Inverse emulsion for hydraulic fracturing

Abstract

The present invention relates to an inverse emulsion and its use in a hydraulic fracturing process of an unconventional underground oil or gas reservoir.

Description

Title of the invention: Reverse emulsion for hydraulic fracturing. Technical field of the invention

[0001] The present invention relates to an inverse emulsion and its use in a hydraulic fracturing process of an unconventional underground reservoir of hydrocarbons (oil and / or gas). Prior state of the art

[0002] The production of hydrocarbons (oil and / or gas) contained in unconventional underground reservoirs has been developing for several years and requires opening fractures in the reservoir to extract the hydrocarbons trapped in the rock.

[0003] In the following description of the prior art and of the invention, "unconventional underground reservoirs" or "unconventional reservoirs" refers to deposits requiring special extraction technologies because hydrocarbons do not exist there in the form of an accumulation in a porous and permeable rock (see Shale hydrocarbons in France Provisional Report - CGIET No. 2011-04-G - Ministry of Ecology, Sustainable Development, Transport and Housing - April 2011).

[0004] For unconventional gas reservoirs, examples include shale gas, coalbed methane, and tight gas. For unconventional oil reservoirs, examples include heavy oil, shale oil, and tight oil.

[0005] The reserves contained in unconventional reservoirs are substantial and extremely widespread in areas that were previously unexploitable. In the United States, shale gas is widely exploited and now accounts for 80% of total natural gas production in the United States, whereas it represented only 28% in 1998. The exploitation of compact reservoirs has been made possible by developments in drilling techniques.

[0006] Production techniques have indeed evolved from vertical to horizontal wells, reducing the number of production wells required and their footprint, while allowing for better coverage of the reservoir volume to recover a maximum of hydrocarbons. However, the permeability of the rocks is insufficient for hydrocarbons to easily migrate from the source rock to the well. It is therefore It is necessary to increase permeability and production areas through stimulation operations and in particular through hydraulic fracturing of the rock in contact with the well.

[0007] Hydraulic fracturing aims to create additional permeability to generate larger volumes of gas or oil production. These hydraulic fracturing operations on horizontal wells began in 1960 in the Appalachian Mountains, and today, tens of thousands of operations have taken place across the United States. They consist of injecting water at high pressure and a very high flow rate to create fractures distributed perpendicularly to the production wells. This is generally done in several stages to create fractures along the entire length of the horizontal well, thus allowing for maximum reservoir volume coverage.

[0008] In order to keep these fractures open, a support agent (for example sand, plastics or calibrated ceramic particles) is added so as to prevent the closure of these fractures and to maintain the capillarity created once the water injection is stopped.

[0009] Water alone is insufficient to achieve good placement efficiency of the support agents due to its low viscosity. This also limits its ability to hold the support agent in place within the fractures. To overcome this problem, fracturing fluids containing viscosifying compounds have been developed.

[0010] In addition to having viscosifying properties, the viscosifying compound, generally a polymer, must have a specific rheological profile. Indeed, the viscosifying compound must be able to generate low viscosity so as not to hinder the transport and pumping of the fluid containing the proppant during the high shear stresses experienced during the injection of the fracturing fluid. Once injected, this same viscosifying compound must generate sufficient viscosity when the shear stress decreases in order to suspend the proppant in the injected fracturing fluid and to retain it within the fractures created.

[0011] The viscoelastic properties of polymers in solution must also be taken into consideration. This viscoelasticity, and its importance for the application of polymers in hydrocarbon recovery, are described in SPE document 147206 (Fracturing Fluid Comprised of Campements Sourced Solely from the Food Industry Provides Superior Proppant Transport - David Loveless, Jeremy Holtsclaw, Rajesh Saini, Phü Harris, and Jeff Fleming, SPE, Halliburton) through visual observations in static or dynamic experiments, or through rheological measurements, such as the measurement of viscous and elastic moduli (G' and G"), or the measurement of viscosity as a function of the shear. Thus, elastic properties are sought to ensure the transport and suspension of the propping agent.

[0012] Ideally, polymers with suitable viscosity-reducing properties are also friction reducers. In other words, these polymers can advantageously reduce pressure loss in turbulent media and thus significantly increase the flow rate at the same power and pipe diameter. This results in a reduction of the energy required to inject the fracturing fluid.

[0013] High molecular weight linear polymers are commonly used in these applications. Stretching the polymer chains in solution makes it possible to delay the turbulent regime that develops during high-speed fluid transport.

[0014] These polymers can be in different forms, such as powder, solution or inverse emulsion.

[0015] When the polymer is in powder form, a dissolution step is necessary. This crucial step is difficult to implement, either because of the need for special logistical equipment, and therefore an additional cost, in addition to its maintenance, or because of the need to control the dissolution of high molecular weight polymers in order to avoid powder agglomeration phenomena and the production of "fish eyes" which can not only deteriorate application performance but also clog pores during production.

[0016] When the polymer is in solution form, it must be diluted before injection to avoid injecting excessively viscous water and causing pore clogging. Furthermore, transporting water is not economically, and especially not environmentally, viable.

[0017] The polymer in the form of an inverse emulsion represents a compromise between a polymer in powder form and a polymer in solution form. The inverse emulsion has the advantage of being more concentrated than a solution and being ready to use without being viscous. However, the presence of oils and surfactants in the emulsion composition leads to an increase in phenomena that deteriorate the permeability of fractures and gaps between the supporting agents, resulting in a loss of production.

[0018] It is also possible to use polymer powder dispersions in oil, i.e., a ready-to-use product, since the powder is first finely ground (< 300 µm) and dissolves almost instantly upon contact with water. However, this dispersion form is very costly (ground powder + oil) and, due to the presence of oil, also carries risks of damaging the underground formation.

[0019] These fracture damage (deterioration) phenomena are characterized by a resurgence of conductivity. The resurgence of conductivity allows us to measure the evolution of the pressure in the fractures. The increase in conductivity makes it possible to determine whether the residues of the fracturing fluid, present in the interstices between the proppants, are released and do not damage the pores which allow the flow of hydrocarbons and therefore their recovery.

[0020] The Applicant has developed a new inverse emulsion that significantly improves conductivity recovery. Furthermore, this inverse emulsion offers improved application performance, particularly with regard to inversion time. Finally, the use of the inverse emulsion according to the invention reduces the amount of oil present in the reflux water. Reflux water is the water used to form fractures and which rises to the surface once the fracturing process is complete. This water is difficult to treat due to its nature, but especially because it is difficult to recover. With less oil present in the inverse emulsion according to the invention, there is less oil in the reflux water and therefore less pollution.

[0021] The use of the inverse emulsion according to the invention is in line with a principle of environmental awareness and the impact of industry and humankind on the planet. By improving the conductivity recovery, hydrocarbon production is increased, thus reducing the amount of greenhouse gases such as CO2 required for its extraction. Description of the invention

[0022] The present invention relates to a reverse emulsion comprising: i) a hydrophilic phase comprising: - at least one polymer representing at least 30% by weight relative to the total weight of the inverse emulsion; - at least one hydrophilic solvent representing between 32 and 59% by weight relative to the total weight of the inverse emulsion; ii) a lipophilic phase comprising: - an Hb oil having a flash point between 40 and 85 °C, representing between 10 and 100% by weight relative to the total weight of oil in the lipophilic phase,

[0023] - possibly an H2 oil representing between 0 and 90% by weight relative to the weight of oil in the lipophilic phase,

[0024] - the quantity of Hiet H2 oil represents between 10 and 20% by weight relative to the weight total of the reverse emulsion;

[0025] - at least one water-in-oil emulsifying agent representing between 1 and 3% by weight relative to the total weight of the inverse emulsion;

[0026] and the inverse emulsion having a weight ratio between the at least one polymer and the Hiet oil possibly H2 of between 1.5 and 4.5.

[0027] The present invention also relates to a hydraulic fracturing process for an unconventional underground reservoir of hydrocarbons (oil and / or gas) comprising the injection of a fracturing fluid comprising at least said inverse emulsion.

[0028] The present invention also relates to a fracturing fluid comprising at least said inverse emulsion.

[0029] The present invention also relates to a method for obtaining said inverse emulsion.

[0030] Finally, the present invention also relates to the use of said inverse emulsion in the fields of hydrocarbon (oil and / or gas) recovery; well drilling; well cementing; hydrocarbon (oil and / or gas) well stimulation other than hydraulic fracturing, for example conformance or diversion; open, closed or semi-closed water treatment; fermentation must treatment; sludge treatment; construction; paper or cardboard manufacturing; the battery sector; wood processing; hydraulic composition treatment (concrete, cement, mortar and aggregates); the mining industry; cosmetic product formulation; detergent formulation; textile manufacturing; geothermal energy; sanitary diaper manufacturing; or agriculture. Description of the invention

[0031] The term "polymer" refers to a homopolymer prepared from a monomer or a copolymer prepared from at least two different monomers. It can therefore be a polymer of at least one monomer chosen from among anionic hydrophilic monomers, cationic hydrophilic monomers, non-ionic hydrophilic monomers, zwitterionic hydrophilic monomers, hydrophobic monomers and mixtures thereof.

[0032] By "hydrophilic monomer" is meant a monomer which has an octanol / water partition coefficient, Kow, less than or equal to 1, in which the partition coefficient Kow is determined at 25 °C in an octanol / water mixture having a volume ratio of 1 / 1, at a pH between 6 and 8.

