CN112358864A

CN112358864A - Nano emulsion acid system and preparation method and application thereof

Info

Publication number: CN112358864A
Application number: CN202011275235.3A
Authority: CN
Inventors: 韩庆建; 孙新元; 任平平; 孙志强; 孙春同
Original assignee: Dongying Spring Petroleum Engineering Technology Co ltd
Current assignee: Dongying Spring Petroleum Engineering Technology Co ltd
Priority date: 2020-11-13
Filing date: 2020-11-13
Publication date: 2021-02-12
Anticipated expiration: 2040-11-13
Also published as: CN112358864B

Abstract

The invention relates to the field of working fluid for oil and gas reservoir transformation, and discloses a nano emulsion acid system and a preparation method and application thereof. The system comprises an oil phase, acid, a cationic gemini surfactant, a nonionic surfactant, a high-temperature resistant viscoelastic polymer, an iron ion stabilizer, inorganic salt and water; the high-temperature-resistant viscoelastic polymer comprises a structural unit A shown in a formula (1), a structural unit B shown in a formula (2) and a structural unit C shown in a formula (3), wherein the structural percentages are p, q and r respectively, and p is 31.26-51.25%, q is 45.71-61.27%, r is 4.08-6.01%, the sum of p, q and r is 1, and z is 12, 14, 16 or 18; the system has the advantages of high temperature resistance, shear resistance, high permeability and simple field construction;

Description

Nano emulsion acid system and preparation method and application thereof

Technical Field

The invention relates to the field of working fluid for oil and gas reservoir transformation, in particular to a nano emulsion acid system and a preparation method and application thereof.

Background

With the increase of the demand of oil and gas resources and the development of exploration and development technologies, the development of low-permeability carbonate rock oil and gas resources is gradually emphasized. In recent years, a batch of deep and ultra-deep carbonate rock oil and gas reservoirs are discovered in China in succession, and great development potential is shown. In general, a carbonate oil and gas reservoir lateral stratum has the characteristics of strong heterogeneity, high ground temperature, deep burial, low permeability and the like, is difficult to develop, and generally needs to be transformed to obtain industrial oil and gas flow. The importance of the acidification technology as a main yield-increasing transformation technology and an effective means suitable for carbonate reservoirs is increasingly highlighted.

The conventional acidizing fluid has the problems of low viscosity, strong corrosion to tools, limited action distance and the like, so that a retarding acid fluid system with low corrosion and low acid rock reaction rate is needed to be used in the high-temperature carbonate reservoir transformation. How to improve the viscosity of the acid liquor and reduce the mass transfer speed between acid liquor protons and the casing pipe and the well wall is a key problem related to the research and exploration of an acid liquor system. The main retarding acids at present comprise emulsified acid and thickening acid, and have better acidification effect on medium, high and even low permeability with cracks.

The thickening acid is mainly prepared by adding a thickening agent into an acid solution, and the commonly used thickening agent mainly comprises a natural high polymer, a synthetic high polymer, a viscoelastic surfactant and the like. However, natural high molecular polymers, such as cellulose and its derivatives, have poor temperature resistance, and can only be applied in low temperature, low shear environment, and are currently applied in a few applications. However, synthetic high molecular polymers and viscoelastic surfactants tend to have problems of large dosage and high cost.

CN102453480A discloses a clean thickening acid for acid fracturing of carbonate reservoir, which comprises 3 to 7 weight percent of hexadecyl trimethyl ammonium bromide, 0.3 to 0.7 weight percent of sodium ortho-hydroxybenzoate, 15 to 28 weight percent of hydrochloric acid, an iron ion stabilizer of citric acid, CX-301 or TW-1, and 0.125 to 0.25 weight percent of citric acid; CX-301: 0.05-0.1%, TW-1: 0.3 to 0.5 percent; 0.2-0.25% of bisimidazoline quaternary ammonium salt, and the balance of water: the sum of the weight percentages of the components is 100 percent. The viscoelastic surfactant cetyl trimethyl ammonium bromide is used as a thickening agent, so that the price is high, and the viscoelastic surfactant cetyl trimethyl ammonium bromide has micro toxicity and limits popularization.

CN102994070A discloses a preparation process of a polymer acid thickener, which comprises the following steps: (a) dissolving polyvinyl, pyrrolidone and a cross-linking agent in a solution, and adding the solution into a reactor in which an organic solvent and an initiator exist; (b) heating to a certain temperature and keeping; (c) then continuously heating to a certain temperature, and keeping the temperature to prepare a polymer; (c) precipitating, filtering and drying to obtain the final product. The preparation process of the polymer acid thickener based on the polyethylene, the pyrrolidone and the cross-linking agent is simple in process and good in product performance stability, but the synthesis temperature is high, so that the large-scale application is limited.

Emulsified acids are generally water-in-oil systems, and the acid reaction rate is slowed down by using an oil phase to prevent the acid phase from contacting with the rock, but some disadvantages exist: the thermodynamic property is unstable, and the temperature resistance and salt tolerance are insufficient; the friction resistance is large, and the construction is limited; the penetration of the emulsified acid is poor due to the giardia effect. The microemulsion acid is a clear and transparent thermodynamic stable system formed by oil, acid, surfactant and cosurfactant, and has a particle size of about 10-100 nm. Due to the special structure, the microemulsion acid becomes a deep penetration retarded acid which can not only keep the advantages of the emulsion acid, but also overcome the defects of the emulsion acid, and has the problems of strong sensitivity, poor temperature resistance (generally not exceeding 100 ℃) and the like.

