CN115490800A

CN115490800A - Filtrate reducer and preparation method and application thereof

Info

Publication number: CN115490800A
Application number: CN202211194082.9A
Authority: CN
Inventors: 荣敏杰; 孙建波; 许永升; 于庆华; 荣帅帅
Original assignee: Shandong Nuoer Biological Technology Co Ltd
Current assignee: Shandong Nuoer Biological Technology Co Ltd
Priority date: 2022-09-28
Filing date: 2022-09-28
Publication date: 2022-12-20
Anticipated expiration: 2042-09-28
Also published as: CN115490800B

Abstract

The invention relates to a fluid loss additive, a preparation method and application thereof, and belongs to the technical field of oil and gas field development. The method comprises the following steps: uniformly mixing acrylamide, acryloyl morpholine, a reinforcing monomer, a hydrolysis-resistant monomer, a cutting monomer, a structure regulator and water to obtain a mixed solution, introducing nitrogen into the mixed solution to remove oxygen, and adding an initiator to initiate polymerization reaction to obtain a polymer block; granulating the polymer rubber block to obtain polymer rubber particles; uniformly mixing a modifier, potassium hydroxide, an activator and water to obtain a modifying solution, spraying the polymeric colloidal particles with the modifying solution, and then carrying out modification reaction to obtain the filtrate reducer. The filtrate reducer prepared by the invention can keep the viscosity and the filtrate reduction performance in a 30wt% calcium chloride aqueous solution, has stable rheological property and can resist the temperature of over 230 ℃.

Description

Filtrate reducer and preparation method and application thereof

Technical Field

The invention relates to the technical field of oil and gas field development, in particular to a fluid loss additive and a preparation method and application thereof.

Background

Shale gas is widely distributed in the global scope and has great development potential. In recent years, research on shale gas development is gradually focused because the shale gas belongs to a clean energy source and is a potential energy source for replacing natural gas. The exploration and development of the shale gas in China are still in an exploration stage, but the development is quite rapid in recent years, and large-scale shale gas development work is respectively carried out in Fuling, wigner and other areas in China currently and medium petrochemistry, and obvious results are obtained.

Due to the fact that the shale gas reservoir develops cracks and is high in water sensitivity, when the drilling tool encounters a long horizontal section, problems such as well collapse and well leakage are prone to occurring, and if lubricating and rock carrying capabilities are insufficient, complex conditions in a well can be caused. In view of the above, the oil-based drilling fluid is commonly used at present to solve the above problems, and the oil-based drilling fluid has the characteristics of strong inhibition, strong anti-pollution capability and good lubricating property, and can meet the drilling requirements of the shale gas horizontal well. However, the oil-based drilling fluid also has some disadvantages, such as environmental pollution, cost, etc., and especially, the environmental protection problem is more and more emphasized in the present country, and it is a trend to develop a water-based drilling fluid with excellent performance for drilling shale gas horizontal wells. The conventional fresh water-based drilling fluid cannot be used for drilling shale layers due to the problems of relatively poor inhibition performance, instability of well walls and the like; the brine-based drilling fluid has strong anti-pollution capacity, can effectively inhibit the hydration of clay minerals in a reservoir stratum, furthest reduces the invasion of solid phases into the reservoir stratum and is gradually concerned, but the hypersalinity in brine-based drilling fluid has very high requirement on additives in the brine-based drilling fluid, requires extremely high salt resistance of the additives, and has good rheological property under the conditions of high temperature and high salinity.

However, relatively few reports are reported on the filtrate reducer of the brine-based drilling fluid at present, and the Chinese patent application CN202111418035.3 discloses a brine-based drilling fluid and a preparation method thereof, wherein the filtrate reducer adopted by the brine-based drilling fluid is JHFR-HP, but the brine-based drilling fluid only has better rheological property and filtrate reducer performance at 200 ℃, and the temperature resistance of the brine-based drilling fluid needs to be further improved; in addition, the patent application directly adopts the filter loss reducer JHFR-HP which is commercially available, and the synthesis process of the filter loss reducer JHFR-HP is not clear.

Disclosure of Invention

The invention aims to provide a fluid loss additive for brine-water based drilling fluid and a preparation method and application thereof, aiming at the requirement of the fluid loss additive in brine-water based drilling fluid. The filtrate reducer prepared by the invention can keep the viscosity and the filtrate reduction performance in a 30wt% calcium chloride aqueous solution, has stable rheological property, and can resist the temperature of over 230 ℃.

The invention provides a preparation method of a fluid loss additive in a first aspect, which comprises the following steps:

(1) Uniformly mixing acrylamide, acryloyl morpholine, a reinforcing monomer, a hydrolysis-resistant monomer, a cutting monomer, a structure regulator and water to obtain a mixed solution, introducing nitrogen into the mixed solution to remove oxygen, and adding an initiator to initiate a polymerization reaction to obtain a polymer block;

(2) Granulating the polymer rubber block to obtain polymer rubber particles;

(3) Uniformly mixing a modifier, potassium hydroxide, an activator and water to obtain a modified solution, and then spraying the modified solution on the polymer colloidal particles to perform a modification reaction to obtain the fluid loss additive.

Preferably, the preparation method further comprises the steps of sequentially crushing, drying, grinding and screening the fluid loss additive.

Preferably, the structure regulator is prepared by the following steps:

(a) Dropwise adding concentrated sulfuric acid into 2-hydroxypropionic acid, and reacting to obtain an intermediate A;

(b) Uniformly mixing the intermediate A, butanol amine and N, N-dimethylformamide and reacting to obtain an intermediate B;

(c) And (3) uniformly mixing the intermediate B,1, 2-dichloroethane and diethylamine, then dropwise adding cinnamoyl chloride and reacting to obtain the structure regulator.

Preferably, in the step (a), the mass fraction of the concentrated sulfuric acid is not less than 98%, the use amount of the concentrated sulfuric acid is 4-6% and more preferably 5% of the mass of the 2-hydroxypropionic acid, and/or the reaction temperature is 55-65 ℃, and the reaction time is 2.5-4 h and preferably 3h; and/or in the step (b), the mass ratio of the intermediate A to the butanol amine is 8: (4-6) is preferably 8, the amount of the N, N-dimethylformamide is 8-15%, preferably 10% of the mass sum of the intermediate A and the butanol amine, and/or the reaction temperature is 40-50 ℃, and the reaction time is 2.5-4 h, preferably 3h.

