WO2020245035A1

WO2020245035A1 - Method for separating polymers in an aqueous fluid by means of functionalised magnetisable particles

Info

Publication number: WO2020245035A1
Application number: PCT/EP2020/064927
Authority: WO
Inventors: Bruno Delfort; Isabelle Henaut; Céline BOUVRY
Original assignee: IFP Energies Nouvelles
Priority date: 2019-06-04
Filing date: 2020-05-28
Publication date: 2020-12-10
Also published as: FR3096903A1; AR119064A1; FR3096903B1

Abstract

The invention relates to a method for treating an aqueous fluid, for example production water from enhanced oil recovery, comprising at least one polymer in aqueous phase, said method comprising: a) a step of placing said aqueous fluid in contact with zerovalent iron particles functionalised by tetraalkylammonium functions in order to immobilise the polymer on the particles; b) a step of separating the aqueous fluid from the particles on which the polymer is immobilised by magnetisation, in particular by applying a magnetic field, in order to produce a polymer-depleted fluid. The invention also relates to an enhanced recovery method implementing a step of treating production water according to the invention.

Description

Process for the separation of polymers in an aqueous fluid by means of functionalized magnetizable particles

Technical area

The present invention relates to the field of exploration and exploitation of an underground formation. The invention relates more particularly to the treatment of an aqueous fluid recovered from the subterranean formation. In the remainder of the description, the term “aqueous fluid” means any fluid comprising a continuous aqueous phase.

The invention relates in particular to the field of enhanced oil recovery (EOR) and to the field of the treatment of produced water. Prior art

For the exploration and exploitation of an underground formation, it is common to inject a fluid into the underground formation in order to increase the efficiency of the processes (Han DK & al, Recent Development of Enhanced oil Recovery in China, J. Petrol. Sci. Eng. 22 (1-3): 181-188; 1999). To optimize these processes, it is customary to include at least one additive in the injected fluid. This additive can take the form of a formulation of organic molecules, such as polymers, copolymers and / or surfactants, etc. This formulation can also contain inorganic molecules such as minerals (clays, barite, etc.), oxide particles (titanium oxides, iron oxides, etc.) etc. The addition of additive (s) poses certain problems linked in particular to the presence of the additive or of molecules constituting it in the water produced. For enhanced oil recovery, when the injected fluid, also called sweeping fluid, is supplemented with compounds such as polymers, surfactants, alkaline compounds, or mixtures of these compounds, it is referred to as tertiary enhanced recovery. Compared to a simple injection of water or brine, the advantage of the presence of a polymer is to increase the viscosity of the flushing fluid and consequently to improve the mobility ratio between the injected fluid and the hydrocarbons. in place in the underground formation.

The hydrocarbon recovery yield is increased with the aid of a better efficiency of the formation sweeping (Han DK & al, Recent Development of Enhanced oil Recovery in China, J. Petrol. Sci. Eng. 22 (1-3 ): 181-188; 1999). The polymers used in this method are generally polymers of high molecular masses chosen for their viscosifying properties at moderate concentrations.

In petroleum production operations water is frequently co-produced with crude oil, a ratio of three barrels of aqueous effluent to one barrel of crude oil is commonly reported.

Crude oil and water must be separated. The oil is transported to its refining site and the water is treated to remove unwanted compounds and meet discharge standards.

Different techniques are applied to treat produced water, in particular to remove dispersed drops of crude oil: sedimentation by gravity separation, centrifugation, flotation with or without gas injection and filtration.

