RU2776701C1 - New composition for oil and gas production - Google Patents

Abstract

FIELD: oil and gas production.

SUBSTANCE: inventions group relates to oil and gas production. The composition for producing an injected fluid for oil and gas production contains an inverse emulsion of a water-soluble polymer A containing cationic monomer units, and solid particles of a water-soluble polymer B containing cationic monomer units. Water-soluble polymer A contains from 10 to 40 mol.% cationic monomer units, based on the total number of monomer units. The mol% cationicity of polymer A is greater than or equal to the mol% cationicity of polymer B. A method for treating a section of a subterranean formation includes providing the above composition, obtaining an injected fluid using at least the above composition, introducing the injected fluid into a section of a subterranean formation. The fracturing method includes providing the above composition, obtaining a fracturing fluid using at least the above composition and at least a proppant, introducing the fracturing fluid into a section of a subterranean formation.

EFFECT: improving the viscosity of the injected fluid, ensuring the suspension of particles in it, including under the condition of high shear force, environmental safety.

22 cl, 4 tbl

Description

The field of technology to which the invention belongs

The present invention relates to a novel composition containing water-soluble polymers for treating a section of a subterranean formation. The present invention also relates to a method for treating a section of a subterranean formation, and in particular to a method for producing oil and gas, where the composition is used. The composition is particularly useful for producing fracturing fluid in fracturing operations and injection fluid in chemically assisted oil recovery (EOR).

State of the art

Water-soluble polymers are widely used in oil and gas production processes such as oil enhancement and hydraulic fracturing operations, as well as other stimulation, cementing, drilling or completion operations. Water-soluble polymers are usually in the form of a solution, in the form of an inverse emulsion, in the form of a powder or in the form of a dispersion. Each of them has known advantages and disadvantages.

In the oil and gas industry, there is generally a need for a highly concentrated sample of a polymer composition that is readily applicable, and therefore preferably in the form of a liquid. WO2017/187150 proposes a composition made by mixing a granular water soluble friction reducing polymer and an inverted polymer emulsion. It proposes a liquid composition that does not require special equipment, and which is considered technically advantageous and economically advantageous. More specifically, the composition has friction reducing characteristics that match or exceed those of prior art friction reducing agents. The level of friction reduction is higher and is achieved faster.

In oil and gas production operations, fluids injected into a subterranean formation may contain particles or colloids. In this case, the particles or colloids must be suspended in the fluid in order to prevent any settling and inhomogeneity of the dispersed particles. For this purpose, polymers are commonly used in injection fluid formulations to increase viscosity. However, the injected fluid composition is typically subjected to high shear conditions, and viscosifying polymers, which are typically pseudoplastic, do not give satisfactory results.

There is a need for such an effect (s) of water-soluble polymers used in oil and gas production methods as improving the viscosity index and / or providing suspension, in particular if high shear conditions occur.

In fracturing operations, particularly in the case of high viscosity friction reducers (HVFRs), the dosage of these HVFRs is important and there is a need for more environmentally friendly solutions such as new products that require less energy to produce and more efficient products to reduce their consumption.

The applicant has developed a new composition, obtained using a combination of specific water-soluble polymers, which solves the above problem.

The essence of the invention

In a first aspect, the present invention provides a composition for producing an injected fluid for oil and gas production, comprising

- an inverse emulsion of water-soluble polymer A containing cationic monomer units, and

- solid particles of water-soluble polymer B containing cationic monomer units, and

while the water-soluble polymer A contains from 10 to 40 mol.% cationic monomer units, calculated on the total number of monomer units, and the cationicity in mol.% of polymer A is higher than or equal to the cationicity in mol.% of polymer B.

Through fine adjustment of the composition in accordance with the present invention, it is possible to achieve the environmental goals inherent in new technical innovations. In this case, the composition leads to a reduction in product consumption due to better characteristics. Because cationic monomers tend to have a higher carbon footprint and require more reaction steps to produce them, there is a need to reduce the cationic monomer content of the polymer as low as possible, i. cationicity.

The composition of the present invention achieves this goal because the average cationicity of the polymers contained in said composition is lower compared to the currently available cationic product. Less cationic monomer usually means more acrylamide, which is preferably produced by bioconversion with lower energy consumption. For all these reasons, the product of the present invention is more environmentally friendly.

In a second aspect, the present invention provides an injection fluid for an oil and gas recovery process, said fluid being produced using a composition of the present invention. The injected fluid may be a polymer injection fluid or a fracturing fluid.

In a third aspect, the present invention provides a method for treating a section of a subterranean formation, comprising providing a composition of the present invention, obtaining an injected fluid with at least said composition, introducing the injected fluid into a section of a subterranean formation.

Treating a section of a subterranean formation includes treating a portion of the subterranean formation or treating the entire subterranean formation.

In a fourth aspect, the present invention provides a method of fracturing comprising providing a composition of the present invention, producing a fracturing fluid with at least said composition and with at least a proppant, introducing the fracturing fluid into a section of a subterranean formation.

In a fifth aspect, the present invention provides a polymer injection method comprising providing a composition of the present invention, producing a polymer injection fluid with at least said composition, introducing the polymer injection fluid into an entire subterranean formation or section thereof.

In a sixth aspect, the present invention provides a method for improving the properties of providing suspension in an injected fluid, including providing a composition of the present invention, obtaining an injected fluid by mixing said composition with water, sea water or brine, introducing the injected fluid into the entire subterranean formation or its section. The water-based treatment fluid may be a fracturing fluid or an injected polymer injection fluid. In other words, this method is to improve the suspension of particles or colloids that are present in the injected fluid.

Detailed description of the invention

It has been found that the particular composition of the present invention leads to an improvement in the suspending effect even in highly concentrated brines and even under high shear conditions.

The effect of providing suspension refers to the formation of a suspension of particles or colloids that are present in the injected fluid and/or the injected fluid. It corresponds to the ability imparted by the composition of the present invention to the injected fluid to form suspensions of particles or colloids such as proppant and prevent settling. This property is very important in a fracturing operation where a proppant such as sand or coated sand is present in the injected fluid to keep the fractures open and this allows efficient oil and gas recovery.

As used herein, the term "water soluble polymer" refers to a polymer which, when appropriately mixed at a dosage of 10 g/l with water at 25° C., produces an aqueous solution substantially free of insoluble particles.

If the term "polymer A" is used in the present invention, it corresponds to water-soluble polymer A. The same is true for water-soluble polymer B.

A "macromonomer" is defined as a polymer or oligomer each molecule of which has a single end group that acts as a monomer molecule such that each polymer or oligomer molecule contributes only one monomer unit to the polymer product chain.

Used in this document, the "cationicity" of the polymer is the percentage of cationic monomer units in mol.% in terms of the total number of monomer units in the polymer.

In the present invention, "weight average molecular weight", also referred to as molecular weight in the present invention, is determined by intrinsic viscosity and is expressed in g/mol. Intrinsic viscosity can be measured using methods known to the person skilled in the art, and in particular it can be calculated from the values of the reduced viscosity for different concentrations in a graphical way, consisting in plotting the values of the reduced viscosity (on the y-axis) from the values of the concentration (along the abscissa) and extrapolating the curve to zero concentration. The intrinsic viscosity value is measured along the y-axis or using the least squares method. The weight average molecular weight can then be determined using the well-known Mark-Houwink equation:

[η] = K M ^α ,

where [η] is the intrinsic viscosity of the polymer, determined using the method of measuring the viscosity of the solution,

K is an empirical constant,

M is the molecular weight of the polymer,

α is the Mark-Huvink coefficient,

α and K depend on the specific polymer-solvent system.

Polymer A and polymer B may be different or identical, but they are in different forms - polymer A is in the form of a water-in-oil emulsion, and polymer B is in the form of particles (powder, fine particles, granules, beads). Polymer A is preferably different from polymer B. More precisely, polymer A and polymer B preferably have a different monomer composition and/or different molecular weight. Polymer A and polymer B are preferably two different polymers.

