WO2023183609A1

WO2023183609A1 - Geothermal cementing system with high thermal conductivity

Info

Publication number: WO2023183609A1
Application number: PCT/US2023/016292
Authority: WO
Inventors: Arash Dahi Taleghani; Maryam TABATABAEI
Original assignee: Geothermic Solution, Inc.
Priority date: 2022-03-25
Filing date: 2023-03-24
Publication date: 2023-09-28
Also published as: TW202346239A

Abstract

Compositions and methods are presented in which a cementitious composition includes surface modified micro-or nanostructured carbon allotropes to thereby form a high thermal coefficient composition. In preferred aspects, the surface modified micro-or nanostructured carbon allotropes are graphite nanoplatelets and/or exfoliated graphite modified with hydroxyl and/or carboxyl groups that allow for uniform dispersion, interfacial bonding between surface-modified particles and cement hydrates, and improved bonding at the cement/steel casing interface.

Description

GEOTHERMAL CEMENTING SYSTEM WITH HIGH THERMAL CONDUCTIVITY [0001] This application claims priority to our copending US provisional patent application with the serial number 63/323,682, filed 3/25/2022, and which is incorporated by reference herein. Field [0002] The field of the disclosure is cementitious compositions with high thermal conductivity, and especially as it relates to cementitious compositions that include surface-modified micro- and nanostructured carbon allotropes for use in heat harvesting in geological formations. Background of the Disclosure [0003] The background description includes information that may be useful in understanding the present disclosure. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed disclosure, or that any publication specifically or implicitly referenced is prior art. [0004] All publications and patent applications herein are incorporated by reference to the same extent as if each individual publication or patent application were specifically and individually indicated to be incorporated by reference. Where a definition or use of a term in an incorporated reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply. [0005] Carbon allotropes such as graphene and single and multi-walled carbon nanotubes have gained considerable attention due to their remarkable mechanical, electrical, and thermal properties, and many materials have been modified with such and other allotropes in the hope to impart at least some of the characteristics into the so modified materials. [0006] In addition to many uses in the electronics field, various carbon allotropes have been included into a variety of building materials. For example, carbon nanomaterials or expandable graphite were included into a cement matrix for vibration dampening, fire protection and thermal insulation as is described in US 2011/0120347 and US 2018/0327313. In other examples, various carbon nanomaterials such as carbon nanofibers, carbon nanotubes, graphene, graphene nanoplates, graphene oxide, and reduced graphene oxide were combined with cement-based composites (see e.g., Nanotechnol Rev 2020; 9:115–135) to enhance mechanical properties, durability, and electrical/thermal conductivity. Here, the thermal conductivity was reported to be about 1.7 W/m-K at a temperature of about 600 °C, with somewhat improved values above and below 600 °C. Similarly, carbon nanoparticulates, and especially graphene nanoplatelets were included into Portland cement (see e.g., Solar Energy Materials and Solar Cells 161 (2017), 77-88) and were reported to improve thermal conductivity and diffusivity, along with significantly increased electrical conductivity and capacitance. However, thermal conductivity was only moderately improved from 0.78 W/m-K to 1.14 W/m-K, and the preparation of the nanocomposite material in the laboratory was impractical for large scale manufacture. [0007] Cementitious materials with high thermal conductivity are particularly desirable for heat transfer in thermal energy harvesting from geological formations for power production. Such is especially significant where the heat transfer is from a high-temperature formation (e.g., 400-600 °C) into a working fluid and where the cementitious materials provide a thermal bridge between the formation and the working fluid. For such use, thermal conductivity of at least 3 W/m-K is particularly advantageous as lower thermal conductivity impedes effective energy transfer and as such power generation. Unfortunately, currently known cementitious compositions, even with selected carbon allotropes fall short of such desirable properties. [0008] Thus, even though various compositions and methods of carbon allotropes in cementitious compositions are known in the art, all or almost all of them suffer from several drawbacks. Most notably, desirable thermal properties of various carbon allotropes have not readily translated into materials with similarly desirable thermal properties where the materials are cementitious compositions. Therefore, there remains a need for improved cementitious compositions that include one or more carbon allotropes to so provide a high thermal conductivity material. Summary of The Disclosure [0009] The disclosure is directed to various compositions and methods of cementitious compositions with high thermal conductivity for use in heat transfer from a geological formation to a closed loop heat recovery system in which surface modified micro- or nanostructured carbon allotropes are distributed to provide significantly improved thermal conductivity for the grout composition upon setting. [0010] Notably, the addition of hydrophilic groups to the micro- or nanostructured carbon allotropes significantly reduces local agglomeration, promotes uniform distribution in a cementitious composition, improves or enables bonding of the surface modified carbon allotropes with the hydrophilic/polar compounds of the cementitious materials, and/or improves or enables bonding of the surface modified carbon allotropes with the metal casing of the closed loop heat recovery system. [0011] In one aspect, a high-thermal conductivity grout composition is contemplated that comprises a cementitious material in admixture with a surface modified micro- or nanostructured carbon allotrope, wherein the surface modified micro-or nanostructured carbon allotrope is present in an amount effective such that the grout composition, upon setting at a target location, has a thermal conductivity of at least 3 W/m-K. [0012] In some aspects, the surface modified micro-or nanostructured carbon allotrope comprises a surface modified exfoliated graphite or surface modified graphite nanoplatelets. Preferably, the surface modified micro-or nanostructured carbon allotrope has a plurality of hydroxyl and/or carboxyl groups, and it is further generally contemplated that the surface modified micro-or nanostructured carbon allotrope has a carbon to oxygen ratio of between 50 and 200. [0013] In further contemplated aspects, the surface modified micro-or nanostructured carbon allotrope is present in an amount of between 2-15 wt% BWOC. Viewed from a different perspective, the surface modified micro-or nanostructured carbon allotrope may be present in an amount effective such that the grout mixture has, upon setting at the target location, a thermal conductivity of at least 5 W/m-K, or at least 8 W/m-K. [0014] As will be readily appreciated, the grout composition may further include a retarder (e.g., a lignosulphonate, a phosphonate, a sugar, a hydroxycarboxylic acid, a borate, and a salt of Zn, Pb, Cu, Sb, or As). Most typically, the retarder will be present in an amount effective that delays setting of the composition at the target location for at least two hours, and wherein the target location has a formation temperature of at least 400 °F or at least 500 °F. Additionally, the grout composition may also comprise at least one functional agent such as a plasticizer, a surfactant, an organic polymer, a silica filler, and/or a clay. [0015] Additionally, it should be recognized that the grout composition may be a hydraulic cement (e.g., Portland cement or calcium aluminate cement), and/or that the grout composition may further include sand (e.g., having an average particle size of between 0.1 mm and 2.0 mm). Most preferably, the grout composition has, upon addition of water, a viscosity that allows pumping the grout composition to the target location. [0016] Therefore, pumpable slurries are also contemplated comprising water in admixture with the grout composition presented herein. Most typically, but not necessarily, the slurry will have a density of between 10 and 20 lb/gal, and/or have a water content of 5 and 30 gal/sk. [0017] In a further aspect, a method of producing a grout composition is provided that includes a step of combining a cementitious material with a surface modified micro- or nanostructured carbon allotrope, wherein the surface modified micro-or nanostructured carbon allotrope has a plurality of hydroxyl and/or carboxyl groups. Most typically, the surface modified micro-or nanostructured carbon allotrope is present in an amount effective such that the grout composition, upon setting at a target location, has a thermal conductivity of at least 3 W/m-K. [0018] In some aspects of contemplated methods, the surface modified micro-or nanostructured carbon allotrope comprises a surface modified exfoliated graphite or surface modified graphite nanoplatelets. Preferably, the micro-or nanostructured carbon allotrope is surface modified by high-temperature exposure and/or by reaction with one or more oxidizing acids. For example, the high-temperature exposure may be performed by thermal exfoliation of graphite flakes at a temperature of about 900 °C in an oxygen-containing atmosphere, and/or the oxidizing acids will be sulfuric acid, nitric acid, and/or phosphoric acid. It is further preferred that in at least some aspects the surface modified micro-or nanostructured carbon allotrope is depleted of carboxylate carbonaceous fragments (e.g., using a wash step with an organic solvent such as acetone). [0019] As noted before, it is contemplated that the surface modified micro-or