RU2786720C2 - Water-gel composition for oil production - Google Patents

Abstract

FIELD: oil production.

SUBSTANCE: group of inventions relates to a special polymerization method, which allows for obtainment of polymer compositions, which can be used, in particular, for modification of rheological properties and adjustment of water yield during production, and which have improved heat resistance. The method for the production of polymer includes stages of (E) micellar radical polymerization, at which, in an aqueous medium (M), monomers (m1) soluble or dispersed in the specified aqueous medium (M), called hydrophilic monomers, are brought into contact with monomers (m2) in the form of a micellar solution, namely containing, in a dispersed state in the medium (M), micelles containing these monomers (m2) called hydrophobic monomers. Moreover, the specified monomers (m1) and/or (m2) include cross-linking monomers (mR) having at least two ethylene unsaturation. At least one radical polymerization initiator preferably soluble or dispersed in water has at least one radical polymerization adjuster. The method additionally includes a stage (E2) after the stage (E), at which polymers obtained at an output of the stage (E) are grounded, as a result of which polymers in the form of dispersed particles are obtained. Concentration of monomers (mR) is from 100 wt. ppm to 1000 wt. ppm, preferably from 200 to 600 wt. ppm, of the total weight of all monomers present in the medium (E). Polymer in the form of dispersed particles, microgel, and the use of microgel as a modifier of rheological properties and a filtration reducer in an underground reservoir, at a temperature of more than or equal to 150°C, and as a modifier of rheological properties and/or a filtration reducer in an underground reservoir in the field of oil recovery are also claimed.

EFFECT: group of inventions allows for development of new compositions suitable for change in rheological properties and/or control of processes of filtration or permeability of rocks during exploration or oil or gas production.

12 cl, 5 tbl, 3 ex

Description

The present invention relates to the field of oil production. More specifically, it relates to a specific polymerization process that provides polymer compositions suitable, in particular, for changing rheological properties and reducing filtration during operations performed at the stages of exploration and production of hydrocarbons.

Water soluble polymers are known to be used to modify rheology and provide filtration reduction, in particular compositions referred to as microgels or nanogels, which contain polymers dispersed as micron or nanometer sized particles.

For example, US 4,172,066 describes the use of a microgel as a viscosifying agent, which also reduces the permeability of the rock. The microgel contains water and a cross-linked polymer based on ethylenically unsaturated hydrophilic monomers obtained by inverse emulsion polymerization (water-in-oil emulsion polymerization), where an aqueous solution of the monomers is added to the oil phase with stirring. The microgels obtained at the exit of the polymerization are separated from the reaction medium by adding a flocculant and then filtered, washed and then dried before use.

US 2010/0256018 describes microgels synthesized from hydrophilic and crosslinkable hydrophilic monomers soluble in the reaction medium. Polymerization results in a dispersion, the resulting polymers being insoluble in the medium and ultimately in the form of insoluble dispersed particles (microgel).

These methods generally result in rather low polymer content, namely relatively dilute microgels, and have disadvantages such as the need for complex recuperative techniques or organic solvent treatments.

Another disadvantage of these methods is that the microgels obtained by the above methods have a rather low resistance, in particular at high temperature, when chemical degradation is often observed (namely, usually at temperatures above 100°C or even above 150°C), which precludes their use in the field of exploration and production of oil, where some minimum period of stability is required (for example, several hours and even several days) and/or where the application temperature is usually high.

One object of the present invention is to develop novel compositions suitable for modifying rheological properties and/or controlling filtration processes or rock permeability during oil or gas exploration or production, and which preferably have better stability than the microgels described in the past, in particular, at temperatures above 100°C or even above 150°C.

To this end, the present invention provides specific polymer compositions, generally hydrophilic in nature, which are both cross-linked and contain hydrophobic blocks. The invention also provides a method allowing the synthesis of the above compositions, which can be used, for example, as a rheology regulator and a filtration reducer.

More specifically, according to the first aspect, the object of the present invention is a method for producing a polymer, including stage (E) polymerization, which is brought into contact in an aqueous medium (M):

- monomers (m1) soluble or dispersible in said aqueous medium (M), called hydrophilic monomers;

- monomers (m2) in the form of a micellar solution, namely containing, in a dispersed state in the medium (M), micelles containing these monomers (m2), called hydrophobic monomers;

wherein said monomers (m1) and/or (m2) include crosslinkable monomers (mR) having at least two ethylenic unsaturations;

- at least one initiator of radical polymerization, preferably soluble or dispersible in water; and

preferably at least one radical polymerization regulator.

The polymers used in the present invention have the special characteristics of micellar radical polymerization polymers.

By "micellar radical polymerization", which will also be referred to as "micellar polymerization" for short, as used herein, is meant a polymerization in which multiblock-type sequenced polymers are synthesized by copolymerization of hydrophilic monomers and hydrophobic monomers in an aqueous dispersion medium (typically water or water/water mixtures). alcohol), which includes:

- hydrophilic monomers dissolved or dispersed in said medium, and

- hydrophobic monomers inside micelles.

Micelles used in micellar polymerization are formed in an aqueous medium from a surfactant (surfactant) that forms these micelles, which is introduced into the specified medium at a concentration above its critical micelle concentration (CMC), in the presence of hydrophilic monomers in the medium (M).

In one particular embodiment, the hydrophobic monomers present in micelles used in micellar polymerization may be monomers that are themselves capable of forming micelles without the need for additional surfactants to do so (such monomers are referred to hereinafter as self-micellating). In this particular embodiment, the surfactant used to form micelles may itself be a self-mycelizing hydrophobic monomer used without another surfactant, however, the presence of an additional surfactant when using self-mycelizing monomers is not excluded.

Thus, when "hydrophobic monomers within micelles" are mentioned in the context of the present description, this expression covers:

- option 1 : hydrophobic monomers located inside the micelles formed by surfactants, and these surfactants differ from these hydrophobic monomers, and/or

Option 2 : self-mycellating monomers which themselves form micelles in an aqueous medium, together with micelles which may in this case be formed, partially or completely, from said self-micelle monomers.

The above options 1 and 2 are compatible and can be combined (for example, non-self-micellating hydrophobic monomers inside micelles formed by another self-mycelizing monomer, or micelles containing a combination of surfactants and self-mycelizing monomers).

In the case of micellar polymerization, regardless of the exact nature of the micelles, the hydrophobic monomers contained in the micelles are said to be in the "micellar solution". Said micellar solution is a microheterogeneous system, usually isotropic, optically transparent and thermodynamically stable.

It should be noted that a micellar solution of the type used in micellar polymerization should be distinguished from a microemulsion. In particular, unlike a microemulsion, a micellar solution is formed at any concentration above the critical micelle concentration of the surfactant used, provided that the hydrophobic monomer is at least somewhat soluble in the interior of the micelles. In addition, a micellar solution differs from an emulsion in the absence of an internal homogeneous phase: micelles contain a very small number of molecules (usually less than 1000, usually less than 500 and usually from 1 to 100, most often from 1 to 50 monomers, and not more than a few hundred molecules). surfactant when a surfactant is present), and the micellar solution usually has physical properties close to those of micelles formed by the surfactant without monomers. In addition, most often the micellar solution is transparent to visible light, given the small size of the micelles, which does not lead to scattering phenomena, unlike emulsion droplets, which scatter the light and give it a cloudy or characteristic white appearance. As a rule, the size of micelles in a micellar solution is less than 50 nanometers and even less than 10 nanometers.

The micellar polymerization method results in characteristic block copolymers, each of which contains several hydrophobic blocks of essentially the same size, and this size can be controlled. Indeed, given that hydrophobic monomers are retained within micelles, each of the formed hydrophobic blocks of controlled size contains essentially a given number n _H of hydrophobic monomers, and this number n _H can be calculated by the following formula ( Macromolecular Chem. Physics , 202, 8, 1384 -1397, 2001):

n _H= N _agg ∙ [M _H ]/([SAW] - CMC)

wherein:

- N _agg means the surfactant aggregation number, which reflects the number of surfactant molecules present in each micelle,

- [M _H ] means the molar concentration of the hydrophobic monomer in the medium,

- [surfactant] means the molar concentration of surfactant in the medium, and

- CMC means the critical concentration (molar) of micellization in the reaction medium.

Thus, the micellar polymerization method provides an advantageous control of the hydrophobic units introduced into the formed polymers, namely:

- global control of the mole fraction of hydrophobic units in the polymer (by modulating the concentration ratio of the two monomers), and

- more specific control of the number of hydrophobic units present in each hydrophobic block (by changing the parameters affecting the number n _H defined above).

The polymers obtained by micellar polymerization are amphiphilic block copolymers that have a special controlled structure, namely, in a nutshell, based on a skeletal chain formed from hydrophilic units (soluble or dispersible in water), interrupted at different places by small hydrophobic sequences, and all such hydrophobic sequences (hydrophobic blocks) have essentially the same number of monomer units.

Considering the use of specific monomers (mR) in step (E), the polymers obtained according to the invention are, moreover, cross-linked. Thus, the polymeric compositions obtained by the method of the present invention are in the form of a chemically crosslinked gel, also referred to below by the term "macrogel".

The crosslinkable monomers (mR) used in step (E) may contain hydrophobic crosslinkable monomers (mR2), which then constitute all or part of the hydrophobic monomers (m2), and/or hydrophilic crosslinkable monomers (mR1), which then usually make up only part of the hydrophilic monomers (m1).

In other words:

- hydrophobic monomers (m2) may include non-crosslinkable hydrophobic monomers (m'2) and/or crosslinkable monomers (mR2), and

- hydrophilic monomers (m1) include non-crosslinkable hydrophilic monomers (m'1) and possibly crosslinkable monomers (mR1),

provided that the monomers (m1) and/or (m2) contain at least crosslinkable monomers (mR1 and/or mR2).

According to a first preferred embodiment, step (E) is carried out in the presence of hydrophobic monomers (m2) which contain or consist exclusively of hydrophobic crosslinkable monomers (mR2). For example, they may contain more than 90%, typically more than 95% or even more than 99% crosslinkable hydrophobic monomers (mR2) by weight based on the total weight of hydrophobic monomers. The macrogels obtained according to this embodiment have a particularly high heat resistance.

According to a second variant, compatible with the first (which are preferably combined within the scope of the invention), step (E) is carried out in the presence of hydrophilic monomers (m1), of which only a part consists of crosslinkable monomers (mR1). In this embodiment, the hydrophilic monomers usually contain less than 5 wt.%, more often less than 1 wt.% monomers (mR1) or even less than 0.5 wt.%, based on the total weight of the hydrophilic monomers.