The use of polymers in tertiary enhanced recovery nevertheless poses practical problems. At the level of the producing wells, a production effluent is recovered comprising a mixture of aqueous fluid and hydrocarbons in the form of an emulsion, the water / hydrocarbon ratio of which changes as a function of the production time. The presence of a polymer in the production effluent, due to the viscosifying effect thereof, makes it more difficult to separate the different fluids (oil / gas / water) and, in particular, the secondary treatments of the latter. 'water (Zhang YQ & al. Treatment of produced water from polymer flooding in oil production by the combined method of hydrolysis acidification dynamic membrane bioreactor-coagulation process, J. Petrol. Sci. Eng., 74 (1-2): 14- 19, 2010). When the production effluent reaches the surface, it is treated in a unit area. This unit makes it possible to separate the various fluids, gas, oil and water. At the end of the surface treatment, the hydrocarbons are ready to be refined. The water is treated and depolluted in order to minimize the discharge of toxic products into the environment, the thresholds of which are subject to standards. The presence of the polymer in the produced fluids, as reported in the document SPE 65390 (2001) "Emulsification and stabilization of ASP Flooding Produced liquid", can lead to the stabilization of the emulsions in the produced fluids and pose problems at the process level surface treatment, at the level of water / oil / gas separation and in particular, at the level of secondary water treatment processes.

If the interest of the presence of a polymer is to increase the viscosity of the flushing fluid to improve the extraction of hydrocarbons in place in the underground formation, the viscosity of the production effluent becomes an obstacle to the separation between water and hydrocarbons. This problem has led operators in the field to consider means to reduce the viscosity of the water produced, that is to say of the aqueous phase in the production effluent, in order to improve the separation between the water. and hydrocarbons. Among these means, the degradation of the viscosifying polymer (s) in the water produced is envisaged and is described in the prior art. The conventional polymers used in EOR are polymers of high molar masses which generally belong to the family of polyacrylamides (PAM) or partially hydrolyzed polyacrylamides (HPAM). They may optionally contain monomer units of the N-vinylpyrrolidone or acrylamido-tert-butylsulfonate (ATBS) type.

Polyacrylamides are obtained by radical polymerization of acrylamide according to the following general scheme.

acrylamide pdyacrylamide (PAM)

The partially hydrolyzed polyacrylamides are copolymers of acrylamide with either acrylic acid or an acrylate, for example an acrylate of an alkaline element such as for example sodium. They can be represented for example by the following general formula in which the alkaline element is sodium. The acrylamide monomer unit is generally in the majority.

The partially hydrolyzed polyacrylamides can be obtained, for example, by copolymerization of acrylamide with acrylic acid, the carboxylic acid function of which can optionally be neutralized to the carboxylate function of an alkaline element such as for example sodium. The partially hydrolyzed polyacrylamides can also be obtained by copolymerization of acrylamide with an acrylate of an alkaline element such as, for example, sodium acrylate. Partially hydrolyzed polyacrylamides can also be obtained by polymerization of acrylamide to polyacrylamide followed by partial hydrolysis of the amide functions into carboxylic acid functions or into carboxylate functions of alkali salts.

HPAMs can be random or block copolymers.

The degradation of these polymers in order to attenuate or eliminate their viscosifying effect is described in particular in the document “SPE-163751 Chemical degradation of HPAM by oxidization in produced water, (2013)” in which the HPAMs are degraded by the action of 'oxidizing agents such as hydrogen peroxide or sodium persulfate or by photodegradation in the presence of titanium dioxide.

The document SPE-169719-MS “Treating back produced polymer to enable use of conventional water treatment technologies, (2014)” describes, in order to reduce the viscosity of the water produced, the degradation of HPAM polymers by the action of various oxidants such as potassium persulfate, potassium percarbonate, hydrogen peroxide, sodium hypochlorite, Fenton's reagent or potassium permanganate.

The document “SPE-179776-MS Management of viscosity of the back produced viscosified water, (2016)” describes, in order to reduce the viscosity of the water produced, the degradation of HPAM polymers by a mechanochemical route, by a thermal route and by a thermal route. chemical in particular by means of chlorinated derivatives.

It is also conceivable not to degrade the polymer in order to suppress its effects, but to separate it from the medium, that is to say to reduce the polymer concentration in the aqueous medium.

The separation by means of particles which are capable of being isolated by magnetization under the action of a magnetic field is a technique already well described, for example in the field of the elimination of polyaromatic compounds present in water in the document "Small, 2018, 14, 1702573", in the field of mercury elimination in the document "Journal of Colloid and Interf. Sci., 2015, 455, 261-270 ”, in the field of metal ion removal in the document“ Chem. Mater., 2004, 16, 1977-1983 ”.

