Enhanced hydrocarbon recovery process using a polymer of a crystalline form of the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid

Abstract

A process for enhanced hydrocarbon recovery comprising the following steps: a) Preparation of an injection fluid comprising at least one water-soluble polymer obtained from 2-acrylamido-2-methylpropane sulfonic acid, with water or with brine, the 2-acrylamido-2-methylpropane sulfonic acid being, before polymerization, a crystalline form of the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid having a powder X-ray diffraction pattern comprising peaks at 11.7°; 12.2°; 13.2°; 13.5°; 15.6°; 16.8°; 17.8°; 18.5°; 19.1°; 20.6°; 21.4°; 23.3°; 25.1°; 25.8°; 26.9°; 29.1°; 29.5°; 31.0°; 33.0°; 33.6°; 34.4°; 35.2°; 35.9°; 37.1°; 38.4°; 39.6°; 41.1°; 42.9°; 45.1°; 46.0°; 47.2°; 47.6° degrees 2-theta; b) Injection of the injection fluid into a subsurface formation; c) Sweeping of the subsurface formation using the injected fluid; d) Recovery of an aqueous and hydrocarbon mixture.

Description

Title of the invention: Enhanced hydrocarbon recovery process using a polymer of a crystalline form of the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid. Field of the invention

[0001] The present invention relates to a process for enhanced recovery of hydrocarbons (oil and / or gas) using water-soluble polymers obtained from the crystalline form of the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid. Prior art

[0002] Most of the oil fields currently being exploited have reached maturity and have, in fact, begun to decline in production or are about to do so. The recovery rate of these fields is currently on the order of 15 to 35% on average compared to the initial quantity of oil. They therefore still offer considerable production potential.

[0003] Generally, the recovery of crude oil contained in the deposits takes place in several stages.

[0004] Production initially results from the natural energy of the fluids and rock as they decompress. Following this depletion phase, the amount of oil recovered at the surface represents on average some 5 to 15% of the initial reserve. It is therefore necessary, in a second stage, to employ techniques aimed at increasing the recovery yield while maintaining field pressure.

[0005] The most frequently implemented method consists of injecting water into the reservoir through injection wells specifically designed for this purpose. This is known as secondary recovery. This second phase stops when the water / oil ratio becomes too high, that is, when the amount of water in the mixture produced by the producing wells is too great. This secondary recovery thus makes it possible to obtain an additional recovery rate of approximately 10 to 20%.

[0006] Other usable techniques are grouped under the name enhanced oil recovery (EOR). Their aim is to recover between 10 and 35% more oil compared to the initial quantity of oil. Under the term enhanced oil recovery, various thermal and non-thermal techniques are known, such as electrical, miscible, steam, or chemical techniques for improving the recovery of oil remaining in place (see "Oil & gas science and technology" - IFP magazine, vol. 63 (2008) no. 1, pp. 9-19).

[0007] The term "petroleum" refers to any type of oil, namely light oil, heavy oil, or even bituminous oil. An oil generally results from the transformation natural organic matter and is composed of a mixture of hydrocarbons. In the description of the prior art or of the invention, the terms "petroleum" and "oil" are used to refer to the same material, except when referring to the composition of an emulsion or dispersion.

[0008] The efficiency of water injection sweeping is generally improved by the addition of water-soluble polymers. The expected and proven benefits of using polymers, through the "viscosification" of the injected water, are improved sweeping and a reduction in viscosity contrast between fluids to control their mobility ratio in the field, thereby enabling rapid and efficient hydrocarbon recovery. These polymers increase the viscosity of the water.

[0009] It is known to those skilled in the art that synthetic water-soluble polymers, in particular polymers based on 2-acrylamido-2-methylpropanesulfonic acid (ATBS), are highly advantageous polymers for increasing the viscosity of aqueous solutions and are used in enhanced recovery. Indeed, ATBS-based polymers are known to be tolerant to divalent salts as well as to high temperatures.

[0010] In addition to increasing the viscosity of water, the polymers used must have good filterability. Polymers with poor filterability tend to clog the formation and slow down or even inhibit the production of hydrocarbons (oil and / or gas). However, filterability deteriorates as the molecular weight of the polymer increases. Therefore, there is a delicate trade-off between molecular weight and filterability.

[0011] Polymers added to injection water are generally subjected to long residence times in the reservoir, between injection wells and production wells, ranging from a few months to a few years. During this time, they can undergo thermal degradation, resulting in an increase in their hydrolysis rate through the conversion of acrylamide or ATBS units into acrylates, or chemical degradation leading to chain breakage (a decrease in molecular weight) through radical attack. In both cases, these mechanisms generally result in a decrease in viscosity and therefore a loss of the effectiveness of the injected aqueous polymer solution in flushing the underground formation. There is therefore a real interest in developing polymers more resistant to these processes involved in any enhanced hydrocarbon recovery (oil and / or gas) project. Description of the invention

[0012] The Applicant has discovered and developed a process for enhanced recovery of hydrocarbons (oil and / or gas) using water-soluble polymers containing as a monomer a crystalline form of the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid, said polymers exhibiting properties improved particularly in terms of filterability and chemical and thermal stability.

[0013] The improved performance of the injection fluid containing polymers obtained from the crystalline form of the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid allows for a reduction in the quantity of product required and therefore a reduction in overall water consumption and greenhouse gas emissions such as CO2.

[0014] More specifically, the invention relates to a process for enhanced recovery of hydrocarbons (oil and / or gas) comprising the following steps: a) Preparation of an injection fluid comprising at least one water-soluble polymer of 2-acrylamido-2-methylpropane sulfonic acid, with water or brine; 2-Acrylamido-2-methylpropane sulfonic acid being, before polymerization, a crystalline form of the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid having a powder X-ray diffraction pattern comprising peaks at 11.7°; 12.2°; 13.2°; 13.5°; 15.6°; 16.8°; 17.8°; 18.5°; 19.1°; 20.6°; 21.4°; 23.3°; 25.1°; 25.8°; 26.9°; 29.1°; 29.5°; 31.0°; 33.0°; 33.6°; 34.4°; 35.2°; 35.9°; 37.1°; 38.4°; 39.6°; 41.1°; 42.9°; 45.1°; 46.0°; 47.2°; 47.6° degrees 2-theta; b) Injection of the injection fluid into an underground formation; c) Scanning of the underground formation using the injected fluid; d) Recovery of an aqueous and hydrocarbon mixture (mixture comprising water and hydrocarbons).

[0015] Quite surprisingly, the use of at least one water-soluble polymer obtained from the crystalline form of the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid allows for the effective treatment of underground formations. It is indeed the use of the crystalline form of the sodium salt of the acid 2-acrylamido-2-methylpropane sulfonic acid, in the preparation of the water-soluble polymer, which gives said polymer particular properties, allowing for improved hydrocarbon recovery. Description of the invention

[0016] The term "polymer" refers to a homopolymer or a copolymer. A copolymer is defined as a polymer obtained from at least two different monomers. It can therefore be a copolymer of at least two monomers chosen from among hydrophilic anionic monomers, hydrophilic cationic monomers, hydrophilic nonionic monomers, hydrophilic zwitterionic monomers, hydrophobic monomers, and mixtures thereof.

[0017] By "hydrophilic monomer" is meant a monomer which has an octanol / water partition coefficient, Kow, of less than 1, wherein the partition coefficient Kow is determined at 25°C in an octanol / water mixture having a volume ratio of 1 / 1, at a pH between 6 and 8.

[0018] By "hydrophobic monomer" is meant a monomer which has an octanol / water partition coefficient, Kow, greater than 1, in which the partition coefficient Kow is determined at 25°C in an octanol / water mixture having a volume ratio of 1 / 1, at a pH between 6 and 8.

[0019] The octanol / water partition coefficient, Kow, represents the ratio of the concentrations (g / L) of a monomer between the octanol phase and the aqueous phase. It is defined as follows:

[0020] [Math.l] _ [ / nonomer] r '1 [nwnamer ejn

[0021] By definition, a water-soluble polymer is a polymer which gives an aqueous solution without insoluble particles when dissolved under stirring at 25°C and with a concentration of 50 gL 1 in water.

[0022] By "X and / or Y" means "X", or "Y", or "X and Y".

[0023] Also part of the invention are all possible combinations between the The disclosure includes various embodiments, whether preferred or given by way of example. Furthermore, when ranges of values ​​are specified, the bounds are included within those ranges. The disclosure also encompasses all combinations of the bounds within those ranges. For example, the value ranges "1-20, preferably 5-15" imply the disclosure of the ranges "1-5", "1-15", "5-20", and "15-20", as well as the values ​​1, 5, 15, and 20.

[0024] Crystalline form of the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid

[0025] The crystalline form of the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid has a powder X-ray diffraction pattern comprising peaks at 11.7°; 12.2°; 13.2°; 13.5°; 15.6°; 16.8°; 17.8°; 18.5°; 19.1°; 20.6°; 21.4°; 23.3°; 25.1°; 25.8°; 26.9°; 29.1°; 29.5°; 31.0°; 33.0°; 33.6°; 34.4°; 35.2°; 35.9°; 37.1°; 38.4°; 39.6°; 41.1°; 42.9°; 45.1°; 46.0°; 47.2°; 47.6° degrees 2-theta. The uncertainty of these peaks is generally on the order of + / - 0.1°.

[0026] X-ray crystallography, also known as X-ray diffractometry, is an analytical technique used to study the structure of crystalline matter at the atomic scale. It relies on the physical phenomenon of X-ray diffraction. A diffractometer with a copper source can be used.

[0027] A powder formed from a particular crystalline phase always exhibits diffraction peaks in the same directions. This diffraction pattern thus forms a a true signature of the crystalline phase. It is therefore possible to determine the nature of each crystalline phase within a mixture or a pure product.

[0028] This signature is specific to each organic or inorganic crystalline compound, and takes the form of a list of position peaks at an angle of 20 (2-theta).

[0029] This technique is used to characterize matter, in particular the different crystalline forms that can exist for the same chemical molecule.

[0030] The crystalline form of the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid has a Fourier transform infrared spectrum comprising peaks at 3576 cm⁻¹, 3485 cm⁻¹, 3310 cm⁻¹, 3079 cm⁻¹, 2975 cm⁻¹, 1658 cm⁻¹, 1629 cm⁻¹, 1543 cm⁻¹, 1403 cm⁻¹, 1321 cm⁻¹, 1301 cm⁻¹, 1205 cm⁻¹, 1187 cm⁻¹, 1163 cm⁻¹, 1046 cm⁻¹, 980 cm⁻¹, and 629 cm⁻¹. The uncertainty of these peaks is generally on the order of 8 cm⁻¹.

[0031] Infrared measurement is carried out by Fourier transform, for example by means of a Perkin Elmer Spectrum 100 type spectrometer equipped with a single reflection ATR Polarization accessory, the accuracy of which is 8 cm'.

[0032] Fourier transform infrared spectroscopy is the analysis of vibrations emitted, absorbed, or scattered by molecules. This technique is sensitive to so-called short interactions (influence of the unit cell on the bonds). In most cases, the Fourier transform infrared spectra of different crystal systems differ significantly. The Fourier transform infrared spectrum therefore reflects the details of the crystal structure of a chemical compound.

