阅读说明：本技术 用于水力压裂的反相乳液 (Inverse emulsion for hydraulic fracturing ) 是由 C·法维罗 O·布劳恩 B·塔维涅尔 于 2020-03-27 设计创作，主要内容包括：本申请涉及油包水反相乳液及其用于水力压裂的用途,该油包水反相乳液包含：-油；-水；-至少一种平均摩尔质量大于3百万道尔顿的水溶性阳离子共聚物,其包含18-32摩尔％的阳离子单体和68-82摩尔％的非离子单体；-至少一种反转剂和至少一种乳化剂,反转剂总量与乳化剂总量的质量比R大于1.8,-该反转剂选自优选具有4-10个乙氧基化的乙氧基化壬基酚；优选具有乙氧基化/丙氧基化以具有C12-C25的总碳数的乙氧基化/丙氧基化醇,乙氧基化十三醇和乙氧基化/丙氧基化脂肪醇,-该乳化剂选自单油酸脱水山梨糖醇酯,聚乙氧基化脱水山梨糖醇酯或者妥尔油脂肪酸的二乙醇酰胺。(The present application relates to a water-in-oil invert emulsion comprising: -an oil; -water; -at least one water-soluble cationic copolymer having an average molar mass greater than 3 million daltons, comprising from 18 to 32 mole% of cationic monomer and from 68 to 82 mole% of nonionic monomer; -at least one inverting agent and at least one emulsifier, the mass ratio R of the total amount of inverting agent to the total amount of emulsifier being greater than 1.8, -the inverting agent being chosen from ethoxylated nonylphenols preferably having from 4 to 10 ethoxylations; preferably ethoxylated/propoxylated alcohols having an ethoxylation/propoxylation to have a total carbon number of C12-C25, ethoxylated tridecyl alcohol and ethoxylated/propoxylated fatty alcohols, the emulsifier being selected from sorbitan monooleate, polyethoxylated sorbitan esters or the diethanolamide of tall oil fatty acids.)

1. A water-in-oil invert emulsion comprising:

-an oil;

-water;

-at least one water-soluble cationic copolymer having an average molar mass, preferably a weight average molar mass, greater than 3 million daltons, comprising from 18 to 32 mole% of cationic monomer and from 68 to 82 mole% of nonionic monomer;

-at least one inversion agent and at least one emulsifier, the mass ratio R of the total amount of inversion agent to the total amount of emulsifier being greater than 1.8,

omicron the inverter is selected from ethoxylated nonylphenol, preferably having 4-10 ethoxylations; preferably ethoxylated/propoxylated alcohols having a total carbon number of ethoxylated/propoxylated to have a carbon number of C12-C25, ethoxylated tridecyl alcohol and ethoxylated/propoxylated fatty alcohols,

omicron the emulsifier is selected from sorbitan monooleate, polyethoxylated sorbitan ester, or diethanolamide of tall oil fatty acid.

2. An emulsion according to claim 1, characterized in that the emulsion comprises 12 to 50 mass%, preferably 12 to 40 mass%, even more preferably 12 to 30 mass% of at least one water-soluble polymer.

3. An emulsion according to claim 1 or 2, characterized in that the mass ratio R of the total amount of inverting agent to the total amount of emulsifier is greater than 2, even more preferably greater than 2.5, even more preferably greater than 3, even more preferably greater than 3.5, even more preferably greater than 4.

4. An emulsion according to any of claims 1 to 3, characterized in that the nonionic monomer of the water-soluble cationic copolymer is selected from the group consisting of acrylamide, methacrylamide, N-alkylacrylamide, N-alkylmethacrylamide, N, N-dialkylacrylamide, N, N-dialkylmethacrylamide, acrylates; a methacrylate ester; of these, acrylamide is the preferred monomer.

5. Emulsion according to any one of claims 1 to 4, characterized in that the cationic monomer of the water-soluble cationic copolymer is selected from dimethylaminoethyl acrylate (ADAME) or quaternary ammonium salts thereof, dimethylaminoethyl methacrylate (MADAME) or quaternary ammonium salts thereof, dimethyldiallylammonium chloride (DADMAC), acrylamidopropyltrimethylammonium chloride (APTAC) and methacrylamidopropyltrimethylammonium chloride (MAPTAC)), preferably the quaternary ammonium salt of the monomer ADAME or MADAME is obtained by quaternization with an alkyl chloride, preferably methyl chloride, preferably the cationic monomer is dimethylaminoethyl acrylate quaternised with methyl chloride.