Thus, the monomers used in step (E) may consist of:

(i) mixtures of non-crosslinkable hydrophilic monomers (m'1), non-crosslinkable hydrophobic monomers (m'2) and crosslinkable hydrophobic monomers (mR2); or

(ii) mixtures of non-crosslinkable hydrophilic monomers (m'1), crosslinkable hydrophilic monomers (mR1) and non-crosslinkable hydrophobic monomers (m'2); or

(iii) mixtures of non-crosslinking hydrophilic monomers (m'1) and crosslinkable hydrophobic monomers (mR2); or

(iv) mixtures of non-crosslinkable hydrophilic monomers (m'1), crosslinkable hydrophilic monomers (mR1) and crosslinkable hydrophobic monomers (mR2); or

(v) mixtures of non-crosslinkable hydrophilic monomers (m'1), crosslinkable hydrophilic monomers (mR1), non-crosslinkable hydrophobic monomers (m'2) and crosslinkable hydrophobic monomers (mR2).

According to one particular embodiment, the monomers used in step (E) consist of a mixture of non-crosslinkable hydrophilic monomers (m'1) and crosslinkable hydrophobic monomers (mR2).

According to another particular embodiment, the monomers used in step (E) consist of a mixture of non-crosslinkable hydrophilic monomers (m'1), non-crosslinkable hydrophobic monomers (m'2) and crosslinkable hydrophobic monomers (mR2).

According to another particular embodiment, the monomers used in step (E) consist of a mixture of non-crosslinkable hydrophilic monomers (m'1), crosslinkable hydrophilic monomers (mR1) and crosslinkable hydrophobic monomers (mR2).

The inventors have surprisingly found that cross-linkable monomers (mR) can be used in a conventional micellar radical polymerization process without disrupting the polymerization mechanism, allowing for the usual advantages of micellar radical polymerization and, in addition, allowing efficient creation of covalent chemical bonds between polymer chains.

Preferably, the method according to the invention after step (E) includes step (E2) in which the polymers obtained in step (E) are ground (usually after a drying step), resulting in polymers in the form of dispersed particles, with reduced sizes , usually in the form of particles with sizes less than 200 μm, more preferably less than 100 μm and usually greater than 0.1 μm, more preferably greater than 1 μm. The particle size obtained can be measured, for example, by dry laser granulometry.

To carry out step (E2), it is desirable to remove all or part of the solvents used in step (E). In this regard, one advantage of the present invention is that since the process is carried out in an aqueous medium, it is easier to isolate the polymers at the end of the polymerization, in particular compared to the preparation methods described above by inverse emulsion polymerization, which usually require laborious post-treatment to separate polymers from oils and/or solvents contained in the reaction medium.

The size of the particles obtained at the output of stage (E2), can be changed through the intensity of grinding, which is known in itself. If drying is carried out, the output of step (E2) is a polymer in powder form. Conventional grinding and drying means known to those skilled in the art may be used. Examples include the fluidized bed drying method and grinding in needle crushers, hammer crushers, ball mills, pneumatic crushers. These methods can be implemented in cryogrinding mode.

The polymer particles obtained in step (E2) form a gel-like aqueous composition after being dispersed in water. The method of the invention thus makes it possible to obtain an aqueous gel composition based on crosslinked polymers. Hereinafter in the description, this composition will be referred to as "microgel".

In the microgel prepared according to the invention, the polymers are in the form of particulate objects, typically less than 1000 μm, typically less than 500 μm, more preferably less than 100 μm, and typically greater than 0.5 μm, more preferably greater than 5 μm. The size of the dispersed particles can be determined, for example, by dynamic light scattering.

The microgels obtained according to the invention have high thermal stability, generally higher than the microgels described in the above documents, in particular under the conditions of temperature and pH used in the field of oil production. Their compositions can be changed depending on the desired temperature and/or the desired pH of the environment of use. In general, monomer-based microgels (mR2) have a particularly high temperature resistance, they can be used at high temperatures, namely usually above 100°C or even above 150°C.

Thus, the invention makes it possible to obtain heat-resistant aqueous microgels that are easy to prepare and handle.

Given the thermal stability of the polymer compositions according to the invention, it is not necessary to adapt the level of crosslinker to provide a sufficient filtration reduction effect depending on the application temperature (in particular with increasing temperature), unlike the microgels described in US 2010/0256018. The microgels of the present invention can be used over a wide range of temperatures without the need to change their formulations.

In addition, the method according to the invention, starting from the macrogel, if necessary, allows to obtain increased concentrations of particles in the microgel.

In another aspect, the invention relates to polymers (macrogels) obtained in step (E), particles obtained in step (E2) and microgels obtained by dispersing these particles in water.

The aqueous medium (M) used in step (E) is a medium containing water, preferably at a level of at least 50% by weight, even at least 80%, for example at least 90% or even at least 95 wt.% of the total weight of the aquatic environment. This aqueous medium optionally may contain, in addition to water, other solvents, such as alcohol, miscible with water. Thus, the medium (M) may be, for example, a water-alcohol mixture. In one possible embodiment, the medium (M) may contain other solvents, preferably at a concentration at which said solvent is miscible with water, which may, in particular, make it possible to reduce the amount of stabilizing surfactants used. For example, medium (M) may contain pentanol or any other additive that allows modulating the aggregation number of surfactants. It is generally preferred that the medium (M) is a continuous aqueous phase and consists of one or more solvents and/or additives miscible with each other and with water at the concentrations in which they are used.

Typically, the concentration of monomers (mR) is from 100 to 10,000 ppm (weight parts per million) based on the total weight of all monomers present in the medium (E). Preferably, the monomers (mR) are used at a concentration of 100 to 1000 wpm, preferably 200 to 600 wpm, e.g. 300 to 500 wpm, based on the total weight of all monomers present in the medium (E).

The molar ratio (mR)/(m1), which corresponds to the amount of crosslinkable monomers (mR) relative to the total amount of hydrophilic monomers, is typically between 0.01% and 0.1%.

In one preferred embodiment, the polymers used according to the invention are polymers obtained from step (E) of a micellar radical polymerization, which in particular is a controlled type radical polymerization, that is, carried out in the presence of a radical polymerization regulator. By "radical polymerization regulator" (or, more simply, simply "regulator" ) as used herein, is meant a compound capable of extending the lifetime of growing polymer chains in a polymerization reaction, and preferably making the polymerization live or controllable.

When a radical polymerization regulator of the above type is used, in addition to the advantages associated with the use of micellar polymerization, it is possible to control the average molecular weight of the polymers resulting from step (E): this molecular weight can be controlled by the amount of regulator used (given the amount of hydrophilic monomers mass usually decreases as this quantity increases).

Thus, if a radical polymerization regulator is used in step (E), the macrogels at the output of step (E) have a controlled average molecular weight.

The inventors have found that under the conditions of step (E), despite the presence of crosslinkable monomers and micelles, the benefits of controlled radical polymerization are retained, thus providing crosslinked polymers of controlled average molecular weight.

Typically, polymers synthesized by the method of the invention may have a molecular weight greater than or equal to 300,000 g/mol. In particular, the selection of the initial concentration of the regulator in the environment (M) stage (E) can usually lead to the synthesis of a block copolymer with a molecular weight Mn greater than or equal to 400,000 g/mol.

According to one preferred embodiment of the process according to the invention, in step (E), the initial concentration of the regulator in the medium is chosen such that the number average molecular weight of the Mn block copolymer is greater than or equal to 500,000 g/mol, for example greater than or equal to 1,000,000 g/mol , or greater than or equal to 2000000 g/mol and even higher.

According to one possible embodiment, in step (E) a regulator can be used which is a radical polymerization regulator of an irreversible type, usually selected from mercaptans, such as mercaptopropionic acid, thioglycolic acid, mercaptoethanol, from primary or secondary alcohols, such as ethanol or isopropanol, or alternatively formic acid and its salts.

Alternatively, in one particularly advantageous embodiment, the regulator used in step (E) is a reversible transfer agent as used in controlled radical polymerization, referred to as the RAFT or MADIX methods, which typically use the addition-fragmentation reversible chain transfer method as described. , for example, in documents WO96/30421, WO 98/01478, WO 99/35178, WO 98/58974, WO 00/75207, WO 01/42312, WO 99/35177, WO 99/31144, FR2794464 or WO 02/26836 .

When a reversible radical polymerization regulator is used, the polymers resulting from step (E) have, in addition to the advantages associated with the implementation of micellar polymerization (namely, control of the mole fraction of hydrophobic units in the polymers and (ii) control of the number of hydrophobic units in each hydrophobic sequence):

- control of the average molecular weight (which can be fine-tuned through the amount of regulator used: for a given amount of hydrophilic monomers, the mass decreases as this amount increases), and

- control of the distribution of hydrophobic blocks in different chains,

- obtaining living polymer chains, which opens up the possibility of obtaining complex polymers with controlled architecture.

These advantages are particularly pronounced when the radical polymerization regulator used is a compound soluble or dispersible in the aqueous medium (M) used in step (E) and/or when this regulator is unable to penetrate into the micelles of the micellar solution. This effect can also be observed when the regulator is not soluble or dispersible in the medium (M) or when the regulator is able to penetrate micelles.

Thus, in the case where a reversible type regulator is used in step (E), the macrogels obtained in step (E) have, in addition to a finely controlled average molecular weight, a uniformity in the distribution of crosslink points that are found in the microgel particles.

The inventors have found that these advantages associated with the use of a reversible regulator are retained under the specific conditions of step (E), under which it was not apparent that the presence of micelles and crosslinkable monomers does not impair the controlled radical polymerization mechanism.

In one particular embodiment, the regulator used in step (E) may be a polymer chain obtained from a controlled radical polymerization process containing a group capable of controlling radical polymerization (a polymer chain known as "living" as it is known). Thus, for example, the regulator may be a polymeric chain (preferably hydrophilic or water-dispersible) functionalized at the end of the chain with a xanthate group or, more generally, containing a -SC=S- group, for example, obtained by the RAFT/MADIX method.

Alternatively, the regulator used in step (E) is a non-polymeric compound containing a radical polymerization control group, in particular a thiocarbonylthio -S(C=S)- group.

In one preferred embodiment, the radical polymerization regulator used in step (E) is a compound containing a thiocarbonylthio group -S(C=S)-. Thus, for example, it may be a compound which contains a xanthate group (carrying groups -SC=S-O-), for example xanthate. Other types of regulators used in controlled radical polymerization are also acceptable (eg, such as those used in CMP, ATRP or NMP processes).