The particles having magnetic properties and which are capable of being isolated by magnetization used are generally nanoparticles or microparticles. The principle is based on the fixation, grafting, creation of chemical bonds or physical interactions between particles capable of being isolated by magnetization and the molecule (s) that one wishes to separate or extract from the medium and which are dissolved in a liquid medium. This fixing is generally carried out by bringing the particles into contact with the liquid medium to be purified, for example by dispersing the particles with stirring. The particles are then separated from the medium under the action of a magnet. The resulting liquid phase is then depleted in products which are retained on the particles.

The document SPE-179576-MS (2016) describes a method aimed at fixing the polymer on iron oxide nanoparticles of magnetite type of formula Fe ₃ 0 ₄ previously coated with silica and functionalized with primary amine functions. The method is carried out in 4 steps:

- a change in pH makes it possible in an acidic medium to convert the primary amine functions present on the surface of the particles into quaternary ammonium functions,

- bringing these particles into contact with an HPAM polymer solution which results in the formation of bonds between the polymer and said particles. These bonds result from an ion exchange between the carboxylate functions of the polymer and the ammonium functions of the magnetic particles according to a well-known chemistry,

- separation by magnetization makes it possible to obtain an aqueous solution depleted in polymer and

- regeneration of magnetic particles by a second change in pH caused by the action of a base.

The method described requires obtaining nanoparticles of magnetite Fe ₃ 0 ₄ which are obtained according to a known method in which the synthesis of the magnetite Fe ₃ 0 ₄ and the formation of the particles are simultaneous. This well-known method is based on an ion exchange in a generally aqueous or hydroalcoholic medium between a mixture of iron (ll) salts such as iron (ll) sulfate or chloride and of iron (lll) such as iron (ll) chloride ( III) while generally respecting a stoichiometric ratio of 2 atoms of iron III for 1 atom of iron II and a base, generally ammonia or sodium hydroxide. Ion exchange leads to the formation of iron oxide Fe ₃ 0 ₄ which is insoluble in aqueous medium and precipitates immediately. This method called co-precipitation with its variants is described in particular by R. Massard in CR Acad. Sc. Paris, t. 291 (July 7, 1980) ”, by Maria Cristina Mascolo in Materials 2013, 6, 5549-5567 by S. Lefebure, in J. Mater. Res., Vol. 13, No. 10, Oct 1998, by An-Hui-Lu in Angew. chem. Int. Ed., 2007, 46, 1222-1244.

Besides the formation of iron oxide Fe ₃ 0 ₄ , the ion exchange also and fatally leads to the formation of salts such as ammonium or sodium chlorides or sulfates soluble in the aqueous medium. These salts are produced in significant quantities. Thus the manufacture of a kilogram of Fe ₃ 0 ₄ particles from, for example, a mixture of iron (II) chloride, iron (III) chloride and ammonia according to the equation

2 FeCI ₃ + FeCI ₂ + 8 NH ₄ OH => Fe ₃ 0 ₄ + 8 NH ₄ CI + 4H ₂ 0

results in the formation of 1.81 kilograms of ammonium chloride. The management of these undesirable salts constitutes an obstacle to the industrial development of this type of synthesis.

Moreover, these magnetite particles can be compared to small magnets and are therefore liable to be deposited on the walls of steel equipment, which can be detrimental for industrial use.

In addition, according to the polymer separation method described in document SPE-179576-MS (2016), two changes in pH are necessary and also involve the mobilization of equipment and the use of chemical reagents.

The Applicant has discovered that it is possible to separate the polymers comprising carboxylate functions, in particular polymers of HPAM type, contained in an aqueous fluid, by immobilizing them on iron particles of zero valence (Fe °) previously functionalized by functions. of tetraalkylammonium types, then using a magnetic field to separate them from said aqueous fluid.

Summary of the invention

The invention relates to a method of treating an aqueous fluid comprising at least one water-soluble polymer carrying carboxylate functions in the aqueous phase, said method comprising: a) a step of bringing said aqueous fluid into contact with zero-valent iron particles functionalized with tetraalkylammonium functions in order to immobilize said polymer on said particles; b) b) a step of separating said aqueous fluid and said particles on which said polymer is immobilized by magnetization, in particular by application of a magnetic field, in order to produce a fluid depleted in polymer (s).