6. An emulsion according to any one of claims 1 to 5, characterized in that the water-soluble cationic polymer has an average molar mass of 3 to 30 million daltons, preferably 8 to 18 million daltons.

7. An emulsion according to any one of claims 1 to 6, characterized in that the emulsion comprises 0.5 to 10 mass% of the inverter and 0.5 to 16 mass% of the emulsifier.

8. A method of preparing a fracturing fluid, comprising:

a) providing an inverse emulsion according to any one of claims 1 to 7,

b) inverting the inverse emulsion by adding the inverse emulsion to brine comprising greater than 30,000ppm of salt and a divalent ratio R⁺≥0.15，R⁺The mass ratio is as follows: the divalent salt/total salt ratio is such that,

c) optionally, at least one proppant is added.

9. Method of preparing a fracturing fluid according to claim 8, characterized in that for step b) the brine contains more than 70,000ppm of salt and preferably more than 100,000ppm of salt.

10. Method for preparing a fracturing fluid according to claims 8 and 9, characterized in that for step b) the brine has a divalent ratio R⁺Not less than 0.20, preferably R⁺≥0.25。

11. A method of preparing a fracturing fluid according to claims 8-10, comprising:

a) providing an inverse emulsion according to the invention comprising at least 12-30 mass% of a water-soluble cationic copolymer comprising 18-32 mol% dimethylaminoethyl acrylate quaternized with methyl chloride and 68-82 mol% acrylamide; at least one reversal agent and at least one emulsifier, the mass ratio R of the total quantity of reversal agent to the total quantity of emulsifier is more than 2.5,

b) inverting the inverse emulsion by adding the inverse emulsion to brine comprising greater than 100,000ppm of salt and a divalent ratio R⁺≥0.2，R⁺The mass ratio is as follows: divalent salt/total salt to obtain a mass concentration of the water-soluble cationic copolymer in the injection fluid of 0.05-1%,

c) optionally, at least one proppant is added.

12. A method of fracturing a subterranean formation comprising:

aa) providing a fracturing fluid obtained according to the preparation process of claims 8 to 11,

bb) introducing the injection fluid into a portion of the subterranean formation,

cc) fracturing the subterranean formation with the injection fluid,

dd) recovering the mixture of gas, oil and aqueous fluid.

13. A method of reducing the friction of a fracturing fluid in a hydraulic fracturing operation of an unconventional oil or gas subterranean reservoir comprising preparing a fracturing fluid according to claims 8 and 11 and injecting the fracturing fluid into a subterranean formation.

Technical Field

The present invention relates to the technical field of polymers in the form of water-in-oil emulsions (also known as inverse emulsions). More particularly, the present invention relates to an inverse emulsion comprising a cationic polymer that is stable under very high salinity conditions.

Other aspects of the invention relate to methods for preparing fracturing fluids and hydraulic fracturing of unconventional oil and gas subterranean reservoirs (r é s) using the invert emulsion, and finally, a final aspect of the invention relates to methods of reducing fracturing fluid friction in hydraulic fracturing operations.

Background

The production of oil (hydrocarbons) and gas in unconventional subterranean reservoirs has developed over the years and it is necessary to open fractures in the reservoir to achieve economical production of hydrocarbons.

In the prior art and the following description of the invention, "unconventional subterranean reservoirs" are used to refer to mineral layers that require special mining techniques because they do not exist in heaped form in porous and permeable rocks (see Les hydrocarbuere de roche-m [ re en France Rapport provisos ire-CGIET No. 2011-04-G-minimum [ re de l' cool rock, des transports et du location-year 4.2011). Unconventional gas includes shale gas (english "coal gas"), coal bed methane (english "coal methane"), and dense gas (english "light gas"). Unconventional oils include heavy oil ("heavy oil" in english), shale oil ("shale oil" in english), and dense oil ("light oil" in english).

Unconventional reservoirs contain vast reserves and are extremely widespread in previously unexploited areas (e.g., bedrock such as shale hydrocarbons, tight gas and coal bed methane). Shale gas is widely mined in the united states and currently accounts for 46% of the total gas production in the united states, while it accounts for only 28% in 1998. Very large basins are known as Barnett shale, Ville Fayette shale, Mowry shale, Marcellus shale, Utica shale, etc. The development of drilling technology has made it possible to produce tight reservoirs.