[0033] By "hydrophobic monomer" is meant a monomer which has an octanol / water partition coefficient, Kow, greater than 1, in which the partition coefficient Kow is determined at 25 °C in an octanol / water mixture having a volume ratio of 1 / 1, at a pH between 6 and 8.

[0034] The octanol / water partition coefficient, Kow, represents the ratio of the concentrations (g / L) of a monomer between the octanol phase and the aqueous phase. It is defined as follows:

[0035] [Math.2] [rnoHowzère] _ , ____ L ~ — \mommère\eau

[0036] By "water-soluble polymer" is meant a polymer which gives an aqueous solution without insoluble particles when dissolved under stirring at 25°C and with a concentration of 10 g.l1 in deionized water.

[0037] By "X and / or Y" means "X", or "Y", or "X and Y".

[0038] Also part of the invention are all possible combinations between the The disclosure includes various embodiments, whether preferred or given by way of example. Furthermore, when ranges of values ​​are specified, the bounds are included within those ranges. The disclosure also encompasses all combinations of the bounds within those ranges. For example, the value ranges "1-20, preferably 5-15" imply the disclosure of the ranges "1-5", "1-15", "5-20", and "15-20", as well as the values ​​1, 5, 15, and 20. Reverse emulsion

[0039] The present invention relates to a reverse emulsion comprising: i) a hydrophilic phase comprising: - at least one polymer representing at least 30% by weight relative to the total weight of the inverse emulsion; - at least one hydrophilic solvent representing between 32 and 59% by weight relative to the total weight of the inverse emulsion; ii) a lipophilic phase comprising: - an Hb oil having a flash point between 40 and 85 °C, representing between 10 and 100% by weight relative to the total weight of oil in the lipophilic phase; - possibly an H2 oil representing between 0 and 90% by weight relative to the weight of oil in the lipophilic phase; - the quantity of Hiet H2 oil represents between 10 and 20% by weight relative to the total weight of the inverse emulsion; - at least one water-in-oil emulsifying agent representing between 1 and 3% by weight relative to the total weight of the inverse emulsion; and the inverse emulsion having a weight ratio between the at least one polymer and the Hiet oil possibly H2 of between 1.5 and 4.5.

[0040] Polymer composition

[0041] The polymer(s) of the hydrophilic phase of the reverse emulsion are obtained from at least one monomer selected from anionic hydrophilic monomers, cationic hydrophilic monomers, non-ionic hydrophilic monomers, zwitterionic hydrophilic monomers and mixtures thereof.

[0042] The polymer can be non-ionic, cationic, anionic or amphoteric.

[0043] By “non-ionic polymer”, we mean a polymer which comprises only non-ionic hydrophilic monomers and optionally zwitterionic and / or hydrophobic hydrophilic monomers.

[0044] By "#cationic polymer#", we mean a polymer which comprises only cationic hydrophilic monomers and optionally non-ionic hydrophilic monomers and / or zwitterionic hydrophilic and / or hydrophobic monomers.

[0045] By "#anionic polymer#", we mean a polymer which comprises only anionic hydrophilic monomers and optionally non-ionic hydrophilic monomers and / or zwitterionic hydrophilic and / or hydrophobic monomers.

[0046] By "#amphoteric polymer#", we mean a polymer which comprises cationic hydrophilic monomers and anionic hydrophilic monomers and optionally non-ionic hydrophilic monomers and / or zwitterionic hydrophilic and / or hydrophobic monomers.

[0047] The polymer may be a natural polymer, such as xanthan gum, guar gum, or compounds from the polysaccharide family, or a synthetic or semi-synthetic polymer. Preferably, the polymer is a synthetic polymer, advantageously water-soluble.

[0048] The term "semi-synthetic polymer" refers to a natural polymer that has undergone chemical reactions involving the grafting of various synthetic substituents. Those skilled in the art are familiar with these types of reactions, which remain classic chemical reactions applied to natural polymers.

[0049] The polymer can be water-soluble, hydro-swelling, or a superabsorbent. Preferably, the polymer is water-soluble.

[0050] Advantageously, the hydrophilic anionic monomer(s) that may be used in the context of the invention may be selected from a wide range. These monomers may have a vinyl functional group, in particular acrylic, maleic, fumaric, malonic, itaconic, or allylic. They may also contain a carboxylate, phosphonate, phosphate, sulfonate, sulfate, or other anionically charged group.Preferred monomers belonging to this class are, for example, acrylic acid; methacrylic acid; dimethylacrylic acid; crotonic acid; maleic acid; fumaric acid; 3-acrylamido-3-methylbutanoic acid; strong acid-type monomers having, for example, a sulfonic acid or phosphonic acid function such as vinylsulfonic acid, vinylphosphonic acid, allylsulfonic acid, methallylsulfonic acid, 2-methylidenepropane-1,3-disulfonic acid, 2-sulfoethyl methacrylate, sulfopropyl methacrylate, sulfopropylacrylate, allylphosphonic acid, ethylene glycol methacrylate phosphate, styrene sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid (ATBS), 2-. acrylamido-2-methylpropane disulfonic acid, 3-allyloxy-2-hydroxypropane sulfonic acid, diethylallylphosphonate, carboxyethyl acrylate; water-soluble salts of these monomers such as their alkali metal, alkaline earth metal, or ammonium salts; and mixtures thereof. Preferably, the anionic hydrophilic monomer is acrylic acid.

[0051] Preferably, the hydrophilic anionic monomer is acrylic acid or 2-acrylamido-2-methylpropane sulfonic acid (ATBS).

[0052] The polymer advantageously comprises between 0 and 100 mol% of hydrophilic anionic monomer(s), preferably between 1 and 99 mol%, more preferably between 5 and 95 mol%, and even more preferably between 10 and 90 mol%.

[0053] In a particular mode, when the anionic hydrophilic monomer is 2-acrylamido-2-methylpropanesulfonic acid (ATBS), it is in its hydrated form. The hydrated form of ATBS is a particular form of ATBS that can be obtained by controlled crystallization of the ATBS monomer. US Patent 10,759,746 describes this hydrated form of ATBS.

[0054] In a particular embodiment of the invention, the anionic monomer(s) may be salified. It may also be a mixture of monomers in acidic and salified forms, for example, a mixture of acrylic acid and acrylate. Salified means the substitution of a proton of at least one acidic functional group of the type -Ra(=O)-OH (with Ra representing P, S, or C) of the anionic monomer by a metal or organic cation to form a salt of the type -Ra(=O)-OX (X being a metal or organic cation). In other words, the unsalified form corresponds to the acidic form of the monomer, for example, Rb-C(=O)-OH in the case of the carboxylic acid functional group, while the salified form of the monomer corresponds to the form Rb-C(=O)-0 X+, X+ being a metal or organic cation. The salification of the acidic functional groups may be partial or complete.

[0055] The metal cation is advantageously an alkali metal salt (Li, Na, K...) or an alkaline earth metal salt (Ca, Mg...), and the organic cation is advantageously the ammonium ion or a tertiary ammonium compound. Sodium salts are preferred.

[0056] Salification can take place before or after polymerization.

[0057] The polymer advantageously comprises between 0 and 100 mol% of hydrophilic anionic monomer(s) in salified form, preferably between 30 and 100 mol%.

[0058] Advantageously, the cationic hydrophilic monomer(s) that can be used in the context of the invention are chosen, in particular, from vinyl-type monomers, especially acrylamide, acrylic, allyl or maleic having a protonable amine or ammonium function, advantageously quaternary ammonium. Examples include, but are not limited to, diallyldialkyl ammonium salts such as dimethyldiallylammonium chloride (DADMAC); acidified or quaternized salts of dialkyl-aminoalkyl(meth)acrylamides, such as (3-methacrylamidopropyl)trimethylammonium chloride (MAPTAC) and (3-acrylamidopropyl)trimethylammonium chloride (APTAC); acidified or quaternized salts of dialkyl-aminoalkyl acrylates such as quaternized or salified dimethylaminoethyl acrylate (ADAME); acidified or quaternized salts of dialkyl aminoalkyl methacrylate such as quaternized or salified dimethylaminoethyl methacrylate (MADAME); and acidified or quaternized salts of N,N-dimethylallylamine. acidified or quaternized salts of diallylmethylamine; acidified or quaternized salts of diallylamine;Vinylamine obtained by the (basic or acidic) hydrolysis of an amide group -N(R2)-CO-R', where R1 and R2 are, independently, a hydrogen atom or an alkyl chain of 1 to 6 carbons, for example, vinylamine from the hydrolysis of vinylformamide; vinylamine obtained by Hofmann degradation; and mixtures thereof. Advantageously, the alkyl groups are in the C1-C7 position, preferably C1-C3, and may be linear, cyclic, saturated, or unsaturated chains. Preferably, the cationic hydrophilic monomer is quaternized or salified dimethylaminoethyl acrylate (ADAME).

[0059] The polymer advantageously comprises between 0 and 100 mol% of cationic hydrophilic monomer(s), preferably between 1 and 99 mol%, more preferably between 5 and 95 mol%, and even more preferably between 10 and 90 mol%.

[0060] A person skilled in the art will know how to prepare the quaternized monomers, for example by means of quaternizing agent of type RX, R being an alkyl group and X being a halogen or a sulfate.

[0061] By “quaternizing agent” is meant a molecule capable of alkylating a tertiary amine.