[0033] Generally, and unless otherwise indicated, the X-ray diffraction pattern and the infrared spectrum are obtained at 20°C and at a pressure of 1 absolute atmosphere (101,325 Pa).

[0034] The crystalline form of the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid has a minimum ignition energy greater than 500 mJ, preferably greater than 1000 mJ (1 mJ = 103 joules).

[0035] The minimum ignition energy represents the minimum energy that must be supplied to a product (chemical compound) to cause it to ignite. The energy can be electrical or thermal. The minimum ignition energy is essential information for considering the risk of explosion during the handling of the product (transfer, storage, reaction, shaping, etc.).

[0036] The minimum ignition energy depends on the properties of the powder (composition) as well as its macromolecular structure (particle size, crystalline shape, specific surface area).

[0037] In the case of solids, this energy is the minimum energy of an electrical spark capable of igniting a dust cloud. The higher the value of the minimum ignition energy, the lower the risk posed by the solid during its use. reading, handling, storage.

[0038] The measurement of the minimum ignition energy is carried out according to the standard NF EN 13821.

[0039] The crystalline form of the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid exhibits four thermal phenomena with the differential scanning calorimetry technique, at 49.8°C; 144.8°C; 169.8°C and 254.3°C. The uncertainty in observing these phenomena is generally on the order of 10°C, advantageously 5°C or less.

[0040] Thermal phenomena are measured by differential scanning calorimetry (DSC). This technique exploits the measurement of the heat variation associated with the thermal denaturation of the compound when it is heated at a constant rate, for example with a heating ramp of 10°C / minute.

[0041] Process for manufacturing the crystalline form of sodium salt

[0042] The process for manufacturing the crystalline form of the sodium salt of the acid 2-Acrylamido-2-methylpropane sulfonic acid comprises at least the following successive steps: 1) mixing of 2-acrylamido-2-methylpropane sulfonic acid with an aqueous solution SAi and at least one sodium salt, advantageously for at least 1 minute, in order to form an aqueous solution or aqueous suspension SA2; 2) distillation at a pressure lower than atmospheric pressure of the aqueous solution or aqueous suspension SA2 in order to form a suspension Si; 3) solid / liquid separation of the Si suspension and isolation of the Si suspension crystals obtained at the end of step 2) in the form of a Cp composition. The crystals obtained are in crystalline form of the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid.

[0043] By sodium salt(s) in step 1), means at least one inorganic salt(s), for example sodium hydroxide, sodium carbonate, sodium bicarbonate or mixtures thereof.

[0044] The temperature and mixing time in step 1) may vary depending, in particular, on the concentration of 2-acrylamido-2-methylpropane sulfonic acid. Those skilled in the art will know how to adjust the temperature variation and mixing time to optimize crystal formation.

[0045] The process for manufacturing the crystalline form of the sodium salt can be carried out on any form of 2-acrylamido-2-methylpropane sulfonic acid, such as the needle form or the hydrated form.

[0046] The manufacturing process can be carried out on any degree of purity of 2-acrylamido-2-methylpropane sulfonic acid.

[0047] Thus the process can be carried out downstream of any type of manufacturing process of 2-acrylamido-2-methylpropane sulfonic acid. It can also be carried out on already obtained crystals of 2-acrylamido-2-methylpropane sulfonic acid.

[0048] Step 1) of the process for manufacturing the crystalline form of sodium salt:

[0049] 2-Acrylamido-2-methylpropane sulfonic acid is produced by a manufacturing process as described above (acrylonitrile, fuming sulfuric acid, and isobutylene). 2-Acrylamido-2-methylpropane sulfonic acid may be in the form of a fine powder or shaped in a controlled manner by a process such as compaction, granulation, or extrusion.

[0050] 2-Acrylamido-2-methylpropane sulfonic acid can be added to an aqueous solution S Ai before, after or in parallel with sodium salt, preferably the addition is done in parallel.

[0051] Advantageously, the concentration of the aqueous solution or aqueous suspension SA2 in sodium salt is between 1% by weight and saturation, preferably between 10% by weight and saturation, more preferably between 20% by weight and saturation, more preferably between 30% by weight and saturation, more preferably between 40% by weight and saturation, and even more preferably between 50% by weight and saturation, by weight relative to the weight of the aqueous solution or aqueous suspension SA2.

[0052] 2-Acrylamido-2-methylpropane sulfonic acid and the sodium salt can be added all at once or in several stages. Preferably, they are added in several stages.

[0053] When the addition is made in several stages, the 2-acrylamido-2-methylpropane sulfonic acid and the sodium salt are added in fractions.

[0054] When 2-acrylamido-2-methylpropane sulfonic acid and sodium salt are added in fractions, there is no limit to the number of fractions, advantageously there are at least two fractions, preferably at least three fractions.

[0055] There is no limitation as to the order of addition between 2-acrylamido-2-methylpropane sulfonic acid and the sodium salt. They can be added at the same time (i.e. in parallel), one after the other (2-acrylamido-2-methylpropane sulfonic acid first then the sodium salt, or vice versa), or alternately (a first fraction of 2-acrylamido-2-methylpropane sulfonic acid, then a first fraction of the sodium salt, followed by a second fraction of 2-acrylamido-2-methylpropane sulfonic acid then a second fraction of the sodium salt and so on), preferably they are added at the same time.

[0056] When adding one after the other or alternately, the start of the addition of the second compound (whether it be 2-acrylamido-2-methylpropane sulfonic acid or sodium salt) can start before the end of the addition of the first compound.

[0057] A first fraction Fl of 2-acrylamido-2-methylpropane sulfonic acid advantageously represents at least 1 mol% of the total 2-acrylamido-2-methylpropane sulfonic acid present in the aqueous solution or aqueous suspension SA2, preferably at least 5 mol%, more preferably at least 10 mol%, even more preferably at least 15 mol% and even more preferably at least 20 mol%.

[0058] A second fraction F2 of 2-acrylamido-2-methylpropane sulfonic acid advantageously represents at least 1 mol% of the total 2-acrylamido-2-methylpropane sulfonic acid present in the aqueous solution or aqueous suspension SA2, preferably at least 5 mol%, more preferably at least 10 mol%, even more preferably at least 15 mol% and even more preferably at least 20 mol%.

[0059] A third fraction F3 of 2-acrylamido-2-methylpropane sulfonic acid advantageously represents at least 1 mol% of the total 2-acrylamido-2-methylpropane sulfonic acid present in the aqueous solution or aqueous suspension SA2, preferably at least 5 mol%, more preferably at least 10 mol%, even more preferably at least 15 mol% and even more preferably at least 20 mol%.

[0060] In a particular mode, the process is carried out continuously; in this case, 2-acrylamido-2-methylpropane sulfonic acid and sodium salt are added continuously.

[0061] The amount of 2-acrylamido-2-methylpropane sulfonic acid in the aqueous solution or aqueous suspension SA2 is advantageously between 10 and 90% by weight relative to the total weight of the aqueous solution or aqueous suspension SA2, preferably between 20 and 85% by weight, more preferably between 30 and 80% by weight.

[0062] The mixing in step 1) is advantageously carried out at a temperature between 0 and 90°C, preferably between 5 and 60°C, more preferably between 10 and 40°C, in order to obtain the aqueous solution or aqueous suspension SA2.

[0063] In a particular mode, the aqueous solution or aqueous suspension SA2 may comprise one or more organic solvents.

[0064] The amount of organic solvent can vary depending on the temperature and the amount of 2-acrylamido-2-methylpropanesulfonic acid or sodium salt. This amount is not limited as long as it does not prevent the formation of the crystalline form of the sodium salt of 2-acrylamido-2-methylpropanesulfonic acid. A person skilled in the art will be able to determine this limit, which is a routine task. Generally, the aqueous solution or aqueous suspension SA2 contains more water (by volume) than organic solvent.

[0065] The organic solvent(s) are advantageously chosen from among the compounds following: - organic acids, advantageously carboxylic acids comprising 1 to 8 carbons; - amides advantageously comprising from 1 to 8 carbon atoms; - alcohols advantageously comprising from 1 to 8 carbon atoms; - ketones advantageously comprising 3 to 8 carbon atoms; - ethers advantageously comprising from 2 to 8 carbon atoms; - esters advantageously comprising from 2 to 8 carbon atoms; - alkanes advantageously comprising 4 to 8 carbon atoms; - halogenated hydrocarbon compounds advantageously comprising from 2 to 8 carbon atoms; - nitriles advantageously comprising from 1 to 8 carbon atoms; or - their mixtures.

[0066] When an organic solvent is used in the context of the invention, the temperature can be adjusted so that the solvent + water mixture remains in liquid form.

[0067] These compounds can be linear or branched. They can be saturated or include unsaturations, an unsaturation corresponding to a double or triple bond (for example C=C or C=C).

[0068] Preferably, the organic solvent is chosen from acrylonitrile, isopropanol, acrylic acid, acetic acid, or mixtures thereof. Preferably, the organic solvent is acrylonitrile.

[0069] The organic solvent is generally in liquid form at the temperature at which steps 2) and 3) are carried out. In addition, it is advantageously partially miscible in water, preferably completely miscible in water.

[0070] The organic solvent may, where appropriate, allow the solubilization of any impurities or by-products present with the 2-acrylamido-2-methylpropane sulfonic acid used to form the aqueous solution or aqueous suspension SA2. However, 2-acrylamido-2-methylpropane sulfonic acid is not necessarily soluble in the solvent.

[0071] In a preferred mode according to the invention, the aqueous solution or aqueous suspension SA2 does not contain any organic solvent.

[0072] The mixing time between the aqueous solution SAb and 2-acrylamido-2-methylpropane sulfonic acid is advantageously at least 1 minute, preferably between 1 minute and 600 minutes, more preferably between 5 minutes and 400 minutes, and even more preferably between 10 minutes and 240 minutes.

[0073] The mixing of the compounds in step 1) can be carried out using various technologies. By way of example and without limitation, we can mention reactors with agitator, loop reactors, static mixers, microreactors, piston reactors, agitated filter-dryer reactors, for example Nutsche, paddle mixers, twin-cone mixers, plowshare mixers, and disc mixers.

[0074] The pH of step 1) is advantageously controlled between 6 and 14, preferably between 8 and 14, more preferably between 10 and 14, even more preferably between 12 and 14, even more preferably between 13 and 14.

[0075] Step 2) of the process for manufacturing the crystalline form of sodium salt:

[0076] The distillation of the aqueous solution or aqueous suspension SA2 is carried out at a pressure lower than atmospheric pressure. It is generally carried out in a vacuum distillation device, which is typically an evaporator. It is therefore also referred to here as "vacuum distillation".

[0077] When the aqueous solution or aqueous suspension SA2 is distilled, typically by passing through an evaporator, crystals of the sodium salt of acrylamido-2-methyl-2-propanesulfonic acid begin to form. There is then coexistence of the aqueous solution or aqueous suspension SA2 comprising acrylamido-2-methyl-2-propanesulfonic acid, at least one sodium salt, and crystalline solid particles of the sodium salt of acrylamido-2-methyl-2-propanesulfonic acid.

