Sulfonate filtrate reducer for low-viscosity drilling fluid as well as preparation method and application of sulfonate filtrate reducer

Abstract

The invention discloses a sulfonate filtrate reducer for a low-viscosity drilling fluid as well as a preparation method and application of the sulfonate filtrate reducer. The sulfonate filtrate reducer is formed by copolymerizing 2-acrylamido-2-methylpropanesulfonic acid, sodium p-styrenesulfonate, acrylamide, allyl polyglycol ether and diethyl maleate which serve as monomers; the ratio of the amount of substance of the five monomers is (30-50): (10-20): (20-30): (5-15): (3-8). The preparation method comprises the following steps: adding 2-acrylamido-2-methylpropanesulfonic acid, sodium p-styrenesulfonate and acrylamide into water to obtain a mixed dispersion liquid A; adjusting the pH value of the mixed solution A to be neutral or alkalescent, and adding allyl polyglycol ether and diethyl maleate to obtain a mixed dispersion solution B; adding an initiator into the mixed dispersion liquid B to carry out polymerization reaction to obtain mixed dispersion liquid C; and drying, crushing and sieving the mixed dispersion liquid C to obtain the product. The sulfonate filtrate reducer for the low-viscosity drilling fluid is applied to drilling fluid of a deep well or an ultra-deep well, and the viscosity of the drilling fluid is basically not increased while excellent filtrate reduction performance is kept in a high-temperature and high-salt environment.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of petroleum drilling aids. Specifically, it is a sulfonate filtrate reducer for low-viscosity drilling fluid, and a preparation method and application thereof. BACKGROUND

[0002] In petroleum drilling operations, the filtration control of drilling fluid is one of the core links: excessive filtration can easily cause wellbore instability, reservoir damage, and even drilling accidents. Traditional filtrate reducers (such as sulfomethyl phenolic resin) have certain temperature resistance, but have defects such as severe viscosity increase and insufficient salt resistance, especially in high-temperature and high-salt environments of deep wells (4500-6000m) and ultra-deep wells (more than 6000m), their performance has been difficult to meet the operation requirements.

[0003] To address this problem, existing technologies have developed a variety of new filtrate reducers. For example, patent CN101691485A discloses a high-temperature-resistant zwitterionic polymer filtrate reducer, which is prepared by copolymerizing AM, AMPS, dimethyl diallyl ammonium chloride and SSS, and has a temperature resistance of more than 220℃, but still has a certain viscosity increase. Patent CN115124667A discloses a filtrate reducer suitable for high-temperature and high-density salt water drilling fluid, which is prepared by a step-by-step polymerization method, and has a temperature resistance of 180℃, but the preparation process is relatively complex. Patent CN112029485A discloses a composite medium-molecular sulfonate filtrate reducer, which is prepared by starch puffing and waste silk kneading process, and has environmental protection advantages, but cannot adapt to high-temperature environments. In addition, patent CN111875758A uses a reverse emulsion polymerization method to prepare a filtrate reducer, which has a fast dissolution speed, but a temperature resistance of only 170℃.

[0004] It can be seen that the performance of existing filtrate reducers cannot meet the application requirements of high-temperature and high-salt environments in deep and ultra-deep wells, and it is urgent to develop a filtrate reducer that has high-temperature and high-salt resistance and does not increase the viscosity of drilling fluid. SUMMARY

[0005] Therefore, the technical problem to be solved by the present application is to provide a sulfonate filtrate reducer for low-viscosity drilling fluid, and a preparation method and application thereof, to solve the problems of severe viscosity increase and insufficient filtration control of existing filtrate reducers in high-temperature and high-salt environments.

[0006] To solve the above technical problems, the present application provides the following technical solutions:

[0007] The low-viscosity drilling fluid sulfonate filtrate reducer is prepared by copolymerization of 2-acrylamido-2-methylpropane sulfonic acid (AMPS), sodium styrene sulfonate (SSS), acrylamide (AM), allyl polyethylene glycol ether (APEG) and maleic acid diethyl ester (DEM) as monomers; the mass ratio of 2-acrylamido-2-methylpropane sulfonic acid, sodium styrene sulfonate, acrylamide, allyl polyethylene glycol ether and maleic acid diethyl ester is (30-50):(10-20):(20-30):(5-15):(3-8); the relative molecular mass of the low-viscosity drilling fluid sulfonate filtrate reducer is 500,000-1,000,000 (in the range, the filtration reduction effect can be ensured, and the viscosity of the drilling fluid cannot be increased).

