RU2278968C1 - Acid treatment method for carbonate reservoir of high-temperature formation - Google Patents

Abstract

FIELD: oil and gas industry, particularly bottomhole formation zone treatment.

SUBSTANCE: method involves serially or simultaneously injecting aqueous acetic ester solution and water plugs in formation; holding the plugs in formation to form acetic acid in formation and to provide acetic acid reaction with formation rock; bringing well into operation. 20% aqueous acetic ester solution mixed with 3% of hydrochloric acid is used. Ratio between aqueous solution and water plugs is 1:1.4-4 in dependence of formation temperature.

EFFECT: increased simplicity and reduced costs due to cheap available reagent usage, increased intensity of oil and water production due to progressive acid forming in formation, increased radius of formation interval to be treated, elimination of oil-field equipment and improved acid treatment.

3 ex, 3 tbl

Description

The method of acid treatment of the carbonate reservoir of a high-temperature formation relates to the oil and gas industry, in particular to acid treatments of the bottom-hole formation zone in order to intensify the flow of oil.

In high-temperature formations, conventional acidic solutions quickly decrease their activity, so the injection of an acid-generating composition in the formation provides a deeper penetration into the formation and is most effective.

With increasing depth of the wells, the processing process is complicated due to the increased effect of acids on the downhole equipment. To reduce the corrosive activity of acids, corrosion inhibitors are used. However, their effectiveness is significantly reduced at high temperatures; the consumption of inhibitors also increases. In addition, in high-temperature wells, large amounts of corrosion inhibitors react with formation rocks to form insoluble solids that clog pores and reduce permeability.

Since hydrochloric acid quickly reacts with carbonate rock, methods have been developed to slow down its reaction by emulsification, gelation and a chemical method.

A known method is used instead of hydrochloric acid to slow down the reaction with carbonates of lower carboxylic acids: formic and acetic acids [1]. The reaction of acetic acid is, of course, slowed down, since the accumulation of the reaction product, carbon dioxide, reduces the reaction rate. When carbon dioxide seeps into the formation or is absorbed by oil, water or hydrocarbon gas, the reaction of acetic acid continues.

To date, slow-speed acids have had limited advantages over conventional hydrochloric acid, since a significant increase in permeability, extending at least 3 m from the wellbore, is necessary in order to achieve significant improvements in oil production [2].

Closest to the proposed technical solution is a method of treating an underground formation, which involves injecting a substrate for the enzyme into the formation, the substrate being able to turn into organic acid by the action of the enzyme [3] (prototype), characterized in that hydralase or lipase is used as the enzyme, or esterase. The disadvantage of this solution is the production of acid as a result of a reaction catalyzed by enzymes obtained from sprouted wheat or animal organs. In addition, used in the known method, the concentration (0.1 - 20 vol.%) Of the starting reagents to reduce their high corrosivity allows you to get a weakly concentrated acid with a small dissolving capacity, with a small radius of the acid on the treated interval of the reservoir, in contrast to the proposed solution .

The problem of the proposed invention is to intensify the extraction of oil and water from the formation due to the gradual formation of acid in the formation, increasing the radius of the treated interval of the formation, eliminating corrosion of oilfield equipment and improving the efficiency of acid treatment.

The problem is achieved in that in the method of acid treatment of the carbonate reservoir of a high-temperature formation, including injecting into the formation simultaneously or sequentially the rims of an aqueous solution of an ester of acetic acid and water, technological exposure to form acetic acid in the formation and its reaction with the rocks of the formation and putting the well into operation, according to the invention, as the specified solution, a 20-60% solution of an ester of acetic acid is used, into which 3% hydrochloric acid is introduced. The ratio of these rims is 1: 1.5-4, depending on the temperature of the formation.

The essence of the proposed method is a technology that provides for the conversion of carboxylic acid esters into acetic acid in the formation under the influence of temperature and a catalyst of hydrogen ions, followed by exposure. The ratio of ethyl acetate rim to water can vary from 1: 4 to 1: 1.5.

Compared with known methods of acid treatment, the present invention has the following advantages:

- represents the way in which acid can be obtained in situ in the reservoir (as in the prototype) and at such a speed that in the immediate vicinity of the wellbore all acid is not produced and not consumed;

- as a catalyst for the reaction in the reservoir, a cheap and affordable reagent is selected - hydrochloric acid,

- does not corrode or very weakly corrodes the equipment of the well,

- a by-product of the conversion of the ester of acetic acid to acid, ethyl alcohol reduces the surface tension between oil and water, helps to accelerate well cleaning,

- the possibility of acid treatment of horizontal wells without the use of special methods,

- esters of acetic acid are not corrosive reagents.