[0078] The distillation of the aqueous solution or aqueous suspension SA2 can be carried out using an evaporator. This can be a falling film evaporator, a rising film evaporator, a scraped thin-film evaporator, a short-path evaporator, a forced-circulation evaporator, a spiral-tube evaporator, or a flash-cooling evaporator. It can also be a continuously stirred reactor. Preferably, the distillation takes place in a scraped thin-film evaporator, a short-path evaporator, or a forced-circulation evaporator. Even more preferably, the distillation takes place in a scraped thin-film evaporator.

[0079] Generally, an evaporator is a device comprising an inlet for the solution to be treated (aqueous solution or aqueous suspension SA2), an outlet for removing the distilled solvent (water and any organic solvents), and an outlet for removing the Sp suspension.

[0080] The residence time of the aqueous solution or aqueous suspension SA2 in the distillation apparatus (advantageously under vacuum), which is advantageously an evaporator, in other words, the distillation time at a pressure lower than atmospheric pressure, is advantageously between 1 second and 600 seconds, preferably between 3 seconds and 300 seconds, and more preferably between 30 seconds and 100 seconds. The residence time corresponds to the time required to carry out step 2), that is, the time required to prepare the suspension Si by Distillation of the aqueous solution or aqueous suspension SA2. In other words, in the case of an evaporator, this refers to the residence time of 2-acrylamido-2-methyl-2-propanesulfonic acid (and / or its crystalline sodium salt form) between the inlet and outlet of the device. This residence time depends on the amount of water (and any organic solvents), 2-acrylamido-2-propanesulfonic acid, and sodium salt present in the aqueous solution or aqueous suspension SA2. A person skilled in the art will be able to adjust this residence time to obtain 2-acrylamido-2-propanesulfonic acid in its crystalline sodium salt form, depending on the quantities of the constituents in the aqueous solution or aqueous suspension SA2.

[0081] Distillation can be carried out in a vertical or horizontal evaporator. Preferably, it is carried out in a vertical evaporator.

[0082] The aqueous solution or aqueous suspension SA2 can flow co-currently or counter-currently with the vapors generated by evaporation. Preferably, it flows counter-currently with the vapors in the distillation apparatus. In other words, the aqueous solution or aqueous suspension SA2 is preferably introduced into the distillation apparatus, advantageously an evaporator, co-currently or counter-currently with respect to the distilled solvent.

[0083] The aqueous solution or aqueous suspension SA2 can circulate through one or more evaporators in series before obtaining the suspension Si. Preferably, it circulates in a single evaporator.

[0084] The pressure during distillation is advantageously between 1 and less than 1000 mbar absolute (1 mbar = 100 Pa). It is preferably less than 900 mbar absolute, more preferably less than 800 mbar absolute, more preferably less than 700 mbar absolute, more preferably less than 600 mbar absolute, more preferably less than 500 mbar absolute, more preferably less than 400 mbar absolute, more preferably less than 300 mbar absolute, more preferably less than 200 mbar absolute, more preferably less than 100 mbar absolute, and even more preferably less than 50 mbar absolute, and advantageously greater than 1 mbar absolute. The absolute pressure corresponds to the pressure relative to zero pressure (vacuum).

[0085] In a particular mode, step 2) includes an optional step 2') to facilitate solvent evaporation. Step 2') then consists of increasing the temperature of the aqueous solution or aqueous suspension SA2; in other words, the distillation according to step 2') is carried out at high temperature.

[0086] Heating during distillation can be achieved using various technologies. By way of example, and without limitation, we can mention heating with steam, hot water, electricity, vapor compression, or a heat pump. Thus, the distillation apparatus can be of the double type. wall, a hot heat transfer fluid circulating between the two walls.

[0087] The aqueous solution or aqueous suspension SA2 is advantageously heated to a temperature between more than 5°C and 95°C, preferably between more than 10°C and 60°C, more preferably between more than 20°C and 40°C.

[0088] When the aqueous solution or aqueous suspension SA2 is heated, the temperature is advantageously higher than the temperature of step 1).

[0089] The temperature rise of the solution or aqueous suspension SA2 is advantageously carried out at a rate of between 0.1 and 10°C / hour, preferably between 0.2 and 9°C / hour, more preferably between 0.3 and 8°C / hour, and even more preferably between 0.5 and 5°C / hour.

[0090] The temperature rise may not be constant throughout the process. For example, the aqueous solution or aqueous suspension SA2 may be heated by 5°C per hour for the first three hours, and then heated at a rate of 10°C per hour until the final temperature is reached.

[0091] According to another particular embodiment of the invention, step 2) may include an optional step 2"), following or instead of step 2"), which increases the productivity and profitability of the process of the invention by accelerating the crystallization of acrylamido-2-methyl-2-propanesulfonic acid in crystalline sodium salt form. Step 2") then consists of lowering the temperature of the aqueous solution or aqueous suspension SA2.

[0092] The aqueous solution or aqueous suspension SA2 is advantageously cooled to a temperature between 5 and less than 95 °C, preferably between 10 and less than 60 °C, more preferably between 20 and less than 40 °C.

[0093] When the aqueous solution or aqueous suspension SA2 is cooled, the temperature is advantageously lower than the temperature of steps 1), 2) and optionally 2').

[0094] The temperature decrease of the aqueous solution or aqueous suspension SA2 is advantageously carried out at a rate of between 0.1 and 10°C / hour, preferably between 0.2 and 9°C / hour, more preferably between 0.3 and 8°C / hour, and even more preferably between 0.5 and 5°C / hour.

[0095] The temperature decrease may not be constant throughout the process. For example, the aqueous solution or aqueous suspension SA2 may be cooled by 5°C per hour for the first three hours, and then cooled at a rate of 10°C per hour until the final temperature is reached.

[0096] During the cooling of the aqueous solution or aqueous suspension SA2, crystals of the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid are formed and a suspension Si is obtained.

[0097] In a particular mode, sodium salt crystals of the acid 2-acrylamido-2-methylpropane sulfonic acid obtained previously can be added During this step, in order to modify the formation of the Sp II suspension, it is a set beginning of crystallization which allows for better control of the crystal temperature lization, crystal particle size, particle size distribution, purity of final product and, possibly, yield. Sodium salt crystals of the acid 2-acrylamido-2-methylpropane sulfonic acid thus added have advantageously a powder X-ray diffraction pattern including peaks at 11.7°; 12.2°; 13.2°; 13.5°; 15.6°; 16.8°; 17.8°; 18.5°; 19.1°; 20.6°; 21.4°; 23.3°; 25.1°; 25.8°; 26.9°; 29.1°; 29.5°; 31.0°; 33.0°; 33.6°; 34.4°; 35.2°; 35.9°; 37.1°; 38.4°; 39.6°; 41.1°; 42.9°; 45.1°; 46.0°; 47.2°; 47.6° degrees 2-theta (+ / - 0.1°).

[0098] According to a particular embodiment of the invention, the solvent distilled in step 2) can be partially or totally recycled to form the aqueous solution SAi of step 1). In other words, the distilled solvent is advantageously recycled at least partially into the aqueous solution SAp

[0099] According to another particular embodiment of the invention, the distilled solvent can be recycled partially or totally, generally to wash the sodium salt crystals of acrylamido-2-methyl-2-propane sulfonic acid obtained after liquid / solid separation step 3), in an optional step 4), with or without a pretreatment step.

[0100] The resulting Sp suspensions advantageously comprise between 30 and 80% by weight of 2-acrylamido-2-methylpropane sulfonic acid in crystalline sodium salt form, relative to the total weight of the Sp suspension, preferably between 50 and 60% by weight.

[0101] During step 2), the pH is advantageously greater than 10, preferably greater than 11, more preferably greater than 12, even more preferably the pH is between 13 and 14.

[0102] Step 3 of the process for manufacturing the crystalline form of sodium salt:

[0103] The sodium salt crystals of 2-acrylamido-2-methylpropane sulfonic acid contained in the Si suspension obtained at the end of step 2) are isolated by a liquid / solid separation step and are in the form of a composition Cp

[0104] The liquid / solid separation step can be carried out using various technologies. By way of example, and without limitation, we can mention the use of a centrifuge, a decanter, a filter press, a stirred smoother filter, a belt filter, a disc filter, or a rotary drum filter. Preferably, the liquid / solid separation is carried out using a centrifuge. The liquid / solid separation can also be carried out by gravity settling.

[0105] Step 3) is advantageously carried out at a temperature between -20 and 40°C, preferably between -5 and 30°C.

[0106] Preferably after step 3) of liquid / solid separation, the sodium salt crystals of 2-acrylamido-2-methylpropane sulfonic acid are not dried.

[0107] The isolated composition Ci has a sodium salt crystal content of 2-acrylamido-2-methylpropane sulfonic acid advantageously between 40 and 99%, preferably between 60 and 99% by weight, more preferably between 60 and 98%, by weight relative to the weight of composition Cp. The remainder of composition Ci may be water and / or solubilized sodium salt of 2-acrylamido-2-methylpropane sulfonic acid, and / or sodium salt introduced in step 1).

[0108] At the end of this step 3), the crystals are characterized as being crystals of the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid.

[0109] In a particular mode, the liquid phase obtained as a result of the liquid / solid separation is used totally or partially in the aqueous solution S Ai of step 1).

[0110] During step 4) the pH is advantageously controlled between 6 and 14, preferably between 8 and 14, more preferably between 10 and 14, even more preferably between 12 and 14, even more preferably between 13 and 14.

[0111] Step 4) of the process for manufacturing the crystalline form of sodium salt:

[0112] In an optional step 4), the composition Ci containing the crystals obtained at the product from step 3) is washed using a washing solution.

[0113] The washing solution may be water, an aqueous solution of sodium salt (saturated or unsaturated), or a solution (saturated or unsaturated) of sodium salt of 2-acrylamido-2-methylpropane sulfonic acid (advantageously in the crystalline form of the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid), preferably it is a saturated solution of a sodium salt of 2-acrylamido-2-methylpropane sulfonic acid.

[0114] Examples of sodium salt solutions include a solution of sodium hydroxide, sodium carbonate, sodium bicarbonate, or mixtures thereof.

[0115] The washing solution may comprise one or more organic solvents.

[0116] The amount of organic solvent may vary depending on the temperature, the amount of sodium salt of 2-acrylamido-2-methylpropane sulfonic acid or the amount of sodium salt.

[0117] Advantageously, the washing solution does not include any organic solvent.

[0118] As already indicated in relation to step 1), the organic solvent is advantageously chosen from organic acids, amides, alcohols, ketones, ethers, esters, alkanes, halogenated hydrocarbon compounds, nitriles, or mixtures thereof. Preferably, the organic solvent is chosen from acrylonitrile, isopropanol, acetic acid, or mixtures thereof. More preferably, the organic solvent is acrylonitrile.

