CN113528111A - Environment-friendly self-gel-breaking resistance-reducing agent and preparation method and application thereof - Google Patents
Environment-friendly self-gel-breaking resistance-reducing agent and preparation method and application thereof Download PDFInfo
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Abstract
The invention relates to the field of oil exploitation, and discloses an environment-friendly self-gel-breaking resistance-reducing agent, and a preparation method and application thereof. The friction reducer comprises an acrylamide copolymer and an oxidant; the oxidant is persulfate; the copolymer contains a structural unit A and a structural unit B; the structural unit A is an acrylamide structural unit; the structural unit B is a carboxylic acid structural unit; the content of the oxidizing agent is 0.2 to 6 wt%, preferably 1 to 2 wt%, based on the total weight of the friction reducer. The environment-friendly self-breaking gel-reducing resistance agent has the resistance-reducing performance of the conventional resistance-reducing agent and has the function of automatically and uniformly breaking gel at the formation temperature of more than 75-80 ℃. Meanwhile, the resistance reducing agent has the environmental protection performance of no oil phase and no surfactant, and the raw material cost and the preparation cost are also reduced.
Description
Technical Field
The invention relates to the field of oil exploitation, in particular to an environment-friendly self-gel-breaking resistance-reducing agent and a preparation method and application thereof.
Background
Since the middle of the last century, hydraulic fracturing technology has been the major production increasing technology in oil and gas development at home and abroad. After the new century, the hydraulic fracturing technology is highly regarded as a key technology for unconventional resource development of compact sandstone oil gas, coal bed gas, shale oil gas and the like.
The water-based fracturing technology used in unconventional resource development is primarily a slickwater fracturing fluid system. The slickwater fracturing fluid mainly comprises a resistance reducing agent and other fracturing additives. The slickwater fracturing fluid is high in discharge capacity to press open the stratum, so that longer cracks can be formed; the slippery water adopting the high-concentration resistance reducing agent can partially replace guar gum sand-carrying liquid, and sand carrying and spreading are realized. The resistance reducing agent used in the slickwater fracturing fluid is mainly acrylamide polymer, and the prior art is mainly water-in-oil type inverse emulsion polyacrylamide. Other fracturing additives include cleanup additives to reduce formation sensitivity and promote fluid flowback, clay stabilizers to prevent clay swelling migration, and breakers to hydrate flowback after fracturing.
In normal construction operations, the various additives are in liquid form and can be automatically metered, mixed and pumped using metering pumps. The gel breaker is usually solid particles or powder, and the solid is usually not metered in a construction site under the condition, so that manual addition is required. This increases the complexity, uncertainty of the process and also creates a significant human hazard. In the new drag reducer fracturing application, the drag reducer adopts high-concentration additive to form sand carrying liquid, which puts more severe requirements on the gel breaker.
Disclosure of Invention
The invention aims to solve the problems that the gel breaker cannot be added automatically and accurately and the gel breaking effect is easy to fluctuate in the conventional slickwater fracturing fluid system, and provides an environment-friendly self-gel-breaking resistance reducing agent, a preparation method and application thereof.
In order to achieve the above object, the first aspect of the present invention provides an environment-friendly self-breaking friction reducer, wherein the friction reducer comprises a copolymer and an oxidant; the oxidant is persulfate;
the copolymer contains a structural unit A and a structural unit B; the structural unit A is an acrylamide structural unit; the structural unit B is a carboxylic acid structural unit;
the content of the oxidizing agent is 0.2 to 6 wt%, preferably 1 to 2 wt%, based on the total weight of the friction reducer.
The second aspect of the present invention provides a method for preparing an environment-friendly self-gel-breaking resistance-reducing agent, wherein the method comprises:
(1) uniformly mixing a polymerization monomer, a stabilizer, an oxidant, a precipitating agent and water to obtain a clear solution;
(2) and mixing a reducing agent with the clarified solution in an inert atmosphere to perform a polymerization reaction to obtain the environment-friendly self-breaking resistance-reducing agent.
The third aspect of the invention provides an environment-friendly self-gel-breaking resistance-reducing agent prepared by the preparation method.