Composition of the present invention

A feature of the present invention is the combination of an inverse emulsion of a water soluble polymer A containing a certain amount of cationic monomer units and solid particles of a water soluble polymer B also containing cationic monomer units, where the cationicity of polymer A is greater than or equal to the cationicity of polymer B.

In accordance with a first aspect, the present invention provides a composition for producing an injected fluid for oil and gas production, containing

- an inverse emulsion of water-soluble polymer A containing cationic monomer units, and

- solid particles of water-soluble polymer B containing cationic monomer units, and

wherein the water-soluble polymer A contains from 10 to 40 mole % of cationic monomer, based on the total number of monomer units; and the cationicity in mol.% of polymer A is greater than or equal to the cationicity in mol.% of polymer B.

In a preferred embodiment, the water soluble polymer A preferably contains 15 to 40 mole % cationic monomer units (i.e. has a cationicity of 15 to 40 mole %), more preferably 18 to 35 mole %, even more preferably 20 up to 35 mol.%, even more preferably from 25 to 30 mol.%, while the specified cationicity is higher than or equal to the cationicity of polymer B, preferably higher.

In a preferred embodiment, the water soluble polymer B preferably contains 2 to 30 mole % cationic monomer units (i.e. has a cationicity of 2 to 30 mole %), preferably 5 to 25 mole %, more preferably 5 to 20 mol.%, while the specified cationicity is lower than or equal to the cationicity of polymer A, preferably lower.

In a preferred embodiment, the mol% cationicity of polymer A is higher than the mol% cationicity of polymer B. The mol% cationicity of polymer A is preferably at least 5% higher compared to the mol% cationicity of polymer B, preferably at least at least 10% higher, more preferably at least 15% higher. For example, if the cationicity of polymer A is 25 mol%, the cationicity of polymer B is preferably 20 mol%, more preferably 15 mol% or less.

The water-soluble polymer A according to the present invention preferably has a weight average molecular weight of 2 million g/mol to 20 million g/mol, more preferably above 4 million g/mol, more preferably above 6 million g/mol, even more preferably above 8 million g/mol.

The water-soluble polymer B according to the present invention preferably has a weight average molecular weight of 2 million g/mol to 20 million g/mol, more preferably above 5 million g/mol, more preferably above 8 million g/mol, even more preferably above 10 million g/mol.

In a preferred embodiment, the weight average molecular weight of water soluble polymer A is preferably lower than the weight average molecular weight of water soluble polymer B, and preferably 10% less, more preferably 20% less, even more preferably 30% less. For example, if the molecular weight of polymer A is 10 million daltons, the molecular weight of polymer B is preferably 9 million daltons or less, more preferably 8 million daltons or less.

Drag reduction and slurry performance has been found to be optimal when inverse emulsion polymer A is more cationic and lower molecular weight than polymer B and vice versa. Without being limited by theory, it appears that polymer A is less susceptible to mechanical breakdown during the initial pumping phase when a drag reduction effect is needed, and that polymer B, which has a higher molecular weight and is less cationic, exhibits its optimum suspension effect characteristics. with a time delay, somewhat later in the pipeline. This optimal configuration provides a very good compromise between the drag reducing effect and the slurry effect.

The composition is in the form of a liquid, even if it contains dispersed solid particles. Therefore, the composition is easily transportable, dispersible, pumpable, storage stable, which facilitates its use in oil and gas production.

As described above, polymer A and polymer B are preferably different, and they have at least a different monomer composition and/or a different molecular weight. Polymer A and polymer B are preferably two different polymers.

The composition is obtained by mixing in an appropriate manner an inverse emulsion of polymer A with solid particles of polymer B obtained in accordance with the present invention. The mixture is preferably obtained by dispersing solid particles in an inverse emulsion. Any suitable means may be used to prepare the mixture, such as a mixer, a rotor-stator mixer, a batch mixer, a dispersant, a polymer cutting device (PSU) such as described in US 8,186,871.

Even if not preferred, the polymer B solids may also be pre-wetted with an oil similar to or different from that used in the inverse emulsion of polymer A, or may be in saline, typically at a concentration of 40% to 80%. % by weight solids (Polymer B) relative to the total amount of liquid (prewetting liquid) and solids (Polymer B). The pre-wet composition contains an oil or saline solution and may also contain surfactant(s) and other ingredients.

In accordance with the present invention, the solid particles of polymer B remain in the solid state in the composition of the present invention. In other words, polymer B is in a solid state and dispersed in the composition, while polymer A is in hydrophilic droplets of a water-in-oil emulsion. Polymer B may absorb all or part of the free water of the inverse emulsion (Polymer A) and be pre-swollen but remain solid. The solid state includes such pre-wetted and pre-swollen states.

In practice, in an oil and gas production process, the composition of the present invention is mixed with an aqueous medium, such as water, sea water, or brine, to form an injection fluid. When the composition is properly mixed with a sufficient amount of aqueous medium in an inverse emulsion, a phase inversion occurs and polymer A is rapidly released, while polymer B begins to dissolve more slowly in the aqueous medium, even when pre-swollen.

In the composition of the present invention, the weight ratio of polymer A inverse emulsion to polymer B solids is preferably 1:1 to 10:1, more preferably 6:1 to 2:1.

In the composition of the present invention, the total concentration of polymer A and polymer B is preferably 30 wt% to 80 wt%, more preferably 37 wt% to 70 wt%, even more preferably 40 wt% to 65 wt%. %.

The composition according to the present invention may also contain other components such as a natural thickener such as clay or a synthetic thickener, salts, an alkaline agent, a surfactant such as an inverse emulsion surfactant, or others, biocides, corrosion inhibitor, acids, scale inhibitors, clay swelling inhibitor, guar, guar derivatives, carboxymethyl cellulose, crosslinkers such as zirconium compounds, titanate or borate compounds, delayed crosslinkers.

In the present invention, particular attention is paid to the rheological analysis of the injected fluids in which the composition of the present invention is used. The measurement of various rheological parameters is carried out in accordance with the method described below.

1) Rheological curve

Viscosity is measured as a function of shear gradient using an Anton Paar MCR302 rheometer equipped with RheoCompass software and a cone-to-plane measuring system (50 mm-2°). The normal force is reset after the sample is loaded and unloaded. The shear gradient can range from 0.001 to 500 s-1 at 25°C.

The resulting curve is then modeled according to the Carro-Yasuda equation, which yields the Newtonian viscosity (η0 in cps), relaxation time (τ in seconds) and flow index (n, flow index). Correction value "a" is considered equal to 2.

During the measurement of the rheological curve, parameter N1 is also recorded. It corresponds to the first normal stress difference and increases with increasing shear gradient in viscoelastic materials. This is a manifestation of the Weisenberg effect. N1 is 0 for an isotropic fluid at rest and is never negative.

2) Vibration measurement

To determine the linearity range of the material, the elastic modulus G' and the elastic modulus G'' are recorded at 1 Hz for strain values in the range from 0.1 to 100%. The response of the device remained linear in general up to 10%.

To realize the frequency sweep of the material, G' and G" are measured over a frequency range of 10 to 0.001 Hz for a strain contained in the linear region, typically 1%.

The intersection point between G' and G", if it can be measured, is used to determine the viscoelastic relaxation time according to the following formula:

.

.

3) Calculation

To distinguish between products, one can characterize such sand slurries statically, by calculating the settling rate, and dynamically, by calculating λ _e/v .

a) Settling rate calculation

Calculation of the sand settling rate in a viscoelastic fluid is described in the literature (this list is not exhaustive: SPE 187255, SPE16221) and is based on the following formula:

,

,

where

g: gravitational acceleration (9.81 m/s²),

Δρ: density difference between sand and fluid (1650 kg/m ³ ),

d: sand particle diameter (0.86 mm/l as an example)

K: consistency factor; and n: flow index.

In this case, the inventors of the present invention neglect the sticking phenomenon and the presence of a wall, which can greatly affect the deposition rate, and use this parameter to classify products.

b) Calculation of λe _/v

The dimensionless value λ _e/v is used to determine the ability of a fluid to suspend sand in shear. This value depends on the following rheological parameters:

,

,

where c: constant (1).