nanostructured carbon allotrope may be present in an amount of between 2-15 wt% BWOC. Typically, and especially where the grout composition is used in geothermic heat recovery, the grout composition will include a retarder in an amount effective that delays setting of the composition at the target location for at least two hours. The target location will typically have a formation temperature of at least 400 °F. [0020] Therefore, a method of producing a surface modified micro- or nanostructured carbon allotrope for use in a grout composition is also provided that includes a step of subjecting graphite flakes and/or graphite nanoplatelets to an oxidation process that generates surface modified micro- or nanostructured exfoliated graphite and/or surface modified micro- or nanostructured graphite nanoplatelets. Where the oxidation process is thermal exfoliation of graphite flakes, oxidation is preferably performed at a temperature of about 900 °C in an oxygen-containing atmosphere to produce the surface modified micro- or nanostructured exfoliated graphite. Where the oxidation process is a reaction, it is preferred that the reaction is oxidation with one or more oxidizing acids to produce the surface modified micro- or nanostructured nanoplatelets. In a further step, carboxylate carbonaceous fragments are removed from the surface modified micro- or nanostructured graphite nanoplatelets using an organic solvent wash step. Finally, the surface modified micro- or nanostructured carbon allotrope are then combined with a cementitious composition or instructions are provided for such combination (e.g., in an amount of between 2-15 wt% BWOC). [0021] In some aspects, the graphite flakes and/or graphite nanoplatelets have after the oxidation process an average particle size of less than 1,000 µm. It is further contemplated that the solvent is acetone, and/or that the oxidizing acids comprise sulfuric acid, nitric acid, and/or phosphoric acid. [0022] Consequently, a method of installing a high-thermal conductivity grout in a wellbore is provided in which a casing is located such that an annular space is formed therebetween. In preferred aspects, the method comprises a step of pumping the pumpable slurry as presented herein to a target location within the wellbore having a target temperature of at least 300 °F, and a further step of allowing the pumpable slurry to set in the annular space to thereby form the high-thermal conductivity grout in the wellbore. Most typically, the high-thermal conductivity grout is in thermal exchange with the casing and a formation surrounding the wellbore, and the time to set for the pumpable slurry is at least two hours at a formation temperature of at least 300 °F. [0023] In some exemplary aspects, the target location is at least 500 ft below ground, which may or may not extend in a substantially vertical orientation. In further aspects, the temperature at the target location is at least 400 °F, or at least 500 °F, and the time to set for the pumpable slurry is at least two hours. In further aspects, routing of the pumpable slurry into the annular space between the wellbore and the casing displaces a fluid in the annular space. Moreover, it is contemplated that the formation may include a plurality of fissures that are at least partially filled with a high-thermal conductivity material (e.g., graphite powder, flaked graphite, pyrolytic graphite, desulfurized petroleum coke, graphene, fly ash, copper powder, aluminum nitride, and/or silicon carbide), and that the high-thermal conductivity material in the fissures is in thermal exchange with the high-thermal conductivity grout in the wellbore. [0024] Various objects, features, aspects, and advantages of the disclosure will become more apparent from the following detailed description of preferred aspects, along with the accompanying drawing figures in which like numerals represent like components. Brief Description of the Drawing [0025] FIGS. 1A-1C are graphs of the thermal conductivity (w/m-K) as a function of the concentration (wt%) of surface modified exfoliated graphite flakes having different nominal particle sizes (FIG.1A: size >75 µm; FIG.1B: size >180 µm; FIG.1C: size >300 µm). [0026] FIG.2 is a graph depicting thermal conductivity (W/m-K) for exemplary compositions containing 10 wt% surface modified exfoliated graphite flakes having a nominal particle size of at least 180 µm without additional additives (straight line) and with varying amounts (1 wt%, 2 wt%, or 3 wt%) of selected additives. The additives include a defoamer, a superplasticizer, or a retarder. [0027] FIG.3 is a graph depicting thermal conductivity (W/m-K) for exemplary compositions containing 10 wt% surface modified exfoliated graphite flakes having a nominal particle size of at least 180 µm with varying concentrations (wt%) of a defoamer. Detailed Description [0028] Various surface modified micro- or nanostructured carbon allotropes have been disclosed that provide substantial improvements in thermal conductivity in cementing compositions, and especially in geothermal cementing compositions. While not wishing to be bound by any specific theory or hypothesis, a possible hypothesis is s that the chemical modifications, and especially the addition of reactive polar groups, improve hydrophilicity and thereby facilitate homogenous distribution of the carbon allotropes within the cementitious phase and as such enable uniform and significant thermal conduction in cementitious compositions containing such modified carbon allotropes. As such, relatively large quantities of the surface modified micro- or nanostructured carbon allotropes can be included into the cementitious material and so dramatically increase thermal conductivity. Moreover, the polar groups further improve or enable bonding of the surface modified carbon allotropes with the hydrophilic/polar compounds of the cementitious materials, and/or improve or enable bonding of the surface modified carbon allotropes with the metal casing of the closed loop heat recovery system. [0029] Among other mechanisms, it is contemplated that the reactive groups in the modified carbon allotropes not only promote interfacial bonding between surface-modified particles and cement hydrates, but also promote bonding at the cement/steel casing interface. Such bonding is further thought to reduce the risk of crack formation and/or propagation, and to strengthen adherence of the hardened grout to the casing leading to improved thermal performance of geothermic heat recovery and power generation. Moreover, due to the polar nature of the modifications, the modified carbon allotropes have decreased hydrophobicity and as such a reduced propensity for clumping. Viewed from a different perspective, it should be appreciated that the presence of polar groups in these materials is fundamental to isotropic distribution, improved bonding to the cementitious phase (interfacial bonding between surface-modified particles and cement hydrates), and even bonding to the steel casing (e.g., via metal oxides). In further results, as is shown in more detail below, curing of the cementitious compositions under high temperature and high pressure further increased thermal conductivity as compared to curing under ambient conditions. [0030] In certain aspects, the micro- or nanostructured carbon allotrope is exfoliated graphite or graphite nanoplatelets having an average particle size of less than 1,000 µm, which may be surface modified by chemical and/or thermal processes to include a plurality of hydroxyl, epoxy, and/or carboxyl groups, typically at a carbon to oxygen ratio of between about 50-200. So prepared surface modified micro-or nanostructured exfoliated graphite or graphite nanoplatelets are then admixed (e.g., in an amount of between about 2-20 wt.% BWOC) with a cementitious material and water to form a slurry that can be pumped to a target location in a geological formation having a temperature of at least 300 °F. Most typically, a closed loop heat recovery system is disposed in the wellbore at the target location, and upon curing of the slurry at the target location, heat is transferred from the formation through the cured grout and the metallic casing of a closed loop heat recovery system into a heat transfer fluid of the closed loop heat recovery system. [0031] With respect to the size of the modified micro- or nanostructured carbon allotropes it is generally preferred that the carbon allotropes will have a nominal size that is smaller than 10 mm, or smaller than 5 mm, or smaller than 1 mm, or smaller than 800 µm, or smaller than 600 µm, or smaller than 400 µm, or smaller than 200 µm, or smaller than 100 µm, or smaller than 50 µm, or smaller than 20 µm, or smaller than 10 µm, or smaller than 5 µm, but larger than 50- 100 nm. As will be readily appreciated, where the carbon allotrope comprises graphene nanoplatelets, the median or average size will be smaller than the particle size for exfoliated graphite flakes. Therefore, suitable median size ranges (D50) include 1-5 µm, or 5-10 µm, or 10-25 µm, or 25-100 µm, or 100-500 µm, or 500-1,000 µm. For example, suitable median sizes for graphene nanoplatelets may be 1-3 µm, or 3-7 µm, or 5-10 µm. On the other hand, suitable median sizes for exfoliated graphite flakes may have a nominal size of at least 75 µm, or at least 180 µm, or at least 300 µm. Of course, it should be appreciated that the size can be modified by various processes, and especially suitable processes include ball milling, griding, high-shear mixing, and/or ultrasonication. [0032] While it is generally preferred that the micro- or nanostructured carbon allotropes are exfoliated graphite flakes or graphite nanoplatelets, numerous alternative carbon allotropes are also deemed suitable for use herein and contemplated allotropes include single and multi- walled carbon nanotubes, Buckminster fullerenes, graphene, graphene oxides, carbon nanofibers, carbon black, graphite, graphite flakes, etc. In this context, it should be noted that the term “graphite nanoplatelets” as used herein refers to high surface area (>150 m²/g) nanometric graphene platelets produced from a graphite