Development and method of gel breaker for recycling drilling fluid

Abstract

The invention belongs to the field of oilfield chemistry, and discloses development and a method of a gel breaker for recycling drilling fluid, and the preparation method comprises the following steps: (1) contacting chitosan with a modifier under an alkaline condition for chemical modification to obtain O-carboxymethyl chitosan; and (2) carrying out radical polymerization on the obtained O-carboxymethyl chitosan and a quaternary ammonium salt monomer in an acid environment under the action of an initiator to obtain the gel breaker.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of oilfield chemistry, in particular, relates to a kind of drilling fluid reutilization gel breaker and method. BACKGROUND

[0002] Drilling fluid is usually composed of fluid and various treating agents, including various polymer treating agents, salts and bentonite, etc., according to the different continuous phase, drilling fluid is divided into water-based drilling fluid, oil-based drilling fluid and gas-based drilling fluid, among which water-based drilling fluid is the most widely used, and is usually used for land and offshore drilling operations, while when drilling fluid enters the wellbore, rocks, sand and other pollutants in the formation will be suspended and mixed into the drilling fluid, and when the drilling fluid is discharged back to the ground, the solid part will become part of the fluid. In traditional drilling operations, drilling fluid is usually recycled after removing the useless solid pollutants in the fluid, therefore, it is crucial to effectively remove the solid pollutants in the drilling fluid.

[0003] For large-diameter particles (usually greater than 74 μm), a vibrating screen can be used to effectively remove them, while smaller solids (usually greater than 2 μm) can be removed by a hydrocyclone, a mud washer and a centrifuge, but it is difficult to remove colloidal particles smaller than 1 μm by physical methods, not only that, the contamination degree of small colloidal particles is much higher than that of other large-diameter solid particles. The stability of small colloidal particles mainly depends on the kinetic stability and the aggregation stability, the kinetic stability is reflected in the ability of Brownian motion of colloidal particles to resist gravity, when the colloidal particles are very small, the effect of gravity is small, the Brownian motion is violent, and the colloidal particles cannot be settled, so methods such as sedimentation cannot be used for removal; the aggregation stability is specifically manifested in that the colloidal particles cannot be aggregated due to the repulsive force of like charges, and when the surface charge disappears, the aggregation stability is destroyed, and sedimentation occurs. The method to achieve sedimentation is to add a gel breaker to change the physicochemical properties of the drilling fluid, destroy its stable system, and achieve mud gel breaking.

[0004] Therefore, it is of great significance to provide a reusable gel breaker for drilling fluid to reduce the time cost of drilling operations. SUMMARY

[0005] The purpose of the present application is to solve the problem of low reutilization of drilling waste liquid and the technical difficulty of difficult solid-liquid separation of drilling fluid.

[0006] In order to achieve the above purpose, the first aspect of the present application provides a preparation method of a gel breaker, which comprises:

[0007] (1) chemically modifying chitosan under alkaline conditions and a modifier to obtain O-carboxymethyl chitosan.

[0008] (2) the O-carboxymethyl chitosan obtained is subjected to radical polymerization with a quaternary ammonium salt monomer under the action of an initiator in an acidic environment to obtain the breaker.

[0009] The second aspect of the present application provides a breaker prepared by the method of the first aspect.

[0010] The third aspect of the present application provides a breaking effect of the breaker of the second aspect on a drilling filtrate.

[0011] The fourth aspect of the present application provides a water-based drilling filtrate for testing the breaking effect of the breaker.

[0012] By the technical solution described above, the present application can achieve the following beneficial effects:

[0013] (1) The breaker prepared by the method provided by the present application has significantly reduced color and viscosity after being added to a water-based drilling filtrate, indicating that the breaker has good breaking effect.

