Non-oxidative weakly acidic polyacrylamide degrading agent and method of making and using same

Abstract

The application discloses a non-oxidative weak-acid polyacrylamide degrading agent and a preparation and use method thereof, and the degrading agent comprises the following components: a reducing agent, a regulator, a mutual solvent and water; the reducing agent is one of 3-O-ethyl ascorbic acid ether and L-ascorbic acid-2,6-dibutyrate; the regulator is ammonium chloride; and the mutual solvent is one of ethylene glycol monobutyl ether and isopropyl alcohol. The problems that the existing degrading agent needs to be isolated by a plug for redox reaction with subsequent injected mud acid or secondary precipitation is caused by metal ions such as Na + , K + , Fe 2+ and the like in the degrading agent and subsequent injected mud acid are effectively solved.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to the technical field of oil production engineering, and relates to a non-oxidizing weak-acidic degrading agent for removing polyacrylamide blockage and a preparation method thereof. BACKGROUND

[0002] The statements in this section merely provide background information related to the present disclosure and do not constitute prior art.

[0003] With the continuous development of oil fields, some oil fields gradually enter the high water cut development stage, and the water cut is more than 90%. For this reason, polymer flooding, ternary compound flooding and other tertiary oil recovery technologies are applied in the field, and the recovery degree of the oil field is greatly improved compared with water flooding. However, because the displacement medium of polymer flooding and ternary compound flooding and the chemical flooding sewage for reinjection all contain polyacrylamide, the reservoir pore becomes smaller due to the adsorption and retention of polyacrylamide, and the inorganic particles are also carried by the viscous polyacrylamide solution to migrate and block the pores between mineral particles. Under the combined action of polyacrylamide and inorganic particles, the reservoir permeability is greatly reduced, and the injection capacity is decreased.

[0004] For the injection wells with decreased injection capacity caused by the above reasons, chemical deplugging measures are used in the field to remove the blockage caused by polyacrylamide and inorganic particles, and good results have been achieved. However, there are the following problems:

[0005] Firstly, most of the conventional degrading agents for removing polyacrylamide blockage are oxidizing agents, which will have an oxidation-reduction reaction with the subsequent injected acid liquid system, such as mud acid, for removing inorganic blockage. For example, the oxidizing agent ammonium persulfate will react with hydrochloric acid in the mud acid system, resulting in a significant decrease in the performance of degrading polyacrylamide. At the same time, a large amount of gas is generated in the reaction in the closed space of the wellbore, which brings safety hazards. Therefore, the injection needs to be separated, and an isolation plug needs to be injected in the middle to avoid the contact between the oxidizing agent and the mud acid system, resulting in complex construction procedures and long construction period.

[0006] Secondly, some polyacrylamide degrading agents contain metal ions such as Na + , K + , Fe 2+ , which have good degrading performance for polyacrylamide. However, the introduction of a large amount of metal ions such as Na + , K + , Fe 2+ will react with the residual mud acid after removing inorganic blockage, generating secondary precipitates of sodium fluorosilicate and potassium fluorosilicate. At the same time, with the gradual increase of the pH value of the formation fluid in the subsequent water injection process, Fe 2+ will also generate precipitates, affecting the effectiveness of the measures. The mud acid after removing inorganic blockage can be replaced by an acid liquid system such as organic acid in the field to avoid the generation of secondary precipitates, but the cost of the reagent will increase.

[0007] It should be noted that the information disclosed in the above background section is only for the purpose of strengthening the understanding of the background of the present disclosure, and thus can contain information that does not constitute prior art. SUMMARY

[0008] Therefore, the present disclosure provides a non-oxidative weak acid polyacrylamide degrading agent, which solves the problem that the existing degrading agent or the subsequent injected mud acid needs to be isolated by a plug for redox reaction, or the problem that the secondary precipitation is caused by the metal ions such as Na + , K + , Fe 2+ and the like in the degrading agent and the subsequent injected mud acid.

[0009] In addition, the present disclosure also provides a preparation method and a use method of the degrading agent.

