WO2020055285A1

WO2020055285A1 - Thickener of aqueous acid solution and method of oil production

Info

Publication number: WO2020055285A1
Application number: PCT/RU2019/000629
Authority: WO
Inventors: Aleksandr Vladimirovich TERESHCHENKO
Original assignee: Tereshchenko Aleksandr Vladimirovich
Priority date: 2018-09-14
Filing date: 2019-09-10
Publication date: 2020-03-19
Also published as: RU2018132818A; RU2018132818A3; RU2698784C2

Abstract

The invention relates to a chemical system for thickening aqueous solutions of inorganic acids. The proposed system comprises: a) a polyethoxylated tallow amine of the formula (I) where m and n = 2; and R represents a fatty acid residue, selected from the group consisting of oleic, palmitic, stearic, myristic, or linoleic acid; b) a compound, selected from the group consisting of: - quaternary ammonium salt of the formula (Ila) or - zwitterionic compound of the formula lib, and c) optionally, an iron converter. Possible embodiments of the proposed chemical system are also disclosed.

Description

THICKENER OF AQUEOUS ACID SOLUTION AND METHOD OF OIL PRODUCTION

TECHNICAL FIELD

The present invention relates to a system for thickening surfactant-based solutions of acids, a method for thickening acids, and the use of a thickened solution of an acid when performing hydraulic fracturing.

BACKGROUND OF THE INVENTION

Hydraulic fracturing includes forming and expansion of fractures in the formation during the creation of high bottom-hole pressures by the fluid, being pumped into the well. In order to prevent a fracture from closing after the pressure removal, proppant, in the form of a granular substance, is injected into the created fractures, thereby ensuring the connection between far formation zones and the wellbore.

The rheological characteristics of standard thickened acid systems do not render possible to keep the hydraulic fracture open and transfer proppant. For the purposes of acid hydraulic fracturing using proppant, a technique of alternating packs of aqueous guar gel with the addition of proppant to water packs, buffer stages with subsequent injection of acid packs is implemented. According to this technique, a guar gel with proppant opens and keeps a fracture open, and the next pack of acid etches the created fracture. The main goal to be achieved by the“traditional” technique of acid hydraulic fracturing is to create connections with the far formation zone by injecting acid as the main working fluid. Staged injections of proppant are used to open and keep a fracture open, allowing acid to pass further and treat the formation.

Furthermore, during the acid treatment, it is frequently required to increase the viscosity of the solution of an acid. This is necessary to be implemented in order to reduce the kinetics of acid treatment, to reduce acid loss during treatment, to ensure the efficiency of proppant transfer, as well as to control the size of fractures, etc.

This technique has a number of disadvantages, the main among which are the following:

1. The aqueous gel contains a polymer gelling agent, for example, guar polysaccharide, which even when the cross and linear bonds are broken by a breaker or acid, forms an insoluble sediment that is not completely removed and contaminates the fracture/ formation, impairing permeability in the treatment zones. 2. Due to occurring the destruction of aqueous gel upon contact with acid, the probability of premature completion of the injection caused by clogging (STOP) increases, the acid depth of penetration decreases.

3. The need to use a large number of various liquids, a large number of equipment and a tank farm for kneading packs and performing this technique implementation.

In order to eliminate the above-mentioned disadvantages, systems and compositions of surfactant-based acid thickeners, that do not comprise polymer compounds, have been developed.

Thus, US patent US8895481 B2 discloses a method of treating a subterranean formation by introducing a viscoelastic acidic fluid medium, containing:

(i) 0.5-5.5 wt.% of zwitterionic surfactant of the formula

in particular, having the following betainic structure

, where n is equal to 3, p is equal to 1, and R is a Cl 7 hydrocarbon radical for BET-O-30 surfactant or R is a C21 hydrocarbon radical for BET-O-40 surfactant;

(ii) more than 15 wt.% of acid such as hydrochloric acid, and

(iii) the rheology enhancer.

As is specified, the fluid medium may additionally contain proppant.