[0062] The quaternizing agent may be selected from dialkyl sulfates comprising from 1 to 6 carbon atoms or alkyl halides comprising from 1 to 6 carbon atoms. Preferably, the quaternizing agent is selected from methyl chloride, benzyl chloride, dimethyl sulfate, or diethyl sulfate. Furthermore, the present invention also covers DADMAC, APTAC, and MAPTAC type monomers in which the counterion is a sulfate, a fluoride, a bromide, or an iodide instead of a chloride.

[0063] Advantageously, the hydrophilic non-ionic monomer(s) that may be used in the context of the invention are chosen, in particular, from Tacrylamide, methacrylamide, N-alkylacrylamides, N-alkylmethacrylamides, N,N-dialkyl acrylamides (e.g., N,N-dimethylacrylamide or N,N-diethylacrylamide), N,N-dialkylmethacrylamides, alkoxylated esters of acrylic acid, alkoxylated esters of methacrylic acid, N-vinylpyrrolidone, N-methylol(meth)acrylamide, N-vinyl caprolactam, N-vinylformamide (NVF), N-vinyl acetamide, N-vinyl imidazole, N-vinyl succinimide, acryloyl morpholine (ACMO), acryloyl chloride, glycidyl methacrylate, vinyl acetate, glyceryl methacrylate, diacetone acrylamide, methacrylic anhydride, acrylonitrile, maleic anhydride, itaconic anhydride, Itaconamide, hydroxyalkyl (meth)acrylates, thioalkyl (meth)acrylates, isoprenol and its alkoxylated derivatives, hydroxyethyl (meth)acrylates and their alkoxylated derivatives, hydroxypropyl (meth)acrylate and its alkoxylated derivatives, and mixtures thereof. Among these nonionic monomers, the alkyl groups are advantageously located at C1-C5, and more advantageously at C1-C3.Preferably, the non-ionic hydrophilic monomer is acrylamide.

[0064] The polymer advantageously comprises between 0 and 100 mol% of non-ionic hydrophilic monomer(s), preferably between 1 and 99 mol%, more preferably between 5 and 95 mol%, and even more preferably between 10 and 90 mol%.

[0065] Advantageously, the hydrophilic zwitterionic monomer(s) that can be used in the context of the invention are chosen, in particular, from derivatives of a vinyl type motif (advantageously acrylamide, acrylic, allyl or maleic), this monomer having a quaternary amine or ammonium function and an acid function of the carboxylic (or carboxylate), sulfonic (or sulfonate) or phosphoric (or phosphate) type.

[0066] Preferably, this monomer comprises a quaternary amine or ammonium function and an acid function of the carboxylic (or carboxylate), sulfonic (or sulfonate) type or phosphoric (or phosphate).

[0067] In particular, and without limitation, dimethylaminoethyl acrylate derivatives, such as 2-((2-9(acryloyloxy)ethyl)dimethylammonio)ethane-1-sulfonate, 3-((2-(acryloyloxy)ethyl)dimethylammonio)propane-1-sulfonate, 4-((2-(acryloyloxy)ethyl)dimethylammonio)butane-1-sulfonate, [2-(acryloyloxy)ethyl](dimethylammonio)acetate, dimethylaminoethyl methacrylate derivatives such as 2-((2-(methacryloyloxy)ethyl)dimethylammonio)ethane-1-sulfonate, 3-((2-(methacryloyloxy)ethyl)dimethylammonio) propane-1-sulfonate, 4-((2-(methacryloyloxy)ethyl)dimethylammonio)butane-1-sulfonate, [2-(methacryloyloxy)ethyl](dimethylammonio)acetate, propylacrylamide dimethylamino derivatives such as 2-((3-acrylamidopropyl)dimethylammonio)ethane-1- sulfonate, 3-((3-acrylamidopropyl)dimethylammonio)propane-1-sulfonate, 4-((3-acrylamidopropyl)dimethylammonio)butane-1-sulfonate, [3-(acryloyl)oxy)propyl](dimethylammonio)acetate, dimethylaminopropyl methylacrylamide, or derivatives such as 2-((3-methacrylamidopropyl)dimethylammonio)ethane-1-sulfonate, 3-((3-me dimethylammonio)propane-1-sulfonate, 4-((3-methacrylamidopropyl)dimethylammonio)butane-1-sulfonate and propyl [3-(methacryloyloxy)](dimethylammonio)acetate and their mixtures.

[0068] Other zwitterionic monomers are described by the Applicant in document WO2021 / 123599 Al.

[0069] The polymer advantageously comprises between 0 and 30 mol% of zwitterionic hydrophilic monomer(s), preferably between 1 and 20 mol% and more preferably between 2 and 15 mol%.

[0070] The polymer according to the invention may further comprise at least one hydrophobic monomer.

[0071] Advantageously, the monomer(s) having a hydrophobic character that can be used within the framework of the invention can be chosen, in particular, from (meth)acrylic acid esters having a (i) C4-C30 alkyl chain, or (ii) arylalkyl (C4-C30 alkyl, C4-C30 aryl), or (iii) propoxylated, or (iv) ethoxylated, or (v) ethoxylated and propoxylated; alkyl aryl sulfonates (C4-C30 alkyl, C4-C30 aryl); Mono- or di-substituted amides of (meth)acrylamide having a (i) C4-C30 alkyl chain, or (ii) an arylalkyl (C4-C30 alkyl, C4-C30 aryl), or (iii) a propoxylated, or (iv) an ethoxylated, or (v) an ethoxylated and propoxylated chain; anionic or cationic monomeric derivatives of (meth)acrylamide or (meth)acrylic acid bearing a hydrophobic chain; and mixtures thereof. The hydrophobic monomers may include halogen atoms, for example, chlorine.

[0072] Among these hydrophobic monomers: - Alkyl groups are preferably in C4-C2O, more preferably in C4-C8. Alkyls in C6-C2O are preferably linear alkyls, while alkyls in C4-C5 are preferably branched. - arylalkyl groups are preferably in C7-C25, more preferably in C7-C 15, - the ethoxylated chains advantageously comprise between 200 -CH2-CH2-O- groups, preferably between 6 and 100, more preferably between 10 and 40, - the propoxylated chains advantageously comprise between 1 and 50 -CH2-CH2-CH2-O- groups, more preferably between 1 and 20.

[0073] Preferred hydrophobic monomers belonging to these classes are, for example: - n-hexyl (meth)acrylate, n-octyl (meth)acrylate, octyl (meth)acrylamide, lauryl (meth)acrylate, lauryl (meth)acrylamide, myristyle (meth)acrylate, myristyle (meth)acrylamide, pentadecyl (meth)acrylate, pentadecyl (meth)acrylamide, cetyl (meth)acrylate, cetyl (meth)acrylamide, oleyl (meth)acrylate, oleyl (meth)acrylamide, erucyl (meth)acrylate, erucyl (meth)acrylamide, N-tert-Butyl(meth)acrylamide, vinylpyridine, 2-ethylhexyl acrylate, C4-C22 itaconic acid hemi-esters, acidified or quaternized salts of C4-C22 dialkyl aminoalkyl (meth)acrylate, acidified or quaternized salts of C4-C22 dialkyl-aminoalkyl (meth)acrylamides, acrylamidoundecanoic acid, and mixtures thereof, - cationic allyl derivatives having formula (I) or (II):

[0074] [Chem.l]

[0075] (I) (II)

[0076] in which: - R5 independently represents an alkyl chain containing 1 to 4 carbons; - R6 represents an alkyl or arylalkyl chain comprising 8 to 30 carbons; - X represents a halide chosen from the group consisting of bromides, chlorides, iodides, fluorides and any negatively charged counter-ion; and, preferably, hydrophobic cationic derivatives of the methacryloyl type corresponding to formula (III):

[0077] [Chem.2] (III)

[0078] in which: - A represents O or N-R9 (preferably A = N-R9), - R7, R8, R9, Rio, Ru independently represent a hydrogen or an alkyl chain comprising 1 to 4 carbons, - Q represents an alkyl chain comprising 1 to 8 carbons, - Represents an alkyl or arylalkyl chain comprising 8 to 30 carbons, - X represents a halide chosen from the group consisting of bromides, chlorides, iodides, fluorides, and any negatively charged counterion.

[0079] The polymer generally comprises less than 5 mol% of hydrophobic monomers. Preferably, this polymer is free of hydrophobic monomers.

[0080] When the polymer is water-soluble, the amount of hydrophobic monomers present is adjusted so that the polymer remains soluble in water.

[0081] In a particular embodiment, the polymer may comprise at least one LCST group.

[0082] According to the general knowledge of those skilled in the art, a LCST group corresponds to a group whose solubility in water, for a given concentration, changes above a certain temperature and depending on the salinity. It is a group exhibiting a heating transition temperature that defines its lack of affinity for the solvent medium. This lack of affinity for the solvent results in opacification or loss of transparency, which can be due to precipitation, aggregation, gelation, or viscosification of the medium. The minimum transition temperature is called the "LCST" (Lower Critical Solution Temperature). For each concentration of an LCST group, a heating transition temperature is observed. This temperature is higher than the LCST, which is the minimum point on the curve.Below this temperature, the polymer is soluble in water; above this temperature, the polymer loses its solubility in water.

[0083] In a particular embodiment, the polymer may comprise at least one UCST group.