[0010] In a first aspect, the non-oxidative weak acid polyacrylamide degrading agent comprises:

[0011] a reducing agent, a regulator, a mutual solvent and water.

[0012] The reducing agent is one of 3-O-ethyl ascorbic acid ether and L-ascorbic acid-2,6-dibutyrate.

[0013] In the present disclosure and possible embodiments, the regulator is ammonium chloride.

[0014] In the present disclosure and possible embodiments, the mutual solvent is one of ethylene glycol monobutyl ether and isopropyl alcohol.

[0015] In the present disclosure and possible embodiments, the amounts of the components are respectively:

[0016] The reducing agent is 0.5-1.0%, the regulator is 1.0-3.0%, the mutual solvent is 0.1-0.3%, and the rest is water.

[0017] In a second aspect, a preparation method of the non-oxidative degrading agent of the first aspect comprises:

[0018] The mutual solvent, the reducing agent and the regulator are added into the water in proportion and mixed to obtain the non-oxidative degrading agent.

[0019] In a second aspect, a use method of the non-oxidative degrading agent of the first aspect comprises:

[0020] The non-oxidative degrading agent is prepared into a solution with a mass concentration of 1% and injected into a water well to be plugged, and then acid liquid is continuously injected.

[0021] The present disclosure has the following beneficial effects:

[0022] The non-oxidative weakly acidic polyacrylamide degrading agent of the present disclosure has good compatibility with acid liquid systems such as mud acid, does not react after mixing, and can be continuously injected on site for the non-oxidative weakly acidic degrading agent for removing polyacrylamide blockage and the acid liquid system such as mud acid for removing inorganic blockage, without the need for a clean water slug for isolation, simplifying the construction process and shortening the construction period. In addition, the degrading agent does not react with the mud acid residual liquid after removing the inorganic blockage to generate secondary precipitation, does not cause secondary damage to the reservoir, and further ensures the effect of the plugging removal measure. The existing degrading agent or the subsequent injected mud acid is effectively solved. Oxidation-reduction reaction needs to be isolated by a slug, or the problem of secondary precipitation produced by the metal ions such as Na + , K + , Fe 2+ and the subsequent injected mud acid. BRIEF DESCRIPTION OF DRAWINGS

[0023] The above and other objects, features and advantages of the present disclosure will become more apparent from the following description of embodiments of the present disclosure with reference to the accompanying drawings, in which:

[0024] Figure 1 is the viscosity change curve of the polyacrylamide solution at 45°C after reacting with the degrading agent in the embodiments of the present disclosure. DETAILED DESCRIPTION

[0025] The present disclosure is described below based on the embodiments, but it is worth noting that the present disclosure is not limited to these embodiments. In the following detailed description of the present disclosure, some specific details are described in detail. However, those skilled in the art can also fully understand the present disclosure without detailed description of the parts.

[0026] In addition, those of ordinary skill in the art should understand that the drawings provided are only for the purpose of illustrating the objects, features and advantages of the present disclosure, and the drawings are not actually drawn to scale. At the same time, unless the context clearly requires otherwise, the terms "including", "containing" and the like in the entire specification and claims should be interpreted as containing the meaning and not as exclusive or exhaustive; that is, as "including but not limited to".

[0027] Example 1:

[0028] Take 3-O-ethyl ascorbic acid ether 3.0 g, ammonium chloride 7.5 g, ethylene glycol monobutyl ether 1.0 g, and water 488.5 g. Mix the above components uniformly to prepare degrading agent I.

[0029] Example 2:

[0030] Take L-ascorbic acid-2,6-dibutyrate 3.0 g, ammonium chloride 7.5 g, ethylene glycol monobutyl ether 1.0 g, and water 488.5 g. Mix the above components uniformly to prepare degrading agent II.

[0031] Example 3:

[0032] Take 3-O-ethyl ascorbic acid ether 3.0 g, ammonium chloride 7.5 g, isopropyl alcohol 1.0 g, water 488.5 g, mix the above components uniformly, and prepare degrader III.