The invention under US patent US 7527102 B2 relates to a method for the controlled-angle introduction of acid into a subterranean formation by injecting a gelled viscoelastic fluid medium, containing:

(i) surfactants, in particular, based on quaternary ammonium salts or betaines of the formula

, where R, in particular, represents a C8-24 alkylamido group, and

R' independently represents Cl -6 alkyl; and

(ii) an acid, such as hydrochloric acid.

As is specified, the fluid medium may additionally contain proppant and a solvent, such as alcohols. In addition, it is worth noting that according to the above-mentioned source, a breaker is specified as a mandatory component of the composition. W02003054352 Al discloses a method of treating a subterranean hydrocarbon formation by introducing a gelled acidic fluid medium, comprising surfactant, based on betainic compound of the formula

acid, such as hydrochloric acid. As is specified, the fluid medium may additionally include a solvent, such as methanol.

US patent US6844297 B2 discloses a method of hydraulic fracturing using a composition of viscoelastic fluid medium, including:

(i) surfactants based on quaternary ammonium salts of the formula

, where, in particular, Rl and R2 are methyl, ethyl, propyl and isopropyl, and R3 represents Cl 2-22 group;

(ii) acid, including hydrochloric acid, and

(iii) a low molecular weight solvent.

As is specified, the fluid medium may additionally contain proppant. US patent US 7776798 B2 (as well as other patents by the same applicant, US 7358215 Bl and EP 2000959792) discloses surfactant compositions based on quaternary ammonium salts of the formula

, in particular, compounds of the formula

, where according to a specific embodiment of the invention, y is equal to 1, R is erucil, R2, R3 and R4 are methyl; to be used as a thickener for oilfield fluid media. As is specified, such compositions are thickened sufficiently to hold the proppant in suspension. In addition, the said compositions may optionally contain alcohols and inorganic acids.

International patent application WO 2014137477 Al discloses a method of treating a zone of a subterranean formation, penetrated by the wellbore, comprising the steps of:

(A) preparing a treatment fluid, comprising:

(i) water;

(ii) a strong acid; and

(iii) a branched viscoelastic surfactant, having

a hydrophobic portion with a total of 16 to 20 carbons;

wherein the pH of the treatment fluid is less than 0.5; and wherein the viscosity of the treatment fluid is less than 5 cP at 40 sec ¹.

(B) introducing the treatment fluid through the wellbore into the zone; and

(C) allowing time for the strong acid in the treatment fluid to interact in the formation.

Hydrochloric acid is used as a strong acid. The preferred viscoelastic surfactant is a compound of the formula

US patent application US 2013306320 Al discloses a composition for treating carbonate reservoirs, comprising:

about 7.5 vol.% of zwitterionic viscoelastic surfactant;

about 15.0 vol.% of hydrochloric acid; and

about 0.6 vol.% of corrosion inhibitor, with the reminder being brine.

The preferred zwitterionic viscoelastic surfactant is erucrylamidopropyl betaine.

RU patent No. 2452851, issued on the basis of application W02007/058813, discloses a method for increasing oil recovery from a field, including

a) introducing a flooding fluid into the field, wherein the fluid contains the following:

i) water and

ii) an amount of one or more non-polymeric viscoelastic surfactants, sufficient to provide the

flooding fluid with an oil/water interfacial surface tension of about 1 mNm or less, and a viscosity of about 10 cP or more, wherein one or more non-polymeric viscoelastic surfactants is selected from the group consisting of: one or more amine surfactants, having the formula:

where Rl is a hydrophobic residue of alkyl, alkylarylalkyl, alkoxyalkyl, alkylaminoalkyl or alkylamidoalkyl, and wherein Rl has from about 16 to about 22 carbon atoms and may be branched or straight-chained and saturated or unsaturated;

wherein R2 and R3 are, independently, i) an aliphatic group or ii) an aliphatic group, bonded with an aromatic or benzylic residue, of one or more zwitterionic surfactants, one or more amphoteric surfactants, and combinations thereof;

b) oil recovery through a well at a location different than the point of introduction of the flooding fluid into the field.

The use of an organic acid to increase the viscosity of the said fluid is also mentioned.