[0084] According to the general knowledge of those skilled in the art, a UCST group corresponds to a group whose solubility in water, for a given concentration, is modified below a certain temperature and as a function of salinity. It is a group exhibiting a cooling transition temperature that defines its lack of affinity for the solvent medium. This lack of affinity for the solvent results in opacification or a loss of transparency, which may be due to precipitation, aggregation, gelation, or viscosification of the medium. The maximum transition temperature is called the "UCST" (Upper Critical Solubility Temperature). Solution Temperature). For each group concentration at UCST, a cooling transition temperature is observed. This temperature is lower than the UCST, which is the maximum point on the curve. Above this temperature, the polymer is soluble in water; below this temperature, the polymer loses its solubility in water.

[0085] The quantities of the different monomers will be adjusted by a person skilled in the art so as not to exceed 100% molar during the preparation of the polymer.

[0086] The polymer can be partially or totally post-hydrolyzed.

[0087] Post-hydrolysis is the hydrolysis reaction of the polymer after its formation by monomer polymerization. This step consists of the reaction of hydrolyzable functional groups of monomers, advantageously non-ionic, more advantageously amide or ester groups, with a hydrolyzing agent. This hydrolyzing agent can, for example, be an enzyme, an ion-exchange resin, or a Brpnsted acid metal (e.g., a hydrohalic acid) or a Brpnsted base (e.g., an alkali hydroxide or an alkaline earth hydroxide). Preferably, the hydrolyzing agent is a Brpnsted base. During this post-hydrolysis step of the polymer, the number of carboxylic acid groups increases. Indeed, the reaction between the base and the amide or ester groups present in the polymer produces carboxylate groups.

[0088] Polymer structure

[0089] According to the invention, the polymer can have a linear, branched, ramified, star-shaped or comb-shaped structure. This structure can be obtained, according to the general knowledge of a person skilled in the art, for example by selection of the initiator, the transfer agent, the polymerization technique such as reversible addition-fragmentation chain transfer polymerization (RAFT), nitroxide-mediated polymerization (NMP) or atom transfer radical polymerization (ATRP), the incorporation of structural monomers, or the concentration.

[0090] The polymer can be a statistical polymer, a block polymer or a gradient polymer.

[0091] By "statistical polymer" is meant a polymer in which the arrangement of the monomers is random. A statistical polymer is obtained by placing all the monomers composing the polymer at the beginning of polymerization.

[0092] By “block polymer” we mean di-block, tri-block or multi-block, grafted sequenced polymers, branched sequenced polymers (also known as linear star polymers).

[0093] Block polymers are polymers composed of at least two different monomer blocks. Diblock polymers have two distinct blocks; triblock polymers have three, etc. They are advantageously obtained by successively polymerizing different species of monomers.

[0094] In a particular mode, the polymer has an XY-type structure when it is composed of two different monomers. In other words, the first fraction comprises only X monomers. These are polymerized initially, and when all the X monomers have reacted, the second fraction, comprising the Y monomers, is then added.

[0095] In a particular mode, the polymer has an XYZ-type structure when it is composed of three different monomers. In other words, the first fraction comprises only X monomers. These are polymerized initially, and when all the X monomers have reacted, the second fraction, comprising the Y monomers, is added. When all the Y monomers have reacted, the third fraction, comprising the Z monomers, is added.

[0096] This polymerization system can be extended to obtain so-called multiblock polymers having a structure Xi-Yi-...-Xn.i-Yn_i-Xn-Yn, n being an integer greater than or equal to 2 representing the number of blocks.

[0097] By “gradient polymer” is meant a polymer whose monomeric composition varies in a controlled manner throughout the polymer chain.

[0098] Polymers with a gradient structure are polymers composed of at least two monomers in which the change in monomer composition is gradual, unlike block polymers, which have an abrupt change in composition, and random polymers, which do not have a continuous change in composition. In the gradient polymer, due to the gradual change in composition along the length of the polymer chain, less intra-chain and inter-chain repulsion is observed.

[0099] The gradient can be formed by a spontaneous or forced gradient. Spontaneous gradient polymerization is due to a difference in the reactivity of the monomers. Forced gradient polymerization involves varying the composition of monomers introduced throughout the polymerization time.

[0100] A forced gradient process comprises (1) introducing a first fraction of monomers into a reactor, (2) adding at least one additional fraction of monomers advantageously different from the first, and (3) polymerizing the monomers introduced into the reactor. Polymerization of the monomers is initiated immediately upon introduction of the first fraction.

[0101] The addition of the additional fraction of monomers can be done in parallel with the introduction of the first fraction of monomers into the reactor (The introduction of the fractions can therefore begin and end simultaneously.) Alternatively, the start of the first monomer feed (first fraction) into the reactor can precede the start of the addition of a second monomer fraction. Alternatively, a first and second fraction can be introduced simultaneously, but the addition time of the second fraction can be longer than the introduction time of the first fraction into the reactor. This embodiment is also applicable to processes using at least three monomer fractions.

[0102] The polymer can further be structured by a branching agent. A structured polymer is defined as a non-linear polymer that has side chains.

[0103] The branching agent is advantageously chosen from: - structural agents, which can be chosen from the group comprising monomers with polyethylenic unsaturation (having at least two unsaturated functions), such as vinyl functions, particularly allylic or acrylic, and examples include methylene bisacrylamide (MBA), triallyamine, or tetraallylammonium chloride or 1,2-dihydroxyethylene bis-(N-acrylamide), - monomers having at least two epoxy functional groups, - monomers having at least one unsaturated function and one epoxy function, - Macroinitiators such as polyperoxides, polyazo compounds, and polytransfer agents such as polymer-capturing polymers and polyols, - Functionalized polysaccharides, - water-soluble metal complexes composed of: * of a metal with a valence greater than 3 such as, by way of example and without limitation, aluminium, boron, zirconium or titanium, and * of a ligand bearing a hydroxyl function.

[0104] The amount of branching agent in the polymer is advantageously less than 40,000 ppm by weight relative to the total weight of the monomers in the polymer, preferably less than 10,000 ppm by weight, more preferably less than 5,000 ppm by weight.

[0105] In a particular mode, the amount of branching agent is at least equal to 0.1 ppm by weight relative to the total weight of the monomers of the polymer, preferably at least 1 ppm by weight, more preferably at least 10 ppm by weight, more preferably at least 100 ppm by weight and even more preferably at least 1,000 ppm by weight.

[0106] When the polymer is water-soluble and comprises at least one branching agent, it remains soluble in water. A person skilled in the art will know how to adjust the amount branching agent, and possibly the amount of transfer agent needed to achieve this result.

[0107] In a particular mode, the polymer does not comprise a branching agent.

[0108] In a particular mode, the polymer may comprise a transfer agent.

[0109] The transfer agent is advantageously chosen from methanol; isopropyl alcohol; sodium hypophosphite; calcium hypophosphite; magnesium hypophosphite; potassium hypophosphite; ammonium hypophosphite; formic acid; sodium formate; calcium formate; magnesium formate; potassium formate; ammonium formate; 2-mercaptoethanol; 3-mercaptopropanol; dithiopropylene glycol; thioglycerol; thioglycolic acid; thiohydracrylic acid; thiolactic acid; thiomalic acid; cysteine; and aminoethanethiol; thioglycolates; allyl phosphites; allyl mercaptans, such as n-dodecyl mercaptan; sodium methallysulfonate; calcium methallysulfonate; magnesium methallysulfonate; potassium methallysulfonate; ammonium methallysulfonate;Alkyl phosphites such as trialkyl (C12-C15) phosphites, di-oleyl-hydrogen phosphites, dibutyl phosphite, dialkyldithiophosphates such as dioctyl phosphonate, tertiary nonylmercaptan, 2-ethylhexyl thioglycolate, n-octyl mercaptan, n-dodecyl mercaptan, tertio-dodecyl mercaptan, iso-octylthioglycolate, 2-Ethylhexyl thioglycolate, 2-Ethylhexyl mercaptoacetate, polythiols and mixtures thereof. Preferably, this is sodium hypophosphite or sodium formate.

[0110] The amount of transfer agent in the polymer is advantageously between 0 and 100,000 ppm by weight relative to the total weight of the polymer monomers, preferably between 0 and 10,000 ppm by weight, more preferably between 0 and 1,000 ppm by weight, and even more preferably between 0 and 100 ppm by weight. When present, the transfer agent represents at least 0.1 ppm by weight relative to the total weight of the polymer monomers, preferably at least 1 ppm by weight.

[0111] In a particular mode, the polymer does not comprise a transfer agent.

[0112] The polymer advantageously has a molecular weight of at least 0.5 million g / mol, preferably between 0.5 and 40 million g / mol, more preferably between 1 and 30 million g / mol, more preferably between 2 and 20 million g / mol, and even more preferably between 3 and 15 million g / mol. The molecular weight is understood to be the average molecular weight by weight. The polymer may also have a molecular weight between 5,000 and 100,000 g / mol or between 100,000 and 500,000 g / mol.

[0113] The molecular weight is determined by the intrinsic viscosity of the polymer. The intrinsic viscosity can be measured by methods known to those skilled in the art and can be calculated from the reduced viscosity values ​​for different Polymer concentrations can be determined graphically by plotting the reduced viscosity values ​​(y-axis) against the concentration (x-axis) and extrapolating the curve to zero concentration. The intrinsic viscosity value is plotted on the y-axis or using the least squares method. The molecular weight can then be determined using the Mark-Houwink equation: [q] = KM [q] represents the intrinsic viscosity of the polymer determined by the solution viscosity measurement method. K represents an empirical constant. M represents the molecular weight of the polymer. a represents the Mark-Houwink coefficient. K and a depend on the particular polymer-solvent system.