Preferably, in step (c): the mass ratio of the intermediate B to the cinnamoyl chloride is 8: (4 to 6) preferably 8; the dosage of the 1, 2-dichloroethane is 10-20% and preferably 15% of the sum of the mass of the intermediate B and the mass of the cinnamoyl chloride; the dosage of the diethylamine is 1 to 5 percent of the mass sum of the intermediate B and the cinnamoyl chloride, and is preferably 3 percent; dripping cinnamoyl chloride at the temperature of-5 to 5 ℃; and/or after the cinnamoyl chloride is dripped, controlling the reaction temperature to be 30-35 ℃, and reacting at the temperature of 30-35 ℃ for 1.5-3 h, preferably 2h.

Preferably, the reinforcing monomer is 3- (3-methoxy-4-methylphenyl) acrylic acid and/or 3- (4-methoxybenzoyl) acrylic acid; the hydrolysis-resistant monomer is vinyltrimethylsilane and/or 4-acetoxystyrene; the extraction and cutting monomer is one or more of 2-phenoxyethyl acrylate, furfuryl methacrylate and 2-ethyl phenylacrylate; the initiator comprises an azo initiator and a redox initiator, wherein the azo initiator is azobisisobutyronitrile and/or azobisisobutylamidine hydrochloride, an oxidant in the redox initiator is one or more of hydrogen peroxide, di-tert-butyl peroxide and tert-butyl hydroperoxide, a reducing agent in the redox initiator is sodium bisulfite, and the mass ratio of the azo initiator to the redox initiator is (1-3): (0.5 to 3); the modifier is hydroxylamine sulfate; and/or the activating agent is fatty alcohol-polyoxyethylene ether.

Preferably, in the step (1), each raw material for preparing the polymer rubber block comprises, by weight, 10-30 parts of acrylamide, 35-60 parts of acryloyl morpholine, 55-85 parts of reinforcing monomer, 40-80 parts of hydrolysis-resistant monomer, 25-45 parts of cutting monomer, 1-5 parts of structure regulator, 650-800 parts of water and 1.5-6 parts of initiator; the particle size of the polymer colloidal particle obtained in the step (2) is less than 0.5mm; and/or in the step (3), the mass ratio of the polymeric colloidal particles, the modifier, the potassium hydroxide, the activator and the water is 1000: (20-25): (5-10): (10-20): (40 to 60), preferably 1000.

Preferably, in the step (1), before introducing nitrogen into the mixed solution to remove oxygen, the pH of the mixed solution is adjusted to 6.5-7.0; in the step (1), the time for introducing nitrogen to remove oxygen is 40-80 min; in the step (1), an initiator is added at 5-7 ℃ to initiate polymerization reaction, and the polymerization reaction time is 2-4 h, preferably 3h; and/or in the step (3), the temperature of the modification reaction is 70-80 ℃, and the time of the modification reaction is 3-4 h.

In a second aspect, the present invention provides a fluid loss additive prepared by the preparation method according to the first aspect of the present invention.

In a third aspect, the invention provides the use of the fluid loss additive prepared by the preparation method in the first aspect in brine-based drilling fluid.

Compared with the prior art, the invention at least has the following beneficial effects:

(1) According to the invention, the monomer with a special structure is added during the preparation of the filtrate reducer, so that the sensitivity of a polymer molecular chain to salt is greatly reduced, the filtrate reducer has extremely high temperature resistance and salt tolerance, and can have good rheological property and filtrate reducer performance in 30wt% calcium chloride aqueous solution; the linear structure of the polymer is changed by adding the optimized structure regulator, so that the temperature resistance of the polymer is greatly improved; the rheological property of the drilling fluid is greatly improved by introducing the shear-improving monomer to modify the polymer, particularly the dynamic shear force, static shear force and apparent viscosity of the brine-based drilling fluid are improved, and the drilling fluid has stronger rheological stability under the conditions of high temperature and high salt.

(2) The fluid loss agent prepared by the invention is subjected to modification treatment, when a shale reservoir is drilled, adsorption groups in the fluid loss agent are adsorbed on the surfaces of clay particles, and meanwhile, the fluid loss agent can form a hydration film when being adsorbed on the surfaces of the clay particles, so that the repulsive force among the clay particles is improved, the dispersion of the clay particles can be maintained, and the coagulation among the clay particles is prevented.

(3) The filtrate reducer prepared by the invention can keep the viscosity and the filtrate reducing performance in a 30wt% calcium chloride aqueous solution, has stable rheological property, has the dynamic shear force of more than 20Pa, the phi 6/phi 3 of more than 12/9 and the filtrate loss of less than 5mL in brine-based drilling fluid.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. It is to be understood that the embodiments described are only a few embodiments of the present invention, and not all embodiments. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, are within the scope of the present invention.

(1) Uniformly mixing acrylamide, acryloyl morpholine (alias: 4-acryloyl morpholine), a reinforcing monomer, a hydrolysis-resistant monomer, a cutting monomer, a structure regulator and water to obtain a mixed solution, introducing nitrogen into the mixed solution to remove oxygen, and adding an initiator to initiate polymerization reaction to obtain a polymer block;

(2) Granulating the polymer rubber block to obtain polymer rubber particles; the operation of the granulation is not particularly limited, and the granulation can be performed by conventional operation, preferably, the granulation is performed in a granulator; preferably, the polymer particles with the particle size of less than 0.5mm are obtained by granulation;

(3) Uniformly mixing a modifier, potassium hydroxide, an activator and water to obtain a modified solution, and then spraying the modified solution on the polymer colloidal particles to perform modification reaction to obtain a filtrate reducer; specifically, for example, a modifier, potassium hydroxide, an activator and water are fully dissolved to obtain a uniformly mixed modification solution, the modification solution is uniformly sprayed on the surface of the polymer micelle and fully mixed, and the polymer micelle sprayed with the modification solution is subjected to modification reaction at 70-80 ℃ for 3-4 hours to obtain the filtrate reducer; the water in step (1) and step (3) of the present invention may be, for example, deionized water; in the invention, the activator is added to promote the modification of the modifier to the polymer and increase the permeability of the modifier.