[0014] (2) After the breaker is added, the proportion of particles smaller than 2 μm in the water-based drilling filtrate is significantly reduced, indicating that the breaker has good breaking effect on submicron particles. DETAILED DESCRIPTION

[0015] The endpoints of the ranges and any values disclosed in this document are not limited to the precise values stated. The ranges or values should be construed to be approximations that allow for significant variation. Various ranges of values that are explicitly delineated in this document are not to be construed as having only the precise values stated. Other explicitly-stated ranges of values should be construed as specifically disclosed. Various ranges of values that are implicitly between ranges or endpoints of values that are explicitly stated in this document are specifically disclosed. For values that are expressly listed herein, each range between, among, and in between the values is also specifically disclosed.

[0016] The specific embodiments of the present application are described in detail below. It should be understood that the specific embodiments described herein are merely illustrative and are not intended to limit the present application.

[0017] The first aspect of the present application provides a preparation method of a breaker, which comprises:

[0018] (1) chemically modifying chitosan under alkaline conditions and a modifier to obtain O-carboxymethyl chitosan.

[0019] (2) subjecting the O-carboxymethyl chitosan obtained to radical polymerization with a quaternary ammonium salt monomer under the action of an initiator in an acidic environment to obtain the breaker.

[0020] According to the present application, after the chemical modification of chitosan in step (1), the content of -COOH and -NH2 groups increases, and the active sites increase. In addition, according to statistics, after the chemical modification of chitosan, the solubility of chitosan at different pH values is improved, and the toxicity and antibacterial activity are reduced.

[0021] According to the present application, the chitosan is deacetylated chitosan, and specifically, the particle size of the deacetylated chitosan is 150 μm, and the molecular weight is 400 KDa.

[0022] According to the present application, the modifier is selected from one of acetic acid, monochloroacetic acid and trichloroacetic acid, and is further preferably monochloroacetic acid.

[0023] According to the present application, in step (1), in order to completely modify the chitosan, the weight ratio of chitosan: sodium hydroxide: deionized water: monochloroacetic acid: isopropyl alcohol: ethanol is preferably 1: (0.9-1.8): (95-120): (0.85-2.15): (1.5-3.5): (12-32), and is further preferably 1: (1-1.6): (98-112): (1.35-1.95): (1.85-3.15): (18-28).

[0024] According to the present application, in step (1), the conditions of the modification process include a temperature of 30-60℃, and is further preferably 50℃, and a time of 2-5h, and is further preferably 3.5h. Providing an alkaline condition for chitosan prevents the hydrolysis of chitosan. Under the action of the modifier monochloroacetic acid, the hydrogen atom on the hydroxyl group of chitosan is replaced by sodium formate, and the hydrogen ion of the -NH2 group is neutralized by the hydroxyl group of sodium hydroxide, so that N is positively charged, providing an active site for the synthesis of the breaker in the next step.

[0025] According to the present application, in step (1), the operation of the modification process includes: adding chitosan, sodium hydroxide and deionized water into a flask according to the corresponding weight ratio, swelling and alkalizing at 50℃ in a water bath for 1h. After mixing monochloroacetic acid and isopropyl alcohol according to the corresponding weight ratio, adding them into the flask, and adding an ethanol solution according to the corresponding weight ratio after reacting at 50℃ for 3.5h, the reaction is completed.

[0026] According to the present application, after the chemical modification process in step (1) is completed, O-carboxymethyl chitosan is obtained, and the obtained solid is filtered and washed with ethanol. Specifically, the O-carboxymethyl chitosan is filtered and washed with a 90% ethanol solution to remove salt and water, and is vacuum dried at 25℃ to obtain O-carboxymethyl chitosan.

[0027] According to the present application, in step (2), the O-carboxymethyl chitosan is subjected to radical polymerization with a quaternary ammonium salt monomer in an acidic environment under the action of an initiator to obtain a breaker.

[0028] According to the present application, in step (2), the solution for creating an acidic environment is an HCl solution, specifically, the HCl solution is a 1wt% HCl solution.

[0029] According to the present application, in step (2), preferably, the initiator is selected from two of hydrogen peroxide, sodium sulfite, sodium bisulfite, potassium persulfate, ammonium persulfate, further preferably potassium persulfate and sodium bisulfite.

