WO1982002073A1

WO1982002073A1 - Copolymers soluble in an aqueous medium and stable in an acid medium,preparation and use thereof

Info

Publication number: WO1982002073A1
Application number: PCT/EP1981/000192
Authority: WO
Inventors: Ag Cassella; Industries Inc Dresser; Friedrich Engelhardt; Klaus Kuehlein; Ulrich Riegel; Sigmar Halasz; Jeffrey C Dawson; Anthony R Reed
Original assignee: Ag Cassella; Dresser Ind
Priority date: 1980-12-15
Filing date: 1981-12-14
Publication date: 1982-06-24
Also published as: GB2102441A; DD202303A5; IT1194128B; DD207726A5; GB2102441B; JPS57502072A; EP0078805B1; NO822764L; EP0078805A1; CA1189649A; IT8125571A0; BR8109019A

Abstract

New copolymers soluble in an aqueous medium, which are stable in a highly concentrated medium of Bronsted-Lowery acids. These copolymers are used as acid lubricants in the field of oil and natural gas boring. The copolymer according to the invention contains in its macromolecule, in statistical distribution, at least 5% by weight of units having each a formylamino group (according to A) and at least 10% by weight of units having each an aminocarbonyl group (according to B).

Description

Water-soluble, acid-stable copolymers, their preparation and use

The present invention relates to new water-soluble copolymers which are stable in high concentrations of Bronsted-Lowery acids and which are used in particular as a friction reducer for acids which in turn are used in the process of acid stirulation in oil or gas wells. The copolymer according to the invention contains at least 5% by weight of units which have a formylamino group (A) and at least 10% by weight of units which contain an aminocarbonyl group (B) in its macromolecule

A well-known stimulation technique for oil and gas wells which is used for the purpose of increasing the production rate and the overall yield from underground carbonate formations is the so-called pressure acidification. Carbonate formations in this sense are, for example, dolomite, limestone or other bedrock that contain lime-like material. The pressure acidification is generally carried out in such a way that an aqueous acid, which may also contain so-called proppants, is pumped into the well to be stimulated, namely under a pressure which exceeds the formation pressure. As a result, new cracks and channels, so-called fractures, are blown into the formation. In the technique of pressure acidification, the surface of the rock fractures is additionally etched by the injected acid and, if the acid additionally contains a proppant, this proppant is transported into the opened fractures. Both the irregular etching of the heterogeneous fracture surface and the incorporation of the support material mean that the fractures can no longer close completely after the pressure has been released. In any case, it is created a more permeable channel that allows oil or gas to flow to the production well after pressure is applied.

With the technique of pressure acidification, it is necessary to pump the acid, the so-called fluid, into the borehole at high speed, so that the required explosive pressure for the rock can build up. This shows that a significant proportion of the injection pressure is lost due to frictional forces that occur between the fluid flowing in the turbulent flow and the line walls. Since this pressure loss, the so-called friction pressure, increases with the injection speed, an ever lower pressure component is transferred hydraulically to the formation as the treatment pressure as the injection speed increases. By adding small concentrations of polymers to the treatment fluid, the flow of the pumped-in fluid is laminarized, so that the friction pressure is considerably reduced even at high injection speeds, and thus a much larger proportion of the head pressure is transferred to the bedrock.

Common friction reducers. which are used in the implementation of pressure acidification are polysaccharides, e.g. Hydroxyethyl cellulose, xanthan gum (metabolite of Xanthomonas campestris) hydroxypropylated guar gum (from the seeds of Cyanaposis tetragonolibus) or synthetic polymers based on polyacrylamide.

Problems arise when using polysaccharides as friction reducers because these compounds are not very stable in highly concentrated acids. Usually, polysaccharides are hydrolysed or broken down in strong acids and the friction-reducing effect is lost. The use of synthetic polyacrylamides as friction reducers also has technical disadvantages:

In the presence of strong acids, polyacrylamides are quickly hydrolyzed to insoluble degradation products. These precipitate out of the treatment fluids and can be caused by constipation the fractures lead to an obstruction of the oil or gas flow and thus to severe damage to the deposit.