Said method may comprise a step c) of regenerating said particles in their active form by an ion exchange reaction by means of a base or a salt, the anion of which has a pKa greater than that of the carboxylate anion carried by said polymer, or by means of an HX acid, the X- anion of which combines with the tetraalkylammonium function to release said polymer in its acid form.

Said iron particles may be covered with a coating made of an inorganic material intended to isolate the iron from the medium of use, preferably silica.

Preferably, said particles are spherical.

Said particles advantageously have an average diameter of between 0.01 μm and 100 μm, preferably between 0.1 μm and 30 μm.

Said particles can be in the form of aggregates of particles. Preferably, said water-soluble polymer is chosen from: partially hydrolyzed polyacrylamides (HPAM), or polymers comprising monomer units of the N-vinylpyrrolidone or acrylamido-tertiobutylsulfonate (ATBS) type.

Advantageously, the temperature of the contacting step a) is between 5 ° C and 90 ° C, preferably between 10 ° C and 80 ° C, very preferably the temperature is room temperature, generally 20 ° vs.

The concentration of functionalized iron particles is advantageously between 0.03% and 25% by weight, preferably between 0.05 and 10% by weight, very preferably between 0.1% and 10% by weight, relative to the weight total aqueous fluid.

The contact time corresponding to the duration of the contacting step a) between said aqueous fluid and said functionalized iron particles is advantageously between 1 minute and 2 hours, preferably between 1 minute and 1 hour. In one embodiment, said aqueous fluid is produced water from enhanced petroleum recovery, said produced water comprising a continuous aqueous phase containing said water-soluble polymer and an organic phase dispersed in said continuous aqueous phase.

The concentration of said polymer in said production water is advantageously between 1 ppm and 1000 ppm.

Preferably, the dispersed organic phase is crude oil.

Advantageously, the concentration of said crude oil in said production water is between 1 ppm and 900 ppm.

The invention also relates to a method for enhanced recovery of crude oil contained in a geological reservoir in which:

- A flushing fluid comprising at least one water-soluble polymer is injected into said reservoir so as to displace said crude oil towards at least one producing well;

- An effluent comprising the major part of the crude oil is collected by said producing well;

a production water comprising a continuous aqueous phase comprising traces of said polymer and an organic phase consisting of droplets of crude oil dispersed in said aqueous phase is recovered at the surface of the producing well;

- Said production water is treated by means of the treatment process according to the invention.

List of Figures

Other characteristics and advantages of the treatment method according to the invention will become apparent on reading the following description of non-limiting examples of embodiments, with reference to the appended figures and described below.

FIG. 1 represents the diagram of the treatment process according to the invention, comprising a step c) of regeneration of the iron particles.

FIG. 2 represents the functionalization of iron particles coated with silica with a grafting agent which is N- [3- (trimethoxysilyl) propyl] -N, N, N-trimethylammonium chloride

FIG. 3 represents the functionalization of iron particles coated with silica with a grafting agent which is chloropropyltriethoxysilane, the introduction of the ammonium function being carried out by means of trimethylamine. FIG. 4 represents the immobilization of a polymer carrying a carboxylate function, for example a copolymer of acrylamide and of a salt of acrylic acid such as an HPAM on an iron particle covered with silica, the bond between the polymer and the particle being of ionic type.

FIG. 5 represents the embodiment according to which the step of regenerating the particles c) is carried out by an ion exchange reaction with a base or a salt, the anion of which has a pKa greater than that of the carboxylate anion. carried by the polymer, the reagent allowing regeneration being sodium hydrogencarbonate.

FIG. 6 represents the embodiment according to which the step of regenerating the particles c) is carried out by means of an HX acid whose anion X- is, after regeneration, associated with the quaternary ammonium function, and the polymer is released in its acid form, the reagent allowing regeneration being phosphoric acid.

