Graphene nanoplatelets enhanced cement with high mechanical strength enduring high temperatures and high pressures

Abstract

A method includes injecting into a subsurface a cement slurry comprising, a cementitious material; an aqueous carrier; graphene nanoplatelets; about 10 wt% to about 35 wt% of silica based on the weight of the cementitious material; and an additive composition comprising at least one of a defoamer, a dispersant, or a binder; and curing the cement slurry at a temperature of about 75 °F to about 600 °F and a pressure of about 500 psi to about 5,000 psi.

Description

67CM-510341-WO-2 (PPS0130PCT) GRAPHENE NANOPLATELETS ENHANCED CEMENT WITH HIGH MECHANICAL STRENGTH ENDURING HIGH TEMPERATURES AND HIGH PRESSURES CROSS REFERENCE TO RELATED APPLICATIONS This application claims the benefit of U.S. Application No. 18 / 451,384, filed on August 17, 2023, which is incorporated herein by reference in its entirety. BACKGROUND

[0001] Geothermal energy is heat within the earth. The heat can come from the radioactive decay of minerals and / or the heat loss from the earth’s original formation. Geothermal is a renewable and sustainable form of energy since heat can be continuously produced. Geothermal is also an environmentally friendly technology because it produces minimal greenhouse gas emissions.

[0002] The production of geothermal energy involves drilling wells into the earth’s crust, and extracting the heat with various methods, for example, using water and steam. Hot water from the earth may be used to heat homes and buildings. Steam generated by geothermal heat can be used to produce electricity in a geothermal power plant when the steam spins turbines on a generator.

[0003] While geothermal energy has a lot of potential, it faces challenges that need to be addressed to enhance the contribution of geothermal energy. Cementing wellbores for geothermal heat harvesting is one such challenge. Geothermal well cementing is demanding because during heat harvesting, there can be repeated heating and cooling cycles in geothermal wells from the repetitive process of shut-in and production, and such dynamic thermal cycles can impose lots of thermal stress on the cement. Geothermal wells can also have high-temperature zones and / or high-pressure areas, which can cause strength retrogression of the cement. Accordingly, there is a continuing need in the art for cementing methods and materials that are suitable for use in high-temperature and high-pressure environments. It would be a further advantage if the methods and materials can provide a cemented wellbore having improved integrity for hydrothermal power, oil and gas, as well as geothermal applications, optionally when exposed to dynamic thermal cycles. BRIEF DESCRIPTION

[0004] A method includes injecting into a subsurface a cement slurry including, a cementitious material; an aqueous carrier; graphene nanoplatelets; about 10 wt% to about 3567CM-510341-WO-2 (PPS0130PCT) wt% of silica based on the weight of the cementitious material; and an additive composition comprising at least one of a defoamer, a dispersant, or a binder; and curing the cement slurry at a temperature of about 75oF to about 600oF and a pressure of about 500 psi to about 5,000 psi.

[0005] A cement slurry includes: a cementitious material; an aqueous carrier; graphene nanoplatelets; about 10 wt% to about 35 wt% of silica based on the weight of the cementitious material; and an additive composition comprising at least one of a defoamer, a dispersant, or a binder. DETAILED DESCRIPTION

[0006] The inventor has found that using a small amount of graphene nanoplatelets in a cement with reduced silica content and fewer additives in lower quantities provides a stable cement that can withstand subsurface stresses under high dynamic temperatures and pressures. In particular, the cement slurry with the graphene nanoplatelets can be cured under high-temperature and high-pressure conditions, providing a cement that can withstand the demanding force loads thus having a long-term stability and integrity. As the cement uses less silica and fewer additives with lower quantities, the cementing method and cement slurry can provide improved performance with reduced cost.

[0007] The graphene nanoplatelets, as disclosed herein, are effectively two- dimensional particles of nominal thickness, having a stacked structure of one or more layers of fused hexagonal rings with an extended delocalized pi-electron system, layered and weakly bonded to one another through pi - pi stacking interaction.

[0008] The graphene nanoplatelets can have a largest surface area of about 500 to about 2,000 square meters per gram (m2 / g), preferably about 800 to about 1,500 m2 / g, more preferably about 800 to about 1,200 m2 / g.