With the deepening of the knowledge of the sustained-release acid and the expansion of the field application of the sustained-release acid technology, the requirement on the sustained-release acid is continuously improved, and the requirements are mainly reflected in the aspects of the viscosity, the stability, the sustained-release performance and the like of the acidizing fluid. Particularly, the deep well temperature of many marine phase reservoirs such as Sichuan basin, Tarim basin, Ordos basin and the like in the low-permeability carbonate rock oil and gas reservoir is over 150 ℃, and higher requirements on temperature resistance are provided.

Therefore, the development of an acidizing fluid with better performance has become one of the research hotspots in the field of acidizing and production increasing.

Disclosure of Invention

The invention aims to overcome the defect that the temperature resistance, viscosity, penetrability and economy of the conventional acidizing fluid cannot be considered at the same time, and provides a nano emulsion acid system and a preparation method and application thereof. The system has the advantages of high temperature resistance, high viscosity and good retarding effect, and is simple in site construction.

In order to achieve the above object, the present invention provides in a first aspect a nanoemulsion acid system, wherein the system comprises an oil phase, an acid, a cationic gemini surfactant, a nonionic surfactant, a high temperature resistant viscoelastic polymer, an iron ion stabilizer, an inorganic salt and water;

wherein the high-temperature-resistant viscoelastic polymer comprises a structural unit A shown in a formula (1), a structural unit B shown in a formula (2) and a structural unit C shown in a formula (3);

wherein the structural percentages of structural units a, B and C are p, q and r, and p is 31.26-51.25%, q is 45.71-61.27%, r is 4.08-6.01%, and the sum of p, q and r is 1;

wherein, in formula (3), z is 12, 14, 16 or 18.

In a second aspect, the present invention provides a method for preparing the aforementioned nanoemulsion acid system, wherein the method includes:

(1) carrying out first contact on acid and an aqueous solution of inorganic salt to obtain a first solution;

(2) carrying out second contact on the high-temperature-resistant viscoelastic polymer and the first solution to obtain a second solution;

(3) carrying out third contact on a cationic gemini surfactant and an iron ion stabilizer with the second solution to obtain a polar phase;

(4) fourthly, the oil phase is contacted with the nonionic surfactant to obtain a nonpolar phase;

(5) and slowly dripping the non-polar phase into the polar phase for fifth contact to obtain a nano emulsion acid system.

The third aspect of the invention provides an application of the nano emulsion acid system in the acidizing and fracturing reformation of the oil and gas reservoir.

Through the technical scheme, the invention has the following technical characteristics and beneficial effects:

(1) the particle size of the nano-emulsion acid system is close to that of the micro-emulsion acid, and the dosage of the surfactant is lower, so that the nano-emulsion acid system has the characteristics similar to that of the micro-emulsion acid: lower proton mass transfer speed, extremely high stability, better penetrability make nanoemulsion acid can act on farther distance, improve nanoemulsion acid's availability factor, possess the characteristic different from microemulsion acid simultaneously: the nano emulsion acid system has the advantages of lower cost, lower temperature, mineralization degree and component sensitivity, so that the nano emulsion acid system can face more complicated formation conditions, and the application range of the nano emulsion acid system is expanded. The technical bottleneck that the micro-emulsion acid has good slow release effect, but does not resist temperature and salt, and the polymer slow release acid possibly has the characteristics of temperature resistance and salt tolerance, but the slow release effect is not as good as the micro-emulsion acid is broken through.

(2) The cationic gemini surfactant with a positive polar end is adopted, so that the water-in-oil structure of the microemulsion acid system is more stable, and the microemulsion acid system has more excellent temperature resistance.

(3) The high-temperature resistant viscoelastic polymer and the surfactant have a synergistic effect, and simultaneously have a temperature-increasing association effect, so that the stability of a temperature-resistant system and the temperature-resistant viscosity stability of a nano emulsion acid system are improved, and the nano emulsion acid system can resist the temperature of 150 ℃; the apparent viscosity at 30 ℃ reaches 160 mPas, the apparent viscosity at 60 ℃ reaches 151 mPas, the apparent viscosity at 90 ℃ reaches 131 mPas, the apparent viscosity at 120 ℃ reaches 124 mPas, and the apparent viscosity at 150 ℃ reaches 107 mPas.

(4) The preparation process has reliable principle, simple preparation, easily obtained materials and low cost, and can meet the requirements of on-site acidification construction.

Drawings

Fig. 1 is a graph showing the change in acid solubility of the acid systems of the nano-emulsion prepared in example 1, comparative example 2 and comparative example 6 of the present invention.

Detailed Description

The endpoints of the ranges and any values disclosed herein are not limited to the precise range or value, and such ranges or values should be understood to encompass values close to those ranges or values. For ranges of values, between the endpoints of each of the ranges and the individual points, and between the individual points may be combined with each other to give one or more new ranges of values, and these ranges of values should be considered as specifically disclosed herein.

The invention provides a nanoemulsion acid system in a first aspect, wherein the system contains an oil phase, acid, a cationic gemini surfactant, a nonionic surfactant, a high-temperature resistant viscoelastic polymer, an iron ion stabilizer, inorganic salt and water;

wherein, in formula (3), z is 12, 14, 16 or 18.

According to the present invention, in formula (3), z is preferably 16.

The inventors of the present invention found that: the microemulsion acid in the prior art has good slow release effect, but does not resist temperature and salt, while the polymer slow release acid may have the characteristics of temperature resistance and salt tolerance, but has inferior slow release effect to the microemulsion acid. The inventor of the invention carries out special design on the characteristics of the emulsion and the polymer on the basis of fully researching the application requirement of the acidizing fluid, the colloid interface chemistry and the polymer chemistry, so that the prepared polymer has high temperature resistance, high viscosity and excellent retarding effect.