If this value is greater than 1, then elastic forces predominate in the system, providing proper suspendability.

Solid particles of water-soluble polymer B

In accordance with the present invention, the water-soluble polymer B is a water-soluble polymer containing cationic monomer units. Polymer B is a cationic polymer or an amphoteric polymer.

In accordance with the present invention, the water-soluble polymer B preferably contains from 2 to 30 mol.% cationic monomer units, preferably from 5 to 25 mol.%, more preferably from 5 to 20 mol.%, while the specified cationicity is lower than or equal to the cationicity of polymer A , preferably is lower.

The cationic monomers are preferably selected from the group consisting of dimethylaminoethyl acrylate (DMAEA), quaternized or salified; dimethylaminoethyl methacrylate (DMAEMA), quaternized or salted; diallyldimethylammonium chloride (DADMAC); acrylamidepropyltrimethylammonium chloride (APTAC); methacrylamidopropyltrimethylammonium chloride (MAPTAC). Dimethylaminoethyl acrylate (DMAEA), quaternized or salted, is preferred.

Water-soluble polymer B may contain various types of cationic monomers, such as DMAEA and DMAEMA, but preferably contains one type of cationic monomers.

The water soluble polymer B may also contain additional monomers such as a nonionic monomer and/or anionic monomers and/or zwitterionic monomers.

The additional nonionic monomers are preferably selected from the group consisting of acrylamide, methacrylamide, acrylamide N-mono derivatives, methacrylamide N-mono derivatives, acrylamide N,N derivatives, methacrylamide N,N derivatives, acrylic acid esters and methacrylic acid esters. The most preferred additional non-ionic monomers are acrylamide, N-vinyl pyrrolidone and N-vinyl formamide, with acrylamide being most preferred.

Additional anionic monomers are preferably selected from the group consisting of monomers containing a carboxyl functional group, and their salts; monomers containing a functional group of sulfonic acid, and their salts, such as acrylamido-tert-butylsulfonic acid (ATBS) and/or its salt(s); monomers containing a phosphonic acid functional group; and salts thereof such as vinylphosphonic acid. They include, for example, acrylic acid, methacrylic acid, maleic acid, itaconic acid; their salts and their half-esters, acrylamide-tert-butylsulfonic acid (ATBS) and/or its salt(s). The most preferred additional anionic monomers are acrylic acid, acrylamide-tert-butylsulfonic acid (ATBS) and/or their salt(s). Typically, the salts are alkali metal salts, alkaline earth metal salts or ammonium salts. Preferred salts are sodium salts.

The additional zwitterionic monomer may be a derivative of a vinyl unit, in particular an acrylamide, acrylic, allyl or maleic unit, this monomer containing an amine or quaternary ammonium functional group and a carboxylic acid (or carboxylate), sulfonic acid (or sulfonate) group or phosphoric acid (or phosphate or phosphonate). Mention may be made of dimethylaminoethyl acrylate derivatives such as 2-((2-(acryloyloxy)ethyl)dimethylammonio)ethane-1-sulfonate, in particular and without limitation 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, dimethylaminopropylacrylamide 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, dimethylaminopropylmethylacrylamide derivatives such as 2-((3-methacrylamidopropyl)dimethylammonio)ethane-1-sulfonate, 3-( (3m ethacrylamidopropyl)dimethylammonio)propane-1-sulfonate, 4-((3-methacrylamidopropyl)dimethylammonio)butane-1-sulfonate and [3-(methacryloyloxy)propyl](dimethylammonio)acetate.

Water-soluble polymer B may also contain at least one hydrophobic monomer or at least one hydrophobic macromonomer. The concentration of hydrophobic monomers and hydrophobic macromonomers in mol. % based on total monomers and macromonomers is preferably 0.0001% to 10%, more preferably 0.001% to 5%, even more preferably 0.01% to 3%, even more preferably 0.1 to 2 %, even more preferably 0.2 to 1.5%, even more preferably 0.3 to 1.3%.

Water-soluble polymer B preferably contains acrylamide. The acrylamide concentration, based on the total content of monomers and macromonomers, is preferably 5 to 98 mol%, more preferably 30 to 95 mol%, even more preferably 50 to 90 mol%.

In a preferred embodiment, the water-soluble polymer B is a copolymer of dimethylaminoethyl acrylate (DMAEA), quaternized or salted, and acrylamide. In this case, the amount of DMAEA is preferably 2 to 30 mol%, preferably 5 to 25 mol%, more preferably 5 to 20 mol%, and the amount of acrylamide is preferably 70 to 98 mol%, preferably 75 up to 95 mol%, more preferably 80 to 85 mol%.

In another preferred embodiment, the water-soluble polymer B is a terpolymer of dimethylaminoethyl acrylate (DMAEA), quaternized or salted, acrylamide and one of the two following monomers: acrylic acid and/or its salt(s) or acrylamide-tert-butylsulfonic acid (ATBS) and/or its salt(s). In this case, the amount of DMAEA is preferably 2 to 30 mol%, preferably 5 to 25 mol%, more preferably 5 to 20 mol%, the amount of acrylic acid and/or its salt(s) or acrylamide-tert- butylsulfonic acid (ATBS) and/or its salt(s) is from 0.5 to 10 mol.%, and the amount of acrylamide is a complementary amount to achieve a total amount of 100%.

One skilled in the art will be able to adjust the appropriate amounts of monomers and macromonomers of polymers B to achieve 100 mol%.

The polymerization of polymer B is usually a radical polymerization. By radical polymerization, we mean radical polymerization using UV initiators, azo compound initiators, redox or thermal initiators, as well as controlled radical polymerization (CRP) or reverse addition-fragmentation (RAFT) chain transfer polymerization techniques or MADIX. In accordance with a very preferred embodiment, polymer B is obtained by RAFT polymerization or CRP or MADIX polymerization techniques.

In another preferred embodiment, if polymer B contains an acrylamide monomer unit, a post-treatment step is applied to polymer B to make it amphoteric, typically slightly amphoteric, for example, 0.5 to 10 mole % anionic monomer unit.

The post-treatment step consists in reacting a hydrolysable functional group, such as an amide, with a hydrolysing agent. The hydrolysis agent may be an enzyme, an ion exchange resin or an alkali metal, preferably a Brønsted base.

After the post-treatment step, a carboxylate group or carboxylic acid moieties are formed. Indeed, the reaction between a hydrolysing agent and a hydrolysable functional group such as an amide group results in the formation of carboxylate moieties or carboxylic acid moieties.

Carboxylate-bearing polyacrylamides can be prepared according to various methods. Among them, one method is to polymerize acrylamide which has been partially or completely pre-hydrolyzed before polymerization with caustic soda or an enzyme such as amidase. Another method consists in the copolymerization of acrylamide and acrylic acid and/or its salt. Another method consists in adding a hydrolyzing agent before, at the beginning and/or during the polymerization, where said addition is carried out in relation to either a concentrated or diluted solution, an emulsion, an anhydrous emulsion, or a gelatinous substance. Another method consists in adding a hydrolyzing agent after polymerization, where said addition is carried out in relation to either a concentrated or dilute medium. The polymerization may be a solution polymerization, an emulsion polymerization, a dispersion polymerization, or a gel polymerization. The post-treatment step may be carried out on the finished polymer, or the polymer may be dissolved in a solvent to a pumpable concentration, the polymer concentration being typically 1 to 6%.

All of the above methods have advantages and disadvantages associated with the formation of off-gas, molecular weight, heat generation, production method.

In a highly preferred embodiment, polymer B is made according to a process which successively comprises:

- providing an aqueous solution of monomers containing at least one hydrophobic monomer or at least one hydrophobic macromonomer and preferably acrylamide;

- ensuring the polymerization of the specified aqueous solution of monomers to obtain a polymer gel;

- cutting said gel into pieces, preferably less than 10 cm ³ , more preferably less than 5 cm ³ , more preferably less than 1 cm ³ ;

- carrying out the post-treatment step by mixing the hydrolyzing agent with said gel pieces;

- obtaining processed pieces of gel polymer B at the end of the stage of additional processing;

- drying said treated gel pieces;

- obtaining a powder of polymer B;

optionally grinding said powder;

optionally sifting said powder.

