WO2026019772A1

WO2026019772A1 - Development of geopolymer cements utilizing red mud for primary well cementing applications

Info

Publication number: WO2026019772A1
Application number: PCT/US2025/037665
Authority: WO
Inventors: Khawlah A. ALANQARI; Abdullah Al-Yami; Mohammad ALHARTHI
Original assignee: Saudi Arabian Oil Co; Aramco Services Co
Current assignee: Saudi Arabian Oil Co; Aramco Services Co
Priority date: 2024-07-16
Filing date: 2025-07-15
Publication date: 2026-01-22
Anticipated expiration: 2027-01-16
Also published as: US20260022288A1

Abstract

A composition and method for well cementing are provided. The composition comprises a geopolymer slurry that is prepared by mixing a particulate material derived from red mud, an alkaline activator, an aqueous solvent, and a SiCh source material added to produce a geopolymer slurry with a Si/Al ratio of from 2 to 6. The method for well cementing includes pumping a geopolymer slurry into a location to be cemented and Harding the geopolymer slurry to form a cement.

Description

ATTORNEY DOCKET NO.18733-1388WO1; CLIENT REF. NO. SA91388 DEVELOPMENT OF GEOPOLYMER CEMENTS UTILIZING RED MUD FOR PRIMARY WELL CEMENTING APPLICATIONS BACKGROUND [0001] Cement mixtures are used in the oil and gas industry for cementing oil and gas wells. For example, cement may be used to hold casing in place and prevent fluid migration between subsurface formations. Primary cementing includes pumping cement down a casing and into an annulus between the formation and the casing (or between casings). Cements used in the oil and gas industry must be able to withstand the extreme temperatures, pressures and chemical environments encountered in hydrocarbon-bearing formations. Thus, there exists a need to produce well cements capable of withstanding down-hole environments. SUMMARY [0002] This summary is provided to introduce a selection of concepts that are further described below in the detailed description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of the claimed subject matter. [0003] In one aspect, embodiments disclosed herein relate to a composition for well cementing comprising a geopolymer slurry. The composition may be prepared by mixing a particulate material derived from red mud, an alkaline activator, an aqueous solvent, and a SiO2 source material present in an amount to produce a Si/Al ratio in the geopolymer slurry of from 2 to 6. [0004] In another aspect, embodiments disclosed herein relate to a method of cementing. The method may include pumping a geopolymer slurry into a location to be cemented and hardening the geopolymer slurry to form a cement. The method may also include where the geopolymer slurry consists of a particulate material derived from red mud, an alkaline activator, an aqueous solvent, and a SiO2 source material present in an amount to produce a Si/Al ratio in the geopolymer slurry of from 2 to 6. [0005] Other aspects and advantages of the claimed subject matter will be apparent from the following description and the appended claims. BRIEF DESCRIPTION OF DRAWINGS ATTORNEY DOCKET NO.18733-1388WO1; CLIENT REF. NO. SA91388 [0006] FIG. 1 is a block-flow diagram of a method of well cementing in accordance with one or more embodiments of the present disclosure. DETAILED DESCRIPTION [0007] The present disclosure generally relates to a geopolymer slurry and a method of cementing that includes delivering the geopolymer slurry to a location to be cemented. The cementing may be primary well cementing and may involve a reduced amount of CO2 associated with cement formation. The geopolymer slurry is based on red mud. The red mud may be obtained from industrial waste. The present disclosure further relates to a method of converting red mud chemically into a geopolymer to be used in the geopolymer slurry. Thus, one or more embodiments in accordance with the present disclosure provide an effective solution for recycling red mud and for reducing the amount of CO₂ associated with cement formation. [0008] In one aspect, embodiments of the present disclosure relate to a geopolymer slurry including a particulate material derived from red mud. Red mud is also known as bauxite residue. Red mud is an industrial waste by-product that is produced during the production of alumina using industrial processes such as the Bayer process. The Bayer process produces one to two tons of red mud for every one ton of