The use of this type of regulator in step (E) in the polymerization reaction allows precise control of the size of the polymer chains and the molecular weight, in particular the degree of crosslinking, which makes it possible to very finely and very accurately modulate the properties of the macrogel. In addition, the use of a regulator results in a homogeneity of the synthesized macrogel, which makes it possible to obtain at the output of stage (E2) particles that all have essentially the same composition and properties.

According to one particular variant, the radical polymerization regulator used in step (E) is a polymer, preferably an oligomer, soluble or dispersible in water and containing a thiocarbonylthio group -S(C=S)-, for example a xanthate group -SC=SO- . This polymer, which is capable of acting simultaneously as a polymerization regulator and as a monomer in step (E), is also referred to hereinafter as a prepolymer. As a rule, this prepolymer is obtained by radical polymerization of hydrophilic monomers in the presence of a regulator containing a thiocarbonylthio group -S(C=S)-, for example xanthate. Thus, for example, in one preferred embodiment, which is illustrated at the end of this description, the regulator used in step (E) may preferably be a prepolymer containing a thiocarbonylthio group -S(C=S)-, for example, a xanthate group -SC ═SO— obtained from the controlled radical polymerization step (E ⁰ ) carried out before step (E). In said step (E ⁰ ), it is usually possible to bring into contact hydrophilic monomers, preferably identical to those used in step (E), a radical polymerization initiator and a thiocarbonylthio group-containing regulator -S(C=S)-, eg xanthate.

Generally speaking, the implementation of the above stage (E ⁰ ) to stage (E) allows you to give hydrophilic properties to many regulators containing thiocarbonylthio groups (for example, xanthates, most of which are inherently hydrophobic), converting them into prepolymers soluble or dispersible in medium (M) stage (E). Preferably, the prepolymer synthesized in step (E ⁰ ) has a short polymer chain, for example, containing a sequence of less than 50, even less than 25 monomer units, for example, from 2 to 15.

In a third aspect, the subject of the invention is also the specific use of the particular microgels obtained according to the invention.

In general, the microgels produced in accordance with the present invention can be used in many areas of the petroleum industry. In particular, they can be used as rheology modifiers, in particular as a thickener and/or suspending agent, in particular in aqueous media.

Microgels can also be used as a fluid loss reducer or lost circulation agent.

The subject of the invention are also methods for modifying aqueous media, in which these microgels are used as modifiers of rheological properties.

The invention also relates to aqueous compositions containing microgels according to the invention, which can be used, in particular, at the stages of exploration and production of hydrocarbons.

The subject of the invention are also methods in which aqueous compositions of this type are used for the exploration and/or exploitation of oil and/or gas fields, in particular, methods using the circulation or introduction of such a composition during the formation of wells (exploration) or during their operation.

For example, the aqueous compositions of the invention may be used in a drilling fluid, a spacer, a cement paste, a well completion fluid, or a fracturing fluid, or an enhanced oil recovery fluid, or an injectivity profiler fluid.

In the following, various characteristics and embodiments of the invention are described in more detail.

Radical polymerization regulator

The control agent (hereinafter regulator) used in step (E) or, if necessary, step (E ⁰ ) of the process according to the invention is preferably a compound containing a thiocarbonylthio group -S(C=S)-. In one particular embodiment, the regulator may contain multiple thiocarbonylthio groups. It may be (but need not be) a polymer chain carrying such a group.

Thus, said controller may correspond to the following formula (A):

wherein:

- Z stands for:

- a hydrogen atom,

- chlorine atom,

- an alkyl radical, optionally substituted, an aryl radical, optionally substituted,

- heterocycle, possibly substituted,

- an alkylthio radical, optionally substituted,

- arylthio radical, optionally substituted,

- alkoxy radical, optionally substituted,

- aryloxy radical, optionally substituted,

- amino radical, optionally substituted,

- hydrazine radical, optionally substituted,

- alkoxycarbonyl radical, optionally substituted,

- aryloxycarbonyl radical, optionally substituted,

- carboxy, acyloxy radical, optionally substituted,

- aroyloxy radical, optionally substituted,

- carbamoyl radical, optionally substituted,

- cyano radical,

- a dialkyl- or diarylphosphonato radical,

- a dialkylphosphinato or diarylphosphinato radical, or

- polymer chain

and

- R ₁ means:

- an alkyl, acyl, aryl, aralkyl, alkene or alkyne group, optionally substituted,

- a carbon ring or heterocycle, whether or not saturated, aromatic, optionally substituted, or

- a polymer chain, preferably hydrophilic or water-dispersible if the agent is used in step (E).

When R groups_one or Z are substituted, they may be substituted with phenyl groups, optionally substituted, aromatic groups, optionally substituted, carbon rings, saturated or unsaturated, heterocycles, saturated or unsaturated, or groups: alkoxycarbonyl or aryloxycarbonyl (-COOR), carboxy (-COOH), acyloxy (-O2CR), carbamoyl (-CONR2), cyano (-CN), alkylcarbonyl, alkylarylcarbonyl, arylcarbonyl, arylalkylcarbonyl, phthalimido, maleimido, succinimido, amidino, guanidino, hydroxy (-OH), amino (-NR2), halogen, perfluoroalkyl C_nF_2n+1, allyl, epoxy, alkoxy (-OR), S-alkyl, S-aryl, groups having a hydrophilic or ionic character, such as alkali metal salts of carboxylic acids, alkali metal salts of sulfonic acids, polyalkylene oxide chains (PEO, POP), cationic substituents (quaternary ammonium salts), where R is an alkyl or aryl group or a polymer chain .

For regulators of formula (A) used in step (E), it is generally preferred that the R1 group be hydrophilic in nature. Preferably, it is a water-soluble or water-dispersible polymer chain.

Alternatively, the R1 group may be amphiphilic, that is, have both hydrophilic and lipophilic properties. Preferably, R1 is not hydrophobic.

With respect to the regulators of formula (A) used in step (E ⁰ ), R ₁ may generally be an alkyl group, whether or not substituted, preferably substituted. However, the regulator of formula (A) used in step (E ⁰ ) may contain other types of R ₁ groups, such as a ring or a polymer chain.

Alkyl, acyl, aryl, aralkyl or alkyne groups, optionally substituted, generally contain 1 to 20 carbon atoms, preferably 1 to 12, and more preferably 1 to 9 carbon atoms. They can be linear or branched. They may also be substituted by oxygen atoms, in particular in the form of esters, sulfur or nitrogen atoms.

Of the alkyl radicals, mention may be made in particular of the methyl, ethyl, propyl, butyl, pentyl, isopropyl, tert-butyl, pentyl, hexyl, octyl, decyl or dodecyl radicals.

Alkyne groups are radicals typically containing from 2 to 10 carbon atoms, they have at least one acetylenic unsaturation, such as an acetylenyl residue.

An acyl group is a radical, typically containing from 1 to 20 carbon atoms, with a carbonyl group.

Of the aryl radicals, there may be mentioned in particular the phenyl radical, optionally substituted, in particular with a nitro group or a hydroxyl group.

Of the aralkyl radicals, there may be mentioned in particular the benzyl or phenethyl radical, optionally substituted, in particular with a nitro group or a hydroxyl group.

When R ₁ or Z is a polymer chain, this polymer chain can be obtained in radical or ionic polymerization or obtained by polycondensation.

It is preferable to use as a regulator in stage (E), and if necessary in stage (E ⁰ ), compounds containing a xanthate group -S(C=S)O-, trithiocarbonate, dithiocarbamate or dithiocarbazate, for example, containing an O-ethyl xanthate group of the formula -S(C=S)OCH ₂ CH ₃ .

When the step (E ⁰ ) is carried out, it is particularly advantageous to use as regulators in this step a compound selected from xanthates, trithiocarbonates, dithiocarbamates or dithiocarbazates. Xanthates, in particular those containing an O-ethylxanthate group -S(C=S)OCH ₂ CH ₃ , such as O-ethyl-S-(1-methoxycarbonylethyl)xanthate (CH ₃ CH(CO ₂ CH ₃ )) have proved particularly advantageous. S(C=S)OEt. Another possible regulator in step (E ⁰ ) is dibenzyl trithiocarbonate of the formula PhCH ₂ S(C=S)SCH ₂ Ph (wherein Ph=phenyl).

The living prepolymers obtained in step (E ⁰ ) using the above regulators are particularly advantageous for step (E).

Initiation and conduct of radical polymerization in steps (E) and (E ⁰ )

When a radical polymerization initiator is used in step (E), it is preferably water-soluble or water-dispersible. Apart from this preferred condition, in step (E) and step (E ⁰ ) of the process according to the invention, any known radical polymerization initiator (source of free radicals) suitable for the conditions chosen for these steps can be used.

Thus, the radical polymerization initiator used according to the invention can be selected, for example, from those conventionally used in radical polymerization. This could be, for example, one of the following initiators:

- hydrogen peroxides such as: tert-butyl hydroperoxide, cumene hydroperoxide, tert-butylperoxyacetate, tert-butylperoxybenzoate, tert-butylperoxyoctoate, tert-butylperoxyneodecanoate, tert-butylperoxyisobutyrate, lauryl peroxide, tert-amyl peroxypivalate, tert-butylperoxypivalate, dicumyl peroxide, benzoyl peroxide, potassium persulfate, ammonium persulfate,

- azo compounds such as: 2-2'-azobis(isobutyronitrile), 2,2'-azobis(2-butanenitrile), 4,4'-azobis(4-pentanoic acid), 1,1'-azobis( cyclohexanecarbonitrile), 2-(tert-butylazo)-2-cyanopropane, 2,2'-azobis[2-methyl-N-(1,1)-bis(hydroxymethyl)-2-hydroxyethyl]propionamide, 2,2'- azobis(2-methyl-N-hydroxyethyl]-propionamide, 2,2'-azobis(N, N'-dimethyleneisobutyramidine) dichloride, 2,2'-azobis(2-amidinopropane) dichloride, 2,2'-azobis(N , N'-dimethyleneisobutyramide), 2,2'-azobis(2-methyl-N-[1,1-bis(hydroxymethyl)-2-hydroxyethyl]propionamide), 2,2'-azobis(2-methyl-N- [1,1-bis(hydroxymethyl)ethyl]propionamide), 2,2'-azobis[2-methyl-N-(2-hydroxyethyl)propionamide], 2,2'-azobis(isobutyramide) dihydrate.