The fourth aspect of the invention provides an application of the environment-friendly self-breaking gel resistance reducing agent in a water-based fracturing technology, preferably a slickwater fracturing system.
By the technical scheme, the environment-friendly self-breaking gel-reducing resistance-reducing agent and the preparation method and application thereof provided by the invention have the following beneficial effects:
the resistance reducing agent provided by the invention is a water-in-water type resistance reducing agent, and has the function of automatically and uniformly breaking the gel at the formation temperature of 75-85 ℃ on the premise of keeping the resistance reducing performance of the resistance reducing agent compared with the conventional water-in-oil resistance reducing agent. The resistance reducing agent provided by the invention saves the process link of applying the gel breaker by workers in the fracturing operation field and saves the cost of the gel breaker.
The invention has the environmental protection performance of no oil phase and no surfactant, and reduces the cost of raw materials and preparation cost.
The invention adopts a water-in-water dispersion reaction polymerization system to prepare the resistance reducing agent, and the continuous phase of the resistance reducing agent is a water phase. In the preparation process, the feeding sequence of the oxidant and the reducing agent and the adding rate of the reducing agent are adjusted, so that the gel breaker is added in advance in the preparation process of the resistance reducing agent, and an equal-proportion uniform liquid phase is formed together with the resistance reducing agent. Therefore, accurate metering pumping is realized, slickwater with uniform gel breaker is formed and directly enters the well, and the process cost is reduced.
Drawings
Figure 1 shows the temperature and shear resistance results of the water-based fracturing fluid of example 1 at 80 ℃.
Detailed Description
The endpoints of the ranges and any values disclosed herein are not limited to the precise range or value, and such ranges or values should be understood to encompass values close to those ranges or values. For ranges of values, between the endpoints of each of the ranges and the individual points, and between the individual points may be combined with each other to give one or more new ranges of values, and these ranges of values should be considered as specifically disclosed herein.
The invention provides an environment-friendly self-gel-breaking resistance-reducing agent, wherein the resistance-reducing agent comprises a copolymer and an oxidant; the oxidant is persulfate; the copolymer contains a structural unit A and a structural unit B; the structural unit A is an acrylamide structural unit; the structural unit B is a carboxylic acid structural unit;
the content of the oxidizing agent is 0.2 to 6 wt%, preferably 1 to 2 wt%, based on the total weight of the friction reducer.
In the invention, the inventor researches and discovers that when the resistance reducing agent contains 0.2-6 wt% of an oxidant, the oxidant can play a role and an effect of a gel breaker, so that the resistance reducing agent can have an automatic and uniform gel breaking function at a formation temperature of 75-85 ℃, a process link of applying the gel breaker by a worker in a fracturing operation field is omitted, uniform mixing and metered addition of the gel breaker and the resistance reducing agent can be realized, and the problem of gel breaking effect fluctuation caused by uneven mixing or dosage fluctuation of the gel breaker and the resistance reducing agent is avoided.
Further, in order to further improve the gel breaking effect of the friction reducer, the content of the oxidant is preferably 1-2 wt% relative to the total weight of the friction reducer.
In the invention, the inventor researches and discovers that the acrylamide copolymer containing the structural unit A and the structural unit B is used as the matrix material of the resistance reducing agent, so that the uniform gel breaking performance of the resistance reducing agent at the formation temperature of 75-85 ℃ can be further improved, the resistance reducing agent has proper gel breaking time, and the resistance reducing agent is suitable for configuration and use of a fracturing operation site.
Specifically, due to the introduction of the structural unit B, the prepared resistance reducing agent has larger hydrodynamic volume occupation, so that the resistance reducing effect can be generated at a lower addition amount. Meanwhile, the structure of the structural unit B is similar to that of the structural unit A, so that chain lock degradation of the polymer can continuously occur in the gel breaking process.
In order to further improve the automatic gel breaking effect of the resistance reducing agent under the formation temperature condition of 75-85 ℃, the inventor researches the content of each structural unit in the copolymer, and finds that when the content of the structural unit A is 30-100 wt% and the content of the structural unit B is 0-70 wt% based on the total weight of the copolymer, the prepared resistance reducing agent is more prone to automatic gel breaking under the formation temperature condition of 75-85 ℃.