alumina produced. Over 175 million tons of red mud are produced globally. Red mud is highly basic, with a highly alkaline pH ranging from 10 to 12. Both the pH and the composition of red mud tend to be regarded as environmentally damaging. However, utilization of red mud to generate value-added products allows for the attainment of more green and sustainable industrial processes. [0009] Red mud has a composition that includes a mixture of minerals. The mineral includes metallic oxides. Exemplary minerals that may be present in the waste red mud include Al₂O₃, SiO₂, CaO, MgO, K₂O, larnite (Ca₂(SiO₄)), cancrinite ((NaCa)8(AlSiO4)6(CO3SO4)2·2H2O), hematite (Fe2O3), goethite (FeO(OH)), calcite (CaCO3), perovskite (CaTiO3), grossite (CaAl4O7), quartz (SiO2), gibbsite (Al(OH)3), and combinations thereof. The mineralogical composition of the red mud may be determined by X-ray powder diffraction (XRD). In one or more embodiments, the elemental composition of the red mud contains one or more elements that include Fe, ATTORNEY DOCKET NO.18733-1388WO1; CLIENT REF. NO. SA91388 A1, Na, Si, Ca, Ti, S, Zn, Sr, Mg, P, Cr, K, Mn, Ce, Pb, Ni, Th, and combinations thereof. The elemental composition of the red mud may be determined by XRD. [0010] A suitable red mud as a basis for the present geopolymer includes Al2O3, and SiO₂. The red mud may contain Al₂O₃ and SiO₂ in a Si/Al molar ratio of from 0.5 to 0.7, for example from 0.50 to 0.63. The oxides in the mixture may be solid and the mixture may be solid. In one or more embodiments of the present disclosure, the red mud is ground to a fine particle size prior to use in the geopolymer slurry. The fine particle size of the ground red mud may be characterized by 80% of the particles being smaller than 50 µm. The particle size may be determined by known methods such as sieving to determine a mesh size and/or by imaging to visualize the particles. [0011] The geopolymer slurry may be prepared by mixing a particulate material derived from red mud; an alkaline activator; an aqueous solvent; and a SiO2 source material added in an amount to produce a Si/Al ratio in the geopolymer slurry of a lower limit of any one of 2 and 4 and an upper limit of any one of 4 or 6, where any lower limit can be paired with any mathematically compatible upper limit. The present inventors have discovered that red mud can be utilized as an aluminosilicate source material for the preparation of geopolymers through a geopolymerization reaction. The geopolymerization reaction involves first a dissolution of silicon and aluminum oxide species under alkaline conditions, followed by a polycondensation reaction to form a gel. The dissolution of silicon and aluminum oxide species under alkaline conditions may form mixed hydroxyl ions. The polycondensation reaction may be a polycondesation reaction of the mixed hydroxyl ions to form the final gel as a 3D chain with a tetrahedral structure that is composed of silicate and aluminate linked to each other through oxygen atoms. The composition of the gel may be described using the following equation: Nan[(-SiO2)z-AlO2]n · yH2O (1) where n is the degree of polymerization, z may be 2, 3, 4, or higher depending on the amount of soluble silicate present in the polymerization, and y represents coordinated waters. [0012] In one or more embodiments of the present disclosure, the alkaline activator is a mixture of sodium silicate and sodium hydroxide. The pH of the sodium silicate may ATTORNEY DOCKET NO.18733-1388WO1; CLIENT REF. NO. SA91388 range from 11 to 13, depending on the SiO₂:Na₂O molar ratio. The SiO₂:Na₂O molar ratio of the present disclosure may be 3.4:1, resulting in a pH of 12-13. [0013] In one or more embodiments of the present disclosure, the aqueous solvent includes one or more waters such as deionized water, tap water, fresh water, municipal water, formation water, produced water, well water, filtered water, distilled water, sea water, or combinations thereof. The aqueous solvent may include one or more organic or inorganic compounds dissolved in the water or otherwise completely miscible with the one or more waters. The aqueous solvent may include salt water, natural, or synthetic brines. Suitable salts may include alkali metal chlorides, hydroxides, or carboxylates. For example, suitable salts may include