[0033] Example 4:

[0034] Take L-ascorbic acid-2,6-dibutyrate 3.0 g, ammonium chloride 7.5 g, isopropyl alcohol 1.0 g, water 488.5 g, mix the above components uniformly, and prepare degrader IV.

[0035] Example 5:

[0036] Take 3-O-ethyl ascorbic acid ether 5.0 g, ammonium chloride 10 g, ethylene glycol monobutyl ether 1.5 g, water 483.5 g, mix the above components uniformly, and prepare degrader V.

[0037] Example 6:

[0038] Take L-ascorbic acid-2,6-dibutyrate 4.0 g, ammonium chloride 8 g, ethylene glycol monobutyl ether 1.2 g, water 486.8 g, mix the above components uniformly, and prepare degrader VI.

[0039] The degraders I-IV prepared by the embodiments of the present disclosure and the commonly used oxidative degraders (5% ammonium persulfate, 10% hydrogen peroxide) in the art are evaluated for performance, as follows:

[0040] 1. Compatibility evaluation:

[0041] Take 100 ml of degrader I, degrader II, degrader III, degrader IV, 5% ammonium persulfate, and 10% hydrogen peroxide, respectively, and add them to 100 ml of conventional mud acid (i.e. a mixed acid of hydrochloric acid and hydrofluoric acid in a proportion of 12:3), mix uniformly, and observe whether gas, flocculation, and precipitate are generated in the solution; after placing the solution in an environment at 45°C for 24 h, observe whether gas, flocculation, and precipitate are generated in the solution; the specific evaluation results are shown in Table 1.

[0042] Table 1. Compatibility evaluation results

[0043]

[0044] As can be seen from Table 1, the degraders I, II, III, and IV have good compatibility with the mud acid, and no gas, flocculation, or precipitate is generated after mixing, while the ammonium persulfate and hydrogen peroxide solutions have poor compatibility with the mud acid, and a large amount of gas is generated after mixing, which cannot meet the requirements of field application.

[0045] 2. Degrading performance evaluation:

[0046] The molecular weight 1600-1900 million polyacrylamide was prepared into a solution with a mass fraction of 300 mg / L, and placed at room temperature for 24 h; 10 ml of each of the degradation agent I, the degradation agent II, the degradation agent III and the degradation agent IV was added into 100 ml of the polyacrylamide solution, mixed uniformly and placed in a 45°C water bath, and the viscosity of the solution was tested every 30 min; the specific evaluation results are shown in Table 2 below and Figure 1 :

[0047] Table 2 Evaluation results of the degradation performance of the degradation agents I-IV

[0048]

[0049] As can be seen from Table 2, after the degradation agent I, the degradation agent II, the degradation agent III and the degradation agent IV reacted with the polyacrylamide solution for 120 min, the viscosity of the polyacrylamide solution was reduced to below 3 mpa.s, and the viscosity of the degraded polyacrylamide solution was close to that of water, so that the plugging of the reservoir by the polyacrylamide solution can be removed.

[0050] As can be seen from Figure 1 , the four non-oxidizing weakly acidic polyacrylamide degradation agents in the examples have good degradation effect on the polymers and fast degradation speed.

[0051] 3. Evaluation of corrosion performance:

[0052] The treated N80 test piece was hung in the solutions of the degradation agent I, the degradation agent II, the degradation agent III and the degradation agent IV, sealed and placed in a 45°C water bath, taken out after 4 h, and the corrosion rate was measured; the specific evaluation results are shown in Table 3 below:

[0053] Table 3 Evaluation results of the corrosion performance of the degradation agents I-IV

[0054]

[0055] As can be seen from Table 3, the corrosion rates of the degradation agent I, the degradation agent II, the degradation agent III and the degradation agent IV on the N80 test piece are all below 1 g / m 2 ·h, which meets the requirements of field application.