Eurasian patent EA No. 2452851, issued on the basis of application W02003/054352, discloses a method of treating a subterranean hydrocarbon reservoir, comprising contacting a formation with a treatment solution, containing an aqueous solution, acid, alcohol and a surfactant that acts as a gelling agent, consisting mainly of erucilamidopropyl betaine or its protonated/deprotonated homologue or salt.

Probably, the closest analogue of the present invention is the technical solution disclosed in US patent US5009799. This document relates to a composition of an inorganic acid thickener based on two surfactants, which is used for acid treatment of hydrocarbon-containing formations, and also as a corrosion inhibitor. In particular, proposed is a thickener for an aqueous solution of hydrochloric acid, comprising a mixture of:

(i) an ethoxy lated fatty amine of the general formula I:

R— N

\

(CH₂CH₂0) H including tallow amine, and

(ii) a betaine salt of an ethoxy lated fatty amine of the general formula II:, and

(iii) quaternary ammonium salt of alkylpyridine and

(iv) various lower alcohols Cl -10 as a solvent.

However, the known systems, proposed for performing acid hydraulic fracturing, are missing the viscosity sufficient to proppant transfer during a long time period, required to perform proper and efficient acid hydraulic fracturing. In particular, the known thickeners render it possible to achieve only a viscosity of 60-80 cP.

Thus, the creation of compositions for performing acid hydraulic fracturing with higher viscosity to increase the efficiency of proppant transfer and enhance the performance while extracting hydrocarbons from the formation is a matter of urgency. SUMMARY OF THE INVENTION

The object of the present invention is to provide a chemical system for thickening an aqueous solution of an acid to obtain a liquid or gel with higher viscosity, required for the implementation of acid hydraulic fracturing technique. Another object of the present invention is to provide a simple and efficient method for oil recovery from a field by the method of acid hydraulic fracturing.

The aforesaid objects are achieved due to developing a chemical system, which includes a combination of chemicals that allows thickening of an aqueous solution of an acid to a viscosity of up to 1320 cP or higher. The specified combination comprises two surfactants, described below, and, optionally, an iron converter.

The first aspect of the present invention involves the use of the combination of

a) a polyethoxylated tallow amine of the formula I

where m and n = 2; and R represents a fatty acid residue, selected from the group consisting of oleic, palmitic, stearic, myristic, or linoleic acid;

b) a compound, selected from the group consisting of:

- quaternary ammonium salt of the formula Ila

where R is a saturated, mono-, di- or tri-unsaturated hydrocarbon radical C9-25; Rl is a hydrogen, methyl, ethyl, propyl, isopropyl, allyl, vinyl, phenyl, and benzyl; R2, R3, R4, R5 are, independently, hydrogen, methyl, ethyl, propyl, isopropyl, allyl, vinyl, phenyl or benzyl; A is a halo, nitro or perchlorate;

or

- zwitterionic compound of the formula lib

where Rl is -COO or -CH₂COO\ and R, R2, R3, R4, and R5 are as specified above; and c) optionally, an iron converter for thickening an aqueous solution of an acid.

R is a saturated, mono-, di- or tri-unsaturated hydrocarbon radical C9-25, in particular, C9,

C10, Cl l, C12, C13, C14, C15, C16, C17, C18, C19, C20, C21, C22, C23, C24, C25, and may contain substituents that do not result to a significant change in the compound properties.

Any acid may act as the specified one. For example, the acid may be a strong acid, selected from the group consisting of hydrochloric acid, hydrobromic acid, hydroiodic acid, sulfuric acid, nitric acid, chromic acid, methanesulfonic acid, trifluoromethanesulfonic acid, trichloroacetic acid, dichloroacetic acid, bromoacetic acid, chloroacetic acid, cyanoacetic acid, 2-chloropropanoic acid, 2-oxobutanoic acid, 2-chlorobutanoic acid, 4-cyanobutanoic acid, perchloric acid and phosphoric acid, and the like. In a preferred embodiment, the acid is an inorganic acid. In a preferred embodiment, a solution of hydrochloric acid, normally used while performing acid hydraulic fracturing technique, is thickened. The acid content in the solution after thickening is in the range from 10 to 20%, preferably from 12 to 16%, and preferably is 15%.