[0114] The reverse emulsion comprises at least: i) a hydrophilic phase comprising: - at least one polymer representing at least 30% by weight relative to the total weight of the inverse emulsion; - at least one hydrophilic solvent representing between 32 and 59% by weight relative to the total weight of the inverse emulsion; ii) a lipophilic phase comprising: - an Hb oil having a flash point between 40 and 85 °C, representing between 10 and 100% by weight relative to the total weight of oil in the lipophilic phase; - possibly an H2 oil representing between 0 and 90% by weight relative to the weight of oil in the lipophilic phase; - the quantity of Hiet H2 oil represents between 10 and 20% by weight relative to the total weight of the inverse emulsion; - at least one water-in-oil emulsifying agent representing between 1 and 3% by weight relative to the total weight of the inverse emulsion.

[0115] Advantageously the inverse emulsion comprises between 30% and 45% by weight of polymer relative to the total weight of the inverse emulsion, more preferably between 32% and 42% by weight.

[0116] The hydrophilic phase comprises at least one hydrophilic solvent capable of solubilizing at least one polymer. Advantageously, this solvent is water.

[0117] The quantity of hydrophilic solvent(s) of the hydrophilic phase of the inverse emulsion is advantageously between 27 and 59% by weight relative to the total weight of the inverse emulsion, preferably between 30 and 45% by weight.

[0118] The lipophilic phase comprises between 10 and 100% by weight of an oil Hi having a flash point between 40 and 85 °C relative to the total weight of oil.

[0119] It may further comprise between 0 and 90% by weight of an H2 oil relative to the total weight of oil.

[0120] It is understood that the total weight of oil corresponds to the weight of Hi oil and H2 oil. Thus, the quantities of Hi and H2 oils will be adjusted by a person skilled in the art so as not to exceed 100% by weight relative to the total weight of oil.

[0121] The lipophilic phase comprises an amount of Hi and H2 oil representing 10 to 20% by weight relative to the weight of the inverse emulsion.

[0122] The Hi oil has a flash point between 40 and 85 °C, preferably between 45 and 85 °C, more preferably between 50 and 85 °C and even more preferably between 55 and 85 °C and represents at least 10% by weight relative to the total weight of the lipophilic solvent.

[0123] Examples of Hb oils having a flash point between 40 and 85 °C are, for example, oils containing saturated and unsaturated hydrocarbons comprising between 9 and 14 carbon atoms, in particular hydrocarbons having carbon chains of C9-Cn, C10-C13, Cw-Cu or C11-C14. Examples include the following commercial products: EXXsol™ D40, EXXsol™ D60, EXXsol™ D70, EXXsol™ D80, Isopar™ G, Isopar™ J, and Isopar™ K. Preferably, this refers to EXXsol™ D60.

[0124] In a preferred mode, the Hi oil represents at least 30% by weight of the oils relative to the total weight of oil in the lipophilic phase, preferably at least 50% by weight, more preferably at least 70% by weight, and even more preferably 100% by weight relative to the total weight of oil in the lipophilic phase.

[0125] The H2 oil of the lipophilic phase can be a mineral oil, a vegetable oil, a synthetic oil or a mixture of several of these oils.

[0126] H2 oil is different from Hi oil.

[0127] Examples of H2 mineral oil are mineral oils containing saturated hydrocarbons of the aliphatic, naphthenic, paraffinic, isoparaffinic, cycloparaffinic, or naphthyl type comprising between 15 and 30 carbon atoms. Examples include Exxsol™ D100, Isopar™ L, Isopar™ M, Isopar™ N marketed by ExxonMobil, and white oils.

[0128] Examples of vegetable oil are squalene, an ester or triglyceride type oil, such as coco caprylate / caprate, octyl decyl myristate, ethoxylated vegetable oils, jojoba oil, macadamia oil.

[0129] Examples of synthetic oil are hydrogenated polydecene or hydrogenated polyisobutene, esters such as octyl stearate or butyl oleate.

[0130] The weight ratio between the hydrophilic solvent(s) of the hydrophilic phase of the inverse emulsion and the oil(s) H] and possibly H2 of the lipophilic phase in the inverse emulsion is advantageously between 1.35 and 5.9, preferably between 1.5 and 4.5.

[0131] The weight ratio between the polymer(s) and the oil(s) Hi and possibly H2 of the lipophilic phase is between 1.5 and 4.5, preferably between 1.8 and 3.

[0132] A "water-in-oil emulsifying agent" is defined as a compound capable of emulsifying water in oil, and an "oil-in-water emulsifying agent" is a compound capable of emulsifying oil in water. Generally, a water-in-oil emulsifying agent is considered to be a surfactant with an HLB strictly less than 8, and an oil-in-water emulsifying agent is considered to be a surfactant with an HLB greater than or equal to 10. A surfactant with an HLB between 8 and 10 is considered a wetting agent. Those skilled in the art may refer to K. Holmberg's "Handbook of Applied Surface and Colloid Chemistry," Chapter 11, if necessary.

[0133] The hydrophilic-lipophilic equilibrium (HLB) of a chemical compound is a measure of its hydrophilic and / or lipophilic properties, determined by calculating the values ​​for the different regions of the molecule, as described by Griffin in 1949.

[0134] In the present invention, we have adopted Griffin's method based on calculating a value based on the chemical groups of the molecule. Griffin assigned a dimensionless number between 0 and 20 to provide information on the solubility of water and oil.

[0135] The HLB value of a substance having a total molecular mass M and a hydrophilic part of a molecular mass Mh is given by: HLB = 20 (Mh / M).

[0136] The water-in-oil emulsifying agent is advantageously chosen from the following list: polyesters having a molecular weight between 1000 and 3000 g / mol, condensation products between poly(isobutenyl) succinic acid or its anhydride and polyethylene glycol, sequenced block polymers having a molecular weight between 2500 and 3500 g / mol, such as those sold under the names Hypermer®, extracts of sorbitan, such as sorbitan monooleate or polyoleates, sorbitan isostearate or sorbitan sesquioleate, polyethoxylated sorbitan esters, or even diethoxylated oleocetyl alcohol or tetraethoxylated lauryl acrylate, condensation products of fatty alcohols greater than ethylene, as a reaction product of oleic alcohol with 2 ethylene oxide units; condensation products of alkylphenols and ethylene oxide, such as the reaction product of nonyl phenol with 4 units of ethylene oxide.Ethoxylated fatty amines such as Witcamide® 511, alkylated phosphate esters, . Betaine-based products and ethoxylated amine are also good candidates as water-in-oil type emulsifying agents.

[0137] The quantity of water-in-oil emulsifying agent in the inverse emulsion is advantageously between 1 and 3% by weight relative to the total weight of the inverse emulsion, preferably between 1 and 2.5% by weight, more preferably between 1.5 and 2.5% by weight.

[0138] The process of the invention may include the addition of at least one oil-in-water emulsifying agent.

[0139] The oil-in-water emulsifying agent(s) are advantageously chosen from ethoxylated nonylphenols, preferably having 4 to 10 ethoxylations (i.e., preferably exhibiting a degree of ethoxylation ranging from 4 to 10); ethoxylated / propoxylated alcohols, preferably having an ethoxylation / propoxylation comprising 12 to 25 carbon atoms; ethoxylated tridecyl alcohols; ethoxylated / propoxylated fatty alcohols; ethoxylated sorbitan esters (advantageously having 20 molar equivalents of ethylene oxide); polyethoxylated sorbitan laurate (advantageously having 20 molar equivalents of ethylene oxide); polyethoxylated castor oil (advantageously having 40 molar equivalents of ethylene oxide); decaethoxylated oleodecyl alcohol; heptaoxyethylated lauryl alcohol; polyethoxylated sorbitan monostearate (advantageously having 20 molar equivalents of ethylene oxide);Polyethoxylated alkylphenols (advantageously having 10 molar equivalents of ethylene oxide) cetyl ether; alkyl aryl ether polyethylene oxide; N-cetyl-N-ethyl morpholinium ethosulfate; sodium lauryl sulfate; condensation products of fatty alcohols with ethylene oxide (advantageously having 10 molar equivalents of ethylene oxide); condensation products of alkylphenols and ethylene oxide (advantageously having 12 molar equivalents of ethylene oxide); condensation products of fatty amines with 5 or more molar equivalents of ethylene oxide (advantageously 5 to 50 equivalents); ethoxylated tristyrylphenols; condensates of ethylene oxide with polyhydric alcohols partially esterified with fatty chains, as well as their anhydrous forms; amine oxides advantageously having alkyl polyglucosides; glucamide; phosphate esters; alkylbenzene sulfonic acids and their salts;and surfactant block polymers and their mixtures. The alkyl groups of these oil-in-water emulsifying agents are linear or branched groups, advantageously having 1 to 20 carbon atoms, more advantageously 3 to 15 carbon atoms. Furthermore, the aryl groups of these oil-in-water emulsifying agents advantageously comprise 6 to 20 carbon atoms, more advantageously 6 to 12 carbon atoms.

[0140] Generally, the inverse emulsion comprises between 1 and 6% by weight of oil-in-water emulsifying agent relative to the total weight of the inverse emulsion.

[0141] The oil-in-water emulsifying agent(s) may be added before, during, or after polymerization. Preferably, the oil-in-water emulsifying agent(s) are added after polymerization.