[0056] 4. Evaluation of natural core plugging removal performance:

[0057] Firstly, the core was driven by the polyacrylamide-containing sewage containing plugging substances such as polyacrylamide and suspended solids, then the plugging core was removed by the degradation agents I-IV and mud acid respectively, and the permeability of the core after the sewage driving, the degradation agent driving and the mud acid driving was measured respectively; the specific evaluation results are shown in Table 4 below:

[0058] Table 4 Evaluation results of the core plugging removal performance of the degradation agents I-IV

[0059]

[0060] From Table 4, it can be seen that the degradation agent I, the degradation agent II, the degradation agent III and the degradation agent IV have obvious effects on the core plugging by sewage, and the permeability increasing rates are all above 100%; the subsequently injected mud acid can further plug the core after sewage plugging, and the core permeability is increased by more than 75% again; the degradation agent and the mud acid solution have good effects when used in combination, and can make the permeability of the core after poly sewage plugging be restored to more than 130% of the initial permeability.

[0061] Through the above examples and evaluation experiment results, the degradation agent of the present application has the following advantages compared with conventional oxidative degradation agents:

[0062] ①Polyacrylamide can be degraded by using the reducing agent 3-O-ethyl ascorbic acid ether or L-ascorbic acid-2,6-dibutyrate, and the viscosity of a polyacrylamide solution with a molecular weight of 16-19 million and a mass fraction of 300 mg / L can be rapidly degraded to below 3 mpa.s within 2 hours;

[0063] ②The 3-O-ethyl ascorbic acid ether or L-ascorbic acid-2,6-dibutyrate is a non-oxidizing agent, and the aqueous solution is weakly acidic, has good compatibility with acid liquid systems such as mud acid, does not react after mixing, and can be continuously injected on site for non-oxidizing weakly acidic degradation agents for removing polyacrylamide plugging, mud acid and other acid liquid systems for removing inorganic plugging materials, without the need for a water slug for isolation, and without the problems of agent failure and ineffective measures, and can also simplify the construction process and shorten the construction period;

[0064] ③The use of the adjusting agent can replace Na + , K + and other metal ions in the reservoir minerals, and can also displace the original Na + , K + and other metal ions in the reservoir fluid to the deep part of the oil layer, prevent the generation of secondary precipitates by contacting the subsequent mud acid residual liquid, and ensure the effect of the plugging removal measures;

[0065] ④The degradation agent itself does not contain Na + , K + , Fe 2+ and other metal ions, does not react with the mud acid residual liquid after removing inorganic plugging materials to generate secondary precipitates, does not cause secondary damage to the reservoir, and further ensures the effect of the plugging removal measures.

[0066] The above-described embodiments are merely illustrative of the implementation of the present disclosure, which are described in a more specific and detailed manner, but should not be understood as a limitation on the scope of the patent of the present disclosure. It should be noted that, for those skilled in the art, without departing from the concept of the present disclosure, a number of modifications, equivalent replacements, improvements, etc. can be made, which are all within the protection scope of the present disclosure. Therefore, the protection scope of the patent of the present disclosure should be subject to the appended claims.

Claims

1. A non-oxidative weakly acidic polyacrylamide degrading agent, characterized by, The application relates to a plugging removal agent for water wells, which comprises the following components: a reducing agent, a regulator, a mutual solvent and water; the reducing agent is one of 3-O-ethyl ascorbic acid ether and L-ascorbic acid-2,6-dibutyrate; the regulator is ammonium chloride; the mutual solvent is one of ethylene glycol monobutyl ether and isopropyl alcohol; the amount of each component is as follows in percentage of mass: the reducing agent is 0.5-1.0%, the regulator is 1.0-3.0%, the mutual solvent is 0.1-0.3%, and the rest is water.

2. The method for preparing the non-oxidative weakly acidic polyacrylamide degrading agent according to claim 1, characterized in that, The application further relates to a preparation method of the plugging removal agent for water wells. The application further relates to a use of the plugging removal agent for water wells.

3. The method of using the non-oxidative weakly acidic polyacrylamide degrading agent of claim 1, characterized in that, The application further relates to a use of the plugging removal agent for water wells. The non-oxidative degradation agent is prepared into a solution with a mass concentration of 1% and then injected into a water well to be plugged, and then acid liquid is continuously injected.

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