TECHNICAL FIELD

[0001] The present disclosure relates generally cementing. More specifically, the present disclosure relates to systems and methods for preparing cement slurries. Still more specifically, the present disclosure relates to systems and methods for making and using cement slurries, wherein graphene is utilized as a cement retarder in the cement slurries.

BACKGROUND

[0002] Cements do not inherently remain in the fluid, but instead begin forming gels, which can, in a time known as the thickening time, become viscous enough to prevent pumping. Cement retarders can be utilized to extend the time that a slurry stays in the pumpable state (e.g., the thickening time), and to ensure there is sufficient time to place the cement slurry in the proper down hole location.

BRIEF DESCRIPTION OF THE DRAWINGS

[0003] For a more complete understanding of this disclosure, reference is now made to the following brief description, taken in connection with the accompanying drawings and detailed description, wherein like reference numerals represent like parts.

[0004] FIG. 1 is a schematic of a cement slurry, according to embodiments of this disclosure;

[0005] FIG. 2 is a schematic flow diagram of a method, according to embodiments of this disclosure;

[0006] FIG. 3 is a schematic flow diagram of a method, according to embodiments of this disclosure;

[0007] FIG. 4 is a schematic of a cementing workspace, according to embodiments of this disclosure;

[0008] FIG. 5 is a plot of thickening time as a function of BRG content, according to the data of Table 2 of Example 1;

[0009] FIG. 6 is a plot of thickening time of the control Slurry 1 of Example 1 at 180°F and

3000 psi; and

[0010] FIG. 7 is a plot of thickening time of the inventive graphene containing Slurry 2 of Example 1 at 180°F and 3000 psi. DETAILED DESCRIPTION

[0011] It should be understood at the outset that although an illustrative implementation of one or more embodiments are provided below, the disclosed systems and/or methods can be implemented using any number of techniques, whether currently known or in existence. The disclosure should in no way be limited to the illustrative implementations, drawings, and techniques below, including the exemplary designs and implementations illustrated and described herein, but can be modified within the scope of the appended claims along with their full scope of equivalents.

[0012] As utilized herein, the phrase “percent by weight of water”, abbreviated “% bwow”, indicates the amount of additive material divided by the weight of water multiplied by 100 and the phrase, “percent by weight of the composition” or “percent by weight of cement”, abbreviated “% bwoc”, indicates the amount of additive material divided by the weight of cementitious material multiplied by 100.

[0013] As utilized herein, bioderived renewable graphene (BRG) is a biorenewable resource that can be renewed via biological means and produced by biological organisms.

[0014] Disclosed herein are systems and methods for preparing cement slurries utilizing graphene as a cement retarder. As noted above, cements do not tend to remain in the fluid, pumpable state (e.g., even at temperatures above about 100°F), but instead begin forming gels, which eventually, in a time known as the thickening time, become viscous enough to prevent pumping. Cement retarders can be utilized to extend the time that a slurry stays in the pumpable state, and to ensure there is sufficient time to place the cement slurry in the proper down hole location.

[0015] As one example of a conventional material, lignosulfonates have been utilized as cement retarders. However, such conventional cement retarders have shortfalls, such as, without limitation, the tendency to disperse the cement slurry, which can negatively affect slurry stability and reduce fluid life, and, thus, available placement time.

[0016] It has been unexpectedly discovered that graphene has the ability to delay the thickening time of cements, and can thus be utilized, as detailed further hereinbelow, as a novel cement retarder.

[0017] The present disclosure describes systems and methods for the use of graphene as a cement retarder. Graphene has not heretofore been utilized as a cement retarder. The system and method of this disclosure can provide one or more of the following attributes: (1) the use of graphene can retard cement; (2) the use of graphene as described herein can impart enhanced mechanical properties of the set cement; and/or (3) the use of graphene as described herein will not disperse cement slurries, but rather can act as a suspending aid to further stabilize the slurries. Accordingly, in embodiments, graphene can operate as a multifunctional cement additive by retarding the setting of a cement slurry, enhancing the mechanical properties of the resulting cement, and/or stabilizing the cement slurry.

[0018] Herein disclosed are cement slurries that comprise graphene as cement retarder, and methods of making and using same. The cement slurry of this disclosure, and methods of making and using same, will now be described with reference to FIG. 1, which is a schematic of a cement slurry 50 (also referred to herein as a “cement composition” 50), according to embodiments of this disclosure; FIG. 2, which is a schematic flow diagram of a method 100 of making such a cement slurry 50 (and enhancing the stability and density control of the cement slurry 50), according to embodiments of this disclosure; and FIG. 3, which is a schematic flow diagram of a method 200 of using the cement slurry 50, according to embodiments of this disclosure. Reference to “cement slurry’ can indicate an unset cement slurry that has not yet hardened to a hardened cement, such as a recently mixed cement slurry.

[0019] With reference to FIG. 1, a cement slurry 50 of this disclosure comprises a set retarder 5 (also referred to herein as a “cement retarder” 5) comprising graphene 10, water 20 (also referred to as “aqueous base fluid” 20), and a cementitious material 30 (e.g., a cement powder, also referred to herein simply as a “cement” 30). The cement slurry 50 can comprise from about 0.01 to about 20, from about 0.1 to about 15, from about 0.5 to about 5, or greater than or equal to about 0, 0.1, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or 15, and/or and less than or equal to about 20, 19, 18, 17, 16, 15, 10, or 5 percent graphene 10 (e.g., bioderived renewable graphene (BRG), as described further hereinbelow) by weight of cementitious material 30 (% BRG bwoc).