[0142] Hydraulic fracturing process for an unconventional underground oil or gas reservoir

[0143] The present invention also relates to a method for hydraulic fracturing of an unconventional underground oil or gas reservoir comprising the injection of a fracturing fluid comprising at least one inverse emulsion comprising: i) a hydrophilic phase comprising: - at least one polymer representing at least 30% by weight relative to the total weight of the inverse emulsion; - at least one hydrophilic solvent representing between 32 and 59% by weight relative to the total weight of the inverse emulsion; ii) a lipophilic phase comprising: - an Hb oil having a flash point between 40 and 85 °C, representing between 10 and 100% by weight relative to the total weight of oil in the lipophilic phase; - possibly an H2 oil representing between 0 and 90% by weight relative to the weight of oil in the lipophilic phase; - the quantity of Hiet H2 oil represents between 10 and 20% by weight relative to the total weight of the inverse emulsion; - at least one water-in-oil emulsifying agent representing between 1 and 3% by weight relative to the total weight of the inverse emulsion; and the inverse emulsion having a weight ratio between the at least one polymer and the Hiet oil possibly H2 of between 1.5 and 4.5.

[0144] The injection is carried out under pressure so as to create fractures distributed throughout the production well.

[0145] Optionally, after the creation of the fractures, at least one oxidizing compound and / or at least one surfactant compound is injected into the reservoir.

[0146] Surfactant injection eliminates the viscosity generated by the polymer by inhibiting inter-chain hydrophobic interactions, while oxidizing compound injection destroys the polymer. In both cases, injection restores a fluid viscosity close to that of water.

[0147] Examples of oxidizing compounds include bleach (aqueous solution of a hypochlorite salt), hydrogen peroxide, ozone, chloramines, persulfates, permanganates or perchlorates.

[0148] The chemical nature of the surfactant compound(s) is not critical. They may be anionic, nonionic, amphoteric, zwitterionic, and / or cationic. Preferably, the surfactant compound(s) of the invention carry anionic charges.

[0149] Preferably, the surfactant compounds used are chosen from anionic surfactants and their zwitterions selected from the group comprising derivatives of alkyl sulfates, alkyl ethers sulfates, arylalkyl sulfates, arylalkyl ethers sulfates, alkylsulfonates, alkyl ethers sulfates, arylalkyl sulfonates, arylalkyl ethers sulfates, alkyl phosphates, alkyl ethers phosphates, arylalkyl phosphates, arylalkyl ethers phosphates, alkyl iphosphonates, alkyl ethers phosphonates, arylalkyl iphosphonates, arylalkyl ethers phosphonates, alkyl carboxylates, alkyl ethers carboxylates, arylalkyl ethers carboxylates, arylalkyl ethers alkyl polyethers, polyethers Ary Lalky the s...

[0150] An alkyl chain is defined as a chain of 6 to 24 carbons, branched or unbranched, with several motifs or not, possibly containing one or more heteroatoms (O, N, S). An arylalkyl chain is defined as a chain of 6 to 24 carbons, branched or unbranched, containing one or more aromatic rings and possibly containing one or more heteroatoms (O, N, S).

[0151] The most commonly used surfactants, for reasons of cost, stability, and availability, are of the sulfonate or sulfate type, presented in the form of alkali metal or ammonium salts. Fracking fluid

[0152] The present invention relates to a fracturing fluid comprising an aqueous fluid, at least one propping agent and at least one inverse emulsion comprising: i) a hydrophilic phase comprising: - at least one polymer representing at least 30% by weight relative to the total weight of the inverse emulsion; - at least one hydrophilic solvent representing between 32 and 59% by weight relative to the total weight of the inverse emulsion; ii) a lipophilic phase comprising: - an Hb oil having a flash point between 40 and 85 °C, representing between 10 and 100% by weight relative to the total weight of oil in the lipophilic phase; - possibly an H2 oil representing between 0 and 90% by weight relative to the weight of oil in the lipophilic phase; - the quantity of Hiet H2 oil represents between 10 and 20% by weight relative to the total weight of the inverse emulsion; - at least one water-in-oil emulsifying agent representing between 1 and 3% by weight relative to the total weight of the inverse emulsion; and the inverse emulsion having a weight ratio between the at least one polymer and the Hiet oil possibly H2 of between 1.5 and 4.5.

[0153] The aqueous fluid is advantageously chosen from: seawater, brine, fresh water. Advantageously, it is brine.

[0154] Brine is defined as a solution comprising water and organic or inorganic salts. The salts may include monovalent salts, divalent salts, trivalent salts, and mixtures thereof. Advantageously, the brine comprises at least 1,000 mg / L of salts, preferably at least 5,000 mg / L, more preferably at least 10,000 mg / L, even more preferably at least 50,000 mg / L, and even more preferably the brine is saturated with salts.

[0155] The support agent can be chosen without restriction from sand, ceramics, bauxite, glass beads, and resin-impregnated sand.

[0156] Advantageously, the amount of propping agent in the fracturing fluid is between 0.5 and 40% by weight relative to the total weight of the fracturing fluid, preferably between 1 and 25%, more preferably between 1.5 and 20%.

[0157] Advantageously, the fracturing fluid comprises between 50 ppm and 50,000 ppm of emulsion according to the invention, preferably between 100 ppm and 20,000 ppm.

[0158] The fracturing fluid may comprise other compounds known to those skilled in the art, such as those mentioned in document SPE 152596, for example: - Anti-swelling agents for clays such as potassium chloride, or choline chloride, and / or - Biocides to prevent the growth of bacteria, particularly sulfate-reducing bacteria, which can form viscous masses that reduce surface area. Examples include glutaraldehyde, the most commonly used, as well as formaldehyde, isothiazolinones, and / or - Oxygen reducers such as ammonium bisulfite to prevent the destruction of other components by oxidation and corrosion of the injection tubes, and / or - Anti-corrosion additives to protect the tubes against oxidation by residual oxygen, with N,N dimethylformamide being preferred, and / or - Lubricants such as oil distillates, and / or - Iron chelating agents such as citric acid, EDTA (ethylenediaminetetraacetic acid), phosphonates, and / or - Anti-scale products such as phosphates, phosphonates, polyacrylates or ethylene glycol. Process for obtaining reverse emulsion

[0159] The invention also relates to a method for preparing a reverse emulsion comprising the following steps: a) Mixing under agitation: i) of a hydrophilic phase comprising: - at least one monomer representing at least 30% by weight relative to the total weight of the inverse emulsion; - at least one hydrophilic solvent representing between 32 and 59% by weight relative to the total weight of the inverse emulsion; and ii) a lipophilic phase comprising: - an Hb oil having a flash point between 40 and 85 °C, representing between 10 and 100% by weight relative to the total weight of oil in the lipophilic phase; - possibly an H2 oil representing between 0 and 90% by weight relative to the weight of oil in the lipophilic phase; - the quantity of Hiet H2 oil represents between 10 and 20% by weight relative to the total weight of the inverse emulsion; - at least one water-in-oil emulsifying agent representing between 1 and 3% by weight relative to the total weight of the inverse emulsion; b) Polymerization of at least one monomer of the hydrophilic phase in order to obtain a polymer in the reverse emulsion; the inverse emulsion having a weight ratio between the at least one polymer and the Hi oil and possibly H2 of between 1.5 and 4.5.

[0160] Polymerization is carried out in an inverse emulsion. The term "inverse emulsion" refers to both inverse emulsions and inverse microemulsions. These are water-in-oil emulsions in which the aqueous phase is dispersed in the lipid phase in the form of drops or droplets.

[0161] An inverse emulsion consists of a two-phase medium. It can be unstable in the absence of a surfactant (surfactants include water-in-oil and oil-in-water emulsifying agents). Upon stirring, hydrophilic phase particles are observed dispersed in a lipophilic phase, exhibiting a wide size distribution around a mean that can be on the order of micrometers. During reverse emulsion polymerization, the monomer is dispersed in the large droplets of the emulsion (diameter: approximately 50 nm to 50 pm) as well as in the small emulsifier micelles (diameter approximately 5 to 10 nm).

[0162] Step a)

[0163] The mixing of the hydrophilic phase and the lipophilic phase is carried out under agitation, advantageously at a speed between 10 and 10,000 rpm (revolutions per minute), preferably between 100 and 1,000 rpm.

[0164] Agitation can be carried out by any system that provides homogeneous mixing; for example, a hand blender or a homogenizer. Preferably, the mixing is carried out with a hand blender.

[0165] Agitation is advantageously maintained during step b).

[0166] Step b)

[0167] The polymerization is a radical polymerization. Radical polymerization includes polymerization using UV, azo, thermal, or redox salt initiators.

[0168] In radical polymerizations, we include controlled radical polymerization (CRP) techniques or matrix polymerization techniques.

[0169] Examples of controlled radical polymerization techniques include, but are not limited to, iodine transfer polymerization (ITP), nitroxide-mediated polymerization (NMP), atom transfer radical polymerization (ATRP), reversible addition-fragmentation chain transfer polymerization (RAFT), which includes MADIX technology (macromolecular design by interchange of xanthates), various organometallic-mediated radical polymerization (OMRP), and organoheteroatom-mediated radical polymerization (CHRP).

[0170] In a preferred mode, the polymerization is carried out by reversible addition-fragmentation chain transfer polymerization (RAFT).

[0171] RAFT is a reversible deactivation radical polymerization (RDRP) technique that combines both the ease of implementation of conventional radical polymerization and the liveness of ionic polymerization.