According to the invention, by adding monomers with special structures (including acryloyl morpholine, an enhanced monomer, a hydrolysis-resistant monomer, a structure regulator and the like) during preparation of the filtrate reducer, the sensitivity of a polymer molecular chain to salt is greatly reduced, so that the filtrate reducer has extremely high temperature resistance and salt tolerance, and can have good rheological property and filtrate reducer performance in 30wt% calcium chloride aqueous solution; according to the invention, the polymer is modified by introducing the shear monomer, so that the rheological property of the drilling fluid is greatly improved, the dynamic shear force, the static shear force and the apparent viscosity of the brine-based drilling fluid are especially improved, and the rheological stability of the drilling fluid is stronger under the conditions of high temperature and high salt; the fluid loss agent prepared by the invention is subjected to modification treatment, when a shale reservoir is drilled, adsorption groups in the fluid loss agent are adsorbed on the surfaces of clay particles, and meanwhile, the fluid loss agent can form a hydration film when being adsorbed on the surfaces of the clay particles, so that the repulsive force among the clay particles is improved, the dispersion of the clay particles can be maintained, and the coagulation among the clay particles is prevented.

According to some preferred embodiments, the preparation method further comprises the steps of sequentially crushing, drying, grinding and screening the fluid loss additive; the conditions of the crushing, drying, grinding and screening are not specifically limited, and the conventional operation is adopted.

According to some preferred embodiments, the structure-modifying agent is prepared by:

(a) Dropwise adding concentrated sulfuric acid into 2-hydroxypropionic acid, and reacting to obtain an intermediate A; the dropping speed of the concentrated sulfuric acid is not particularly required, the concentrated sulfuric acid is slowly dropped, and preferably, the dropping time of the concentrated sulfuric acid is 0.5-1.5 h, and more preferably 1h; in the present invention, the reaction formula for preparing the intermediate a is, for example, as shown in formula I:

(b) Uniformly mixing the intermediate A, butanol amine (alias: 2-amino-1-butanol) and N, N-dimethylformamide, and reacting to obtain an intermediate B; in the present invention, the N, N-dimethylformamide is used as a solvent, and the reaction formula for preparing the intermediate B is, for example, as shown in formula II:

(c) Uniformly mixing the intermediate B,1, 2-dichloroethane and diethylamine (alias: aminodichloroethane), then dropwise adding cinnamoyl chloride and reacting to obtain a structure regulator; in the invention, in the step (c), 1, 2-dichloroethane is used as a solvent, and diethylamine is added, so that diethylamine hydrochloride can be produced in the reaction process, and chloride ions in the reaction can be combined to facilitate the reaction; the reaction formula between the intermediate B and cinnamoyl chloride is shown in formula III, for example, when the structure regulator is prepared.

The structure regulator prepared through the steps (a) to (c) is preferably added, the preferable structure regulator can change the linear structure of the polymer, the temperature resistance of the polymer is greatly improved compared with the conventional structure regulator, the viscosity and the filtration performance of the filtration-reducing agent can be effectively maintained at high temperature and high mineralization degree, and the filtration-reducing agent has high dynamic shear force, high phi 6/phi 3 and low filtration loss in brine-based drilling fluid.

According to some preferred embodiments, in step (a), the mass fraction of the concentrated sulfuric acid is not less than 98%, the amount of the concentrated sulfuric acid is 4 to 6% (e.g., 4%, 4.5%, 5%, 5.5%, or 6%) and more preferably 5% of the mass of the 2-hydroxypropionic acid, and/or the temperature of the reaction is 55 to 65 ℃ (e.g., 55 ℃, 60 ℃, or 65 ℃), and the time of the reaction is 2.5 to 4 hours (e.g., 2.5, 3, 3.5, or 4 hours), preferably 3 hours; and/or in the step (b), the mass ratio of the intermediate A to the butanol amine is 8: (4-6) (e.g. 8, 4.5, 8, 5, 8, 5.5 or 8.

According to some preferred embodiments, in step (c): the mass ratio of the intermediate B to the cinnamoyl chloride is 8: (4-6) (e.g. 8; the amount of 1, 2-dichloroethane used is preferably 15% to 10 to 20% (e.g. 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19% or 20%) of the sum of the masses of intermediate B and cinnamoyl chloride; the amount of diethylamine is preferably 3% in the range of 1 to 5% (e.g. 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5% or 5%) of the sum of the masses of intermediate B and cinnamoyl chloride; dripping the cinnamoyl chloride at-5 ℃ (for example, -5 ℃, -4 ℃, -3 ℃, -2 ℃, -1 ℃, 0 ℃,1 ℃,2 ℃,3 ℃,4 ℃ or 5 ℃), wherein the dripping speed of the cinnamoyl chloride is not specifically limited, and the cinnamoyl chloride is slowly dripped, preferably for 1.5-2.5 hours; and/or after the addition of the cinnamoyl chloride is completed, controlling the reaction temperature to be 30-35 ℃ (for example, 30 ℃ or 35 ℃), and reacting at 30-35 ℃ for 1.5-3 h (for example, 1.5, 2, 2.5 or 3 h), preferably 2h.

According to some specific embodiments, step (a) is: adding 2-hydroxypropionic acid into a three-neck flask with a stirrer, a condenser pipe and a thermometer, starting a water bath to control the temperature to be 55-65 ℃, dropwise adding concentrated sulfuric acid accounting for 5% of the total mass of the 2-hydroxypropionic acid, continuously reacting for 3 hours, cooling to room temperature after the reaction is finished, performing rotary evaporation by using a rotary evaporator, and evaporating a solvent to obtain a light yellow transparent liquid, namely an intermediate A; in the present invention, the concentrated sulfuric acid is preferably an aqueous sulfuric acid solution having a mass fraction of not less than 98%.

According to some specific embodiments, step (b) is: adding the intermediate A, the butanol amine and the N, N-dimethylformamide into a three-neck flask with a stirrer, a condenser pipe and a thermometer, starting a water bath to control the temperature to be 40-50 ℃, and reacting for 3 hours at constant temperature; after the reaction is finished, obtaining yellow transparent liquid, performing rotary evaporation by using a rotary evaporator, and evaporating the solvent to obtain yellow liquid, namely an intermediate B; wherein, the mass ratio of the intermediate A to the butanol amine is preferably 8, and the dosage of the N, N-dimethylformamide is 10% of the sum of the mass of the intermediate A and the butanol amine.