[0020] The cement slurry 50 can have an increased thickening time relative to a same cement slurry absent the graphene 10 containing set retarder 5. In embodiments, a thickening time at 70 Beardon Consistency Units (Be), as measured according to API 10B-2 of the cement slurry 50 is increased relative to a same cement slurry absent the graphene (e.g., BRG). The thickening time can be increased by at least 10, 50, 75, 100, 200, 500, or 1000 percent relative to the same cement slurry absent the graphene 10. Increased thickening time can be beneficial in applications, for example, to allow additional time for placement of the cement slurry 50 in a desired workspace prior to hardening, and facilitate pumping of the cement slurry 50.

[0021] In embodiments, the set retarder 5 consists of or consists essentially of the graphene 10, and no other set retarders are added to form the cement slurry 50.

[0022] In embodiments, the graphene 10 does not comprise or does not consist of a synthetic graphene. According to embodiments of this disclosure, the graphene 10 can comprise bioderived renewable graphene (BRG). In embodiments, the BRG comprises graphene 10 derived from a plant. In embodiments, the BRG comprises graphene 10 derived from a carbohydrate. For example, in embodiments, the carbohydrate comprises cassava (e.g., cassava root), corn (e.g., corn grain, corn flour), sugar cane (e.g., sucrose), and/or rice (e.g., rice grain), and the graphene 10 comprises graphene derived from cassava, corn, and/or rice. The BRG can comprise graphene with a fused sheet-like morphology (e.g., graphene nanosheets, referred to herein as “nanosheets”). Sheet-like indicates stratified, deposited, or arranged in horizontal layers. For example, such BRG derived from cassava and comprising graphene nanosheets is described in U.S. Patent Publication No. 2021/0061661, U.S. Patent Publication No. 2021/0238040, and U.S. Patent Publication No. 2019/0144280, the disclosure of each of which is hereby incorporated herein in its entirety for purposes not contrary to this disclosure. In embodiments, the graphene 10 comprises BRG such as described in the aforementioned patent applications and/or obtained from SurgePower Materials, Inc., New Braunfels, TX.

[0023] In embodiments, graphene 10 comprises a carbon nanosheet with distinct properties that can be produced from a renewable carbonaceous raw materials such as, without limitation, cassava root extract, corn flour, rice grain, wheat flour, yam root extract, potatoes root extract, sugar beet roots extract and sucrose (generally referred to herein as carbohydrates). The process for making carbon nanosheet from these carbohydrates can be as follows.

[0024] First, the aforementioned carbohydrate can be placed in a solvent, such as a solvent containing water or ethylene glycol or ethanol, to aid hydrolysis. This can be followed by gradual removing of glycosidic linkages in the carbohydrate via chemical and/or thermal activation. This pre-treatment step causes formation of intermediate fused carbon material, which contains limited amount of glycosidic bonds, hydroxyl and carbonyl groups. Chemicals that can be effective include, without limitation, sodium hydroxide, hydrochloric acid, phosphoric acid, phosphorous acid, and nitric acid. In addition, catalyst such as yeast, aluminum-nickel alloy, cobalt, BaHe, zinc, and copper can be employed.

[0025] The mixture of carbonaceous material and chemical and/or catalyst can be exposed to approximately 45 to 1050° C, in air or inert atmosphere to aid formation of a fused carbon network with a sheet-like morphology, referred to herein as an intermediate carbon material .

[0026] Another step can include thermochemical activation of the intermediate carbon based material to initiate chemical bonding of carbon atoms to form a hexagonal planar network of mainly sp2 hybridization carbons. This occurs by at least switching oxygen atom and releasing hydroxyl portion of said intermediate carbon material to result in a short range or long range of aromatic ring structure or a mixture of both within the sheet that is retained and other groups or molecules are released. This step can be performed at temperature in the range of 500 to 1500° C, in an inert gas containing hydrogen gas, in embodiments, and can result in a network of high surface area and pore volume sp2 bonded carbon nanosheet.

[0027] The resulting carbon nanosheet powders can be washed with up to 10 volume percent hydrochloric acid (HC1) to remove any remaining precursors and catalyst in the final product, and can be followed by heat treatment at 700 to 1500° C, for example in inert atmosphere.

[0028] Alternatively or additionally, the step of treating the intermediate carbon product to form mainly sp2 hybridization carbons can be accomplished via chemical process. Such process can include, without limitation, treating the intermediate carbon product with a chemical, such as a chemical chosen from the group of hydrazine, LiAlFU, B2H6, and/or NaBH/g in embodiments, hydrazine, and in other embodiments NaBHfi.

[0029] As mentioned above, the process of producing carbon nanosheets can begin with a renewable carbonaceous raw material, such as cassava root extract, corn flour, rice grain, wheat flour, or sucrose. These renewable carbonaceous materials contain a high content of carbohydrates on a water free basis, typically more than 70% by weight. The renewable carbonaceous material can contain various percentages of glucose, and fructose bonded together by glycosidic linkages to form polymeric units such as amylase and amylopectin. Although the molecular formula for glucose and fructose are the same, thus (CsIfeOe), they have different molecular structures.

[0030] In order to obtain a carbon nanosheet, each carbohydrate unit can be pre-treated with a dehydration solution, for example containing at least 1 % of acid or catalyst. The pretreatment can result in an intermediate carbon material with dark-grey color made up of fused sheet-like morphology.