The first surfactant in the combination or composition according to the present invention is a polyethoxylated tallow amine of the formula I, preferably a tallow amine, ethoxylated with an ethoxylation degree of 2 (CAS#61791-26-2).

The second surfactant in the composition according to the present invention is a compound of the quaternary ammonium salt of the formula Ila, such as [2,2-dimethyl-3- (octodecanoylamino) propyl] -dimethyl-prop-2-enylammonium bromide or a zwitterionic compound of the formula lib, preferably, erucilamidopropyl betaine (synonym -2-[3-[docos-l3-enoyl] aminopropyl- dimethylammonium] acetate).

An iron converter is a compound or composition of compounds, capable to eliminate the effect of Fe (III), for example, by reducing Fe (III) to Fe (II) with the conversion of iron to a more soluble divalent form and to form stable chelate complexes with Fe (III), preventing the occurrence in the formation of an amorphous precipitate of iron hydroxide Fe(OH)₃, which in addition to a negative effect on the formation permeability is an intermediate product during rusting of iron.

The use of an iron converter is desirable, for example, when using metallic equipment, and also due to the fact that iron (III) salts reduce the viscosity of gelled aqueous solutions of an acid.

Examples of iron converters include, but are not limited to, ascorbic acid, citric acid, a mixture of mercaptoethanol, copper chloride and methanol, an iron converter AS-IR.

When implementing the present invention, it is possible to use various ratios of components of the chemical system: a) - polyethoxylated tallow amine of the formula I and b) - compounds of the formula Ila or lib. Those skilled in the art will be able to choose the optimal ratio by way of performing routine experiments. In particular, the ratio of surfactants can be approximately 1 : 100, 1 :50, 1 :20, 1 :10, 1 :5, 1 :3, 1 :2, 1 :1, 2:1, 3:1, 5:1, 10:1, 20:1, 50:1, 100:1.

The content of each surfactant, or combinations thereof, in the final composition may be about 20%, about 10%, about 5%, about 2.5%, about 2%, about 1%, about 0.5% or less, including all intermediate ranges and values.

The second aspect of the present invention is a method of thickening an aqueous solution of an acid, comprising adding a combination of two surfactants described above, to the said aqueous solution of an acid, and, optionally, an iron converter. In accordance with the present invention, the surfactants and the iron converter can be added to the solution of an acid to be thickened both simultaneously, for example, in the form of a single composition, or in any combination or separately.

The third aspect of the present invention is a set of components of the chemical system for the use while thickening an aqueous solution of an acid or for implementing the described method of thickening an aqueous solution of an inorganic acid. The said set of components contains two surfactants described above, and, optionally, an iron converter.

The fourth aspect of the present invention is a composition for performing acid hydraulic fracturing, comprising an aqueous solution of an inorganic acid, the aforesaid set of components of the chemical system, and, optionally, a proppant.

Any inorganic acid may be used as the acid. The use of hydrochloric acid is preferred. The content of hydrochloric acid in the said aqueous solution and the resulting gel may be in the range from 10% to 20%, optionally from 12 to 16%. In one embodiment, a 15% aqueous solution of a hydrochloric acid is used.

The preferred content of components in the proposed composition, containing an aqueous solution of an acid, is the following:

- polyethoxylated tallow amine of the formula I 2.5 - 5.0 wt.%;

- a compound of the formula Ila or the formula lib 1.5 to 5.0 wt.%,

- an iron converter 0.2 to 1.0 wt.%.

In one embodiment, the composition contains proppant.

Propant (or proppant, after the English propping agent -“prop open agent”) is a granular material that is used in the oil industry to increase well performance using hydraulic fracturing technique. It is required for keeping open (preventing from closing under the rock pressure) the fractures created while performing hydraulic fracturing. It is in the form of granules of similar size, with a typical diameter of 0.5 to 1.2 mm. In accordance with the present invention, any proppant that is normally used for implementing acid hydraulic fracturing technique can be used.

The proppant is added in amounts that are normally used when performing acid hydraulic fracturing. In some embodiments, the proppant is added at the rate of 800 kg/m³ of gel. The fifth aspect of the present invention is a method for producing oil from a field by the method of acid hydraulic fracturing, including:

- introducing the aforesaid composition of the thickened solution of an acid into a field, preferably containing carbonate rocks, and

- oil recovery from the said field.