According to some specific embodiments, step (c) is: adding the intermediate B,1, 2-dichloroethane and diethylamine into a three-neck flask with a stirrer, a condenser tube and a thermometer, uniformly mixing, starting to control the temperature to be-5-5 ℃, slowly dropwise adding cinnamoyl chloride, controlling the temperature to be 30-35 ℃ after dropwise adding is completed for about 2 hours, continuously reacting for 2 hours to complete the reaction, filtering, performing rotary evaporation by using a rotary evaporator, and evaporating the solvent to obtain brown liquid, namely the structure regulator; wherein, the mass ratio of the intermediate B to the cinnamoyl chloride is preferably 8, the dosage of the 5,1, 2-dichloroethane is 15% of the mass sum of the intermediate B and the cinnamoyl chloride, and the dosage of the diethylamine is 3% of the mass sum of the intermediate B and the cinnamoyl chloride.

According to some preferred embodiments, the reinforcing monomer is 3- (3-methoxy-4-methylphenyl) acrylic acid (CAS number: 209287-19-4) and/or 3- (4-methoxybenzoyl) acrylic acid (CAS number: 5711-41-1); according to the invention, a special enhanced monomer 3- (3-methoxy-4-methylphenyl) acrylic acid and/or 3- (4-methoxybenzoyl) acrylic acid is preferably introduced into a molecular chain, so that the sensitivity of the molecular chain of the polymer to salt is greatly reduced, the filtrate loss reducer has extremely high temperature resistance and salt tolerance, and can have better rheological property and filtrate loss reduction performance in 30wt% calcium chloride aqueous solution; the hydrolysis-resistant monomer is vinyl trimethylsilane and/or 4-acetoxystyrene; the extraction and cutting monomer is one or more of 2-phenoxyethyl acrylate, furfuryl alcohol methacrylate and 2-ethyl phenylacrylate; the initiator comprises an azo initiator and a redox initiator, wherein the azo initiator is azobisisobutyronitrile and/or azobisisobutylamidine hydrochloride, an oxidant in the redox initiator is one or more of hydrogen peroxide, di-tert-butyl peroxide and tert-butyl hydroperoxide, a reducing agent in the redox initiator is sodium bisulfite, and the mass ratio of the azo initiator to the redox initiator is (1-3): (0.5-3), wherein the mass ratio of the oxidizing agent to the reducing agent is 1: (0.8-1.2); the modifier is hydroxylamine sulfate; and/or the activator is fatty alcohol-polyoxyethylene ether; the fatty alcohol-polyoxyethylene ether is not specifically limited, and any product which can be directly purchased in the market can be adopted, and specifically, the fatty alcohol-polyoxyethylene ether can be fatty alcohol-polyoxyethylene ether AEO-7 and fatty alcohol-polyoxyethylene ether AEO-9.

According to some preferred embodiments, in step (1), each raw material for preparing the polymer block comprises 10-30 parts (such as 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29 or 30 parts) of acrylamide, 35-60 parts (such as 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 5, 3, 54, 55, 56, 57, 58, 59 or 60 parts) of acryloyl morpholine, 55-85 parts (such as 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 77, 78, 79, 80, 82, 83, 9, 23, 21, 40, 41, 42, 43, 44, 45, 46, 47, 48, 50, 51, 52, 5, 3, 54, 55, or 60 parts of reinforcing monomer 84 or 85 parts), hydrolysis resistant monomer 40-80 parts (e.g., 40, 42, 45, 48, 50, 52, 55, 58, 60, 62, 65, 68, 70, 72, 75, 78, or 80 parts), cut-to-length monomer 25-45 parts (e.g., 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, or 45 parts), structure modifier 1-5 parts (e.g., 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, or 5 parts), water 650-800 parts (e.g., 650, 660, 670, 680, 690, 700, 710, 720, 730, 740, 750, 760, 770, 780, 790, or 800 parts), and initiator 1.5-6 parts (e.g., 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5.5, or 6 parts); in the invention, preferably, each raw material for preparing the polymer rubber block comprises 10-30 parts of acrylamide, 35-60 parts of acryloyl morpholine, 55-85 parts of reinforced monomer, 40-80 parts of hydrolysis-resistant monomer, 25-45 parts of shear-improving monomer, 1-5 parts of structure regulator, 650-800 parts of water and 1.5-6 parts of initiator by weight, so that the temperature resistance and salt tolerance of the filtrate reducer are improved, the filtrate reducer can have better rheological property and filtrate reduction performance in 30wt% of calcium chloride aqueous solution, the dynamic shear force, static shear force and apparent viscosity of the brine-based drilling fluid are especially ensured to be improved, and the rheological stability of the brine-based drilling fluid is stronger and the filtrate reduction performance is better under the conditions of high temperature and high salt.

In the present invention, "parts" means "parts by weight", and in the specific examples and comparative examples, the units of parts by weight may be unified into, for example, "g" or "kg" or other units by weight.

According to some preferred embodiments, the particle size of said polymeric crumb obtained in step (2) is less than 0.5mm.

According to some preferred embodiments, in the step (3), the mass ratio of the polymeric colloidal particles, the modifier, the potassium hydroxide, the activator and the water is 1000: (20-25): (5-10): (10-20): (40-60), preferably 1000.

According to some preferred embodiments, in the step (1), before the nitrogen is introduced into the mixed solution to remove oxygen, the pH of the mixed solution is adjusted to 6.5-7.0; in the present invention, for example, ammonia water may be used to adjust the pH of the mixed solution to 6.5 to 7.0, and the amount of ammonia water used is not particularly limited, and the pH of the mixed solution may be adjusted to a target range, and in the present invention, it is preferable that the volume concentration (i.e., volume percentage concentration) of the ammonia water used is, for example, 25%; in the step (1), the time for introducing nitrogen and removing oxygen is 40-80 min (for example, 40, 45, 50, 55, 60, 65, 70, 75 or 80 min); in the step (1), an initiator is added at 5-7 ℃ to initiate polymerization reaction, and the polymerization reaction time is 2-4 h, preferably 3h; in the step (1), the initiation temperature of the polymerization reaction is 5-7 ℃; in the invention, after the polymerization reaction is initiated at 5-7 ℃, the temperature of the reaction system is naturally raised, the reaction system carries out the polymerization reaction with natural temperature rise, and the reaction time is 2-4 h; and/or in step (3), the temperature of the modification reaction is 70 to 80 ℃ (e.g., 70 ℃, 75 ℃ or 80 ℃), and the time of the modification reaction is 3 to 4 hours (e.g., 3, 3.5 or 4 hours).