According to the invention, p is preferably 34.23 to 48.1%, q is 46.26 to 60.24%, r is 4.28 to 5.64%, and the sum of p, q and r is 1.

According to the invention, the high temperature resistant viscoelastic polymer is preferably a sodium acrylate-acrylamide-hexadecyl allyl dimethyl ammonium chloride triblock copolymer.

According to the present invention, the weight average molecular weight of the high-temperature resistant viscoelastic polymer is preferably 11 to 15 ten thousand, and specifically, may be any value in a range of 11 ten thousand, 11.5 ten thousand, 12 ten thousand, 12.5 ten thousand, 13 ten thousand, 13.5 ten thousand, 14 ten thousand, 14.5 ten thousand, 15 ten thousand, or any two of these points, for example.

According to the invention, the high-temperature resistant viscoelastic polymer can be synthesized by a laboratory, and specifically, the synthesis method comprises the following steps:

(1) dissolving a monomer A, a monomer B and a monomer C in deionized water, then adding a sodium hydroxide solution with the concentration of 5mol/L, and adjusting the pH to 4-5;

(2) setting the water bath temperature to be 60-65 ℃, and sequentially assembling a three-neck flask, an electric stirrer, a constant-pressure dropping funnel, a condensing tube and other reaction devices; transferring the sodium acrylate, the acrylic acid and the hydrophobic monomer solution into a three-neck flask, and stirring by adopting an electric stirrer at the stirring speed of 400-450 r/min;

(3) introducing nitrogen to remove oxygen, respectively weighing ammonium persulfate and sodium bisulfite with equal mass, and preparing the ammonium persulfate and the sodium bisulfite with deionized water into aqueous solution with the mass concentration of 1-1.5%, preparing to form initiator solution, and dropwise adding the initiator solution into a three-neck flask by using a constant-pressure dropping funnel until the mass of the ammonium persulfate and the sodium bisulfite accounts for 0.2-0.3% of the total mass of the reaction monomer;

(3) after the dropwise addition is finished, the rotating speed is maintained unchanged, after the reaction is carried out for 6-6.5 hours at the set temperature, the faint yellow slightly viscous liquid is cooled to the room temperature and then is purified for 3-5 times by acetone, and the high-temperature retarder for well cementation, namely the high-temperature resistant viscoelastic polymer, is obtained.

Wherein the monomer A is acrylic acid and has a structure shown in a formula (5); the monomer B is acrylamide and has a structure shown in a formula (6); the monomer C is a hydrophobic monomer and has a structure shown in a formula (7);

wherein, in formula (7), z is 12, 14, 16 or 18;

wherein the monomers A, B and C are used in such amounts that the structural percentages of the structural units A, B and C contained in the high temperature resistant viscoelastic polymer are p, q and r, and p is 31.26-51.25%, q is 45.71-61.27%, r is 4.08-6.01%, and the sum of p, q and r is 1;

according to the invention, the monomers A, B and C are used in a weight ratio of 1: (1.47-1.85): (0.11-0.18); preferably 1: (1.6-1.7): (0.13-0.16).

In the invention, the high-temperature viscoelastic polymer contains a structural unit A, wherein the structural unit A contains unsaturated carboxylic acid groups with carboxyl functional groups, so that the polymer has better water solubility in a high-temperature environment; the high-temperature viscoelastic polymer contains a structural unit B, wherein the structural unit B contains an amide group, so that the rigidity and the steric hindrance effect of a molecular chain of the high-temperature viscoelastic polymer can be improved, and the temperature resistance and the salt resistance can be improved; the high-temperature viscoelastic polymer contains a structural unit C with a hydrophobic group with a long hydrophobic chain, and the hydrophobic groups on each molecular chain can be mutually associated under the action of hydrophobic force to form a space network structure, so that the viscoelasticity of the solution is improved; wherein the monomer having a hydrophobic group with a long hydrophobic chain is a quaternary ammonium salt hydrophobic monomer group having a long carbon chain, the number of the long chain alkyl groups is an even number of 12 to 18, and the hydrophobicity of the monomer is increased as the length of the long chain alkyl group increases (z value increases).

In the present invention, the weight ratio of the cationic gemini surfactant, the nonionic surfactant and the high temperature resistant viscoelastic polymer is 1: 1: (0.02-0.1); the high-temperature-resistant viscoelastic polymer has both a hydrophilic group (unsaturated carboxylic acid group) and a hydrophobic group (long-chain alkane group), has certain surface activity, can form a film with a surfactant in a synergistic manner, and has high strength and a synergistic effect because the molecular weight of the viscoelastic polymer is large and the molecules have high rigidity; meanwhile, the high-temperature-resistant viscoelastic polymer has a certain proportion of hydrophobic groups, and in the temperature rise process, the hydrophobic groups are opened and spread in the oil phase to form a spatial network structure in the continuous oil phase, and the 'temperature-raising hydrophobic association' action is generated in the water phase, so that the viscosity is improved, and the viscoelasticity of the system is ensured. Through the action, the stability of the emulsion temperature-resistant system and the stability of temperature-resistant viscosity are improved, and the high-temperature polymer thickening nanoemulsion acid system can resist the temperature of 150 ℃.