[0172] It is based on a reversible activation-deactivation equilibrium between a dormant species and an active species (growing macroradical). This activation-deactivation process allows the chains to grow at the same rate until the monomer is completely consumed, making it possible to control the molecular weights of the polymers and obtain narrow molecular weight distributions. This also minimizes compositional heterogeneity. The reversible deactivation of the growing chains is the basis of The minimization of irreversible termination reactions means that the vast majority of polymer chains remain in a dormant state and are therefore reactivatable. This allows for the functionalization of chain ends to initiate other polymerization modes or to create chain extensions. This is key to achieving high molecular weights, controlled compositions, and architectures.

[0173] Controlled radical polymerization therefore has the following distinctive aspects: 1. the number of polymer chains is fixed throughout the duration of the reaction, 2. the polymer chains all grow at the same rate, which results in: * a linear increase in molecular weights, * a tight distribution of molecular weights, 3. the average molecular weight is controlled by the monomer / precursor molar ratio.

[0174] The controlled nature of the reaction is all the more pronounced when the rate of reactivation of the chains into radicals is much greater than the rate of chain growth (propagation). However, in some cases, the rate of reactivation of the chains into radicals is greater than or equal to the rate of propagation. In these cases, conditions 1 and 2 are not observed and, consequently, control of the molecular weights is not possible.

[0175] Reversible addition-fragmentation chain transfer polymerization requires the use of a control agent.

[0176] In the context of the invention, the control agent is water-soluble of formula (IV):

[0177] [Chem.3] RI *A (IV)

[0178] in which - A represents an oxygen atom (O), a sulfur atom (S) or an amine (NR3); - Ri, R2, and R3, whether identical or different, represent: * a group (i), alkyl, acyl, alkenyl or alkynyl, possibly substituted, or * a carbon ring (ii), saturated or unsaturated, possibly substituted or aromatic, or * a heterocycle (iii), saturated or unsaturated, possibly substituted or aromatic, these groups and rings (i), (ii) and (iii) being able to be substituted by substituted aromatic groups or by alkoxycarbonyl or aryloxycarbonyl groups (-COOR), carboxy (-COOH), acyloxy (-O2CR), carbamoyl (-CON(R)2), cyano (-CN), alkylcarbonyl, alkylarylcarbonyl, arylcarbonyl, arylalkylcarbonyl, phthalimido, maleimido, succinimido, amidino, guanidimo, hydroxy (-OH), amino (-N(R)2), halogen, allyl, epoxy, alkoxy (-OR), S-alkyl, S-aryl, groups exhibiting hydrophilic or ionic character such as alkali salts of carboxylic acids, alkali salts of sulfonic acid, polyalkylene oxide chains (POE, POP), cationic substituents (quaternary ammonium salts); - R represents an alkyl or aryl group in C1-C20; - R3 can also represent a hydrogen atom. - Q is a linear or structured polymeric chain comprising n identical or different hydrophilic monomers comprising at least one ethylenic function and n being between 4 and 500, preferably between 4 and 100; - p is an integer equal to 0 or 1.

[0179] The monomer(s) used to form Q are advantageously chosen from the same monomers as those described for forming the hydrophilic phase polymer. They are preferably hydrophilic monomers.

[0180] In functions N(R)2, the two groups R can be identical or different from each other.

[0181] According to a preferred mode, the water-soluble control agent of formula (I) is a dithiocarbonate or xanthate derivative in which A represents an oxygen atom (O).

[0182] According to another preferred embodiment, the water-soluble controlling agent has formula (I) in which: - A represents an oxygen atom (O); - p = 1 and Q is a linear or structured polymer chain obtained from 4 to 100 monomers comprising at least one non-ionic hydrophilic monomer and / or at least one anionic hydrophilic monomer and / or at least one cationic hydrophilic monomer.

[0183] According to another preferred embodiment, the water-soluble controlling agent has formula (I) in which: - A represents an oxygen atom (O); - p = 1 and Q is a linear or structured polymeric chain obtained from 4 to 100 monomers comprising at least one non-ionic hydrophilic monomer and / or at least one anionic hydrophilic monomer and / or at least one monomer containing an LCST group.

[0184] According to another preferred embodiment, the water-soluble controlling agent has the formula (V):

[0185] [Chem.4] (V)

[0186] in which n is an integer between 4 and 100, preferably between 1 and 50.

[0187] In another preferred mode, the control agent is of formula (VI):

[0188] [Chem.5] XX J< R4OOC COOR4 (VI)

[0189] wherein: the R4s are identical or different, independently represent an H or a CH3 or a salt, advantageously chosen from the salts of alkali metals (Li, Na, K...), alkaline earth metals (Ca, Mg...) or ammonium ions (for example the ammonium ion or a tertiary ammonium), preferably a sodium salt.

[0190] In another preferred mode, the controlling agent is a trithiocarbonate of the following formula (VII): (VII)

[0192] in which; - the R4s are identical or different, independently represent an H or a CH3 or a monovalent or divalent cation, advantageously chosen from the cations of alkali metals (Li, Na, K...), alkaline earth metals (Ca, Mg...) or ammonium ion (for example the ammonium ion or a tertiary ammonium), preferably it is sodium; - n and n' are independent integers between 4 and 100, preferably between 2 and 50.

[0193] In another preferred mode, the control agent is of the following formula (VIII):

[0194] [Chem.7] COOR4 (VIII)

[0195] wherein: the R4s are identical or different, independently represent an H, a CH3 or a salt, advantageously chosen from the salts of alkali metals (Li, Na, K...), alkaline earth metals (Ca, Mg...) or ammonium ions (for example the ammonium ion or a tertiary ammonium). Preferably it is a sodium salt.

[0196] In another preferred mode, the control agent is of formula (IX):

[0197] [Chem.8] (IX)

[0198] in which: - the R4s are identical or different, independently representing an H, a CH3, or a monovalent or divalent cation, advantageously chosen from alkali metal cations (Li, Na, K...), alkaline earth metal cations (Ca, Mg...) or ammonium ion (for example, the ammonium ion or a tertiary ammonium), preferably sodium; and - n is an integer, between 4 and 100, preferably between 4 and 50.

[0199] The initiator(s) can be added to the hydrophilic phase before or after the formation of the reverse emulsion.

[0200] The polymerization initiators used are advantageously chosen from among compounds that dissociate into radicals under the polymerization conditions, for example: organic peroxides, hydroperoxides, hydrogen peroxide, persulfates, azo compounds, and redox salts. The use of water-soluble initiators is preferred. In some cases, it is advantageous to use mixtures of various polymerization initiators, for example, mixtures of redox salts and azo compounds.

[0201] In a preferred mode, the polymerization initiator is a pair of redox salts.

[0202] The reducing agent of the redox salt pair is advantageously chosen from among the sulfites of alkali metal salts (Li, Na, K...), alkaline earth metals (Ca, Mg...) or ammonium (for example the ammonium ion or a tertiary ammonium, sulfur dioxide, metabisulfites of alkali metal salts (Li, Na, K...), alkaline earth metals (Ca, Mg...) or ammonium (for example the ammonium ion or a tertiary ammonium.

[0203] The oxidant of the redox salt couple is advantageously chosen from among peroxides such as tert-butyl hydroperoxide, perfulfates of alkali metals (Li, Na, K...), of alkaline earth metals (Ca, Mg...) or of ammonium (for example the ammonium ion or a tertiary ammonium, hydrogen peroxide.

[0204] Advantageously, the amount of initiator is between 0.01 and 100,000 ppm relative to the total weight of monomer(s) of the polymer, preferably between 0.1 and 10,000 ppm, more preferably between 1 and 1,000 ppm, and even more preferably between 10 and 100 ppm.

[0205] The initiator(s) can be added all at once, in several stages, or continuously, i.e., by pouring. Preferably, the initiator(s) are added continuously.

[0206] In the case of redox salts, the reducing agent and the oxidizing agent can be added continuously, i.e., by pouring, in parallel or one after the other. Advantageously, at least one reducing agent or oxidizing agent is added to the reverse emulsion, and the other component of the redox couple is added continuously, i.e., by pouring, throughout the polymerization.

[0207] The initial polymerization temperature is advantageously between more than 0 °C and 50 °C.

[0208] Once polymerization has begun, the temperature is controlled to advantageously be between 30 °C and less than 100 °C.

[0209] The polymerization time is advantageously between 15 minutes and 600 minutes, preferably between 30 minutes and 320 minutes.

[0210] The polymerization process according to the invention can be carried out in batch, semi-batch or continuous, advantageously it is carried out in batch.

[0211] In a preferred mode, the polymerization is carried out at a pressure lower than atmospheric pressure, preferably at a pressure between 20 mbar and less than 800 mbar, more preferably between 30 and 500 mbar, more preferably between 40 and 400 mbar.

[0212] In a preferred mode, polymerization is carried out in a smooth-walled polymerization reactor and does not include a cooling system. Using this type of polymerization reactor makes it possible to avoid the formation of micro-gel spots during polymerization, which could damage the fractures.

[0213] In a particular embodiment, the process of the invention comprises, following polymerization, a step for removing residual monomers. The removal of residual monomers can be carried out, for example, by adding an excess of initiator.