[0008] In the sulfonate filtrate reducer, the two monomers of AMPS and SSS can provide sulfonic acid groups for the sulfonate filtrate reducer, and the viscosity of the drilling fluid can be reduced through the charge repulsion of the anionic monomers; the introduction of AM can increase the water solubility and adsorbability of the sulfonate filtrate reducer; APEG is a hydrophilic long chain, and can improve the compatibility of the sulfonate filtrate reducer in a high salinity system; DEM can enhance the tolerance of the sulfonate filtrate reducer to high valence ions, so as to adapt to the divalent ions encountered in the current drilling process. Maleic anhydride has high reactivity, and is easy to hydrolyze in the reaction process, which is not conducive to the polymerization reaction; compared with maleic anhydride, maleic acid diethyl ester is used as a monomer to be polymerized with AMPS, SSS, AM and APEG in the present application, and the polymer molecules obtained through the reaction are more stable. If the amount of AM is too large, the temperature resistance and salt resistance of the polymer generated through polymerization will be poor; if SSS is excessive, the viscosity of the water phase will be increased, and local polymerization will be uneven; if APEG and DEM, as the stabilizing materials of the polymer, are used in too large an amount, the polymerization reaction will be affected. In the present application, AMPS, SSS and AM are used as the main reaction monomers, APEG and DEM are used as the monomers for improving the stability of the polymer, and the amount ratio of the five monomers of AMPS, SSS, AM, APEG and DEM and the relative molecular mass of the sulfonate filtrate reducer are controlled in a specific range, so that the sulfonate filtrate reducer can maintain excellent filtration reduction performance in a high-temperature and high-salt environment, and the viscosity of the drilling fluid is basically not increased.

[0009] In the preparation method of the low-viscosity drilling fluid sulfonate filtrate reducer, the mass ratio of 2-acrylamido-2-methylpropane sulfonic acid, sodium styrene sulfonate, acrylamide, allyl polyethylene glycol ether and maleic acid diethyl ester is 45:10:22:18:5; the relative molecular mass of the low-viscosity drilling fluid sulfonate filtrate reducer is 720,000.

[0010] A preparation method of a low-viscosity drilling fluid sulfonate filtrate reducer comprises the following steps:

[0011] Step (1), 2-acrylamido-2-methylpropanesulfonic acid, sodium styrene sulfonate and acrylamide are stirred and dissolved in water to obtain a mixed dispersion A;

[0012] Step (2), the pH of the mixed solution A is adjusted to neutral or weak alkaline, then allyl polyethylene glycol ether and maleic acid diethyl ester are added and mixed uniformly to obtain a mixed dispersion B; since the solubility of DEM is small in acidic solution and the mixed dispersion A is acidic, the mixed solution A is first adjusted to neutral or weak alkaline, then APEG and DEM are added, which is conducive to the sufficient dissolution of DEM and APEG, so as to ensure that the monomers are uniformly mixed in the mixed dispersion B, which is conducive to the subsequent full polymerization between the monomers; in addition, APEG and DEM have little effect on the pH of the monomer mixed system, and the neutralization reaction that occurs when the pH is adjusted will cause the temperature of the system to rise, so adjusting the pH and then adding APEG and DEM can have a cooling effect, avoiding the premature local polymerization of monomers caused by too high temperature of the monomer mixed system before polymerization, which affects the performance of the final polymerization product;

[0013] Step (3), after oxygen is removed by passing nitrogen into the mixed dispersion B, an initiator is added, and the polymerization reaction is carried out under the protection of nitrogen; after the polymerization reaction is completed, a mixed dispersion C is obtained;

[0014] Step (4), the mixed dispersion C is placed in a vacuum drying box for drying, and the solid product obtained by drying is crushed and sieved to obtain the above-mentioned low-viscosity sulfonate filtrate reducer for drilling fluid.

[0015] In step (1) of the preparation method of the above-mentioned low-viscosity sulfonate filtrate reducer for drilling fluid, the stirring and dissolving time is 20-30 min; in the mixed dispersion A, the substance concentration of acrylamide is 0.10-0.15 mol / L, and by controlling the concentration of monomers in the reaction system, the subsequent polymerization reaction can be carried out mildly, which can not only ensure that the monomers are more fully and completely polymerized, but also effectively avoid the problem of "explosive polymerization" caused by too fast polymerization.

[0016] In step (2) of the preparation method of the above-mentioned low-viscosity sulfonate filtrate reducer for drilling fluid, the pH of the mixed solution A is adjusted to 7-8 using a sodium hydroxide solution with a mass fraction of 8-15 wt% (when the pH is in this range, a polymer with a relatively low molecular weight can be obtained, and if the pH is lower than 7 or higher than 8, the obtained polymer has a too high molecular weight); the degree of polymerization n of the allyl polyethylene glycol ether is 20-50, and the use of the allyl polyethylene glycol ether with this degree of polymerization range in the polymerization reaction can ensure that the allyl polyethylene glycol ether fully participates in the polymerization, and its certain steric hindrance can ensure that it is not prone to side reactions in the polymerization reaction, and the polymerization obtained polymer has a more stable molecular structure.