According to the invention, in the nano emulsion acid system, the oil phase accounts for 20-40 parts by weight, the acid accounts for 25-45 parts by weight, the cationic gemini surfactant accounts for 3-7 parts by weight, the nonionic surfactant accounts for 3-7 parts by weight, the high temperature resistant viscoelastic polymer accounts for 0.1-0.6 part by weight, the iron ion stabilizer accounts for 0.3-1.2 parts by weight, the inorganic salt accounts for 0.5-4 parts by weight, and the water accounts for 5-12 parts by weight.

Preferably, in the nano emulsion acid system, the oil phase is 25 to 30 parts by weight, the acid is 30 to 40 parts by weight, the cationic gemini surfactant is 3 to 5 parts by weight, the nonionic surfactant is 3 to 5 parts by weight, the high temperature resistant viscoelastic polymer is 0.2 to 0.5 part by weight, the iron ion stabilizer is 0.5 to 1 part by weight, the inorganic salt is 0.6 to 1 part by weight, and the water is 10 to 12 parts by weight.

In the invention, the components and the component content are controlled within the range, especially the dosage of the cationic gemini surfactant and the nonionic surfactant is low, and the application cost of the nano emulsion acid can be effectively reduced.

According to the present invention, the cationic gemini surfactant has a structure represented by formula (4):

wherein n is 12, 14, 16 or 18; m is 3, 4, 5, 6; (ii) a X is halogen;

preferably, n-16 or 18; m is 3 or 4; and X is Cl or Br.

In the invention, the cationic gemini surfactant is a quaternary ammonium salt gemini surfactant which has a positively charged polar end and a double oleophylic group structure, so that the emulsibility and the temperature resistance of the nano emulsion can be greatly improved, and finally the water-in-oil structure of the nano emulsion acid system is more stable.

According to the invention, the oil phase is selected from one or more of diesel oil, white oil and vegetable oil; preferably diesel oil; more preferably, the diesel is selected from one or more of-20 diesel, -10 diesel and 0 diesel.

According to the invention, the acid is hydrochloric acid and/or earth acid, preferably hydrochloric acid, more preferably the concentration of the hydrochloric acid is 30%, and even more preferably the hydrochloric acid is industrial hydrochloric acid with the concentration of 30%.

According to the invention, the non-ionic surfactant is selected from one or more of Span20, Span40 and Span 60; wherein Span20, Span40 and Span60 are all polyol esters, Span20 is Span20, Span40 is Span40, and Span60 is Span 60. In the present invention, the nonionic surfactant can be purchased from the chinese medicinal group.

According to the invention, the iron ion stabilizer is citric acid and/or disodium ethylene diamine tetraacetate (EDTA disodium salt), and in the invention, the iron ion stabilizer is used for preventing the pH value of emulsified acid from being reduced after the emulsified acid reacts in a stratum to cause the contained iron ions to form Fe (OH)₃The precipitation causes pollution.

According to the invention, the inorganic salt is sodium chloride and/or potassium chloride, preferably sodium chloride.

According to the invention, the water is tap water (clean water).

According to the invention, the average particle size of the system is 50-230nm, preferably 120-220nm, more preferably 139-216 nm; in the invention, the average particle size of the system is measured by scanning with an electron microscope and analyzing with image analysis software.

According to the invention, the viscosity of the system is 107-160 mPa.s at the temperature of 120-150 ℃; in the present invention, the viscosity of the system is measured using a high temperature high pressure rheometer.

According to the invention, under the conditions that the pressure is-10 MPa and the temperature is 60-150 ℃, the system has no delamination; has high temperature stability.

In a second aspect, the present invention provides a method for preparing a nanoemulsion acid system, wherein the method comprises:

(5) and slowly dripping the nonpolar phase into the polar phase under the stirring condition, and carrying out fifth contact to obtain a nanoemulsion acid system.

According to the invention, z is preferably 16.

According to the invention, the weight ratio of the non-ionic surfactant, the cationic gemini surfactant and the high temperature resistant viscoelastic polymer is 1: 1: (0.1-0.6), preferably 1: 1: (0.2-0.5).

According to the present invention, in the step (2), the conditions of the second contacting include: under the condition of 40-60 ℃, firstly stirring for 10-30min under the stirring condition of 800-; preferably, the mixture is stirred for 15-25min under the stirring condition of 900-1100r/min and then stirred for 0.8-1.2h under the stirring condition of 180-250r/min at the temperature of 45-50 ℃.

According to the present invention, in the step (3), the conditions of the third contacting include: stirring for 5-15min under the stirring condition of 150-; preferably, stirring is carried out for 8-12min under the stirring condition of 180-250 r/min.

According to the present invention, in the step (4), the conditions of the fourth contact include: stirring for 5-15 mins under the stirring condition of 150-; preferably, stirring is carried out for 8-12min under the stirring condition of 180-250 r/min.

According to the present invention, in the step (5), the conditions of the fifth contacting include: stirring for 80-100min under the stirring conditions that the temperature is 40-65 ℃ and the stirring speed is 150-300 r/min. Preferably, the stirring is carried out for 80-90min under the stirring conditions that the temperature is 45-55 ℃ and the stirring speed is 180-250 r/min. In addition, in the fifth contacting of the polar phase with the non-polar phase, the polar phase is preferably added dropwise to the non-polar phase at a dropping rate of 4 to 6 mL/min.

According to the invention, the conditions for acidizing, fracturing and reforming the oil and gas reservoir comprise: the depth is within 7000m under the conventional condition.

The present invention will be described in detail below by way of examples.

In the following examples and comparative examples:

(1) stability test

And (3) placing the nano emulsion acid system in an acid-resistant reaction kettle, sealing at room temperature (25 ℃) and normal pressure, and observing whether each sample is layered or not in the long-term storage process.