sodium, calcium, cesium, zinc, aluminum, magnesium, potassium, strontium, silicon, lithium, chlorides, bromides, carbonates, iodides, chlorates, bromates, formates, nitrates, sulfates, phosphates, oxides, fluorides, and combinations thereof. [0014] Without being bound by any theory, the density of the geopolymer slurry may be varied by incorporating salts or organic compounds into the aqueous solvent. Increasing the saturation of the aqueous solvent by increasing the salt concentration or amount of dissolved organics may increase the density of the aqueous solvent, and thus, the density of the geopolymer slurry. [0015] In one or more embodiments, the geopolymer slurry includes the aqueous solvent in a range of from 10 to 70 wt%, based on the weight of the red mud. In one or more embodiments, the geopolymer slurry includes the aqueous solvent in a range of from 10 to 40 wt%, from 10 to 30 wt%, from 10 to 20 wt%, from 20 to 40 wt%, from 25 to 35 wt%, or from 20 to 30 wt% based on the weight of the red mud. [0016] In one or more embodiments, the SiO₂ source material is silica fume. The SiO₂ source material may be cement. The source material may be fine material. For example, the source material may be fine sand. Fine sand is commercially available. Fine sand may be provided with a predetermined sieve size range. For example, the size range may be provided as a sieve size. Fine sand may be a sieve size from sieve size #30 (30 mesh) to sieve size #100 (100 mesh). Thus, for example when the sieve size is 100 mesh, the fine sand may have an average particle size of less than 150 µm. The source material may be nanosilica. Nanosilica is commercially available. Nanosilica may be ATTORNEY DOCKET NO.18733-1388WO1; CLIENT REF. NO. SA91388 provided in a predetermined average size. For example, the average size may be a predetermined average size within the range from 1 nanometers to 200 nanometers, with an approximate distribution width with the range of from 2% to 20%. When the SiO₂ source is cement, the SiO₂ may be present in amounts up to 0.1 to 50 wt.%. In one or more embodiment, the geopolymerization reaction does not use any source of Ordinary Portland Cement (OPC). [0017] In one or more embodiments of the present disclosure, the mixture used to form the geopolymer slurry includes other one or more additives known to be suitable for cement slurries. The one or more additives may include accelerators, retarders, extenders, weighting agents, fluid loss control agents, lost circulation control agents, surfactants, antifoaming agents, specialty additives such as elastomers or fibers, and combinations thereof. The one or more additives do not include Saudi Arabian volcanic ash. [0018] The composition of the red mud, the alkaline activator, the aqueous solvent, and the SiO2 source material and optional components may be stirred for a sufficient amount of time in order to achieve suitable homogeneity. That is, the mixing may include stirring for a sufficient amount of time in order to achieve suitable homogeneity. The composition may be stirred according to methods known in the art, such as, for example, with an API blender. A sufficient amount of time may range from about 15 seconds to about 1 minute. For example, the solution may be stirred for an amount of time ranging from a lower limit of one of 15 seconds at 4,000 rpm, to an upper limit of 35 seconds at 12,000 rpm. The sufficient amount of mixing time may be determined according to the following equation: where E corresponds to mixing energy in kJ, M corresponds to the mass of the geopolymer slurry in kg, k = 6.1x10^-8 m⁵/s, ω corresponds to rotational speed in radians per second, t corresponds to mixing time in seconds, and V corresponds to volume of the geopolymer slurry in m³. [0019] In one or more embodiments of the present disclosure, the geopolymer slurry has a thickening time at a temperature greater than or equal to 100 °F of greater than 1, 1.5, 1.75, 2, 4, 6, 8, or 10 hours. In one or more embodiments, the thickening time is ATTORNEY DOCKET NO.18733-1388WO1; CLIENT REF. NO. SA91388 be decreased by increasing the temperature to greater than 180 °F. A thickening time test may be used to simulate pumping conditions in order to determine the length of time before the geopolymer slurry becomes difficult or impossible to pump. Thickening time is determined via a pressurized consistometer. This device allows pressure and temperature to be applied to a cement slurry while it is being