parent material where each platelet is made from multiple monoatomic graphene layers (e.g., commercially available as ‘Graphite Nanoplatelets (GNP)’ from Asbury Carbons). The term “exfoliated graphite” as used herein refers to a graphite material that has been produced from a graphite parent material with intercalated propellant that upon exposure to heat rapidly expands and partially forces graphitic planes apart, thereby forming characteristic vermiculite or worm-shaped macroscopic structures (e.g., parent material ‘Expandable Graphite’ commercially available from Asbury Carbons). Therefore, it should be noticed that exfoliated graphite is not the same as graphite flakes (a naturally occurring form of graphite found in discrete flakes). As will be readily appreciated, and depending on the particular material, the carbon allotrope may be subjected to one or more steps of comminution, or shear or sonication disaggregation to increase surface area and to produce the micro- or nanostructured carbon allotrope that is then subjected to surface modification. [0033] Most preferably, the carbon allotrope is subjected to a process of surface modification in which one or more type of polar groups are introduced to the carbon scaffold. As will be recognized, such modification can be performed by associating the carbon allotrope with a polymer that includes polar groups (e.g., using polyacrylic acid or polyvinyl alcohol in a polymer wrapping process), and more preferably by direct introduction of polar groups to the carbon allotrope. Most typically, such direct introduction will comprise an oxidative process that may be thermally driven or that may use one or more strong oxidizing agent. In still other aspects, the direct introduction of polar groups may also use an electrochemical process or plasma gas exposure. [0034] In one contemplated surface modification, the oxidation process is a thermal process that is also used to restructure a graphitic starting material to thereby form the micro- and/or nanostructured carbon allotrope. Here the starting material is expandible graphite in which an intercalated propellant in the graphite starting material explosively expands upon sudden heat exposure, which partially forces the graphitic planes apart and so produces the characteristic vermiculite or worm-shaped macroscopic structures. Contrary to common procedure, heat exposure is typically performed in an oxygen containing atmosphere (e.g., ambient air or environment with controlled oxygen content) at temperatures of at least 600 °C, or at least 700 °C, or at least 800 °C, or at least 900 °C, which not only exfoliates graphitic planes but also partially oxidizes the carbon in the graphitic planes. [0035] As will be readily appreciated, the specific conditions (e.g., temperature, duration of thermal exposure, oxygen content, etc.) can be used to control the degree of oxidation of the micro- and/or nanostructured carbon allotrope. For example, the oxygen content during heat exposure can be between 1-4%, or between 4-8%, or between 8-12% or between 12-16%, or between 16-20%, or at atmospheric oxygen content. Likewise, the exposure duration at the elevated temperature in the presence of oxygen will typically be about 5-15 seconds, or between 15-60 seconds, or between 1-10 minutes, or between 10-30 minutes, or between 30- 60 minutes, or between 1-3 hours, and even longer. Moreover, it should be noted that where the intercalated propellant decays in an exothermic reaction, the initial heat exposure may be significantly lower, and the exothermic decay may then drive the exfoliation and oxidation process. [0036] However, numerous alternative exfoliation processes are also deemed suitable for use herein and include shear force based processes, ultrasound based processes, electrochemical exfoliation, solvent-based exfoliation, etc. In most instances, such processes will not yield exfoliated graphite with sufficient polar groups. Consequently, the polar groups will typically then be introduced by chemical oxidation as is described in more detail below. [0037] In another contemplated surface modification, the oxidation process is a chemical oxidation using one or more oxidizing acids such as sulfuric acid, nitric acid, and/or phosphoric acid. In especially preferred aspects, the carbon allotrope will be graphite nanoplatelets. However, numerous other micro- and/or nanostructured carbon allotropes as noted above are also expressly deemed suitable for use with chemical oxidation. Most typically, the micro-or nanostructured carbon allotrope will be exposed at elevated temperature (e.g., at least 40 °C, or at least 50 °C, or at least 60 °C, or at least 70 °C, or at least 80 °C, or at least 90 °C, or higher) to the oxidizing agent(s) for a time sufficient to partially oxidize the micro-or nanostructured carbon allotrope (e.g., such as at least 1 hour, or at least 2 hours, or at least 3 hours, or at least 4 hours, or longer). Once more, it will be readily appreciated that the strength of the acid, and the temperature, and/or duration of the oxidation reaction will determine the degree of oxidation of the micro- and/or nanostructured carbon allotrope. [0038] Therefore, the so produced surface modified micro-or nanostructured carbon allotrope will have a plurality of hydroxyl, epoxy, keto, and/or carboxyl groups. In most cases, the polar groups will be covalently bound to only a fraction of carbon atoms, and the ratio of carbon atoms to oxygen atoms will be at least 10:1, or at least 20:1, or at least 50:1, or at least 100:1, or at least 200:1, or at least 500:1, or at least 1,000:1, or even higher. Viewed from a different perspective, contemplated carbon to heteroatom ratios may be between 10:1 and 10,000:1, or between 20:1 and 5,000:1, or between 30:1 and 1,000:1, or between 40:1 and 500:1, or between 50:1 and 200:1. [0039] In such and other oxidative processes, it should be recognized that various carboxylate carbonaceous fragments can be produced that have significant reactivity with the cementitious components/calcium-silicate-hydrate, that will not contribute to improvements in thermal conductivity, and that may adversely affect curing times and/or mechanical properties of the cured materials. Therefore, and where required, it is generally preferred that carboxylate carbonaceous fragments will be removed in a post-oxidation wash step. Such fragments may have a molecular weight of between 20-500Da, or between 250-1,000 Da, or between 1-5 kDa and in some cases even higher. Removal of such carboxylated fragments can advantageously be achieved by one or more wash steps using an aqueous acid and/or an organic solvent. Preferably, the aqueous acid will be non-oxidizing (e.g., HCl) and the organic solvent will be acetone. [0040] Of course, it should be noted that numerous other chemical modification processes are also deemed suitable for use herein so long as they introduce one or more polar groups into the micro-or nanostructured carbon allotrope. For example, alternative groups include sulfate, nitro, and/or phosphate groups, which can be included into the materials following processes well known in the art. Therefore, and viewed from a different perspective, it should be noted that the introduction of a heteroatom (and more particularly a heteroatomic polar group) to the micro-or nanostructured carbon allotrope will produce a surface modified micro-or nanostructured carbon allotrope that will have significantly improved uniform dispersion (due to reduced hydrophobic aggregation), significantly improved interfacial bonding between surface-modified particles and cement hydrates, and significantly improved bonding at the cement/steel casing interface (due to covalent and non-covalent interactions). [0041] Regardless of the manner of surface modification, it is generally preferred that the surface modified micro-or nanostructured carbon allotrope has a carbon to heteroatom ratio of between 10:1 and 10,000:1, or between 20:1 and 5,000:1, or between 30:1 and 1,000:1, or between 40:1 and 500:1, or between 50:1 and 200:1. Most typically, the heteroatom will be oxygen, and additional heteroatoms will include sulfur and nitrogen. [0042] Of course, it should be appreciated that the cementitious compositions and slurries presented herein may include more than one type of surface modified micro- or nanostructured carbon allotrope, and in at least some aspects two or more distinct allotropes (e.g., EGF or GNP, and/or nanotubes) may be present in synergistic quantities with regard to thermal conductivity. Indeed, synergistic improvements in thermal conductivity are expected due to the interconnection of the surface modified carbon allotropes into a three-dimensional thermal transfer network. For such network to exist (with single or multiple distinct surface modified micro- or nanostructured carbon allotrope), uniform or homogenous distribution is believed to be a significant property, which is achieved by addition of polar groups to the micro- or nanostructured carbon allotrope. [0043] Once the surface modified micro-or nanostructured carbon allotrope are prepared, they can be included into a cementitious composition either into a dry mixture or into a liquid (typically water) phase that is then combined with the dry cementitious materials. As will be readily appreciated, the surface modified micro-or nanostructured carbon allotrope may be present in a wide range of concentrations, depending on the particular desired function. Therefore, suitable concentrations will be at least 0.1 wt% BWOC, or at least 0.5 wt% BWOC, or at least 1 wt% BWOC, or at least 2 wt% BWOC, or at least 5 wt% BWOC, or at least 7.5 wt% BWOC, or at least 10 wt% BWOC, or at least 15 wt% BWOC, or at least 20 wt% BWOC, and even higher. Viewed from a different perspective, contemplated concentration ranges for improved thermal conductivity will be between 0.5-3 wt% BWOC, or between 2-5 wt% BWOC, or between 5-8 wt% BWOC, or between 7.5-10 wt% BWOC, or between 10-15 wt% BWOC, or between 15-25 wt% BWOC. [0044] Consequently, and as is shown in more detail below, the surface modified micro-or nanostructured carbon