[0031] The mechanism can unfold in two stages. First, the treatment of the carbohydrate via chemical and/or thermal activation can result in hydrolysis and removal of the glycosidic linkages in the polymeric carbohydrate unit to form individual glucose and fructose units. This can be followed by a second mechanism to remove water molecules from each of glucose or fructose units by a dehydration solution. The pretreatment can be accomplished by gradual heating of the carbohydrate and hydration solution, for example at 45 to 1050° C, preferably 80° C, e.g., for up to 36 hours or more. In the process, the carbon atoms can rearrange to form a ring with neighboring carbon atoms. The hydration solution can cause intercalation of the layers of carbon after ring formation, thus giving rise to a layered structure.

[0032] The intermediate carbon product can undergo a second treatment to exfoliate the intercalated carbon layers. Several thermal and/or chemical methods can be used to exfoliate the carbon sheet. Thermal methods include direct heating of the intermediate carbon material. Radiant heating in a resistive furnace, or on top of a hotplate, laser irradiation and microwave irradiation can be effective for exfoliating carbon nanosheet and removal of water molecules to form mainly sp2 bonded carbon nanosheets.

[0033] Thermal exfoliation via microwave heating can remove substantial amount of HiO molecules from the intermediate carbon materials, with a reduction in oxygen content from the intermediate carbon materials, for example from 39.5 to 14.6 weight percent,

[0034] Exfoliated carbon nanosheets can be washed (e g., with a 10 volume percent HC1) to remove remaining hydration solution and/or catalyst compounds. Subsequently, the resulting product can be washed with de-ionized water one or several times, for example until the pH is about 7 The resulting material can be thermally treated at high temperature in inert atmosphere to remove any groups attached to the nanosheet and terminate the ends with hydrogen. The carbon nanosheets can have a sheet-like morphology, and carbon composition can be up to 90, 91, 92, 93, or 94 weight percent or more.

[0035] In an alternate method of producing carbon nanosheets, the carbohydrate can be soaked in dehydration solution, as previously discussed. The mixture can be directly exposed to rapid and uniform high temperature heating immediately after thorough and uniform mixing. This can cause removal of glycosidic bonds and release of water molecules, thereby forcing the resulting intermediate carbon materials to exfoliate into carbon nanosheet. Specifically, heating can be accomplished by microwave irradiation and/or heating in an oven preheated, for example, to at least 500° C, to yield the carbon nanosheet.

[0036] In other embodiments, after thorough and uniform mixing of said carbohydrate and dehydration solution (e.g., containing excess deionized water), this mixture can be slowly heated to temperature below 100° C, and held there a time of, for example, less than 24 hours. The mixture can form a dark colored intermediate solution containing carbon. The dark intermediate solution can be coated on a substrate to form thin films. The resulting films can be exposed to high temperatures in inert atmosphere containing, for example, at least 2% by volume hydrogen gas. The films can be slowly heated, for example in the range of 700- 1500° C, to form a thin layer of conducting carbon nanosheet on a substrate. The substrate can include, for example, copper foil, silicon wafer, glass slide or a quartz substrate.

[0037] In embodiments, a process for forming the nanosheets can comprise providing a renewable carbohydrate source to a reactor comprising a solvent to obtain a soaked or dissolved carbohydrate source; adding a dehydration solution and a catalyst to the reactor comprising the soaked or dissolved carbohydrate source to obtain a reaction mixture, e.g., where the dehydration solution has a hydrogen ions concentration of at least approximately 1 %; charging said reactor with air or inert gas; heating the reaction mixture to remove glycosidic linkages and water molecules from the carbohydrate, thereby producing an intermediate mixture with sheet-like morphology; and further heating the intermediate mixture in inert gas to form the carbon nanosheet material. The carbon nanosheet material can be in the form of a powder. The carbohydrate source can comprise yam root extract, potato root extract, cassava root extract, cassava root flour, tapioca flour, dried cassava root pulp, dried and fried cassava root flakes, sugarcane extract, sugar beet root extract, sucrose, rice grain, corn, or wheat grain.

[0038] In embodiments, the solvent can be chosen from distilled water, deionized water, ethanol, and ethylene glycol. In embodiments, the dehydration solution can be chosen from sodium hydroxide, hydrochloric acid, phosphoric acid, phosphorous acid, and nitric acid. In embodiments, the process further comprises removing the dehydration solution by washing and diluting with excess distilled or deionized water prior to further heating of the intermediate mixture.

[0039] The catalyst can be chosen from platinum, palladium, LiAIEU, nickel, yeast, aluminumnickel alloy, cobalt, BjHe, zinc, NaBJB, copper, or combinations thereof. The process can further include removing the catalyst by washing, filtering, magnetic separation, sonication, sieving, and/or centrifugation prior to further heating of the intermediate mixture.

[0040] The heating of the reaction mixture can be carried out in air or inert gas, for example at approximately 45 to 1050° C. The process can further include, prior to further heating the intermediate mixture, drying the intermediate mixture to produce an intermediate mixture in form of a powder; wherein the intermediate mixture in form of powder is heated in the inert gas, for example at approximately 500 to 1500° C, to produce the carbon nanosheet material. The inert gas can comprise, for example, argon, helium, or nitrogen, and can optionally further comprise a partial pressure of hydrogen gas. The intermediate mixture can be heated to a temperature of approximately 45 to 1050° C.

[0041] The carbon nanosheet material can have a specific surface area of at least 2000, 2100, 2200, 2300, 2400, or 2496 m ² /g and/or a pore volume of at least 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, or 3.6 cc/g. The carbon nanosheet material can have a pore volume of up to 3.0, 4.0, or 5.0 cc/g.