In fact, production technology has evolved from vertical wells to horizontal wells, reducing the number of production wells required and their footprint, and allowing better coverage of the reservoir volume for recovery of as much natural gas as possible. However, insufficient permeability does not allow easy migration of gas from the matrix into the well and thus economical, high volume production of gas or oil. It is therefore necessary to increase the permeability and the production face by stimulation operations and in particular by hydraulic fracturing of the rock in contact with the well.

Hydraulic fracturing

The purpose of hydraulic fracturing is to create additional permeability and create a larger gas or oil production zone. This is because the low permeability, the natural barrier of the tight formation and the impermeability of the drilling operation greatly limit the production. The gas or oil contained in the unconventional reservoir cannot easily migrate from the rock into the well without stimulation measures.

These horizontal well hydraulic fracturing operations began in the 1960's applacaches and several tens of thousands of operations have been performed in the united states today.

The techniques of research, reservoir modeling, drilling, cementing and stimulation are becoming more complex and use equipment that allows these operations to be performed in shorter and shorter times and accurately analyze the results.

Stimulation of a reservoir by hydraulic fracturing

These operations consist in injecting water at high pressure and very high flow rates to create fractures distributed perpendicular to the production well. This is typically done in several steps to create fractures along the entire length of the horizontal well to cover the maximum volume of the reservoir.

To keep these fractures open, proppants (e.g., sand, plastic, or gradient ceramic) are added to prevent these fractures from closing and to maintain capillary action once the injection stops.

To reduce the hydraulic power required to rapidly inject water or brine into a subterranean formation, polymers known as friction reducers de frictions are used. The use of such polymers enables pressure losses due to internal friction of the fluid to be reduced by up to 70%.

Polymers in the form of inverse emulsions are commonly used because of their ease of implementation. Their use is based on the dissolution of the polymer in water or saline. To this end, the inverse emulsion is inverted so that the polymer contained in the aqueous phase of the inverse emulsion is released. After release, the polymer is in water or saline to which an inverse emulsion is added.

Fracturing fluids are increasingly based on water containing large amounts of dissolved salts. In this context, there is a need in the industry for friction reducers that work effectively in high brine (brine with high concentrations of dissolved salts), some of which may contain over 30,000mg.l^-1Even more than 100,000mg.l of dissolved salts of^-1Especially with a high content of divalent salts.

Disclosure of Invention

The applicant has surprisingly found that a water-in-oil invert emulsion of specific composition provides excellent performance in friction reduction under very high salinity conditions with a high content of divalent salts.

The invention also relates to a method for preparing a fracturing fluid by using the emulsion.

A third aspect of the invention relates to a hydraulic fracturing method wherein an injection fluid has been prepared according to the aforementioned inventive method.

Finally, a final aspect of the invention relates to a method of reducing fracturing fluid friction in a hydraulic fracturing operation using the emulsion of the invention.

More specifically, the present invention relates firstly to a water-in-oil invert emulsion comprising:

-an oil;

-water;

-at least one water-soluble cationic copolymer having an average molecular weight greater than 3 million daltons, comprising from 18 to 32 mole% of cationic monomer and from 68 to 82 mole% of nonionic monomer;

-at least one inversion agent and at least one emulsifier, the mass ratio R of the total amount of inversion agent to the total amount of emulsifier being greater than 1.8,

o the inverting agent is selected from ethoxylated nonylphenols preferably having 4-10 ethoxylations; ethoxylated/propoxylated alcohols, ethoxylated tridecanol and ethoxylated/propoxylated fatty alcohols having an ethoxylated/propoxylated total carbon number to have a C12-C25 are preferred.

Omicron the emulsifier is selected from sorbitan monooleate, polyethoxylated sorbitan ester, or diethanolamide of tall oil fatty acid.

The oil used to prepare the water-in-oil emulsion of the present invention may be a mineral oil, a vegetable oil, a synthetic oil or a mixture of a plurality of these oils. Examples of mineral oils are mineral oils comprising saturated hydrocarbons of the aliphatic, naphthenic, paraffinic, isoparaffinic, cyclic paraffinic or napthalenyl type. Examples of synthetic oils are hydrogenated polydecenes or hydrogenated polyisobutenes, esters such as octyl stearate or butyl oleate. Of ExxonThe product family is very suitable.