stirred (typically at 150 rpm). A resistor arm on a potentiometer indicates resistance to the paddle turning as the cement sets. The apparatus is calibrated to a standard output in Bearden Consistency units. The device is fully automated and can simulate squeeze schedules and/or batch mixing. [0020] In one or more embodiments of the present disclosure, the geopolymer slurry has a density of from 70 to 170 lb/ft³ as determined by a pressurized fluid density scale. [0021] In one or more embodiments of the present disclosure, the viscosity of the geopolymer slurry is measured using a standard oilfield viscometer, such as a FANN^® Model 35 viscometer manufactured by Fann Instrument Company, for example, according to test methods provided in the API Recommended Practice for Field Testing Water-Based Cement Slurries (RP 13B-1/ISO 10414-1:2002). The viscometer reports shear stress readings at various shear rates. The shear stress readings are reported in units of pounds of force per 100 square feet (lbf/100ft²) and are measured in rpm. The viscometer may report shear stress readings at shear rates of at least one of 600 rpm, 300 rpm, 200 rpm, 100 rpm, 6 rpm, or 3 rpm. According to one or more embodiments of the present disclosure, these shear stress readings are used to determine the viscosity of the geopolymer slurry at any of the shear rates, using Equation 3, assuming a viscometer with an R1 rotor sleeve, B1 bob, and F1 torsion spring: where µ corresponds to the viscosity in cP, N corresponds to the viscometer shear rate in rpm, and θ_N corresponds to the viscometer shear stress in lbf/100ft². [0022] In one or more embodiments of the present disclosure, the rheology of geopolymer slurry is modeled based on Bingham plastic flow behavior. The rheological behavior of the geopolymer slurry may be determined by measuring the shear stress on the geopolymer slurry at different shear rates, which may be accomplished by measuring the shear stress and/or shear rate on the geopolymer slurry ATTORNEY DOCKET NO.18733-1388WO1; CLIENT REF. NO. SA91388 using a FANN^® Model 35 viscometer operated at 3 rpm, 6 rpm, 100 rpm, 200 rpm, 300 rpm, or 600 rpm, for example. A Bingham plastic fluid may then be modeled using the following equation: _{[0023] ^ ൌ ^^^^γ^ ^ 4.79^^ (4)} where τ corresponds to shear stress in dynes per square centimeter, PV corresponds to p_{lastic viscosity in cP, γ^ corresponds to shear rate in s-1, and YP corresponds to yield} point in lbf/100ft². [0024] The rheology of the geopolymer slurry may be evaluated from the plastic viscosity (PV) and the yield point (YP), which are parameters from the Bingham plastic rheology model. The plastic viscosity is related to the resistance of the geopolymer slurry to flow due to mechanical interaction between the solids of the geopolymer slurry and represents the viscosity of the geopolymer slurry extrapolated to infinite shear rate. In other words, the plastic viscosity is the slope of the shear stress versus shear rate curve of the Bingham plastic model. The plastic viscosity reflects the type and concentration of the solids in the geopolymer slurry, and a lesser plastic viscosity is preferred. In one or more embodiments, the plastic viscosity of the geopolymer slurry is estimated by measuring the shear stress of the geopolymer slurry using a FANN^® Model 35 viscometer at shear rates of 300 rpm and 600 rpm and subtracting the 300 rpm shear stress measurement from the 600 rpm shear stress measurement according to the following equation: ^_{^ ൌ ^^^^ െ ^ଷ^^ (5)} where PV corresponds to plastic viscosity in cP, θ600 corresponds to the shear stress viscometer reading at 600 rpm in lbf/100ft², and θ₃₀₀ corresponds to the shear stress viscometer reading at 300 rpm in lbf/100ft². [0025] In one or more embodiments of the present disclosure, the geopolymer slurry has a plastic viscosity of from 40 to 350 cP. The plastic viscosity of the geopolymer slurry may be determined according to test methods provided in the API Recommended Practice For Field Testing Water-Based Cement slurries (RP 13B-1/ISO 10414- 1:2002). The geopolymer slurry may have a plastic viscosity of from 50 to 350 cP, from 50 to 300 cP, from 50 to 200 cP, from 50 to 150 cP, from 50 to 125 cP, from 50 to 100 cP, from 50 to 80 cP, from 50 to 60 cP, from 60 to 350 cP, from 60 to 300 cP, ATTORNEY DOCKET NO.18733-1388WO1; CLIENT REF. NO. SA91388 from 