[0009] The graphene nanoplatelets can be formed by exfoliation from a graphite source. Exemplary exfoliation methods include fluorination, acid intercalation, acid intercalation followed by thermal shock treatment, and the like. It will be appreciated that exfoliation of a graphite may provide the graphene nanoplatelets as a single sheet only one molecule thick, or as a layered stack of relatively few sheets. In an aspect, the graphene nanoplatelets have fewer than 10 single sheet layers, specifically fewer than 8 single sheet layers, more specifically about 3 to about 6 single sheet layers. The graphene nanoplatelets can have a thickness of about 1 to about 10 nanometers (nm) or about 2 to about 8 nm.67CM-510341-WO-2 (PPS0130PCT)

[0010] The graphene nanoplatelets can have a carbon purity of greater than greater than 80%, greater than 85%, greater than 90%, greater than 95%, greater than 98%, or greater than 99%, and preferably greater than 99.5%. Preferably, the graphene nanoplatelets do not contain graphene oxide, and the graphene nanoplatelets are not functionalized with any functional group.

[0011] The content of the graphene nanoplatelets in the cement slurry can be about 0.05 wt% to about 0.5 wt%, preferably about 0.08 wt% to about 0.3 wt%, and more preferably about 0.09 wt% to about 0.2 wt%, or about 0.1 wt%, by weight of the cementitious material.

[0012] Preferably the graphene nanoplatelets are blended with other components of the cement slurry as a dispersion of the graphene nanoplatelets in a liquid such as water. Such a dispersion is also referred to as a “graphene dispersion.” The concentration of the graphene nanoplatelets in the graphene dispersion can be from about 1 wt% to about 15 wt%, preferably from about 2 wt% to about 10 wt%, and more preferably from about 3 wt% to about 8 wt%, based on the total weight of the graphene dispersion. The graphene dispersion (about 0.5 wt% to about 5 wt% or about 1 wt% to about 4 wt% for example based on the weight of the cementitious material) can be blended with the cementitious material, the aqueous carrier, the silica, and the additive composition to make the cement slurry.

[0013] In addition to the graphene nanoplatelets, the cement slurry further comprises a cementitious material. The cementitious material can be a material that sets and hardens by reaction with water and is suitable for forming a set cement downhole. Suitable cementitious materials can be those typically employed in a wellbore environment, for example those comprising calcium, magnesium, barium, aluminum, silicon, oxygen, and / or sulfur. Such cementitious materials include, but are not limited to, Portland cements, pozzolan cements, gypsum cements, high alumina content cements, silica cements, and high alkalinity cements, or combinations of these. Portland cements are particularly useful. In an aspect, the cementitious material can include some but not all the required components of a Portland cement. The cementitious material can also include precursors such as calcium sulfate and fly ash. Preferably the cementitious material is a Class G or Class H cement as defined by American Petroleum Institute, API Specification for Materials and Testing for Well Cements.

[0014] The cement slurry further comprises an aqueous carrier. The aqueous carrier can be fresh water or a brine (including seawater). It will be appreciated that other polar liquids such as alcohols and glycols, alone or together with water, can be used in the aqueous carrier. Preferably, the cement slurry comprises the aqueous carrier such as water in an amount of about 30 wt% to about 65 wt%, preferably in an amount of about 40 wt% to about 55 wt% or about67CM-510341-WO-2 (PPS0130PCT) 45 wt% to about 50 wt%, and more preferably in an amount of about 45 wt% to about 48 wt%, based on the weight of the cementitious material in the cement slurry.

[0015] The cement slurry also comprises silica in an amount of about 10 wt% to about 35 wt%, about 10 wt% to about 30 wt%, or about 10 wt% to about 25 wt%, preferably about 12 wt% to about 23 wt%, and more preferably about 15 wt% to about 20 wt%, based on the weight of the cementitious material in the cement slurry. Without the graphene nanoplatelets, a cement slurry needs to include about 45 wt% to about 55 wt% of silica based on the weight of the cementitious material in order to provide a cement having the desired compressive strength when used at a high temperature of about 600oF. The inventor surprisingly found that using a small amount of graphene nanoplatelets can reduce the amount of the silica to 35 wt% or less, 30 wt% or less, or 25 wt% or less, yet the cement has comparable or even improved performance as compared to the cement containing higher amounts of silica but without graphene nanoplatelets. As used therein, the silica can include fumed silica, silica flour, α quartz, or a combination comprising at least one of the foregoing. The silica can be in a liquid form, for example, a liquid dispersion of silica can be combined with the cementitious material, the graphene nanoplatelets, and the additive composition to make the cement slurry.