The present invention now relates to a copolymer which can be used as an improved friction reducer for the pressure acidification of subterranean, calcareous formations. The polymer of the invention is acid-soluble, and its degradation products are both acid-soluble and stable.

The new copolymers according to the invention are preferably composed of 5 to 50% by weight of units of the formula

10 to 95% by weight of units of the formula II

and 0 to 85% by weight of units of the formula III

wherein R ^{1 is} hydrogen, methyl or hydroxymethyl and R ^{2 is} hydrogen or methyl and X is cyano, carboxyl, or its alkali or ammonium salts, alkoxycarbonyl with 1 to 6, preferably 1 to 3, carbon atoms, hydroxyalkoxycarbonyl with 1 to 3 carbon atoms; N-methylolamidocarbonyl of the formula HOCH ₂ NH-CO-, the methylol group of which may be etherified with alkanols having 1 to 4 carbon atoms; Alkanoylamino having 1 to 4 carbon atoms, which may optionally be N-substituted by methylol or alkyl having 1 to 4 carbon atoms; Pyrrolidonyl- (1); Phenyl; Pyridinium; the sulfonic acid group; Sulfoalkylamidocarbonyl of 1 to 4 carbon atoms; the Pbosphonsäuregruppe where sulfonic acid and phosphonic acid groups can also be present as alkali or ammonium salts; a radical of formula IV -

wherein R ³ and R ^{4 are the} same or different and represent alkyl having 1 to 4, preferably 1 or 2, carbon atoms; a radical of formula V

wherein R ³ and R ^{4 have} the meanings given above and p stands for a number from 1 to 4; or a residue of the formula

VI

wherein R ⁵ and R ^{6 are} identical or different and represent alkyl having 1 to 4, preferably 1 or 2, carbon atoms and p represents a number from 1 to 4; as well as the formulas

V and VI mean corresponding groups, for example quaternized by dimethyl sulfate or methyl chloride.

The copolymers according to the invention are statistical, i.e. that the distribution of units I to III in the macromolecule is statistical.

Of course, the copolymers according to the invention can contain several different units of the formulas I and III, for example different units of the formula III which differ from one another in that the X or R ² radicals have different meanings. As a rule, X in a single macromolecule has no more than 3, preferably no more than two, different meanings. Copolymers of this type are prepared by using several different comonomers, usually not more than three, preferably not more than two, which differ from one another in the meanings of the radical X and / or R ² , in the copolymerization. As a rule, the copolymers of this invention have K values (cf. Fikentscher, "Cellulosechemie" vol. 13,

S. 58 (1932)) between 25 and 250, which corresponds to molecular weights between 20,000 and 15 × 10 ⁶ . As a friction those copolymers according to the invention are preferred which have K values between 50 and 200 corresponding to molecular weights between 100,000 and 4 × 10 ⁶ .

Preferred copolymers according to the invention consist of

5 to 30% by weight of units of the formula I,

50 to 80% by weight of units of the formula II and

1 to 60% by weight of units of the formula III.

Copolymers in which R ^{2 is} hydrogen or methyl or in which X

Carboxyl, the sulfonic acid group, 3-sulfo-2-methyl-propyl- (2) - amidocarbonyl of the formula

Alkanoylamino of 1 to 4 carbon atoms, which may optionally be N-substituted with methylol or alkyl of 1 to 4 carbon atoms; Pyrrolidonyl (1) or a radical of the formulas V or VI given and defined above, where each acid group can also be present as the sodium potassium or ammonium salt.

Particularly preferred for use as a friction reducer in the stimulation of natural gas or oil wells are such copolymers according to the invention in which the units of the formula I by the use of N-vinylformamide and the units of the formula III by the use of N-vinyl-N-methyl-acetamide , N-vinylpyrrodilone or 2-acrylamido-2-methylpropane sulfonic acid or mixtures thereof were introduced in the copolymerization.