Generally, the amount of initiator used is preferably determined so that the amount of radicals formed does not exceed 50 mol%, preferably does not exceed 20 mol%, based on the amount of regulator or transfer agent.

In particular, in step (E) it is generally advantageous to use a redox-type radical initiator, which has the advantage, inter alia, that it does not require heating of the reaction medium (no thermal initiation), the inventors have also found that it is suitable for micellar polymerization in step (E).

Thus, the radical polymerization initiator used in step (E) can generally be a redox initiator, usually requiring no heat for its thermal activation. Usually we are talking about a mixture of at least one oxidizing agent with at least one reducing agent.

The oxidizing agent present in this redox system is preferably water soluble. This oxidizing agent can be selected, for example, from peroxides such as: hydrogen peroxide, t-butyl peroxide, cumene hydroperoxyl, t-butylperoxyacetate, t-butylperoxybenzoate, t-butylperoxyoctoate, t-butylperoxyneodecanoate, t-butylperoxyisobutyrate, lauryl peroxide, t-amylperoxypivalate, tert-butyl peroxypivalate, dicumyl peroxide, benzoyl peroxide; from sodium persulfate, potassium persulfate, ammonium persulfate or potassium bromate.

The reducing agent present in the redox system is preferably also water soluble. This reducing agent can generally be selected from sodium sulfoxylate formaldehyde (particularly in its dihydrate form known as rongalite or anhydride), ascorbic acid, erythorbic acid, sulfites, bisulfites or metasulfites (in particular sulfites, bisulfites or metasulfites alkali metals), nitrilotrispropionamides and tertiary amines, as well as ethanolamines (preferably water soluble).

Possible redox systems include combinations such as:

- mixtures of water-soluble persulfates with water-soluble tertiary amines,

- mixtures of water-soluble bromates (e.g. alkali metal bromate) with water-soluble sulfites (e.g. alkali metal sulfites),

- mixtures of hydrogen peroxide, alkyl, perethers, percarbonates, etc. with any of iron salts, titanium salts, zinc sulfoxylate formaldehyde or sodium sulfoxylate formaldehyde and reducing sugars,

- persulfates, perborate or perchlorate of an alkali metal or ammonium in combination with an alkali metal bisulfite such as sodium metabisulphite and reducing sugars, and

- alkali metal persulfates in combination with arylphosphinic acid such as benzenephosphonic acid and the like and reducing sugars.

A preferred redox system contains, and preferably consists of, a combination of ammonium persulfate and sodium sulfoxylate formaldehyde.

As a rule, and in particular in the case of using a redox system of the ammonium persulfate/sodium sulfoxylate formaldehyde type, it has proven to be preferable that the reaction medium in step (E) does not include copper. If copper is present, it is generally desirable to add a copper complexing compound, such as EDTA, in an amount capable of masking its presence.

Whatever the nature of the initiator used, the radical polymerization in step (E ⁰ ) can be carried out in any suitable physical form, e.g. in solution in water or in a solvent, e.g. alcohol or THF, emulsified in water (called "latex" method) , in bulk, if necessary under temperature and/or pH control, to render the compounds liquid and/or soluble or insoluble.

After step (E), considering the use of a regulator, polymers functionalized with chain transfer groups (living polymers) are obtained. The absence of termination allows these polymers to be used in later polymerization reactions, if desired, in accordance with well known techniques. Alternatively, if desired, chain transfer groups can be deactivated or destroyed, for example by hydrolysis, ozonolysis, or reaction with amines, according to known techniques. Thus, in one particular embodiment, the process of the invention may include, after step (E), a step (E1) of hydrolysis, ozonolysis, or reaction with amines capable of deactivating and/or destroying all or part of the transfer groups present in the polymer obtained in step (E ).

Hydrophilic monomers (m1)

The method according to the invention can be used with a very large number of hydrophilic monomers (m1), including monomers of the non-crosslinking type (m'1) and possibly crosslinkable monomers (mR1).

As non-crosslinking monomers (m1) there may be mentioned, in particular, monomers (m1) selected from the following compounds:

- ethylenically unsaturated carboxylic acids, sulfonic acids and phosphoric acids, and/or their derivatives, such as acrylic acid (AA), methacrylic acid, ethacrylic acid, α-chloroacrylic acid, crotonic acid, maleic acid, maleic anhydride, itaconic acid, citraconic acid , mesaconic acid, glutaconic acid, aconitic acid, fumaric acid, monoesters of monoethylenically unsaturated dicarboxylic acids containing from 1 to 3, preferably 1 or 2 carbon atoms, e.g. , sulfopropyl acrylate, sulfopropyl methacrylate, 2-hydroxy-3-acryloyloxypropyl sulfonic acid, 2-hydroxy-3-methacryloyloxypropyl sulfonic acid, styrene sulfonic acids, 2-acrylamido-2-methylpropane sulfonic acid, vinylphosphonic acid, α-methylvinylphosphonic acid, and allylphosphonic acid;

- esters of α,β-ethylenically unsaturated mono- and dicarboxylic acids and C2-C3-alkanediols, e.g. hydroxypropyl methacrylate and polyalkylene glycol (meth)acrylates;

- amides of α,β-ethylenically unsaturated monocarboxylic acids and their N-alkyl and N,N-dialkyl derivatives such as acrylamide, methacrylamide, N-methyl(meth)acrylamide, N-ethyl(meth)acrylamide, N-propyl( meth)acrylamide, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, morpholinyl(meth)acrylamide and metholilacrylamide (particularly acrylamide and N,N-dimethyl(meth)acrylamide have proven to be particularly advantageous );

- N-vinyl lactams and their derivatives, for example N-vinylpyrrolidone, N-vinylpiperidone;

- acyclic N-vinylamide compounds, for example, N-vinylformamide, N-vinyl-N-methylformamide, N-vinylacetamide, N-vinyl-N-methylacetamide, N-vinyl-N-ethylacetamide, N-vinylpropionamide, N-vinyl-N -methylpropionamide and N-vinylbutyramide;

- esters of α,β-ethylenically unsaturated mono- and dicarboxylic acids and amino alcohols, for example, N, N-dimethylaminomethyl (meth) acrylate, N, N-dimethylaminoethyl (meth) acrylate, N, N-diethylaminoethyl acrylate and N, N- dimethylaminopropyl(meth)acrylate;

- amides of α,β-ethylenically unsaturated mono- and dicarboxylic acids with diamines containing at least one primary or secondary amino group, such as N-[2-(dimethylamino)ethyl]acrylamide, N[2-(dimethylamino)ethyl] -methacrylamide, N-[3-(dimethylamino)propyl]acrylamide, N-[3-(dimethylamino)propyl]methacrylamide,

- nitrogen-containing heterocycles substituted with vinyl and allyl groups, for example, N-vinylimidazole, N-vinyl-2-methylimidazole; heteroaromatic compounds substituted with vinyl and allyl groups, for example 2- and 4-vinylpyridine, 2- and 4-allylpyridine, and salts thereof;

- acrylamidosulfobetaines and

- mixtures and combinations of two or more of the above monomers.

According to one particular embodiment, these monomers may contain, in particular, acrylic acid (AA). In one possible embodiment, all monomers are acrylic acids, but it is also possible to use as monomers a mixture containing, inter alia, acrylic acid mixed with other hydrophilic monomers.

Monomers containing acidic groups can be used for polymerization in free acid form or in partially or completely neutralized form. For neutralization, for example, KOH, NaOH, ammonia or another base can be used.

According to another particular embodiment, the monomers used in the process according to the invention are, in particular, acrylic acid, methacrylic acid and/or their salts and/or mixtures.

In another embodiment, the monomers (m1) used in step (E) comprise, and usually consist of, (meth)acrylamide monomers, or more generally (meth)acrylamido monomers, including:

- acrylamide monomers, namely acrylamide, its sulfonate derivative (AMPS), quaternary ammonium (APTAC) and sulfopropyldimethylammonium propylacrylamide;

- methacrylamido monomers such as sulfopropyl dimethylammonium propylmethacrylamide (SPP), sulfohydroxypropyl dimethylammonium propylmethacrylamido.

In one particular embodiment, the m1 monomers from step (E) are acrylamides. The acrylamide used in step (E) is preferably non-copper stabilized acrylamide. If copper is present, it is preferable to introduce a copper complexing agent such as EDTA, if necessary, preferably at a level of 20-2000 ppm. When acrylamides are used in step (E), they can usually be used as a powder, an aqueous solution (possibly, but not necessarily, stabilized with hydroquinone monomethyl ether, MEHQ, or copper salts (if necessary, preferably with the addition of EDTA)).

Typically, the initial concentration of monomers (m1) in the reaction medium in step (E) can be up to 40 wt.% and even up to 50 wt.%, and this concentration usually remains below 30 wt.% of the total weight of the reaction medium. For example, the initial concentration of monomers m1 in the reaction medium of step (E) is from 0.5% to 35%, in particular from 1 to 20% by weight, based on the total weight of the reaction medium.

In one particular embodiment, the hydrophilic monomers used in step (E) are thermosensitive macromonomers that are insoluble in water above a certain temperature (cloud point or, in English, "cloud point"), but soluble at a lower temperature. temperature, and stage (E) is carried out at a temperature below the cloud point temperature. Macromonomers of this type usually contain a polymerizable acrylamide type group and have a side chain consisting of ethyleneoxy or propylene oxide sequences (random or block), or based on N-isopropylacrylamide or N-vinyl caprolactam. This embodiment makes it possible to obtain, in particular, polymers having thermal thickener properties applicable, for example, in the oil industry.

Crosslinkable hydrophilic monomers (mR1) can be selected from N,N'-methylenebisacrylamide (MBA), N,N'-ethylenebisacrylamide, polyethylene glycol diacrylate (PEG), triacrylate, divinyl ether, usually trifunctional divinyl ether, such as divinyl ether triethylene glycol (TEGDE), from N-diallylamines, N,N-diallyl-N-alkylamines, their acid addition salts and their quaternization products, the alkyl used here being preferably C1-C3-alkyl; N,N-diallyl-N-methylamine and N,N-diallyl-N,N-dimethylammonium compounds, for example chlorides and bromides; or ethoxylated trimethylol propane triacrylate, ditrimethylol propane tetraacrylate (DiTMPTTA).

In one preferred embodiment, the crosslinkable hydrophilic monomers (mR1) are selected from N,N'-methylenebisacrylamide (MBA), polyethylene glycol diacrylate (PEG), triacrylate, divinyl ether, and derivatives thereof.