[0016] Including a small amount of graphene nanoplatelets in the cement slurry can also reduce the total number of the additives used and / or lower the amounts of the additives used. The cement slurry can comprise an additive composition which includes at least one, at least two, or all of a dispersant, a defoamer, or a binder (also referred to as a “bonding agent”).

[0017] The dispersant can include polynaphthalene sulphonates, naphthalene sulfonate formaldehyde condensates, acetone formaldehyde sulfite condensates, glucan delta lactone derivatives, sulfonated styrene maleic anhydride copolymer, sulfonated vinyltoluene maleic anhydride copolymer, sulfonated acetone condensed with formaldehyde, allyloxybenzene sulfonate, lignosulfonates, melamine sulfonates, sulfonated melamine formaldehyde condensates, urea formaldehyde-based dispersants, polycarboxylate, polyaspartate, oligomeric dispersants, or a combination comprising at least one of the foregoing. As used herein the described dispersants include the corresponding salt forms. As an example, polynapthalene sulphonates are available as sodium and / or calcium salts. Other dispersants can also be used depending on the application of interest. The content of the dispersant in the cement slurry can be greater than zero to less than 1 wt%, preferably about 0.1 wt% to about 0.5 wt%, more preferably about 0.25 wt% to about 0.28 wt%, based on the weight of the cementitious material in the cement slurry.

[0018] The defoamer can include polysiloxanes, paraffinic oils, mineral oils, vegetable67CM-510341-WO-2 (PPS0130PCT) oils, alcohols, or a combination comprising at least one of the foregoing. The content of the defoamer in the cement slurry can be greater than zero to less than 1 wt%, preferably about 0.01 wt% to about 0.5 wt%, more preferably about 0.05 wt% to about 0.2 wt%, or about 0.1 wt% to about 0.15 wt%, based on the weight of the cementitious material in the cement slurry.

[0019] The binder can include clays such as hydrous aluminum silicates (e.g., bentonite (85% mineral clay smectite)), and pozzolan (finely ground pumice of fly ash). The content of the binder in the cement slurry can be greater than zero to less than 1 wt%, preferably about 0.1 wt% to about 0.9 wt%, more preferably about 0.5 wt% to about 0.9 wt%, or about 0.7 wt% to about 0.9 wt%, based on the weight of the cementitious material in the cement slurry.

[0020] An example of the cement slurry can comprise, based on the weight of the cementitious material, about 45 wt% to about 50 wt% of the aqueous carrier; about 0.08 to about 0.15 wt% of graphene nanoplatelets; about 10 wt% to about 25 wt% of the silica; about 0.05 wt% to about 0.2 wt% of the defoamer comprising polysiloxanes, paraffinic oils, mineral oils, vegetable oils, alcohols, or a combination comprising at least one of the foregoing; about 0.1 wt% to about 0.5 wt% of the dispersant; about 0.5 wt% to about of 0.9 wt% of the binder comprising clays; and the cementitious material, which is a Class G cement or Class H cement, wherein the graphene nanoplatelets are blended with the cementitious material, the aqueous carrier, the silica, the additive composition as a graphene dispersion, and a content of the graphene nanoplatelets in the graphene dispersion is about 1 wt% to about 15 wt% based on the total weight of the graphene dispersion.

[0021] Optionally the cement slurry can include further additives such as a retarder for low temperature applications. Advantageously, the additive composition only contains the dispersant, the defoamer, and the binder, each present in an amount of less than 1 wt% based on the weight of the cementitious material.

[0022] The pH of the cement slurry can be about 8 to about 13, about 9 to about 13, about 10 to about 13 or about 11 to about 13.

[0023] In the cement slurry, a weight ratio of the aqueous carrier such as water relative to a combined weight of all the solids in the cement slurry can be about 0.1 to about 1, about 0.1 to about 0.8, or about 0.4, preferably when a gas is not present in the cement slurry.

[0024] Optionally, the cement slurry can also include a gas. For example, the aqueous carrier can be foamed with a gas or liquefied gas such as nitrogen or air. Other suitable gas may also be used.