Oil recovery from a field can be performed via using standard means and methods, being applied in this technical field, for example, discussed in the following sources: Bulatov A.I., et al. Technique and technology of oil and gas wells drilling: Textbook for higher education - M:“Nedra - Business Center”, LLC 2003 - p.1007; Usachev P.M. Hydraulic fracturing treatment - M.: Nedra, 1986.— p.165.

The technical result of the proposed technique is to increase the viscosity, in particular, providing an acid solution with viscoelastic properties, which, inter alia, makes possible to efficiently transfer proppant, and also ensures the efficient implementation of acid hydraulic fracturing. It is worth noting that the authors of the present invention have succeed in creation of a thickener composition for an aqueous solution of an inorganic acid with an unexpectedly high degree of viscosity, up to 1332 cP, through the experiments, sufficient to hold and transfer proppant for a long time (up to 6 hours or more), required for performing proper and highly efficient acid hydraulic fracturing. At the same time, via using one acid gel obtained, it is possible to simultaneously create a hydraulic fracture, transfer proppant, fix the fracture with proppant, treat the carbonate formation with acid and create highly permeable channels in the critical zone of the fracture, thereby allowing more efficient and prolonged operation of the hydraulic fracture.

In other words, the present invention provides a new acid hydraulic fracturing technique using substantially only one working fluid - an acid gel, optionally, containing proppant.

The stages of a well treatment using proppant and an acid, without applying the present invention, are as follows:

- Preparatory packs

- Aqueous gel - forming a hydraulic fracture

- Aqueous gel with proppant - expansion of the hydraulic fracture, fixing with proppant

- Buffer stage

- 15% hydrochloric acid - etching the fracture

- Buffer stage

- Aqueous gel with proppant - fixing the fracture

- Buffer stage

- 15% hydrochloric acid

- Buffer stage

- Aqueous gel with proppant

- Buffer stage

- 15% hydrochloric acid

- Squeezing of fracturing fluids and removal of by-products.

A large number of fluids are used at different stages, and the implementation of every single one of them requires using a separate tank and additional equipment.

The use of the present invention can significantly simplify the procedure of acid hydraulic fracturing implementation, minimizing the number of fluids, tanks and equipment involved:

- Preparatory packs

- Acid gel - forming a hydraulic fracture and performing acid treatment, fixing the fracture

- Acid gel with proppant - fixing the fracture, acid treatment, fixing the fracture

- Squeezing of fracturing fluids and removal of by-products. In brief, the method of oil production according to the present invention has the following advantages:

1. Simplicity of use, since there is no need in a large number of chemical agents used when performing the hydraulic fracturing according to the traditional technique (cross-linkers, breakers, biocides, stabilizers, demulsifier, etc.)

2. Much lesser equipment and smaller tank farm is required to prepare the composition compared to the traditional hydraulic fracturing technique.

3. It renders possible to create a longer fracture by using only one fluid for the entire treatment. This is achieved by virtue of the formation of micelles, which provide gel-like structure to the acid. The formed gel clogs the etched channels and prolongs the time of their interaction with the acid.

4. The stage of using a pack with an aqueous polymer gel based on guar is excluded, wherein the said acid system breaks down completely. The resulting reaction products are easily removed from the bottom-hole zone during development.

5. The use of only one fluid, having the required characteristics for performing acid hydraulic fracturing with proppant.

6. Double system of gel destruction (lowering the concentration of acid, mixing with hydrocarbons).

7. Low friction loss.

8. The cost of work is reduces significantly due to less number of chemical agents and treatment stages.

According to the proposed technique, substantially only one fluid is used. Compared to the traditional and combined schemes for performing (alternating guar gel with proppant-acid) hydraulic fracturing, the following advantages can be achieved:

the absence of a polymer component, maximum fracture conductivity and permeability of the fracture walls,

limiting fracture expansion in vertical direction (increase in “areal” concentration of proppant in the productive zone),

minimizing the fluid injected,

high sand-bearing ability of the fluid, minimal subsidence of proppant and, as a result, uniform distribution of proppant in the fracture. The present invention will be disclosed in greater detail below with reference to the drawings and examples, given for illustration purposes only, without limiting the scope of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows a diagram for the dependence of acid viscosity on the content of tallow amine and erucilamidopropyl betaine.