The degree of conversion is the number of hydrolysable functional groups, such as amide groups, which are converted into carboxylate or carboxylic acid fragments, expressed in mol.%, relative to the total number of moles of monomer units and macromonomer units in the polymer before further processing (including capable of hydrolysis and non-hydrolyzable monomer units).

In a preferred embodiment, the conversion is at least 1 mol%, preferably at least 5 mol%. The maximum degree of conversion depends on such parameters as the content of monomers containing a hydrolysable functional group, the number of hydrolyzable functional groups in each monomer, and the total content of carboxylate functional groups in the polymer. Typically, the maximum conversion is 20 mol%, preferably 15 mol%. The preferred degree of conversion is from 1 to 10 mol%.

According to a preferred embodiment, the hydrolysable functional group in polymer B prior to the post-treatment step is an amide group from an acrylamide monomer or an ester group from a cationic monomer, and in the post-treatment step, the amide group is converted to a carboxylate group or a carboxylic acid group. More preferably, the amide functional group of the acrylamide monomer units or the ester group from the cationic monomer is converted into carboxylate salt and/or carboxylic acid moieties.

For example, if the polymer is obtained by polymerization of 80 mol% acrylamide, 20 mol% dimethylaminoethyl acrylate (DMAEA) quaternized before post-treatment, with the post-treatment step carried out with caustic soda, and the conversion is 5 mol%, then the composition of the resulting polymer B is as follows: 78 mol% acrylamide, 5 mol% sodium carboxylate moieties, 17 mol% dimethylaminoethyl acrylate (DMAEA) quaternized.

The degree of conversion refers to the functional groups converted into carboxylate moieties or carboxylic acid moieties during the post-treatment step. It does not include carboxylate moieties and carboxylic acid moieties that do not result from the post-treatment step. For example, if a polymer is obtained by polymerizing acrylamide, a cationic monomer, ATBS, and acrylic acid, the conversion rate does not include the carboxylic acid group of acrylic acid.

A branching agent may also be used. The agent is for example selected from methylene bis-acrylamide (MBA), ethylene glycol diacrylate, tetraallylammonium chloride, polyethylene glycol dimethacrylate, diacrylamide, cyanomethyl acrylate, vinyloxyethyl acrylate, vinyloxymethacrylate, triallylamine, formaldehyde, glyoxal, glycidyl ethers such as ethylene glycol diglycidyl ether, and epoxy compounds. , as well as their mixtures. When such a branching agent is used, the amount used is such that polymer B remains a water-soluble polymer. Those skilled in the art will adjust the amount of branching agent in a manner known to them.

It is also possible to use a free radical polymerization transfer agent, otherwise known as a chain size limiter. The use of a chain transfer agent is particularly preferred for controlling the molecular weight of the resulting polymer. As an example of a chain transfer agent, methanol, isopropanol, sodium hypophosphite, 2-mercaptoethanol, sodium metallylsulfonate and mixtures thereof can be mentioned. Those skilled in the art will adjust the amount of DM in a manner known to them.

In accordance with the present invention, the water-soluble polymer B may have a structure that is linear, branched, star-shaped, comb-shaped, block or microblock structure, or controlled polydispersity in terms of molecular weight. Such properties can be obtained by selecting an initiator, a chain transfer agent, a polymerization technique such as matrix polymerization, controlled radical polymerization known as RAFT (Reversible Chain Transfer Fragmentation), NMP (Nitroxide Mediated Polymerization), or ATRP (Radical atom transfer polymerization) or MADIX type polymerization, incorporation of structural monomers and/or concentrations. The general knowledge of a person skilled in the art enables him or her to obtain a water-soluble polymer characterized by one of these types of structure. Polymer B in accordance with the present invention, regardless of its structure, remains water-soluble.

In accordance with the present invention, the solid particles of the water-soluble polymer B may be in the form of a powder, fine particles, granules or beads. They may or may not be spherical.

In a preferred embodiment, the particles of polymer B are of small particle size and are referred to as fine particles. The fine particles are preferably obtained by sieving and/or grinding the powder obtained by the above-described gel polymerization process after drying. Prior to mixing with the inverse emulsion of polymer A, the fine particles of polymer B preferably have a particle size distribution, represented by a D50 value, of 5 µm to 500 µm, more preferably 50 µm to 400 µm, even more preferably 100 µm to 350 µm . The choice of fine particles is particularly useful for achieving optimal performance in terms of the effect of increasing the viscosity and the effect of providing suspension in the injected fluid.

There are a number of methods used to control particle size distribution. The most popular methods include sieve analysis, direct imaging and laser diffraction. Traditionally, particle size distribution values have been calculated from the results of sieve analysis. Sieve analysis provides particle size information in the form of an S-curve of total mass held on each sieve versus sieve mesh size. The most commonly used parameters when describing particle size distribution values are D-values (D10, D50 and D90), which are cut-off parameters for 10%, 50% and 90% of the total mass.

D-values can be thought of as the diameter of a sphere that separates the mass of the sample at a set percentage when the particles are distributed with increasing mass. For example, D10 is the diameter at which 10% of the mass of the sample consists of particles with a diameter less than this value. D50 is the particle diameter at which 50% of the mass of the sample is less than this value and 50% of the mass of the sample is greater than this value.

The polymer B particles may absorb all or part of the free water of the inverse emulsion and be pre-swollen but remain solid. The particle size in the composition tends to increase due to the absorption of water. The particle size of polymer B in the composition is preferably 10 µm to 1500 µm, more preferably 80 µm to 1000 µm, even more preferably 150 µm to 800 µm.

The water-soluble polymer B according to the present invention preferably has a weight average molecular weight of 2 million g/mol to 20 million g/mol, more preferably above 5 million g/mol, more preferably above 8 million g/mol, even more preferably above 10 million g/mol. In a preferred embodiment, the weight average molecular weight of water soluble polymer B is preferably higher than the weight average molecular weight of water soluble polymer A, and preferably 10% more, more preferably 20% more, even more preferably 30% more. For example, if the molecular weight of polymer A is 10 million daltons, the molecular weight of polymer B is preferably 9 million daltons or less, more preferably 8 million daltons or less.

Inverse emulsion of associative water-soluble polymer A

In accordance with the present invention, the water-soluble polymer A contains from 10 to 40 mole% of cationic monomer units, preferably from 15 to 40 mole%, more preferably from 18 to 35 mole%, even more preferably from 20 to 35 mole%, even more preferably 25 to 30 mole %, said cationicity being greater than or equal to the cationicity of polymer B, preferably greater.

The cationic monomers are preferably selected from the group consisting of dimethylaminoethyl acrylate (DMAEA), quaternized or salified; dimethylaminoethyl methacrylate (DMAEMA), quaternized or salted; diallyldimethylammonium chloride (DADMAC); acrylamidepropyltrimethylammonium chloride (APTAC); methacrylamidopropyltrimethylammonium chloride (MAPTAC). Dimethylaminoethyl acrylate (DMAEA), quaternized or salted, is preferred.

Water-soluble polymer A may contain various types of cationic monomers, such as DMAEA and DMAEMA, but preferably contains one type of cationic monomers.

Water-soluble polymer A is a cationic or amphoteric polymer.

The water soluble polymer A may also contain additional monomers such as nonionic monomers and/or anionic monomers and/or zwitterionic monomers. Said monomers are preferably selected in accordance with the lists and preferences mentioned above with respect to polymer B.

The water-soluble polymer A may also contain at least one hydrophobic monomer or at least one hydrophobic macromonomer. The hydrophobic monomer or hydrophobic macromonomer and their content are preferably selected in accordance with the lists and preferences mentioned above with respect to polymer B.

Water-soluble polymer A preferably contains acrylamide. The acrylamide concentration, based on the total content of monomers and macromonomers, is preferably 5 to 90 mol%, more preferably 30 to 90 mol%, even more preferably 50 to 80 mol%.

