Method for treating a rock formation against the inflitration of sand using a geopolymer cement grout

Abstract

Treatment method for a rock formation against sand infiltration during production of fluid from this rock formation via a well drilled through said rock formation, comprising at least one step of injecting a geopolymer cement grout into said rock formation, in particular around the edges of said well and/or through said well.

Claims

1. A method of treatment of a geological reservoir for the storage of a first fluid in a rock formation against sand infiltration during production of the first fluid from said geological reservoir via a well drilled through said rock formation, the method comprising: at least one step of injecting a geopolymer cement grout into said rock formation, said geopolymer cement grout comprising a mass fraction of water, relative to its total mass, greater than or equal to 50%, and after, at least one first step of injecting a first gas around edges of said well and/or through said well to reconnect the first fluid produced from the geological reservoir to said well, and to expel the water contained in the geopolymer cement grout, and after, at least a drying phase comprising a second gas injection or the continuation of the first gas injection, wherein the rock formation has a porosity higher than or equal to 15%; and wherein said geopolymer cement grout comprises at least one aluminosilicate component, or a mixture of several components that is a source of aluminosilicate, and wherein at least 50% by cumulative volume of particles, of said at least one aluminosilicate component, or of said mixture of several components that is a source of aluminosilicate, (i) have a particle size that is less than or equal to one-sixth the size of at least 50% by cumulative volume of the pores of the rock formation or (ii) have a particle size that is less than or equal to one-sixth the mean hydraulic diameter dh of the pores of the rock formation.

2. The method according to claim 1, comprising performing several injection cycles, wherein each injection cycle comprises injecting the geopolymer cement grout followed by injecting the first gas.

3. The method according to claim 1, wherein the rock formation comprises pores having walls, and wherein said method comprises polymerizing the geopolymer cement grout to form a geopolymer cement coating that at least partially covers the walls of the pores of the rock formation.

4. The method according to claim 1, wherein prior to said injecting of the geopolymer cement grout, the rock formation is permeable and contains the first fluid, and wherein the rock formation remains permeable and contains a second fluid, after said drying phase.

5. The method according to claim 1, wherein the geopolymer cement grout comprises: a) at least one aluminosilicate component, or a mixture of several components that is a source of aluminosilicate, and b) an alkaline silicate solution.

6. The method according to claim 5, wherein the size of at least 50% by cumulative volume of the particles of the aluminosilicate component or of the mixture of several components that is a source of aluminosilicate is less than or equal to 5 μm.

7. The method according to claim 5, further comprising: preparing the particles of said at least one aluminosilicate component or said mixture of several components that is a source of aluminosilicate, so that at least 50% of the cumulative volume of said particles (i) have a particle size that is less than or equal to one-sixth the size of at least 50% by cumulative volume of the pores of the rock formation or (ii) have a particle size that is less than or equal to one-sixth the mean hydraulic diameter dh of the pores of the rock formation.

8. The method according to claim 7, wherein said preparing comprises grinding.

9. The method according to claim 5, further comprising reducing the particle size of said at least one aluminosilicate component or said mixture of several components that is a source of aluminosilicate.

10. The method according to claim 5, wherein said at least one aluminosilicate component or said mixture of several components that is a source of aluminosilicate is selected from the group consisting of: a metakaolin, a kaolin, a bentonite, fly ash, blast furnace slag, silica smoke, and mixtures thereof.

11. The method according to claim 5, wherein the alkaline silicate solution includes a potassium, sodium or calcium alkaline silicate solution.

12. The method according to claim 5, wherein the geopolymer cement grout comprises a mass fraction of said at least one aluminosilicate component or of the mixture of several components that is a source of aluminosilicate relative to its total mass, that is greater than 0% and less than or equal to 30%.