According to the invention, when the content of the structural unit A is 60-90 wt% and the content of the structural unit B is 10-40 wt% based on the total weight of the copolymer, the automatic gel breaking effect of the friction reducer is more excellent.
More preferably, the content of the structural unit a is 75 to 85% by weight and the content of the structural unit B is 15 to 25% by weight, based on the total weight of the copolymer.
In the present invention, the carboxylic acid structural unit is derived from at least one of acrylic acid, sodium acrylate, methacrylic acid and sodium methacrylate.
According to the invention, the weight average molecular weight of the copolymer is between 300 and 1400 ten thousand, preferably between 600 and 1000 ten thousand.
According to the invention, the oxidizing agent is potassium persulfate and/or ammonium persulfate.
In the invention, the solid content of the environment-friendly self-gel-breaking resistance-reducing agent is 10-25 wt%.
The second aspect of the present invention provides a method for preparing an environment-friendly self-gel-breaking resistance-reducing agent, wherein the method comprises:
(1) uniformly mixing a polymerization monomer, a stabilizer, an oxidant, a precipitating agent and water to obtain a clear solution;
(2) and mixing a reducing agent with the clarified solution in an inert atmosphere to perform a polymerization reaction to obtain the environment-friendly self-breaking resistance-reducing agent.
In the invention, a polymerization system of water-in-water dispersion reaction is adopted to prepare the resistance reducing agent, and the continuous phase of the resistance reducing agent is a water phase. In the preparation process, the feeding sequence of the oxidant and the reducing agent is adjusted, so that the gel breaker is added in advance in the preparation process of the resistance reducing agent, and the gel breaker and the copolymer in the resistance reducing agent form a uniform liquid phase together. Therefore, the accurate metering pumping of the resistance reducing agent is realized, when the resistance reducing agent is used for slickwater, the accurate metering pumping of the resistance reducing agent and the gel breaker can be realized, meanwhile, the provided resistance reducing agent can automatically break gel, and the actual requirement of the fracturing technology is met.
In order to ensure that the prepared resistance reducing agent can realize the automatic gel breaking effect under the formation temperature condition of 75-85 ℃, the inventor researches the use amount of each component when preparing the resistance reducing agent, and the research shows that when the total weight of the resistance reducing agent is taken as a reference, the use amount of the polymerization monomer is 10-30 wt%, the use amount of the stabilizer is 0.3-1.5 wt%, the use amount of the precipitant is 10-25 wt%, the use amount of the oxidant is 0.5-6 wt%, and the use amount of the reducing agent is 0.12-0.38 wt%, the prepared resistance reducing agent can realize automatic and uniform gel breaking under the formation temperature condition of 75-85 ℃ on the premise of keeping the resistance reducing performance of the resistance reducing agent, and further can be applied to the fracturing technology.
Further, the resistance reducing agent with more excellent performance can be obtained when the dosage of the polymerized monomer is 15-22 wt%, the dosage of the stabilizer is 1-1.4 wt%, the dosage of the precipitating agent is 15-25 wt%, the dosage of the oxidizing agent is 1.5-4 wt%, and the dosage of the reducing agent is 0.15-0.3 wt% based on the total weight of the resistance reducing agent.
Furthermore, based on the total weight of the resistance reducing agent, the dosage of the polymerized monomer is 17-20 wt%, the dosage of the stabilizer is 1.2-1.3 wt%, the dosage of the precipitation agent is 20-23 wt%, the dosage of the oxidizing agent is 2-2.5 wt%, and the dosage of the reducing agent is 0.19-0.21 wt%.
After a great deal of experiments, the inventors have further studied and found that when the molar ratio of the oxidizing agent to the reducing agent is greater than 1, particularly when the amount ratio of the oxidizing agent to the reducing agent is 1.7-14:1, the prepared friction reducer has more excellent effects.
In the present invention, the molar amount of electrons obtained by the oxidizing agent refers to the total molar amount of electrons required to be obtained when the oxidizing agent is completely reduced.
The molar amount of electron loss of the reducing agent refers to the total molar amount of electrons that need to be lost when the reducing agent is completely oxidized.
In the invention, the oxidant potassium persulfate is completely reduced to become potassium sulfate; the ammonium persulfate is completely reduced to ammonium sulfate.