In a preferred embodiment, the water-soluble polymer A is a copolymer of dimethylaminoethyl acrylate (DMAEA), quaternized or salted, and acrylamide. In this case, the amount of DMAEA is preferably 10 to 40 mol%, preferably 25 to 35 mol%, and the amount of acrylamide is preferably 60 to 90 mol%, preferably 65 to 75 mol%.

In another preferred embodiment, the water-soluble polymer A is a terpolymer of dimethylaminoethyl acrylate (DMAEA), quaternized or salted, acrylamide and one of the two following monomers: acrylic acid and/or its salt(s) or acrylamide-tert-butylsulfonic acid (ATBS) and/or its salt(s). In this case, the amount of DMAEA is preferably 10 to 40 mol%, preferably 25 to 35 mol%, the amount of acrylic acid and/or its salt(s) or acrylamide-tert-butylsulfonic acid (ATBS) and/or its salt (salts) is from 0.5 to 10 mol.%, and the amount of acrylamide is an additional amount to achieve a total amount of 100%.

One skilled in the art will be able to adjust the appropriate amounts of monomers and macromonomers of polymers A to achieve 100 mol%.

Due to the specific monomeric composition of polymer A in the form of an inverse emulsion in combination with solid particles of polymer B, the composition of the present invention has optimal characteristics in terms of the effect of increasing the viscosity and the effect of providing suspension.

The polymerization of polymer A is usually a radical polymerization. By radical polymerization, we mean radical polymerization using UV initiators, azo compound initiators, redox or thermal initiators, as well as controlled radical polymerization (CRP) or reverse addition-fragmentation (RAFT) chain transfer polymerization techniques or MADIX. In accordance with a very preferred embodiment, polymer A is obtained by RAFT polymerization or CRP or MADIX polymerization techniques.

An inverse emulsion, otherwise known as a water-in-oil emulsion, consists of an oil phase, usually a lipophilic solvent or oil, constituting a continuous phase in which polymer-containing water droplets are in suspension, such water droplets forming a dispersed phase. An emulsifying surfactant (called a water-in-oil emulsion surfactant) that is placed at the water/oil interface stabilizes the dispersed phase (water + polymer) in the continuous phase (lipophilic solvent or oil).

The inverse emulsion of water-soluble polymer A can be obtained in accordance with any method known to the person skilled in the art. Typically, the aqueous solution containing the monomer(s) is emulsified into an oil phase containing at least one emulsifying agent. The polymerization is then carried out by adding a free radical polymerization initiator. Mention may be made of redox couples including cumene hydroperoxide, t-butyl hydroxyperoxide or persulfates among the oxidizing agents, sodium sulfite, sodium metabisulfite and Mohr's salt among the reducing agents. Azo compounds such as 2,2'-azobis(isobutyronitrile) and 2,2'-azobis(2-amidinopropane) hydrochloride can also be used.

The inverse emulsion of the water-soluble polymer A is preferably prepared according to a process comprising the following steps:

a) obtaining an aqueous phase containing at least one hydrophobic monomer or at least one hydrophobic macromonomer and optionally other water-soluble monomers,

b) obtaining an oil phase containing at least one oil and at least one surfactant to form a water-in-oil emulsion,

c) mixing the aqueous phase and the oil phase to form a water-in-oil emulsion,

d) immediately after the formation of the water-in-oil emulsion, ensuring polymerization under practically oxygen-free conditions of the monomers of the aqueous phase with at least one system of free radical polymerization initiators,

e) obtaining an inverse emulsion of the polymer at the end of the polymerization,

f) optionally and preferably diluting or concentrating by distillation said inverse emulsion;

g) optionally carrying out further processing of the polymer of said inverse emulsion.

The optional step f) can be performed before or after step g). Preferably step f) is carried out after step g). The mixing in step c) is preferably carried out at high shear.

First Specific and Preferred Embodiment of Inverse Emulsion of Water Soluble Polymer A

According to a first specific and preferred embodiment, an inverse emulsion of water-soluble polymer A is obtained by first preparing an inverse emulsion and then diluting said inverse emulsion with an aqueous solution to form a diluted inverse emulsion. This diluted inverse emulsion is then combined with polymer B solids to form a composition of the present invention.

Before dilution, the inverse emulsion of polymer A preferably contains from 10 to 50% by weight of oil, more preferably from 15 to 45% by weight. The inverse emulsion of polymer A preferably contains from 5 to 55% by weight of water, more preferably from 5 to 35% by weight.

In this preferred embodiment, the dilution rate is preferably 2.5% to 20% by weight based on the total weight of the inverse emulsion obtained at the end of polymerization, more preferably 3 to 15% by weight, even more preferably 3 to 10% by weight. .%. The dilution ratio is the weight of the aqueous solution based on the weight of the inverse emulsion obtained at the end of the polymerization.

The aqueous solution used for dilution may be water or saline, preferably saline.

Even if the composition of the present invention already has better viscosity increasing effect and suspending effect, the additional step of diluting the inverse emulsion with an aqueous solution according to this preferred embodiment further improves the performance in terms of viscosity increasing effect and suspending effect.

Second Specific and Preferred Embodiment of Inverse Emulsion of Water Soluble Polymer A

According to a second specific and preferred embodiment, the inverse emulsion of the water-soluble polymer A is obtained by carrying out polymerization partially or completely under pressure, preferably between 0.1 and 200 mbar (1 bar = 10 ⁵ Pa), more preferably between 5 and 150 mbar, even more preferably 20 to 100 mbar.

Even though the composition of the present invention already has better viscosity increasing effect and slurry effect compared to the prior art composition, inverse emulsion polymerization under a certain vacuum level further improves the performance in terms of viscosity increasing effect and slurry effect.

According to a specific and preferred embodiment, if the inverse emulsion polymerization of the water-soluble polymer A is carried out partially at a pressure of less than 200 mbar, then the polymerization time under reduced pressure is preferably at least 10% of the total polymerization time, preferably at least 30%, more preferably more than 50%, even more preferably more than 80%. In a preferred embodiment, the polymerization is carried out entirely at a pressure of less than 200 mbar.

The polymerization is preferably carried out in batches. From an industrial point of view, it is preferable to obtain a large batch, but it is usually difficult to increase the batch size. It has been found that the volume of the batch to be polymerized can be more than 10 m ³ , preferably more than 20 m ³ and more preferably more than 40 m ³ if the polymerization is carried out at a pressure of less than 200 mbar.

If the polymerization is carried out partially or completely at a pressure between 0.1 and 200 mbar, then in practice steps a), b) and c) are carried out at atmospheric pressure, and the pressure is reduced to a value of at least below 200 mbar throughout the duration of the polymerization, or part of it, preferably during the entire polymerization. Additional steps of degassing with nitrogen and raising the reaction temperature may be added to the steps previously described.

At the end of the polymerization, the reactor is returned to atmospheric pressure to discharge the water-in-oil emulsion. It is also possible to maintain the pressure below 200 mbar during steps a and/or b) and/or c) and/or during discharge and/or during storage of the inverse emulsion.

All means of reducing pressure are known means, but this is not a limitation. Examples that may be mentioned include positive displacement pumps such as liquid ring pumps or diaphragm pumps, pulse pumps, regenerative pumps, entrapment pumps, steam ejectors.

The polymerization is preferably carried out in a reactor adapted to maintain the low pressure preferred for the process. It may also be useful to use a condenser to remove water and/or a mixture of volatiles or oil from the off-gas released from the emulsion during polymerization at low pressure or under vacuum.

The polymerization is generally initiated after depressurization of the reactor, but may also be initiated before or during the depressurization step. The depressurization step usually lasts a few seconds, or even a few minutes, depending on the volume of the reactor and depending on the equipment used to provide the vacuum.

Thus, in accordance with one particular embodiment, the following are performed in sequence:

- carrying out steps a), b) and c) at atmospheric pressure and bubbling with nitrogen,

- reduce pressure

- initiate stage d) polymerization.

In another embodiment, the following are performed in sequence:

- carrying out steps a), b) and c) at atmospheric pressure and bubbling with nitrogen,

- simultaneously reduce the pressure and initiate polymerization.