13. The method according to claim 5, wherein the chemical composition resulting from the mixture of said at least one aluminosilicate component or mixture of several components that is a source of aluminosilicate with the alkaline silicate solution, has the formula: Al.sub.2O.sub.3; nSiO.sub.2; r(M.sup.1.sub.2O or M.sub.2O); zH.sub.2O, wherein 2≤n≤500 and z≥25, 1≤r≤500, and M.sup.1 is Na or K and M.sup.2 is Ca.

Description

DESCRIPTION OF THE FIGURES

(1) FIG. 1 schematically shows the different steps of the treatment method for a rock formation according to the invention in view of its consolidation to treat sand infiltrations;

(2) FIG. 2 schematically shows a well drilled through an underground rock formation;

(3) FIG. 3 shows the cumulative pore volume (%) as a function of the pore size (μm) for various natural sandstone samples tested, referenced A to D, by mercury injection porosimetry;

(4) FIG. 4 shows the minimum, mean and maximum porosities measured for sandstone samples A to D and the complete sand model;

(5) FIG. 5 shows the cumulative pore volume (%) as a function of the pore diameters (μm) for the sand model tested by microtomography, in particular, the pore size distribution is obtained by numerical simulation between two parallel faces (XY, XZ or YZ in one direction then the other) on 1000 segmented microtomography images, using Image J software (Fiji) and the Beat plugin;

(6) FIG. 6A schematically shows the injection by means of a syringe of the treatment solution to be tested through the channel of the upper plug of a plastic tube receiving the complete sand used as a model material to be consolidated;

(7) FIG. 6B schematically shows the injection of compressed air through the channel of the upper plug;

(8) FIG. 7 shows the particle size distribution of metakaolin as a function of the cumulative volume of the pores % measured by laser granulometry; the various curves correspond to wet grinding times;

(9) FIG. 8 shows a table summarizing the compositions of Examples 1 to 10 and Comparative Examples 11 to 13;

(10) FIG. 9 schematically shows the protocol for measuring the gas permeability of the consolidated sand model;

(11) FIG. 10 shows the mean, minimum and maximum rupture pressures (mbars) measured for the Comparative Examples (CEX1, CEX3) and the mean rupture pressures (mbars) measured for Examples 1 to 9 according to the invention;

(12) FIG. 11 shows the mean, minimum and maximum permeabilities (m.sup.2) measured for the Comparative Examples (CEX1, CEX3) and the mean permeabilities (m.sup.2) measured for Examples 1 to 9 according to the invention;

(13) FIG. 12 shows the mean, and optionally, minimum and maximum, rupture pressures (mbars) measured for the Comparative Examples (CEX1, CEX2) and Examples 5 to 8 according to the invention on blank consolidated sand models and then on consolidated sand models onto which fresh water was injected;

DESCRIPTION OF EXAMPLES OF EMBODIMENT

I—The Following Components are Used

(14) Metakaolin:

(15) ARGICAL™ brand powdered MK 1000 sold by IMERYS, comprising 57% of SiO.sub.2, and 37% of Al.sub.2O.sub.3, having a d.sub.90 of 40 μm, a d.sub.50 of 11.55 μm and a d.sub.10 of 2.44 μm, these values being measured by laser granulometry such as described below. ARGICAL brand powdered MK 1200S sold by IMERYS, comprising 56% of SiO.sub.2, and 36% of Al.sub.2O.sub.3, having a d.sub.90 of 16.61 μm, a d.sub.50 of 5.02 μm and a d.sub.10 of 1.64 μm, these values being measured by laser granulometry such as described below. Complete siliceous sand model: Leucate standard (EN 196-1 standard, ISO 679:2009 compliant), known density of 2.6 g/cm.sup.3. Sodium silicate: BETOL 39® T sold by Woellner.

II—Treatment Method for a Rock Formation According to the Invention

(16) Steps 2 and 3 according to the invention can be done, respectively, n times and p times, n and p being integer numbers, greater than or equal to 1.

(17) In the context of the tests conducted below, n and p are equal to 1.

(18) Step 4 may take place at ambient temperature and pressure; the polymerization time is in this case at least 7 days, preferably at least 25 days, more preferably at least 40 days.