The copolymers according to the invention are readily soluble in water or aqueous acids and are therefore easy to handle. At the. When used in pressure acidification processes, the polymers of the acid can be added in the form of aqueous 0.5 to 6% by weight solutions (polymer solutions with a concentration above 6% by weight are too viscous and therefore difficult to handle), in the form of hydrocarbon dis persions containing emulsifiers and 20 to 50% by weight of the polymer, or in the form of oil-in-water or water-in-oil emulsions containing emulsifiers and 20 to 50% by weight of the polymer. The copolymers according to the invention are preferably used in the form of a water-in-oil emulsion with the highest possible polymer content, normally 20 to 75% by weight. Oils suitable for the preparation of these water-in-oil emulsions are, for example, branched or unbranched paraffin-hydrocarbon fractions with a boiling range of 150 to 250 ° C. Depending on the monomer composition and the properties resulting therefrom, the copolymers according to the invention in concentrations of 0.06 to 0.12% by weight, at temperatures from normal room temperature to temperatures above 80 ° C., act as highly effective friction reducers, the duration of action being long, for example more lasts for more than 10 days. Even when hydrolytic degradation of side chains of the copolymer occurs, the degradation products remain acid-soluble and do not separate from the solution. The copolymers according to the invention are preferably combined with acids which are liquid under normal conditions and in particular with inorganic or strong lower organic acids. Examples of acids which can be used together with the copolymer according to the invention are hydrofluoric acid, hydrochloric acid, formic acid, acetic acid, monochloroacetic acid, dichloroacetic acid or trichloroacetic acid. The most common is the use of hydrochloric acid, which is used in concentrations of 3 to 28% by weight, depending on the required treatment conditions and the properties of the deposit.

The copolymers according to the invention are prepared by copolymerization of 5 to 50% by weight of an optionally N-substituted vinylformamide of the formula Ia »

10 to 95% by weight of acrylamide and 0 to 85% by weight of an ethylenic unsaturated monomer of formula IIIa

wherein R ¹ , R ² and X have the meanings given above.

Preferably 5 to 30% by weight of the vinylformamide of the formula (Ia), 50 to 80% by weight of acrylamide and 1 to 60% by weight of the monomer of the formula are copolymerized in purple. A particularly preferred composition is 10 to 20% by weight of N-vinylformamide, 50 to 70% by weight of acrylamide and 10 to 40% by weight of a monomer of the formula purple.

If copolymers are to be produced which have several different radicals X and / or R ² in component III, then several different, usually 3, or preferably 2, different comonomers of the formula purple are used for the copolymerization.

The copolymerization can be carried out by all known polymerization processes in the range from pH 4 to 12, preferably 6 to 9.

To adjust the pH, alkaline salts of alkali metals, e.g. Alkali carbonates, alkali hydrogen carbonates, alkali borate, di- or tri-alkali phosphates, alkali hydroxides, ammonia or organic

Amines of the formula NR ₃ ⁷ are used, in which R ^{7 is} hydrogen, alkyl having 1 to 4 carbon atoms or hydroxyethyl and where at least one of the radicals R ^{7 is} different from hydrogen.

Preferred bases for adjusting the pH are the abovementioned alkali compounds, in particular sodium hydroxide, potassium hydroxide, sodium carbonate, sodium hydrogen carbonate, potassium carbonate and potassium hydrogen carbonate and sodium or potassium borates. Another preferred base is NH ₃ .

The polymerization reaction can be initiated by high-energy electromagnetic or corpuscular radiation or by substances. which form radicals. Accordingly, organic per-compounds are suitable as polymerization initiators, such as benzoyl peroxide, alkyl hydroperoxide such as butyl hydroperoxide, cumene hydroperoxide, p-menthane hydroperoxide, dialkyl peroxides such as di-tert-butyl peroxide or inorganic per-compounds such as potassium or ammonium persulfate and hydrogen peroxide, as well as azo compounds such as azo-bisisobutobutobut 2,2'-azo-bis (2-amidinopropane) hydrochloride or azo-bis-isobutyramide. It is advantageous to use the organic or inorganic per compounds in combination with reducing substances. Examples of suitable reducing substances are sodium pyrosulfite, sodium hydrogen sulfite or condensation products of formaldehyde with sulfoxylates. The polymerization can be carried out particularly advantageously using Mannich adducts of sulfinic acids, aldehydes and amino compounds, as described, for example, in German Patent 1,301,566 are.