[0119] In a particular embodiment, the washing of composition Ci obtained at the end of step 3) is carried out by spraying the washing solution onto said composition Cp

[0120] In a particular mode, the washing of the composition Ci obtained at the end of step 3) is carried out by suspending the composition Ci in the washing solution.

[0121] The weight ratio between the aqueous washing solution and the composition Ci obtained at the end of step 3) is advantageously between 0.05:1 and 10:1 and more preferably between 0.1:1 and 5:1.

[0122] This washing step is advantageously carried out at a temperature between -5 and 40°C, preferably between 0 and 30°C. A person skilled in the art will know how to adjust the temperature so as not to solubilize the crystals of the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid.

[0123] The sodium salt crystals of 2-acrylamido-2-methylpropane sulfonic acid obtained at the end of this optional step 4) can be isolated from the washing solution by a liquid / solid separation step, in the form of a C2 composition.

[0124] The liquid / solid separation step can be carried out using various technologies. By way of example, and without limitation, we can mention the use of a vertical or horizontal centrifuge, a decanter, a filter press, a belt filter, a disc filter, a pusher filter, or a rotary drum filter. Liquid / solid separation can also be carried out by gravity settling.

[0125] In a particular mode, the recovered washing solution can be used, totally or partially, again in step 4), with or without a prior treatment step.

[0126] In a particular mode, the recovered washing solution can be used, totally or partially, in the aqueous solution SAi in step 1), with or without a prior treatment step.

[0127] The pH of the washing solution in step 5 is advantageously controlled between 6 and 14, preferably between 8 and 14.

[0128] Step 5) of the process for manufacturing the crystalline form of sodium salt:

[0129] In an optional step 5), the composition Ci obtained at the end of step 3) or the composition C2 obtained at the end of step 4) is dried.

[0130] The drying stage can be carried out by various technologies. By way of example and without limitation, we can cite the use of all drying technologies by convection, conduction or radiation (fluidized bed dryer, flow bed dryer, conveyor belt dryer, microwave dryer, heated agitated smoothing filter dryer, high frequency radiation dryer, infrared dryer, spray drying).

[0131] The drying operation can be carried out at atmospheric pressure or under vacuum.

[0132] The drying step can be carried out discontinuously (batch) or continuously.

[0133] Other steps in the process of manufacturing the crystalline form of sodium salt:

[0134] During the manufacturing process, i.e., during steps 1) to 5), and regardless of the step, it is possible to introduce at least one polymerization inhibitor to prevent the possible polymerization of 2-acrylamido-2-methylpropanesulfonic acid or its salt. This inhibitor may be chosen, without limitation, from hydroquinone, paramethoxyphenol, phenothiazine, 2,2,6,6-tetramethyl(piperidin-l-yl)oxyl, 4-hydroxy-2,2,6,6-tetramethyl(piperidin-l-yl)oxyl, phenylenediamine derivatives, or mixtures thereof.

[0135] Preferably, the inhibitor is paramethoxyphenol or 4-hydroxy-2,2,6,6-tetramethyl(piperidin-l-yl)oxyl.

[0136] The amount of inhibitor introduced relative to the amount of 2-acrylamido-2-methylpropane sulfonic acid introduced in step 1) is advantageously between 0.001% and 5% by weight, more preferably between 0.01% and 1% by weight.

[0137] The inhibitor can be introduced during any one or more steps of the process. Preferably, it is introduced in additional quantity during step 1). More preferably, the inhibitor is part of the aqueous solution SAi introduced in step 1).

[0138] The manufacturing process (steps 1) to 5)) can be carried out continuously or discontinuously (in batch). Composition of the water-soluble polymer

[0139] The water-soluble polymer is obtained from the crystalline form of the sodium salt of 2-acrylamido-2-methylpropanesulfonic acid, and advantageously from at least one other monomer which may be selected from hydrophilic nonionic monomers and / or hydrophilic anionic monomers and / or hydrophilic cationic monomers and / or hydrophilic zwitterionic monomers and / or hydrophobic monomers and mixtures thereof. It may therefore be a polymer of several distinct monomers or a homopolymer.

[0140] Advantageously, the nonionic hydrophilic monomer(s) that may be used in the context of the invention are chosen, in particular, from the following group: acrylamide, methacrylamide, N-alkylacrylamides, N-alkylmethacrylamides, N,N-dialkylacrylamides, N,N-dialkylmethacrylamides, N-vinylpyrrolidone, hydroxyalkyl acrylates, hydroxyalkyl methacrylates, and mixtures thereof. Among these nonionic monomers, the alkyl groups are advantageously C1-C5, more advantageously C1-C3. They are preferably linear alkyls. Preferably, the nonionic hydrophilic monomer is acrylamide.

[0141] The water-soluble polymer advantageously comprises between 0 and 99 mol% of non-ionic monomer(s), preferably between 5 and 99 mol%, more preferably between 25 and 99 mol%.

[0142] Advantageously, the hydrophilic anionic monomer(s) that may be used in the context of the invention may be selected from a wide range. These monomers may have vinyl functional groups (advantageously acrylic, maleic, fumaric, malonic, itaconic, or allylic), and contain a carboxylate, phosphonate, phosphate, sulfate, sulfonate, or other anionically charged group. The anionic monomer may be in acidic form or as an alkaline earth metal salt, an alkali metal salt, or an ammonium salt.Examples of suitable monomers include acrylic acid; methacrylic acid; dimethylacrylic acid; itaconic acid; crotonic acid; maleic acid; fumaric acid; acrylamidoundecanoic acid; 3-acrylamido-3-methylbutanoic acid; maleic anhydride; 2-acrylamido-2-methylpropanesulfonic acid (ATBS); strong acid monomers having, for example, a sulfonic acid or phosphonic acid function such as vinylsulfonic acid, vinylphosphonic acid, allylsulfonic acid, methallylsulfonic acid, 2-methylidenepropane-1,3-disulfonic acid, 2-sulfoethyl methacrylate, sulfopropyl methacrylate, sulfopropylacrylate, allylphosphonic acid, styrene sulfonic acid, 2-acrylamido-2-methylpropane disulfonic acid; water-soluble salts of these monomers such as their alkali metal, alkaline earth metal, or ammonium salts; and mixtures thereof.In this list, the monomers mentioned as strong acid type exhibiting a sulfonic acid type function do not include the crystalline form of the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid.

[0143] The water-soluble polymer advantageously comprises between 1 and 100 mol% of hydrophilic anionic monomer(s), preferably between 5 and 60 mol%, more preferably between 10 and 50 mol%, these percentages including the monomer corresponding to the crystalline form of the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid.

[0144] In a particular mode, the hydrophilic anionic monomer(s), other than 2-acrylamido-2-methylpropane sulfonic acid in crystalline form of the sodium salt, can be salified.

[0145] By "salified," it is understood that at least one acid function of the anionic monomer is replaced by a salt that neutralizes the negative charge of the acid function. In other words, the non-neutralized (non-salified) form corresponds to the acidic form of the monomer, for example RC(=O)-OH in the case of the carboxylic acid function, while the neutralized form of the monomer corresponds to the form RC(=O)-OH X+, X+ being a a positively charged counterion (e.g., a metal salt or an ammonium compound). Neutralization of the acidic functions of the water-soluble polymer can be partial or total.

[0146] The salt form advantageously corresponds to the salts of alkali metals (Li, Na, K...), alkaline earth metals (Ca, Mg...) or ammonium (for example the ammonium ion or a tertiary ammonium). The preferred salt is the sodium salt.

[0147] Salification can take place before, during or after polymerization.

[0148] In a particular mode, the water-soluble polymer advantageously comprises between 1 and 100 mol% of anionic monomer(s) in salified form, preferably between 20 and 100 mol%, more preferably between 50 and 100 mol% and even more preferably between 80 and 100 mol%.

[0149] Advantageously, the cationic hydrophilic monomer(s) that may be used in the context of the invention are chosen, in particular, from monomers derived from vinyl-type motifs (advantageously acrylamide, acrylic, allylic, or maleic), these monomers having a quaternary phosphonium or ammonium function. Examples include, in particular and without limitation, quaternized dimethylaminoethyl acrylate (ADAME), quaternized dimethylaminoethyl methacrylate (MADAME), dimethyldiallylammonium chloride (DADMAC), acrylamido propyltrimethyl ammonium chloride (APTAC), and methacrylamido propyltrimethyl ammonium chloride (MAPTAC). The quaternizing agent may be chosen from alkyl chlorides, dialkyl sulfates, or alkyl halides. The alkyl groups are advantageously C1-C3 and linear. Preferably, the quaternizing agent is chosen from methyl chloride or diethyl sulfate.Preferably, the quaternizing agent is chosen from methyl chloride or diethyl sulfate.

[0150] A person skilled in the art will know how to prepare the quaternized monomers, in particular by protonation, for example using an alkyl halide of the type RX, where R is an alkyl group and X is a halogen (in particular methyl chloride). Furthermore, the present invention also covers DADMAC, APTAC, and MAPTAC type monomers in which the halide counterion is fluoride, bromide, or iodide instead of chloride.

[0151] In a preferred embodiment according to the invention, the cationic hydrophilic monomer is selected from diallyldialkyl ammonium salts such as diallyl dimethyl ammonium chloride (DADMAC); acidified or quaternized dialkylaminoalkylacrylamides; acidified or quaternized dialkylaminoalkylmethacrylamides, such as methacrylamidopropyl trimethyl ammonium chloride (MAPTAC), acrylamidopropyl trimethyl ammonium chloride (APTAC), and mixtures thereof. Advantageously, the alkyl groups are in the C1-C3 configuration.

[0152] The water-soluble polymer advantageously comprises between 0 and 20 mol% of cationic monomer(s), preferably between 0 and 6 mol%.

[0153] Advantageously, the hydrophilic zwitterionic monomer(s) may be a derivative of a vinyl type motif (advantageously acrylamide, acrylic, allyl or maleic), this monomer having a quaternary amine or ammonium function and an acid function of the carboxylic (or carboxylate), sulfonic (or sulfonate) or phosphoric (or phosphate) type. Examples include, but are not limited to, derivatives of dimethylaminoethyl acrylate, such as 2-((2-(acryloyloxy)ethyl) dimethylammonio) ethane-1-sulfonate, 3-((2-(acryloyloxy)ethyl) dimethylammonio) propane-1-sulfonate, 4-((2-(acryloyloxy)ethyl) dimethylammonio) butane-1-sulfonate, [2-(acryloyloxy)ethyl] (dimethylammonio) acetate, and derivatives of dimethylaminoethyl methacrylate such as 2-((2-(methacryloyloxy) ethyl) dimethylammonio) ethane-1-sulfonate and 3-((2-(methacryloyloxy) ethyl) dimethylammonio) propane-1-sulfonate.4-((2-(methacryloyloxy)ethyl)dimethylammonio)butane-1-sulfonate, [2-(methacryloyloxy)ethyl](dimethylammonio)acetate, dimethylamino propylacrylamide derivatives such as 2-((3-acrylamidopropyl)dimethylammonio)ethane-1-sulfonate, 3-((3-acrylamidopropyl)dimethylammonio)propane-1-sulfonate, 4-((3-acrylamidopropyl)dimethylammonio)butane-1-sulfonate, [3-(acryloyloxy)propyl](dimethylammonio)acetate, dimethylamino propyl methylacrylamide derivatives such as 2-((3-methacrylamidopropyl)dimethylammonio)ethane-1-sulfonate, 3-((3-methacrylamidopropyl)dimethylammonio) propane-1-sulfonate, 4-((3-methacrylamidopropyl)dimethylammonio)butane-1-sulfonate and [3-(methacryloyloxy)propyl](dimethylammonio)acetate and mixtures thereof.