Description of embodiments

The method according to the invention aims to separate one or more water-soluble polymers comprising carboxylate functions, for example a polymer of HPAM type, present in an aqueous fluid:

- By bringing said aqueous fluid into contact with metallic particles, preferably micrometric, the metallic part of which consists of zero-valent iron (Fe °), and which are functionalized by functions of tetraalkylammonium type. The surface of the Fe ° particles can be covered with a preferably inorganic material such as an oxide, for example silica.

- By separating the particles from the fluid by applying a magnetic field to the medium, that is to say by subjecting the particles to the action of a magnetization system which isolates them from the fluid which is then depleted in polymers.

- Optionally regenerating the particles on which the polymers are immobilized in a single step by means, for example, of washing in a basic medium or in an acidic medium.

The method according to the invention in its embodiment where the iron particles are regenerated can be illustrated by the diagram of Figure 1 in which the particle is a zero-valent iron particle covered with a layer of silica on which are grafted with tetraalkylammonium functions. In Figure 1, the nitrogen atom is bonded to the silica layer through a propyl group, but any other hydrocarbon unit may be suitable. R is an alkyl or aryl group containing 1 to 8 carbon atoms, preferably 1 to 6 carbon atoms. The R group can, for example, be a methyl, ethyl, propyl or isopropyl group.

X- is an anion which can be for example a halide, a hydroxide, a hydrogencarbonate, a carboxylate such as an acetate, a hydrogensulfate, a nitrate, and X- can indifferently represent a mixture of the anions mentioned above.

In a non-limiting manner, the polymer is represented here under the general formula of a partially hydrolyzed polyacrylamide, that is to say of a copolymer of acrylamide and of a salt of acrylic acid, here a salt of sodium but it can be a salt of another monovalent cation.

The invention can be applied to all polymers containing a carboxylate function allowing the creation of an ionic bond with the tetraalkylammonium function grafted on the iron particle.

The functionalization of the particles with tetraalkylammonium functions can be carried out according to several methods.

It is possible for example to graft directly onto the layer of silica coating the iron particle tetraalkylammonium functions by means, for example, of grafting agent molecules such as an N-alkylammoniumtrialkoxysilane, for example N- [3- (trimethoxysilyl) propyl chloride. ] -N, N, N-trimethylammonium, according to a well known method. The bond between the silica layer and the grafting agent is effected by an exchange reaction between the alkoxysilane units and the silanol functions present at the surface of the silica. This functionalization is shown for example in Figure 2 where the grafting agent is N- [3- (trimethoxysilyl) propyl] -N, N, N-trimethylammonium chloride.

It is also possible to graft onto the layer of silica coating the iron particle first of all alkyl halide functions by means for example of molecules grafting agents such as for example chloropropyltriethoxysilane, then from the halide function of obtain by reaction with a tertiary amine a tetraalkylammonium function.

This functionalization is for example represented by the diagram of FIG. 3 where the grafting agent is chloropropyltriethoxysilane, and the introduction of the ammonium function is carried out by means of trimethylamine. When the polymer carrying a carboxylate function, for example a copolymer of acrylamide and a salt of acrylic acid such as an HPAM, is immobilized on the iron particle, the bond between the polymer and the particle is of the ionic type. (Figure 4).

Regeneration can be carried out by any means permitted by chemistry to regenerate the particles carrying tetraalkylammonium functions which will again be associated with X - anions as defined above.

The regeneration of the particle in its active form to be reused to immobilize again a polymer carrying a carboxylate function can be carried out by an exchange reaction with a base or a salt, the anion of which has a pKa greater than that of carboxylate anion carried by the polymer. Mention may in particular be made, without being limiting, of carbonate, hydrogencarbonate, dihydrogenphosphate or hydroxide anions. These anions can be combined in the context of the invention with monovalent cations such for example sodium cations. This particle regeneration reaction is for example represented by the diagram of FIG. 5 where the reagent allowing regeneration is sodium hydrogencarbonate. Regeneration can also be carried out by means of an acid HX whose anion X- is, after regeneration, associated with the quaternary ammonium function, and the polymer is released in its acid form. Any acid can be used. Preferably, phosphoric acid, monosodium sulfuric acid can be used. This particle regeneration reaction is for example represented by FIG. 6 where the reagent allowing regeneration is phosphoric acid. The iron particles are advantageously essentially particles of spherical shape. Their metal part is made of zero valence iron. They are not inherently magnetic, but are "magnetizable". This is understood to mean that they are sensitive to the action of a magnetic field and that they are attracted and held by magnets. The interruption of the magnetic field causes the release of the particles. The particles of the invention can have an average diameter of between 0.01 μm and 100 μm, preferably between 0.1 μm and 30 μm.