[0025] The density of the cement slurry can vary widely depending on downhole conditions. Such densities can include about 10 pounds per gallon (ppg) to about 20 ppg, about67CM-510341-WO-2 (PPS0130PCT) 11 ppg to about 18 ppg, about 13 ppg to about 17 ppg, or about 13.3 to about 16.4 ppg.

[0026] The various properties of the cement slurry such as pH, density, setting time, as well as the specific temperatures and pressures that the slurry can be cured can be varied and adjusted according to well control and compatibility parameters of the particular fluid with which it is associated for example a drilling fluid, or a geofluid.

[0027] A pumpable or pourable cement slurry can be formed by any suitable method. In particular, a pumpable slurry can be prepared as per the API requirements to set at the desired time. In an exemplary embodiment, the components of the cement slurry are combined using conventional cement mixing equipment. The cement slurry can then be injected, e.g., pumped and placed by various cement pumps and tools to any desired location within the wellbore to fill any desired shape form. In an embodiment, injecting the cement slurry comprises pumping the cement slurry via a tubular in the wellbore. For example, the cement slurry can be pumped into an annulus between a tubular such as a casing and the rock formation via the tubular. Once the cement slurry has been placed and assumed the shape form of the desired downhole article, the cement slurry is allowed to set and form a permanent shape of an article, for example, a cement sheath.

[0028] The cement slurry as described herein can be cured under high-temperature and high-pressure conditions. For example, the cement slurry can be cured at a temperature of about 75oF to about 600oF, preferably about 150oF to about 600oF, and more preferably about 300oF to about 600oF, or about 400oF to about 600oF, and a pressure of about 500 pounds per square inch (psi) to about 5,000 psi, preferably about 1,000 psi to about 4,000 psi, and more preferably about 2,000 psi to about 3,000 psi. In an aspect, the cement slurry is cured at a temperature of about 300oF to about 600oF or about 400oF to about 600oF and a pressure of about 1,000 psi to about 4,000 psi or about 2,000 psi to about 3,000 psi.

[0029] Advantageously, the cement slurry can form a cement with a compressive strength of about 8,000 psi to about 20,000 psi, preferably about 10,000 psi to about 15,000 psi, when cured at a temperature of about 250oF and a pressure of about 3,000 psi for about 170 hours.

[0030] The cement can also have a Young’s modulus of about 0.5 megapound per square inch (Mpsi) to about 2 Mpsi, or about 1 to about 1.5 Mpsi when the cement slurry is cured at a temperature of about 250oF and a pressure of about 3,000 psi for about 170 hours.

[0031] The cement can further have a permeability of about 0.0001 to about 0.01 millidarcy (mD) when the cement slurry is cured at a temperature of about 250oF and a pressure of about 3,000 psi for about 170 hours.67CM-510341-WO-2 (PPS0130PCT)

[0032] The cement can also have a Poisson's ratio of about 0.1 to about 0.3 when the cement slurry is cured at a temperature of about 250oF and a pressure of about 3,000 psi for about 170 hours.

[0033] The method is particularly useful for cementing a wellbore, which includes injecting, generally pumping, into the wellbore the cement slurry at a pressure sufficient to displace a drilling fluid, for example a drilling mud, a cement spacer, or the like, optionally with a “lead cement slurry” or a “tail cement slurry”. While the method and the cement slurry are useful for cementing geothermal wells, it is appreciated the method and the cement slurry as described herein can also be used to cement wellbores for oil and gas and hydrothermal power applications. The method can provide a cemented wellbore having improved integrity when exposed to static as well as dynamic thermal cycles. The method can also be used for zonal isolation, plugging and abandonment, and the like. Examples

[0034] The materials used for preparing the cement slurry include: Class G cement, Water, Graphene nanoplatelets (GNP), defoamer, dispersant, binder or bonding agent, and silica.

[0035] Procedure: Class G cement and the dry components (dispersant, binder, silica) were weighed in proportions with a permissible error of 1%. Water was weighed and poured in a jar blender, then mixed with the individually weighed fluid components at low speed for about 5-10 seconds for uniform / homogenous dispersion of the GNP. Then following the API specifications, the thoroughly mixed dry components were added to the liquid components at low speed (4000 rpm) for 15 seconds and at a high speed for 35 seconds (12000 rpm). This slurry was immediately poured into the prepared molds and set in the curing chamber at 250oF and 3,000 psi.