Hydrophobic monomers (m2)

These monomers used in step (E) are in the form of a micellar solution, namely, containing in a state of dispersion in the medium (M), micelles comprising these hydrophobic monomers. Any monomers with hydrophobic properties are suitable for step (E), provided that they can be incorporated into micelles of this type.

These hydrophobic monomers typically have a solubility in the reaction medium at the temperature of step (E) of less than 1000 wpm/million, for example less than 500 wpm/million and even less than 100 wpm/million.

Hydrophobic monomers (m2) may include non-crosslinkable monomers (m'2) and/or crosslinkable monomers (mR2).

As non-crosslinking hydrophobic monomers (m'2) the following can be mentioned in particular:

- vinylaromatic monomers such as styrene, α-methylstyrene, p-chloromethylstyrene, vinyltoluene, 2-methylstyrene, 4-methylstyrene, 2-(n-butyl)styrene, 4-(n-decyl)styrene, 2-(tert-butyl)styrene ;

- halogenated vinyl compounds, such as vinyl or vinylidene halides, such as vinyl or vinylidene chlorides or -fluorides, corresponding to the formula R _b R _c C=CX ¹ X ² in which

X ¹ =F or Cl

X ²⁼ H, F or Cl

each of R _{b and} R _c independently means

- H, Cl, F or

- an alkyl group, preferably chlorinated and/or fluorinated, more preferably perchlorinated or perfluorinated;

- esters of α,β-ethylenically unsaturated mono- or dicarboxylic acids with C2-C30-alkanols, e.g. butyl (meth) acrylate, sec-butyl (meth) acrylate, tert-butyl (meth) acrylate, tert-butyl ethacrylate, n-hexyl (meth) acrylate, n-heptyl (meth) acrylate, n-octyl (meth) acrylate, 1,1,3,3-tetramethylbutyl (meth) acrylate, ethylhexyl (meth) acrylate, n-nonyl (meth) acrylate, n-decyl (meth) acrylate, n-undecyl (meth) acrylate, tridecyl (meth) acrylate, myristyl(meth)acrylate, pentadecyl(meth)acrylate, palmityl(meth)acrylate, heptadecyl(meth)acrylate, nonadecyl(meth)acrylate, araquinyl(meth)acrylate, behenyl(meth)acrylate, lignoceryl(meth)acrylate, cerotinyl( meth)acrylate, melissinyl(meth)acrylate, palmitoleyl(meth)acrylate, oleyl(meth)acrylate, linolyl(meth)acrylate, linolenyl(meth)acrylate, stearyl(meth)acrylate, lauryl(meth)acrylate and mixtures thereof;

- esters of vinyl or allyl alcohol with C1-C30 monocarboxylic acids, for example vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl laurate, vinyl stearate, vinyl propionate, vinyl versatate and mixtures thereof;

- ethylenically unsaturated nitriles such as acrylonitrile, methacrylonitrile and mixtures thereof;

- esters of α,β-ethylenically unsaturated mono- and dicarboxylic acids with C3-C30 alkanediols, e.g. , 4-hydroxybutyl methacrylate, 6-hydroxyhexyl acrylate, 6-hydroxyhexyl methacrylate, 3-hydroxy-2-ethylhexyl acrylate and 3-hydroxy-2-ethylhexyl methacrylate;

- primary amides of α,β-ethylenically unsaturated mono- and dicarboxylic acids and N-alkyl and N, N-dialkyl derivatives such as N-propyl(meth)acrylamide, N-(n-butyl)(meth)acrylamide, N -(tert-butyl)(meth)acrylamide, N-(n octyl)(meth)acrylamide, N-(1,1,3,3-tetramethylbutyl)(meth)acrylamide, N-ethylhexyl(meth)acrylamide, N- (n-nonyl)(meth)acrylamide, N-(n-decyl)(meth)acrylamide, N-(n-undecyl)(meth)acrylamide, N-tridecyl(meth)acrylamide, N-myristyl(meth)acrylamide, N-pentadecyl(meth)acrylamide, N-palmityl(meth)acrylamide, N-heptadecyl(meth)acrylamide, N-nonadecid(meth)acrylamide, N-araquinyl(meth)acrylamide, N-behenyl(meth)acrylamide, N- lignoceryl(meth)acrylamide, N-cerotinyl(meth)acrylamide, N-melissinyl(meth)acrylamide, N-palmitoleyl(meth)acrylamide, N-oleyl(meth)acrylamide, N-linolyl(meth)acrylamide, N-linolenyl( meth)acrylamide, N-stearyl(meth)acrylamide and N-lauryl(meth)acrylamide;

- N-vinyl lactams and their derivatives, such as N-vinyl-5-ethyl-2-pyrrolidone, N-vinyl-6-methyl-2-piperidone, N-vinyl-6-ethyl-2-piperidone, N-vinyl- 7-methyl-2-caprolactam and N-vinyl-7-ethyl-2-caprolactam;

- esters of α,β-ethylenically unsaturated mono- and dicarboxylic acids with amino alcohols, for example N,N-dimethylaminocyclohexyl(meth)acrylate, and

- amides of α,β-ethylenically unsaturated mono- and dicarboxylic acids with diamines containing at least one primary or secondary amino group, for example, N-[4-(dimethylamino)butyl] (meth)acrylamide, N-[4-( dimethylamino)cyclohexyl](meth)acrylamide.

In one preferred embodiment, the non-crosslinking hydrophobic monomers (m'2) used according to the invention may be selected from:

- α,β-unsaturated alkyl esters with C1-C30, preferably C4-C22 alkyls, in particular alkyl acrylates and methacrylates, such as methyl-, ethyl-, butyl-, 2-ethylhexyl-, isoactyl-, lauryl-, isodecyl - or stearyl acrylates and - methacrylates (particularly interesting was, in particular, lauryl methacrylate);

- α,β-unsaturated alkylamides with C1-C30, preferably C4-C22 alkyls, in particular alkylacrylamide and -methacrylamide, such as methyl-, ethyl-, butyl-, 2-ethylhexyl-, isoactyl-, lauryl-, isodecyl- or stearylacrylamide and β-methacrylamide (particularly advantageous has been lauryl methacrylamide);

- vinyl esters or allyl alcohols of saturated carboxylic acids, such as vinyl or allyl acetate, -propionate, -versatate or -stearate;

- α,β-unsaturated nitriles containing from 3 to 12 carbon atoms, such as acrylonitrile or methacrylonitrile, and

- mixtures and combinations of two or more of the above monomers.

In one particular embodiment, the non-crosslinking hydrophobic monomers (m'2) are selected from: α,β-unsaturated alkyl esters with C1-C30 alkyls, preferably C4-C22 alkyls, in particular from alkyl acrylates and -methacrylates such as methyl-, ethyl, butyl, 2-ethylhexyl, isoactyl, lauryl, isodecyl or stearyl acrylates and methacrylates (in particular, lauryl methacrylate has proven to be particularly advantageous).

Hydrophobic cross-linking monomers (mR2) can be selected from divinylbenzene (DVB), ethoxylated or propoxylated bisphenol-A diacrylate, dipropylene glycol diacrylate (DPGDA), tripropylene glycol diacrylate (TPGDA), propoxylated di(meth)acrylate, butoxylated di(meth)acrylate, dimethylacrylamide , 1,4-butanediol dimethacrylate (BDDMA), 1,6-hexanediol dimethacrylate (HDDMA), 1,3-butylene glycol dimethacrylate (BGDMA) and derivatives thereof.

In one preferred embodiment, the crosslinkable hydrophobic monomers (mR2) are selected from divinylbenzene (DVB) and its derivatives.

Surfactants

Any suitable surfactant may be used to prepare a micellar solution of the hydrophobic monomers used in step (E), for example, but not limited to, surfactants selected from the following list may be used:

Anionic surfactants can be selected from:

- alkyl ester sulfonates, for example of the formula R-CH(SO ₃ M)-CH2COOR', or alkyl ester sulfates, for example of the formula R-CH(OSO ₃ M)-CH2COOR', where R is an alkyl radical of C ₈ - C ₂₀ , preferably C ₁₀ -C ₁₆ , R' is a C ₁ -C ₆ alkyl radical, preferably C ₁ -C ₃ , and M is an alkaline earth metal cation, eg sodium, or an ammonium cation. More specifically, methyl ester sulfonates may be mentioned in which R is a C ₁₄ -C ₁₆ radical;

- alkylbenzenesulfonates, more specifically C ₉ -C ₂₀ primary or secondary alkylsulfonates, in particular C ₈ -C ₂₂ alkylglycerol sulfonates;

- alkyl sulfates, for example, formula ROSO ₃ M, where R denotes an alkyl or hydroxyalkyl radical C ₁₀ -C ₂₄ , preferably C ₁₂ -C ₂₀ ; M is a cation as defined above, eg sodium dodecyl sulfate (SDS);

- sulfates of simple alkyl ethers, for example, the formula RO(OA) _n SO ₃ M, where R denotes an alkyl or hydroxyalkyl radical C ₁₀ -C ₂₄ , preferably C ₁₂ -C ₂₀ ; wherein OA means an ethoxylated or propoxylated group; M is a cation as defined above, n typically ranges from 1 to 4, eg lauryl ether sulfate with n=2;

- alkylamide sulfates, for example of the formula RCONHR'OSO ₃ M, in which R is a C ₂ -C ₂₂ alkyl radical, preferably C ₆ -C ₂₀ , R' is a C ₂ -C ₃ alkyl radical, M is a cation as defined above, as well as their polyalkoxylated (ethoxylated and/or propoxylated) derivatives (alkylamidoether sulfates);

- salts of saturated or unsaturated fatty acids, for example C ₈ -C ₂₄ , preferably C ₁₄ -C ₂₀ , and an alkaline earth cation, N-acyl or N-alkyl taurates, alkyl isethionates, alkyl succinamates and alkyl sulfosuccinates, alkyl glutamates, mono- or diesters of sulfosuccinates , N-acyl-sarcosinates, polyethoxycarboxylates;

- complex mono- and diesterphosphates, for example, of the following formula: (RO) _x -P(=O)(OM) _x , where R is an alkyl, alkylaryl, arylalkyl, aryl radical, optionally polyalkoxylated, x and x' are equal to 1 or 2 , provided that the sum of x and x' is equal to 3, M means an alkaline earth cation.