The appearance of "and/or" between a plurality of technical features in the present invention means that the technical features are all connected in an "and/or" relationship, and means that any one of the technical features or a combination of any two or more of the technical features can be used.

According to some specific embodiments, the preparation of the fluid loss additive of the present invention comprises the following processes:

(1) preparation of Polymer masses

The polymer gel block of the fluid loss additive for the brine-based drilling fluid is prepared from the following raw materials in parts by weight: 10-30 parts of acrylamide, 35-60 parts of acryloyl morpholine, 55-85 parts of reinforcing monomer, 40-80 parts of hydrolysis-resistant monomer, 25-45 parts of cutting monomer, 1-5 parts of structure regulator, 0-45 parts of ammonia water, 650-800 parts of water, 1-3 parts of high-temperature initiator (azo initiator) and 0.5-3 parts of low-temperature initiator (redox initiator). The preparation method comprises the following steps: fully and uniformly mixing acrylamide, acryloyl morpholine, a reinforcing monomer, a hydrolysis-resistant monomer, a cutting monomer, a structure regulator and water, adjusting the pH value to 6.5-7.0 by using ammonia water, transferring into a reaction kettle, introducing nitrogen to remove oxygen for 60min, adding a high-temperature initiator and a low-temperature initiator at the temperature of 5-7 ℃ to initiate polymerization, and reacting for 3h to obtain the polymer gel block.

(2) Modification of polymer rubber blocks

The polymer gel block modification of the fluid loss additive for the brine-based drilling fluid adopts the following raw materials: the polymer micelle, potassium hydroxide, a modifier, water and an activator, wherein the mass ratio of the polymer micelle, the modifier, the potassium hydroxide, the activator and the water is (1000). The preparation method comprises the following steps: granulating a polymer rubber block in a granulator to obtain polymer rubber particles with the particle size (particle diameter) of less than 0.5mm, fully dissolving a modifier, potassium hydroxide, water and an activator to obtain a uniformly mixed modified solution, uniformly spraying the modified solution on the surface of the polymer rubber particles, fully mixing, pressing the polymer rubber particles into a closed tank with a certain heat preservation temperature for modification reaction, and after the modification is finished, sequentially crushing, drying, grinding and screening to obtain the filtrate reducer for the brine-based drilling fluid.

The invention will be further illustrated by way of example, but the scope of protection is not limited to these examples.

The structure modifiers used in the following examples 1 to 5 and comparative examples 1 to 8 of the present invention were prepared:

(1) adding 500 parts of 2-hydroxypropionic acid into a three-neck flask with a stirrer, a condenser pipe and a thermometer, starting a water bath to control the temperature to be 60 ℃, dropwise adding 25 parts of concentrated sulfuric acid with the mass fraction of 98% within 1 hour, continuously reacting for 3 hours (comprising dropwise adding 1 hour of the concentrated sulfuric acid and continuously reacting for 2 hours after the dropwise adding is finished), cooling to room temperature after the reaction is finished, performing rotary evaporation by using a rotary evaporator, and evaporating the solvent to obtain an intermediate A.

(2) Adding 240 parts of intermediate A, 150 parts of butanol amine and 39 parts of N, N-dimethylformamide into a three-neck flask with a stirrer, a condenser and a thermometer, uniformly mixing, starting a water bath, controlling the temperature to be 45 ℃, and reacting for 3 hours at constant temperature; after the reaction, the intermediate B was obtained by rotary evaporation using a rotary evaporator and evaporation of the solvent.

(3) Adding 320 parts of intermediate B,78 parts of 1, 2-dichloroethane and 15.6 parts of diethylamine into a three-neck flask with a stirrer, a condenser tube and a thermometer, starting to control the temperature, controlling the temperature to be 0 ℃, dropwise adding 200 parts of cinnamoyl chloride within 2h, controlling the temperature to be 30 ℃ after the dropwise adding is finished, continuing to react for 2h, filtering after the reaction is finished, performing rotary evaporation by using a rotary evaporator, and evaporating the solvent to obtain the structure regulator.

Example 1

(1) Polymer cement block preparation

The raw material composition for preparing the polymer rubber block is as follows: 10 parts of acrylamide, 35 parts of acryloyl morpholine, 55 parts of 3- (3-methoxy-4-methylphenyl) acrylic acid, 40 parts of vinyl trimethylsilane, 25 parts of 2-phenoxyethyl acrylate, 3 parts of a structure regulator, 800 parts of water, 1 part of azobisisobutyronitrile, 0.5 part of hydrogen peroxide and 0.5 part of sodium bisulfite. The preparation method comprises the following steps: fully and uniformly mixing acrylamide, acryloylmorpholine, 3- (3-methoxy-4-methylphenyl) acrylic acid, vinyl trimethylsilane, 2-phenoxyethyl acrylate, a structure regulator and water to obtain a mixed solution, regulating the pH value of the mixed solution to 6.6 by using ammonia water with the volume concentration of 25%, transferring the mixed solution into a reaction kettle, introducing nitrogen to remove oxygen for 60min, adding azodiisobutyronitrile, hydrogen peroxide and sodium bisulfite at the temperature of 5 ℃ to initiate polymerization reaction, and reacting for 3h to obtain the polymer block.

(2) Polymer cement block modification

Modification of the polymer gum block: granulating the polymer rubber block in a granulator to obtain polymer rubber particles with the average particle size of 0.4mm, uniformly mixing hydroxylamine sulfate, fatty alcohol-polyoxyethylene ether AEO-9 and potassium hydroxide in water to obtain a modified solution, uniformly spraying the modified solution on the surface of the polymer rubber particles, after fully mixing, carrying out modification reaction on the polymer rubber particles sprayed with the modified solution at 70 ℃ for 3 hours, and after the modification is finished, sequentially crushing, drying, grinding and screening to obtain the filtrate reducer; wherein the mass ratio of the polymer colloidal particles, hydroxylamine sulfate, potassium hydroxide, fatty alcohol-polyoxyethylene ether AEO-9 to water is 1000.