The particles of the invention can be present in isolation or in the form of aggregates of particles. Preferably, the particles of the invention are covered with a coating intended to isolate the iron from the medium in which they are used. This coating is preferably made of silica. Several iron particles can be covered together by a layer of silica.

The deposition of silica on iron particles generally consists in causing the formation of silica by carrying out in situ the hydrolysis of silica precursors such as an alkyl orthosilicate, for example tetraethylorthosilicate.

This general method is described in particular in the documents “Chem. Mater., 2006, 18, 2701-2706 ”and“ Environ. Sci. Technol., 2010, 44, 7908-7913 ”.

The Fe ° particles are generally obtained by reduction of pentacarbonyl iron Fe (CO) ₅ . These are compounds whose cost is low, produced industrially and available commercially. They are often called Carbonyl Iron Particles (or CIP). The preparation of these particles is for example described in document GB684054A. There are different particle size ranges for these particles including in particular micrometric particles which are compatible with the application referred to here.

Another advantage of these particles is their lack of intrinsic magnetizing power, unlike magnetite particles which are similar to small magnets and which are liable to be deposited on the walls of steel equipment. With Fe ° particles, it is permissible to consider their use in installations where the steel is in contact with the medium to be treated, which is the case with conventional industrial installations.

The presence of tetraalkylammonium functions at the surface of the particles allows the immobilization of polymers comprising carboxylate functions, in particular of polymers of HPAM type, without having recourse to a prior pH change step such as when the particles are functionalized by primary amine functions. for example.

The particles used in the context of the invention carry tetraalkylammonium functions and are therefore in active form, ready for use. EXAMPLES

Example 1: synthesis of zerovalent iron particles functionalized with tetraalkylammonium functions

0.168 g of sodium fluoride is introduced to a dispersion of 0.37 g of iron particles, the median diameter of which is between 3 and 5 microns in 55 g of ethanol and 12.5 g of water. After stirring under an inert atmosphere, 1.61 g of tetraethylorthosilicate (TEOS) are introduced dropwise over 10 minutes. After stirring at ambient temperature for 30 minutes, the medium is brought to 60 ° C and then a mixture consisting of 7.2 g of TEOS and 0.763 g of N- [3- (trimethoxysilyl) propyl] -N chloride is gradually introduced. , N, N-trimethylammonium, over 1 hour and then stirring is continued at this temperature for 4 hours. After returning to ambient temperature, the particles are separated by means of a magnet and then these particles are washed 4 times with 100 ml of ethanol. After drying the particles at 90 ° C. under 80 mbar for 1 hour, 10.79 g of zerovalent Fe particles functionalized with tetraalkylammonium functions are collected.

Examples 2 to 9: Separation of the HPAM polymers dissolved in an aqueous solution by means of the particles of the invention

30.00 g of an aqueous solution containing 310 ppm of a viscosifying polymer, of HPAM copolymer type, of molar mass of 6 MDa, are brought into contact with particles of zerovalent iron functionalized with tetraalkylammonium functions obtained according to Example 1.

Eight samples are thus prepared containing respectively different amounts of particles which are specified in Table 1 below.

Each sample is stirred at room temperature for 1 hour, then on each sample, the particles are separated from the liquid medium using a magnet. A viscosity measurement is carried out on each sample using a rotary rheometer (DHR3 from TA Instruments). Double cylinder geometry is used. A logarithmic flow sweep is performed between 1 and 200 s ¹ . The values are measured at 10 s ¹ .

The measured values are reported in Table 1 below.