To implement the proposed method, ethyl acetate or butyl acetate is used according to GOST 8981-78, which are currently used as a solvent in various industries. According to the physicochemical properties, ethyl acetate or butyl acetate must comply with the requirements and standards specified in table 1.

To prove the compliance of the claimed invention with the criterion of "industrial applicability", we give specific examples of determining the effectiveness of the proposed method in laboratory conditions in terms of changes in the concentration of CH ₃ COOH.

Example 1. The study of the self-generation of acetic acid as a result of hydrolysis of ethyl acetate at high temperatures

The self-generation (without the introduction of a catalyst) of acetic acid was studied as a result of hydrolysis of ethyl acetate at temperatures of 50, 70, 90 ° С. The methodology for studying the reaction of hydrolysis of ethyl acetate was as follows: each composition was placed in a thermostat for a certain time, after exposure to a given temperature, the composition determined the total and free acidity. The concentration of CH ₃ COOH was determined by the difference between total and free acidity. The degree of hydrolysis of ethyl acetate was calculated from the found concentration of CH ₃ COOH.

Table 2.
Self-generation of acetic acid by hydrolysis of ethyl acetate at high temperatures Composition, wt.% Temperature ° C The equilibrium concentration of CH ₃ COOH,% Time, hour. The degree of hydrolysis of ethyl acetate,% ethyl acetate water twenty 80 fifty 1,1 5 22.6 twenty 80 70 3,1 2 23.0 twenty 80 90 3.6 1,5 23,2 40 60 fifty 2 6 10.0 40 60 70 2.7 four 7.5 40 60 90 eighteen 1,0 66.1 60 40 fifty 3.0 6 7.2 60 40 70 3.0 6 7.2 60 40 90 16.9 3,5 41.3

Optimization of catalyst concentration in the hydrolysis of ethyl acetate.

The saponification reaction of ethyl acetate in the presence of hydrogen ions was studied. Hydrochloric acid was used as a catalyst for the saponification reaction, while its concentration varied within 1, 3, 15%. The change in the concentration of CH ₃ COOH in the compositions over time was determined. The maximum achieved concentration of CH ₃ COOH and the time it was reached are shown in Table 3. Also, Table 3 gives the characteristics of the catalyst operation — an increase in the yield of acetic acid (expressed as a percentage) with the introduction of HCl compared to the concentration of CH ₃ COOH obtained by saponification of ethyl acetate without a catalyst .

Table 3
The equilibrium concentration of acetic acid achieved as a result of the catalytic effect of hydrochloric acid on the saponification of ethyl acetate at high temperatures Composition, wt.% Temperature ° C The concentration of CH ₃ COOH,% Time, hour. The degree of hydrolysis of ethyl acetate,% The increase in acid yield with the introduction of HCl,% ethyl acetate Hcl water twenty one 79 fifty 7.5 four 53.9 85 twenty 3 77 fifty 8.7 6 63.7 87.4 twenty fifteen 65 fifty 8.7 four 63.7 87.4 twenty one 79 70 7.5 one 55.3 58.7 twenty 3 77 70 8.4 one 61,4 63.1 twenty fifteen 65 70 7.5 6 54.7 58.7 twenty one 79 90 9.1 1,5 64.0 60,4 twenty 3 77 90 9.6 1,0 68.3 62.5 twenty fifteen 65 90 9.5 1,0 70.9 62.1 40 one 59 fifty 13.8 5 50,5 85.5 40 3 57 fifty 18.9 5.5 69,4 88.2 40 fifteen 45 fifty 7.2 6.5 26.6 72,2 40 one 59 70 12.6 3 46.3 78.6 40 3 57 70 12.5 3 46.9 78.8 40 fifteen 45 70 14.7 5 58.4 81.6 40 one 59 90 18.8 2.0 69.0 4.2 40 3 57 90 18.3 1,5 67.2 1,6 40 fifteen 45 90 15.6 2.0 57.3 0 60 one 39 fifty 7.8 6 19 61.5 60 3 37 fifty 14.7 6 36 79.6 60 fifteen 25 fifty 8.1 6 19.9 63.0 60 one 39 70 20.8 3 50.8 85.6 60 3 37 70 23.1 3 56.5 87.0 60 fifteen 25 70 21 3 51.8 85.7 60 one 39 90 23,2 2,5 56 26.7 60 3 37 90 22 2,5 54.5 22.7 60 fifteen 25 90 23.7 2 46.6 28.3

At a temperature of 50 ° C and 70 ° C, the greatest yield of acetic acid is observed with the introduction of 3% HCl in 20-60% ethyl acetate compositions. At a temperature of 90 ° C, the highest yield of acetic acid is observed with the introduction of 3% HCl in 20% ethyl acetate compositions, the introduction of HCl in 60% ethyl acetate compositions increases the yield of acetic acid by 23-28%.