It is also known to add small amounts of so-called moderators to the polymerization batches, which harmonize the course of the reaction by flattening the reaction rate diagram. They thus lead to an improvement in the reproducibility of the reaction and thus make it possible to produce uniform products with extremely low quality deviations. Examples of suitable moderators of this type are nitrilotris-propionylamide or hydrohalides of monoalkylamines, dialkylamines or trialkylamines, e.g. Dibutylamine hydrochloride. Such moderators can also be used advantageously in the preparation of the copolymers according to the invention.

So-called regulators can also be added to the polymerization batches; these are compounds that influence the molecular weight of the polymers produced. Known regulators that can be used are, for example, alcohols, such as methanol, ethanol, propanol, isopropanol, n-butanol, sec-butanol and amyl alcohols, alkyl mercaptans, such as dodecyl mercapto and tert-dodecyl mercaptan, isooctyl thioglycolate and some halogen compounds, such as carbon tetrachloride, chloroform. The polymerization is usually carried out in a protective gas atmosphere, preferably under nitrogen.

The reaction can be carried out in solution, in emulsion, or under the conditions of precipitation polymerization at temperatures from 20 to 120 ° C, preferably from 40 to 100 ° C. If water is used as a solvent for the polymerization reaction, it runs in solution and an aqueous viscous solution of the copolymer is obtained. The reaction product can be isolated, either by distilling off the water from the solution, or by mixing the aqueous solution with organic solvents which are completely miscible with water, but in which the copolymer is insoluble. When such organic solvents are added to the aqueous polymer solution, the resulting polymer or copolymer precipitates and can be separated from the liquid phase, e.g. Separate by filtration. However, the aqueous solution of the polymer or copolymer obtained is preferably used directly for further use, if appropriate after adjustment to a certain desired concentration.

If the copolymerization in an organic solvent, e.g. in a lower alkanol, e.g. carried out in tert-butanol, it proceeds under the conditions of the precipitation polymerization. In this case, the resulting polymer or copolymer precipitates out in solid form in the course of the reaction and can easily be used in a conventional manner, e.g. by suction and subsequent drying.

Of course it is also possible and in some cases preferred to distill the solvent out of the reaction mixture.

Monomers which introduce units of the formula I into the copolymers are N-vinylformamide, N-vinyl-N-methylformamide and N-vinyl-N-hydroxymethylformamide, the former two being preferred. By using acrylamide in the copolymerization units of formula II in introduced the copolymer. Units of the formula III are introduced into the copolymer according to the invention by using one or more, preferably 2, monomers of the

formula

wherein R ² and X have the following meanings:

① Since N-vinylamides are not stable under acidic conditions, batches containing acidic substances must be neutralized before the polymerization, for example with the above-mentioned inorganic or organic bases or basic comonomers. Examples of preferred monomers which introduce units of the formula III into the copolymers according to the invention:

N-vinylformamide,

N-vinyl-N-methylformamide,

N-vinyl acetamide,

N-vinyl-N-methyl-acetamide,

N-vinyl pyrrolidone,

Acrylic acid, alkali or ammonium salts of acrylic acid,

or their alkali or ammonium salts,

or

To the best of our knowledge, the copolymers according to the invention described above are new, with the exception of those in which X denotes a sulfo group or a sulfoalkyl amidocarbonyl group or a salt of one of these groups (cf. US Pat. No. 4,048,077).

The copolymers according to the invention described above can also be used for thickening or for gelling acid solutions, e.g. in the process of pressure acidification, as described in our simultaneously filed patent application entitled "Water-soluble crosslinkable polymer composition, its preparation and its use" and in the priority US patent application entitled "Watersoluble Crosslinkable Polymer Compositions Containing a Metal Compound, Their Preparation and Use ", by Jeffery C. Dawson, Robert R. Mc-Daniels and Lawrence Sedillo.