Generally, the weight ratio of the aqueous phase to the oil phase in the inverse emulsion is preferably from 50/50 to 90/10, preferably from 70/30 to 80/20.

The water-in-oil emulsion advantageously comprises 12 to 24% by weight, more advantageously 15 to 22% by weight of oil.

The water-in-oil emulsion advantageously comprises from 30 to 55% by weight, more advantageously from 35 to 48% by weight, of water.

The term "water-soluble polymer" as used herein refers to a polymer that when dissolved with stirring at 25 ℃ for 4 hours and at a concentration in water of 20g.L-1, produces an aqueous solution free of insoluble particles.

In the present invention, the term "emulsifier" refers to an agent capable of emulsifying water in oil, and "inverter" is an agent capable of emulsifying oil in water. More specifically, the inverter is considered to be a surfactant having an HLB of greater than or equal to 10, and the emulsifier is considered to be a surfactant having an HLB strictly less than 10.

The hydrophilic-lipophilic balance (HLB) of a compound is a measure of its degree of hydrophilicity or lipophilicity, and is determined by calculating the values of different regions of the molecule, as described by Griffin in 1949 (Griffin WC, Classification of Surface-Active Agents by HLB, Journal of the Society of Cosmetic Chemists,1949,1, p. 311-326).

In the present invention, we have used the Griffin method based on the value calculations based on the chemical groups of the molecule. Griffin specifies a dimensionless number between 0 and 20 to provide information about solubility in water and oil. The substance with HLB value 10 is distributed between the two phases so that the hydrophilic groups (molecular weight Mh) are fully extended into the water, while the hydrophobic hydrocarbon groups (molecular weight Mp) are adsorbed in the non-aqueous phase.

The HLB value of substances whose hydrophilic part has a molecular weight Mh and whose total molecular weight is M is:

HLB＝20(Mh/M)

the water-in-oil emulsion according to the present invention may be prepared according to any method known to the person skilled in the art. Typically, an aqueous solution comprising monomers and an emulsifier is emulsified in the oil phase. The polymerization is then carried out by adding a free radical initiator. Reference may be made to the redox couple, among which oxidizing agents are cumene hydroperoxide, tert-butyl hydroperoxide or persulphate, and among reducing agents are sodium sulphite, sodium metabisulphite and Mohr's salt. Azo compounds, such as 2,2 '-azobis (isobutyronitrile) hydrochloride and 2, 2' -azobis (2-amidinopropane) hydrochloride, may also be used.

Typically, the polymerization is carried out isothermally, adiabatically or at a controlled temperature. That is, the temperature is kept constant, typically 10-60 ℃ (isothermal), or the temperature is allowed to rise naturally (adiabatic) and in this case the reaction is usually started at a temperature below 10 ℃ and the final temperature is usually above 50 ℃, or finally the temperature rise is controlled so that the temperature curve is between the isothermal and adiabatic curves.

Typically, the inverter is added at the end of the polymerization reaction, preferably at a temperature below 50 ℃.

Preferably, the emulsion of the invention comprises from 12 to 50 mass%, preferably from 12 to 40 mass%, even more preferably from 12 to 30 mass% of water-soluble polymer (dry weight).

According to another preference, the mass ratio R of the total amount of inverting agent to the total amount of emulsifier for the emulsion of the invention is greater than 1.8, preferably greater than 2, even more preferably greater than 2.5, even more preferably greater than 3, even more preferably greater than 3.5, even more preferably greater than 4.

The water-soluble cationic polymer contained in the emulsion of the present invention is a copolymer of nonionic and cationic monomers.

The nonionic monomer is preferably selected from the group consisting of acrylamide, methacrylamide, N-alkylacrylamide, N-alkylmethacrylamide, N-dialkylacrylamide, N-dialkylmethacrylamide, acrylates and methacrylates. The preferred nonionic monomer is acrylamide.

The cationic monomer is preferably selected from dimethylaminoethyl acrylate (ADAME) or a quaternary ammonium salt thereof, dimethylaminoethyl methacrylate (MADAME) or a quaternary ammonium salt thereof, dimethyldiallylammonium chloride (DADMAC), acrylamidopropyltrimethylammonium chloride (APTAC) and methacrylamidopropyltrimethylammonium chloride (MAPTAC). Preferably, the quaternary ammonium salt of the monomer ADAME or MADAME is obtained by quaternization with an alkyl chloride, preferably methyl chloride. The preferred cationic monomer is dimethylaminoethyl acrylate quaternized with methyl chloride.