(2) High temperature test

The nano emulsion acid system is placed in a high-temperature high-pressure visible reaction kettle for sealing, and 5 groups of temperature/pressure conditions are set: 30 ℃/0.1Mpa, 60 ℃/10Mpa, 90 ℃/20Mpa, 120 ℃/30Mpa and 150 ℃/40Mpa, and whether each sample is layered at different temperatures is observed.

(3) Viscosity measurement

Placing the nano emulsion acid system in a high-temperature high-pressure visible reaction kettle, sealing and pressurizing, and setting 5 groups of temperature/pressure conditions: 30 ℃/0.1Mpa, 60 ℃/10Mpa, 90 ℃/20Mpa, 120 ℃/30Mpa and 150 ℃/40Mpa, and the viscosity of each sample is tested at different temperatures/pressures.

(4) High temperature creep performance test

Measuring a certain amount of nano emulsion acid at normal temperature, placing the nano emulsion acid in an aging tank, and placing the core in a high-temperature and high-pressure aging tank, wherein the nano emulsion and the core in the aging tank are provided with an interlayer. And (3) heating to 120 ℃, enabling the nano emulsion acid to contact and react with the rock core, taking out the rock core at regular time, drying, weighing, and calculating the rock core corrosion rate at different time.

(5) The industrial hydrochloric acid is a product sold in market by Weifang Hengfeng chemical Limited company; sodium chloride was analytically pure and purchased from the national pharmaceutical group; the cationic gemini surfactant is purchased from Haian petrochemical, is reagent grade, and has an effective content of more than 80%.

Preparation example 1

This preparation is intended to illustrate the high temperature resistant viscoelastic polymers prepared according to the invention.

(1) Respectively weighing 41.4 parts of acrylamide, 52 parts of acrylic acid and 6 parts of hydrophobic monomer, dissolving in deionized water, wherein the total mass concentration of all the monomers is 35%, then adding a sodium hydroxide solution with the concentration of 5mol/L, and adjusting the pH value to 4; wherein, the structural formula of the hydrophobic monomer is as follows:

(2) the temperature of the water bath is set to be 60 ℃, and the three-neck flask, the electric stirrer, the constant-pressure dropping funnel, the condensing tube and other reaction devices are assembled in sequence. Transferring the sodium acrylate, the acrylic acid and the hydrophobic monomer solution into a three-neck flask, and stirring by using an electric stirrer at the stirring speed of 400 r/min;

(3) introducing nitrogen to remove oxygen, respectively weighing ammonium persulfate and sodium bisulfite with equal mass, and preparing the ammonium persulfate and the sodium bisulfite with deionized water into an aqueous solution with the mass concentration of 1.0 percent to prepare an initiator solution, and dropwise adding the initiator solution into a three-neck flask by using a constant-pressure dropping funnel until the mass of the ammonium persulfate and the sodium bisulfite accounts for 0.2 percent of the total mass of the reaction monomer;

(3) after the dropwise addition, maintaining the rotation speed unchanged, reacting for 6 hours at a set temperature, cooling the faint yellow slightly viscous liquid to room temperature, and purifying for 3 times by using acetone to obtain the high-temperature retarder for well cementation, namely the high-temperature resistant viscoelastic polymer marked as Z1.

The high temperature resistant viscoelastic polymer Z1 has the structure:

wherein, p is 34.23%, q is 60.24%, r is 5.53%; and

the weight average molecular weight of the high temperature retarder S1 was 11 ten thousand.

Preparation example 2

A high temperature resistant viscoelastic polymer was prepared in the same manner as in example 1, except that: the structural formula of the hydrophobic monomer is as follows:

the result is a high temperature viscoelastic polymer, designated Z2.

Wherein, the high-temperature retarder Z2 has the structure as follows:

wherein, p is 45.57%, q is 55.21%, r is 4.28%; and

the weight average molecular weight of the high temperature retarder S1 was 13 ten thousand.

Preparation example 3

A high temperature viscoelastic polymer was prepared in the same manner as in example 1, except that: weighing acrylamide, acrylic acid and hydrophobic monomer according to the weight ratio

The result was a high temperature retarder, designated Z3.

Wherein, the high temperature retarder S3 has the structure as follows:

wherein, p is 48.1%, q is 46.26%, r is 5.64%; and

the weight average molecular weight of the high temperature retarder S3 was 15 ten thousand.

Example 1

This example is presented to illustrate a nanoemulsion acid system prepared using the method of the present invention.

The nano-emulsion acid system prepared in the embodiment is prepared from the following raw materials in parts by weight:

28 parts by weight of No. 10 diesel oil;

35 parts by weight of industrial hydrochloric acid with the concentration of 37%;

12 parts by weight of tap water;

0.6 part of sodium chloride and 1.14 percent of polar phase concentration;

1 part by weight of iron ion stabilizer (specifically citric acid) accounts for 1.90 percent of the mass ratio of the polar phase;

4 parts of cationic gemini surfactant (specifically quaternary ammonium salt gemini surfactant, n is 16, m is 3, and X is Cl) by weight, accounting for 7.60% of the mass ratio of the polar phase;

4 parts by weight of a nonionic surfactant, namely polyol ester Span 20;

the high-temperature resistant viscoelastic polymer prepared in the preparation example 1 accounts for 0.3 weight part and accounts for 0.57 mass percent of the polar phase;

the weight ratio of the dosage of the nonionic surfactant, the cationic gemini surfactant and the high-temperature resistant viscoelastic polymer is 1: 1: 0.3.

specifically, the preparation method comprises the following steps:

(1) dissolving an inorganic salt in tap water at a ratio as listed in example 1 at room temperature (25 ℃) to prepare an aqueous solution of the inorganic salt, and then mixing hydrochloric acid with the aqueous solution of the inorganic salt to obtain a first solution;

(2) adding the high-temperature-resistant viscoelastic polymer prepared in the preparation example 1 into the first solution in a water bath at 50 ℃, stirring at a high speed of 1000r/min for 30min, and then stirring at a low speed of 200r/min for 1h to obtain a second solution;

(3) adding a cationic gemini surfactant and an iron ion stabilizer into the second solution at room temperature (25 ℃), and stirring at a low speed of 200r/min for 5min to obtain a polar phase;

(4) adding diesel oil into another slurry cup at room temperature (25 ℃), adding nonionic surfactant into the diesel oil, and stirring at low speed of 200r/min for 5min to obtain a nonpolar phase;

(5) slowly dripping the polar phase into the non-polar phase at the dripping speed of 5mL/min in a water bath at 50 ℃, stirring at a low speed of 200r/min in the dripping process, and continuing stirring for 30min after dripping is finished to prepare a nano emulsion acid system.

The mean particle size of the nanoemulsion acid system prepared as a result was 184 nm.

Example 2

A nanoemulsion acid system was prepared in the same manner as in example 1, except that:

30 parts by weight of No. 10 diesel oil;

30 parts by weight of industrial hydrochloric acid with the concentration of 37%;

10 parts by weight of tap water;

0.5 part by weight of sodium chloride, and the concentration of a polar phase is 1.13%;

0.5 part of iron ion stabilizer (specifically citric acid) accounting for 1.13 percent of the mass ratio of the polar phase;

3 parts of cationic gemini surfactant (specifically quaternary ammonium salt gemini surfactant, n is 16, m is 3, and X is Cl) by weight, accounting for 6.79% of the mass ratio of the polar terms;

3 parts by weight of a nonionic surfactant, namely polyol ester Span 20;

the high-temperature resistant viscoelastic polymer prepared in the preparation example 2 accounts for 0.2 part by weight and accounts for 0.45 percent of the mass ratio of the polar phase;

the weight ratio of the dosage of the nonionic surfactant, the cationic gemini surfactant and the high-temperature resistant viscoelastic polymer is 1: 1: 0.2.

the mean particle size of the nanoemulsion acid system prepared as a result was 139 nm.

Example 3

25 parts by weight of No. 10 diesel oil;

10 parts by weight of tap water;

0.8 part of sodium chloride and 1.69 percent of polar phase concentration;

1 part by weight of iron ion stabilizer (specifically citric acid) accounts for 2.11 percent of the mass ratio of the polar phase;

5 parts by weight of cationic gemini surfactant (specifically quaternary ammonium salt gemini surfactant, n is 16, m is 3, and X is Cl) accounting for 10.55% of the mass ratio of the polar phase;

5 parts by weight of a nonionic surfactant, namely polyol ester Span 20;

the high-temperature resistant viscoelastic polymer prepared in preparation example 3 accounts for 0.4 weight part and accounts for 0.84 percent of the mass ratio of the polar phase;

the weight ratio of the dosage of the nonionic surfactant, the cationic gemini surfactant and the high-temperature resistant viscoelastic polymer is 1: 1: 0.4.

as a result, the average particle size of the prepared nanoemulsion acid system was 174 nm.

Example 4

30 parts by weight of No. 10 diesel oil;

40 parts by weight of industrial hydrochloric acid with the concentration of 31 percent;

10 parts by weight of tap water;

1 part by weight of sodium chloride, and the concentration of a polar phase is 1.75 percent;

1 part by weight of iron ion stabilizer (specifically citric acid) accounts for 1.75 percent of the mass ratio of the polar phase;

5 parts of cationic gemini surfactant (specifically cationic gemini surfactant, n is 16, m is 3, and X is Cl) accounting for 8.73% of the mass ratio of the polar terms;

5 parts by weight of a nonionic surfactant, namely polyol ester Span 20;

the high-temperature resistant viscoelastic polymer prepared in preparation example 3 accounts for 0.5 weight part and accounts for 0.87 mass percent of the polar phase;

the weight ratio of the dosage of the nonionic surfactant, the cationic gemini surfactant and the high-temperature resistant viscoelastic polymer is 1: 1: 0.5.

the mean particle size of the nanoemulsion acid system prepared as a result was 216 nm.

Example 5

28 parts by weight of No. 10 diesel oil;

12 parts by weight of tap water;

0.6 part of sodium chloride and 1.14 percent of polar phase concentration;

4 parts of cationic gemini surfactant (specifically quaternary ammonium salt gemini surfactant, n is 18, m is 4, and X is Br) by weight, accounting for 7.60% of the mass ratio of the polar phase;

4 parts by weight of a nonionic surfactant, namely polyol ester Span 20;

comparative example 1

A nanoemulsion acid system was prepared in the same manner as in example 1, except that: the high temperature resistant viscoelastic polymer prepared in preparation example 1 was not added.

As a result, the average particle size of the prepared nanoemulsion acid system was 124 nm.