According to the present invention, the polymerized monomers include acrylamide and carboxylic acid monomers.
According to the present invention, the carboxylic acid monomer is selected from at least one selected from the group consisting of acrylic acid, sodium acrylate, methacrylic acid and sodium methacrylate.
According to the invention, the stabilizer is selected from at least one of sodium poly-2-acrylamido 2-dimethylpropanesulfonate, a water-soluble derivative of cellulose and a vegetable gum.
In the invention, the weight average molecular weight of the poly 2-acrylamide 2-dimethylpropanesulfonic acid sodium is 30-50 ten thousand.
In the present invention, the water-soluble derivative of cellulose may be a water-soluble derivative of cellulose commonly used in the art, such as hydroxymethylcellulose and/or carboxymethylcellulose.
In the present invention, the vegetable gum can be a vegetable gum commonly used in the prior art, such as guar gum and its derivatives.
According to the invention, the precipitation agent is selected from at least one of sodium sulfate, potassium sulfate and ammonium sulfate.
According to the invention, the oxidizing agent is selected from potassium persulfate and/or ammonium persulfate.
According to the present invention, the reducing agent is selected from at least one of sodium thiosulfate, sodium bisulfite, sodium sulfite, and sodium metabisulfite.
In the present invention, the reducing agent is introduced into the polymerization system in the form of an aqueous solution, and preferably, the reducing agent is a sodium bisulfite solution having a mass concentration of 10 to 16 wt%, the reducing agent is a sodium thiosulfate solution having a mass concentration of 10 wt%, the reducing agent is a sodium metabisulfite solution having a mass concentration of 15 to 16 wt%, and the reducing agent is sodium sulfite having a mass concentration of 16 wt%.
According to the invention, the weight ratio of said acrylamide to said carboxylic acid monomer is from 30 to 100:0 to 70, preferably from 60 to 90:10 to 40, more preferably from 75 to 85:15 to 25.
According to the invention, the conditions of the polymer reaction comprise: the reaction temperature is 25-50 ℃, preferably 28-32 ℃; the reaction time is 4-16h, preferably 5-8 h.
The third aspect of the present invention provides an environment-friendly self-breaking friction reducer prepared by the preparation method of the present invention, wherein the friction reducer comprises 0.2-6 wt%, preferably 1-2 wt%, of an oxidizing agent, relative to the total weight of the friction reducer.
The fourth aspect of the invention provides an application of the environment-friendly self-breaking gel resistance reducing agent in a water-based fracturing technology, preferably a slickwater fracturing system.
The present invention will be described in detail below by way of examples.
The content of the oxidant in the resistance reducing agent is calculated by the content of the residual oxidant after the oxidant is consumed by the reducing agent according to the amount of the substances in the preparation process;
the resistance reducing performance of the resistance reducing agent adopts a friction resistance tester, and the obtained resistance reducing agent product is tested under the discharge capacity of 30L/min;
the viscosity of the glue solution and the viscosity of the gel breaking solution of the slickwater are measured by a rheometer at the temperature of 60 ℃ and the shear rate of 170S-1Carrying out the test;
the other raw materials used in the examples and comparative examples of the present invention are all commercially available products.
Example 1
At room temperature, 5g of poly 2-acrylamide-based 2-dimethylpropanesulfonic acid sodium salt with the molecular weight of 50 ten thousand, 217g of deionized water, 60g of acrylamide, 15g of acrylic acid and 8g of potassium persulfate are added into a 500ml three-neck flask, and after uniform dissolution, 90g of ammonium sulfate is added and fully dissolved to form a clear solution. Nitrogen was passed through for 20 minutes with stirring. Under the protection of nitrogen, 5g of 16 wt% sodium metabisulfite solution is uniformly added within 6 hours at the temperature of 30 ℃. The molar ratio of the oxidizing agent to the reducing agent is 7.03: 1. the system gradually whitens within the 6 hours to form a white emulsion drag reducer A1, which was tested to have an oxidizer content of 1.72 wt% in the drag reducer A1. The solids content was 18.75% by weight, the acrylamide copolymer had an acrylamide unit content of 80% by weight and a structural monomer B content of 20% by weight.