allotrope will be present in an amount effective such that a grout composition formed from contemplated compositions has, upon setting at a target location, a thermal conductivity of at least 3 W/m-K, or at least 4 W/m-K, or at least 5 W/m-K, or at least 6 W/m-K, or at least 7 W/m-K, or at least 8 W/m-K, or at least 9 W/m-K, or at least 10 W/m- K, or at least 12 W/m-K, or at least 15 W/m-K, and even higher. Thermal conductivity can be determined, for example, using a guarded version of a heat flow meter (GHFM-02 conforming to ASTM E1530-19, manufactured by Thermtest Instruments) with disc-shaped samples having 2 inch diameter and a thicknesses of up to 1 inch. [0045] In this context it should be remembered that contemplated compositions are particularly suitable for geothermic heat harvesting applications in which a closed loop heat recovery system is placed into a dry geothermal wellbore (typically in hot dry rock such as intrusive igneous or metamorphous rock) and in which the heat transfer fluid in the heat recovery system receives heat from the geologic formation by conduction through the grout between the formation and the heat recovery system. Exemplary heat recovery systems are described in US 10,954,924, which is incorporated by reference herein. Consequently, it should be recognized that the temperature at the target location in the well bore will be at least 400 °F, or at least 500 °F, or at least 550 °F, or at least 600 °F, or even higher, which will in most (if not all) cases require that a retarder is present in a cementitious composition or slurry to allow for installation of the material at the target location. There are numerous types of retarders known in the art, and all of them are deemed suitable for use herein. However, especially preferred retarders include various lignosulphonates, phosphonates, sugars, hydroxycarboxylic acid, borates, and also various salts of Zn, Pb, Cu, Sb, and/or As. [0046] Most typically, the retarder(s) will be present in the cementitious composition or slurry in an amount effective that delays setting of the composition at the target location for at least two hours, or at least three hours, or at least four hours, or at least 6 hours, wherein the target location has a formation temperature of at least 400 °F, or at least 500 °F, or at least 550 °F, or at least 600 °F, or even higher. That being said, it should be appreciated that the compositions and methods presented herein are not limited to high-temperature formation environments, but that the compositions and methods are suitable for use in any setting where heat transfer from a formation to a heat transfer fluid is desired (e.g., temperatures of equal of less than 400 °F, or less than 300 °F, or less than 250 °F, or less than 200 °F, or less than 150 °F). [0047] In further contemplated aspects, the grout composition may also include additional functional agents such as one or more (super)plasticizers, surfactants, organic polymers, defoamers, silica fillers, and/or a clay. In addition, the compositions may further include sand (e.g., having an average particle size of between 0.1 mm and 2.0 mm). Regardless of the type or quantity of the additional agents(s), it is generally contemplated that the slurries prepared from the grout compositions presented herein will be pumpable to so allow for deployment to a down-hole target location. Consequently, pumpable slurries are particularly contemplated. Among other options, typical slurries may have a density of between 10 and 20 lb/gal, and/or may have a water content of 5 and 30 gal/sk. Further contemplated cementitious materials and methods suitable for use in conjunction with the teachings presented herein include those in our co-pending International patent applications with the serial numbers PCT/US23/61279 and PCT/US23/61379, both of which are incorporated by reference herein. Aspects [0048] The present disclosure will be better understood upon reading the following numbered aspects, which should not be confused with the claims. In some instances, each of the aspects described below can be combined with other aspects, including combined with other aspects described elsewhere in the disclosure or other aspects from the examples below, without departing from the spirit of the disclosure. [0049] 1. A high-thermal conductivity grout composition for use in heat transfer from a geological formation to a heat recovery system, the grout composition comprising: [0050] a cementitious material in admixture with a surface modified micro- or nanostructured carbon allotrope; [0051] wherein the surface modified micro- or nanostructured carbon allotrope is modified to have an increased hydrophilicity as compared to the otherwise same carbon allotrope without the surface modification; and [0052] wherein the surface modified micro-or nanostructured carbon allotrope is present in the grout composition in an effective amount to impart the grout composition, upon setting at a target location, a thermal conductivity of at least 3 W/m-K. [0053] 2. The high-thermal conductivity grout of aspect 1, wherein the surface modified micro-or nanostructured carbon allotrope is present in the grout composition in an effective amount to impart the grout composition, upon setting at a target location, a thermal conductivity of 3 W/m-K to 30 W/m-K. [0054] 3. The high-thermal conductivity grout of aspect 1, wherein the surface modified micro-or nanostructured carbon allotrope is present in the grout composition in an effective amount to impart the grout composition, upon setting at a target location, a thermal conductivity of 8 W/m-K to 30 W/m-K. [0055] 4. The high-thermal conductivity grout of any one of aspects 1-3, wherein the surface modified micro-or nanostructured carbon allotrope is selected from the group consisting of an exfoliated graphite, a graphite nanoplatelet, graphene, a single-walled carbon nanotube, a multi-walled carbon nanotube, and a combination thereof. [0056] 5. The high-thermal conductivity grout of any one of aspects 1-3, wherein the surface modified micro-or nanostructured carbon allotrope has a plurality of hydroxyl and/or carboxyl groups. [0057] 6. The high-thermal conductivity grout of any one of aspects 1-5, wherein the surface modification comprises a surface modification selected from the group consisting of chemical oxidation such as treatment with strong acids such as sulfuric acid, nitric acid, or a combination thereof, electrochemical oxidation, covalent functionalization such as amidation, esterification, or click chemistry, grafting of hydrophilic polymers, and a combination thereof. [0058] 7. The high-thermal conductivity grout of any one of aspects 1-6 wherein the surface modified micro-or nanostructured carbon allotrope comprises a surface modified exfoliated graphite or surface modified graphite nanoplatelets. [0059] 8. The high-thermal conductivity grout of any one of aspects 1-7, the surface modified micro-or nanostructured carbon allotrope has a plurality of hydroxyl and/or carboxyl groups. [0060] 9. The high-thermal conductivity grout of any one of aspects 1-8, wherein the surface modification comprises a surface modification selected from the group consisting of chemical oxidation such as treatment with strong acids such as sulfuric acid, nitric acid, or a combination thereof, electrochemical oxidation, covalent functionalization such as amidation, esterification, or click chemistry, grafting of hydrophilic polymers, and a combination thereof. [0061] 10. The grout composition according to any one of aspects 1-9, wherein the surface modified micro-or nanostructured carbon allotrope has a carbon to oxygen ratio of between 50 and 200. [0062] 11. The grout composition according to any one of aspects 1-10, wherein the surface modified micro-or nanostructured carbon allotrope is present in an amount of between 2-15 wt% BWOC. [0063] 12. The grout composition according to any one of aspects 1-11, wherein the surface modified micro-or nanostructured carbon allotrope is present in an amount effective such that the grout composition has, upon setting at the target location, a thermal conductivity of at least 5 W/m-K. [0064] 13. The grout composition according to any one of aspects 1-11, wherein the surface modified micro-or nanostructured carbon allotrope is present in an amount effective such that the grout composition has, upon setting at the target location, a thermal conductivity of at least 8 W/m-K. [0065] 14. The grout composition according to any one of aspects 1-13, further comprising a retarder. [0066] 15. The grout composition of aspect 14, wherein the retarder is selected form the group consisting of a lignosulphonate, a phosphonate, a sugar, a hydroxycarboxylic acid, a borate, and a salt of Zn, Pb, Cu, Sb, or As. [0067] 16. The grout composition according to aspects 14-15, wherein the retarder is present in an amount effective that delays setting of the composition at the target location for at least two hours, and wherein the target location has a formation temperature of at least 400 °F. [0068] 17. The grout composition according to aspects 14-15, wherein the retarder is present in an amount effective that delays setting of the composition at the target location for at least two hours, and wherein the target location has a formation temperature of at least 500 °F. [0069] 18. The grout composition according to aspects 1-17, further comprising at least one functional agent. [0070] 19. The grout composition of aspect 18, wherein the functional agent is selected from the group consisting of a plasticizer, a surfactant, an organic polymer, a silica filler, and a clay. [0071] 20. The grout composition according to aspects 1-19, wherein the cementitious material is a hydraulic cement. [0072] 21. The grout composition of aspect 20, wherein the cementitious material is a Portland cement or calcium aluminate cement. [0073] 22. The grout composition according to any one of aspects 1-20, wherein the grout composition is pumpable upon addition of water to a water content of 5-30 gal/sk. [0074] 23. Use of the grout composition of any one of the preceding aspects as a heat transfer agent