(19) The polymerization time may also be shortened if the geopolymer is heated, preferably to a temperature less than or equal to 70° C.

(20) In practice, the polymerization temperature and pressure applied during polymerization will depend on the depth at which the geopolymer injected into the rock formation is found. Since the period between the end of one extraction campaign and the resumption of the next campaign is at least 2 months and generally more than 7 months, the geopolymer has the time to polymerize in situ in the rock formation.

(21) Well 10 shown in FIG. 2, in cross section, extends from surface 12 through soil 14 down to underground rock formation 16 comprising fluid 11, especially gas, to be extracted. Rock formation 16 is not consolidated, and particles, fine and/or more or less coarse are produced in well 10 when fluid 11 is extracted through well 10. Well 10 comprises an extraction conduit 18 for fluid 11, extending from surface 12 down to near, in or under rock formation 16. Well 10 also has a tubular casing 20, surrounded by a material 22 consolidating it, for example a layer of cement, said casing 20 being arranged around withdrawal conduit 18 but at a distance from this conduit 18. Casing 20 and material 22 consolidating it comprise, in their lower parts, orifices 24 opening into rock formation 16 comprising fluid 11, in this specific example, gas. Gravel packs 26 may be arranged between casing 20 and extraction conduit 18, in their lower parts, in order to limit sand infiltration. Well 10 also comprises a packer device 28, for securing the lower part of conduit 18 to well 10 and especially to casing 20. This device 28 is, for example, a rubber ring encased in the annular space between conduit 18 and casing 20, to ensure a seal and anchor conduit 18.

(22) In operation, a volume of geopolymer cement grout according to the invention (determined according to the volume of the pores to be treated in the formation) is injected around the edges of said wells 10, for example in a radius of approximately 10 meters from the well and/or through extraction conduit 18. The grout will then fill the pores of the rock formation and therefore push fluid 11 to be extracted out of this formation. Then, a given volume of gas (also depending on the volume of pores to be treated in the formation) is injected, in the same way as the grout, so as to reconnect the fluid to the underground formation, and then expel the water contained in the grout injected into the rock formation. This operation may be repeated to promote the inter-particle adherence of the geopolymer and dry the capillary bridges formed between the particles of the formation and the geopolymer. Once the reconnection phase is established, it is possible to conduct the drying phase by filling underground formation 16 with storage fluid 11.

(23) The method according to the invention is described in reference to a particular arrangement of wells, but is not limited to this arrangement and may be applied to all wells drilled in a rock formation to be consolidated.

III—Characterization of a Test Medium

1—Sandstone Samples A to D

(24) Mercury injection porosimetry is conducted according to standard ISO 15901-1:2016, with Micromeritics AutoPore IV 9500 V1.03 of 0/200 MPa.

(25) This measurement method was implemented, in particular, with the following parameters: contact angle of 130 degrees, mercury density of 13.5335 g/l, surface tension of 485 dynes/cm, equilibration time 20 sec, evacuation time 5 minutes, white correction, 15 cc-0.68 cc solid cell and associated manufacturer software.

(26) Table 1 below indicates the pore size of sandstone samples A to D sampled in situ in micrometers at 90%, 50% or 10% of the cumulative volume distribution of pore sizes. These data result from FIG. 3.

(27) TABLE-US-00001 TABLE 1 Sample d.sub.90 d.sub.50 d.sub.10 Sample A 152.71 μm  5.42 μm 0.03 μm Sample B  78.81 μm 26.22 μm 0.26 μm Sample C 182.83 μm 51.99 μm 2.09 μm Sample D 294.52 μm 21.61 μm 0.15 μm

2—Sand Model

(28) The porosities of samples A to D in FIG. 4 are determined by ethanol saturation.