Thus, the proposed method of acid treatment contains:

1. Injection of an aqueous solution of an ester of acetic acid and 3% hydrogen ions. The ratio of ethyl acetate rim to water can vary between: 1: 4 or 1: 1.5, depending on the concentration of acetic acid necessary for the processing of carbonates or iron oxides.

2. Exposure to the conversion of the ester of acetic acid to acetic acid and for reaction with the rock. (At temperatures of 50-70 ° C, the exposure time is 6-8 hours. At temperatures of 90 ° C and above - 2-4 hours.)

Dissolution of carbonate rock.

The experiments were carried out in flasks with a reflux condenser, which were placed in a thermostat with a given temperature. Marble plates with a fixed mass and surface were used as carbonate rock. The amount of composition per unit surface of the marble plate was constant in the experiments and was 3 cm ³ / cm ² . The results of the study of the solubility of marble in 20% ethyl acetate compositions at a temperature of 50 ° C are presented (table 4). The methodology for the study of the solubility of a marble plate in the test composition was as follows: each composition was placed in a thermostat for 0.5 hours, after exposure to a given temperature, a marble plate was introduced into the composition and the reaction time was maintained at a predetermined temperature. After that, the plate was washed, dried, and its weight was determined after reaction with the acid composition.

Table 4. Time, hour. The solubility of marble (%) in the following compositions: 20% ethyl acetate + 80% water 20% ethyl acetate + 3% HCl + 77% water 13.6% CH ₃ COOH one 0.42 6.31 2.70 2 0.67 7.53 2.81 3 0.92 9.22 3.68 four 1,50 10.94 5 1.75 11.11 6 2.10 11.43

The theoretical yield of 20% ethyl acetate is 13.6% CH ₃ COOH. Comparison of the rate of dissolution of marble with acid, formed from the aqueous composition of ethyl acetate, with the rate of dissolution of marble with acetic acid shows a slowdown in the dissolution of marble by 4-6 times. When using hydrogen ions as a catalyst for the reaction of saponification of ethyl acetate, the solvent capacity of the composition increases, but the slowdown of the dissolution rate of the marble is preserved.

Example 2

In the method for acidizing a carbonate reservoir of a high temperature formation (50 ° C.), the rims of a 40% aqueous solution of an acetic acid ester solution, into which 3% hydrochloric acid and water are introduced, are simultaneously pumped into the formation. The ratio of these rims is 1: 4. Carry out technological exposure for the formation of acetic acid in the formation and its reaction with the rocks of the formation for 6 hours and put the well into operation.

Example 3

In the method for acidizing a carbonate reservoir of a high temperature formation (90 ° C.), the rims of a 20% aqueous solution of an acetic acid ester solution, into which 3% hydrochloric acid and water are introduced, are sequentially pumped into the formation. The ratio of these rims is 1: 1.5. Carry out technological exposure for the formation of acetic acid in the formation and its reaction with the rocks of the formation for 4 hours and put the well into operation.

The application of the proposed method is economically beneficial not only from the point of view of efficiency, but also due to the smaller amount of work and the number of workers, lengthening the life of pipes, packers and other equipment.

Information sources

1. M. Christian and others. Increase in productivity and injectivity of wells. - M .: Nedra, 1985, p. 53-54.

2. Williams, Gidley and Schechier, 1979, Ch 10, in Acidizing Funamentals, Soc. Petrol. Eng. ofALME, New York, Dallas.

3. RU 2122633 C1, E 21 B 43/27, 11/27/1998, Bull. No. 33.

Claims (1)

A method of acidizing a carbonate reservoir of a high-temperature formation, including injecting into the formation simultaneously or sequentially the rims of an aqueous solution of an ester of acetic acid and water, technological exposure for the formation of acetic acid in the formation and its reaction with the rocks of the formation and putting the well into operation, characterized in that As the specified solution, a 20-60% solution of acetic acid ester is used, into which 3% hydrochloric acid is introduced, and the ratio of the rims of the specified solution and water is nent 1: 1.5-4, depending on the temperature of the formation.