Example 2

(1) Polymer cement block preparation

The raw material composition for preparing the polymer rubber block is as follows: 20 parts of acrylamide, 50 parts of acryloyl morpholine, 70 parts of 3- (4-methoxybenzoyl) acrylic acid, 60 parts of 4-acetoxystyrene, 35 parts of furfuryl methacrylate, 2 parts of structure regulator, 725 parts of water, 2 parts of azodiisobutyl amidine hydrochloride, 1 part of di-tert-butyl peroxide and 1 part of sodium bisulfite. The preparation method comprises the following steps: fully and uniformly mixing acrylamide, acryloylmorpholine, 3- (4-methoxybenzoyl) acrylic acid, 4-acetoxystyrene, furfuryl methacrylate, a structure regulator and water to obtain a mixed solution, regulating the pH value of the mixed solution to 6.8 by using ammonia water with the volume concentration of 25%, transferring the mixed solution into a reaction kettle, introducing nitrogen to remove oxygen for 60min, adding azodiisobutyl amidine hydrochloride, di-tert-butyl peroxide and sodium bisulfite at 6 ℃ to initiate polymerization reaction, and reacting for 3h to obtain the polymer block.

(2) Polymer cement block modification

Modification of the polymer gel block: granulating the polymer rubber block in a granulator to obtain polymer rubber particles with the average particle size of 0.4mm, uniformly mixing hydroxylamine sulfate, fatty alcohol-polyoxyethylene ether AEO-9 and potassium hydroxide in water to obtain a modified solution, uniformly spraying the modified solution on the surface of the polymer rubber particles, after fully mixing, carrying out modification reaction on the polymer rubber particles sprayed with the modified solution at 75 ℃ for 3.5 hours, and after the modification is finished, sequentially crushing, drying, grinding and screening to obtain the filtrate reducer; wherein the mass ratio of the polymer colloidal particles, hydroxylamine sulfate, potassium hydroxide, fatty alcohol-polyoxyethylene ether AEO-9 to water is 1000.

Example 3

(1) Preparation of Polymer masses

The raw material composition for preparing the polymer rubber block is as follows: 30 parts of acrylamide, 60 parts of acryloyl morpholine, 85 parts of 3- (4-methoxybenzoyl) acrylic acid, 80 parts of vinyl trimethylsilane, 45 parts of ethyl 2-phenylacrylate, 4 parts of structure regulator, 650 parts of water, 3 parts of azobisisobutyronitrile, 1.5 parts of tert-butyl hydroperoxide and 1.5 parts of sodium bisulfite. The preparation method comprises the following steps: fully and uniformly mixing acrylamide, acryloylmorpholine, 3- (4-methoxybenzoyl) acrylic acid, vinyl trimethylsilane, 2-ethyl phenylacrylate, a structure regulator and water to obtain a mixed solution, regulating the pH value of the mixed solution to 7.0 by using ammonia water with the volume concentration of 25%, transferring the mixed solution into a reaction kettle, introducing nitrogen to remove oxygen for 60min, adding azobisisobutyronitrile, tert-butyl hydroperoxide and sodium bisulfite at the temperature of 7 ℃ to initiate polymerization reaction, and reacting for 3h to obtain the polymer block.

(2) Polymer cement block modification

Modification of the polymer gum block: granulating the polymer rubber block in a granulator to obtain polymer rubber particles with the average particle size of 0.4mm, uniformly mixing hydroxylamine sulfate, fatty alcohol-polyoxyethylene ether AEO-9 and potassium hydroxide in water to obtain a modified solution, uniformly spraying the modified solution on the surface of the polymer rubber particles, after fully mixing, carrying out modification reaction on the polymer rubber particles sprayed with the modified solution at 80 ℃ for 4 hours, and after the modification is finished, sequentially crushing, drying, grinding and screening to obtain the filtrate reducer; wherein the mass ratio of the polymer colloidal particles, hydroxylamine sulfate, potassium hydroxide, fatty alcohol-polyoxyethylene ether AEO-9 to water is 1000.

Example 4

Example 4 is essentially the same as example 1, except that:

(1) preparation of Polymer masses

The raw material composition for preparing the polymer rubber block is as follows: 40 parts of acrylamide, 35 parts of acryloyl morpholine, 40 parts of 3- (3-methoxy-4-methylphenyl) acrylic acid, 30 parts of vinyl trimethylsilane, 20 parts of 2-phenoxyethyl acrylate, 3 parts of a structure regulator, 800 parts of water, 1 part of azobisisobutyronitrile, 0.5 part of hydrogen peroxide and 0.5 part of sodium bisulfite. The preparation method comprises the following steps: fully and uniformly mixing acrylamide, acryloylmorpholine, 3- (3-methoxy-4-methylphenyl) acrylic acid, vinyl trimethylsilane, 2-phenoxyethyl acrylate, a structure regulator and water to obtain a mixed solution, regulating the pH value of the mixed solution to 6.6 by using ammonia water with the volume concentration of 25%, transferring the mixed solution into a reaction kettle, introducing nitrogen to remove oxygen for 60min, adding azodiisobutyronitrile, hydrogen peroxide and sodium bisulfite at the temperature of 5 ℃ to initiate polymerization reaction, and reacting for 3h to obtain the polymer block.

Example 5

Example 5 is essentially the same as example 1, except that:

(2) polymer cement block modification

Modification of the polymer gum block: granulating a polymer rubber block in a granulator to obtain polymer rubber particles with the average particle size of 0.4mm, fully dissolving hydroxylamine sulfate, fatty alcohol-polyoxyethylene ether AEO-9 and potassium hydroxide in water to obtain uniformly mixed modification liquid, uniformly spraying the modification liquid on the surfaces of the polymer rubber particles, after fully mixing, carrying out modification reaction on the polymer rubber particles sprayed with the modification liquid at 70 ℃ for 3 hours, and after the modification is finished, sequentially crushing, drying, grinding and screening to obtain the filtrate reducer; wherein the mass ratio of the polymer colloidal particles, hydroxylamine sulfate, potassium hydroxide, fatty alcohol-polyoxyethylene ether AEO-9 to water is 1000.