In another embodiment, the following are performed in sequence:

- carrying out steps a), b) and c) at atmospheric pressure and bubbling with nitrogen,

- initiate polymerization

- during the polymerization, the pressure is reduced.

In a preferred embodiment, the off-gas formed during the polymerization under vacuum, consisting of a mixture of water and oil, is not returned to the polymerization mass, but is condensed using a condenser and removed from polymer A.

General description of the inverse emulsion of water-soluble polymer A

In general, at the end of the polymerization reaction, at least one phase inversion agent is added, preferably at a temperature below 50°C.

Traditionally, the polymerization is generally carried out under isothermal, adiabatic, or controlled temperature conditions. In other words, the temperature is kept constant, usually at 10-60°C (isothermal process), or the temperature is allowed to rise naturally (adiabatic process), in which case the reaction usually starts at a temperature below 10°C, and the final temperature usually exceeds 50°C, or, finally, the temperature rise is controlled so that the temperature curve is between the isothermal curve and the adiabatic curve.

The polymerization start temperature is preferably 0.1 to 40°C, more preferably 10 to 30°C. The polymerization end temperature is preferably 20°C to 90°C, more preferably 35°C to 70°C.

The polymerization time is preferably less than 24 hours, more preferably less than 10 hours, even more preferably less than 8 hours.

For polymer A, the same additional monomers, branching agent, free radical chain transfer agent as described above can be used.

In accordance with the present invention, the water-soluble polymer A may be characterized by a structure that is linear, branched, star-shaped, comb-shaped, block or microblock structure, or controlled polydispersity in molecular weight. These properties can be obtained by selecting an initiator, a chain transfer agent, a polymerization technique such as matrix polymerization, controlled radical polymerization known as RAFT (Reversible Chain Transfer Fragmentation), NMP (Nitroxide Mediated Polymerization), or ATRP ( atom transfer radical polymerization), or MADIX type polymerization (macromolecular design by xanthate replacement), incorporation of structural monomers and/or concentration. The general knowledge of a person skilled in the art enables him or her to obtain a water-soluble polymer characterized by one of these types of structure. Polymer A according to the present invention, regardless of its specific structure, remains water soluble.

The water-soluble polymer A according to the present invention preferably has a weight average molecular weight of 2 million g/mol to 20 million g/mol, more preferably above 4 million g/mol, more preferably above 6 million g/mol, even more preferably above 8 million g/mol. The weight average molecular weight of water soluble polymer A is preferably lower than the weight average molecular weight of water soluble polymer B, and preferably 10% less, more preferably 20% less, even more preferably 30% less.

The oil used to prepare the inverse emulsion of the present invention may be mineral oil, vegetable oil, synthetic oil, or a mixture of several of these oils. Examples of mineral oil are mineral oil containing saturated hydrocarbons of the aliphatic, naphthenic, paraffinic, isoparaffinic, cycloparaffinic or naphthyl type. An example of a synthetic oil is hydrogenated polydecene or hydrogenated polyisobutene; an ester such as octyl stearate or butyl oleate. A number of Exxsol® products from Exxon are suitable oils.

Generally, the weight ratio of the aqueous phase to the oil phase during the polymerization is preferably 50/50 to 90/10, more preferably 70/30 to 80/20.

The inverse emulsion of polymer A preferably contains from 10 to 50% by weight of oil, more preferably from 15 to 45% by weight. The inverse emulsion of polymer A preferably contains from 5 to 55% by weight of water, more preferably from 5 to 35% by weight. Typically, if the inverse emulsion is concentrated by distillation, the concentrated inverse emulsion contains 44% to 60% by weight of polymer A, preferably 51 to 58%.

The phase inversion agent is a surfactant typically characterized by an HLB value greater than 10. As an example of such a phase inversion agent, ethoxylated esters of sorbitan can be mentioned, such as sorbitan oleate ethoxylated with 20 equivalents of ethylene oxide (EO 20), sorbitan laurate, polyethoxylated with 20 moles of ethylene oxide, castor oil polyethoxylated with 40 moles of ethylene oxide, decaethoxylated oleodecyl alcohol, heptaethoxylated lauryl alcohol, or sorbitan monostearate polyethoxylated with 20 moles of ethylene oxide. The phase inversion agent may also be a polyoxyethylene alkylphenol; polyoxyethylene cetyl ether (10 mol); simple alkylaryl ether of polyoxyethylene; quaternary ammonium derivatives; potassium oleate; N-cetyl-N-ethylmorpholinium ethosulfate; sodium lauryl sulfate; condensation products of higher fatty alcohols with ethylene oxide, such as the reaction product of oleyl alcohol with 10 units of ethylene oxide; condensation products of alkylphenols and ethylene oxide, such as the reaction products of isooctylphenol with 12 units of ethylene oxide; condensation products of higher fatty acid amines with five or more ethylene oxide units; tristerylphenol ethylene oxide; condensation products of ethylene oxide and partial esters of polyhydric alcohols and higher fatty acids and their internal anhydrides (for example, mannitol anhydride and sorbitol anhydride); amine oxide; alkylpolyglucoside; glucamide; an ester of phosphoric acid or a salt of alkylbenzenesulfonic acid; water-soluble polymeric surfactant.

In a preferred embodiment, the phase inversion agent is an ethoxylated nonylphenol, preferably having an ethoxylation index of 4 to 10, an ethoxy/propoxyalcohol, preferably having an ethoxy/propoxylation index of C12 to C25, or an ethoxylated tridecyl alcohol, or a fatty ethoxy/propoxyalcohol , or ethoxy/propoxylated castor oil.

The inverse emulsion of polymer A may contain at least two phase inverters, preferably at least three phase inverters, even more preferably at least four phase inverters.

The emulsifying agent is a surfactant typically having an HLB value of less than 10. As an example of such an emulsifying agent, mention may be made of surfactant polymers such as polyesters with a molecular weight of 1000 to 3000, condensation products of poly(isobutenyl ) succinic acid or its anhydride and polyethylene glycol, block copolymers with a molecular weight of 2500 to 3500, for example sold under the trade names Hypermer®, extracts based on sorbitan, for example sorbitan monooleate, sorbitan isostearate or sorbitan sesquioleate, polyethoxylated esters of sorbitan or alternatively diethoxylated oleocetyl alcohol or tetraethoxylated lauryl acrylate, condensation products of higher fatty alcohols with ethylene oxide, such as the reaction product of oleyl alcohol with 2 units of ethylene oxide; condensation products of alkylphenols and ethylene oxide, such as the reaction product of nonylphenol with 4 units of ethylene oxide. Products like Witcamide® 511, betaine based products and ethoxylated amine are also good options for emulsifying agents.

In a preferred embodiment, the emulsifying agent is sorbitan monooleate, polyethoxylated sorbitan esters, or tall oil fatty acid diethanolamide.

The inverse emulsion of polymer A may contain at least two emulsifying agents, preferably at least three emulsifying agents, even more preferably at least four emulsifying agents. The inverse emulsion of polymer A preferably contains from 0.8 to 6% by weight, more preferably from 0.8 to 3 wt. % of at least one emulsifying agent.

The inverse emulsion of polymer A preferably contains 1 to 12% by weight, more preferably 2 to 8% by weight, of at least one phase inversion agent.

The inverse emulsion of polymer A may contain from 1 to 17% by weight of salts.

The salts present in the inverse emulsion may be, for example, sodium salts, lithium salts, potassium salts, magnesium salts, aluminum salts, ammonium salts, phosphate salts, sulfate salts, chloride salts, fluoride salts, citrate salts, acetate salts, tartrate salts, hydrophosphate salts, water-soluble inorganic salts, other inorganic salts, and mixtures thereof. Such salts include sodium chloride, sodium sulfate, sodium bromide, calcium chloride, ammonium sulfate, ammonium chloride, lithium chloride, lithium bromide, potassium chloride, potassium bromide, magnesium sulfate, aluminum sulfate, ammonium hydrogen phosphate, sodium hydrogen phosphate, potassium hydrogen phosphate, and mixtures thereof. . Sodium chloride, calcium chloride, ammonium chloride, ammonium sulfate are preferred and mixtures thereof are particularly preferred.