[0042] Cementitious material 30 (also referred to herein simply as “cement” 30) can comprise a cement powder, such as, without limitation, a Portland cement. A variety of cementitious materials 30 can be used in the cement slurry 50, including cements comprised of calcium, aluminum, silicon, oxygen, and/or sulfur which set and harden by reaction with water. Such hydraulic cements include Portland cements, gypsum cements, high alumina content cements, slag cements, high magnesia content cements, shale cements, acid/base cements, fly ash cements, zeolite cement systems, kiln dust cement systems, microfine cements, metakaolin, pumice and their combinations. In embodiments, cementitious material 30 comprises a Type I, IA, II, IIA, III, IIIA, IV, V, VI, or VII Portland cement, or a combination or subtype thereof, such as, for example, a Type IL (e.g., limestone) cement powder, as defined in the ASTM standard (e.g., ASTM C150). In embodiments, cementitious material 30 comprises a non- API cement. In embodiments, cementitious material 30 comprises an API cement, such as, for example, an API cement from Class A, B, C, D, E, F, G, H, K, and/or L, such as, for example, a Portland cementitious material 30 from one or more of Classes A, C, H, and G.

[0043] In embodiments, cement 50 can comprise a construction grade cementitious material 30. According to this disclosure, a construction grade cement is a non-API cement, such as a cementitious powder 30 comprising greater than about 1% by weight of calcium aluminate, C3A. In embodiments, the cementitious material 30 has an aluminate content (e g., C3A) in a range of from about 1 to about 30, from about 3 to about 20, from about 5 to about 15, or greater than or equal to about 1, 3, or 5 percent aluminate by mass of cementitious material 30.

[0044] The cement slurry 50 of this disclosure can contain one or more additives. In embodiments, the additives comprise one or more selected from resins, latex, stabilizers, silica, pozzolans, microspheres, aqueous superabsorbers, viscosifying agents, suspending agents, dispersing agents, salts, accelerants, surfactants, retardants, defoamers, settling-prevention agents, weighting materials, fluid loss control agents, elastomers, vitrified shale, cement kiln dust, gas migration control additives, formation conditioning agents, or combinations thereof.

[0045] Water 20 can comprise an aqueous base fluid. An aqueous base fluid 20 can be present in the cement slurry 50 in an amount sufficient to make a slurry which is pumpable for introduction to a desired location in a workspace, for example, down hole, in embodiments. In embodiments, the aqueous base fluid or water 30 comprises fresh water; brackish water; saltwater; or a combination thereof. In embodiments, the water 20 can be present in the cement slurry 50 in an amount of from about 20% to about 80% by weight of cementitious material 30 ("bwoc"), from about 28% to about 60% bwoc, or from about 36% to about 66% bwoc.

[0046] As noted hereinabove, the cement slurry 50 can have an increased thickening time relative to a same cement slurry absent the set retarder 5 comprising graphene 10. In embodiments, a thickening time at 70 Beardon Consistency Units (Be), as measured according to API 10B-2 of the cement slurry 50 is increased relative to a same cement slurry absent the set retarder 5 comprising graphene (e g., BRG) 10. The thickening time can be increased by at least 10, 50, 75, 100, 200, 500, or 1000 percent relative to the same cement slurry absent the graphene 10.

[0047] In embodiments, the cement slurry 50 can have a slurry density which is pumpable for introduction down hole. In embodiments, the density of the cement slurry 50 is from about 7 pounds per gallon (ppg) to about 20 ppg, from about 10 ppg to about 18 ppg, or from about 13 ppg to about 17 ppg.

[0048] Also provided herein is a method of forming cement slurry 50 having graphene 10 as set retarder 5. The method can enable adjusting of a set time of the cement slurry 50 via the use of graphene 10 as set retarder 5. The method will now be described with reference to FIG. 2, which is schematic flow diagram of a method 100, according to embodiments of this disclosure. Method 100 of making the cement slurry 50, that utilizes graphene 10 as a set retarder 5, comprises, combining the set retarder 5 comprising graphene 10 and cementitious material 30 with water 20 to provide the cement slurry 50. Tn embodiments, as depicted at 110, set retarder 5 comprising graphene 10 is combined with water 20 to provide a mix water 40, and, at 120, the mix water 40 is combined with the cementitious material (e.g., cement powder) 30 to provide the cement slurry 50. Alternatively or additionally, graphene 10 can be otherwise incorporated into cement slurry 50. For example, in embodiments, graphene 10 can be dry blended into cement slurry 50. As depicted in FIG. 2, Method 100 can further include, at 130, placing (e.g., pumping) the cement slurry 50 into a workspace.

[0049] As depicted in FIG. 1, lines 15, 25, and 35 can be utilized to combine set retarder 5 comprising graphene 10, water 20, and cementitious material 30, respectively. Alternatively or additionally, lines 15A and 25 A can be utilized to combine set retarder 5 comprising graphene 10 with water 20 to provide mix water 40, and lines 40A and 35 can be utilized to combine the mix water 40 and cementitious material 30 to provide the cement slurry 50. The order of combination of the set retarder 5 comprising graphene 10, water 20, and cementitious material 30 can be adjusted, and remain within the scope of this disclosure.

[0050] As described hereinabove, the graphene 10 can comprise bioderived renewable graphene (BRG), such as, without limitation, BRG comprising graphene derived from a plant, such as the cassava plant. The BRG can comprise graphene with a fused sheet-like morphology (e.g., graphene nanosheets), such as the graphene 10 described in U.S. Patent Publication No. 2021/0061661, U.S. Patent Publication No. 2021/0238040, and/or U.S. Patent Publication No. 2019/0144280, incorporated hereinabove by reference. Without being limited by theory, BRG can provide enhanced results relative to non-bioderived graphene due to characteristics of the BRG provided by the production thereof.