[0030] Preferably, the quaternary ammonium salt monomer is selected from one of dimethyldiallylammonium chloride, vinyltrimethylammonium bromide, vinylphenyltrimethylammonium bromide, vinylphenyltrimethylammonium chloride, further preferably vinylphenyltrimethylammonium chloride.

[0031] According to the present application, in step (2), to obtain the best gel breaker, preferably, the weight ratio of O-carboxymethyl chitosan:HCl solution:potassium persulfate:sodium bisulfite:vinylphenyltrimethylammonium chloride is 1:(5-15):(0.015-0.065):(0.01-0.05):(0.9-2.4), further preferably 1:(8-12):(0.028-0.04):(0.02-0.034):(1.2-1.85).

[0032] According to the present application, in step (2), the conditions of the polymerization process include: temperature is 40-60℃, further preferably 55℃, time is 2.5-5.5h, further preferably 4h.

[0033] According to the present application, in step (2), the operation of the polymerization process includes: dissolving O-carboxymethyl chitosan and HCl according to the corresponding weight ratio and adding to a three-necked flask and stirring at a speed of 300r / min under N2 atmosphere for 30min, adding corresponding weight ratio of potassium persulfate and sodium bisulfite, adding corresponding weight ratio of vinylphenyltrimethylammonium chloride after stirring for 10min, and reacting at 55℃ for 4h until the reaction is completed.

[0034] According to the present application, after the polymerization process is completed, a gel breaker is obtained, and after the reaction is completed, the product is filtered and extracted. Specifically, the product is mixed with ethanol to obtain a solid product, which is filtered and extracted in a Soxhlet extractor with ethanol as the solvent for 48h to ensure that impurities are fully removed, and dried in an oven at 80℃ for 48h.

[0035] The second aspect of the present application provides a gel breaker prepared by the method of the aforementioned first aspect, wherein the gel breaker significantly reduces the particles of less than 2μm in the water-based drilling filter press after being added to the water-based drilling filter press, indicating that the gel breaker has a good gel breaking effect on submicron colloidal particles.

[0036] According to the present application, the breaker has good breaking property, and the chroma and viscosity of the water-based drilling filter are reduced after the breaker is added. This is because chitosan has adsorption property, and the surface of chitosan contains hydroxyl and amino groups, which can combine with metal ions. The quaternary ammonium group has polarity, which can attract anionic substances and adsorb clay particles. Secondly, the quaternary ammonium group has charge neutralization effect, which can destroy the suspension stability of the water-based drilling filter, so that the solid particles in the filter are flocculated.

[0037] The third aspect of the present application provides the use of the breaker of the second aspect in the water-based drilling filter as a breaker.

[0038] The fourth aspect of the present application provides a water-based drilling filter, which is an evaluation liquid for evaluating the breaking effect of the breaker.

[0039] According to the present application, the water-based drilling filter comprises the following components: 100 parts by weight of water, 4-11 parts by weight of a flow type regulator, 7-12 parts by weight of a filtrate reducer, 4.8-7.2 parts by weight of an inhibitor, 4.9-7.2 parts by weight of an alkalinity regulator, and 22-28 parts by weight of a weighting agent.

[0040] Preferably, the flow type regulator is selected from one of tannin liquor, tannic acid, polyacrylamide potassium salt, and sulfonated styrene, and is further preferably polyacrylamide potassium salt.

[0041] Preferably, the filtrate reducer is selected from one of sulfonated lignite, humic acid potassium, sulfonated phenolic aldehyde resin, and sulfonated lignite resin, and is further preferably sulfonated phenolic aldehyde resin.

[0042] Preferably, the inhibitor is selected from one of methyl glucoside, epoxypropyl trimethyl ammonium chloride, potassium chloride, and chitosan quaternary ammonium salt, and is further preferably potassium chloride.