(29) The method for measuring porosity by ethanol saturation is preferably conducted by first drying the sample at 105° C. until stabilization of its mass to within +/−0.5% enabling its dry mass (mdry) to be determined, then immersing in ethanol until stabilization of its mass to within +/−0.5% enabling its saturated mass (msat) to be determined. Finally, the sample mass is determined by hydrostatic weighing (mhydro). The porosity (%) is then calculated by the relationship 100*(msat−mdry)(msat−mhydro).

(30) The porosities of complete siliceous sand are determined by microtomography (the measurements are done on tubes filled with sand such as described in Section IV). The siliceous sand is impregnated with an epoxy resin to stabilize it. The images obtained by microtomography (source 160 kV, tungsten filament, voxel size 1.06 μm) are analyzed by Image J software.

(31) Table 2 below shows the average, minimum and maximum porosities from FIG. 4.

(32) TABLE-US-00002 TABLE 2 Porosity Samples Mean (%) Minimum (%) Maximum (%) Samples A to D 24.77% 20.59 27.76 Siliceous sand model 26.3 24.7 28.2

(33) The porosity of sandstone samples A to D is comprised between 20% and 30% with a mean porosity of around 24.77%. The complete sand model (i.e., comprising fines and sand) has a mean porosity of 26.3%, ranging from 25% to 30%. The porosity of the sand model is slightly greater than that of sandstone samples A to D. In contrast, according to FIG. 5, 50% by cumulative volume of model sand pores have a diameter comprised between 28 μm and 34 μm. Thus, the d.sub.50 of the sand model is equivalent to those measured for samples A to D (d.sub.50=21.6 μm to 52.0 μm).

(34) In conclusion, the complete siliceous sand selected is a good model to reproduce the porous network of the underground rock formation.

IV—Preparation of a PAM (Polyacrylamide) Sample, (CEX1)

(35) An amount of 1.101 g of a PAM powder, sold by Floerger under reference FA 920 SH, is dissolved in 198.9 g of water with gentle stirring (approximately 200 rpm), for 3 h. The stock solution obtained is then diluted by the addition of water until obtaining the tested solution at 2500 ppm (or 2.5 g of PAM per 1000 g of solution). The activity index is 90.85%.

V—Preparation of the Basic Activator Solution as Comparative Sample (CEX2, CEX3)

(36) The basic solution thus comprises 36.76 g of sodium silicate including 64% of water by mass, 10.15 g of sodium hydroxide and 53.09 g of water added for CEX2 or 0.96 moles of SiO.sub.2 and 1 mole of Na.sub.2O and 25 moles of water, serving as comparative example CEX3; the amount of water added is doubled, or 106.18 g (50 mol), the molar proportions of SiO.sub.2 and Na.sub.2O are unchanged. The sodium silicate used also comprises 64% by mass of water for CEX2 and CEX3.

VI—Compressive Strength of a Standard Metakaolin-Based Mortar (MK 1000) Measured by Mixing with Demineralized Water or Brine (20 g/L)

(37) It is not possible to measure the compressive strength of Comparative Examples CEX1 and CEX2 because the solutions are too liquid (there is too much water) to provide a resistant and non-cracking paste within the framework of standard EN 196-1 (manufacture of standardized mortar). The mortar is prepared according to a manufacturing method well known to the skilled person. Standardized sand (siliceous Leucate 0/1.25 mm according to EN 196-1 and compliant with ISO 679:2009) is mixed with the geopolymer cement based on MK 1000 (312 g), sodium silicate (244 g), sodium hydroxide (65 g) and water (106 g). The compressive strength of mortar based on metakaolin MK1000 is around 42-43 MPa at 7 days, and 49 MPa at 28 days when it is malaxed with demineralized water. This compressive strength is similar for the same mortar based on metakaolin MK 1000 when brine (20 g/l) is used to manufacture it.

(38) The advantage of a geopolymer cement grout as treatment solution compared to polyacrylamide polymers (CEX1) or the basic sodium silicate solution (CEX2) especially resides in the formation of a coating lining the pores to be consolidated that has good water resistance properties, in particular to brine.