[0036] Once set (usually happened within 24 hours), the samples were demolded and set back in the curing chamber for different hydration periods (3, 7, and 28 days). The design had sixteen (1"×2”) molds and 3 (2”×1”) Brazilian tensile molds prepared for testing.

[0037] The sample was prepared accordingly to be able to look into the microstructural properties (SEM including elemental analysis, XRD) on different locations.

[0038] Three samples each were tested for mechanical properties by triaxial test and unconfined compressive strength, three for Brazilian tensile test, and three samples for petrophysical properties (porosity and permeability). The slurry was also prepared for testing rheological properties, pumpability (thickening time); Ultrasonic Cement Analyzer (UCA) for67CM-510341-WO-2 (PPS0130PCT) time taken for strength development.

[0039] After curing at 250oF and 3,000 psi for 3 days, the formed cement has a compressive strength of about 13,000 psi, a Young’s modulus of 1.623 megapound per square inch (Mpsi), a Poisson’s ratio of 0.208, a porosity of 35.13%, and a permeability of 0.007 mD.

[0040] For Brazilian testing with a molding pressure of 699 psi, about 12,000 psi compressive strength was obtained after curing at 250oF and 3000 psi for 7 days. Young's Modulus was 1.24 Mpsi, Poisson's ratio was 0.153, porosity was 36.15%, and permeability was 0.05 mD.

[0041] For Brazilian testing with a molding pressure of 682 psi, about 12,800 psi compressive strength was obtained after curing at 250oF and 3000 psi at 28 days. Young's modulus was 1.69 Mpsi, Poisson's ratio was 0.186, porosity was 37.61%, and permeability was 0.01 mD.

[0042] The results show that the cured cement has excellent elasticity, which means that it can withstand force loads with high axial strain. Compressive strengths for different hydration periods more or less remained the same with increased elasticity for each increased hydration period.

[0043] Set forth are various embodiments of the disclosure.

[0044] Aspect 1. A method comprising injecting into a subsurface a cement slurry comprising, a cementitious material; an aqueous carrier; graphene nanoplatelets; about 10 wt% to about 35 wt% or about 10 wt% to about 25 wt% of silica based on the weight of the cementitious material; and an additive composition comprising at least one of a defoamer, a dispersant, or a binder; and curing the cement slurry at a temperature of about 75oF to about 600oF and a pressure of about 500 psi to about 5,000 psi.

[0045] Aspect 2. The method as in any prior aspect, wherein the cement slurry comprises about 0.05 wt% to about 0.5 wt% of graphene nanoplatelets, based on the weight of the cementitious material.

[0046] Aspect 3. The method as in any prior aspect, wherein the graphene nanoplatelets have a carbon purity of greater than 80%.

[0047] Aspect 4. The method as in any prior aspect, wherein the graphene nanoplatelets are not functionalized.

[0048] Aspect 5. The method as in any prior aspect, further comprising blending a graphene dispersion with the cementitious material, the aqueous carrier, the silica, and the additive composition to make the cement slurry, and the graphene dispersion comprises the graphene nanoplatelets in an amount of about 1 wt% to about 15 wt%, based on the total weigh67CM-510341-WO-2 (PPS0130PCT) of the graphene dispersion.

[0049] Aspect 6. The method as in any prior aspect, wherein the cementitious material is a Class G cement, or a Class H cement.

[0050] Aspect 7. The method as in any prior aspect, wherein the cement slurry comprises the dispersant in an amount of greater than 0 wt% to less than 1 wt%, based on the weight of the cementitious material.

[0051] Aspect 8. The method as in any prior aspect, wherein the cement slurry comprises the defoamer in an amount of greater than 0 wt% to less than 1 wt%, based on the weight of the cementitious material.

[0052] Aspect 9. The method as in any prior aspect, wherein the defoamer comprises alcohols, polysiloxanes, paraffinic oils, mineral oils, vegetable oils, or a combination comprising at least one of the foregoing.

[0053] Aspect 10. The method as in any prior aspect, wherein the cement slurry comprises the binder in an amount of greater than 0 wt% to less than 1 wt%, based on the weight of the cementitious material.