[0051] The cement slurry 50 can be a cement slurry 50 as described hereinabove. For example, the cement slurry 50 can comprise from about 0.01 to about 20, from about 0.1 to about 15, from about 0.5 to about 5, or greater than or equal to about 0, 0.1, or 0.5 and less than or equal to about 20, 15, or 5 percent set retarder 5 comprising graphene 10 (e.g., BRG) by weight of cementitious material 30 (% BRG bwoc).

[0052] As noted above, the cementitious material 30 can comprise a Portland cement, such as, for example, a Type I, IA, II, IIA, III, IIIA, IV, V, VI, or VII Portland cement, a subtype thereof, or a combination thereof. In embodiments, the cementitious material 30 comprises a construction grade (e g., non-API) cement, as described herein. The construction grade cement can be a cement comprising greater than about 1 weight percent (wt%) calcium aluminate (C3A). Tn embodiments, the cementitious material 30 comprises an API grade cement (e.g., API grade A, B, C, D, E, F, G, K, L or H cement).

[0053] The cement slurry 50 can have an increased thickening time relative to a same cement slurry absent the graphene 10 containing set retarder 5, as noted hereinabove.

[0054] Also disclosed herein is a method of using the cement slurry 50 of this disclosure, wherein set retarder 5 comprising graphene 10 is employed. Such a method will now be described with reference to FIG. 3, which is a schematic flow diagram of a method 200, according to embodiments of this disclosure. Method 200 comprises: providing a cement slurry 50 of this disclosure at 210, placing the cement slurry 50 in a workspace at 220, and allowing the cement slurry 50 to set to provide a hardened cement (also referred to herein as a “set” cement) at 230. The cement slurry can be a cement slurry 50 as described hereinabove with reference to FIG. 1 and/or made as described hereinabove with reference to FIG. 2, wherein the cement slurry 50 comprises set retarder 5 comprising graphene 10 (e.g., BRG), a cementitious material 30, and water 20. In embodiments, the cement slurry 50 an increased thickening time relative to a same cement slurry absent the graphene 10.

[0055] The workspace can comprise an oilwell workspace, such as, for example and without limitation, a subterranean workspace, such as a wellbore. In embodiments, the workspace comprises a non-oilwell workspace, such as, for example and without limitation, a construction site, roadway repair, tunnel/mining, bridges, etc. The placing of the cement slurry 50 can be effected during a primary cementing operation, or another cementing application, in an oil and gas or non-oil and gas operation.

[0056] As detailed hereinabove, the graphene 10 can comprise bioderived renewable graphene (BRG), such as graphene 10 derived from a plant, such as, without limitation, the cassava plant. The BRG can comprise graphene nanosheets, in embodiments. Such BRG is described in U.S. Patent Publication No. 2021/0061661, U.S. Patent Publication No. 2021/0238040, and U.S. Patent Publication No. 2019/0144280, which are incorporated herein by reference hereinabove.

[0057] As noted hereinabove, the cement slurry 50 can comprise from about 0.01 to about 20, from about 0.1 to about 15, from about 0.5 to about 5, or greater than or equal to about 0, 0.1, or 0.5 and less than or equal to about 20, 15, or 5 percent graphene (e.g., BRG) by weight of cementitious material 30 (% BRG bwoc).

[0058] As noted above, in embodiments, the cementitious material 30 comprises a Portland cement, such as a Type I, IA, II, IIA, III, IIIA, IV, V, VI, or VII Portland cement, a subtype thereof, or a combination thereof. In embodiments, the cementitious material 30 comprises a construction grade (e.g., non-API) cement, wherein, as described hereinabove, a construction grade cement is a cement comprising greater than about 1 wt% calcium aluminate (C3A). As noted above, in embodiments, the cementitious material 30 comprises an API grade cement (e.g., API grade A, B, C, D, E, F, G, or H cement).

[0059] By way of non-limiting example, the exemplary cement slurries 50 disclosed herein may be employed in an oilwell workspace. For example, a cement slurry 50 can be deployed at the workspace via any methods known in the art and with the help of this disclosure. For example, cement slurry 50 can be introduced downhole via a cementing apparatus.

[0060] FIG. 4 shows an illustrative schematic of cementing workspace or system 300 that can deliver cement slurry 50 of the present disclosure to a downhole location, according to one or more embodiments. It should be noted that while FIG. 4 generally depicts a land-based system, it is to be recognized that like systems may be operated in subsea locations as well. As depicted in FIG. 4, system 300 may include mixing tank 310, in which a cement slurry 50 of the present disclosure may be formulated. Again, in some embodiments, the mixing tank 310 may represent or otherwise be replaced with a transport vehicle or shipping container configured io deliver or otherwise convey the final cement slurry to the well site The cement slurry 50 may be conveyed via line 312 to wellhead 314, where the cement slurry 50 enters tubular 316 (e.g., a casing, drill pipe, production tubing, coiled tubing, etc.), tubular 316 extending from wellhead 314 into wel Shore 322 penetrating subterranean formation 318. Upon being ejected from tubular 316, the cement slurry 50 may subsequently return up the wellbore in the annulus between the tubular 316 and the wellbore 322 as indicated by flow lines 324. In other embodiments, the cement slurry 50 may be reverse pumped down through the annulus and up tubular 316 back to the surface, without departing front the scope of the disclosure. Pump 320 may be configured to raise the pressure of the cement slurry to a desired degree before its introduction into tubular 316 (or annulus). It is to be recognized that system 300 is merely exemplary in nature and various additional components may be present that have not necessarily been depicted in FIG 4 in the interest of clarity. Non-limiting additional components that may be present include, but are not limited to, supply hoppers, valves, condensers, adapters, joints, gauges, sensors, compressors, pressure controllers, pressure sensors, flow rate controllers, flow rate sensors, temperature sensors, and the like. Moreover, reverse cementing, where the final cement slurry is directly placed in the annulus between the tubular 316 and the wellbore 322 may also be performed in accordance with the embodiments described herein, without departing from the present disclosure.