Non- ionic surfactants can be selected from:

- alkoxylated fatty alcohols, such as laureth-2, laureth-4, laureth-7, olet-20,

- alkoxylated triglycerides, alkoxylated fatty acids, alkoxylated sorbitol esters, alkoxylated fatty amines, alkoxylated di(phenyl-1-ethyl)phenols, alkoxylated tri(phenyl-1-ethyl)phenols, alkoxylated alkylphenols,

products obtained by condensing ethylene oxide with a hydrophobic compound obtained by condensing propylene oxide with propylene glycol, such as Pluronic, commercially available from BASF;

- products obtained by condensing ethylene oxide with a compound obtained by condensing propylene oxide with ethylenediamine, such as Tetronic from BASF;

- alkyl polyglycosides as described in US 4,565,647 or alkyl glucosides;

fatty acid amides, eg C8-C20, in particular fatty acid monoalkanolamides, eg MEA cocamide or MIPA cocoamide.

Amphoteric surfactants (truly amphoteric, containing an ionic group and a potentially ionic group with an opposite charge, or zwitterionic, simultaneously containing two opposite charges) can be:

betaines in the broadest sense, in particular carboxybetaines, for example lauryl betaine (Mirataine BB from Rhodia) or octyl betaine or cocobetaine (Mirataine BB-FLA from Rhodia); amidoalkyl betaines such as cocamidopropyl betaine (CAPB) (Mirataine BDJ from Rhodia or Mirataine BET C-30 from Rhodia);

- sulfobetaines or sultaines, such as cocamidopropyl hydroxysultaine (Mirataine CBS from Rhodia);

- alkylamphoacetates and alkylamphodiacetates, for example containing a coco chain, lauryl (Miranol, in particular C2M Conc NP, C32, L32, from Rhodia);

- alkylamphopropionates or alkylamphodipropionates, (Miranol C2M SF);

- alkylamphohydroxypropyl sultaines (Miranol CS),

- alkylamine oxides, for example lauramine oxide (INCI);

- (carboxylatomethyl)hexadecyl dimethylammonium (Mackam CET from Solvay).

Cationic surfactants can be salts of primary, secondary or tertiary fatty amines, possibly polyethoxylated, quaternary ammonium salts such as tetraalkylammonium, alkylamidoalkylammonium, trialkylbenzylammonium, trialkylhydroxyalkylammonium or alkylpyridinium chlorides or bromides, imidazoline derivatives, amine oxides with cationic properties. One example of a cationic surfactant is cetrimonium chloride or bromide (INCI).

The surfactants used according to the present invention may be block copolymers containing at least one hydrophilic block and at least one hydrophobic block other than the hydrophilic block, preferably obtained by a polymerization process in which:

(a ₀ ) at least one hydrophilic monomer (respectively hydrophobic), at least one source of free radicals and at least one radical polymerization regulator of the -S(C=S)- type are combined in the aqueous phase;

(a ₁ ) contacting the polymer obtained at the output of step (a ₀ ) with at least one hydrophobic monomer (respectively hydrophilic) different from the monomer used in step (a ₀ ) and at least one source of free radicals ;

resulting in a diblock copolymer.

Triblock polymers or polymers containing even more blocks can optionally be obtained by carrying out, after step (a ₁ ), step (a ₂ ), in which the polymer obtained in step (a ₁ ) is brought into contact with at least one monomer, different from the monomer used in step (a ₁ ) and at least one source of free radicals; and more generally, carrying out (n+1) stages such as the above stages (a ₁ ) and (a ₂ ), where n is an integer, usually from 1 to 3, and in each stage (a _n ), when n≥ 1: the polymer obtained in step (a _n-1 ) is brought into contact with at least one monomer other than the monomer used in step (a _n-1 ) and at least one source of free radicals. According to the invention, copolymers of the type described in WO03068827, WO03068848 and WO2005/021612 can be used.

The use of microgels according to the invention

The microgels of the present invention can be used in subterranean formations to control rheology in oil and natural gas exploration and production. They can be used, for example, in drilling fluids, cementing fluids, completion fluids, as a spacer fluid, lost circulation pill, fracturing, stimulation, acidification, injectivity profile alignment, and for enhanced oil recovery.

For example, they may serve as suspending agents or as agents having the effect of reducing filtration of fluids injected under pressure into subterranean formations.

In one embodiment, microgels can be used for water absorption, in particular as superabsorbents (they can contain more than 99% water).

Various aspects and advantages of the invention will be further illustrated by the following examples, in which the polymers were obtained by the method according to the invention.

Examples

Example 1

Synthesis of polymer gels: stage E

- (counter-example) Polymer P1 (poly(AM/DMA/AMPS/Xa)) with a target molecular weight of 2,000,000 g/mol was prepared under the following conditions:

In a 2000 ml glass bottle were weighed 521.4 g of acrylamide (AM) in the form of an aqueous solution with a concentration of 50 wt.%, 550.5 g of AMPS in the form of an aqueous solution with a concentration of 50 wt.%, 123.4 g of dimethylacrylamide (DMA) and 983 .1 g of demineralized water. After stirring the previously prepared solution with a magnetic stirrer, the pH was measured using a calibrated pH meter, the pH of the solution was 9.9, it was brought to 6.0 by adding an aqueous solution of sulfuric acid 10 wt.%. Then 6.87 g of a solution of Rhodixan A1 (1 wt% in ethanol) was added. This new solution was injected at ambient temperature (20°C) into a Dewar (3000 ml) equipped with a lid that provides isolation from the environment, an anchor stirrer, a temperature probe and a nitrogen inlet. The mixture was degassed by nitrogen bubbling and stirred for 60 minutes. 3.3 g of an aqueous solution of 2,2'-azobis(2-methylpropionamidine)dihydrochloride, 11.0 g of potassium persulfate (KPS) (aqueous solution of 4 wt.%) and 4.4 g of sodium sulfoxylate formaldehyde in the form of an aqueous solution with a concentration of 5 wt.%. The KPS solution was pre-degassed by bubbling nitrogen for 15 minutes. Then, the polymerization reaction was carried out without stirring for 16 hours.

- (counter-example) Polymer P2 (poly(AM/DMA/AMPS/MBA/Xa)) containing 3 hydrophilic cross-linking units per chain, with a target molecular weight of 2,000,000 g/mol was prepared under the following conditions:

In a 2000 ml glass bottle were weighed 521.2 g of acrylamide in the form of an aqueous solution with a concentration of 50 wt.%, 550.5 g of AMPS in the form of an aqueous solution with a concentration of 50 wt.%, 123.4 g of dimethylacrylamide (DMA), 15.3 g a solution of methylenebisacrylamide (MBA) 0.5 wt.% in water and 967.8 g of demineralized water. After stirring the previously prepared solution with a magnetic stirrer, the pH was measured using a calibrated pH meter, the pH of the solution was 10.0, it was adjusted to 6.0 by adding an aqueous solution of sulfuric acid 10 wt.%. Then 6.87 g of a solution of Rhodixan A1 (1 wt% in ethanol) was added. This new solution was injected at ambient temperature (20°C) into a Dewar (3000 ml) equipped with a lid that provides isolation from the environment, an anchor stirrer, a temperature probe and a nitrogen inlet. The mixture was degassed by nitrogen bubbling and stirred for 60 minutes. 0.33 g of an aqueous solution of 2,2'-azobis(2-methylpropionamidine) dihydrochloride, 11.0 g of potassium persulfate (KPS) (aqueous solution of 4 wt.%) and 4.4 g of sodium sulfoxylate formaldehyde in the form of an aqueous solution with a concentration of 5 wt.%. The KPS solution was pre-degassed by bubbling nitrogen for 15 minutes. Then, the polymerization reaction was carried out without stirring for 16 hours.

- (counter-example) Polymer P3 (poly(AM/DMA/AMPS/TEGDE/Xa)), containing 6 hydrophilic crosslinking units per chain, with a target molecular weight of 2,000,000 g/mol was prepared under the following conditions:

In a 2000 ml glass bottle were weighed 521.5 g of acrylamide in the form of an aqueous solution with a concentration of 50 wt.%, 550.8 g of AMPS in the form of an aqueous solution with a concentration of 50 wt.%, 123.4 g of dimethylacrylamide (DMA), 0.2 g triethylene glycol divinyl ether (TEGDE) and 989.8 g of demineralized water. After stirring the solution with a magnetic stirrer, the pH was measured using a calibrated pH meter, the pH of the solution was 9.9, it was adjusted to 6.0 by adding an aqueous solution of sulfuric acid 10 wt.%. Then 6.86 g of a solution of Rhodixan A1 (1 wt% in ethanol) was added. This new solution was injected at ambient temperature (20°C) into a Dewar (3000 ml) equipped with a lid that provides isolation from the environment, an anchor stirrer, a temperature probe and a nitrogen inlet. The mixture was degassed by nitrogen bubbling and stirred for 60 minutes. 3.3 g of an aqueous solution of 2,2'-azobis(2-methylpropionamidine) dihydrochloride at a concentration of 10 wt.%, 4.4 g of sodium persulfate (NaPS) (aqueous solution of 10 wt.%) and 2, 2 g of sodium sulfoxylate formaldehyde in the form of an aqueous solution with a concentration of 10 wt.%. The NaPS solution was pre-degassed by bubbling nitrogen for 15 minutes. Then, the polymerization reaction was carried out without stirring for 16 hours.

- (counter-example) Polymer P4 (poly(AM/DMA/AMPS/styrene/Xa)) containing 3 hydrophobic units per chain, with a target molecular weight of 2,000,000 g/mol was prepared under the following conditions:

In a 2000 ml glass bottle, at ambient temperature (20°C), 15.4 g of Stepanol WA extra, 0.11 g of styrene and 6.7 g of demineralized water were introduced. The mixture was stirred with a magnetic stirrer for 60 min until the styrene was completely dissolved. In the same 2000 ml glass bottle were weighed 520.7 g of acrylamide in the form of an aqueous solution with a concentration of 50 wt.%, 558.7 g of AMPS in the form of an aqueous solution with a concentration of 50 wt.%, 122.8 g of dimethylacrylamide (DMA) and 962. 2 g demineralized water. After stirring the solution with a magnetic stirrer, the pH was measured using a calibrated pH meter, the pH of the solution was 9.8, it was adjusted to 6.0 by adding an aqueous solution of sulfuric acid 10 wt.%. Then 6.97 g of a solution of Rhodixan A1 (1 wt% in ethanol) was added. This new solution was injected at ambient temperature (20°C) into a Dewar (3000 ml) equipped with a lid that provides isolation from the environment, an anchor stirrer, a temperature probe and a nitrogen inlet. The mixture was degassed by nitrogen bubbling and stirred for 60 minutes. 3.3 g of an aqueous solution of 2,2'-azobis(2-methylpropionamidine) dihydrochloride at a concentration of 10 wt.%, 4.4 g of sodium persulfate (NaPS) (aqueous solution of 10 wt.%) and 2, 2 g of sodium sulfoxylate formaldehyde in the form of an aqueous solution with a concentration of 10 wt.%. The NaPS solution was pre-degassed by bubbling nitrogen for 15 minutes. Then, the polymerization reaction was carried out without stirring for 16 hours.