VII—Support, Treatment Fluid Injection and Gas Injection (Flushing)

(39) The support for injecting a treatment solution is a plastic tube 30 (see FIGS. 6A and 6B), with a diameter of around 10 mm and a height h of around 30 mm, comprising an upper plug 32 and a lower plug 34, each of said plugs 32, 34 comprising a channel passing through it and opening onto the interior volume of tube 30. Tube 30, comprising the lower plug 34, is filled with sand model 36 in one go and sand 36 is packed using upper plug 32. A volume of grout 38 equivalent to 10 porous volumes (10 times the porous volume of sand model 36), or approximately 10 ml, is injected using a syringe 40 through the channel of upper plug 32 (see FIG. 6A). This injection step may be repeated if necessary. Then, compressed air 42 is injected (flushing) for 1 minute through the channel of upper plug 32 so as to expel the water contained in the injected grout (see FIG. 6B). In this specific example, the maximum compressed air pressure is 2 bars. This step may be repeated if necessary. These steps of injecting geopolymer cement grout and compressed air, then the step of polymerizing the geopolymer, are carried out at ambient temperature (in particular of around 20° C.) and at atmospheric pressure for Examples 3 to 10 (EX3 to EX10), and Comparative Examples 11 to 13 (CEX11-CEX13). For Examples 1 and 2 (EX1-2), the polymerization step is accelerated by subjecting the sand models treated to a heat treatment aimed at accelerating setting in the laboratory and consisting of subjecting them to a temperature of 70° C. in an oven for 24 h (ambient pressure).

(40) The treated sand samples are tested after the heat treatment in the case of Examples 1 and 2, and at the end of at least 10 days so that the consolidation is effective (i.e., that the geopolymer is polymerized) for a polymerization at ambient pressure and temperatures.

VIII—Preparation of Geopolymer Cement Grout

(41) Different examples of geopolymer cement grout are prepared from the proportions described in the table shown in FIG. 8. The basic activator solution, comprising sodium silicate, sodium hydroxide and added water (not included in the sodium silicate solution), is prepared in advance so that it cools to ambient temperature. Then the solid particles, in particular metakaolin, are introduced into the basic solution, with stirring with a magnetic stirrer, for 30 minutes. The added water is demineralized. The grout obtained is ready to use.

IX—Injectability Into the Sand Model

1—Comparative Examples: CEX1, CEX2 and CEX3, and CEX11-13

(42) The polyacrylamide (CEX1) and sodium silicate (CEX2, CEX3) solutions are injected with no difficulty into the filled tubes of the sand model.

(43) In contrast, it is not possible to inject the geopolymer cement grout according to Comparative Examples 11 (CEX11) and 12 (CEX12). Reduction of the mass concentration of metakaolin does not improve injectability (since CEX11 is less concentrated in metakaolin than CEX12). The injectability of a geopolymer cement (CEX13) with a metakaolin (MK 1200S) comprising finer particles also does not improve injectability since injection is still impossible.

2—Wet Grinding

(44) The inventors then proceeded to wet grinding of metakaolin MK 1200S. A volume of 200 ml of demineralized water is mixed with 60 g of MK 1200S powder then the whole is ground using a planetary grinder, Pulverisette 7 (marketed by the Fritsch company); the balls have a diameter of around 0.5 mm. The grinding speed is around 100 revolutions per minute and the grinding time is variable (in Table 3 below comprised between 3 h and 8 h). The mixture is then recovered and dried in the oven at 105° C. for 24 h. The values indicted in Table 3 below result from FIG. 7.

(45) TABLE-US-00003 TABLE 3 Grinding d.sub.90 d.sub.50 d.sub.10 BH60-3 h 8.74 3.34 1.14 BH60-4 h 7.72 3.16 1.19 BH60-5 h 7.01 2.81 1.05 BH60-6 h 6.83 2.65 0.98 BH60-8 h 5.89 2.57 0.95

(46) The geopolymer cement grouts according to Examples EX1 to EX10, including EX2A, for which the metakaolin has been ground, are all injectable into the sand model, regardless of the grinding time of 3 h, 4 h, 5 h, 6 h, 7 h or 8 h, for a mass of metakaolin relative to the mass of the geopolymer cement grout greater than or equal to 0% and less than or equal to 30%.