[0061] One skilled in the art, with the benefit of this disclosure, should recognize the changes to the system described in FIG. 4 to provide for other cementing operations squeeze operations, reverse cementing (where the cement is introduced into an annulus between a tubular and the wellbore and returns to the wellhead through the tubular), and the like.

[0062] It is also to be recognized that the disclosed cement slurries 50 may also directly or indirectly affect the various downhole equipment and tools that may come into contact with the final cement slurry during operation. Such equipment and tools may include, but are not limited, to, wellbore casing, wellbore liner, completion string, insert strings, drill siring, coiled tubing, slickline, wireline, drill pipe, drill collars, mud motors, downhole motors and/or pumps, surface- mounted motors and/or pumps, centralizers, turbolizers, scratchers, floats (e.g., shoes, collars, valves, etc ), wellbore projectiles (e.g., wipers, plugs, darts, balls, etc.), logging tools and related telemetry equipment, actuators (e.g., electromechanical devices, hydromechanical devices, etc.), sliding sleeves, production sleeves, plugs, screens, filters, flow control devices inflow control devices, autonomous inflow control devices, outflow control devices, etc.), couplings (e.g , electro-hydraulic wet connect, dry connect, inductive coupler, etc.), control lines (e.g., electrical, fiber optic, hydraulic, etc. ), surveillance lines, drill bits and reamers, sensors or distributed sensors, downhole heat exchangers, valves and corresponding actuation devices, tool seals, packers, cement plugs, bridge plugs, and other wellbore isolation devices, or components, and the like. Any of these components may be included in the systems generally described above and depicted in FIG. 4.

[0063] Upon setting, the hardened cement produced from cement slurry 50 can have a compressive strength, a tensile strength, a Young’s modulus, a Poisson’s ratio, or a combination thereof that is at least as high as a compressive strength, a tensile strength, a Young’s modulus, a Poisson’s ratio, or a combination thereof of a hardened cement produced from a same cement slurry absent the graphene (e g., absent the BRG) and optionally comprising a different set retarder. [0064] In embodiments, graphene (e.g., BRG) can be utilized as a suspension aid in a cement slurry 50 of this disclosure, for example, as described in U.S. Patent Application No. **/*** *** (4727-37900), entitled, “Graphene Fluid Utilized to Suspend Particulates”, the disclosure of which is hereby incorporated herein in its entirety for purposes not contrary to this disclosure; graphene (e.g., BRG) can be utilized to mitigate transient gels in a cement slurry 50 of this disclosure, for example, as described in U.S. Patent Application No. **/***,*** (4727-38100), entitled, “Mitigation of Transient Gels in Cement”, the disclosure of which is hereby incorporated herein in its entirety for purposes not contrary to this disclosure; and/or graphene (e.g., BRG) can be utilized to enhance stability and density control in a cement slurry 50 of this disclosure, for example, as described in U.S. Patent Application No. **/***,*** (4727-38200), entitled, “ Use of Graphene To Enhance Stability and Density Control of Cement Slurries”, the disclosure of which is hereby incorporated herein in its entirety for purposes not contrary to this disclosure.

[0065] Unexpectedly, graphene 10 can be utilized as described herein to delay the thickening time of cement slurries 50, and can thus be utilized, as detailed herein, as a novel cement retarder 5.

[0066] The system and method of this disclosure can provide one or more of the following: (1) graphene 10 can be utilized as set retarder 5 to retard setting of a cement slurry; (2) graphene 10 can be utilized, as described herein, to impart enhanced mechanical properties of the hardened cement; (3) graphene 10 can be utilized, as described herein, as described herein, to act as a suspending aid to further stabilize the slurries 50, rather than dispersing the cement slurries 50; and/or (4) graphene 10 can be utilized as described herein at ultra high temperatures (e.g., greater than or equal to about 1000°C). Accordingly, in embodiments, the system and method of this disclosure enable the use of graphene 10 as a multifunctional cement additive for retarding the setting of a cement slurry 50, enhancing the mechanical properties of the resulting hardened cement, stabilizing the cement slurry 50, and/or exhibiting ultra-high temperature resistance.

[0067] Other advantages will be apparent to those of skill in the art and with the help of this disclosure.

EXAMPLES

[0068] The embodiments having been generally described, the following examples are given as particular examples to demonstrate the practice and advantages of this disclosure. It is understood that the examples are given by way of illustration and are not intended to limit the specification or the claims in any manner.

Example 1: Thickening Time

[0069] To exemplify the retardation properties of bioderived renewable graphene (BRG) in cement slurries 50, four cement slurries 50 were first prepared following the formulations below in Table 1. Slurry 1 contained no BRG for use as a control and Slurries 2, 3 and 4 comprised successively higher loadings of BRG.

[0070] Each of the cement slurries 50 was prepared and blended according to standard API procedure and placed in a consistometer to measure the thickening time. Thickening times were measured with a consistometer at a bottom hole temperature and pressure of 80 °F and 3000 psi. The procedure is specified in API Recommended Practice 10B-2 (2013) “Recommended Practice for Testing Well Cements” Section 9. Common practice is to consider 70 Be as the point at which the slurry will be gelled enough that it can no longer be pumped. The following thickening times are therefore reported as the time from when temperature and pressure is applied to the slurry until the end point of 70 Be.