A variety of nonionic and cationic monomers can be selected to form the cationic copolymer. Advantageously, the water-soluble cationic polymer is a copolymer of acrylamide and dimethylaminoethyl acrylate quaternized with methyl chloride.

The water-soluble cationic polymer has an average molecular weight greater than 3 million daltons. Preferably, this average molecular weight is between 3 and 30 million daltons, even more preferably between 8 and 18 million daltons.

The "average molecular weight" according to the invention is determined by the intrinsic viscosity. Intrinsic viscosity can be measured by methods known to those skilled in the art and can be calculated from reduced viscosity values of different concentrations, in particular by a graphical method consisting in plotting the reduced viscosity value (on the y-axis) as a function of concentration (on the x-axis) and extrapolating the curve to zero concentration. The intrinsic viscosity values are read on the y-axis or using the least squares method. The weight average molecular weight can then be determined by the well-known Mark-Houwink equation:

[η]＝KM^α

[ eta ] is the intrinsic viscosity of the polymer measured by the solution viscosity method,

k is an empirical constant that is calculated by,

m is the molecular weight of the polymer,

alpha is Mark-Houwink coefficient

Alpha and K depend on the particular polymer-solvent system.

The emulsion of the present invention preferably contains 0.5 to 10 mass% of an inverter and 0.5 to 16 mass% of an emulsifier.

The water-in-oil emulsion advantageously comprises from 0.8 to 2% by weight of at least one emulsifier.

The water-in-oil emulsion advantageously comprises 3 to 6% by weight of at least one inversion agent.

Optionally, the water-in-oil emulsion comprises 1-40 wt% salt, preferably 3-30 wt%, more preferably 5-25 wt% and even more preferably 7-17 wt% salt.

The salts present in the water-in-oil emulsion may be, for example, sodium, lithium, potassium, magnesium, aluminum, ammonium, phosphate, sulfate, chloride, citrate, acetate, tartrate, water-soluble or other inorganic salts and mixtures thereof. These salts include sodium chloride, sodium sulfate, sodium bromide, calcium chloride, ammonium sulfate, ammonium chloride, lithium bromide, potassium chloride, potassium bromide, magnesium sulfate, aluminum sulfate, sodium hydrogen phosphate, potassium hydrogen phosphate, and mixtures thereof. Sodium chloride, calcium chloride, ammonium sulfate are preferred, and further a mixture thereof is preferred.

Another aspect of the invention relates to a method of preparing a fracturing fluid comprising:

a) there is provided an inverse emulsion according to the present invention,

b) inverting the inverse emulsion by adding the inverse emulsion to a brine (salt) that contains greater than 30,000ppm of salt and a divalent ratio R⁺≥0.15，R⁺The mass ratio is as follows: the divalent salt/total salt ratio is such that,

c) optionally, at least one proppant is added.

Total salt refers to the total amount of salt in the brine.

The brine may comprise monovalent and/or multivalent salts or combinations thereof. Examples of salts include, but are not limited to, sodium, lithium, potassium, aluminum, ammonium, phosphate, sulfate, magnesium, barium, nitrate and other inorganic salts and mixtures thereof.

The brine preferably comprises at least one of the following components: sodium chloride, calcium chloride, sodium bromide, calcium bromide, barium chloride, magnesium chloride, zinc bromide, sodium formate, and potassium formate.

Preferably the brine used to prepare the fracturing fluid comprises more than 70,000ppm salt and preferably more than 100,000ppm salt, preferably the brine comprises 70,000-350,000ppm salt, preferably 100,000-350,000ppm salt.

According to an advantageous embodiment of the method for preparing a fracturing fluid:

when the brine contains from 30,000ppm to 70,000ppm (excluding the upper limit) of salt (step b), the ratio R of the emulsion (step a) is preferably greater than 1.8,

when the brine comprises from 70,000ppm to 100,000ppm (excluding the upper limit), the ratio R of the emulsion is preferably greater than 2,

when the brine contains 100,000ppm to 150,000ppm (excluding the upper limit) of salt, the ratio R of the emulsion is preferably greater than 2.5,

when the brine contains from 150,000ppm to 200,000ppm (excluding the upper limit) of salt, the ratio R of the emulsion is preferably greater than 3,

when the brine comprises from 200,000ppm to 250,000ppm (excluding the upper limit) of salt, the ratio R of the emulsion is preferably greater than 3.5, and

when the brine contains more than 250,000ppm (excluding the upper limit) of salt, the ratio R of the emulsion is preferably more than 4.