Injected Fluid and Method for Treating a Section of an Underground Reservoir

The composition of the present invention has an improved suspending effect that is less sensitive to shear conditions. The composition of the present invention also improves efficacy at the same dosage or maintains the same efficacy at a lower dosage. This is of particular interest in a fracturing operation, particularly in the case of high viscosity friction reducers (HVFRs), since HVFR dosage is usually important.

Also, the advantage of the composition is that it is presented in the form of a liquid and therefore is easily transportable, dispersible, pumpable, storage stable, which facilitates its use in oil and gas production.

In a second aspect, the present invention provides an injection fluid for an oil and gas recovery process, said fluid being produced using a composition of the present invention. The injected fluid may be a polymer injection fluid or a fracturing fluid.

In the process of the present invention, the fluid to be injected is typically produced by mixing the composition of the present invention with an aqueous medium such as water, sea water, or brine. When the composition is mixed with a sufficient amount of an aqueous medium in an inverse emulsion, a phase inversion occurs and polymer A is rapidly released, while polymer B begins to dissolve more slowly in an aqueous medium, even when pre-swollen.

The injected fluid contains water-soluble polymers A and B in a total amount of preferably 0.0005 wt% to 3 wt%, more preferably 0.02 wt% to 2 wt%, even more preferably 0.05 wt%. .% to 1 wt.%, even more preferably from 0.1 wt.% to 1 wt.%. The amount of water soluble polymers A and B will vary depending on the oil and gas production method, conditions in the subterranean formation (eg, salinity and/or temperature) and the desired results.

The injected fluid may also contain other components such as proppants (such as sand, coated sand, ceramic beads), alkaline agents, surfactants, complex nanofluids, microemulsions, biocides, corrosion inhibitors, acids, scale inhibitors, clay swelling inhibitors, guar, guar derivatives, carboxymethyl cellulose derivatives, crosslinkers such as zirconium compounds, titanate or borate compounds, delayed crosslinkers, chain breakers, encapsulated chain breakers, preformed particles of gels, nanogels, colloidal gels dispersions, clays, bentonites, depending on the nature of the oil and gas extraction method.

Surfactants are particularly useful for the injected fluid of the present invention because they can improve the performance of said fluid, especially in an oil and gas recovery process. They are preferably selected from anionic or cationic surfactants and betaines.

Due to the improved suspending effect provided by the composition of the present invention in an injection fluid that contains particles such as proppants, encapsulated chain breakers, preformed gel, nanogel, or microgel particles, which particles tend to be more stable in the injection fluid, and precipitation is greatly reduced.

In a third aspect, the present invention provides a method for treating a section of a subterranean formation, comprising providing a composition of the present invention, obtaining an injected fluid with at least said composition, introducing the injected fluid into a section of a subterranean formation.

Treating a section of a subterranean formation includes treating a portion of the subterranean formation or treating the entire subterranean formation.

In a fourth aspect, the present invention provides a method of fracturing comprising providing a composition of the present invention, producing a fracturing fluid with at least said composition and with at least a proppant, introducing the fracturing fluid into a section of a subterranean formation.

In a fifth aspect, the present invention provides a polymer injection method comprising providing a composition of the present invention, producing a polymer injection fluid with at least said composition, introducing the polymer injection fluid into an entire subterranean formation or section thereof.

In a sixth aspect, the present invention provides a method for improving the effect of providing suspension in an injected fluid, including providing a composition of the present invention, obtaining an injected fluid by mixing said composition with water, sea water or brine, introducing the injected fluid into the entire subterranean formation or its section. The water-based treatment fluid may be a fracturing fluid or an injected polymer injection fluid.

More specifically, the present invention provides a method for improving the effect of providing suspension in an injected fluid, including providing a composition of the present invention, obtaining an injected fluid by mixing said composition with water, sea water or brine, where the resulting injected fluid is characterized by an improvement in the effect of providing suspension compared to the same injected fluid, in which the composition of the present invention is replaced by an identical composition, except that the polymers do not contain cationic monomer units in accordance with the present invention.

The composition of the present invention can also be used in any subsurface treatment such as drilling operations, stimulation treatments, completion operations, and oil recovery enhancement processes.

In a preferred embodiment, the present invention provides a fracturing method comprising:

a. providing a composition of the present invention;

b. adding said composition to a water-based fluid to form an injection fluid;

c. adding at least a proppant to the injected fluid either before or after step b;

d. introducing the injected fluid into a section of the subterranean formation;

e. fracturing a section of a subterranean formation with an injected fluid;

f. removal of a mixture of gas, oil and water-based fluid.

The composition of the present invention can also advantageously be used in the paper industry, in the water or waste water treatment industry, in the construction industry, in the mining industry, in the cosmetics, textile or detergent industry, in agriculture, in civil engineering work.

The present invention will be further described with reference to the following examples. The following examples are merely illustrative of the present invention and are not intended to be limiting. Unless otherwise indicated, all percentages are by weight (wt%).

Examples

Inverse emulsion of polymer A

Method for obtaining an inverse emulsion

To a 1000 ml beaker was added 365.33 g of a 50% acrylamide solution, 266.67 g of DMAEA.MeCl and 136.74 g of deionized water. The pH was maintained at 4.5. 0.4 g of Versenex 80 and 1.98 g of sodium bromate solution were added to the aqueous phase . In the reactor, an organic phase was obtained by adding 175.1 grams of Exxsol D100S and 25 grams of sorbitan monooleate. The aqueous phase was added to the reactor at 500 rpm using a crescent-shaped stirrer. An emulsion was formed by using a high shear mixer.

Oxygen present in the emulsion was removed by purging with nitrogen for 30 min. The temperature of the emulsion was raised and set at 22°C before polymerization. To initiate polymerization, the mixture was stirred at 400 rpm and MBS was added dropwise at a rate of 0.5 ml per minute. The temperature was raised and maintained at 50° C. until a decrease in temperature was noted. 30 g of nonylphenol-9-ethoxylates were added to the emulsion with stirring at 30°C. EMI1 - EMI 6 was obtained using the same synthesis protocol, adjusting the compositions of the monomers, as presented in table 1.

EMI 6 was subjected to polymerization such that all polymerization steps were carried out at a pressure of 80 mbar.

Table 1. Chemical composition of emulsions

Solid particles

Method for obtaining solid particles

a) Polymerization step

To a 2000 ml beaker was added 670.2 g of deionized water, 1015.4 g of 50% acrylamide (AM) solution, and 171 g of 80% DMAEA⋅MeCl solution. pH was 3.4–3.8.

The solution thus obtained was cooled to 0-5° C. and transferred to adiabatic conditions for a polymerization reaction. Nitrogen bubbling was performed for 30 min to remove any trace amounts of oxygen.

The following compounds were added to the reactor:

• 1 g 2,2'-azobis(2-methylpropionitrile) AZDN

• 2 ml ammonium persulfate at a concentration of 2 g/l

• 2.5 ml solution of ammonium-iron(II) sulfate hexahydrate (Mohr's salt) at a concentration of 2 g/l.

After a few minutes the reactor was closed. The duration of the reaction was from 2 to 5 hours until the maximum temperature was reached. After standing overnight, the polymer gel was removed from the reactor and then cut into small pieces of gel with a particle size ranging from 1 to 6 mm.

Table 2. Chemical composition of the granular polymer

Obtaining small polymer particles

A grinder was used to reduce particle size, then a sieve was used to obtain particles smaller than 350 µm, and a typical particle size distribution was as follows: D (10) 72.3 µm, D (50) 133 µm, D (90) 225 µm. Fine particles F1 - F3 were obtained in accordance with the indicated method from the corresponding powders P1 - P3.

Getting the composition (solid particles + inverse emulsion)

The compositions were prepared by incorporating small particles into an emulsion with magnetic stirring at 500 rpm for 10 minutes. Table 3 describes the compositions of 8 compositions, with 5 examples in accordance with the present invention and 3 comparative examples. The compositions contain 90 wt% inverse emulsion and 10 wt% solids.