60 to 200 cP, from 60 to 150 cP, from 60 to 125 cP, from 60 to 100 cP, from 60 to 80 cP, from 80 to 350 cP, from 80 to 300 cP, from 80 to 200 cP, from 80 to 150 cP, from 80 to 125 cP, from 80 to 100 cP, from 100 to 350 cP, from 100 to 300 cP, from 100 to 200 cP, from 100 to 150 cP, from 100 to 125 cP, from 100 to 100 cP, from 100 to 80 cP, from 125 to 350 cP, from 125 to 300 cP, from 125 to 200 cP, from 125 to 150 cP, from 150 to 350 cP, from 150 to 300 cP, from 150 to 200 cP, from 200 to 300 cP, from 200 to 350 cP, or from 300 to 350 cP. [0026] In one or more embodiments of the present disclosure, the geopolymer slurry has a yield point of from 1 to 70 lbf/100ft². The yield point represents the shear stress less than which the geopolymer slurry behaves as a rigid body and greater than which the geopolymer slurry flows as a viscous fluid. In other words, the yield point represents the amount of stress required to move the geopolymer slurry from a static condition. The yield point is the resistance of initial flow of a fluid, or the stress required in order to move the fluid. It can be simply stated that the yield point is the attractive force among colloidal particles in cement slurry. The yield point of a geopolymer slurry is correlated with the capacity of the geopolymer slurry to carry rock cuttings through the annulus, which in simplified terms indicates the geopolymer slurry’s hole-cleaning ability. The determination of yield points of a geopolymer slurry is important in the overall description of slurry flow properties. Yield point affects both the start-up pressure after a temporary shut-down and the void filling properties of geopolymer slurry during cementing operations. The yield point of the geopolymer slurry may be estimated from the plastic viscosity from Equation 4 according to the following equation: ^_{^ ൌ ^ଷ^^ െ ^^ (6)} [0027] In one or more embodiments of the present disclosure, the geopolymer slurry of the present disclosure has a yield point of from 5 to 60 lbf/100ft², from 5 to 55 lbf/100ft², from 5 to 40 lbf/100ft², from 5 to 30 lbf/100ft², from 5 to 25 lbf/100ft², from 5 to 20 lbf/100ft², from 5 to 15 lbf/100ft², from 5 to 10 lbf/100ft², from 10 to 70 lbf/100ft², from 10 to 60 lbf/100ft², from 10 to 55 lbf/100ft², from 10 to 40 lbf/100ft², from 10 to 30 lbf/100ft², from 10 to 25 lbf/100ft², from 10 to 20 lbf/100ft², from 10 to 15 lbf/100ft², from 15 to 70 lbf/100ft², from 15 to 60 lbf/100ft², from 15 to 55 lbf/100ft², from 15 to 40 lbf/100ft², from 15 to 30 lbf/100ft², from 15 to 25 lbf/100ft², from 15 to ATTORNEY DOCKET NO.18733-1388WO1; CLIENT REF. NO. SA91388 20 lbf/100ft², from 20 to 70 lbf/100ft², from 20 to 60 lbf/100ft², from 20 to 55 lbf/100ft², from 20 to 40 lbf/100ft², from 20 to 30 lbf/100ft², from 20 to 25 lbf/100ft², from 25 to 70 lbf/100ft², from 25 to 60 lbf/100ft², from 25 to 55 lbf/100ft², from 25 to 40 lbf/100ft², from 25 to 30 lbf/100ft², from 30 to 70 lbf/100ft², from 30 to 60 lbf/100ft², from 30 to 55 lbf/100ft², from 30 to 40 lbf/100ft², from 40 to 70 lbf/100ft², from 40 to 60 lbf/100ft², from 40 to 55 lbf/100ft², from 55 to 70 lbf/100ft², from 55 to 60 lbf/100ft², or from 60 to 70 lbf/100ft². [0028] As described above, the geopolymer slurry may have various properties that enable pumping the geopolymer slurry to a location and cementing. For example, the geopolymer slurry may be formulated to have a specific thickening time, density, free fluid values, plastic viscosity, and yield point, among others. [0029] In one or more embodiments of the present disclosure, the geopolymer slurry is pumped to a well, a wellbore, an annulus, or other downhole locations for cementing. Cementing is performed when the geopolymer slurry is deployed into the well via pumps, displacing the drilling fluids still located within the well, and replacing them with the geopolymer slurry. The geopolymer slurry flows to the bottom of the wellbore through the casing, which will eventually be the pipe through which the hydrocarbons flow to the surface. From there, the geopolymer slurry fills in the space between the casing and the actual wellbore, and hardens. This creates a seal so that outside materials cannot enter the well flow, as well as permanently positions the casing in place. [0030] In one or more embodiments, the properties of the geopolymer slurry are tailored to a specific well environment. This may be done by