[0054] Aspect 11. The method as in any prior aspect, wherein the binder comprises clays.

[0055] Aspect 12. The method as in any prior aspect, wherein the cement slurry comprises, based on the weight of the cementitious material, about 45 wt% to about 50 wt% of the aqueous carrier; about 0.08 wt% to about 0.15 wt% of graphene nanoplatelets; about 10 wt% to about 25 wt% of the silica; about 0.05 wt% to about 0.2 wt% of the defoamer comprising polysiloxanes, paraffinic oils, mineral oils, vegetable oils, alcohols, or a combination comprising at least one of the foregoing; about 0.1 wt% to about 0.5 wt% of the dispersant; about 0.5 wt% to about of 0.9 wt% of the binder comprising clays; and the cementitious material, which is a Class G cement or Class H cement; wherein the graphene nanoplatelets are blended with the cementitious material, the aqueous carrier, the silica, the additive composition as a graphene dispersion, and a content of the graphene nanoplatelets in the graphene dispersion is about 1 wt% to about 15 wt% based on the total weight of the graphene dispersion.

[0056] Aspect 13. The method as in any prior aspect, wherein the cement slurry is cured at a temperature of about 300oF to about 600oF and a pressure of about 1,000 psi to about 4,000 psi.

[0057] Aspect 14. The method as in any prior aspect, wherein the cement slurry when cured at a temperature of about 250oF and a pressure of about 3,000 psi for 170 hours has a67CM-510341-WO-2 (PPS0130PCT) compressive strength of about 8,000 psi to about 20,000 psi.

[0058] Aspect 15. A cement slurry comprising: a cementitious material; an aqueous carrier; graphene nanoplatelets; about 10 wt% to about 35 wt% or about 10 wt% to about 25 wt% of silica based on the weight of the cementitious material; and an additive composition comprising at least one of a defoamer, a dispersant, or a binder.

[0059] Aspect 16. The cement slurry as in any prior aspect, comprising, based on the weight of the cementitious material, about 45 wt% to about 50 wt% of the aqueous carrier; about 0.08 wt% to about 0.15 wt% of graphene nanoplatelets; about 10 wt% to about 25 wt% of the silica; about 0.05 wt% to about 0.02 wt% of the defoamer comprising alcohols, polysiloxanes, paraffinic oils, mineral oils, vegetable oils, or a combination comprising at least one of the foregoing; about 0.1 wt% to about 0.5 wt% of the dispersant; about 0.5 wt% to about of 0.9 wt% the binder comprising clays; and the cementitious material, which is a Class G cement or Class H cement.

[0060] Aspect 17. The cement slurry as in any prior aspect, wherein the cement slurry when cured at a temperature of about 250oF and a pressure of about 3,000 psi for 170 hours has a compressive strength of about 8,000 psi to about 20,000 psi.

[0061] Aspect 18. The cement slurry as in any prior aspect, wherein the graphene nanoplatelets have a carbon purity of greater than 80%.

[0062] Aspect 19. The cement slurry as in any prior aspect, wherein the graphene nanoplatelets are not functionalized.

[0063] All ranges disclosed herein are inclusive of the endpoints, and the endpoints are independently combinable with each other. As used herein, “combination” is inclusive of blends, mixtures, alloys, reaction products, and the like. All references are incorporated herein by reference.

[0064] The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The modifier “about” used in connection with a quantity is inclusive of the stated value and has the meaning dictated by the context (e.g., it includes the degree of error associated with measurement of the particular quantity). In an embodiment, the term “about” means that the value associated with about can vary by 10%. As used herein, size means largest dimension. Unless defined otherwise, technical and scientific terms used herein have the same meaning as is commonly understood by one of skill in the art to which this invention belongs.67CM-510341-WO-2 (PPS0130PCT)

[0065] All references cited herein are incorporated by reference in their entirety. While typical embodiments have been set forth for the purpose of illustration, the foregoing descriptions should not be deemed to be a limitation on the scope herein. Accordingly, various modifications, adaptations, and alternatives can occur to one skilled in the art without departing from the spirit and scope herein.