- (counter-example) Polymer P5 (poly(AM/DMA/AMPS/styrene/Xa)_ containing 4.5 hydrophobic units per chain, with a target molecular weight of 2,000,000 g/mol was prepared under the following conditions:

In a 2000 ml glass bottle, at ambient temperature (20° C.), 23.0 g of Stepanol WA extra, 0.16 g of styrene and 10.0 g of demineralized water were introduced. The mixture was stirred with a magnetic stirrer for 60 min until the styrene was completely dissolved. In the same 2000 ml glass bottle were weighed 156.9 g of acrylamide in the form of an aqueous solution with a concentration of 50 wt.%, 506.1 g of AMPS in the form of an aqueous solution with a concentration of 50 wt.%, 328.3 g of dimethylacrylamide (DMA) and 1159, 2 g demineralized water. After stirring the solution with a magnetic stirrer, the pH was measured using a calibrated pH meter, the pH of the solution was 9.9, it was adjusted to 6.0 by adding an aqueous solution of sulfuric acid 10 wt.%. Then 6.87 g of a solution of Rhodixan A1 (1 wt% in ethanol) was added. This new solution was injected at ambient temperature (20°C) into a Dewar (3000 ml) equipped with a lid that provides isolation from the environment, an anchor stirrer, a temperature probe and a nitrogen inlet. The mixture was degassed by nitrogen bubbling and stirred for 60 minutes. 3.3 g of an aqueous solution of 2,2'-azobis(2-methylpropionamidine) dihydrochloride at a concentration of 10 wt.%, 4.4 g of sodium persulfate (NaPS) (aqueous solution of 10 wt.%) and 2, 2 g of sodium sulfoxylate formaldehyde in the form of an aqueous solution with a concentration of 10 wt.%. The NaPS solution was pre-degassed by bubbling nitrogen for 15 minutes. Then, the polymerization reaction was carried out without stirring for 16 hours.

- Polymer P6 (poly(AM/DMA/AMPS/DVB/Xa)), containing 6 hydrophobic cross-linking units per chain, with a target molecular weight of 2,000,000 g/mol was prepared under the following conditions:

In a 2000 ml glass bottle, at ambient temperature (20° C.), 15.4 g of Stepanol WA extra, 0.17 g of 80% pure divinylbenzene (DVB) and 6.6 g of demineralized water were introduced. Stirred with a magnetic stirrer for 60 min until complete dissolution of DVB. In the same 2000 ml glass bottle were weighed 519.7 g of acrylamide in the form of an aqueous solution with a concentration of 50 wt.%, 558.6 g of AMPS in the form of an aqueous solution with a concentration of 50 wt.%, 120.8 g of dimethylacrylamide (DMA) and 962. 2 g demineralized water. After stirring the solution with a magnetic stirrer, the pH was measured using a calibrated pH meter, the pH of the solution was 9.8, it was adjusted to 6.0 by adding an aqueous solution of sulfuric acid 10 wt.%. Then 6.87 g of a solution of Rhodixan A1 (1 wt% in ethanol) was added. This new solution was injected at ambient temperature (20°C) into a Dewar (3000 ml) equipped with a lid that provides isolation from the environment, an anchor stirrer, a temperature probe and a nitrogen inlet. The mixture was degassed by nitrogen bubbling and stirred for 60 minutes. 3.3 g of an aqueous solution of 2,2'-azobis(2-methylpropionamidine) dihydrochloride at a concentration of 10 wt.%, 4.4 g of sodium persulfate (NaPS) (aqueous solution of 10 wt.%) and 2, 2 g of sodium sulfoxylate formaldehyde in the form of an aqueous solution with a concentration of 10 wt.%. The NaPS solution was pre-degassed by bubbling nitrogen for 15 minutes. Then, the polymerization reaction was carried out without stirring for 16 hours.

- Polymer P7 (poly(AM/DMA/AMPS/DVB/Xa)), containing 6 hydrophobic cross-linking units per chain, with a target molecular weight of 2,000,000 g/mol was prepared under the following conditions:

In a 2000 ml glass bottle, at ambient temperature (20° C.), 15.4 g of Stepanol WA extra, 0.17 g of 80% pure divinylbenzene (DVB) and 6.6 g of demineralized water were introduced. Stirred with a magnetic stirrer for 60 min until complete dissolution of DVB. In the same 2000 ml glass bottle were weighed 156.9 g of acrylamide in the form of an aqueous solution with a concentration of 50 wt.%, 506.1 g of AMPS in the form of an aqueous solution with a concentration of 50 wt.%, 328.4 g of dimethylacrylamide (DMA) and 1148, 5 g demineralized water. After stirring the solution with a magnetic stirrer, the pH was measured using a calibrated pH meter, the pH of the solution was 9.8, it was adjusted to 6.0 by adding an aqueous solution of sulfuric acid 10 wt.%. Then 6.87 g of a solution of Rhodixan A1 (1 wt% in ethanol) was added. This new solution was injected at ambient temperature (20°C) into a Dewar (3000 ml) equipped with a lid that provides isolation from the environment, an anchor stirrer, a temperature probe and a nitrogen inlet. The mixture was degassed by nitrogen bubbling and stirred for 60 minutes. 3.3 g of an aqueous solution of 2,2'-azobis(2-methylpropionamidine) dihydrochloride at a concentration of 10 wt.%, 4.4 g of sodium persulfate (NaPS) (aqueous solution of 10 wt.%) and 2, 2 g of sodium sulfoxylate formaldehyde in the form of an aqueous solution with a concentration of 10 wt.%. The NaPS solution was pre-degassed by bubbling nitrogen for 15 minutes. Then, the polymerization reaction was carried out without stirring for 16 hours.

- Polymer P8 (poly(AM/DMA/AMPS/DVB/Xa)), containing 12 hydrophobic cross-linking units per chain, with a target molecular weight of 2,000,000 g/mol was prepared under the following conditions:

In a 2000 ml glass bottle, at ambient temperature (20° C.), 30.7 g of Stepanol WA extra, 0.341 g of divinylbenzene (DVB) 80% pure and 13.2 g of demineralized water were introduced. Stirred with a magnetic stirrer for 60 min until complete dissolution of DVB. In the same 2000 ml glass bottle were weighed 156.9 g of acrylamide in the form of an aqueous solution with a concentration of 50 wt.%, 506.1 g of AMPS in the form of an aqueous solution with a concentration of 50 wt.%, 328.4 g of dimethylacrylamide (DMA) and 1148, 5 g demineralized water. After stirring the solution with a magnetic stirrer, the pH was measured using a calibrated pH meter, the pH of the solution was 9.8, it was adjusted to 6.0 by adding an aqueous solution of sulfuric acid 10 wt.%. Then 6.84 g of a solution of Rhodixan A1 (1 wt% in ethanol) was added. This new solution was injected at ambient temperature (20°C) into a Dewar (3000 ml) equipped with a lid that provides isolation from the environment, an anchor stirrer, a temperature probe and a nitrogen inlet. The mixture was degassed by nitrogen bubbling and stirred for 60 minutes. 3.3 g of an aqueous solution of 2,2'-azobis(2-methylpropionamidine) dihydrochloride at a concentration of 10 wt.%, 4.4 g of sodium persulfate (NaPS) (aqueous solution of 10 wt.%) and 2, 2 g of sodium sulfoxylate formaldehyde in the form of an aqueous solution with a concentration of 10 wt.%. The NaPS solution was pre-degassed by bubbling nitrogen for 15 minutes. Then, the polymerization reaction was carried out without stirring for 16 hours.

- Polymer P9 (poly(AM/DMA/AMPS/LMA/MBA/Xa)) containing 37 hydrophobic units per chain and 3 hydrophilic crosslinking units per chain, with a target molecular weight of 2,000,000 g/mol was prepared under the following conditions:

In a 2000 ml glass bottle, at ambient temperature (20° C.), 62.7 g of Stepanol WA extra, 3.21 g of lauryl methacrylate (LMA) and 24.4 g of demineralized water were introduced. Stirred with a magnetic stirrer for 60 min until complete dissolution of LMA. In the same 2000 ml glass bottle were weighed 517.4 g of acrylamide in the form of an aqueous solution with a concentration of 50 wt.%, 556.2 g of AMPS in the form of an aqueous solution with a concentration of 50 wt.%, 120.2 g of dimethylacrylamide (DMA) 3.8 g of a solution of methylenebisacrylamide (MBA) 2 wt.% in water and 895.7 g of demineralized water. After stirring the solution with a magnetic stirrer, the pH was measured using a calibrated pH meter, the pH of the solution was 9.58, it was brought to 6.0 by adding an aqueous solution of sulfuric acid 10 wt.%. Then 6.84 g of a solution of Rhodixan A1 (1 wt% in ethanol) was added. This new solution was injected at ambient temperature (20°C) into a Dewar (3000 ml) equipped with a lid that provides isolation from the environment, an anchor stirrer, a temperature probe and a nitrogen inlet. The mixture was degassed by nitrogen bubbling and stirred for 60 minutes. 3.3 g of an aqueous solution of 2,2'-azobis(2-methylpropionamidine)dihydrochloride at a concentration of 10 wt.%, 14.7 g of potassium persulfate (KPS) (aqueous solution of 3 wt.%) and 2, 2 g of sodium sulfoxylate formaldehyde in the form of an aqueous solution with a concentration of 10 wt.%. The NaPS solution was pre-degassed by bubbling nitrogen for 15 minutes. Then, the polymerization reaction was carried out without stirring for 16 hours.

