid material, to remove the metal carbonate and weaken the geopolymer system. Such materials are known to be effective as alternatives to acid for stimulating carbonate materials in subterranean formations, and they can be similarly used here to treat the solid components to weaken the geopolymer system. These materials include ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (ETPA), cyclohexanediaminetetraacetic acid (CDTA), hydroxyethylenediaminetriacetic acid (HEDTA), and L-glutamic acid.

[0048] In some embodiments, the subterranean wells described herein may be used for carbon capture, utilization, and storage (CCUS) and/or for recovery and use of geothermal energy. Geothermal energy is a promising source of renewable energy that captures energy from heat generated or stored within the earth. For example, geothermal energy may be used to perform climate control (e.g., heating, cooling) for structures (e.g., buildings) using heat pumps and/or to generate electricity (e.g., by heating water to generate steam and drive a turbine with the steam). The wells described herein may be used to circulate a working fluid that exchanges heat within the earth formation through which the wellbore extends. The working fluid may be circulated to the surface where a surface heat exchanger is used to transfer thermal energy to another fluid used to generate electricity and/or for climate control. After the thermal energy is transferred from the working fluid in the surface heat exchanger, the working fluid is circulated back to the earth formation to continue the cycle. Such wells can benefit from the methods and compositions described herein.

[0049] CCUS facilitates the capture, use, and/or storage of carbon (e.g., carbon dioxide), which has a goal of achieving carbon neutrality and/or net zero carbon emissions (NZE). Carbon capture may include the capture of carbon dioxide from large point sources, such as power plants, refineries, cement plants, other industrial processing plants, or other industrial facilities that use fossil fuels, biomass fuels, or other fuels that generate carbon dioxide. The captured carbon dioxide may be converted into valuable products such as, for example, ethanol, sustainable aviation fuel, chemicals, mineral aggregates, and/or other products. Alternatively, the carbon dioxide may be stored in geologic formations, such as in depleted hydrocarbon reservoirs. The carbon dioxide may be introduced into the earth formation through a wellbore, such as the wellbores described herein. In the earth formation, the carbon in the carbon dioxide may be dispersed in an aqueous phase and stored as carbon dioxide, may be stored in mineral form (e.g., as a carbonate, such as calcium carbonate, magnesium carbonate, iron(ll) carbonate), or as another form of carbon.

[0050] 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

CLAIMS We claim:

1. A method, comprising: obtaining a geopolymer precursor comprising an aluminosilicate source, an alkali activator, an acid responsive solid additive, and an aqueous material; pumping the geopolymer precursor into a subterranean well; causing the geopolymer precursor to harden and set within the subterranean well to form a geopolymer system; and treating the geopolymer using an acid to remove a portion of the geopolymer system.

2. A method, comprising: forming a geopolymer system in a subterranean well using a pumpable precursor comprising an aluminosilicate source, an alkali activator, an acid responsive solid additive comprising an alkaline earth metal carbonate, and an aqueous material; and treating the geopolymer system using an acid to remove a portion of the geopolymer system.

3. A method, comprising: in a subterranean well, treating a geopolymer system having an acid responsive solid additive using an organic acid, an inorganic acid, or both to degrade the geopolymer system.

4. The method of any of claims 1 to 3, wherein a first portion of the acid responsive solid additive comprises particles having dimension at least 1 mm and a second portion of the acid responsive solid additive comprises particles having dimension no more than 0.1 mm.

5. The method of any of claims 1 to 4, wherein the geopolymer precursor or the geopolymer system further comprises a density modifier, an accelerator, a retarder, an antifoam agent, a defoamer, a silica, a fluid-loss control additive, a viscosifier, a dispersant, an expanding agent, an anti-settling additive, or a combination thereof.

6. The method of an of claims 1 to 5, wherein the subterranean well is located proximate to a geologic formation, and treating the geopolymer system using an acid comprises treating the geologic formation with an acid.

7. The method of any of claims 1 to 6, wherein the acid responsive solid additive is calcium carbonate.

8. The method of any of claims 1 to 7, wherein the acid responsive solid additive is present in an amount that is not more than 300% by weight of the amount of the aluminosilicate source.

9. The method of any of claim 1 to 8, wherein the geopolymer system is made using an aluminosilicate source for the precursor that is ASTM type C fly ash, ASTM type F fly ash, ground blast furnace slag, ground granulated blast furnace slag (GGBS), clay, aluminum-containing silica fume, natural aluminosilicate, synthetic aluminosilicate glass powder, zeolite, scoria, allophone, bentonite, red mud, pumice, or a combination thereof.

10. The method of any of claims 1 to 9, wherein the geopolymer system is made using an aqueous material for the precursor that is a nonactivating aqueous material and the precursor is made by adding the nonactivating aqueous material to a dry mixture comprising the aluminosilicate source, the alkali activator, and the acid responsive solid additive.

11. The method of any of claims 1 to 10, wherein the geopolymer system is made using a precursor that comprises a metal silicate, a salt, a polysaccharide material, a surfactant, a latex, a solvent, or a combination thereof.

12. A geopolymer precursor comprising an aluminosilicate source, an alkali activator, a polymeric acid responsive solid additive, and an aqueous material.

13. The geopolymer precursor of claim 12, wherein the polymeric acid responsive solid additive is selected from the group consisting of polyglycolic acid, polylactic acid, polyester, poly(a-hydroxybutyric acid), poly(hydroxyvaleric acid), poly(caprolactone), combinations thereof, copolymers thereof, and multipolymers thereof.

14. A dry geopolymer precursor mixture, comprising an aluminosilicate source, an alkali activator, and an inorganic mineral acid responsive solid additive.

15. The dry geopolymer precursor mixture of claim 1 , wherein the inorganic mineral acid responsive additive is an acid responsive clay or feldspar.

16. The geopolymer precursor or dry geopolymer precursor mixture of any of claims 12 to 15, wherein a first portion of the acid responsive solid additive comprises particles having dimension at least 1 mm and a second portion of the acid responsive solid additive comprises particles having dimension no more than 0.1 mm.

17. The geopolymer precursor or dry geopolymer precursor mixture of any of claims 12 to 16, wherein the aluminosilicate source is ASTM type C fly ash, ASTM type F fly ash, ground blast furnace slag, ground granulated blast furnace slag (GGBS), clay, aluminum-containing silica fume, natural aluminosilicate, synthetic aluminosilicate glass powder, zeolite, scoria, allophone, bentonite, red mud, pumice, or a combination thereof.

18. The geopolymer precursor or dry geopolymer precursor mixture of any of claims 12 to 17, wherein the acid responsive solid additive is present in an amount that is 50% to 250% by weight of the amount of the aluminosilicate source.

19. The geopolymer precursor or dry geopolymer precursor mixture of any of claims 12 to 18, wherein the aluminosilicate source is at least 18% by weight calcium oxide.