Comparative example 2

A nanoemulsion acid system was prepared in the same manner as in example 1, except that: the content of each component is not within the range defined by the invention, and specifically:

50 parts by weight of No. 10 diesel oil;

20 parts by weight of industrial hydrochloric acid with the concentration of 37%;

10 parts by weight of tap water;

0.5 part by weight of sodium chloride, and the concentration of a polar phase is 1.46 percent;

0.5 part of iron ion stabilizer (specifically citric acid) accounting for 1.46 percent of the mass ratio of the polar phase;

3 parts of cationic gemini surfactant (specifically cationic gemini surfactant, n is 16, m is 3, and X is Cl) by weight, accounting for 8.77% of the mass ratio of the polar terms;

3 parts of nonionic surfactant polyol ester Span20, wherein the mass ratio of the nonionic surfactant polyol ester Span20 to the cationic gemini surfactant is 1: 1;

the high-temperature-resistant viscoelastic polymer prepared in preparation example 1 was 0.3 part by weight, accounting for 0.88% by mass of the polar phase.

The mean particle size of the nanoemulsion acid system prepared as a result was 136 nm.

Comparative example 3

2 parts of cationic gemini surfactant (specifically quaternary ammonium salt gemini surfactant, n is 16, m is 3, and X is Cl) accounting for 3.78% of the mass ratio of the polar terms;

the mass ratio of the nonionic surfactant, namely the polyol ester Span20, to the cationic gemini surfactant is 1: 1.

comparative example 4

a nanoemulsion acid system was prepared in the same manner as in example 1, except that: the weight ratio of the dosage of the nonionic surfactant, the cationic gemini surfactant and the high-temperature resistant viscoelastic polymer is 1: 0.5: 0.05.

comparative example 5

In the step (5), the polar phase is added into the non-polar phase at one time at 25 ℃, the mixture is stirred at a low speed of 100r/min, and the stirring is continued for 30min after the dripping is finished, so that an emulsion acid system is prepared.

Comparative example 6

The nonpolar phase was prepared in the same manner as in example 1 and was directly subjected to the test.

Test example 1

The nanoemulsion acid systems prepared in examples 1 to 5 and comparative examples 1 to 6 were subjected to stability experiments, and the results are shown in table 1.

TABLE 1

As can be seen from the experimental results in table 1:

the nanoemulsion acid systems prepared in examples 1-5 of the present invention all have good long-term stability. In example 4, the oil-water ratio is high, so the particle size of the nano emulsion is large and the stability is slightly lower than that of other examples. In comparative example 1, a high temperature resistant viscoelastic polymer was not added, but the nanoemulsion itself had better stability, so it could be stored for a long period of time without destabilization. In the comparative example 2, the proportion of the continuous phase oil phase is increased, and the formed nano emulsion has smaller particle size and better stability. The amounts and the proportions of the components in comparative examples 3 and 4 are not within the range defined by the present invention, and in addition, the strength of the oil-water interfacial film is reduced, the stability is affected, and even the nano emulsion cannot be formed due to the change of the concentration and the proportion of the surfactant. The preparation method in comparative example 5 is different from the method defined in the present invention, resulting in failure to form a nano emulsion system. Comparative example 6 uses only the non-polar phase and is therefore a surfactant/hydrochloric acid/polymer solution with better stability.

Test example 2

The nanoemulsion acid systems prepared in examples 1 to 5 and comparative examples 1 to 6 were subjected to a high temperature resistance test, and the results are shown in table 2.

TABLE 2

The experimental results in table 2 show that the nanoemulsion acid systems prepared in examples 1 to 5 of the present invention have good stability at 150 ℃, and the systems are not layered, which indicates that the structure of the nanoemulsion acid system is not changed, and indicates that the nanoemulsion acid system of the present invention can resist temperature up to 150 ℃, and can meet deep acidizing fracturing reformation of oil and gas reservoirs under various working conditions. The high-temperature resistant viscoelastic polymer can generate a synergistic effect with the surfactant under a proper addition amount, so that the temperature resistance of the system is improved. In comparative example 1, no high temperature resistant viscoelastic polymer was added, so it withstood only 100 ℃. The components and the content of the components in the comparative example 2 are not in the range defined by the invention, the oil-water ratio is increased, and the formed nano emulsion has smaller particle size and also has better heat resistance. The components and the component contents in the comparative examples 3 and 4 are not in the range defined by the invention, especially the concentration and the proportion of the surfactant are changed, and the concentration and the proportion of the surfactant are changed, so that the strength of an oil-water interfacial film is reduced, and the temperature resistance is influenced. The preparation method in the comparative example 5 is different from the limited method of the invention, so that a nano emulsion system cannot be formed and the temperature resistance is poor. Comparative example 6 uses only the non-polar phase and is therefore a surfactant/hydrochloric acid/polymer solution with better stability and temperature resistance.

Test example 3

The nanoemulsion acid systems prepared in examples 1 to 5 and comparative examples 1 to 6 were subjected to viscosity test, and the results are shown in table 3.

TABLE 3

Numbering	30℃	60℃	90℃	120℃	150℃
						Example 1	147mPa·s	141mPa·s	131mPa·s	124mPa·s	111mPa·s
Example 2	104mPa·s	99mPa·s	87mPa·s	79mPa·s	75mPa·s
						Example 3	158mPa·s	149mPa·s	125mPa·s	116mPa·s	109mPa·s
Example 4	160mPa·s	151mPa·s	126mPa·s	117mPa·s	104mPa·s
						Example 5	158mPa·s	147mPa·s	121mPa·s	104mPa·s	97mPa·s
Comparative example 1	35mPa·s	27mPa·s	16mPa·s	/	/
						Comparative example 2	139mPa·s	117mPa·s	98mPa·s	96mPa·s	91mPa·s
Comparative example 3	/	/	/	/	/
						Comparative example 4	/	/	/	/	/
Comparative example 5	/	/	/	/	/
						Comparative example 6	133mPa·s	124mPa·s	112mPa·s	101mPa·s	95mPa·s

As can be seen from the experimental results in Table 2, the nanoemulsion acid systems prepared in examples 1 to 5 of the present invention all have good viscosifying properties at 150 ℃. The nano emulsion acid system has good thermal stability, and meanwhile, the polymer generates hydrophobic association effect, thereby playing the thermal tackifying effect and further improving the high-temperature viscosity stability of the nano emulsion acid system. While example 3 had a slightly lower viscosity due to the lower amount of hydrophobic polymer added. In comparative example 1, since no viscoelastic polymer was added, the viscosity and high temperature viscosity stability were greatly reduced, and in comparative example 2 and comparative example 6, the viscosity and high temperature viscosity stability also tended to be reduced.