Example 2 constitutes the reference example, when the viscosity measurement is carried out on a polymer solution which has not been brought into contact with the iron particles. No reduction in viscosity is therefore reported. Examples 3 to 9 correspond to the implementation of the process according to the invention comprising the addition of the functionalized zerovalent iron particles in each sample of aqueous polymer solution. For each sample, the balance to 100% of the ratio between the measured viscosity and that measured for the reference (example 2) is reported as a percentage, that is to say the reduction in viscosity thanks to the treatment. This value, expressed here as a percentage, illustrates the level of reduction in the viscosity of the viscosifying polymer solution after treatment according to the invention, and therefore the decrease in the polymer content in the aqueous fluid (polymer solution) after treatment.

Table 1

These results illustrate the effectiveness of the treatment process according to the invention making it possible to separate an HPAM polymer in an aqueous solution with the particles of zerovalent iron.

Claims

1. A method of treating an aqueous fluid comprising at least one water-soluble polymer carrying carboxylate functions in the aqueous phase, said method comprising: a) a step of bringing said aqueous fluid into contact with zero-valent iron particles functionalized by tetraalkylammonium functions in order to immobilize said polymer on said particles; b) a step of separating said aqueous fluid and said particles on which said polymer is immobilized by magnetization, in particular by application of a magnetic field, in order to produce a fluid depleted in polymer (s).

2. The treatment process according to claim 1 comprising a step c) of regenerating said particles in their active form by an ion exchange reaction using a base or a salt, the anion of which has a pKa greater than that. of the carboxylate anion carried by the said polymer, or by means of an HX acid, the X- anion of which combines with the tetraalkylammonium function to release the said polymer in its acid form.

3. The treatment method according to claim 1 or 2 wherein said iron particles are covered with a coating made of an inorganic material intended to isolate the iron from the medium of use, preferably silica.

4. The treatment method according to claim 1 to 3 wherein said particles are spherical.

5. Treatment method according to one of claims 1 to 4 wherein said particles have an average diameter between 0.01 pm and 100 pm, preferably between 0.1 pm and 30 pm.

6. Treatment method according to one of claims 1 to 5 wherein said particles are in the form of aggregates of particles.

7. Treatment process according to one of the preceding claims, in which said water-soluble polymer is chosen from: partially hydrolyzed polyacrylamides (HPAM), or polymers comprising monomer units of N-vinylpyrrolidone or acrylamido-tertiobutylsulfonate (ATBS) type.

8. Treatment process according to one of the preceding claims wherein the temperature of the contacting step a) is between 5 ° C and 90 ° C, preferably between 10 ° C and 80 ° C, so most preferably the temperature is room temperature.

9. Treatment method according to one of the preceding claims wherein the concentration of functionalized iron particles is between 0.03% and 25% by weight, preferably between 0.05% and 10% by weight, very preferably between 0.1% and 10% by mass, relative to the total mass of aqueous fluid.

10. Treatment method according to one of the preceding claims wherein the contact time corresponding to the duration of the contacting step a) between said aqueous fluid and said functionalized iron particles is between 1 minute and 2 hours. , preferably between 1 minute and 1 hour.

11. Treatment process according to one of the preceding claims wherein said aqueous fluid is produced water from enhanced oil recovery, said produced water comprising a continuous aqueous phase containing said water-soluble polymer and an organic phase dispersed in said. continuous aqueous phase.

12. The treatment method according to claim 11 wherein the concentration of said polymer in said produced water is between 1 ppm and 1000 ppm.

13. Treatment process according to one of claims 11 or 12 wherein the dispersed organic phase is crude oil.

14. The treatment process according to claim 13 wherein the concentration of said crude oil in said produced water is between 1 and 900 ppm.

15. Process for the enhanced recovery of crude oil contained in a geological reservoir in which:

- An effluent comprising the major part of the crude oil is collected by said producing well; a production water comprising a continuous aqueous phase comprising traces of said polymer and an organic phase consisting of droplets of crude oil dispersed in said aqueous phase is recovered at the surface of the producing well;

- Said production water is treated by means of the treatment process according to one of claims 11 to 14.