in a geothermic well. [0075] 24. A pumpable slurry comprising water in admixture with the grout composition of any one of aspects 1-22. [0076] 25. The pumpable slurry of aspect 24, having a density of between 10 and 20 lb/gal, and/or having a water content of 5 and 30 gal/sk. [0077] 26. A method of producing a grout composition for use in heat transfer from a geological formation to a heat recovery system, the method comprising: [0078] combining a cementitious material with a surface modified micro- or nanostructured carbon allotrope, wherein the surface modified micro- or nanostructured carbon allotrope is modified to have an increased hydrophilicity as compared to the otherwise same carbon allotrope without the surface modification; and [0079] wherein the surface modified micro-or nanostructured carbon allotrope is present in the grout composition in an amount that imparts to the grout composition, upon setting at a target location, a thermal conductivity of at least 3 W/m-K. [0080] 27. The method of aspect 26, wherein the surface modified micro-or nanostructured carbon allotrope comprises a surface modified exfoliated graphite or surface modified graphite nanoplatelets. [0081] 28. The method of any one of aspects 26-27, wherein the micro-or nanostructured carbon allotrope is surface modified by high-temperature exposure and/or chemical oxidation such as treatment with an oxidizing acid such as sulfuric acid, nitric acid, or a combination thereof, or by electrochemical oxidation, covalent functionalization such as amidation, esterification, or click chemistry, grafting of hydrophilic polymers, and a combination thereof. [0082] 29. The method of aspect 28, wherein the high-temperature exposure is performed by thermal exfoliation of graphite flakes at a temperature of about 900 °C in an oxygen-containing atmosphere. [0083] 30. The method of aspect 28, wherein the one or more oxidizing acids comprise sulfuric acid, nitric acid, and/or phosphoric acid. [0084] 31. The method of any one of aspects 26-30, wherein the surface modified micro-or nanostructured carbon allotrope is depleted of carboxylate carbonaceous fragments. [0085] 32. The method of aspect 31, wherein the carboxylate carbonaceous fragments are removed from the surface modified micro-or nanostructured carbon allotrope using a wash step with an organic solvent. [0086] 33. The method of aspect 32, wherein the organic solvent is acetone. [0087] 34. The method of any one of aspects 26-33, wherein the surface modified micro-or nanostructured carbon allotrope is present in an amount of between 2-15 wt% BWOC. [0088] 35. The method of any one of aspects 26-34, further comprising including a retarder into the composition in an amount effective that delays setting of the composition at the target location for at least two hours, and wherein the target location has a formation temperature of at least 400 °F. [0089] 36. A method of producing a surface modified micro- or nanostructured carbon allotrope for use in a grout composition for use in heat transfer from a geological formation to a closed loop heat recovery system, comprising: [0090] subjecting graphite flakes and/or graphite nanoplatelets to an oxidation process that generates surface modified micro- or nanostructured exfoliated graphite and/or surface modified micro- or nanostructured graphite nanoplatelets; [0091] wherein the oxidation process is [0092] (a) thermal exfoliation of graphite flakes at a temperature of about 900 °C in an oxygen- containing atmosphere to produce the surface modified micro- or nanostructured exfoliated graphite, or [0093] (b) a reaction with one or more oxidizing acids to produce the surface modified micro- or nanostructured nanoplatelets; [0094] removing carboxylate carbonaceous fragments from the surface modified micro- or nanostructured graphite nanoplatelets and/or surface modified micro- or nanostructured exfoliated graphite using an organic solvent wash step; and [0095] combining or instructing to combine the surface modified micro- or nanostructured carbon allotrope with a cementitious composition. [0096] 37. The method of aspect 36, wherein the graphite flakes and/or graphite nanoplatelets have after the oxidation process an average particle size of less than 1,000 µm. [0097] 38. The method of any one of aspects 36-37, wherein the solvent is selected from the group consisting of acetone, methyl acetate, methyl ethyl ketone, ethyl acetate, mixtures thereof, and mixture of any of the foregoing with one or more additional cosolvents. [0098] 39. The method of any one of aspects 36-38, wherein the oxidizing acids comprise sulfuric acid, nitric acid, and/or phosphoric acid. [0099] 40. The method of any one of aspects 36-39, wherein the surface modified micro-or nanostructured carbon allotrope is combined with the cementitious composition in an amount of between 2-15 wt% BWOC. [00100] 41. A method of installing a high-thermal conductivity grout in a wellbore, wherein a casing is located in the wellbore such that an annular space is formed therebetween, the method comprising: [00101] pumping the pumpable slurry of any one of aspects 18-19 to a target location within the wellbore having a target temperature of at least 300 °F; [00102] allowing the pumpable slurry to set in the annular space to thereby form the high- thermal conductivity grout in the wellbore, wherein the high-thermal conductivity grout is in thermal exchange with the casing and a formation surrounding the wellbore; [00103] wherein the time to set for the pumpable slurry is at least two hours at a formation temperature of at least 300 °F. [00104] 42. The method of aspect 41, wherein the target location is at least 500 ft below ground. [00105] 43. The method of any one of aspects 41-42, wherein the target location extends in a substantially vertical orientation. [00106] 44. The method of any one of aspects 41-43, wherein the target temperature at the target location is at least 400 °F, and wherein the time to set for the pumpable slurry is at least two hours. [00107] 45. The method of any one of aspects 41-43, wherein the target temperature at the target location is at least 500 °F, and wherein the time to set for the pumpable slurry is at least two hours. [00108] 46. The method of any one of aspects 41-45, wherein routing the pumpable slurry into the annular space between the wellbore and the casing displaces a fluid in the annular space. [00109] 47. The method of any one of aspects 41-46, wherein the formation includes a plurality of fissures that are at least partially filled with a high-thermal conductivity material, and wherein the high-thermal conductivity material in the fissures is in thermal exchange with the high-thermal conductivity grout in the wellbore. [00110] 48. The method of aspect 47, wherein the high-thermal conductivity material in the fissures is selected from the group consisting of graphite powder, flaked graphite, pyrolytic graphite, desulfurized petroleum coke, graphene, fly ash, copper powder, aluminum nitride, and silicon carbide. [00111] 49. A heat recovery system comprising a wellbore comprising a cement, wherein the cement is comprised of a high-thermal conductivity grout composition according to any one of aspects 1-22. [00112] 50. The heat recovery system according to aspect 49, wherein the wellbore comprises a first casing positioned in the wellbore forming a first annulus between an exterior surface of the casing and a wall of the wellbore; and [00113] wherein the cement is positioned in the annulus along a segment of the casing and in thermal exchange with the casing. [00114] 51. The method of any one of aspects 49-50, further comprising a plurality of fissures along a segment of the wall of the wellbore, wherein the fissures in the plurality of fissures are at least partially filled with a high-thermal conductivity material, and [00115] wherein the high-thermal conductivity material in the fissures is in thermal exchange with the high-thermal conductivity grout. [00116] 52. The method of any one of aspects 49-51, wherein the segment of the casing is at a depth in the wellbore having a target temperature of about 300ׄ°F to about 450°F. [00117] 53. The method of any one of aspects 51-52, wherein the high-thermal conductivity material in the fissures is selected from the group consisting of graphite powder, flaked graphite, pyrolytic graphite, desulfurized petroleum coke, graphene, fly ash, copper powder, aluminum nitride, silicon carbide, and a combination thereof. [00118] 54. The heat recovery system according to any one of aspects 49-53, wherein the wellbore comprises a heat-transfer fluid. [00119] 55. The heat recovery system according to aspect 54, wherein the heat-transfer fluid comprises water. [00120] 56. The heat recovery system according to any one of aspects 53-54, wherein the heat-transfer fluid is located along an inner space of the first casing. [00121] 57. The heat recovery system according to any one of aspects 53-56, further comprising a second tubular along the inner space of the first casing, wherein the heat transfer fluid is circulated from a top of the wellbore to a bottom of the wellbore, passing along the segment of the casing. [00122] 58. The heat recovery system according to any one of aspects 53-57, wherein the heat-recovery system is a closed-loop heat recovery system. [00123] 59. The heat recovery system according to any one of aspects 53-58, made by a method according to any one of aspects 41-48. Examples [00124] The following examples, in conjunction with the above teachings, are provided to give a skilled artisan sufficient guidance to make, use, and practice the subject matter as is claimed. However, nothing in the examples should be construed as limiting the scope of the disclosure. [00125] For both graphene nanoplatelets (GNP) and exfoliated graphite flakes (EGF), three different particle size distributions (PSD) were examined. The GNP and EGF materials were obtained from Asbury Carbon, and the particle sizes for GNP and EGF are shown in Table 1 and Table 2. Different types of cement were also examined, API classes H and G, and selected calcium alumina cements (CAC).