[0071] Table 2 shows that increasing the amount of BRG in the cement slurry 50 also increased the thickening time. This indicates that BRG was functioning as a cement set retarder 5 by preventing the gelation and thickening of cement slurries 50 for an amount of time dependent on the concentration of BRG graphene 10 in the slurry. FIG. 5 is a plot of thickening time as a function of BRG content, according to the data of Table 2.

[0072] FIG. 5 shows that increasing the BRG content up to about 0.7 % by weight of cement (bwoc) shows a fairly linear response in the increase of thickening time. After 0.7 % bwoc, the thickening time increases dramatically compared to lower BRG content and the control slurry 1 with no BRG. This indicates that BRG makes an operable cement retarder 5 for wellbore cements.

[0073] As can be ascertained from the data below in Table 3, a secondary effect of the BRG cement retarder 5 is the general increase of mechanical properties of the set cement. The cement blends were mixed according to API specifications and cured at 170 °F and 3000 psi for 7 days prior to mechanical properties testing

[0074] The compressive and tensile strengths showed a general increase with the increasing amounts of graphene, with the exception of the tensile strength for Slurry 3, which may have been an anomalous result. Interestingly, Young’s modulus improved relative to compressive strength, while Poisson’s ratio was unaffected.

Example 2: Retarding Effect

[0075] As an example of the retarding effectiveness of the graphene, as described herein, two thickening time tests were performed. The first was a control slurry composed of Class H cement and water, and the second was a cement slurry 50 which contained 0.7 %BWOC graphene 10, as per this disclosure. Table 4 provides the formulations of the slurries of this Example 2.

[0076] Following API procedures, the slurries were prepared and placed into HPHT Consistometers. The thickening time tests were performed at 180 F and 3000 psi. The results from the tests are shown in FIG. 6, which depicts the thickening time of Control Slurry 1 at 180°F and 3000 psi, and FIG. 7, which depicts thickening time of Graphene Slurry 2 at 180°F and 3000 psi. As can be seen in FIG. 6, the Control Slurry 1 reached 70 Be at about 7.7 hours and in FIG. 7, the Graphene Slurry 2 reached 70 Be in 10.4 hours. This Example 2 showed that the graphene 10 retarded the cement slurry 50 and extended the fluid life by about 25%.

Example 3: Mechanical Property Enhancement

[0077] As an example of the mechanical property enhancement of the cement by graphene 10 as per this disclosure, two slurries were mixed, according to API, using the same formulations as above for Control Slurry 1 and Graphene Slurry 2, as depicted in Table 4. After mixing, the slurries were poured into three 2x5 molds and cured for 72 hours in a water bath at 180°F and ambient pressure. After curing, the samples were de-molded, and the samples were crushed with a Tinius- Olsen load-frame to obtain compressive strength and tensile strength values, that are shown in Table 5. [0078] As can be seen in Table 5, the graphene 10 containing cement slurry 50 (Graphene Slurry 2) resulted in a set cement having a higher compressive and tensile strengths relative to the slurry without graphene (Control Slurry 1).

ADDITIONAL DISCLOSURE

[0079] The following are non-limiting, specific embodiments in accordance with the present disclosure:

[0080] In a first embodiment, a cement slurry comprises: a set retarder comprising graphene, wherein the graphene comprises bioderived renewable graphene (BRG); a cementitious material; and water, wherein the cement slurry comprises from about 0.01 to about 20, from about 0.1 to about 15, or from about 0.5 to about 5 percent graphene by weight of cementitious material (% graphene bwoc), and wherein the cement slurry has an increased thickening time relative to a same cement slurry absent the graphene.

[0081] A second embodiment can include the cement slurry of the first embodiment, wherein the BRG comprises graphene with a fused sheet-like morphology.

[0082] A third embodiment can include the cement slurry of the second embodiment, wherein the BRG comprises graphene derived from a plant.

[0083] A fourth embodiment can include the cement slurry of the third embodiment, wherein the plant comprises cassava.

[0084] A fifth embodiment can include the cement slurry of any one of the second to fourth embodiments, wherein the BRG comprises graphene with a fused sheet-like morphology.

[0085] A sixth embodiment can include the cement slurry of any one of the first to fifth embodiments, wherein a thickening time at 70 Beardon Consistency Units (Be), as measured according to API 10B-2, of the cement slurry is increased relative to a same cement slurry absent the graphene.

[0086] A seventh embodiment can include the cement slurry of the sixth embodiment, wherein the thickening time is increased by at least 10, 100, or 1000 percent relative to the same cement slurry absent the graphene.

[0087] An eighth embodiment can include the cement slurry of any one of the first to seventh embodiments, wherein the set retarder consists of or consists essentially of the graphene.

[0088] A ninth embodiment can include the cement slurry of any one of the first to eighth embodiments, wherein the cementitious material comprises a Portland cement. [0089] A tenth embodiment can include the cement slurry of any one of the first to ninth embodiments, wherein the cementitious material comprises a cement selected from the group consisting of Type I, IA, II, IIA, III, IIIA, IV, V, VI, VII Portland cements, and combinations thereof.

[0090] An eleventh embodiment can include the cement slurry of any one of the first to tenth embodiments, wherein the cementitious material comprises an API grade cement.

[0091] In a twelfth embodiment, a method of making a cement slurry comprises: combining a set retarder comprising graphene with water to provide a mix water, wherein the graphene comprises bioderived renewable graphene (BRG); combining the mix water with a cementitious material to provide the cement slurry, wherein the cement slurry has an increased thickening time relative to a same cement slurry absent the graphene; and pumping the cement slurry into a workspace.

[0092] A thirteenth embodiment can include the method of the twelfth embodiment, wherein the cementitious material comprises a Portland cement.