Table 3 Compositions of compositions

General Procedures for Evaluating Viscosity and Suspension Effect

Polymer solutions were obtained that matched the exemplary injection fluids by adding the required amount of compositions 1-8 under shear conditions to achieve an active polymer concentration of 5040 ppm in 400 ml of API brine. API saline contains 85 g/L NaCl and 33 g/L CaCl2⋅2H2O in deionized water. The solution was then stirred for 30 minutes at 500 rpm.

The rheological properties were evaluated at 25° C. using an Anton Paar MCR302 rheometer equipped with a cone-plane measuring system, stainless steel, 50 mm and 2°. Both the viscosity (η) and the first normal stress difference (N1) were recorded by plotting a rheological curve over a shear rate range of 0.1-50 s ^-1 . The viscoelastic properties were evaluated on the same equipment by measuring the dependence of the viscoelastic properties on the oscillation amplitude in the linear viscoelasticity mode. The modulus of elasticity (G') and the modulus of viscosity (G'') were recorded in the frequency range of 0.1-10 Hz at 10% stretch.

Rheological measurements were used to determine the following parameters.

- Fluid viscoelastic relaxation time:

.

.

- The value of λe _/v :

.

.

- Theoretical sedimentation velocity of sand particles at rest (d: 0.86 mm, Δρ: 1650 kg/m ³ , g: 9.81 m/s², K and n are coefficients in the power law of viscosity, from 100 to 400 s ^{- 1} ):

.

.

results

Evaluation of compositions 1-8 in API saline

Using the flow and oscillation data, the value of λ _e/v at a shear rate of 500 s ^-1 can be calculated. If λ _e/v > 1, then the elastic characteristics prevail in the system, while satisfactory properties of providing suspension are manifested. On the contrary, if λ _e/v < 1, then the system is dominated by viscous characteristics, while exhibiting poor suspending properties.

For formulations 1-8, the measured data are summarized in Table 4. Viscosity, settling rate, relaxation time, and λ _e/v show better suspending properties for all examples compared to comparative examples.

Table 4. Rheological measurements in API brine

The composition of the present invention (2, 3, 6, 7, 8) showed good results in comparison with comparative examples (1, 4, 5), for which the results were poor. Compositions 2 and 3, characterized by the amount of DMAEA⋅MeCl in the range of the present invention (10-40 mol.%), gave good results compared to the poor results of compositions 1 and 4, in which the content of DMAEA⋅MeCl is outside this range.

The results are good when the cationicity of the inverse emulsion polymer is higher than the cationicity of the particulate polymer (composition 3), while the results are poor when the cationicity of the inverse emulsion polymer is lower than the cationicity of the particulate polymer (composition 5).

The results are even better when the molecular weight of the emulsion polymer is lower than the molecular weight of the particulate polymer (formulation 2 compared to composition 6 and composition 3 compared to composition 7).

The results are further improved when the inverse emulsion is made under vacuum (formulation 8 versus composition 3).

Claims (31)

1. Composition for producing an injected fluid for oil and gas production, containing - an inverse emulsion of water-soluble polymer A containing cationic monomer units, and - solid particles of water-soluble polymer B containing cationic monomer units, and while the water-soluble polymer A contains from 10 to 40 mol.% cationic monomer units, calculated on the total number of monomer units, and the cationicity in mol.% of polymer A is greater than or equal to the cationicity in mol.% of polymer B. 2. The composition of claim. 1, where polymer A contains from 15 to 40 mol.% cationic monomer units. 3. The composition according to claim 1, wherein polymer B contains from 2 to 30 mole % of cationic monomer units. 4. The composition of claim 1, wherein the mol% cationicity of polymer A is at least 5% higher than the mol% cationicity of polymer B. 5. The composition of claim. 1, where the average molecular weight of polymer A and polymer B is from 2 million g/mol to 20 million g/mol. 6. The composition of claim 1 wherein the weight average molecular weight of water soluble polymer A is lower than the weight average molecular weight of water soluble polymer B. 7. The composition of claim 1, wherein the weight ratio of polymer A inverse emulsion to polymer B solids is between 1:1 and 10:1. 8. The composition of claim. 1, where the total concentration of polymer A and polymer B in the composition is from 30 wt.% to 80 wt.%. 9. The composition of claim 2 wherein the cationic monomer is selected from the group consisting of dimethylaminoethyl acrylate (DMAEA) quaternized or salified, dimethylaminoethyl methacrylate (DMAEMA) quaternized or salified, diallyldimethylammonium chloride (DADMAC), acrylamidepropyltrimethylammonium chloride (APTAC), methacrylamidopropyltrimethylammonium chloride (MAPTAC). 10. The composition of claim 1 wherein the cationic monomer is dimethylaminoethyl acrylate (DMAEA) quaternized or salified. 11. The composition of claim 1, wherein polymer A and polymer B further comprise additional nonionic monomers and/or anionic monomers and/or zwitterionic monomers. 12. The composition of claim. 1, where polymer B is a copolymer of dimethylaminoethyl acrylate (DMAEA), quaternized or converted into a salt, and acrylamide, while the amount of DMAEA is from 2 to 30 mol.%, and the amount of acrylamide is from 70 to 98 mol .%. 13. Composition according to claim 1, wherein polymer B is a terpolymer of dimethylaminoethyl acrylate (DMAEA), quaternized or salted, acrylamide and one of the two following monomers: acrylic acid and/or its salt(s) or acrylamide-tert-butylsulfonic acid (ATBS) and/or its salt(s), and at the same time - the amount of DMAEA is from 2 to 30 mol.%, - the amount of acrylic acid and/or its salt(s) or acrylamide-tert-butylsulfonic acid (ATBS) and/or its salt(s) is from 0.5 to 10 mol%, and - the amount of acrylamide is an additional amount to achieve a total amount of 100 mol.%. 14. The composition of claim. 1, where polymer A is a copolymer of dimethylaminoethyl acrylate (DMAEA), quaternized or converted into a salt, and acrylamide, and the amount of DMAEA is from 10 to 40 mol.%, and the amount of acrylamide is from 60 to 90 mol.%. 15. Composition according to claim 1, wherein polymer A is a terpolymer of dimethylaminoethyl acrylate (DMAEA), quaternized or salted, acrylamide and one of the two following monomers: acrylic acid and/or its salt(s) or acrylamide-tert-butylsulfonic acid (ATBS) and/or its salt(s), and at the same time - the amount of DMAEA is from 2 to 30 mol.%, - the amount of acrylic acid and/or its salt(s) or acrylamide-tert-butylsulfonic acid (ATBS) and/or its salt(s) is from 0.5 to 10 mol%, and - the amount of acrylamide is an additional amount to achieve a total amount of 100 mol.%. 16. Composition according to claim. 1, where the inverse emulsion is obtained by polymerization carried out partially or completely at a pressure ranging from 0.1 to 200 mbar. 17. The composition of claim. 1, where the solid particles of water-soluble polymer B are in the form of a powder, fine particles, granules or beads. 18. Injectable fluid obtained by mixing water or brine with a composition according to any one of paragraphs. 1-17, where in the specified injected fluid, the total amount of polymer A and polymer B is from 0.0005 wt.% to 1 wt.%. 19. A method of treating a section of an underground formation, including providing a composition according to any one of paragraphs. 1-17, producing an injection fluid using at least said composition and introducing the injection fluid into a section of a subterranean formation. 20. A method of fracturing a formation, including providing a composition according to any one of paragraphs. 1-17, producing a fracturing fluid using at least said composition and at least a proppant, and introducing the fracturing fluid into a section of a subterranean formation. 21. The method of injection of the polymer, including providing the composition according to any one of paragraphs. 1-17, producing a polymer injection fluid using at least said composition, and introducing the polymer injection fluid into an entire subterranean formation or portion thereof. 22. A method for improving the effect of providing suspension in the injected fluid, including providing a composition according to any one of paragraphs. 1-17, producing an injection fluid by mixing said composition with water, sea water, or brine and injecting the injection fluid into the entire subterranean formation or portion thereof.