[0154] The water-soluble polymer advantageously comprises 0 and 20 mol% of zwitterionic monomer(s), more preferably between 0 and 10 mol%.

[0155] Hydrophobic monomers, having a partition coefficient Kow greater than 1, may also be used in the preparation of the water-soluble polymer used in the process of the invention. They are preferably selected from the following list: alkyl, arylalkyl, and / or ethoxylated and / or propoxylated (meth)acrylamide esters; alkyl, arylalkyl, or dialkyl and / or ethoxylated and / or propoxylated (meth)acrylamide derivatives; cationic allyl derivatives having an alkyl, arylalkyl, or dialkyl chain and / or an ethoxylated and / or propoxylated chain; hydrophobic anionic or cationic (meth)acryloyl derivatives; and anionic or cationic monomeric (meth)acrylamide derivatives bearing a hydrophobic chain. The hydrophobic monomers may include halogen atoms, for example, chloride.

[0156] Among these hydrophobic monomers: - Alkyl groups are preferably at C3-C20. Alkyls at C6-C20 are preferably linear alkyls, while alkyls at C3-C5 are preferably branched. - the arylalkyl groups are preferably at C7-C25, more preferably at C7-C15, - the ethoxylated chains preferably comprise 6 to 100 -CH2-CH2-O- groups, more preferably 10 to 40, - the propoxylated chains preferably comprise 0 to 50 -CH2-CH2-CH2 -O- groups, more preferably 0 to 20.

[0157] The water-soluble polymer advantageously comprises less than 5 mol% of hydrophobic monomers.

[0158] When the water-soluble polymer includes hydrophobic monomers, they are present in such quantity that the polymer remains soluble in water.

[0159] Monomers exhibiting a fluorescent function can also be used within the scope of the invention. A monomer exhibiting a fluorescent function can be detected by any suitable method, for example, by fluorometry with a fixed-wavelength fluorometer. Generally, detection of the monomer exhibiting a fluorescent function occurs at the excitation and emission maxima, which can be determined using a scanning fluorometer.

[0160] Monomers having a fluorescent function are chosen, for example, from monomers comprising sodium styrene sulfonate and styrene sulfonic acid, vinylimidazole and its derivatives, 9-vinyl anthracene and its derivatives, pyranine and its derivatives, coumarin and its derivatives, quinolaxin and its derivatives, pi-nacyanol and its derivatives, xanthydrol and its derivatives, luminol and its derivatives, dabsyl and its derivatives, 3-hydroxy-2-methylene-3-(l-naphthyl)propionic acid and its derivatives, rhodamine and its derivatives, N-dibenzosuberenylacrylamide and its derivatives, N-9-xanthenyllacrylamide and its derivatives, naphthalic derivatives, fluorescein and its derivatives, pyrene and its derivatives, carbostyril and its derivatives, pyrazoline and its derivatives, allyl dibenzosuberenol and its derivatives, chinconicine and its derivatives, quininone and its derivatives, luminol and its derivatives, and cinchoninone and its derivatives.

[0161] In a particular embodiment according to the invention, the water-soluble polymer may comprise at least one cyclic monomer having a hydrolyzable function. Advantageously, the cyclic monomer(s) having a hydrolyzable function are chosen from cyclic ketene acetals, thionolactones, and mixtures thereof.

[0162] The cyclic ketene acetal is advantageously chosen from: 2-methylene-1,3-dioxepane (MDO), 5,6-benzo-2-methylene-1,3-dioxepane (BMDO), 2-methylene-4-phenyl-1,3-dioxolane (MPDL), 2-methylene-1,3,6-trioxocane (MTC), and mixtures thereof. Preferably, it is 2-methylene-1,3-dioxepane (MDO).

[0163] The thionolactone is advantageously chosen from: Dibenzo[c,e]oxepine(7H)-5-thione (DOT), e-thionocaprolactone, 3,3-dimethyl-2,3-dihydro-5Hbenzo[e][l,4]dioxepine-5-thione (DBT) and mixtures thereof. Preferably, it is 3,3-dimethyl-2,3-dihydro-5Hbenzo[e][l,4]dioxepine-5-thione.

[0164] In a particular embodiment according to the invention, the water-soluble polymer may comprise at least one LCST group.

[0165] According to the general knowledge of those skilled in the art, a LCST group corresponds to a group whose solubility in water, for a given concentration, changes above a certain temperature and depending on the salinity. It is a group exhibiting a heating transition temperature that defines its lack of affinity for the solvent medium. This lack of affinity for the solvent results in opacification or loss of transparency, which can be due to precipitation, aggregation, gelation, or viscosification of the medium. The minimum transition temperature is called the "LCST" (Lower Critical Solution Temperature). For each concentration of an LCST group, a heating transition temperature is observed. This temperature is higher than the LCST, which is the minimum point on the curve.Below this temperature, the polymer is soluble in water; above this temperature, the polymer loses its solubility in water.

[0166] In a particular embodiment according to the invention, the water-soluble polymer may comprise at least one UCST group.

[0167] According to the general knowledge of those skilled in the art, a UCST group corresponds to a group whose solubility in water, for a given concentration, changes below a certain temperature and depending on the salinity. It is a group exhibiting a cooling transition temperature that defines its lack of affinity for the solvent medium. This lack of affinity for the solvent results in opacification or a loss of transparency, which can be due to precipitation, aggregation, gelation, or viscosification of the medium. The maximum transition temperature is called the "UCST" (Upper Critical Solution Temperature). For each concentration of a UCST group, a cooling transition temperature is observed. This temperature is lower than the UCST, which is the maximum point on the curve.Above this temperature, the polymer is soluble in water; below this temperature, the polymer loses its solubility in water.

[0168] The quantities of the different monomer(s) will be adjusted by a person skilled in the art so as not to exceed 100% molar during the preparation of the water-soluble polymer. Water-soluble polymer

[0169] The 2-acrylamido-2-methylpropane used to obtain the water-soluble polymer is advantageously at least 50 mol% in the crystalline form of the sodium salt before polymerization, preferably between 70 and 100 mol%. More preferably, 100 mol% of the 2-acrylamido-2-methylpropane sulfonic acid used is in the crystalline form of the sodium salt.

[0170] In a particular embodiment according to the invention, the water-soluble polymer comprises between 1 and 100 mol% of 2-acrylamido-2-methylpropane sulfonic acid, preferably between 5 and 100 mol% of 2-acrylamido-2-methylpropane sulfonic acid, and even more preferably between 25 and 100 mol% of 2-acrylamido-2-methylpropane sulfonic acid; advantageously, at least 50 mol% of the 2-acrylamido-2-methylpropane sulfonic acid is used in the crystalline form of the sodium salt, preferably between 70 and 100 mol%. More preferably, 100 mol% of the 2-acrylamido-2-methylpropane sulfonic acid used is in the crystalline form of the sodium salt.

[0171] In a preferred embodiment according to the invention, the water-soluble polymer contains only anionic monomeric units and non-ionic monomeric units. In other words, it is preferably obtained from at least one anionic hydrophilic monomer and at least one non-ionic hydrophilic monomer.

[0172] In a particular embodiment of the invention, the water-soluble polymer is a polymer based on acrylamide and 2-acrylamido-2-methylpropanesulfonic acid, at least 50 mol% of the 2-acrylamido-2-methylpropanesulfonic acid used being, before polymerization, in the crystalline form of the sodium salt. Preferably, the water-soluble polymer is a polymer consisting of acrylamide, acrylic acid, and 2-acrylamido-2-methylpropanesulfonic acid, at least 50 mol% of the 2-acrylamido-2-methylpropanesulfonic acid being, before polymerization, in the crystalline form of the sodium salt.

[0173] In a preferred mode according to the invention, the water-soluble polymer is a homopolymer of 2-acrylamido-2-methylpropane sulfonic acid with at least 50 mol% of the 2-acrylamido-2-methylpropane sulfonic acid used in the crystalline form of the sodium salt.

[0174] The water-soluble polymer can be partially or totally post-hydrolyzed.

[0175] According to the invention, the water-soluble polymer can have a linear, branched, cross-linked, star-shaped, or comb-shaped structure. This structure can be obtained, according to the general knowledge of a person skilled in the art, for example, by selecting the initiator, the transfer agent, and the polymerization technique such as RAFT (Reversible Addition Fragmentation Chain Transfer), NMP (Natural Multipolymerization). presence of nitroxide, from the English "Nitroxide Mediated Polymerization") or ATRP (Atom Transfer Radical Polymerization), incorporation of structural monomers, or concentration.

[0176] The water-soluble polymer can further be structured by a branching agent. A structured polymer is defined as a non-linear polymer that has side chains such that, when this polymer is dissolved in water, it exhibits a high degree of entanglement leading to very high low-gradient viscosities.

[0177] The branching agent is advantageously chosen from: - structural agents, which may be chosen from the group comprising polyethylene unsaturation monomers (having at least two unsaturated functions), such as vinyl, allylic, acrylic and epoxy functions, and examples include methylene bisacrylamide (MBA), triallyamine, or tetraallylammonium chloride or 1,2-dihydroxyethylene bis-(N-acrylamide), and / or - monomers having at least two epoxy functional groups, - monomers having at least one unsaturated function and one epoxy function, - macroinitiators such as polyperoxides, polyazo compounds and polytransfer agents such as polymer-capturing polymers, and polyols, and / or - functionalized polysaccharides.

[0178] The amount of branching agent in the water-soluble polymer is advantageously less than 40,000 ppm, relative to the total weight of monomers in the water-soluble polymer, preferably less than 10,000 ppm, more preferably less than 5,000 ppm.

[0179] In a particular mode, the amount of branching agent is at least equal to 0.1 ppm, relative to the total weight of monomers of the water-soluble polymer, preferably at least 1 ppm.

[0180] When the water-soluble polymer includes a branching agent, the polymer remains soluble in water. A person skilled in the art will know how to adjust the amount of branching agent, and possibly the amount of transfer agent, to achieve this result.

[0181] In a preferred mode according to the invention, the water-soluble polymer does not comprise a branching agent.

[0182] In a particular mode according to the invention, the water-soluble polymer comprises a transfer agent.

[0183] The transfer agent is advantageously chosen from methanol, isopropyl alcohol, sodium, calcium, magnesium or potassium hypophosphite; 2-mercaptoethanol; 3-mercaptopropanol; dithiopropylene glycol; thioglycerol; thioglycolic acid; thiohydracrylic acid; thiolactic acid; thiomalic acid; cysteine; and aminoethanethiol; methallysulfonate of sodium, calcium, magnesium or potassium; and mixtures thereof. Preferably, sodium hypophosphite.