Table 1 – GNP Size Parameters

Table 2 – EGF Size Parameters [00126] To provide a uniform dispersion of graphite nanoplatelets in aqueous medium, the surface properties were first modified to render the nanoplatelets more hydrophilic. To this end, both physical techniques based on polymer wrapping and chemical approaches based on acid functionalization can be applied for the introduction of high concentrations of hydroxyl, epoxy, and carboxyl (OH, -O-, and COOH) groups on the surface of GNPs. For instance, polyacrylic acid or polyvinyl alcohol can be used for the purpose of polymer wrapping. In chemical methods, GNPs or EGFs can be added to a mixture of oxidizing acids, for example, a solution of nitric and sulfuric acids with a volume ratio of 1:3, or a solution of phosphoric acid and sulfuric acid with a volume ratio of 1:9. Hydrophilicity can be measured using various methods. For example, suitable methods for determination of hydrophilicity include contact angle measurements as is described in ASTM D7334-08 (2013) in which a decrease in contact angle is representative of an increase in hydrophilicity. Suitable devices include commercially available contact angle meters, such as JC2000D2 (Shanghai Zhongchen Digital Technic Apparatus Co. Ltd, China) using sessile drop technique. [00127] In one typical set of experiments, 10 wt.% of GNPs were added to a solution of nitric acid (70 wt.%) and sulfuric acid (96 wt.%) at a volume ratio of 1:3. Next, the mixture was stirred using magnetic stirring at 80 °C for 3 − 4 hours. The so surface modified particles were then iteratively washed by 5% HCl, DI water, and acetone until a clean and colorless filtrate were obtained. In this context, it should be noted that the acetone wash removed a significant portion of carboxylate carbonaceous fragments. To prepare surface modified EGFs, commercially available expandable graphite flakes were rapidly heated up to 900 ℃ in an oxygen containing atmosphere (using ambient air at about 21% oxygen) to exfoliate the graphite flakes into accordion- or worm-like structures. As will be readily appreciated, and contrary to conventional exfoliation that use non-oxidative gases (e.g., nitrogen, argon, or helium) to preserve chemical integrity of the expanded graphite, the present thermal expansion conditions introduced a significant amount of polar groups (e.g., hydroxyl, keto, epoxy, and/or carboxyl groups) into the EGFs. The so prepared surface modified GNPs and worm-like EGFs were then used as additive to prepare cement samples. [00128] Cement Slurry Preparation: Surface-modified GNPs and surface modified EGFs were added to either API cement classes like H and G or CAC. According to API Specification 10A, 38% water by weight of cement (BWOC) is required to make slurry using cement class H, while it is 44% for the cement class G. For CAC, a water concentration not higher than 40% BWOC is recommended. The CAC used here is a cement with very high alumina content about 80% (commercially available by Kerneos Inc.). Cementitious composites were prepared by adding surface-modified GNPs to cement class H. To provide a uniform dispersion of particles within the cement matrix, the surface modified GNPs were first added to the required amount of water to make a slurry. Next, the mixture was sonicated for about 1 hour, followed by magnetic stirring for 3-4 hrs. Then, cement was added to this mixture and mixed by a high shear speed mixer. For each PSD (particle sized distribution) of GNPs of Table 1, different concentrations of 2 and 4wt.% BWOC were examined. [00129] The EGFs with worm-like structure were added to the required amount of dry cement to prepare a slurry. Then, the ingredients were dry-mixed using a high-shear speed mixer for about 1 min. CAC was used for this series of tests. Then, the mixed dry components were added to 40% water BWOC to prepare the slurry. For each PSD of EGFs given in Table 2, different concentrations of 2, 4, 6, 8, and 10, 12, and 15wt.% were tested. [00130] As will be readily recognized, different sizes of cement samples may be prepared for testing. For example, according to API Recommended Practice 10B-2, cubic samples with the length of 2 inch were used for unconfined compressive strength (UCS) measurements. According to the instrument used for thermal conductivity measurement, disc shape samples with 2 inch diameter and 1 inch height were used. For sample preparation, cement slurries are first poured inside cylindrical or cubic molds, then cured for 24 hours at ambient temperature under water or under a high temperature and high pressure conditions inside a high-temperature high-pressure chamber with a temperature of 240 ℉ and a pressure of 3000 psi. Results [00131] Thermal conductivity measurements: Thermal conductivity were measured using either steady-state or non-steady-state (transient) methods. A heat flow meter (HFM) method was employed by establishing a constant temperature gradient through the thickness of the sample to measure its thermal conductivity. In particular, a guarded version of a HFM, GHFM- 02 conforming to ASTM E1530-19 (manufactured by Thermtest Instruments), was used to prevent lateral heat losses. Disc shape samples with 2 inch diameter and thicknesses up to 1 inch were used for this purpose. [00132] A variety of cement samples composed of different concentrations and different particle size distributions (PSDs) of surface modified GNPs, surface modified EGFs, as well as hybrid methods combining both surface modified GNPs and EGFs was prepared. In the following, the effect of these surface modified carbon allotropes on the thermal conductivity of the various cement compositions is presented. Table 3 below summarizes the thermal conductivity of the cementitious composites after adding different concentrations of surface- modified GNPs having different PSD. Cement slurries were cured at ambient conditions under water for 24hr. The maximum improvement in the thermal conductivity of cement was measured by adding 2 wt.% of surface-modified GNPs with the largest median particle size, D50~8 − 11μm to thereby improve thermal conductivity of the baseline cement by 98.2%. One published study (Geothermics 81: 1–11; Xianzhi et al.2019) investigated the effect of graphite additives on the thermal conductivity of cement. In that study, a maximum improvement of 20% in the thermal conductivity of API class G cement was obtained by adding 0.05 wt.% of unmodified graphite. Notably, this study reported that increasing the concentration of graphite above 0.05 wt.% reduced the thermal conductivity of cement. Such deleterious effect can be explained by the agglomeration of graphite particles at increasing concentrations of the particles and/or a lack of interaction of cement components with the graphite. [00133] In the current examples, the employed surface modification rendered particles more hydrophilic, enabling an increase in the concentration of particles up to 2 wt.% without their agglomeration, and increasing bonding or other non-covalent interaction with the cement components (and other surface modified carbon allotropes) to so stabilize homogenous particle distribution and thermal conductivity. Comparing with the maximum experimentally determined thermal conductivity, 0.8 W⁄(m − K) for a known geothermal cement system (API Cement H), the addition of 2 wt.% of treated GNPs remarkably improved the thermal conductivity by 232.5%.

Table 3 Figures 1, panels (a)-(c) show how the thermal conductivity of cement changes with respect to the concentration of EGFs with nominal sizes of 75 ^^^^m, 180 ^^^^m, and 300 ^^^^m, respectively. For these series of tests, additives were added to the CAC, and slurries were cured under both ambient conditions and inside the chamber under high-pressure high-temperature conditions. It was found that for all cases, curing under high-pressure high-temperature conditions resulted in higher thermal conductivity of the cementitious material as compared to the same sample cured under ambient condition. In this context, it should be appreciated that such finding is particularly significant considering downhole conditions in geothermal wells. Therefore, it should be recognized that curing the slurries presented herein under conditions after pumping and placing downhole is expected to yield better thermal conductivity for the set cement. While not wishing to be bound by any theory or hypothesis, it is contemplated that the polar groups of the surface modified carbon allotrope may contributed to increased covalent and/or non- covalent interactions with the cement components as well as with other surface modified carbon allotrope, thereby leading to a thermal transfer network with increased thermal conductivity. In addition, as can be seen from Figure 1, EGFs with larger nominal sizes lead to higher thermal conductivities. For example, the addition of 15 wt.% EGFs with the nominal size of 75 μm (Figure 1(a)), 12 wt.% EGFs with the nominal size of 180 μm (Figure 1(b)), and 10 wt.% EGFs with the nominal size of 300 μm (Figure 1(c)) increased the thermal conductivity of cement by 964%, 1027%, and 1041%, respectively, as compared to the maximum experimentally determined thermal conductivity for known geothermal cement systems. [00134] Hybrid methods by combining both EGFs and modified GNPs were also examined for improving the thermal conductivity of cement. Following the results given in Table 3, 2wt.% of treated GNPs with the median particle size of D50~8 − 11μm was selected for this study. By keeping the concentration of water fixed at 38% BWOC recommended for the API class H cement, the effect of combining 6wt.% of EGFs with the nominal size > 75 ^^^^m with the above-mentioned GNPs on the thermal conductivity of baseline cement was tested. Defoamer with the concentration of 2wt.% BWOC was also added to this composition. Notably, for the sample cured under ambient conditions for 24 hours, the thermal conductivity of composite was measured as 4.357W⁄m − K. From Table 3, the addition of only 2wt.% of treated GNPs with D₅₀~8−11μm improved the thermal conductivity of the baseline cement by 98.2%. However, using a hybrid method by combining 6wt.% of EGFs with the nominal size > 75 ^^^^m with 2wt.% of treated GNPs with D50~8−11μm, the thermal conductivity of the baseline cement improved by 224.7%. Such examples once more demonstrate that the surface modified carbon presented herein are capable for forming thermal transfer networks with high conductivity. Moreover, the concentration of the carbon allotropes was remarkably high, which is also attributable to at least some degree to the surface modifications. [00135] Examination of Pumpability: The pumpability of a cement slurry containing the surface modified carbon allotropes can be adjusted by various additives, including a superplasticizers, defoamers, and/or retarders, and the pumpability of such cement slurries changes by adding any of the above-mentioned additives was investigated. For this purpose, a cement slurry made of 10 wt.% EGFs with the nominal size of > 180 ^^^^m was tested. Corresponding to each additives, superplasticizer, defoamer, and/or retarder, different concentrations were considered. Moreover, the effect of adding these additives to the cement slurry on the thermal conductivity of the cementitious composite was also tested. [00136] To quantify the effect of additives on the pumpability of the cement slurry, a modified scope of Funnel Viscosity test, ASTM D6910/D6910M-19, was employed. Cement slurry was poured inside the funnel, and the flow duration through the funnel was measured. Cement slurries composed of different concentrations of additives were tested, the flow duration of which is given in Table 4. For better comparison, measurements corresponding to the plain (without any additives) cements of CAC, API classes of H and G have also been added to Table 4. As can be readily taken from Table 4, additives can significantly improve the pumpability of the base cement, CAC + 10wt.% EGF>180μm.