Figure 2 shows the subsidence of 16/20 proppant at the rate of 800 kg/m³ in the optimal composition, containing 3.5% of tallow amine and 2.5% of zwitterionic compound erucilamidopropyl betaine.

Figure 3 shows the results of comparison of the abilities to hold proppant for the normally used cross-linked guar gel and the optimal composition according to the present invention.

Figure 4 shows the impact of temperature on the viscosity of the optimal composition according to the present invention.

Figure 5 shows the experimental results for studying the recovery of viscosity of the optimal composition according to the present invention after stress at temperatures of 25°C and 55°C.

Figure 6 shows the experimental results for studying the destruction of gel of the chemical system, obtained when using the optimal composition according to the present invention, while interacting with carbonate rocks.

DETAILED DESCRIPTION OF THE INVENTION.

Example 1. Preparing a composition according to the present invention.

The composition was prepared as follows. Tallow amine, ethoxylated with a degree of ethoxylation 2 was added, while stirring, to 15% synthetic hydrochloric acid. The resulting solution was stirred. The result was a moderately thickened acid with a viscosity of 35-80 cP, measured using a FANN 35 R1B1 viscometer at 100 RPM

Then, the zwitterionic compound, namely erucilamidopropyl betaine, was added to the resulting solution, while vigorous stirring, using a bottom-drive stirrer. The viscosity of the solution increased significantly.

Typical concentrations of the components are presented in the table below:

Example 2. The selection of the optimal composition according to the present invention

The dependence of the viscosity of hydrochloric acid on the concentration of chemical agents of the composition according to the present invention was determined. A surfactant solution was prepared by the aforesaid method.

To study the rheological characteristics of the obtained system, a Brookfield viscometer of

DV2TLVTJ0 model, with a spindle LV4 (64), 100 RPM was used.

The data obtained are presented in Table 1 and in Figures 1 and 7.

Table 1. The dependence of acid viscosity (cP) on the content of tallow amine and zwitterionic compound

Example 3. Assessment of ability of the compositions according to the present invention with different content of components to hold proppant

In accordance with the present invention, in order to assess the ability of compositions with different content of components to hold proppant, 16/20 proppant was added to the said compositions at the rate of 800 kg/m³ and the mixtures were placed in a measuring cylinder. Then, the process of proppant subsidence was observed and the time of proppant complete subsidence was recorded.

The data obtained are presented in Table 2.

Based on the experiments performed, it can be concluded that the selected tallow amine with a concentration from 2.5 to 5.0% in a mixture with the selected zwitterionic compound, namely erucilamidopropyl betaine, with a concentration from 1.5 to 5.0% thicken hydrochloric acid to the state of being able to hold and transfer proppant. The optimal concentration of amine and zwitterionic compound was selected based on the requirements for minimum concentration of substances at maximum holding capacity.

A composition containing 5% of tallow amine and 2.5% of zwitterionic compound meets these requirements. In the said optimal composition, the complete subsidence of proppant occurred in 6 hours, which is sufficient for performing acid hydraulic fracturing. Figure 2 shows the process of proppant subsidence in the said optimal composition.

Example 4. Comparison of the abilities to hold proppant for the normally used cross-linked guar gel and the optimal composition according to the present invention

To study the ability of fluids to hold proppant (fractions 16/20) at the rate of 800 kg/m³, the normally used cross-linked guar gel and the optimal composition according to the present invention were placed in measuring cylinders. Then, the process of proppant subsidence was observed and the time of proppant complete subsidence was recorded.

The composition of the guar gel is as follows:

The experimental results are shown in Figure 3. As is seen from the data presented, in the cross-linked guar gel, the complete subsidence of proppant occurred in 2 hours. It is difficult to perform a proper and efficient large-volume hydraulic fracturing during this time. At the same time, in the optimal composition according to the present invention, the complete subsidence of proppant occurred in 6 hours, i.e. during the period, sufficient for performing proper and efficient acid hydraulic fracturing, in a trouble-free manner.