Test example 4

The acid solubility of the acid systems of the nano-emulsion prepared in the

embodiments

1, 2 and 6 of the present invention is measured, and the results are shown in fig. 1, and it can be seen from fig. 1 that the acid solubility of the acid system of the nano-emulsion prepared in the embodiments 1 of the present invention is the lowest within the same acid dissolution time, and the acid system has a good retarding effect. The retarding effect is good, so that the acid liquor has larger penetration depth in the stratum, the filtration rate is reduced, and the acidification effect of the acid liquor on medium, high and even low permeability stratum with cracks is improved; in the comparative example 2, the concentration of hydrochloric acid is reduced and the acid dissolution effect is greatly reduced due to the increase of the oil-water ratio; the hydrochloric acid solution in comparative example 6 did not have a retarding effect, and the core was rapidly dissolved.

The preferred embodiments of the present invention have been described above in detail, but the present invention is not limited thereto. Within the scope of the technical idea of the invention, many simple modifications can be made to the technical solution of the invention, including combinations of various technical features in any other suitable way, and these simple modifications and combinations should also be regarded as the disclosure of the invention, and all fall within the scope of the invention.

Claims

1. A nanoemulsion acid system, characterized in that the nanoemulsion acid system contains an oil phase, an acid, a cationic gemini surfactant, a non-ionic surfactant, a high temperature resistant viscoelastic polymer, an iron ion stabilizer, an inorganic salt and water;

wherein, in formula (3), z is 12, 14, 16 or 18.

2. The nanoemulsion acid system of claim 1, wherein p ═ 34.23-48.1%, q ═ 46.26-60.24%, r ═ 4.28-5.64%;

preferably, the high temperature resistant viscoelastic polymer is a sodium acrylate-acrylamide-hexadecyl allyl dimethyl ammonium chloride triblock copolymer;

preferably, the high temperature resistant viscoelastic polymer has a weight average molecular weight of 11 to 15 ten thousand.

3. The nanoemulsion acid system of claim 1, wherein the cationic gemini surfactant has a structure represented by formula (4):

wherein n is 12, 14, 16 or 18; m is 3, 4, 5 or 6; x is halogen;

preferably, n-16 or 18; m is 3 or 4; and X is Cl or Br.

4. The nanoemulsion acid system of claim 1 or 3, wherein the nonionic surfactant is selected from one or more of Span20, Span40, and Span 60;

preferably, the weight ratio of the cationic gemini surfactant, the nonionic surfactant and the high temperature resistant viscoelastic polymer is 1: 1: (0.02-0.1);

preferably, the oil phase is selected from one or more of diesel oil, white oil and vegetable oil; preferably diesel oil;

preferably, the iron ion stabilizer is citric acid and/or disodium ethylene diamine tetraacetate;

preferably, the inorganic salt is sodium chloride and/or potassium chloride.

5. The nanoemulsion acid system of any of claims 1-4, wherein the nanoemulsion acid system has 20-40 parts by weight of the oil phase, 25-45 parts by weight of the acid, 3-7 parts by weight of the cationic gemini surfactant, 3-7 parts by weight of the nonionic surfactant, 0.1-0.6 parts by weight of the high temperature resistant viscoelastic polymer, 0.3-1.2 parts by weight of the ferric ion stabilizer, 0.5-4 parts by weight of the inorganic salt, and 5-12 parts by weight of water.

6. The nanoemulsion acid system of any of claims 1-5, wherein the mean particle size of the nanoemulsion acid system is between 50 and 230nm, preferably 120-220 nm;

preferably, the viscosity of the nanoemulsion acid system is 75-124 mPa.s at the temperature of 120-150 ℃.

7. A method of preparing a nanoemulsion acid system according to any one of claims 1-6, characterised in that it comprises:

(1) carrying out first contact on acid and an inorganic salt water solution to obtain a first solution;

(3) carrying out third contact on a cationic gemini surfactant, an iron ion stabilizer and the second solution to obtain a polar phase;

8. The method of claim 7, wherein the weight ratio of the nonionic surfactant, the cationic gemini surfactant and the high temperature resistant viscoelastic polymer is 1: 1: (0.1-0.6).

9. The method of claim 7, wherein, in step (2), the conditions of the second contacting comprise: under the condition of 40-60 ℃, firstly stirring for 10-30min under the stirring condition of 800-;

preferably, in step (3), the conditions of the third contacting include: the stirring speed is 150-300r/min, and the stirring time is 5-15 min;

preferably, in step (4), the conditions of the fourth contacting include: the stirring speed is 150-300r/min, and the stirring time is 5-15 min;

preferably, in step (5), the conditions of the fifth contacting include: the temperature is 40-65 ℃, the dropping speed is 4-6mL/min, the stirring speed is 150-300r/min, and the stirring time is 80-100 min.

10. Use of a nanoemulsion acid system according to any one of claims 1 to 6 in the acidizing fracturing reformation of oil and gas reservoirs.