Table 4 [00137] Following the mathematical predictions for the thermal conductivity of cementitious composites, the thermal conductivity of composite, k can be calculated as the summation of the conductivity of components represented by their volume fractions, as below,

in which, K_i is the individual thermal conductivity of the ith component with the volume fraction of V_i . Based on this calculation, it can be concluded that adding high concentrations of additives with low thermal conductivities to the cementitious composite will deteriorate its overall thermal conductivity. Although the volume fraction of additives used in the current study are relatively low, a series of tests were conducted to examine how the concentration of the additives (superplasticizer, defoamer, retarder) changes the thermal conductivity of cementitious composite. Figure 2 and Figure 3 present exemplary experimental results. As expected, the thermal conductivity of composite decreases by increasing the concentration of additives. Notably, however, it was found that the decrease was only very slight for the case of defoamer as can be taken from Figure 3. Moreover, for all concentrations of defoamer from 1 to 5wt.%, the thermal conductivity of the composite remained higher than that of the base cement, CAC + 10wt.% EGF>180μm without any defoamer. This can possibly be attributed to the effect of defoamer on decreasing the porosity of composite. [00138] Based on the foregoing data and discussion, it should be appreciated that the cement compositions presented herein provide a thermal conductivity that is an order of magnitude higher than currently known plain cement under high-pressure and high-temperature environments. Considering that heat extraction in the systems with no mass withdrawal is mainly achieved through conductivity, the thermal conductivity of the region around the wellbore plays a critical role in the success of closed-loop systems. The cementitious compositions disclosed herein are therefore particularly suitable for heat exchange at the bottomhole of geothermal wells. [00139] In some aspects, the numbers expressing quantities of ingredients, properties such as concentration, reaction conditions, and so forth, used to describe and claim certain aspects of the disclosure are to be understood as being modified in some instances by the term “about.” Accordingly, in some aspects, the numerical parameters set forth in the written description and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by a particular aspect. The recitation of ranges of values herein is merely intended to serve as a shorthand method of referring individually to each separate value falling within the range. Unless otherwise indicated herein, each individual value is incorporated into the specification as if it were individually recited herein. [00140] All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided with respect to certain aspects herein is intended merely to better illuminate the disclosure and does not pose a limitation on the scope of the claims. No language in the specification should be construed as indicating any non-claimed element is essential. [00141] All publications, patents, and patent applications mentioned or cited herein are incorporated herein by reference to disclose and describe the methods and/or materials in connection with which the publications, patents, or patent applications are cited. All such publications, patents, and patent applications are herein incorporated by references as if each individual publication, patent, or patent application were specifically and individually indicated to be incorporated by reference. Such incorporation by reference is expressly limited to the methods and/or materials described in the cited publications, patents, and patent applications and does not extend to any lexicographical definitions from the cited publications, patents, and patent applications. Any lexicographical definition in the publications, patents, and patent applications cited, including any lexicographical definition in any patent or patent application in the priority claim, that is not also expressly repeated in the instant specification should not be treated as such and should not be read as defining any terms appearing in the accompanying claims. The publications, patents, and patent applications discussed herein are provided solely for their disclosure prior to the filing date of the present application. Nothing herein is to be construed as an admission that the present disclosure is not entitled to antedate such publication by virtue of prior disclosure. Further, the dates of publication provided herein can be different from the actual publication dates, which can require independent confirmation. [00142] As used in the description herein and throughout the claims that follow, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise. As also used herein, and unless the context dictates otherwise, the term "coupled to" is intended to include both direct coupling (in which two elements that are coupled to each other contact each other), and indirect coupling (in which at least one additional element is located between the two elements). Therefore, the terms "coupled to" and "coupled with" are used synonymously. [00143] It should be apparent to those skilled in the art that many more modifications besides those already described are possible without departing from the disclosure. The disclosure, therefore, is not to be restricted except in the scope of the appended claims. Moreover, in interpreting both the specification and the claims, all terms should be interpreted in the broadest possible manner consistent with the context. In particular, the terms “comprises” and “comprising” should be interpreted as referring to elements, components, or steps in a non-exclusive manner, indicating that the referenced elements, components, or steps may be present, or utilized, or combined with other elements, components, or steps that are not expressly referenced. Where the specification or claims refer to at least one of something selected from the group consisting of A, B, C ... a.nd N, the text should be interpreted as requiring only one element from the group, not A plus N, or B plus N, etc.

Claims

CLAIMS What is claimed is: 1. A high-thermal conductivity grout composition for use in heat transfer from a geological formation to a heat recovery system, the grout composition comprising: a cementitious material in admixture with a surface modified micro- or nanostructured carbon allotrope; wherein the surface modified micro- or nanostructured carbon allotrope is modified to have an increased hydrophilicity as compared to the otherwise same carbon allotrope without the surface modification; and wherein the surface modified micro-or nanostructured carbon allotrope is present in the grout composition in an effective amount to impart the grout composition, upon setting at a target location, a thermal conductivity of at least 3 W/m-K.

2. The high-thermal conductivity grout of claim 1, wherein the surface modified micro-or nanostructured carbon allotrope is present in the grout composition in an effective amount to impart the grout composition, upon setting at a target location, a thermal conductivity of 3 W/m-K to 30 W/m-K.

3. The high-thermal conductivity grout of claim 1, wherein the surface modified micro-or nanostructured carbon allotrope is present in the grout composition in an effective amount to impart the grout composition, upon setting at a target location, a thermal conductivity of 8 W/m-K to 30 W/m-K.

4. The high-thermal conductivity grout of claim 1, wherein the surface modified micro-or nanostructured carbon allotrope is selected from the group consisting of an exfoliated graphite, a graphite nanoplatelet, graphene, a single-walled carbon nanotube, a multi- walled carbon nanotube, and a combination thereof.

5. The grout composition of claim 4, wherein the surface modified micro-or nanostructured carbon allotrope has a plurality of hydroxyl and/or carboxyl groups.

6. The grout composition of claim 4, wherein the surface modification comprises a surface modification selected from the group consisting of chemical oxidation such as treatment with strong acids such as sulfuric acid, nitric acid, or a combination thereof, electrochemical oxidation, covalent functionalization such as amidation, esterification, or click chemistry, grafting of hydrophilic polymers, and a combination thereof.

7. The grout composition of claim 1, wherein the surface modified micro-or nanostructured carbon allotrope comprises a surface modified exfoliated graphite or surface modified graphite nanoplatelets.

8. The grout composition of claim 7, wherein the surface modified micro-or nanostructured carbon allotrope has a plurality of hydroxyl and/or carboxyl groups.

9. The grout composition of claim 7, wherein the surface modification comprises a surface modification selected from the group consisting of chemical oxidation such as treatment with strong acids such as sulfuric acid, nitric acid, or a combination thereof, electrochemical oxidation, covalent functionalization such as amidation, esterification, or click chemistry, grafting of hydrophilic polymers, and a combination thereof.

10. The grout composition according to any one of claims 1-9, wherein the surface modified micro-or nanostructured carbon allotrope has a carbon to oxygen ratio of between 50 and 200.

11. The grout composition according to any one of claims 1-9, wherein the surface modified micro-or nanostructured carbon allotrope is present in an amount of between 2-15 wt% BWOC.

12. The grout composition according to any one of claims 1-9, wherein the surface modified micro-or nanostructured carbon allotrope is present in an amount effective such that the grout composition has, upon setting at the target location, a thermal conductivity of at least 5 W/m-K.

13. The grout composition according to any one of claims 1-9, wherein the surface modified micro-or nanostructured carbon allotrope is present in an amount effective such that the grout composition has, upon setting at the target location, a thermal conductivity of at least 8 W/m-K.