measuring the diameter of the borehole along its depth, using a caliper log. Utilizing both mechanical and sonic means, multi-finger caliper logs measure the diameter of the well at numerous locations simultaneously in order to accommodate for irregularities in the wellbore diameter and determine the volume of the openhole. Additionally, the required physical properties of the geopolymer slurry are essential before commencing cementing operations. The proper set geopolymer slurry may also be determined, including the density and viscosity of the material, before actually pumping the geopolymer slurry into the hole. ATTORNEY DOCKET NO.18733-1388WO1; CLIENT REF. NO. SA91388 EXAMPLES [0031] Referring to FIG. 1, exemplary compositions and methods were investigated. ExRed mud was obtained as a byproduct and waste product of aluminum production from Maadn, sodium hydroxide was obtained from Fisher and prepared overnight in 6- 10 M sodium silicate obtained from Halliburton, lime was obtained from Halliburton, and silica fume was obtained from Halliburton. [0032] A red mud sample was homogenized and manually ground to obtain a fine particle size. Then, 4 grams of red mud was mixed well and homogenized with 0.9 grams of a binder (Licowax C micropowder PM, Hoechstwax) and pressed with 20 tons of pressure to a pellet with 31 mm diameter. The mineralogical composition of the red mud was characterized by wavelength dispersive X-ray fluorescence (WDXRF) showed the following oxides: CaO (5.59%), SiO2 (15.178%), Al2O3 (25.645%), Fe2O3 (30.74%), MgO (0.17%), and K2O (0.036%). The red mud sample was also characterized using elemental analysis, Table 1 shows the results. Table 1 ATTORNEY DOCKET NO.18733-1388WO1; CLIENT REF. NO. SA91388 O 33.800 33.800 33.960 33.900 33.900 33.856 33.740 33.670 33.800 33.500 33.500 33.628 Fe 11.530 11.600 11.440 11.600 11.620 11.560 Al 6.720 6.750 6.720 6.729 6.850 6.744 Si 3.915 3.906 3.890 3.913 3.932 3.887 Ca 3.053 3.080 3.060 3.104 3.036 3.058 Ti 2.972 2.980 3.020 2.984 3.024 2.994 S 2.124 2.080 2.087 2.167 2.094 2.094 F 1.100 0.954 0.944 0.963 0.917 0.942 P 0.090 0.097 0.096 0.100 0.096 0.094 Mg 0.072 0.070 0.077 0.073 0.073 0.073 Cr 0.060 0.058 0.057 0.058 0.057 0.058 [0033] For the preparation method of the geopolymer slurry, the quantities are used based on the following molar ratios: 1- SiO2/ Al2O3 = a Si/Al molar ratio of 2 to 4. The SiO2 amount was increased by the addition of silica fume. This is important to produce a geopolymer with good strength. 2- (Na₂O, NaOH solution)/Al₂O₃ in red mud = a Na/Al molar ratio of 1 to 0.4 3- (Na2O/SiO2) in Sodium Silicate = a SiO2:Na2O molar ratio of 3.4:1 The NaOH 6M aqueous solution was prepared by dissolving NaOH in water, stirring for 10 to 30 minutes, and allowing the solution to cool overnight. Na₂SiO₃ is used as a solution. The pH of the activated solution was 11.6-13. Table 2 shows the compositions of Formulations 1-4. Table 2 Component Formulation Formulation Formulation Formulation 1 2 3 4 Distilled Water 140 mL 140 mL 140 mL 140 mL NaOH 82 mL 82 mL 82 mL 82 mL ATTORNEY DOCKET NO.18733-1388WO1; CLIENT REF. NO. SA91388 Sodium Silicate 130 mL 130 mL 130 mL 130 mL Lime - - 10 g (3.3%) 20 g (6.6%) Red Mud 300 g 300 g 300 g 300 g Silica Fume 90 g 150 g 90 g 90 g [0034] Table 3 shows rheology test results for Formulation 1 at room temperature, Formulation 1 after 1 hour at 180 °F, and Formulation 2 at room temperature. As shown below, the rheology values of Formulation 1 increased after conditioning, that is thickening, for 1 hour at 180 °F as opposed to thickening for 1 hour at room temperature. This shows that the thickening time may be decreased by increasing the temperature. Larger rheology values indicate gel formation. Table 3 also shows that increasing the amount of silica fume (Formulation 2) may also be used to shorten thickening times and accelerate formation of the gel. Table 3 Rheology Formulation 1 Formulation 1 Formulation 2 600 42 63 88 300 25 48 46 200 16-18 42 32 100 11 36 21 6 2 22 4 3 2 14 3 10 seconds 5 15 4 ATTORNEY DOCKET NO.18733-1388WO1; CLIENT REF. NO. SA91388 10 minuets 9 25 12 Free fluid in 250 mL graduated cylinder for 2 0 mL 0 mL 0 mL hours Note ^{At room} After 1 hour at temperature _{180 °F} ^{At room temperature} [0035] Table 4 shows the silica fume addition. The silica fume was added directly to the geopolymer slurry after the red mud addition.