Preferably, the divalent ratio R⁺The mass ratio is as follows: divalent salt/total salt greater than or equal to 0.20, even more preferably R⁺≥0.25。

The inversion of the emulsion of the invention in saline water can advantageously be achieved by the device and process of document US 8383560, wherein the emulsion is continuously dissolved with a multiple static mixer arrangement.

The invention also relates to a fracturing fluid obtained by the method of the invention, in particular a fracturing fluid comprising:

-a saline solution;

-a water-soluble cationic (co) polymer according to the invention;

-the oil of the inverse emulsion of the invention;

-water.

The proppant may be selected from, without limitation, sand, ceramic, bauxite, glass beads, and resin-impregnated sand. It preferably constitutes from 0.5 to 40%, more preferably from 1 to 25%, even more preferably from 1.5 to 20% by weight of the fracturing fluid.

The fracturing fluid according to the invention preferably comprises from 0.01% to 3% by weight and even more preferably from 0.05% to 1% by weight of a water-soluble cationic (co) polymer of the invention (added in the form of an emulsion).

The brine making up the fracturing fluid may contain other compounds known to those skilled in the art, such as those listed in SPE 152596, for example:

clay anti-swelling agents, such as potassium chloride or choline chloride, and/or

Biocides to prevent the growth of bacteria, in particular sulfate-reducing bacteria, which can form sticky substances that reduce the surface of the channels. Examples include the most commonly used glutaraldehyde, or formaldehyde or isothiazolinone, and/or

Oxygen reducing agents, such as ammonium bisulphite, to avoid oxidative destruction of other components and corrosion of injection lines, and/or

Anti-corrosion additives to prevent oxidation of the pipes by residual amounts of oxygen, preferably N, N dimethylformamide, and/or

Lubricants, such as petroleum fractions, and/or

Iron chelators, such as citric acid, EDTA (ethylenediaminetetraacetic acid), phosphonates, and/or

Anti-fouling products, such as phosphates, phosphonates, polyacrylates or glycols.

According to a preferred embodiment, the method of preparing a fracturing fluid comprises:

a) providing an inverse emulsion according to the invention comprising at least 12-30 mass% of a water-soluble cationic copolymer comprising 18-32 mol% dimethylaminoethyl acrylate quaternized with methyl chloride and 68-82 mol% acrylamide; at least one reversal agent and at least one emulsifier, the mass ratio R of the total quantity of reversal agent to the total quantity of emulsifier is more than 2.5,

b) inverting the inverse emulsion by adding the inverse emulsion to brine comprising greater than 100,000ppm of salt and a divalent ratio R⁺≥0.2，R⁺The mass ratio is as follows: divalent salt/total salt to obtain a mass concentration of water-soluble cationic copolymer in the injection fluid of 0.05-1%.

c) Optionally, at least one proppant is added.

A third aspect of the invention relates to a method for hydraulically fracturing an unconventional oil or gas subterranean reservoir comprising preparing a fracturing fluid as described above and injecting the fracturing fluid into a subterranean formation.

More particularly, the present invention relates to a method of fracturing a subterranean formation comprising:

aa) providing a fracturing fluid obtained according to the above preparation method,

bb) introducing the injection fluid into a portion of the subterranean formation,

cc) fracturing the subterranean formation with the injection fluid,

dd) recovering the mixture of gas, oil and aqueous fluid.

The injection is performed under pressure to create fractures distributed along the length of the production well.

Optionally, after creating the fracture, at least one oxidizing compound and/or at least one surfactant compound is injected into the reservoir.

Injection of these compounds enables the fluid viscosity to be restored close to that of water.

Examples of oxidizing compounds are bleaching agents (aqueous solutions of hypochlorites), hydrogen peroxide, ozone, chloramines, persulfates, permanganates or perchlorates.

The chemical type of surfactant is not critical. They may be anionic, nonionic, amphoteric, zwitterionic, and/or cationic. Preferably, the surface-active compounds of the present invention carry an anionic charge.