[0043] Preferably, the alkalinity regulator is selected from one of sodium hydroxide and calcium oxide, and is further preferably sodium hydroxide.

[0044] Preferably, the weighting agent is selected from one of three-might tetraoxide, API barite, calcium carbonate, and ultra-fine calcium carbonate, and is further preferably API barite.

[0045] The water-based drilling filter provided by the present application is close to the formula of the field water-based drilling filter, and the prepared water-based drilling filter can show the breaking effect of the breaker through color change.

[0046] The present application will be described in detail through examples. The following are preparation examples, examples, comparative examples, and test examples.

[0047] Preparation Example 1

[0048] (1-1) Chitosan, sodium hydroxide and deionized water were added to a flask in a weight ratio of 1:1.35:105, and the alkalization was performed by swelling in a water bath at 50°C for 1 h. Monochloroacetic acid and isopropyl alcohol were mixed in a weight ratio of chitosan:monochloroacetic acid:isopropyl alcohol of 1:1.65:2.5, and then added to the flask. After reaction at 50°C for 3.5 h, an ethanol solution was added in a weight ratio of chitosan:ethanol solution of 1:22, and the reaction was completed.

[0049] (1-2) The O-carboxymethyl chitosan was filtered and washed with a 90% ethanol solution to remove salt and water, and then dried in a vacuum oven at 25°C to obtain O-carboxymethyl chitosan.

[0050] (1-3) The O-carboxymethyl chitosan and HCl were dissolved in a weight ratio of 1:10 and added to a three-necked flask, and stirred at a speed of 300 r / min under N2 atmosphere for 30 min. Potassium persulfate and sodium bisulfite were added in a weight ratio of O-carboxymethyl chitosan:potassium persulfate:sodium bisulfite of 1:0.035:0.028, and stirred for 10 min. Vinylbenzyltrimethylammonium chloride was added in a weight ratio of O-carboxymethyl chitosan:vinylbenzyltrimethylammonium chloride of 1:1.5, and reacted at 55°C for 4 h until the reaction was completed.

[0051] (1-4) The product was mixed with ethanol to obtain a solid product, which was filtered and extracted in a Soxhlet extractor for 48 h with ethanol as the solvent to ensure that impurities were removed, and then dried in an oven at 80°C for 48 h to obtain a breaker (denoted as S1).

[0052] Preparation Example 2

[0053] (2-1) Chitosan, sodium hydroxide and deionized water were added to a flask in a weight ratio of 1:1:98, and the alkalization was performed by swelling in a water bath at 50°C for 1 h. Monochloroacetic acid and isopropyl alcohol were mixed in a weight ratio of chitosan:monochloroacetic acid:isopropyl alcohol of 1:1.35:1.85, and then added to the flask. After reaction at 50°C for 3.5 h, an ethanol solution was added in a weight ratio of chitosan:ethanol solution of 1:18, and the reaction was completed.

[0054] (2-2) The O-carboxymethyl chitosan was filtered and washed with a 90% ethanol solution to remove salt and water, and then dried in a vacuum oven at 25°C to obtain O-carboxymethyl chitosan.

[0055] (2-3) O-carboxymethyl chitosan and HC1 were dissolved and added into a three-necked flask in a weight ratio of 1:8 and stirred at a speed of 300 r / min under N2 atmosphere for 30 min, and then potassium persulfate and sodium bisulfite were added in a weight ratio of O-carboxymethyl chitosan: potassium persulfate: sodium bisulfite of 1:0.028:0.02, and after stirring for 10 min, vinylbenzyltrimethylammonium chloride was added in a weight ratio of O-carboxymethyl chitosan: vinylbenzyltrimethylammonium chloride of 1:1.2, and reacted at 55°C for 4 h until the reaction was completed.

[0056] (2-4) The product was mixed with ethanol to obtain a solid product, which was filtered and extracted in a Soxhlet extractor with ethanol as the solvent for 48 h to ensure that the impurities were fully removed, and then dried in an oven at 80°C for 48 h to obtain the breaker (denoted as S2).