The following working examples illustrate the preparation of the copolymers according to the invention.

The abbreviations used in the examples and tables AM: acrylamide

VIMA: N-vinyl-N-methylacetamide

AMPS: 2-acrylamido-2-methylpropane sulfonic acid being the exponent

1) the ammonium salt,

2) the salt with dimethyl-β-hydroxyethylamine,

3) the potassium salt and

4) the sodium salt means

AS: acrylic acid

MAS: methacrylic acid

MAM: N-methylol acrylamide

VSSNa: Na salt of vinyl sulfonic acid

NMVA: N-methylol vinylacetamide

VIA: vinyl acetamide

VIFA: vinyl formamide

VIMFA: vinyl methyl formamide

MVIFA: N-methylol vinyl formamide

MVIA: N-methylol-vinvlacetamide VPA: vinylphosphonic acid VIP: N-vinylpyrrolidone A: ammonium peroxydisulfate

B: A combination of ammonium peroxydisulfate +

Dibutylammonium hydrochloride

C: Azo-isobutyronitrile.

example 1

400 ml of deionized water and 17.7 ml of a 25% by weight aqueous ammonia solution are placed in a 2 l flask equipped with a water bath, stirrer, reflux condenser, dropping funnel and gas inlet. While introducing a weak stream of nitrogen, 9.3 g of acrylamido-methylpropanesulfonic acid and, as soon as a clear solution is present, 60 g of acrylamide, 18.6 g of N-vinylpyrrolidone and 14.7 g of N-vinylformamide are added. The pH of the solution is 6.5. The mixture is heated to 50 ° C and the polymerization is initiated by adding 5 ml of a 20% strength by weight aqueous solution of ammonium peroxydisulfate. Start after an induction period of about 10 minutes the reaction, the temperature rises to 65 ° C and the mixture becomes viscous. The mixture is then heated to 80 ° C. and held at this temperature for 2 hours. After cooling to room temperature, a highly viscous solution of the copolymer is obtained.

Example 2

500 ml of tert-butanol are placed in a 2 l flask equipped with a water bath, stirrer, reflux condenser, dropping funnel and gas inlet tube and 20 g of AMPS are suspended therein with stirring.

Then 2.2 l of ammonia gas are introduced and 65 g of acrylamide and 15 g of N-vinylformamide are added. While introducing a weak stream of nitrogen, the mixture is warmed to 50 ° C. and 1 g of azo-isobutyronitrile is added. The polymerization reaction starts after an induction period of a few minutes. The temperature rises to 81 ° C and the polymer precipitates. The reaction mixture is kept at 80 ° C. for a further 2 hours, a viscous suspension being formed. The polymer can be isolated by suction and dried at 50 ° C in a vacuum. However, it is also possible to isolate the polymer by distilling off the solvent under reduced pressure. The polymer obtained is a white, light powder which is readily soluble in water. The K value according to Fikentscher is 148.

The copolymers of the following Tables 1 and 2 can also be prepared in accordance with the above exemplary embodiments:

Example 67

A solution of 0.23 g sorbitan monolaurate, 1.09 sorbitan monostearate, 0.14 g sorbitan monooleate and 3.61 g polyoxyethylene sorbitan is placed in a 500 ml flask equipped with a water bath, stirrer, reflux condenser, dropping funnel and gas inlet -monostearate in 56.4 g of a straight-chain paraffin hydrocarbon fraction (Norpar 13 from Exxon). The solution is heated to 60 ° C. while introducing nitrogen.