Preferably, the surface-active compounds used are selected from anionic surfactants and their zwitterions, selected from the group comprising derivatives of: alkyl sulfates, alkyl ether sulfates, arylalkyl ether sulfates, alkyl sulfonates, alkyl ether sulfonates, arylalkyl ether sulfonates, alkyl phosphate, alkyl ether phosphates, arylalkyl ether phosphates, alkyl phosphonates, alkyl ether phosphonates, arylalkyl ether phosphonates, alkyl carboxylates, alkyl ether carboxylates, arylalkyl ether carboxylates, polyalkyl ethers and arylalkyl polyethers.

Finally, a fourth and final aspect of the invention relates to a method for reducing the friction of a fracturing fluid in a hydraulic fracturing operation of an unconventional oil or gas subterranean reservoir, comprising preparing a fracturing fluid as described above and injecting said fracturing fluid into a subterranean formation.

Friction reduction enables friction related losses during injection of the fracturing fluid to be reduced or eliminated.

For hydraulic fracturing, friction reduction involves the polymer in the fracturing fluid providing rheological fluidization (rhe of the fractures) properties to the solution, allowing it to have a relatively low viscosity during injection (under high shear) and a high viscosity when the shear is reduced to keep the proppant suspended at the fracture.

Detailed Description

The invention and the advantages resulting therefrom will become apparent from the following examples.

Examples

Example 1 (counter example): emulsion comprising 20% by weight of a polymer containing 15 mol% of cationic monomers

The aqueous phase was prepared with 27.00 wt% acrylamide solution (50 wt% in water), 8.12 wt% ADAME-MC solution (methyl chloride quaternized dimethylaminoethyl, 80 wt% in water), 39.87 wt% deionized water, and 0.02 wt% Versenex 80.

The oil phase was prepared from the following: 23.45% by weight of oil (C)D100S) and the following emulsifiers: 1.16% by weight of(tall oil fatty acid diethanolamine), 0.16% by weight80 (sorbitan monooleate) and 0.23% by weight81 (sorbitan monooleate 5 EO).

The aqueous phase was added to the oil phase while mixing to form an emulsion. The resulting dispersion was bubbled with nitrogen for 30 minutes while the temperature was stabilized at 25 ℃, at which time 0.002 wt% peroxide was added to the emulsion and 0.075 wt% sodium Metabisulfite (MBS) solution was introduced into the dispersion at a flow rate of 0.1 ml/min. The polymerization temperature was controlled at 38 ℃ to 42 ℃ for about 90 minutes. Residual monomer was captured by introducing a 0.03 wt% sodium Metabisulfite (MBS) solution at a rate of 1.0 ml/min. A water-in-oil polymer emulsion containing 20% of a living copolymer of acrylamide and ADC was obtained.

1.75% by weight of an inverter (NP 8, nonylphenol polyglycol ether 8OE) is added to the water-in-oil polymer emulsion to facilitate conditioning during use. The mass ratio R was 1.5.

Example 2 (counter example): emulsion comprising 20% by weight of a polymer containing 20 mol% of cationic monomers

The aqueous phase was prepared with 23.78 wt% acrylamide solution (50 wt% in water), 10.14 wt% ADAME-MC solution (methyl chloride quaternized dimethylaminoethyl, 80 wt% in water), 41.08 wt% deionized water, and 0.02 wt% Versenex 80.

The oil phase was prepared from the following: 23.45% by weight of oil (C)D100S) and the following emulsifiers: 1.16% by weight of(tall oil fatty acid diethanolamine), 0.16% by weight80 (sorbitan monooleate) and 0.23% by weight81 (sorbitan monooleate 5 EO).

The aqueous phase was added to the oil phase while mixing to form an emulsion. The resulting dispersion was bubbled with nitrogen for 30 minutes while the temperature was stabilized at 25 ℃, at which time 0.002 wt% peroxide was added to the emulsion and a 0.075 wt% Sodium Metabisulfite (SMBS) solution was introduced into the dispersion at a flow rate of 0.1 ml/min. The polymerization temperature was controlled at 38 ℃ to 42 ℃ for about 90 minutes. Residual monomer was captured by introducing a 0.03 wt% Sodium Metabisulfite (SMBS) solution at a rate of 1.0 ml/min. A water-in-oil polymer emulsion containing 20% of a living copolymer of acrylamide and ADAME-MC was obtained.