Comparative example 1

Comparative example 1 is substantially the same as example 1 except that:

in step (1), no acryloyl morpholine is added, and the amount of acryloyl morpholine used is replaced by acrylamide, i.e. 45 parts of acrylamide are added.

Comparative example 2

Comparative example 2 is substantially the same as example 1 except that:

in the step (1), no reinforcing monomer 3- (3-methoxy-4-methylphenyl) acrylic acid is added, and the amount of the 3- (3-methoxy-4-methylphenyl) acrylic acid is replaced by acrylamide, namely 65 parts of acrylamide is added.

Comparative example 3

Comparative example 3 is substantially the same as example 1 except that:

in the step (1), hydrolysis-resistant monomer vinyltrimethylsilane is not added, and the amount of vinyltrimethylsilane is replaced by acrylamide, namely, 50 parts of acrylamide is added.

Comparative example 4

Comparative example 4 is substantially the same as example 1 except that:

in the step (1), no extraction monomer 2-phenoxyethyl acrylate is added, and the dosage of the 2-phenoxyethyl acrylate is replaced by acrylamide, namely 35 parts of acrylamide is added.

Comparative example 5

Comparative example 5 is substantially the same as example 1 except that:

in step (2), the polymer cement is granulated in a granulator to form polymer cement having an average particle size of 1 mm.

Comparative example 6

Comparative example 6 is substantially the same as example 1 except that:

(2) polymer cement block modification

Modification of the polymer gum block: granulating the polymer rubber block in a granulator to obtain polymer rubber particles with the average particle size of 0.4mm, uniformly mixing hydroxylamine sulfate and fatty alcohol-polyoxyethylene ether AEO-9 in water to obtain a modified solution, uniformly spraying the modified solution on the surfaces of the polymer rubber particles, fully mixing, carrying out modification reaction on the polymer rubber particles sprayed with the modified solution at 70 ℃ for 3 hours, and after the modification is finished, sequentially crushing, drying, grinding and screening to obtain the filtrate reducer; wherein the mass ratio of the polymer colloidal particles, hydroxylamine sulfate, fatty alcohol-polyoxyethylene ether AEO-9 to water is 1000.

Comparative example 7

Comparative example 7 is substantially the same as example 1 except that:

(2) polymer cement block modification

Modification of the polymer gum block: granulating a polymer rubber block in a granulator to obtain polymer rubber particles with the average particle size of 0.4mm, uniformly mixing hydroxylamine sulfate and potassium hydroxide in water to obtain a modified liquid, uniformly spraying the modified liquid on the surface of the polymer rubber particles, fully mixing, carrying out modification reaction on the polymer rubber particles sprayed with the modified liquid at 70 ℃ for 3 hours, and after the modification is finished, sequentially crushing, drying, grinding and screening to obtain the filtrate reducer; wherein the mass ratio of the polymer colloidal particles, hydroxylamine sulfate, potassium hydroxide and water is 1000.

Comparative example 8

The raw materials for preparing the fluid loss agent comprise: 10 parts of acrylamide, 35 parts of acryloyl morpholine, 55 parts of 3- (3-methoxy-4-methylphenyl) acrylic acid, 40 parts of vinyl trimethylsilane, 25 parts of 2-phenoxyethyl acrylate, 3 parts of a structure regulator, 800 parts of water, 1 part of azobisisobutyronitrile, 0.5 part of hydrogen peroxide and 0.5 part of sodium bisulfite. The preparation method comprises the following steps: fully and uniformly mixing acrylamide, acryloylmorpholine, 3- (3-methoxy-4-methylphenyl) acrylic acid, vinyltrimethylsilane, 2-phenoxyethyl acrylate, a structure regulator and water to obtain a mixed solution, regulating the pH value of the mixed solution to 6.6 by using ammonia water with the volume concentration of 25%, transferring the mixed solution into a reaction kettle, introducing nitrogen to remove oxygen for 60min, adding azodiisobutyronitrile, hydrogen peroxide and sodium bisulfite at the temperature of 5 ℃ to initiate polymerization reaction, and reacting for 3h to obtain a polymer block; and then sequentially granulating, drying, crushing and screening the polymer gel block to obtain the fluid loss agent.

Comparative example 9

Comparative example 9 is substantially the same as example 1 except that:

in step (1), the structure modifier used is prepared by: adding 500 parts of 2-hydroxypropionic acid into a three-neck flask with a stirrer, a condenser pipe and a thermometer, starting a water bath to control the temperature to be 60 ℃, dropwise adding 25 parts of concentrated sulfuric acid with the mass fraction of 98% within 1 hour, continuously reacting for 3 hours (comprising dropwise adding 1 hour of the concentrated sulfuric acid and continuously reacting for 2 hours after the dropwise adding is finished), cooling to room temperature after the reaction is finished, carrying out rotary evaporation by using a rotary evaporator, and evaporating a solvent to obtain an intermediate A which is used as a structure regulator.

Comparative example 10

Comparative example 10 is substantially the same as example 1 except that:

in step (1), the structure-regulating agent used is prepared by:

(2) Adding 240 parts of the intermediate A, 150 parts of butanol amine and 39 parts of N, N-dimethylformamide into a three-neck flask with a stirrer, a condenser and a thermometer, uniformly mixing, starting a water bath, controlling the temperature to be 45 ℃, and reacting for 3 hours at constant temperature; after the reaction is finished, performing rotary evaporation by using a rotary evaporator, and evaporating the solvent to obtain an intermediate B serving as a structure regulator.

Comparative example 11

Comparative example 11 is substantially the same as example 1 except that:

in step (1), no structure regulator is added, and the amount of the structure regulator is replaced by acrylamide, namely 13 parts of acrylamide is added.

Performance evaluation:

the fluid loss performance (including fluid loss) of the fluid loss additive prepared in each example and each comparative example is evaluated by referring to the method in Q/SH 0047-2007 general technical requirements of high temperature resistant and salt resistant fluid loss additive for drilling fluid, wherein the saline adopts 30wt% calcium chloride aqueous solution (the mass fraction of calcium chloride contained in the calcium chloride aqueous solution is 30%). Rheological properties (including indexes AV, PV, YP and phi 6/phi 3) of the fluid loss additives prepared in each example and each comparative example are evaluated by referring to a method SY/T5660-95 coating agent PAC141, fluid loss additive PAC142 and fluid loss additive PAC143 for drilling fluid, wherein the saline water is a 30wt% calcium chloride aqueous solution, and the results are shown in Table 1.