[0057] Preparation Example 3

[0058] (3-1) Chitosan, sodium hydroxide and deionized water were added into a flask in a weight ratio of 1:1.6:112, and then swelled and alkalized in a water bath at a temperature of 50°C for 1 h. Monochloroacetic acid and isopropyl alcohol were mixed in a weight ratio of chitosan: monochloroacetic acid: isopropyl alcohol of 1:1.95:3.15, and then added into the flask, and after reacting at a temperature of 50°C for 3.5 h, an ethanol solution was added in a weight ratio of chitosan: ethanol solution of 1:28, and the reaction was completed.

[0059] (3-2) The O-carboxymethyl chitosan was filtered and rinsed with a 90% ethanol solution to remove salt and water, and then dried in a vacuum oven at 25°C to obtain O-carboxymethyl chitosan.

[0060] (3-3) O-carboxymethyl chitosan and HC1 were dissolved and added into a three-necked flask in a weight ratio of 1:12 and stirred at a speed of 300 r / min under N2 atmosphere for 30 min, and then potassium persulfate and sodium bisulfite were added in a weight ratio of O-carboxymethyl chitosan: potassium persulfate: sodium bisulfite of 1:0.04:0.034, and after stirring for 10 min, vinylbenzyltrimethylammonium chloride was added in a weight ratio of O-carboxymethyl chitosan: vinylbenzyltrimethylammonium chloride of 1:1.85, and reacted at 55°C for 4 h until the reaction was completed.

[0061] (3-4) The product was mixed with ethanol to obtain a solid product, which was filtered and extracted in a Soxhlet extractor with ethanol as the solvent for 48 h to ensure that the impurities were fully removed, and then dried in an oven at 80°C for 48 h to obtain the breaker (denoted as S3).

[0062] Example 1

[0063] 100 parts by weight of tap water were added with 7.5 parts by weight of potassium polyacrylamide and stirred at a stirring rate of 5000 r / min for 10 minutes, then 9.2 parts by weight of sulfonated phenolic resin were added and stirred at a stirring rate of 5000 r / min for 10 minutes, then 5.6 parts by weight of potassium chloride were added and stirred at a stirring rate of 5000 r / min for 10 minutes, then 5.8 parts by weight of sodium hydroxide were added and stirred at a stirring rate of 5000 r / min for 10 minutes, then 25 parts by weight of API barite were added and stirred at a stirring rate of 5000 r / min for 30 minutes to obtain a water-based drilling filtrate, and then 2.56 parts by weight of a gel breaker were added to observe its gel breaking condition to obtain a water-based drilling hydraulic filtrate after gel breaking (denoted as F1).

[0064] Example 2-3

[0065] The method of Example 1 was followed, except that S2 and S3 were used as breakers, respectively. Other conditions were the same as those of Example 1, to obtain water-based drilling filtrate after breakage (denoted as F2 and F3, respectively).

[0066] Comparative Example 1

[0067] The method of Example 1 was followed, except that the breaker S1 was not added. Other conditions were the same as those of Example 1 (denoted as DF1).

[0068] Comparative Example 2

[0069] The method of Example 1 was followed, except that S1 was replaced by step (1) to prepare the obtained O-carboxymethyl chitosan (denoted as DF2).

[0070] Comparative Example 3

[0071] The method of Example 1 was followed, except that the amount of S1 was adjusted to 8 parts by weight, and other conditions were the same as those of Example 1. A water-based drilling filtrate (denoted as DF3) after gel breaking was obtained.

[0072] The components and contents of Examples 1-3 and Comparative Examples 1-3 are shown in Table 1.