[0093] A fourteenth embodiment can include the method of any one of the twelfth or thirteenth embodiments, wherein the cementitious material comprises a cement selected from the group consisting of Type I, IA, II, IIA, III, IIIA, IV, V, VI, VII Portland cements, and combinations thereof.

[0094] A fifteenth embodiment can include the method of any one of the twelfth to fourteenth embodiments, wherein the cementitious material comprises an APT grade cement.

[0095] A sixteenth embodiment can include the method of any one of the twelfth to fifteenth embodiments, wherein the BRG comprises graphene nanosheets.

[0096] A seventeenth embodiment can include the method of the sixteenth embodiment, wherein the BRG comprises graphene derived from a plant.

[0097] An eighteenth embodiment can include the method of the seventeenth embodiment, wherein the plant comprises cassava.

[0098] A nineteenth embodiment can include the method of the eighteenth embodiment, wherein the BRG comprises graphene with a fused sheet-like morphology.

[0099] In a twentieth embodiment, a method comprises: providing a cement slurry comprising: a set retarder comprising graphene, wherein the graphene comprises a bioderived renewable graphene (BRG); a cementitious material; and water, wherein the cement slurry comprises from about 0.01 to about 20, from about 0.1 to about 15, or from about 0.5 to about 5 percent graphene by weight of cementitious material (% graphene bwoc); placing the cement slurry in a workspace; and allowing the cement slurry to set to form a hardened cement, wherein the cement slurry has an increased thickening time relative to a same cement slurry absent the graphene.

[00100] A twenty first embodiment can include the method of the twentieth embodiment, wherein the hardened cement has a tensile strength, a Young’s modulus, a Poisson’s ratio, or a combination thereof that is at least as high as a tensile strength, a Young’s modulus, a Poisson’s ratio, or a combination thereof of a hardened cement produced from a same cement slurry absent the BRG and optionally comprising a different set retarder.

[00101] A twenty second embodiment can include the method of any one of the twentieth or twenty first embodiments, wherein the workspace comprises an oilwell workspace.

[00102] A twenty third embodiment can include the method of the twenty second embodiment, wherein the placing of the cement slurry is effected during a primary cementing operation.

[00103] A twenty fourth embodiment can include the method of any one of the twentieth to twenty third embodiments, wherein the workspace comprises a non-oilwell workspace.

[00104] A twenty fifth embodiment can include the method of any one of the twentieth to twenty fourth embodiments, wherein the cementitious material comprises a Portland cement.

[00105] A twenty sixth embodiment can include the method of the twenty fifth embodiment, wherein the cementitious material comprises a cement selected from the group consisting of Type I, IA, II, IIA, III, IIIA, IV, V, VI, VII Portland cements, and combinations thereof.

[00106] A twenty seventh embodiment can include the method of any one of the twentieth to twenty sixth embodiments, wherein the cementitious material comprises an API grade cement.

[00107] A twenty eighth embodiment can include the method of any one of the twentieth to twenty seventh embodiments, wherein the BRG comprises graphene with a fused sheet-like morphology.

[00108] A twenty ninth embodiment can include the method of the twenty eighth embodiment, wherein the BRG comprises graphene derived from a plant.

[00109] A thirtieth embodiment can include the method of the twenty ninth embodiment, wherein the plant comprises cassava. [00110] A thirty first embodiment can include the method of any one of the twenty eighth to thirtieth embodiments, wherein the BRG comprises graphene with a fused sheet-like morphology. [00111] While embodiments have been shown and described, modifications thereof can be made by one skilled in the art without departing from the spirit and teachings of this disclosure. The embodiments described herein are exemplary only, and are not intended to be limiting. Many variations and modifications of the embodiments disclosed herein are possible and are within the scope of this disclosure. Where numerical ranges or limitations are expressly stated, such express ranges or limitations should be understood to include iterative ranges or limitations of like magnitude falling within the expressly stated ranges or limitations (e.g., from about 1 to about 10 includes, 2, 3, 4, etc.; greater than 0.10 includes 0.11, 0.12, 0.13, etc.). For example, whenever a numerical range with a lower limit, Rl, and an upper limit, Ru, is disclosed, any number falling within the range is specifically disclosed. In particular, the following numbers within the range are specifically disclosed: R=R1 +k* (Ru-Rl), wherein k is a variable ranging from 1 percent to 100 percent with a 1 percent increment, i.e., k is 1 percent, 2 percent, 3 percent, 4 percent, 5 percent, 50 percent, 51 percent, 52 percent, , 95 percent, 96 percent, 97 percent, 98 percent, 99 percent, or 100 percent. Moreover, any numerical range defined by two R numbers as defined in the above is also specifically disclosed. Use of broader terms such as comprises, includes, having, etc. should be understood to provide support for narrower terms such as consisting of, consisting essentially of, comprised substantially of, etc. When a feature is described as “optional,” both embodiments with this feature and embodiments without this feature are disclosed. Similarly, the present disclosure contemplates embodiments where this “optional” feature is required and embodiments where this feature is specifically excluded.

[00112] Accordingly, the scope of protection is not limited by the description set out above but is only limited by the claims which follow, that scope including all equivalents of the subject matter of the claims. Each and every claim is incorporated into the specification as embodiments of the present disclosure. Thus, the claims are a further description and are an addition to the embodiments of the present disclosure. The discussion of a reference herein is not an admission that it is prior art, especially any reference that can have a publication date after the priority date of this application. The disclosures of all patents, patent applications, and publications cited herein are hereby incorporated by reference, to the extent that they provide exemplary, procedural, or other details supplementary to those set forth herein.