5.4 g of AMPS, 6.6 g of N-methyl-N-vinylacetamide, 6.6 g of N-vinyl formamide and 7.8 g of vinyl-pyrrolidone are dissolved in a mixture by dissolving 33.6 g of acrylamide a monomer solution was prepared from 78.8 g of deionized water and 2.6 ml of 10% by weight sodium hydroxide solution. The pH of this solution is 7.4. The monomer solution is mixed with 23 mg of 2,2'-azobis (2-amidinopropane) hydrochloride and then obtain a milky white emulsion is obtained quickly added dropwise with vigorous stirring into the initially charged organic Emulgatorenlösung _/. As soon as the temperature of the batch rose again to 60 ° C, the stirring speed was reduced to about 60 revolutions per minute. A temperature rise begins after an induction time of 10 minutes. At about 80 ° C the emulsion becomes transparent. and the stirring speed is increased. The temperature continues to rise to max. 97 ° C. After the batch has cooled again to 80 ° C., stirring is continued at this temperature for a further 2 hours. A stable emulsion is obtained which contains 30% by weight of active polymer.

Example 68

67 g of a deodorized kerosene fraction with a boiling range of 190 to 240 ° C. (Exsol D, sales product of Esso Chemie, Germany) are heated to a temperature of 60 ° C. in a 1 l polymerization vessel. 0.27 g of sorbitan monolaurate, 1.3 g of sorbitan monostearate, 0.17 g of sorbitan monooleate and 4.3 g of polyoxyethylene sorbitan monostearate are successively dissolved therein with gentle stirring. With further gentle stirring and introducing a stream of nitrogen then heated the solution to 60 ° C. In a second vessel, 94 ml of water, 6.4 g of AMPS, 44.8 g of acrylamide, 9.2 g of vinyl pyrrolidone and 10.6 g of N-vinyl-formamide are dissolved with stirring. The solution thus obtained is adjusted to a pH of 8 to 10 by dropwise addition of 10% by weight aqueous sodium hydroxide solution and 0.1 g of ammonium persulfate is added. The aqueous monomer solution thus obtained is dropped into the organic emulsifier solution introduced and emulsified with rapid stirring through a dropping funnel. The polymerization reaction starts after about 30 minutes with an increase in temperature. The temperature rises to 80 to 90 ° C. in the course of 15 minutes. After the polymerization had subsided, the solution was stirred at 80 ° C. for a further 2 hours. A stable emulsion with a polymer content of 30% by weight is obtained. The molecular weight of the polymer is 95,000.

Example 69

1.85 g of sorbitan monostearate are dissolved in a technical isomeric hydrocarbon mixture with a boiling range from 200 to 240 ° C. (Isopar M from Exxon Corp.). This solution is placed in a 2 1 reaction flask equipped with a stirrer, thermometer and gas inlet tube.

A monomer solution is then prepared in a separate vessel by dissolving 25 g of acrylamide, 3.7 g of acrylic acid and 9.2 g of N-vinylformamide in 40 ml of deionized water, and the pH of this solution is adjusted by adding an aqueous 20% by weight. % sodium hydroxide solution set to 8.5. With vigorous stirring, the aqueous monomer solution is slowly run into the organic sorbitan monostearate solution and then the air in the reaction vessel is displaced by nitrogen.

After adding 0.07 g of 2,2'-azo-bis-isobutyronitrile, dissolved in acetone, the emulsion is slowly heated to 60 ° C with stirring. The polymerization is complete after 2.5 hours and a stable emulsion of the copolymer is obtained. Example 70

67 g of a technical isomeric hydrocarbon fraction with a boiling range of 200 to 240 ° C (Isopar M from Exxon Corp.) are placed in a 1 1 polymerization vessel and heated to 60 ° C. While stirring, 0.27 g of sorbitan monolaurate, 1.3 g of sorbitan monostearate, 0.17 g of sorbitan monooleate and 4.3 g of polyoxyethylene sorbitan monostearate are dissolved in succession.

In a separate vessel, 12.8 g of VIMA, 39.8 g of acrylamide, 12.0 g of vinyl pyrrolidone and 6.6 g of N-vinylformamide are dissolved in 94 ml of water with stirring. The pH of this solution is adjusted to 8 to 10 by dropwise addition of 10% by weight aqueous sodium hydroxide solution, and 0.1 g of amraonium persulfate is then added. This monomer solution is then added dropwise with vigorous stirring through a dropping funnel into the submitted organic emulsifier solution and emulsified therein. The polymerization reaction starts after about 30 minutes. the reaction temperature rising to 80-90 ° C over 15 minutes. After the reaction has subsided, the solution is stirred at 80 ° C. for a further 2 hours. A stable emulsion with a polymer content of 30% by weight is obtained. The molecular weight of the polymer is 95,000.