Table 1: the results of evaluating the performance of the fluid loss additives of examples 1 to 5 and comparative examples 1 to 11.

In Table 1, AV represents an apparent viscosity; PV represents a plastic viscosity; YP represents dynamic shear force; phi 6/phi 3 respectively represents the reading of the six-speed viscometer under the test conditions of 6 revolutions and 3 revolutions; in Table 1, the symbol "-" indicates that the fluid loss before aging was not measured.

The data in table 1 show that the molecular chain of the fluid loss additive prepared by the invention has extremely high temperature resistance and salt tolerance, can keep the viscosity and the fluid loss property in ultra-high mineralized water, and has stable rheological property, the dynamic shear force of the fluid loss additive prepared in some more preferable embodiments in the brine-based drilling fluid is more than 20Pa, can reach 21 Pa-30 Pa, phi 6/phi 3 is more than 12/9, and the fluid loss is less than 5mL.

The invention has not been described in detail and is in part known to those of skill in the art.

Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.

Claims

1. The preparation method of the fluid loss agent is characterized by comprising the following steps:

(1) Uniformly mixing acrylamide, acryloyl morpholine, a reinforcing monomer, a hydrolysis-resistant monomer, a cutting monomer, a structure regulator and water to obtain a mixed solution, introducing nitrogen into the mixed solution to remove oxygen, and adding an initiator to initiate polymerization reaction to obtain a polymer block;

(2) Granulating the polymer rubber block to obtain polymer rubber particles;

(3) Uniformly mixing a modifier, potassium hydroxide, an activator and water to obtain a modified liquid, and then spraying the modified liquid on the polymer colloidal particles to perform modification reaction to obtain the fluid loss additive.

2. The preparation method according to claim 1, further comprising the steps of sequentially crushing, drying, grinding and sieving the fluid loss additive.

3. The method of claim 1, wherein the structure-modifying agent is prepared by:

(c) And (3) uniformly mixing the intermediate B,1, 2-dichloroethane and diethylamine, then dropwise adding cinnamoyl chloride, and reacting to obtain the structure regulator.

4. The production method according to claim 3, characterized in that:

in the step (a), the mass fraction of the concentrated sulfuric acid is not less than 98%, the dosage of the concentrated sulfuric acid is 4-6% and more preferably 5% of the mass of the 2-hydroxypropionic acid, and/or the reaction temperature is 55-65 ℃, and the reaction time is 2.5-4 h and preferably 3h; and/or

In the step (b), the mass ratio of the intermediate A to the butanol amine is 8: (4-6) is preferably 8, the amount of the N, N-dimethylformamide is 8-15% and preferably 10% of the mass sum of the intermediate A and the butanolamine, and/or the reaction temperature is 40-50 ℃, and the reaction time is 2.5-4 h and preferably 3h.

5. The method of claim 3, wherein in step (c):

the mass ratio of the intermediate B to the cinnamoyl chloride is 8: (4 to 6) preferably 8;

the dosage of the 1, 2-dichloroethane is 10-20% and preferably 15% of the sum of the mass of the intermediate B and the mass of the cinnamoyl chloride;

the dosage of the diethylamine is 1-5% of the sum of the mass of the intermediate B and the mass of the cinnamoyl chloride, and is preferably 3%;

dripping cinnamoyl chloride at the temperature of-5 to 5 ℃; and/or

After the cinnamoyl chloride is dripped, the reaction temperature is controlled to be 30-35 ℃, and the reaction is carried out for 1.5-3 h, preferably 2h at the temperature of 30-35 ℃.

6. The production method according to any one of claims 1 to 3, characterized in that:

the reinforcing monomer is 3- (3-methoxy-4-methylphenyl) acrylic acid and/or 3- (4-methoxybenzoyl) acrylic acid;

the hydrolysis-resistant monomer is vinyltrimethylsilane and/or 4-acetoxystyrene;

the extraction and cutting monomer is one or more of 2-phenoxyethyl acrylate, furfuryl methacrylate and 2-ethyl phenylacrylate;

the initiator comprises an azo initiator and a redox initiator, wherein the azo initiator is azobisisobutyronitrile and/or azobisisobutylamidine hydrochloride, an oxidant in the redox initiator is one or more of hydrogen peroxide, di-tert-butyl peroxide and tert-butyl hydroperoxide, a reducing agent in the redox initiator is sodium bisulfite, and the mass ratio of the azo initiator to the redox initiator is (1-3): (0.5 to 3);

the modifier is hydroxylamine sulfate; and/or

The activator is fatty alcohol-polyoxyethylene ether.

7. The production method according to any one of claims 1 to 3, characterized in that:

in the step (1), each raw material for preparing the polymer rubber block comprises, by weight, 10-30 parts of acrylamide, 35-60 parts of acryloyl morpholine, 55-85 parts of reinforcing monomer, 40-80 parts of hydrolysis-resistant monomer, 25-45 parts of cutting monomer, 1-5 parts of structure regulator, 650-800 parts of water and 1.5-6 parts of initiator;

the particle size of the polymer colloidal particle obtained in the step (2) is less than 0.5mm; and/or

In the step (3), the mass ratio of the polymer colloidal particles, the modifier, the potassium hydroxide, the activator and the water is 1000: (20 to 25): (5-10): (10-20): (40 to 60), preferably 1000.

8. The production method according to any one of claims 1 to 3, characterized in that:

in the step (1), before introducing nitrogen into the mixed solution to remove oxygen, the pH value of the mixed solution is adjusted to 6.5-7.0;

in the step (1), the time for introducing nitrogen to remove oxygen is 40-80 min;

in the step (1), an initiator is added at 5-7 ℃ to initiate polymerization reaction, and the polymerization reaction time is 2-4 h, preferably 3h; and/or

In the step (3), the temperature of the modification reaction is 70-80 ℃, and the time of the modification reaction is 3-4 h.

9. Fluid loss additive prepared by the preparation method of any one of claims 1 to 8.

10. Use of a fluid loss additive prepared by the preparation method of any one of claims 1 to 8 in brine-based drilling fluids.