[0214] In a particular mode, once the reverse emulsion has been obtained, it is possible to dilute it, in particular with the aid of a brine. Use of reverse emulsion

[0215] Finally, the present invention also relates to the use of the inverse emulsion described above in the fields of hydrocarbon (oil and / or gas) recovery; well drilling; well cementing; hydrocarbon (oil and / or gas) well stimulation, other than hydraulic fracturing such as conformance and diversion; open, closed or semi-closed circuit water treatment; fermentation must treatment; sludge treatment; construction; paper or cardboard manufacturing; the battery field; wood processing; hydraulic composition treatment (concrete, cement, mortar and aggregates); in the mining industry; cosmetic product formulation; detergent formulation; textile manufacturing; geothermal energy; sanitary diaper manufacturing; or agriculture. Examples Example 1#: Preparation of inverse emulsions#

[0216] Preparation of the hydrophilic phase: In a reactor equipped with an agitation system, the following are mixed at room temperature: - 138 g of acrylamide (50% by weight in water); - 30 g of acrylic acid; - 70 g of deionized water; - 30 g of sodium hydroxide (50% by weight in water) - 50 ppm of tertiary butyl hydroperoxide.

[0217] Preparation of the lipophilic phase: 2.0% by weight relative to the weight of the alkanolamide inverse emulsion and 0.5% by weight relative to the weight of the sorbitan mono oleate inverse emulsion are mixed in 45 g of Exxsol D100 (H2) oil and 5 g of Exxsol D40 (Hi) oil.

[0218] Emulsification and polymerization: The hydrophilic phase is mixed and emulsified in the lipophilic phase. The resulting inverse emulsion (EMU) is then degassed for 60 minutes before polymerization is initiated at room temperature by pouring 8 mL of a 1 g / L aqueous solution of sodium metabisulfite.

[0219] The inverse emulsions, according to the invention, EMU to EMI9 are prepared according to the protocol above, as are the inverse emulsions, counterexamples, EMLCE1 to EMI-CE11. The composition of these EMIs is presented in Table 1.

[0220] [Tables 1] ÜIÎÎUtsiâB. Quantity of polymer (% by weight) C upr-Lon 0 Quantity of oil He and (% by weight relative to the weight of the EMD Quantity of oil H; (% by weight relative to the total weight 426) Flash point value of oil Hi Quantity of emulsifying agent water-oil (% by weight) Weight ratio between the epohmer and the total quantity of oil EMU 30% AM-AA. (70130) H % 10% 40 "C 1.5 35 ? EMI2 30% AM-AA {70603 15% 30 54 40- X 1.5% 2 EMIS 30% AM-AA (70-30) 15% 50% 40 X 1.5% 2- EMI4 30% AMAA f7O;3O\ 15% 70% 40 X 15% ■J ISSUED 30% AMAA C0-30) 15% 100% 40 13% 10% 4Q X 1.5%? EMI7 30% AMAA C030) 15% 10% 45 X 1.5% EMIS 30% AMAA C030? 15% 10% 50- X 1.5%? EW 30% AMAA (7030) 15% 10% 60 C0-30) 15% io% 40 X 1.5% 2 m-CE3 30% AM-AA (7O.-3O) 5% 10% 40-5% 2 EMI CE4 30% AMAA (70-30) 25% 10 34 40 EMI-CE? 30% AMAA 170 30' 15% 0 90 X - 2 EMLCE8 30 % AM AA BQ 3% 15 % 10% 40 % AM AM C0 30> 15% 10% 40 X 1.5% 1.3 EMI-CEH 30% AM AA C0 307 15% 10% 40

[0221] Table 1 - Composition of inverse emulsions

[0222] Example 2: Evaluation of the recovery of the activity of inverse emulsions

[0223] Sand (200-400 µm) is placed between two laboratory presses at a pressure of 4,000 psi to simulate fracture conditions. The injection pressure is measured using Yokogawa™ EJA130E differential pressure sensors.

[0224] Initially, a brine (2% KCl) is injected at a rate of 3 ml / minute to measure the initial pressure loss during fracturing. Once stabilized, this value serves as a reference and corresponds to the initial injection pressure. A fracturing fluid is then injected for 4 hours at a rate of 3 ml / minute, comprising the emulsion according to the invention, previously inverted (10 ppm relative to the total weight of the fluid). Finally, the brine is injected again, at a rate of 3 ml / minute, to measure the final pressure loss corresponding to the final injection pressure. We then calculate a fracture damage factor FD according to the formula:

[0225] [Math.l] Afinal injection water — Ainitial injection water

[0226] The value of the conductivity recovery RC% is calculated according to the formula:

[0227] [Math.2] RC% = 1-FD

[0228] The longer the polymer remains trapped in the fracture, the higher the FD value will be, and the lower the RC% conductivity recovery will be.

[0229] The conductivity recovery values ​​of the different inverse emulsions and of a linear guar solution, used as a reference, are summarized in Table 2.

[0230] [Tables2] Emulsion Regain: œnd&ctkité after a first cleaning phase Guar 4*% EMU SÜ% EMIS EMIS 93% EMI4 98% EMIS 114% EMI6 89% EMI7 S 5.%¾ EMIS 9134 EMIO 9S% EMI-CE1 55% EMI-CE2 54% EM-CE3 ëü% EMI-CE4 40% EMI-CE5 34%. EMI-CE6 37% EMI-CE7 23% EMI-CES 60% EMI-CE9 5.3'î'sb EMI-CElû 61% EMI-CE11 63%

Claims

Demands

1. Inverse emulsion comprising: i) a hydrophilic phase comprising: - at least one polymer representing at least 30% by weight relative to the total weight of the inverse emulsion; - at least one hydrophilic solvent representing between 32 and 59% by weight relative to the total weight of the inverse emulsion; ii) a lipophilic phase comprising: - an oil Hh having a flash point between 40 and 85 °C, representing between 10 and 100% by weight relative to the total weight of oil in the lipophilic phase; - optionally an oil H2 representing between 0 and 90% by weight relative to the weight of oil in the lipophilic phase; - the quantity of oil Hi and H2 representing between 10 and 20% by weight relative to the total weight of the inverse emulsion; - at least one water-in-oil emulsifying agent representing between 1 and 3% by weight relative to the total weight of the inverse emulsion;and the inverse emulsion having a weight ratio between the at least one polymer and the Hi oil and possibly H2 of between 1.5 and 4.5.;

2. Reverse emulsion according to claim 1, characterized in that at least one polymer represents 30% to 45% by weight relative to the total weight of the reverse emulsion.

3. Inverse emulsion according to claim 1 or 2, characterized in that at least one polymer is a polymer of at least one monomer selected from anionic hydrophilic monomers, cationic hydrophilic monomers, non-ionic hydrophilic monomers, zwitterionic hydrophilic monomers, hydrophobic monomers and mixtures thereof.

4. Inverse emulsion according to any one of claims 1 to 3, characterized in that at least one polymer is a water-soluble synthetic polymer.

5. Inverse emulsion according to any one of claims 1 to 4, characterized in that at least one polymer has a molecular weight between 0.5 and 40 million g / mol.

6. Inverse emulsion according to any one of claims 1 to 5, characterized in that the Hi oil represents at least 30% by weight of the oils relative to the total weight of oil in the lipophilic phase.

7. Inverse emulsion according to any one of claims 1 to 6, characterized in that the Hi oil is selected from saturated and unsaturated hydrocarbons comprising between 9 and 14 carbon atoms.

8. A method for hydraulically fracturing an unconventional underground oil or gas reservoir comprising the injection of a fracturing fluid prepared from the inverse emulsion according to any one of claims 1 to 7.

9. Fracture fluid prepared from the reverse emulsion according to any one of claims 1 to 7.

10. A process for preparing a reverse emulsion comprising the following steps: a) Mixing under stirring: i) a hydrophilic phase comprising: * at least one hydrophilic solvent; * at least one monomer representing at least 30% by weight relative to the total weight of the reverse emulsion; * at least one hydrophilic solvent representing between 32 and 59% by weight relative to the total weight of the reverse emulsion, and capable of solubilizing the polymer; - a lipophilic phase comprising: * an Hb oil having a flash point between 40 and 85 °C, representing between 10 and 100% by weight relative to the total weight of oil in the lipophilic phase; * optionally an H2 oil representing between 0 and 90% by weight relative to the weight of oil in the lipophilic phase; * the quantity of Hi and H2 oil representing between 10 and 20% by weight relative to the total weight of the reverse emulsion;* at least one water-in-oil emulsifying agent representing between 1 and 3% by weight relative to the total weight of the inverse emulsion; b) Polymerization of at least one monomer of the hydrophilic phase to obtain a polymer in the inverse emulsion; the inverse emulsion having a weight ratio between the at least one polymer and the oil Hi and possibly H2 of between 1.5 and 4.

5.

11.

12.

13.

14.

15. A process according to claim 10, characterized in that the polymerization is initiated by a pair of redox salts. A process according to claim 11, characterized in that at least the reducer or oxidant of the redox salt pair is added to the reverse emulsion feed, and the other component of the redox salt pair is added continuously. A process according to any one of claims 10 to 12, characterized in that the polymerization is carried out at a pressure lower than atmospheric pressure. A process according to any one of claims 10 to 13, characterized in that the polymerization is carried out in a smooth-walled polymerization reactor and does not include a cooling system. Use of the inverse emulsion according to any one of claims 1 to 7 in the fields of hydrocarbon recovery; well drilling; well cementing; hydrocarbon well stimulation other than hydraulic fracturing; open, closed, or semi-closed water treatment; fermentation must treatment; sludge treatment; construction; paper or cardboard manufacturing; battery manufacturing; wood processing; hydraulic composition processing; mining; cosmetic formulation; detergent formulation; textile manufacturing; geothermal energy; sanitary diaper manufacturing; or agriculture.