1.75% by weight of an inverter (NP 8, nonylphenol polyglycol ether 8OE) is added to the water-in-oil polymer emulsion to facilitate conditioning during use. The mass ratio R was 1.5.

Example 3 (counter example): emulsion comprising 20% by weight of a polymer containing 35 mol% of cationic monomers

The aqueous phase was prepared with 16.20 wt% acrylamide solution (50 wt% in water), 14.87 wt% ADAME-MC solution (methyl chloride quaternized dimethylaminoethyl, 80 wt% in water), 43.92 wt% deionized water, and 0.02 wt% Versenex 80.

The oil phase was prepared from the following: 23.45% by weight of oil (C)D100S) and the following emulsifiers: 1.16% by weight of(tall oil fatty acid diethanolamine), 0.16% by weight80 (sorbitan monooleate) and 0.23% by weight81 (sorbitan monooleate 5 EO).

The aqueous phase was added to the oil phase while mixing to form an emulsion. The resulting dispersion was bubbled with nitrogen for 30 minutes while the temperature was stabilized at 25 ℃, at which time 0.002 wt% peroxide was added to the emulsion and a 0.075 wt% Sodium Metabisulfite (SMBS) solution was introduced into the dispersion at a flow rate of 0.1 ml/min. The polymerization temperature was controlled at 38 ℃ to 42 ℃ for about 90 minutes. Residual monomer was captured by introducing a 0.03 wt% Sodium Metabisulfite (SMBS) solution at a rate of 1.0 ml/min. A water-in-oil polymer emulsion containing 20% of a living copolymer of acrylamide and ADC was obtained.

1.75% by weight of an inverter (NP 8, nonylphenol polyglycol ether 8OE) is added to the water-in-oil polymer emulsion to facilitate conditioning during use. The mass ratio R was 1.5.

The following examples are carried out with a mass ratio R according to the invention. Examples 4 and 7, then examples 5 and 8, and finally examples 6 and 9 were made using the same procedure as examples 1, 2 and 3, but using higher amountsNP 8 (reversal agent). Table 1 describes the mass ratio R of each example.

[ Table 1]

Table 1: mass ratio of water-in-oil emulsion R

Friction flow loop test

The tribological flow circuit was constructed of 1/4 "od stainless steel tubing having a total length of 20 feet. The test solution was pumped to the bottom of a 5 liter conical tank. The solution passes through the tube and returns to the tank. The flow is obtained by a three-cylinder pump equipped with a variable speed drive.

4 liters of 9% CaCl are prepared in a sample tank₂Brine, or API or 2xAPI brine, and the pump was started and set to deliver 1.5 gallons per minute. 9% of CaCl₂Saline corresponds to 9g of CaCl in 100ml of water₂R of which⁺Is 1.00. API brine is defined as 8.5g NaCl +2.5g CaCl in 100ml water₂R of which⁺Equal to 0.20. 2xAPI saline corresponds to 17g NaCl +5g CaCl in 100ml water₂R of which⁺Equal to 0.20. The brine solution was recirculated until the temperature equilibrated to 25 ℃ and a steady pressure differential was reached. This pressure was recorded as 9% CaCl₂Or "initial pressure" of API or 2xAPI brines "。

A test amount of water-in-oil emulsion polymer was rapidly injected with a syringe into a bottle containing 9% CaCl₂Or API or 2xAPI brine, and a timer is started. The dosage is 9% CaCl per thousand gallons₂Or gallons (gpt) of water-in-oil emulsion of API or 2xAPI brine. The pressure was recorded every second for 5 minutes. The percent friction reduction (% FRt) for a given time "t" is calculated from the initial pressure drop Δ Pi and the pressure drop Δ Pt for time t using the following equation:

results

In table 2, all emulsions contained 20 wt% cationic polymer.

[ Table 2]

The results show that the friction reducing performance is improved when the mass ratio R is increased. The friction reducing properties decrease with increasing salt concentration.

However, when the mass ratio R is chosen and adjusted (within the scope of the invention), very good tribological properties can be obtained in saline water, even in high-saline water.

When the cationicity of the polymer is 20 mol%, the friction reducing property is improved. Lower cationicity (15%) and higher cationicity (35%) provide lower performance.