According to working examples 68 to 70, the products in the following Table III can also be produced, which can also be used as valuable friction reducers for aqueous acids.

All amounts in Table III are parts by weight

Examples 71

In order to demonstrate the friction-reducing property of the copolymers according to the invention, flow tests with 7.5% by weight hydrochloric acid were carried out once without and once with an addition of the copolymer according to the invention prepared according to embodiment 1.

A tube loop was used to carry out the experiment, in which the fluid is pumped through a series of tubes of known length and diameter with a certain flow rate. The hydromechanical pressures are measured at both ends of a given, defined pipe section. Since the flow rate and the pressure differences at the pipe section in question are known, it is thus possible to determine the friction pressure of various fluids as a function of the flow rate of the fluid graphically in the pipe.

The first test was carried out with 208 1 7.5% by weight hydrochloric acid, which contained 760 ml of a commercially available corrosion inhibitor, pump speeds of 38 to 57 1 / min using a tube with an inner diameter of 0.925 cm, 19 to 170 1 / min when using a tube with an inner diameter of 1.25 cm and 19 to 454 1 / min using a tube with an inner diameter of 2.66 cm. After this test series, 224 g of the copolymer prepared in Example 1 were added to the 7.5% by weight hydrochloric acid, corresponding to a copolymer concentration of 0.1% by weight in the acid. The flow-through experiment was repeated with this polymer-containing acid. The measurement results obtained in both cases on the tube sections with an internal diameter of 0.925 cm, 1.25 cm and 2.66 cm have been illustrated in FIGS. 1, 2 and 3, respectively.

Example 72

To demonstrate the acid solubility of copolymers according to the invention, they were subjected to the following test in comparison with commercially available friction reducers:

200 ml of 15% strength by weight hydrochloric acid were introduced into three 225 ml vessels. The acid in vessel 1 was then prepared according to Example 2, 2.0 g of the polymer according to the invention, 2.9 g of a commercially available friction reducer emulsion LFR-1 in vessel 2 and 3.2 g of a commercially available friction reducer emulsion in vessel 3 LFR-2 added. The commercial products LFR-1 and LFR-2 are copolymers of acrylamide and acrylic acid with molecular weights from 500,000 to 2,000,000. The polymer contents of the emulsions LFR-1 and LFR-2 are unknown, but it can be assumed that there are differences between the two products with regard to the amount of active copolymer, the coraonomer ratio of the polymers and the type of emulsifier. The samples in the three vessels were heated to 60 ° C for 24 hours. After this time, the solution in vessel 1 which contains the copolymer according to the invention was still completely clear, and the copolymer was therefore full constantly soluble. In contrast, vessels 2 and 3 had white plugs of precipitation. The separated solids were suctioned off and washed out with water and then with methanol. The filter residues were then dried in vacuo at 40 ° C. overnight. The amounts obtained are shown in Table IV below.

Example 73

A natural gas well in West Texas is selected for pressurization. The well has a production interval of between 1100 and 1120 meters. The sole temperature in this interval is 43 ° C, the permeability of the formation on average 0.15 md (millidarcy). The tube width is 6.0 cm; The spontaneous productivity of the well before treatment is approximately 168 m ³ gas per day.

The pressurizing fluid to be used is prepared by first 3785 1 28 wt. % hydrochloric acid mixed with 35960 l of fresh water and then 79.5 l (0.2 wt.%) of the polymer emulsion prepared according to Example 3 are added to the dilute acid obtained. The fluid thus obtained is at a rate of 1589.8 1 / min. pressed into the bore under a pressure of 310.5 bar. After 25 minutes the pumping is finished and the hole is closed to give the acid an opportunity to react with the rock.

After 60 minutes, the pressure at the top of the bore is released and production is restored. A measurement of the production rate shows a significant increase in the productivity of the well.