[0184] The amount of transfer agent in the water-soluble polymer is advantageously between 0 and 100,000 ppm relative to the total weight of the monomers in the polymer, preferably between 0 and 10,000 ppm, more preferably between 0 and 1,000 ppm, and even more preferably between 0 and 100 ppm. When present, the transfer agent represents at least 0.1 ppm relative to the total weight of the monomers in the water-soluble polymer, preferably at least 1 ppm.

[0185] In a particular mode according to the invention, the water-soluble polymer does not comprise a transfer agent.

[0186] In general, the water-soluble polymer does not require the development of a specific polymerization process. Indeed, it can be obtained using all polymerization techniques well known to those skilled in the art. These may include, in particular, solution polymerization; gel polymerization; precipitation polymerization; emulsion polymerization (aqueous or inverse); suspension polymerization; reactive extrusion polymerization; water-in-water polymerization; or micellar polymerization.

[0187] Polymerization is generally a radical polymerization, preferably by inverse emulsion polymerization or gel polymerization. By radical polymerization, we include free radical polymerization using UV, azo, redox, or thermal initiators, as well as controlled radical polymerization (CRP) techniques or matrix polymerization techniques.

[0188] Examples of controlled radical polymerization techniques include, but are not limited to, iodine transfer polymerization (ITP), nitroxide-mediated polymerization (NMP), atom transfer radical polymerization (ATRP), reversible addition-fragmentation chain transfer polymerization (RAFT), which includes MADIX technology (macromolecular design by interchange of xanthates), various organometallic-mediated radical polymerization (OMRP), and heteroatomic-mediated radical polymerization. (“OrganoHeteroatom-mediated Radical Polymerization” in English (OHRP)).

[0189] As already indicated, the water-soluble polymer can be post-hydrolyzed. Post-hydrolysis is the hydrolysis reaction of the polymer after its formation by polymerization of monomer(s). This step consists of the reaction of hydrolyzable functional groups of advantageously non-ionic monomers, more advantageously the amide or ester groups are hydrolyzed with a carboxylic acid. This carboxylic acid can be an enzyme, an ion-exchange resin, or a Brpnsted acid (e.g., a hydrohalic acid) or a Brpnsted base (e.g., an alkali hydroxide or an alkaline earth hydroxide). Preferably, the carboxylic acid is a Brpnsted base. During this post-hydrolysis step of the water-soluble polymer, the number of carboxylic acid groups increases. This is because the reaction between the base and the amide or ester groups present in the water-soluble polymer produces carboxylate groups.

[0190] The water-soluble polymer can be in liquid, gel or solid form when its preparation includes a drying step such as spray drying, drum drying, radiation drying such as microwave drying, or fluidized bed drying.

[0191] The water-soluble polymer advantageously has a weight-average molecular weight of at least 1 million g / mol, preferably between 2 and 40 million g / mol, more preferably between 5 and 30 million g / mol. Molecular weight is understood to mean weight-average molecular weight.

[0192] The weight-average molecular weight is determined by the intrinsic viscosity of the polymer. The intrinsic viscosity can be measured by methods known to those skilled in the art and can be calculated from the reduced viscosity values ​​for different polymer concentrations by a graphical method consisting of plotting the reduced viscosity values ​​(ordinate axis) against the concentration (abscissa axis) and extrapolating the curve down to zero concentration. The intrinsic viscosity value is plotted on the ordinate axis or using the least squares method. The molecular weight can then be determined by the Mark-Houwink equation: [q] = KM" [q] represents the intrinsic viscosity of the polymer determined by the solution viscosity measurement method. K represents an empirical constant. M represents the molecular weight of the polymer, a represents the Mark-Houwink coefficient. K and a depend on the particular polymer-solvent system.

[0193] The water-soluble polymer advantageously has a filtration ratio (FR) of less than 1.5, preferably less than 1.3, more preferably less than 1.1.

[0194] The term filtration quotient is used in this document to refer to a test used to determine the performance of the polymer solution under conditions approaching the permeability of the reservoir, consisting of measuring the time taken The filterability (FR) is measured by comparing the filterability of a polymer solution for two consecutive equivalent volumes / concentrations, indicating the solution's tendency to clog the filter. Lower FR values ​​indicate better filter efficiency.

[0195] The test used to determine the FR consists of measuring the time it takes for given volumes of a solution containing 1000 ppm (by weight) of polymer to flow through a filter. The solution is contained in a cell pressurized to two bars, and the filter is 47 mm in diameter with a defined pore size. Generally, the FR is measured with filters having a pore size of 1.2 µm, 3 µm, 5 µm, or 10 µm.

[0196] The times required to obtain 100 ml (t200mi), 200 ml (t200mi) and 300 ml (t300mi) of filtrate are measured, and a FR is then defined, expressed as:

[0197] [Math.2] "f 3GB ml LiK: mi rR = —--------- taDO m5 L<»O mj

[0198] Times are measured to the nearest 0.1 seconds.

[0199] FR thus represents the ability of the polymer solution to clog the filter for two consecutive equivalent volumes.

[0200] The polymers used according to the invention exhibit improved resistance to chemical and thermal degradation compared to polymers of equivalent molecular weight obtained from 2-acrylamido-2-methylpropane sulfonic acid not being in crystalline form of the sodium salt.

[0201] The test used to determine resistance to chemical degradation consists of preparing a polymer solution at a given concentration in a given brine under aerobic conditions and bringing it into contact with a chemical contaminant such as iron or hydrogen sulfide. The viscosity of the polymer solution is measured before and after 24 hours of exposure to the contaminant. The viscosity measurements are carried out under the same temperature and shear gradient conditions.

[0202] The test used to determine resistance to mechanical degradation consists of preparing a polymer solution at a given concentration in a brine of a given composition under anaerobic conditions (using an inert glove box, for example, with nitrogen) and allowing it to age in a stainless steel cell placed at a given temperature for a predetermined time. At the end of this period, the stainless steel cell is cooled to room temperature, and then the viscosity of the polymer solution it contains is measured and compared to its initial value. All handling of the stainless steel cell is carried out within the glove box. To avoid any exposure to oxygen, the stainless steel cells are sealed to prevent oxygen from entering the solution during temperature aging. Viscosity measurements before and after aging are performed in a glove box under identical temperature and velocity gradient conditions.

[0203] Resistance to chemical and thermal degradation is quantified by the viscosity loss value expressed as a percentage and determined at maturity by:

[0204] [Math.3] Viscosity loss (%) - t ÏSC6SÎ échêàitcs 4 --;--X 10U V lSC0SlteinMai*

[0205] Enhanced hydrocarbon recovery process (oil and / or gas)

[0206] The invention relates to a method for enhanced recovery of hydrocarbons (oil and / or gas) comprising the following steps: a) Preparation of an injection fluid comprising at least one water-soluble polymer of 2-acrylamido-2-methylpropane sulfonic acid, with water or brine; 2-Acrylamido-2-methylpropane sulfonic acid being, before polymerization, a crystalline form of the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid having a powder X-ray diffraction pattern comprising peaks at 11.7°; 12.2°; 13.2°; 13.5°; 15.6°; 16.8°; 17.8°; 18.5°; 19.1°; 20.6°; 21.4°; 23.3°; 25.1°; 25.8°; 26.9°; 29.1°; 29.5°; 31.0°; 33.0°; 33.6°; 34.4°; 35.2°; 35.9°; 37.1°; 38.4°; 39.6°; 41.1°; 42.9°; 45.1°; 46.0°; 47.2°; 47.6° degrees 2-theta; b) Injection of the injection fluid into an underground formation; c) Sweeping of the underground formation using the injected fluid; d) Recovery of an aqueous and hydrocarbon mixture.

[0207] When the water-soluble polymer used in the preparation of the injection fluid is in powder form, the average size of the water-soluble polymer particles is advantageously less than 1.5 millimeters, preferably less than 850 micrometers. The average size of the water-soluble polymer particles is advantageously greater than 5 µm.

[0208] The average particle size of water-soluble polymer is the average size of the largest dimension, for example, the diameter for spherical particles. It is advantageously measured with a laser measuring device using conventional techniques that are part of the knowledge of those skilled in the art. For example, a Mastersizer-type device from Malvern, such as the MS2000, can be used for this purpose. This type of device allows the particle size distribution of particles in liquid or solid form to be measured by laser diffraction.

[0209] When the water-soluble polymer is in granular form, it can be dissolved in an aqueous medium in a dispersion device. An example of a dispersion device is the polymer slicing unit (PSU) described in US Patent 8,186,871, which allows the preparation of a concentrated aqueous polymer solution.

[0210] The water or brine used for preparing the injection fluid may be production water. "Production water" refers to all salt or non-salt water, brines, seawater, and aquifer water originating from a hydrocarbon reservoir. This production water may be pre-treated before preparing the injection fluid as described in patent application WO 2018 / 020175.

[0211] Water-soluble polymers can be combined with stabilizing compounds. Stabilizing compounds (stabilizing agents) can be compounds that adequately protect polymers, for example, against thermal, chemical, and / or mechanical degradation. Examples of suitable stabilizing agents are given in patent application WO 2010 / 133258.

[0212] The injection of the injection fluid comprising the water-soluble polymer, depending on the technique employed, is carried out alone or in conjunction with one or more chemical compounds useful for the enhanced recovery of hydrocarbons (oil and / or gas). Among these chemical compounds, mention may be made of weak, strong, or super-strong bases, mineral or organic, capable of saponifying crude oils and producing in-situ surfactants that solubilize hydrocarbons, particularly petroleum. Examples include sodium or potassium carbonate, caustic soda, borate and metaborate compounds, amines, and basic polymeric compounds. Another family of compounds widely injected with polymers is that of surfactants, often anionic, zwitterionic, cationic, and sometimes also nonionic.These compounds are rarely injected pure, but generally with a co-surfactant and a co-solvent to improve their compatibility and effectiveness in the reservoir (underground formation).

[0213] The injection fluid advantageously comprises between 10 and 15,000 ppm by weight of water-soluble polymer, preferably between 50 and 10,000 ppm, more preferably between 100 and 5,000 ppm.

[0214] Quite surprisingly, the Applicant discovered that water-soluble polymers obtained from the crystalline form of the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid have better filterability as well as better resistance to chemical and thermal degradation compared to polymers of equivalent molecular weight obtained from 2-acrylamido-2-methylpropane sulfonic acid not in the crystalline form of the salt of sodium. Furthermore, it is known that filterability deteriorates as the molecular weight of the polymer increases. One of the advantages of the invention lies in the possibility of obtaining water-soluble polymers with very high molecular weights that also exhibit good filterability. In addition, the concentration of water-soluble polymer required to achieve a target injection fluid viscosity is reduced, which improves the economic conditions for recovering hydrocarbons (oil and / or gas) contained in the underground formation.

[0215] The water-soluble polymers according to the invention have the function of viscosifying the waters injected into reservoirs (underground formations) containing hydrocarbons (oil and / or gas) to ensure mobility control without the need for crosslinking, i.e. chemical bridging between chains.