Example 2
At room temperature, 6g of poly 2-acrylamide-based 2-dimethylpropanesulfonic acid sodium salt with the molecular weight of 50 ten thousand, 223.7g of deionized water, 50g of acrylamide, 20g of methacrylic acid and 5.3g of ammonium persulfate are added into a 500ml three-neck flask, and after uniform dissolution, 90g of ammonium sulfate is added and fully dissolved to form a clear solution. Nitrogen was passed through for 20 minutes with stirring. Under the protection of nitrogen, 5g of 16% sodium bisulfite solution was added uniformly over 6 hours at 30 ℃. The molar ratio of the oxidizing agent to the reducing agent is 3.02: 1. the system gradually whitens within the 6 hours to form a white emulsion resistance reducer A2, which was tested to have an oxidizer content of 0.89 wt% in resistance reducer A2. The solids content was 17.5% by weight, the acrylamide copolymer had an acrylamide structural unit content of 71.4% by weight and a structural monomer B content of 28.6% by weight.
Example 3
At room temperature, 5g of carboxymethyl cellulose, 255.7g of deionized water, 23g of acrylamide, 17g of acrylic acid and 4.3g of ammonium persulfate are added into a 500ml three-neck flask, and after uniform dissolution, 60g of ammonium sulfate and 30g of sodium sulfate are added and fully dissolved to form a clear solution. Nitrogen was passed through for 20 minutes with stirring. Under the protection of nitrogen, 5g of 10% sodium thiosulfate solution is uniformly added in 10 hours at the temperature of 30 ℃. The molar ratio of the oxidizing agent to the reducing agent is 5.96: 1. the system gradually whitens in the 10 hours to form a white emulsion resistance reducer A3, which was tested to have an oxidizer content of 0.89 wt% in resistance reducer A3. The solids content was 10% by weight, and in the acrylamide copolymer, the content of acrylamide structural units was 57.5% by weight and the content of structural monomer B was 42.5% by weight.
Example 4
At room temperature, 1.5g of hydroxypropyl guar gum, 180.5g of deionized water, 45g of acrylamide, 40g of methacrylic acid, 15g of acrylic acid, 11.5g of potassium persulfate and 11.5g of ammonium persulfate are added into a 500ml three-neck flask, and after uniform dissolution, 50g of ammonium sulfate, 20g of potassium sulfate and 20g of sodium sulfate are added and fully dissolved to form a clear solution. Nitrogen was passed through for 20 minutes with stirring. Under the protection of nitrogen, 5g of 16% sodium sulfite solution was added uniformly over 6 hours at 30 ℃. The molar ratio of oxidant to reductant was 14.64: 1. the system gradually whitens within the 6 hours to form a white emulsion resistance reducer A4, which was tested to have an oxidizer content of 5.35 wt% in resistance reducer A4. The solid content was 25% by weight, and in the acrylamide copolymer, the content of acrylamide structural units was 45% by weight and the content of structural monomer B was 55% by weight.
Example 5
At room temperature, 5g of poly 2-acrylamide-based 2-dimethylpropanesulfonic acid sodium salt with the molecular weight of 50 ten thousand, 198g of deionized water, 60g of acrylamide, 20g of sodium acrylate and 17g of ammonium persulfate are added into a 500ml three-neck flask, and after uniform dissolution, 45g of ammonium sulfate and 45g of sodium sulfate are added and fully dissolved to form a clear solution. Nitrogen was passed through for 20 minutes with stirring. Under the protection of nitrogen, 10g of 15% sodium metabisulfite solution is uniformly added within 12 hours at the temperature of 30 ℃. Molar ratio of oxidant to reductant 9.44: 1. the system gradually whitens within the 6 hours to form a white emulsion resistance reducer A5, which was tested to have an oxidizer content of 3.8 wt% in resistance reducer A5. The solid content was 20% by weight, the acrylamide copolymer had an acrylamide structural unit content of 75% by weight and a structural monomer B content of 25% by weight.