Claims

P a t e n t a n s r u c h e

1. A method for stimulating natural gas and oil drilling by pressure acidification with an acid solution, characterized in that the acid contains 0.06 to 0.12% by weight of a copolymer which is soluble in water or aqueous acids and contains at least 5% in its macromolecule. % of units containing a formylamino group of the formula

exhibit,

wherein R ^{1 is} hydrogen, methyl or hydroxymethyl, and at least 10% by weight of units having an aminocarbonyl group of the formula

exhibit,

contains.

2. The method according to claim 1, characterized in that the copolymer is in a statistical distribution

5 to 50% by weight from units of the formula I.

(I)

10 to 95% by weight from units of the formula II ( _{II) and}

O to 85% by weight from units of the formula III

(III)

composed in which R is hydrogen, methyl or hydroxymethyl and R ^{2 is} hydrogen or methyl and X is cyan, carboxyl, or its alkali or ammonium salts, alkoxycarbonyl having 1 to 6 carbon atoms, hydroxyalkoxycarbonyl having 1 to 3

Carbon atoms; N-methylolamidocarbonyl of the formula HOCH ₂ NH-CO-, the methylol group of which may be etherified with alkanols having 1 to 4 carbon atoms; Alkanoylamino having 1 to 4 carbon atoms, which may optionally be substituted by methylol or alkyl having 1 to 4 carbon atoms; Pyrrolidonyl- (1); Phenyl; Pyridinium; the sulfonic acid group; Sulfoalkylamidocarbonyl of 1 to 4 carbon atoms; the phosphonic acid group, where sulfonic acid and phosphonic acid groups can also be present as alkali or ammonium salts; a radical of formula IV

wherein R ³ and R ^{4 are the} same or different and represent alkyl having 1 to 4 carbon atoms; a radical of formula V

VI

6 wherein R ⁵ and R ^{6 are the} same or different and represent alkyl having 1 to 4 carbon atoms and p is a number of

1 to 4; and the quaternized groups corresponding to formulas V and VI.

3. Process according to claims 1 and 2, characterized in that the copolymer consists of

5 to 30% by weight of units of the formula I,

50 to 80% by weight of units of the formula II and

1 to 60% by weight of units of the formula III.

4. Process according to claims 1 to 3, characterized in that a copolymer is used in which

X carboxyl, the sulfonic acid group, 3-sulfo-2-methyl-propyl- (2) amidocarbonyl of the formula

HOCH ₂ NH-CO-, the methylol group of which may be etherified with alkanols with 1 to 4 carbon atoms; Alkanoylamino having 1 to 4 carbon atoms, which may optionally be substituted by methylol or alkyl having 1 to 4 carbon atoms; Pyrrolidonyl- (1); Phenyl; Pyridinium; the phosphonic acid group or its alkali or ammonium salts; a radical of formula IV

(IV)

(V)

VI

(VI)

wherein R ⁵ and R ^{6 are the} same or different and represent alkyl having 1 to 4 carbon atoms and p is a number of

1 to 4; and the quaternized groups corresponding to formulas V and VI.

7. Water-soluble copolymer according to claim 6, characterized in that it consists of

5 to 30% by weight of units of the formula I,

50 to 80% by weight of units of the formula II and

1 to 60% by weight of units of the formula III.

8. Water-soluble copolymer according to claims 6 and 7, characterized in that X carboxyl, alkanoylamino with 1 to 4 carbon atoms, which may be N-substituted with methylol or alkyl with 1 to 4 carbon atoms may mean pyrrolidonyl (1) or a radical of the formulas V or VI given and defined above, where the carboxyl group may also be present as the sodium, potassium or ammonium salt.

9. Water-soluble copolymer according to claims 6 to 8, characterized in that it has a K value between 25 and

250 corresponding to a molecular weight of 20,000 to

15. 10 ⁶ has.

10. Aqueous copolymer solution containing 0.5 to 6% by weight of a copolymer according to claims 6 to 9.

11. Water-in-oil emulsion which has as the aqueous phase a copolymer solution of a copolymer according to claims 6 to 9.