[0216] In a particular embodiment, the enhanced hydrocarbon (oil and / or gas) recovery process comprises the following steps: a) Preparation of an injection fluid comprising a water-soluble polymer having a molecular weight greater than 5 million g / mol: - the injection fluid having a salt concentration greater than 100 g / l of which at most 50 g / l of divalent salt(s); - the polymer comprising at least 80 mol% of ATBS of which advantageously at least 50 mol% of ATBS is, before polymerization, in the crystalline form of the sodium salt, preferably at least 70 mol%, more preferably 100 mol%; - the concentration of water-soluble polymer in the injection fluid being less than 3,000 ppm by weight, - the injection fluid before the shearing step b) having a viscosity Vj; b) Shearing of the injection fluid to obtain a further decrease in viscosity 25% compared to Vj with:

[0217] [Math.4] V2 — Calf -------> 3^ Calf

[0218] where, VI corresponds to the viscosity of the injection fluid before the shearing step at the formation temperature; V2 is the viscosity of the injection fluid after the shearing step at the formation temperature; Veau is the viscosity of the water used for preparing the injection fluid at the formation temperature; c) Injection of the injection fluid into an underground formation, the underground formation being a carbonate formation, having an in- permeability less than 300 millidarcy and a temperature greater than 100°C; d) Scanning of the underground formation using the injected fluid; e) Recovery of an aqueous and hydrocarbon mixture (oil and / or gas).

[0219] The shearing step can be carried out, for example, using a valve, an orifice or a pump.

[0220] Preferably, the concentration of divalent salt(s) in the injection fluid is between 3 and 50 g / l.

[0221] Carbonate formations are sedimentary rock formations whose carbonate composition is at least 50%.

[0222] The invention and its advantages will be more clearly illustrated by the following figures and examples, which are given to illustrate the invention and not by way of limitation. Description of figures

[0223] [Fig.1] Fig.1 illustrates the X-ray diffraction pattern of the crystals obtained according to Example 1.

[0224] [Fig.2] Fig.2 illustrates the X-ray diffraction pattern of the crystals obtained according to Example 2.

[0225] [Fig.3] The [Fig.3] illustrates the loss of viscosity as a function of the shape of the ATBS and the iron content of the polymers.

[0226] [Fig.4] Fig.4 illustrates the loss of viscosity as a function of the shape of ATBS during aging at 90°C of polymers.

[0227] [Fig.5] The [Fig.5] illustrates the loss of viscosity as a function of the shape of the ATBS and the iron content of homopolymers. Examples of implementation of the invention

[0228] Example 1: Synthesis of 2-acrylamido-2-methylpropane sulfonic acid

[0229] In a 2000 ml double-jacketed stirred reactor, 1522 grams of acrylonitrile containing 0.4% water by weight and 180 grams of fuming sulfuric acid containing 104% H2SO4 (18% oleum) are added. The mixture is stirred for 1 hour and cooled by the reactor's double jacket, which maintains the temperature of the sulfonant mixture at -20°C.

[0230] 97 grams of isobutylene are added to the previous sulfonant mixture, at a flow rate of 1.6 grams / minute.

[0231] The temperature of the mixture is controlled at 45°C during the introduction of isobutylene. The particles of 2-acrylamido-2-methylpropanesulfonic acid precipitate in the mixture, and the solids content is approximately 20% by weight. The reaction mixture is filtered through a Buchner filter and dried under vacuum at 50°C. The solid obtained is 2-acrylamido-2-methylpropanesulfonic acid and is in the form of a very fine white powder.

[0232] Example 2: Synthesis of the crystalline form of the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid

[0233] In a 1000 mL double-jacketed stirred reactor, 439 grams of a 22% sodium hydroxide solution (by weight in water) are added. To the preceding mixture are added 452 grams of 2-acrylamido-2-methylpropanesulfonic acid (white powder obtained from Example 1).

[0234] The mixture is stirred for 30 minutes, at 10°C, to form an aqueous solution SA2.

[0235] The aqueous solution SA2 is heated to a temperature of 40°C under a vacuum of 50 mbar for 20 minutes, then the temperature is maintained at atmospheric pressure for 30 minutes, and then cooled to a temperature of 10°C. The cooling time between 40°C and 10°C is 6 hours. A suspension Si of sodium salt crystals of 2-acrylamido-2-methylpropanesulfonic acid is obtained. The suspension Si is filtered using a Robatel vertical centrifuge. A solid of composition Ci is obtained, containing 80% by weight of sodium salt crystals of 2-acrylamido-2-methylpropanesulfonic acid. Example 3: X-ray diffraction analysis

[0236] The solids obtained in Examples 1 and 2 are first ground into powders and are analyzed by X-ray diffraction over an angular range of 10 to 90° (Figures 1 and 2). The equipment used is a Rigaku Miniflex II diffractometer equipped with a copper source.

[0237] We can observe that the solid obtained from Example 2 ([Fig.2]) has an X-ray diffraction pattern with the following characteristic peaks: 11.7°; 12.2°; 13.2°; 13.5°; 15.6°; 16.8°; 17.8°; 18.5°; 19.1°; 20.6°; 21.4°; 23.3°; 25.1°; 25.8°; 26.9°; 29.1°; 29.5°; 31.0°; 33.0°; 33.6°; 34.4°; 35.2°; 35.9°; 37.1°; 38.4°; 39.6°; 41.1°; 42.9°; 45.1°; 46.0°; 47.2°; 47.6° degrees 2-theta (+ / -0.1°).

[0238] Example 4: Preparation of polymers (PI, P2 and P3) acrylamide / 2-acrylamido-2-methylpropane sulfonic acid in crystalline form of the sodium salt (75 / 25 mol%)

[0239] In a 2000 mL beaker are added 1035 g of deionized water, 520.5 g of acrylamide (in 50% by weight solution in water), 16.2 g of urea and 285 g of 2-acrylamido-2-methylpropane sulfonic acid crystals (crystalline form of the sodium salt) obtained in Example 2.

[0240] The solution thus obtained is cooled to between 5 and 10°C and transferred to an adiabatic polymerization reactor; nitrogen bubbling is carried out for 30 minutes to eliminate any trace of dissolved oxygen.

[0241] The following are then added to the reactor: - 0.45 g of 2,2'-azobisisobutyronitrile, - 1.5 ml of a 2.5 g / l solution of 2,2'-azobis dihydrochloride [2-(2-imidazolin-2-yl)propane], - 1.5 to 10 ml of a 1 g / L sodium hypophosphite solution, - 1.5 ml of a 1 g / L tert-butyl hydroperoxide solution, - 1.5 ml of a 1 g / 1 solution of ammonium sulfate and iron(II) hexahydrate (Mohr's salt).

[0242] After a few minutes, the nitrogen supply is closed and the reactor is shut down. The polymerization reaction proceeds for 2 to 5 hours until a temperature peak is reached. The resulting rubbery gel is chopped and dried to obtain a coarse powder, which is then ground and sieved to obtain the polymer in powder form.

[0243] Example 5: Preparation of polymers (P'1, P'2 and P'3) acrylamide / 2-acrylamido-2-methylpropane sulfonic acid in non-crystalline form of the sodium salt (75 / 25 mol%)

[0244] The polymers are obtained as in Example 3, but by replacing the crystalline form of 2-acrylamido-2-methylpropane sulfonic acid of sodium salt (Example 2) with 257 g of 2-acrylamido-2-methylpropane sulfonic acid not being in crystalline form of sodium salt (obtained in Example 1) and 99 g of sodium hydroxide at 50% weight concentration in water.

[0245] Example 6: Measurement of the filtration quotient of polymer solutions

[0246] Filtration tests were carried out on 3 polymers obtained from the form non-crystalline 2-acrylamido-2-methylpropane sulfonic acid P'1, P'2 and P'3 of increasing molecular weights of 6.5, 9 and 11.5 million Da respectively, obtained as described in Example 4, and on 4 polymers obtained from the crystalline form as sodium salt of 2-acrylamido-2-methylpropane sulfonic acid PI, P2, P3 and P4 of increasing molecular weights of 6.5, 9, 11 and 13 million Da respectively, obtained as described in Example 3.

[0247] The polymer solutions were obtained at an active concentration of 1,000 ppm in a brine containing water, 30,000 ppm NaCl, and 3,000 ppm CaCl2·2H2O (ppm by weight). The filtration quotient (FR) was measured on filters with a pore size of 1.2 pm, representative of low-permeability deposits.

[0248] [Tables 1] Form of ATBS sodium salt used Molecular weight (in millions of Da) Filtration quotient PI Crystalline 6.5 1.06 P2 Crystalline 9 1.04 P3 Crystalline 11 1.06 P4 Crystalline 13 1.19 PT Non-crystalline 6.5 1.13 P'2 Non-crystalline 9 1.17 P'3 Non-crystalline 11.5 1.42

[0249] Table 1: Polymers tested for filterability quotient

[0250] We can observe in Table 1 that, at equivalent molecular weights, the polymers obtained from the crystalline form of the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid (P1-P3) always exhibit a lower FR than the polymers obtained from the non-crystalline form of the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid (P'1-P'3). This difference becomes increasingly significant as the molecular weight of the polymer increases. The polymer obtained from the crystalline form of the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid with a molecular weight of 13 million Da (P4) even exhibits a lower FR than the polymer obtained from the non-crystalline form of the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid with a lower molecular weight (11.5 million Da, P'3).

[0251] Example 7: Measurement of the resistance to chemical degradation of solutions of polymers of equivalent molecular weight

[0252] Chemical degradation resistance tests of polymers P3 and P'3 were carried out under aerobic conditions in the presence of different iron(II) concentrations (2, 5, 10, and 20 ppm) in a brine composed of water, 37,000 ppm NaCl, 5,000 ppm Na2SO4, and 200 ppm NaHCO3 (ppm by weight). These tests were performed on a polymer obtained from the non-crystalline form of the sodium salt of 2-acrylamido-2-methylpropanesulfonic acid (P'3) and on a polymer obtained from the crystalline form of the sodium salt of 2-acrylamido-2-methylpropanesulfonic acid (P3). Both polymers have the same chemical composition. The results obtained after 24 hours of contact between the polymer solution and the contaminant are shown in [Fig. 3].

[0253] We can observe that, for each concentration of iron(II), the polymer P3 undergoes a less significant loss of viscosity than that of the equivalent polymer P'3.

[0254] Example 8: Measurement of the resistance to thermal degradation of solutions of polymers of equivalent molecular weight

[0255] Thermal degradation resistance tests of polymers P3 and P'3 were carried out under anaerobic conditions at an active concentration of 2,000 ppm in a brine composed of 30,000 ppm NaCl and 3,000 ppm CaCl2·2H2O (ppm by weight). These tests were performed on a polymer obtained from the non-crystalline form of the sodium salt of 2-acrylamido-2-methylpropanesulfonic acid (P'3) and on a polymer obtained from the crystalline form of the sodium salt of 2-acrylamido-2-methylpropanesulfonic acid (P3). Both polymers have the same chemical composition. The polymer solutions were aged for 6 months at 90°C. The results obtained are presented in [Fig. 4] in terms of viscosity loss. We can observe that P3 loses less viscosity than the equivalent polymer P'3.