Example 6
At room temperature, 5g of carboxymethyl cellulose, 213g of deionized water, 70g of acrylamide and 12g of ammonium persulfate are added into a 500ml three-neck flask, and after uniform dissolution, 40g of ammonium sulfate and 50g of sodium sulfate are added and fully dissolved to form a clear solution. Nitrogen was passed through for 20 minutes with stirring. 10g of 10% sodium bisulfite solution is added uniformly at 30 ℃ for 12 hours under the protection of nitrogen. The molar ratio of the oxidizing agent to the reducing agent is 5.5: 1. the system gradually whitens within the 6 hours to form a white emulsion resistance reducer A5, which was tested to have an oxidizer content of 2.45 wt% in resistance reducer A5. The solid content was 17.5% by weight, and in the acrylamide copolymer, the content of an acrylamide structural unit was 100% by weight and the content of the structural monomer B was 0% by weight.
Example 7
Drag reducer a7 was prepared with reference to example 1, except that the amount of oxidizer used was 2g and the ratio of oxidizer to reducer used was 1.76: 1. The content of the oxidant in the resistance reducing agent A7 was tested to be 0.22 wt%.
Comparative example 1
The drag reducer D1 was prepared by reference to the method of example 1, except that the amount of potassium persulfate added was 0.4 g. The molar ratio of the oxidizing agent to the reducing agent is less than 1. The content of the oxidizer in the resistance reducing agent D1 was tested to be 0 wt%.
Comparative example 2
The drag reducer D2 was prepared by referring to the method of example 1, except that potassium persulfate was changed to ammonium persulfate, and the amount added was 0.4 g. The molar ratio of the oxidizing agent to the reducing agent is less than 1. The content of the oxidizer in the resistance reducing agent D2 was tested to be 0 wt%.
Test example 1
The slickwater was prepared with tap water in an amount of 0.1% by volume. The resistance reducing performance of the example and the comparative resistance reducing agent were tested, and the results are shown in table 1.
TABLE 1
| 0.1% by volume drag reduction (%) | |
| A1 | 68.5 |
| A2 | 69.4 |
| A3 | 60.3 |
| A4 | 71.2 |
| A5 | 63.8 |
| A6 | 67.2 |
| A7 | 68.3 |
| D1 | 68.3 |
| D2 | 67.6 |
Test example 2
The rheological viscosity properties of the example and comparative drag reducing agents were tested using tap water formulated into high viscosity slickwater at 1.2 volume percent addition and the results are shown in table 2.
TABLE 2
| 1.2 v% gum viscosity @25 ℃ (mPa.s) | 1.2 v% gel breaker viscosity @80 ℃ (mPa.s) | |
| A1 | 64.24 | 2.35 |
| A2 | 59.21 | 3.45 |
| A3 | 53.46 | 2.27 |
| A4 | 66.49 | 1.72 |
| A5 | 62.89 | 1.19 |
| A6 | 64.31 | 2.22 |
| A7 | 64.27 | 12.23 |
| D1 | 64.19 | 59.04 |
| D2 | 64.35 | 59.63 |
The rheological test data for example 1 and comparative example 1 are shown in the graph of FIG. 1@80 ℃.
As can be seen from Table 1, the prepared drag reduction rate exceeds 50% under the conventional discharge capacity test, and the excessive addition of the oxidant has no obvious influence on the performance of the drag reduction agent. As can be seen from fig. 1 and table 2, the conventional slickwater system cannot break gel without adding a gel breaker; the slickwater prepared by the method can automatically break gel within 120 minutes at 80 ℃ without adding a gel breaker, and the gel is broken thoroughly.
The preferred embodiments of the present invention have been described above in detail, but the present invention is not limited thereto. Within the scope of the technical idea of the invention, many simple modifications can be made to the technical solution of the invention, including combinations of various technical features in any other suitable way, and these simple modifications and combinations should also be regarded as the disclosure of the invention, and all fall within the scope of the invention.
Claims (10)
1. An environment-friendly self-gel-breaking friction reducer, wherein the friction reducer comprises a copolymer and an oxidant; the oxidant is persulfate; the copolymer contains a structural unit A and a structural unit B; the structural unit A is an acrylamide structural unit; the structural unit B is a carboxylic acid structural unit;
the content of the oxidizing agent is 0.2 to 6 wt%, preferably 1 to 2 wt%, based on the total weight of the friction reducer.