ATTORNEY DOCKET NO.18733-1388WO1; CLIENT REF. NO. SA91388 Table 4 Silica Fume Addition 30% 50% Thickening Time 6 hrs 4-6 hrs Free fluid in 250 ml graduated cylinder for 0 ml 0 ml 2 hours below Crushing Test 650-700 psi [0036] After conditioning for 1 hour at 180 °F, Formulations 3 and 4 showed strong gelling and clear initial setting, while remaining capable of pumping. After conditioning for 24 hours at 180 °F and cooling for two days, Formulation 2 solidified. Table 4 also shows that greater amounts of silica fume can increase the compressive strength of the resulting gel, as evidenced by a Crushing Test value of greater than 500 psi, while remaining capable of pumping before thickening, as evidenced by the free fluid values of zero. [0037] Although only a few example embodiments have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the example embodiments without materially departing from this invention. Accordingly, all such modifications are intended to be included within the scope of this disclosure as defined in the following claims.

Claims

ATTORNEY DOCKET NO.18733-1388WO1; CLIENT REF. NO. SA91388 CLAIMS What is claimed: 1. A composition for well cementing comprising a geopolymer slurry prepared by mixing: a particulate material derived from red mud; an alkaline activator; an aqueous solvent; and a SiO2 source material, present in an amount to produce a Si/Al ratio in the geopolymer slurry of from 2 to 6. 2. The composition of claim 1, wherein the particulate material is prepared by grinding red mud to a fine particle size. 3. The composition of claim 1 or 2, wherein the alkaline activator comprises sodium silicate with a ratio of Na₂O to SiO₂ of 3.4 to 1. 4. The composition of any one of the preceding claims, wherein the alkaline activator has a pH of 12-13. 5. The composition of any one of the preceding claims, wherein the aqueous solvent comprises one or more waters selected from the group consisting of deionized water, tap water, fresh water, municipal water, formation water, produced water, well water, filtered water, distilled water, sea water, salt water, natural brine, synthetic brine, or a combination thereof. 6. The composition of any one of the preceding claims, wherein the SiO2 source material is selected from the group consisting of silica fume, cement, nanosilica, and sand. 7. The composition of any one of the preceding claims, further comprising an additive selected from the group consisting of accelerators, retarders, extenders, weighting agents, fluid loss control agents, lost circulation control agents, surfactants, antifoaming agents, elastomers, fibers, or combinations thereof. 8. A method of cementing, the method comprising: pumping a geopolymer slurry into a location to be cemented, and ATTORNEY DOCKET NO.18733-1388WO1; CLIENT REF. NO. SA91388 hardening the geopolymer slurry to form a cement; wherein the geopolymer slurry consists of: a particulate material derived from red mud; an alkaline activator; an aqueous solvent; and a SiO2 source material, present in an amount to produce a Si/Al ratio in the geopolymer slurry of from 2 to 6. 9. The method of claim 8, wherein the location to be cemented is a well, a well bore, or an annulus. 10. The method of claim 8 or 9, wherein hardening the geopolymer slurry comprises exposing the geopolymer to conditions of the location to be cemented. 11. The method of any one of claims 8-10, wherein the particulate material is prepared by grinding red mud to a fine particle size. 12. The method of any one of claims 8-11, wherein the alkaline activator is comprised of sodium silicate with a ratio of Na₂O to SiO₂ of 3.4 to 1. 13. The method of any one of claims 8-12, wherein the alkaline activator has a pH of 12- 13. 14. The method of any one of claims 8-13, wherein the aqueous solvent comprises one or more waters selected from the group consisting of deionized water, tap water, fresh water, municipal water, formation water, produced water, well water, filtered water, distilled water, sea water, salt water, natural brine, synthetic brine, or a combination thereof. 15. The method of any one of claims 8-14, wherein the SiO2 source material is selected from the group consisting of silica fume, cement, nano-silica, and sand. 16. The method of any one of claims 8-15, further comprising an additive selected from the group consisting of accelerators, retarders, extenders, weighting agents, fluid loss control agents, lost circulation control agents, surfactants, antifoaming agents, elastomers, fibers, or combinations thereof.