(47) According to the porosity examined above for the siliceous sand model (d.sub.50 comprised between 28 μm and 34 μm) and d.sub.50 of metakaolin particles measured, the jamming ratio is comprised between 8.4 and 13.2.

3—Laser Granulometry Measurement Protocol

(48) The reference for the measurement device is: Shimadzu SALD 2300, the software is WING SALD II. 0.1 g of sample powder to be tested is mixed in 50 ml of pure water, then the powder is dispersed for 3 min with ultrasound. The powder in suspension is arranged in the particle size analyser (batch cell), is filled with pure water; stirring of the batch cell is at maximum; dropwise addition of the powder obtained into the batch cell; the batch cell must be filled between the two lines after addition of the solution. For acquisition, the parameters for kaolinite in the software are used. Then, addition of the suspension into the batch cell is stopped when the luminous intensity is comprised between 20 and 60%. Adsorbence is thus comprised between 0 (and strictly greater than 0) and 0.2. Manual grinding is optionally done dry for 1 minute to deagglomerate the ground powder.

X—Evaluation of Permeability and Rupture Pressure (mbar) of Sand Models Treated by the Geopolymer Cement Grout According to the Invention, the Polyacrylamide Solution (CEX1) and the Basic Sodium Silicate Solution (CEX3)

1—Permeability Measurement Protocol (m.SUP.2.)

(49) The sample to be tested, i.e., tube 30 comprising model sand 36 having undergone at least one treatment fluid injection, in this specific example a single injection, then at least one neutral treatment gas injection, in particular argon, in this specific example, a single gas injection, is in fluid connection with a pressure gauge 50 by means of a tight fitting 52. Upper plug 32 and lower plug 34 of tube 30 were removed beforehand.

(50) A gas 54, in this specific example compressed air, is injected into the sample. The gas flow rate and gas pressure are regulated by means of a flow-rate controller device 56 and a pressure regulator 58 coupled to pressure gauge 50.

(51) The permeability is measured according to the following Forchheimer formula:

(52) $\frac{\left(P_i^2-P_0^2\right)}{{\mathrm{LP}}_0}=\frac{\mu }{K}\times \frac{Q}{A}+\frac{10.44}{D}\rho \frac{Q^2}{A^2}$

(53) wherein P.sub.0 is atmospheric pressure (Pa), P.sub.i is the upstream pressure (Pa), L is the height of the sample tested (m), μ is the dynamic viscosity (Pa.Math.s), K is the permeability (m.sup.2), Q is the volume flow rate reduced to P.sub.0 (m.sup.3.Math.s−.sup.1), A is the area of the cross section (m.sup.2), D is the mean pore diameter (m) and ρ is the density of the fluid (kg.Math.m.sup.−3).

(54) In order to determine values D and K of the Forchheimer equation, a density ρ of the injected fluid is used (argon: 1.7 kg/m.sup.3), then curve (Pi.sup.2−P.sub.0.sup.2)/LP.sub.0 is plotted according to flow rate Q, and the leading coefficients of the polynomial of degree 2 are recovered and interpolated in the sense of least squares by Excel. The intercept is set to zero and the interpolation is of the form a x+b x.sup.2. From coefficients a and b calculated in the sense of least squares, K and D are calculated as: K=μ/(a*A) and D=10.44*ρ/(b*A.sup.2).

2—Mass Percent of Metakaolin in the Geopolymer Cement Grout Versus Rupture Pressure

(55) For the measurement of the rupture pressure, upper 32 plug and lower plug 34 of tube 30 have been removed beforehand, then argon is injected at increasing pressure at the lower portion of tube 30 (corresponding to the one receiving lower plug 34). The pressure value from which the consolidated sand breaks and disintegrates until it comes completely out of the tube is noted.