[0073] Table 1

[0074]

[0075]

[0076] Test Case

[0077] The breakers prepared in Preparation Examples S1-S3 were tested for their breaking effects on water-based drilling filtrate. Specifically, the breaking performance of the breakers was determined by studying the changes in viscosity, color, and average particle size of the water-based drilling filtrate. In the following test examples,

[0078] The viscosity of the water-based drilling pressure filter liquid is measured by a rotary viscometer according to the method in GB / T 16783.1-2014;

[0079] The colority of the water-based drilling pressure filter liquid is measured by a colority tester according to the method in GB / T 605-2006;

[0080] The average particle size of the water-based drilling pressure filter liquid is measured by a laser particle size analyzer according to the method in GB / T 19077-2016.

[0081] The manufacturer of the rotary viscometer is Shanghai Pingxuan Scientific Instrument Co., Ltd., and the model is SNB-1 rotary viscometer;

[0082] The manufacturer of the colority tester is Bell Analytical Instrument (Dalian) Co., Ltd., and the model is BSC5300.

[0083] The manufacturer of the laser particle size analyzer is Malvern Panalytical, and the model is MASTERSIZER 3000+ laser particle size analyzer.

[0084] 1. Viscosity test

[0085] 1g of S1-S3 obtained in the preparation example was accurately weighed and placed in the water-based drilling pressure fracturing fluid, and the viscosity of the water-based drilling pressure fracturing fluid was measured after standing for 4h. The results are shown in Table 2.

[0086] Table 2 Viscosity test results

[0087] F1 F2 F3 DF1 DF2 DF3 Viscosity (mPa-s) 5.3 6.2 5.8 18 12 7.3

[0088] As can be seen from Table 2, with the increase of the amount of the gel breaker, the viscosity of the water-based drilling pressure fracturing fluid decreases rapidly, showing excellent gel breaking performance. This is because after adding the gel breaker, the gel breaker contains chitosan and quaternary ammonium salt polymer. The adsorption performance of chitosan enables it to adsorb solid particles in the water-based drilling pressure fracturing fluid. The quaternary ammonium salt polymer adsorbs anions due to the presence of quaternary ammonium groups, causing the solid particles to flocculate and settle, reducing the viscosity of the water-based drilling pressure filter liquid and greatly improving the reusability of the pressure filter liquid.

[0089] 2. Colority determination

[0090] After adding the gel breaker to the water-based drilling pressure filter liquid, stirring at a stirring rate of 200r / min for 5min, 80mL was taken into a centrifuge tube for centrifugation, the centrifugal speed was 2000r / min, the centrifugation time was 5min, and the colority of the supernatant was detected. The results are shown in Table 3.

[0091] Table 3 Colority test results

[0092] F1 F2 F3 DF1 DF2 DF3 Color (multiple) 4.2 6 5.9 14 11 8

[0093] From the colorimetric test results, it can be seen that with the increase of the amount of the breaker, the colorimetry of the supernatant in the centrifuge tube decreases. In addition, it can be observed during the experiment that with the increase of the amount of the breaker, the supernatant of the water-based drilling fracturing fluid after gel breaking gradually becomes transparent, indicating that the breaker has good gel breaking effect. Moreover, it can be seen that when the amount of the breaker is too much, the colorimetry increases instead. This is because when the amount of the breaker is too much, the breaker and the solid particles in the water-based drilling fracturing fluid produce stronger repulsive force, resulting in that they cannot flocculate and settle but are more dispersed, and the gel breaking effect becomes poor.

[0094] 3. Average particle size test

[0095] After the breaker is added into the water-based drilling fracturing fluid according to the corresponding weight ratio, it is stirred at a stirring rate of 200 r / min for 5 min, at which time the average particle size is determined. Subsequently, it is allowed to settle for 1 h, and the average particle size is determined again. The test results are shown in Table 4.

[0096] Table 4 Average particle size test results

[0097]

[0098]

[0099] From the average particle size test results, it can be seen that the average particle size of the water-based drilling fracturing fluid after the addition of the breaker increases, indicating that the breaker generates precipitation after being added, and small particles aggregate to become large particles, resulting in an increase in the average particle size. The proportion of the gel particles smaller than 2 μm decreases after the addition of the breaker, indicating that the breaker effectively adsorbs the sub-micron particles after being added, so that they realize flocculation, and the breaker can also achieve good gel breaking effect on the micron-level particles which are difficult to remove.