- Polymer P10 (poly(AM/DMA/AMPS/LMA/DVB/Xa)) containing 18 hydrophobic units per chain and 6 crosslinkable hydrophilic units per chain, with a target molecular weight of 2,000,000 g/mol was prepared under the following conditions:

In a 2000 ml glass bottle, at ambient temperature (20° C.), 28.5 g Stepanol WA extra, 0.346 g divinylbenzene (DVB), 1.47 g lauryl methacrylate (LMA) and 24.4 g demineralized water were introduced. Stirred with a magnetic stirrer for 180 min until complete dissolution of LMA and DVB. In the same 2000 ml glass bottle were weighed 156.6 g of acrylamide in the form of an aqueous solution with a concentration of 50 wt.%, 505.3 g of AMPS in the form of an aqueous solution with a concentration of 50 wt.%, 327.6 g of dimethylacrylamide (DMA) and 1145, 3 g demineralized water. After stirring the solution with a magnetic stirrer, the pH was measured using a calibrated pH meter, the pH of the solution was 9.58, it was brought to 6.0 by adding an aqueous solution of sulfuric acid 10 wt.%. Then 6.84 g of a solution of Rhodixan A1 (1 wt% in ethanol) was added. This new solution was injected at ambient temperature (20°C) into a Dewar (3000 ml) equipped with a lid that provides isolation from the environment, an anchor stirrer, a temperature probe and a nitrogen inlet. The mixture was degassed by nitrogen bubbling and stirred for 60 minutes. 3.3 g of an aqueous solution of 2,2'-azobis(2-methylpropionamidine)dihydrochloride at a concentration of 10 wt.%, 14.7 g of potassium persulfate (KPS) (aqueous solution of 3 wt.%) and 2, 2 g of sodium sulfoxylate formaldehyde in the form of an aqueous solution with a concentration of 10 wt.%. The NaPS solution was pre-degassed by bubbling nitrogen for 15 minutes. Then, the polymerization reaction was carried out without stirring for 16 hours.

- Polymer P11 (poly(AM/DMA/AMPS/LMA/DVB/Xa)), containing 37 hydrophobic units per chain and 6 hydrophobic cross-linking units per chain, with a target molecular weight of 2,000,000 g/mol was prepared under the following conditions:

56.9 g of Stepanol WA extra, 0.33 g of divinylbenzene (DVB), 2.91 g of lauryl methacrylate (LMA) and 24.4 g of demineralized water were introduced into a 2000 ml glass bottle at ambient temperature (20° C.). Stirred with a magnetic stirrer for 180 min until complete dissolution of LMA and DVB. Into the same 2000 ml glass bottle were weighed 156.6 g of an aqueous solution of 50 wt.% acrylamide, 505.3 g of an aqueous solution of AMPS at a concentration of 50 wt.%, 327.6 g of dimethylacrylamide (DMA) and 111.72 g of demineralized water. . After stirring the solution with a magnetic stirrer, the pH was measured using a calibrated pH meter, the pH of the solution was 9.58, it was brought to 6.0 by adding an aqueous solution of sulfuric acid 10 wt.%. Then 6.84 g of a solution of Rhodixan A1 (1 wt% in ethanol) was added. This new solution was injected at ambient temperature (20°C) into a Dewar (3000 ml) equipped with a lid that provides isolation from the environment, an anchor stirrer, a temperature probe and a nitrogen inlet. The mixture was degassed by nitrogen bubbling and stirred for 60 minutes. 3.3 g of an aqueous solution of 2,2'-azobis(2-methylpropionamidine) dihydrochloride with a concentration of 10 wt.%, 14.7 g of potassium persulfate (KPS) (aqueous solution of 3 wt.%) and 2, 2 g of sodium sulfoxylate formaldehyde in the form of an aqueous solution with a concentration of 10 wt.%. The NaPS solution was pre-degassed by bubbling nitrogen for 15 minutes. Then, the polymerization reaction was carried out without stirring for 16 hours.

Drying and Grinding: Stage E2

The polymer gels obtained according to the synthesis conditions described above are cut and dried in a fluidized bed or on a plate, and then crushed to obtain microgels. Grinding is carried out using an Alpine 160 hammer mill. Particle sizes are determined by laser granulometry in dry mode on a Malvern Mastersizer granulometer.

Polymer mR1 (ppm) mR2 (ppm) m2 (ppm) particle size (median diameter, µm) P1 0 0 0 57 P2 116 0 0 45 P3 303 0 0 47 P4 0 0 166 59 P5 0 0 242 60 P6 0 258 0 57 P7 0 258 0 96 P8 0 515 0 40 P9 116 0 4900 51 P10 0 523 2235 24 P11 0 502 4425 28

Example 2 Evaluation of Thermal Stability by Rheology at Elevated Temperature

The thermal stability of microgels is evaluated by directly measuring their shear viscosity at a constant temperature of 176°C. A pressure rheometer model 5550 from Chandler Engineering equipped with a B05 spindle is used to monitor the change in viscosity of the microgel suspensions over time at 176° C. and a constant shear of 100 s ^-1 . The study is carried out within 3-4 hours, which is a typical time of use in drilling fluid, buffer fluid or cementing.

First, 2% suspensions of microgels are prepared only in a 2% potassium chloride solution with stirring with a magnetic stirrer and left to hydrate for 2 hours. At the moment of introduction into the rheometer, 200 wpm sodium metabisulphite is added to the solution as an oxygen trap to avoid oxidative degradation processes that are not typical for real application conditions.

Counter examples (viscosity) Examples (viscosity) Polymer P2 P3 P6 initially at 176°C 240 245 275 1h at 176°C 160 196 211 2h at 176°C 84 198 170 3h at 176°C 36 242 257 4h at 176°C 31 70 291

In order to more realistically represent application conditions under more aggressive conditions with a highly alkaline pH, lime is added to the potassium chloride solution in an amount of 0.1%. Spend identical aging at 176°C.

Counter examples (viscosity) Examples (viscosity) Polymer P2 P3 P6 P7 P8 P10 P11 initially at 176°C 245 258 214 100 179 225 256 1h at 176°C 220 151 111 91 172 205 229 2h at 176°C 32 270 138 90 167 195 224 3h at 176°C thirty 93 142 81 158 190 218 4h at 176°C 28 43 102 74 / / / % viscosity after 3h 12% 36% 66% 81% 88% 84% 85%

Example 3 Barite Particle Slurry

The improved ability of the microgels of the invention to suspend particles is demonstrated using a mud-type composition in which barite particles are to be held in suspension. In a 2% aqueous solution of potassium chloride, to which 0.1% lime (CaOH ₂ ) is added, the microgels of the polymers obtained in the previous synthesis examples, as well as barite, are dispersed. The compositions were prepared in a two-liter beaker with stirring with a 55 mm diameter deflocculator blade at a rotation speed of 400–1000 rpm.

The preparation of dispersions is briefly described in the table below.

Product Weight (g) Introduction order Mixing period base fluid
(KCl 2% + Ca(OH) ₂ 0.1%) 700 one polymer microgel 7 2 mixing 15 min barite (BaSO ₄ ) 196 3 mixing 15 min

The resulting dispersions are then conditioned for 20 minutes in an atmospheric consistometer (model 1250 from Chandler Engineering) at 88°C. The stability of the suspension after conditioning was assessed by transferring the dispersion to a 100 ml stoppered tube, which was placed in an oven at 88° C. for 2 hours.

After 2 hours at 88°C, measure the densities of the top 10 ml (ρ ₉₀ ) and bottom 10 ml (ρ ₁₀ ) tubes and determine the percentage difference in density using the following formula:

When the stability of the slurry is sufficiently good, i.e., no excessive settling of barite particles is observed, a filtration reduction test is performed at 88°C in a filter press (model 170-01-2 from OFITE) at 35 bar pressure on a 40 µm ceramic disc ( model 170-51 from OFITE Instruments). The reduction in filtration under these conditions is considered very satisfactory if the volume collected in 30 minutes is less than 25 ml.

Counter examples Examples Example P1 P2 P4 P5 P7 P9 P10 P11

27 fifteen 29 32 4.2 3.7 1.8 1.8 filtration (ml in 30 min) / / / / 13 16 7 10

Claims (19)

1. The method of obtaining a polymer, including stage (E) micellar radical polymerization, which is brought into contact in an aqueous medium (M): - monomers (m1) soluble or dispersible in said aqueous medium (M), called hydrophilic monomers; - monomers (m2) in the form of a micellar solution, namely containing in a dispersed state in the medium (M) micelles containing these monomers (m2), called hydrophobic monomers; wherein said monomers (m1) and/or (m2) include crosslinkable monomers (mR) having at least two ethylenic unsaturations; - at least one radical polymerization initiator, preferably water-soluble or dispersible, and - at least one radical polymerization regulator, and further comprising step (E2) after step (E), in which the polymers obtained from the output of step (E) are crushed, resulting in polymers in the form of dispersed particles, wherein the monomer concentration (mR) is between 100 wpm and 1000 wpm, preferably between 200 and 600 wpm, based on the total weight of all monomers present in medium (E). 2. Process according to claim 1, wherein step (E) is carried out in the presence of hydrophobic monomers (m2) which contain or even consist exclusively of hydrophobic crosslinkable monomers (mR2). 3. Process according to claim 1 or 2, wherein step (E) is carried out in the presence of hydrophilic monomers (m1), of which only a part consists of crosslinkable monomers (mR1). 4. The method according to any one of paragraphs. 1-3, wherein the molar ratio (mR)/(m1) corresponding to the amount of crosslinkable monomers (mR) relative to the total amount of hydrophilic monomers is from 0.01% to 0.1%. 5. The method according to any one of paragraphs. 1-4, and the radical polymerization regulator is a compound containing a thiocarbonylthio group -S(C=S), for example, xanthate. 6. The method according to any one of paragraphs. 1-5, wherein the crosslinkable hydrophobic monomers (mR2) are selected from divinylbenzene (DVB) and its derivatives. 7. The method according to any one of paragraphs. 1-6, wherein the hydrophilic crosslinking monomers (mR1) are selected from N,N'-methylenebisacrylamide (MBA), polyethylene glycol diacrylate (PEG), triacrylate, divinyl ether, and derivatives thereof. 8. The polymer in the form of dispersed particles obtained at the output of stage (E2) according to any one of paragraphs. 1-7. 9. Microgel obtained after dispersion of particles in water according to item 8. 10. Use of the microgel according to claim 9 as a rheological modifier and/or filtration reducer in a subterranean formation. 11. Use of the microgel according to claim 10 as a rheology modifier and/or filtration reducer at a temperature greater than or equal to 150°C. 12. The use of microgel according to one of paragraphs. 9-11 as a rheology modifier and/or filtration reducer in a subterranean formation in an oil production area.