Example 5. Studying the impact of temperature on the viscosity of the optimal composition.

The prepared optimal composition was carefully heated and the change in viscosity was monitored using a Brookfield viscometer of DV2TLVTJ0 model, with a spindle LV4 (64), at a rotation speed of 100 RPM.

The experimental results are shown in Figure 4.

Example 6. Studying the recovery of viscosity of the optimal composition according to the present invention after stress.

The gelled acid was tested for the rate of viscosity recovery under stress using a Brookfield viscometer of DV2TLVTJ0 model, with a spindle LV4 (64). Stress conditions were created via the change of a rotation speed (RPM - r/min). The dependence obtained confirms that the viscosity recovery takes place immediately upon the change in the applied rotational force. The experimental results are shown in Figure 5.

Example 7. Studying the destruction of gel obtained when using the optimal composition according to the present invention, while interacting with carbonate rocks.

An acid, when entering the formation, interacts with carbonate rocks, and as a result its concentration decreases, and the content of Ca2+ ions increases. To simulate this process, the reaction of an acid with calcium carbonate is unsuitable because of a large amount of foam being formed, which is highly stabilized due to the high viscosity of the solution. Therefore, the reaction of the interaction of acid with slaked lime, resulting to the same products, was used.

Slaked lime was poured in small portions, while vigorous stirring. The reaction was time- lagged due to the high viscosity of the solution. Upon complete dissolution of calcium hydroxide, the solution was cooled to room temperature and its viscosity was measured. The procedure was repeated until total neutralization of the acid. Viscosity was measured using a Brookfield viscometer of DV2TLVTJ0 model, with a spindle LV4 (64), at a rotation speed of 100 RPM. The experimental results are shown in Figure 6. Based on the data shown in Figure. 6, it can be concluded that when interacting with carbonate rocks, the system breaks down, and the viscosity of the thickened acid decreases.

Other embodiments of the system according to the present invention are studied in accordance with the same layout of experiments. It should be understood that the previous description is given only for the purpose of explaining the present invention. Those of ordinary skill in the art can develop various alternative variants and modifications without departing from the scope of the present invention, as defined by the appended claims. Thus, it is contemplated that the present invention will cover any such alternative variants, modifications and variations that fall within the scope of the appended claims. All numerical values given in this document are approximate and allow normal variations, for example, within +/- 10-15% of the specified value. The given percentage values may refer to weight, volume, or weight/volume percent.

Claims

1. Use of the combination of

a) a polyethoxylated tallow amine of the formula I

where m and n = 2; and R represents a fatty acid residue, selected from the group consisting of oleic, palmitic, stearic, myristic, or linoleic acid; and

b) a compound, selected from the group consisting of:

- quaternary ammonium salt of the formula Ila

where R is a saturated, mono-, di- or tri -unsaturated hydrocarbon radical C9-25; Ri is a hydrogen, methyl, ethyl, propyl, isopropyl, allyl, vinyl, phenyl, and benzyl; R₂, R3, Ri, R₅ are, independently, hydrogen, methyl, ethyl, propyl, isopropyl, allyl, vinyl, phenyl or benzyl; A is a halo, nitro or perchlorate; or

- zwitterionic compound of the formula lib

where Ri is -COO or -CH₂COO , and R, R₂, R3, R4, and R₅ are as specified above; and c) optionally, an iron converter for thickening an aqueous solution of an acid.

2. The use as claimed in claim 1 , characterized in that [2,2-dimethyl-3-

(octodecanoylamino)propyl]-dimethyl-prop-2-enylammonium bromide is used as the compound of the formula Ila.

3. The use as claimed in any one of claims 1 - 2, characterized in that erucilamidopropyl betaine is used as the compound of the formula lib.

4. The use as claimed in any one of claims 1 - 3, characterized in that a mixture of mercaptoethanol, copper chloride and methanol is used as an iron converter.