Claims

67CM-510341-WO-2 (PPS0130PCT) CLAIMS 1. A method characterized by: injecting into a subsurface a cement slurry; and curing the cement slurry; the method characterized in that the cement slurry comprises: a cementitious material; an aqueous carrier; graphene nanoplatelets; about 10 wt% to about 35 wt% of silica based on the weight of the cementitious material; and an additive composition characterized by at least one of a defoamer, a dispersant, or a binder; and the cement slurry is cured at a temperature of about 75oF to about 600oF and a pressure of about 500 psi to about 5,000 psi.

2. The method of claim 1, wherein the cement slurry comprises about 0.05 wt% to about 0.5 wt% of graphene nanoplatelets, based on the weight of the cementitious material.

3. The method of claim 1, wherein the graphene nanoplatelets are not functionalized.

4. The method of claim 1, further characterized by blending a graphene dispersion with the cementitious material, the aqueous carrier, the silica, and the additive composition to make the cement slurry, and the graphene dispersion comprises the graphene nanoplatelets in an amount of about 1 wt% to about 15 wt%, based on the total weigh of the graphene dispersion.

5. The method of claim 1, wherein the cementitious material is a Class G cement, or a Class H cement.

6. The method of claim 1, wherein the cement slurry comprises the dispersant in an amount of greater than 0 wt% to less than 1 wt%, based on the weight of the cementitious material.67CM-510341-WO-2 (PPS0130PCT) 7. The method of claim 1, wherein the cement slurry comprises the defoamer in an amount of greater than 0 wt% to less than 1 wt%, based on the weight of the cementitious material.

8. The method of claim 7, wherein the defoamer comprises alcohols, polysiloxanes, paraffinic oils, mineral oils, vegetable oils, or a combination characterized by at least one of the foregoing.

9. The method of claim 1, wherein the cement slurry comprises the binder in an amount of greater than 0 wt% to less than 1 wt%, based on the weight of the cementitious material; and the binder comprises clays.

10. The method of any one of claims 1 to 9, wherein the cement slurry comprises, based on the weight of the cementitious material, about 45 wt% to about 50 wt% of the aqueous carrier; about 0.08 wt% to about 0.15 wt% of graphene nanoplatelets; about 10 wt% to about 25 wt% of the silica; about 0.05 wt% to about 0.2 wt% of the defoamer characterized by polysiloxanes, paraffinic oils, mineral oils, vegetable oils, alcohols, or a combination characterized by at least one of the foregoing; about 0.1 wt% to about 0.5 wt% of the dispersant; about 0.5 wt% to about of 0.9 wt% of the binder characterized by clays; and the cementitious material, which is a Class G cement or Class H cement; wherein the graphene nanoplatelets are blended with the cementitious material, the aqueous carrier, the silica, the additive composition as a graphene dispersion, and a content of the graphene nanoplatelets in the graphene dispersion is about 1 wt% to about 15 wt% based on the total weight of the graphene dispersion.

11. The method of any one of claims 1 to 9, wherein the cement slurry is cured at a temperature of about 300oF to about 600oF and a pressure of about 1,000 psi to about 4,000 psi.

12. The method of any one of claims 1 to 9, wherein the cement slurry when cured at a temperature of about 250oF and a pressure of about 3,000 psi for 170 hours has a67CM-510341-WO-2 (PPS0130PCT) compressive strength of about 8,000 psi to about 20,000 psi.

13. A cement slurry characterized by: a cementitious material; an aqueous carrier; graphene nanoplatelets; about 10 wt% to about 35 wt% of silica based on the weight of the cementitious material; and an additive composition characterized by at least one of a defoamer, a dispersant, or a binder.

14. The cement slurry of claim 13, characterized by, based on the weight of the cementitious material, about 45 wt% to about 50 wt% of the aqueous carrier; about 0.08 wt% to about 0.15 wt% of graphene nanoplatelets; about 10 wt% to about 25 wt% of the silica; about 0.05 wt% to about 0.02 wt% of the defoamer characterized by alcohols, polysiloxanes, paraffinic oils, mineral oils, vegetable oils, or a combination characterized by at least one of the foregoing; about 0.1 wt% to about 0.5 wt% of the dispersant; about 0.5 wt% to about of 0.9 wt% the binder characterized by clays; and the cementitious material, which is a Class G cement or Class H cement.

15. The cement slurry of claim 14, wherein the graphene nanoplatelets are not functionalized.