[0256] Example 9: Preparation of homopolymers (P5, P6 and P7) of the crystalline form of the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid

[0257] In a 2000 mL beaker, 800 g of deionized water and 500 g of 2-acrylamido-2-methylpropane sulfonic acid crystals (crystalline form of the sodium salt) obtained in Example 2 are added.

[0258] The solution thus obtained is cooled to between 5 and 10°C and transferred to an adiabatic polymerization reactor; nitrogen bubbling is carried out for 30 minutes to eliminate any trace of dissolved oxygen.

[0259] The following are then added to the reactor: - 0.45 g of 2,2'-azobisisobutyronitrile, - 1.5 ml of a 2.5 g / l solution of 2,2'-azobis dihydrochloride [2-(2-imidazolin-2-yl)propane], - 1.5 to 30 ml of a 1 g / L sodium hypophosphite solution, - 1.5 ml of a 1 g / L tert-butyl hydroperoxide solution, - 1.5 ml of a 1 g / 1 solution of ammonium sulfate and iron(II) hexahydrate (Mohr's salt).

[0260] After a few minutes, the nitrogen supply is closed and the reactor is shut down. The polymerization reaction proceeds for 2 to 5 hours, until a temperature peak is reached. The resulting rubbery gel is chopped and dried to obtain a coarse powder, which is then ground and sieved to obtain the polymer in powder form.

[0261] Example 10: Preparation of homopolymers (P'5 and P'6) of 2-acrylamido-2-methylpropane sulfonic acid in non-crystalline form of the sodium salt.

[0262] The polymers are obtained as in Example 7, but by replacing the crystalline form of 2-acrylamido-2-methylpropane sulfonic acid of sodium salt (Example 2) with 452 g of 2-acrylamido-2-methylpropane sulfonic acid not being in crystalline form of sodium salt synthesized in Example 1 and 175 g of sodium hydroxide at 50% weight concentration in water.

[0263] Example 11: Measurement of the filtration quotient of polymer solutions

[0264] Filtration tests were carried out on 2 polymers obtained from the non-crystalline form of 2-acrylamido-2-methylpropane sulfonic acid P'5, P'6 with increasing molecular weights of 3.1 and 5.3 million Da respectively, obtained as described in Example 10, and on 3 polymers obtained from the crystalline form of the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid P5, P6 and P7 with increasing molecular weights of 3.1, 5.3 and 15 million Da respectively, obtained as described in Example 9. The 15 million Da molecular weight grade is not accessible when using the non-crystalline form of the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid.

[0265] The polymer solutions were obtained at an active concentration of 1,000 ppm in a brine containing water, 30,000 ppm NaCl, and 3,000 ppm CaCl2·2H2O (ppm by weight). The filtration quotient (FR) was measured on filters with a pore size of 1.2 pm, representative of low-permeability deposits.

[0266] [Tables2] Sodium salt form of ATBS used Molecular weight (in millions of Da) Filtration quotient P5 Crystalline 3.1 1.06 P6 Crystalline 5.3 1.04 P7 Crystalline 15 1.27 P'5 Non-crystalline 3.1 1.18 P'6 Non-crystalline 5.3 1.58

[0267] Table 2: Polymers tested for filterability quotient

[0268] We can see from Table 2 that, at equivalent molecular weights, polymers obtained from the crystalline form of the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid (P5-P6) always exhibit a lower FR than polymers obtained from the non-crystalline form of the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid (P'5-P'6). This difference becomes increasingly significant as the molecular weight of the polymer increases. The polymer obtained from the crystalline form of the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid with a molecular weight of 15 million Da (P7) even exhibits a lower FR than the polymer obtained from the non-crystalline form of the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid with a lower molecular weight (5.3 million Da, P'6).

[0269] Example 12: Measurement of resistance to chemical degradation of solutions of polymers P6 and P'6.

[0270] Chemical degradation resistance tests of P6 and P'6 polymers of weight Molecular strength tests of 5.3 million Da were carried out under aerobic conditions in the presence of different iron(II) concentrations (2, 5, 10, and 20 ppm) in a brine composed of water, 37,000 ppm NaCl, 5,000 ppm Na₂SO₄, and 200 ppm NaHCO₃ (ppm by weight). These tests were performed on a polymer obtained from the non-crystalline form of the sodium salt of 2-acrylamido-2-methylpropanesulfonic acid (P₆) and on a polymer obtained from the crystalline form of the sodium salt of 2-acrylamido-2-methylpropanesulfonic acid (P₆). Both polymers have the same chemical composition. The results obtained after 24 hours of contact between the polymer solution and the contaminant are shown in [Fig. 5].

[0271] We can observe that for each concentration of iron(II) the polymer P6 loses less viscosity than the equivalent polymer P'6.

[0272] Example 13: Preparation of the P8 acrylamide / 2-acrylamido-2-methylpropane sulfonic acid polymer in crystalline form from the post-hydrolyzed sodium salt (75 / 25 mol%).

[0273] In a 2000 mL beaker are added 1035 g of deionized water, 520.5 g of acrylamide (in 50% by weight solution in water), 16.2 g of urea and 285 g of 2-acrylamido-2-methylpropane sulfonic acid crystals (crystalline form of the sodium salt) obtained in Example 2.

[0274] The solution thus obtained is cooled to between 0 and 5°C and transferred to an adiabatic polymerization reactor, nitrogen bubbling is carried out for 30 minutes in order to eliminate any trace of dissolved oxygen.

[0275] The following are then added to the reactor: - 0.45 g of 2,2'-azobisisobutyronitrile, - 1.5 ml of a 5 g / l solution of 2,2'-azobis dihydrochloride [2-(2-imidazolin-2-yl)propane], - 1.5 ml of a 1 g / L sodium hypophosphite solution, - 2.25 ml of a 1 g / L tert-butyl hydroperoxide solution, - 3.0 ml of a 1 g / 1 solution of ammonium sulfate and iron(II) hexahydrate (Mohr's salt).

[0276] After a few minutes, the nitrogen supply is closed and the reactor is shut down. The polymerization reaction proceeds for 2 to 5 hours until a temperature peak is reached. The resulting rubbery gel is chopped into particles with a size between 1 and 6 mm.

[0277] Post-hydrolysis of acrylamide: 500.0 g of previously chopped gel are then mixed with 16.0 g of 50% by weight sodium hydroxide solution in water, the mixture is brought and maintained at a temperature of 90°C for a period of 90 minutes.

[0278] The gel is then dried and ground to obtain the polymer in powder form.

[0279] Example 14: Preparation of the P'8 acrylamide / acid polymer 2-acrylamido-2-methylpropane sulfonic acid in non-crystalline form of the sodium salt (75 / 25 mol%) post-hydrolyzed.

[0280] The polymer is obtained as in Example 13, but by replacing the crystalline form of 2-acrylamido-2-methylpropane sulfonic acid of sodium salt (Example 2) with 257g of 2-acrylamido-2-methylpropane sulfonic acid not being in crystalline form of sodium salt (Example 1), and 99.5g of sodium hydroxide at 50% weight concentration in water.

[0281] Example 15: Measurement of the filtration quotient of polymer solutions

[0282] Filtration tests were carried out on a polymer obtained from the non-crystalline form of 2-acrylamido-2-methylpropane sulfonic acid P'8 with a molecular weight of 22 million Da, obtained as described in Example 14, and on a polymer obtained from the crystalline form of the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid P8 with a molecular weight of 26 million Da, obtained as described in Example 13.

[0283] The polymer solutions were obtained at an active concentration of 1,000 ppm in a brine containing water, 30,000 ppm NaCl, and 3,000 ppm CaCl2·2H2O (ppm by weight). The filtration quotient (FR) was measured on filters with a pore size of 3 pm, representative of low-permeability deposits.

[0284] [Tables3] Form of the sodium salt of ATBS used Molecular weight (in millions of Da) Filtration quotient PS Crystalline 26 1.06 P' 8 Non-crystalline 9^ 1.15

[0285] Table 3: Polymers tested for filterability quotient

[0286] We can observe in Table 3 that, despite a higher molecular weight, the polymer obtained from the crystalline form of the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid (P8) has an equivalent FR to that of the polymer obtained from the non-crystalline form of 2-acrylamido-2-methylpropane sulfonic acid (P'8).

Claims

Demands

1. A process for enhanced hydrocarbon recovery comprising the following steps: a) Preparation of an injection fluid comprising at least one water-soluble polymer of 2-acrylamido-2-methylpropane sulfonic acid, with water or with brine, the 2-acrylamido-2-methylpropane sulfonic acid being, prior to polymerization, a crystalline form of the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid having a powder X-ray diffraction pattern comprising peaks at 11.7°; 12.2°; 13.2°; 13.5°; 15.6°; 16.8°; 17.8°; 18.5°; 19.1°; 20.6°; 21.4°; 23.3°; 25.1°; 25.8°; 26.9°; 29.1°; 29.5°; 31.0°; 33.0°; 33.6°; 34.4°; 35.2°; 35.9°; 37.1°; 38.4°; 39.6°; 41.1°; 42.9°; 45.1°; 46.0°; 47.2°; 47.6° degrees 2-theta; b) Injection of the injection fluid into a subsurface formation; c) Sweeping of the subsurface formation using the injected fluid; d) Recovery of an aqueous and hydrocarbon mixture.

2. A method according to claim 1, characterized in that the injection fluid comprises between 10 and 15,000 ppm by weight of water-soluble polymer.

3. A process according to any one of the preceding claims, characterized in that at least 50 mol% of the 2-acrylamido-2-methylpropane acid of the water-soluble polymer is, prior to polymerization, in the crystalline form of the sodium salt.

4. A process according to any one of the preceding claims, characterized in that the water-soluble polymer comprises between 10 and 100 mol% of anionic monomer(s), this percentage including the monomer corresponding to the crystalline form of the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid.

5. A process according to any one of the preceding claims, characterized in that the water-soluble polymer contains only anionic monomeric units and non-ionic monomeric units.

6. A process according to any one of the preceding claims, characterized in that the water-soluble polymer consists of acrylamide and 2-acrylamido-2-methylpropane sulfonic acid, of which at least 50 mol% is, before polymerization, in the crystalline form of the sodium salt.

7. A method according to any one of the preceding claims, characterized in that that the water-soluble polymer has a filtration quotient of less than 1.

5.

8. A process according to claim 1, characterized in that the water-soluble polymer is a homopolymer of 2-acrylamido-2-methylpropane sulfonic acid, at least 50 mol% of the 2-acrylamido-2-methylpropane sulfonic acid being, prior to polymerization, in the crystalline form of the sodium salt.

9. A process according to claim 8, characterized in that the water-soluble polymer has a filtration quotient of less than 1.

5.

10. A method according to claim 8 or 9, characterized in that the injection fluid comprises between 10 and 15,000 ppm by weight of water-soluble polymer.

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