5. A method of thickening an aqueous solution of an inorganic acid, including adding to the said aqueous solution of an inorganic acid

a) a polyethoxylated tallow amine of the formula I

b) a compound, selected from the group consisting of:

- quaternary ammonium salt of the formula Ila

where R is a saturated, mono-, di- or tri-unsaturated hydrocarbon radical C9-25; Ri is a hydrogen, methyl, ethyl, propyl, isopropyl, allyl, vinyl, phenyl, and benzyl; R₂, R₃, R₄, R₅ are, independently, hydrogen, methyl, ethyl, propyl, isopropyl, allyl, vinyl, phenyl or benzyl; A is a halo, nitro or perchlorate;

or

- zwitterionic compound of the formula lib

where Ri is -COO or -CH₂COO\ and R, R₂, R3, R₄, R₅ are as specified above; and c) optionally, an iron converter.

6. The method as claimed in claim 5, characterized in that [2,2-dimethyl-3- (octodecanoylamino)propyl]-dimethyl-prop-2-enylammonium bromide is used as the compound of the formula Ila.

7. The method as claimed in any one of claims 5 - 6, characterized in that erucilamidopropyl betaine is used as the compound of the formula lib.

8. The method as claimed in any one of claims 5 - 7, characterized in that a mixture of mercaptoethanol, copper chloride and methanol is used as an iron converter.

9. The method as claimed in any one of claims 5 - 8, characterized in that the amine of the formula I, the compound of the formula Ila or lib and an iron converter are added simultaneously.

10. The method as claimed in any one of claims 5 - 9, characterized in that the amine of the formula I, the compound of the formula Ila or lib and an iron converter are added separately.

1 1. A set of components for the use as claimed in any one of claims 1 - 4 or the implementation of the method as claimed in any one of claims 5 - 10, comprising:

a) a polyethoxylated tallow amine of the formula I

b) a compound, selected from the group consisting of:

- quaternary ammonium salt of the formula Ila

where R is a saturated, mono-, di- or tri -unsaturated hydrocarbon radical C9-25; Ri is a hydrogen, methyl, ethyl, propyl, isopropyl, allyl, vinyl, phenyl, and benzyl; R₂, R₃, R , R₅ are, independently, hydrogen, methyl, ethyl, propyl, isopropyl, allyl, vinyl, phenyl or benzyl; A is a halo, nitro or perchlorate;

or

- zwitterionic compound of the formula lib

where Ri is -COO- or -CH2COO-, and R, R₂, R₃, R4, R5 are as specified above, and c) optionally, an iron converter.

12. The set as claimed in claim 1 1, characterized in that [2,2-dimethyl-3- (octodecanoylamino)propyl]-dimethyl-prop-2-enylammonium bromide is used as the compound of the formula Ila.

13. The set as claimed in claim 11 or claim 12, characterized in that erucilamidopropyl betaine is used as the compound of the formula lib.

14. The set as claimed in any one of claims 11 - 13, characterized in that a mixture of mercaptoethanol, copper chloride and methanol is used as an iron converter.

15. The set of components as claimed in any one of claims 11 - 14, characterized in that the set of components is in the form of a composition.

16. A composition for the implementation of acid hydraulic fracturing, comprising an aqueous solution of an inorganic acid, a set of components as claimed in any one of claims 11 - 15 and proppant.

17. The composition as claimed in claim 16, characterized in that the said inorganic acid is hydrochloric acid.

18. The composition as claimed in claim 17, characterized in that the content of hydrochloric acid is 12-16%, preferably, 15%.

19. The composition as claimed in claim 16, characterized by the following content of components:

- polyethoxylated tallow amine of the formula I 2.5 - 5.0 wt.%;

- a compound of the formula Ila or formula lib 1.5 to 5.0 wt.%;

- an iron converter 0.2 to 1.0 wt.%.

20. A method of producing oil from a field using an acid hydraulic fracturing method, including:

- introducing the composition as claimed in any one of claims 16 - 19 to the field, and

- oil recovery from the field.

21. The method as claimed in claim 20, characterized in that the inorganic acid is hydrochloric acid.

22. The method as claimed in claim 20 or claim 21, characterized in that the said field contains carbonate rocks.