Claims

1. A method for the preparation of a drilling fluid reusable breaker, characterized in that: The method includes: (1) chemically modifying chitosan by contacting it with a modifier under alkaline conditions to obtain O-carboxymethyl chitosan; (2) The obtained O-carboxymethyl chitosan is subjected to radical polymerization with a quaternary ammonium salt monomer under the action of an initiator in an acidic environment to obtain a gel breaker.

2. The method according to claim 1, wherein In step (1), the modifier is selected from one of acetic acid, monochloroacetic acid, and trichloroacetic acid, and is more preferably monochloroacetic acid.

3. The method according to claim 1, wherein In step (2), the initiator is selected from two of hydrogen peroxide, sodium sulfite, sodium bisulfite, potassium persulfate, and ammonium persulfate, More preferably, potassium persulfate and sodium bisulfite; Preferably, the quaternary ammonium salt monomer is selected from one of dimethyldiallylammonium chloride, vinyltrimethylammonium bromide, vinylphenyltrimethylammonium bromide and vinylphenyltrimethylammonium chloride, and more preferably vinylphenyltrimethylammonium chloride.

4. The method according to claim 1, wherein: In step (1), the chitosan: The weight ratio of sodium hydroxide: deionized water: monochloroacetic acid: isopropyl alcohol: ethanol is 1: (0.9-1.8): (95-120): (0.85-2.15): (1.5-3.5): (12-32), and more preferably 1: (1-1.6): (98-112): (1.35-1.95): (1.85-3.15): (18-28).

5. The method according to any one of claims 1 to 3, wherein: In step (2), the weight ratio of the O-carboxymethyl chitosan: HCl solution: potassium persulfate: sodium bisulfite: vinylphenyltrimethylammonium chloride is 1: (5-15): (0.015-0.065): (0.01-0.05): (0.9-2.4), and more preferably 1: (8-12): (0.028-0.04): (0.02-0.034): (1.2-1.85).

6. The method according to any one of claims 1 to 4, wherein: In step (1), the conditions of the modification process include: temperature of 30-60°C, more preferably 50°C, time of 2-5h, more preferably 3.5h; Preferably, in step (2), the conditions of the polymerization process include: temperature of 40-60°C, more preferably 55°C, and time of 2.5-5.5h, more preferably 4h.

7. A gel breaker obtained by the preparation method according to any one of claims 1 to 5.

8. Use of the gel breaker according to claim 6 as a gel breaker in water-based drilling fracturing fluid.

9. A water-based drilling fracturing fluid, used as an evaluation fluid for evaluating the breaking effect of the breaker according to claim 6.

10. According to the present invention, the water-based drilling filter fluid comprises the following components: 100 parts by weight of water, 4-11 parts by weight of a flow pattern regulator, 7-12 parts by weight of a fluid loss reducer, 4.8-7.2 parts by weight of an inhibitor, 4.9-7.2 parts by weight of an alkalinity regulator, and 22-28 parts by weight of a weighting agent; Preferably, the flow pattern regulator is selected from one of tannin lye, tannic acid, polyacrylamide potassium salt, and sulfonated styrene, and more preferably polyacrylamide potassium salt; Preferably, the fluid loss reducer is selected from one of sulfonated lignite, potassium humate, sulfonated phenolic resin, and sulfonated lignite resin, and more preferably sulfonated phenolic resin; Preferably, the inhibitor is selected from one of methyl glucoside, glycidyltrimethylammonium chloride, potassium chloride, and chitosan quaternary ammonium salt, more preferably potassium chloride; Preferably, the alkalinity regulator is selected from one of sodium hydroxide and calcium oxide, more preferably sodium hydroxide; Preferably, the weighting agent is selected from one of manganese tetroxide, API barite, calcium carbonate, and ultrafine calcium carbonate, and is more preferably API barite.

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