2. The friction reducer according to claim 1, wherein the content of the structural unit a is 30-100 wt% and the content of the structural unit B is 0-70 wt% based on the total weight of the copolymer;
preferably, the content of the structural unit A is 60 to 90 wt% and the content of the structural unit B is 10 to 40 wt% based on the total weight of the copolymer;
more preferably, the content of the structural unit A is 75 to 85% by weight and the content of the structural unit B is 15 to 25% by weight, based on the total weight of the copolymer;
preferably, the carboxylic acid structural unit is derived from at least one of acrylic acid, sodium acrylate, methacrylic acid and sodium methacrylate.
3. The friction reducer of claim 1 or 2 wherein the weight average molecular weight of the copolymer is from 300 to 1400, preferably from 600 to 1000, ten thousand;
the oxidant is potassium persulfate and/or ammonium persulfate.
4. A preparation method of an environment-friendly self-gel-breaking resistance-reducing agent comprises the following steps:
(1) uniformly mixing a polymerization monomer, a stabilizer, an oxidant, a precipitating agent and water to obtain a clear solution;
(2) and mixing a reducing agent with the clarified solution in an inert atmosphere to perform a polymerization reaction to obtain the environment-friendly self-breaking resistance-reducing agent.
5. The preparation method according to claim 4, wherein the amount of the polymerized monomer is 10-30 wt%, the amount of the stabilizer is 0.3-1.5 wt%, the amount of the precipitation agent is 10-25 wt%, the amount of the oxidant is 0.5-6 wt%, and the amount of the reducing agent is 0.12-0.38 wt%, based on the total weight of the resistance reducing agent;
preferably, based on the total weight of the resistance reducing agent, the dosage of the polymerized monomer is 15-22 wt%, the dosage of the stabilizer is 1-1.4 wt%, the dosage of the precipitation agent is 15-25 wt%, the dosage of the oxidizing agent is 1.5-4 wt%, and the dosage of the reducing agent is 0.15-0.3 wt%;
more preferably, based on the total weight of the resistance reducing agent, the dosage of the polymerized monomer is 17-20 wt%, the dosage of the stabilizer is 1.2-1.3 wt%, the dosage of the precipitation agent is 20-23 wt%, the dosage of the oxidizing agent is 2-2.5 wt%, and the dosage of the reducing agent is 0.19-0.21 wt%;
preferably, the quantity of said oxidizing agent and reducing agent is such that the ratio between the molar quantity of electrons taken up by the oxidizing agent and the molar quantity of electrons lost by the reducing agent during said polymerization reaction is greater than 1, preferably in the range from 1.7 to 14: 1.
6. The production method according to claim 4 or 5, wherein the polymerized monomers include acrylamide and carboxylic acid monomers;
preferably, the carboxylic acid monomer is selected from at least one selected from the group consisting of acrylic acid, sodium acrylate, methacrylic acid and sodium methacrylate;
preferably, the stabilizer is selected from at least one of sodium poly-2-acrylamido 2-dimethylpropanesulfonate, a water-soluble derivative of cellulose and a vegetable gum;
preferably, the precipitation agent is selected from at least one of sodium sulfate, potassium sulfate and ammonium sulfate;
preferably, the oxidizing agent is selected from potassium persulfate and/or ammonium persulfate;
preferably, the reducing agent is selected from at least one of sodium thiosulfate, sodium bisulfite, sodium sulfite, and sodium metabisulfite.
7. The production method according to claim 6, wherein the weight ratio of the acrylamide to the carboxylic acid monomer is 30-100:0-70, preferably 60-90:10-40, more preferably 75-85: 15-25.
8. The production method according to any one of claims 4 to 7, wherein the conditions of the polymerization reaction include: the reaction temperature is 25-50 ℃, preferably 28-32 ℃; the reaction time is 4-16h, preferably 5-8 h.
9. The environment-friendly self-breaking friction reducer prepared by the preparation method of any one of claims 4-8, wherein the friction reducer comprises 0.2-6 wt%, preferably 1-2 wt% of an oxidant, relative to the total weight of the friction reducer.
10. Use of the environmentally friendly self-breaking friction reducer of any one of claims 1-3 and claim 9 in water-based fracturing technologies, preferably slickwater fracturing systems.
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