(56) The geopolymer cement grouts according to Examples EX1 to EX9 were injected into the sand model, then compressed air is injected to expel the water, such as described in Section VII. The breaking pressures (see FIG. 10) are therefore measured in the consolidated sand models. FIG. 10 also shows on the x-axis the number of days or hours after the last gas injection performed at the end of which the rupture pressure was measured. The rupture pressures measured in FIG. 10 for Examples 1 to 9 (EX1-9) were obtained for geopolymer cement grouts for which the metakaolin has undergone wet grinding for 8 h. It was noted that from 7% by mass of metakaolin in the grout the rupture pressure (mbar) is increased by 2 relative to PAM (CEX1), and 3 for 25% by weight of metakaolin in the grout.

3—Mass Percent of Metakaolin in the Geopolymer Cement Grout Versus Permeability kgas (m.SUP.2.) (FIG. 11)

(57) The gas permeabilities (argon) are measured in the initial state at low pressure gradient (100 to 500 mbars) on consolidate sand (such as described in Section VII). FIG. 11 also shows on the x-axis (EX3-EX9) the number of days after the last gas injection performed at the end of which the rupture pressure was measured. Permeability was measured for the geopolymer cement grouts (EX1-9) whose metakaolin has undergone wet grinding for 8 h.

(58) In the first approach, the consolidated sand model permeability tested with the basic solution (CEX3) is considered to be equivalent to the permeability of the model sand before consolidation. It is noted that up to 15% of metakaolin by mass, the permeability of the sand model tested and consolidated is of the same order of magnitude as that of CEX3.

(59) The permeability of Examples 8 and 9 could be improved, especially by increasing the size of metakaolin particles further, especially the d.sub.50 of the metakaolin particles.

4—Mass Percent of Metakaolin in the Geopolymer Cement Grout Versus Rupture Pressure

(60) The sole differences with Examples 5 to 8 tested at point X.3. above are that: the treated sand models undergo a heat treatment aimed at accelerating setting in the laboratory and consisting of subjecting them to a temperature of 70° C. in an oven for 24 hours (ambient pressure), then allowing them to stand at ambient pressure and temperature (20° C.) for 6 days; the wet grinding of metakaolin is 6 hours; the pressure measurements are first done on consolidated sand, then on the same consolidated sand that has also undergone an injection of fresh water.

(61) It is observed in FIG. 12 that the consolidations with PAM (CEX1) and the basic sodium silicate solution (CEX3) are poor, since the sand samples are destroyed following the injection of fresh water (leakage of the sand by the lower part of the tube and zero measured rupture pressure).

(62) It is also observed that the geopolymer cement grout according to the invention (EX5-8) conserves an equivalent rupture pressure before and after freshwater injection. Then, from 15% of metakaolin by mass in the grout (EX7), the rupture pressure is tripled compared to Comparative Examples CEX1 and CEX3.

XI—Viscosity Measurements

(63) TABLE-US-00004 TABLE 4 Pre-shearing Examples σ max (Pa) of 1 sec (Pa) μ measured (mPa.s) CEX1 1  0 12.8 CEX3 1  0  2 EX10 5 25 45.5 EX9 5 20  5.8 EX7 5 20  5.9

(64) Viscosity measurement protocol: the measuring device is a Kinexus rheometer, Malvern brand, with a cone-plane geometry. For each test, the maximum climb stress σ and the duration of ascent and descent, and a pre-shear (20 Pa or 25 Pa) are fixed if necessary. The viscosity is determined by calculating the slope of the linear part of the ascent curve (the curve corresponds to the shear stresses (Pa) measured on the y-axis as a function of the shear rate (s.sup.−1) on the x-axis). The most easily injectable geopolymer cement grouts are those with a viscosity close to water, i.e., those of Examples 7 and 5.