14. The grout composition according to any one of claims 1-9, further comprising a retarder.

15. The grout composition of claim 14, wherein the retarder is selected form the group consisting of a lignosulphonate, a phosphonate, a sugar, a hydroxycarboxylic acid, a borate, and a salt of Zn, Pb, Cu, Sb, or As.

16. The grout composition according to claim 14, wherein the retarder is present in an amount effective that delays setting of the composition at the target location for at least two hours, and wherein the target location has a formation temperature of at least 400 °F.

17. The grout composition according to claim 14, wherein the retarder is present in an amount effective that delays setting of the composition at the target location for at least two hours, and wherein the target location has a formation temperature of at least 500 °F.

18. The grout composition according to any one of claims 1-9, further comprising at least one functional agent.

19. The grout composition of claim 18, wherein the functional agent is selected from the group consisting of a plasticizer, a surfactant, an organic polymer, a silica filler, and a clay.

20. The grout composition according to any one of claims 1-9, wherein the cementitious material is a hydraulic cement.

21. The grout composition of claim 20, wherein the cementitious material is a Portland cement or calcium aluminate cement.

22. The grout composition according to any one of claims 1-9, wherein the grout composition is pumpable upon addition of water to a water content of 5-30 gal/sk.

23. Use of the grout composition of any one of the preceding claims as a heat transfer agent in a geothermic well.

24. A pumpable slurry comprising water in admixture with the grout composition of any one of claims 1-16.

25. The pumpable slurry of claim 24 having a density of between 10 and 20 lb/gal, and/or having a water content of 5 and 30 gal/sk.

26. A method of producing a grout composition for use in heat transfer from a geological formation to a heat recovery system, the method comprising: combining a cementitious material with a surface modified micro- or nanostructured carbon allotrope, wherein the surface modified micro- or nanostructured carbon allotrope is modified to have an increased hydrophilicity as compared to the otherwise same carbon allotrope without the surface modification; and wherein the surface modified micro-or nanostructured carbon allotrope is present in the grout composition in an amount that imparts to the grout composition, upon setting at a target location, a thermal conductivity of at least 3 W/m-K.

27. The method of claim 26, wherein the surface modified micro-or nanostructured carbon allotrope comprises a surface modified exfoliated graphite or surface modified graphite nanoplatelets.

28. The method of any one of claims 26-27, wherein the micro-or nanostructured carbon allotrope is surface modified by high-temperature exposure and/or chemical oxidation such as treatment with an oxidizing acid such as sulfuric acid, nitric acid, or a combination thereof, or by electrochemical oxidation, covalent functionalization such as amidation, esterification, or click chemistry, grafting of hydrophilic polymers, and a combination thereof.

29. The method of claim 28, wherein the high-temperature exposure is performed by thermal exfoliation of graphite flakes at a temperature of about 900 °C in an oxygen-containing atmosphere.

30. The method of claim 28, wherein the one or more oxidizing acids comprise sulfuric acid, nitric acid, and/or phosphoric acid.

31. The method of claim 28, wherein the surface modified micro-or nanostructured carbon allotrope is depleted of carboxylate carbonaceous fragments.

32. The method of claim 31, wherein the carboxylate carbonaceous fragments are removed from the surface modified micro-or nanostructured carbon allotrope using a wash step with an organic solvent.

33. The method of claim 32, wherein the organic solvent is acetone.

34. The method of claim 26, wherein the surface modified micro-or nanostructured carbon allotrope is present in an amount of between 2-15 wt% BWOC.

35. The method of claim 26, further comprising including a retarder into the composition in an amount effective that delays setting of the composition at the target location for at least two hours, and wherein the target location has a formation temperature of at least 400 °F.

36. A method of producing a surface modified micro- or nanostructured carbon allotrope for use in a grout composition for use in heat transfer from a geological formation to a closed loop heat recovery system, comprising: subjecting graphite flakes and/or graphite nanoplatelets to an oxidation process that generates surface modified micro- or nanostructured exfoliated graphite and/or surface modified micro- or nanostructured graphite nanoplatelets; wherein the oxidation process is (a) thermal exfoliation of graphite flakes at a temperature of about 900 °C in an oxygen-containing atmosphere to produce the surface modified micro- or nanostructured exfoliated graphite, or (b) a reaction with one or more oxidizing acids to produce the surface modified micro- or nanostructured nanoplatelets; removing carboxylate carbonaceous fragments from the surface modified micro- or nanostructured graphite nanoplatelets and/or surface modified micro- or nanostructured exfoliated graphite using an organic solvent wash step; and combining or instructing to combine the surface modified micro- or nanostructured carbon allotrope with a cementitious composition.

37. The method of claim 36, wherein the graphite flakes and/or graphite nanoplatelets have after the oxidation process an average particle size of less than 1,000 µm.

38. The method of claim 36, wherein the solvent is selected from the group consisting of acetone, methyl acetate, methyl ethyl ketone, ethyl acetate, mixtures thereof, and mixture of any of the foregoing with one or more additional cosolvents.

39. The method of claim 36, wherein the oxidizing acids comprise sulfuric acid, nitric acid, and/or phosphoric acid.

40. The method of claim 36, wherein the surface modified micro-or nanostructured carbon allotrope is combined with the cementitious composition in an amount of between 2-15 wt% BWOC.

41. A method of installing a high-thermal conductivity grout in a wellbore, wherein a casing is located in the wellbore such that an annular space is formed therebetween, the method comprising: pumping the pumpable slurry of any one of claims 18-19 to a target location within the wellbore having a target temperature of at least 300 °F; allowing the pumpable slurry to set in the annular space to thereby form the high- thermal conductivity grout in the wellbore, wherein the high-thermal conductivity grout is in thermal exchange with the casing and a formation surrounding the wellbore; wherein the time to set for the pumpable slurry is at least two hours at a formation temperature of at least 300 °F.

42. The method of claim 41, wherein the target location is at least 500 ft below ground.

43. The method of claim 41, wherein the target location extends in a substantially vertical orientation.

44. The method of claim 41, wherein the target temperature at the target location is at least 400 °F, and wherein the time to set for the pumpable slurry is at least two hours.

45. The method of claim 41, wherein the target temperature at the target location is at least 500 °F, and wherein the time to set for the pumpable slurry is at least two hours.

46. The method of claim 41, wherein routing the pumpable slurry into the annular space between the wellbore and the casing displaces a fluid in the annular space.

47. The method of any one of claims 41-46, wherein the formation includes a plurality of fissures that are at least partially filled with a high-thermal conductivity material, and wherein the high-thermal conductivity material in the fissures is in thermal exchange with the high-thermal conductivity grout in the wellbore.

48. The method of claim 47, wherein the high-thermal conductivity material in the fissures is selected from the group consisting of graphite powder, flaked graphite, pyrolytic graphite, desulfurized petroleum coke, graphene, fly ash, copper powder, aluminum nitride, and silicon carbide.

49. A heat recovery system comprising a wellbore comprising a cement, wherein the cement is comprised of a high-thermal conductivity grout composition according to any one of claims 1-22.

50. The heat recovery system according to claim 49, wherein the wellbore comprises a first casing positioned in the wellbore forming a first annulus between an exterior surface of the casing and a wall of the wellbore; and wherein the cement is positioned in the annulus along a segment of the casing and in thermal exchange with the casing.

51. The heat recovery system according to claim 50, further comprising a plurality of fissures along a segment of the wall of the wellbore, wherein the fissures in the plurality of fissures are at least partially filled with a high-thermal conductivity material, and wherein the high-thermal conductivity material in the fissures is in thermal exchange with the high-thermal conductivity grout.

52. The heat recovery system according to claim 51, wherein the segment of the casing is at a depth in the wellbore having a target temperature of about 300ׄ°F to about 450°F.

53. The heat recovery system according to claim 52, wherein the high-thermal conductivity material in the fissures is selected from the group consisting of graphite powder, flaked graphite, pyrolytic graphite, desulfurized petroleum coke, graphene, fly ash, copper powder, aluminum nitride, silicon carbide, and a combination thereof.

54. The heat recovery system according to any one of claims 49-53, wherein the wellbore comprises a heat-transfer fluid.

55. The heat recovery system according to claim 54, wherein the heat-transfer fluid comprises water.

56. The heat recovery system according to claim 54, wherein the heat-transfer fluid is located along an inner space of the first casing.

57. The heat recovery system according to claim 55, further comprising a second tubular along the inner space of the first casing, wherein the heat transfer fluid is circulated from a top of the wellbore to a bottom of the wellbore, passing along the segment of the casing.

58. The heat recovery system according to any one of claims 49-53, wherein the heat-recovery system is a closed-loop heat recovery system.

59. The heat recovery system according to any one of claims 49-53, made by a method according to any one of claims 41-48.