[0017] The preparation method of the low-viscosity drilling fluid sulfonate filtrate reducer, in step (3), the flow rate of the nitrogen gas is 1-5 L / min, and the oxygen removal time of the nitrogen gas is 20-40 min.

[0018] The preparation method of the low-viscosity drilling fluid sulfonate filtrate reducer, in step (3), the initiator is an ammonium persulfate aqueous solution and a sodium bisulfite aqueous solution, the mass fraction of ammonium persulfate in the ammonium persulfate aqueous solution is 1-3 wt%, the mass fraction of sodium bisulfite in the sodium bisulfite aqueous solution is 1-3 wt%, the molar ratio of ammonium persulfate to sodium bisulfite is 1:(1.8-2.2), and the total mass of the added ammonium persulfate and sodium bisulfite is 0.1-0.3 wt% of the total mass of 2-acrylamido-2-methylpropanesulfonic acid, styrene sulfonic acid sodium, and acrylamide, acrylamide, allyl polyethylene glycol ether, and maleic acid diethyl ester; the initiator is added in the following manner: the ammonium persulfate aqueous solution is added into the mixed dispersion B at one time, and then the sodium bisulfite aqueous solution is slowly added dropwise (30-60 min for dropwise addition).

[0019] The preparation method of the low-viscosity drilling fluid sulfonate filtrate reducer, in step (3), the conditions of the aqueous solution polymerization reaction are as follows: the temperature is increased to 70-80 DEG C at a temperature increasing rate of 1-2 DEG C / min, the stirring rate during the polymerization reaction is 100-200 rpm, and the polymerization reaction time is 4-6 h; under the polymerization reaction conditions, the specific proportions of the monomers in the mixed dispersion C can fully participate in the polymerization reaction due to the synergistic effect of the steric hindrance effect and the electronic effect during the polymerization reaction, so that polymer molecules with stable structures and uniform side chain distribution are obtained, the relative molecular mass of the polymer molecules obtained by polymerization can be controlled within the range of 0.5-1 million, the sulfonic acid groups, ester groups and ether oxygen groups introduced can synergistically play a modification role on the polymer molecules, and the polymer as a sulfonate filtrate reducer can improve the filtration reduction performance in a high-temperature and high-salt environment and the improvement effect on the rheological properties of the drilling fluid.

[0020] The preparation method of the low-viscosity drilling fluid sulfonate filtrate reducer, in step (4), the drying conditions are as follows: the drying temperature is 70-90 DEG C, and the drying time is 16-32 h; and the solid product is crushed and sieved through a 40-mesh screen.

[0021] The application of the low-viscosity drilling fluid sulfonate filtrate reducer, the low-viscosity drilling fluid sulfonate filtrate reducer is used in the drilling fluid for deep wells or ultra-deep wells.

[0022] The technical scheme of the present application has the following beneficial technical effects:

[0023] 1. The sulfonate fluid loss additive for low-viscosity drilling fluid of the present application uses 2-acrylamido-2-methylpropanesulfonic acid (AMPS), sodium styrene sulfonate (SSS), acrylamide (AM), allyl polyethylene glycol ether (APEG), and diethyl maleate (DEM) as monomer raw materials. By controlling the amount-of-substance ratio of the monomers within a specific range and controlling the polymerization process conditions, the monomers are polymerized to produce a sulfonate fluid loss additive with a relative molecular mass of 500,000-1,000,000. The sulfonic acid group, ester group, and ether oxygen group introduced by molecular design and various functional monomers enable the sulfonate fluid loss additive of the present application to maintain excellent fluid loss performance in a high-temperature high-salt environment, effectively control the viscosity of the drilling fluid, and improve the rheological properties of the drilling fluid.

[0024] 2. The preparation method of the sulfonate fluid loss additive for low-viscosity drilling fluid of the present application uses AMPS, SSS, and AM as the main reaction monomers, and uses APEG and DEM as the monomers for improving the stability of the polymer. By designing the mixing method and order of the monomer raw materials, controlling the pH of the polymerization reaction system to be neutral or weakly alkaline, controlling the addition amount and addition method of the initiator, and controlling the conditions of the polymerization reaction (heating rate, reaction temperature, and reaction time), the sulfonate fluid loss additive prepared by redox polymerization has a relative molecular mass of 500,000-1,000,000. The sulfonate fluid loss additive has a temperature resistance of 200℃ or higher and a salt resistance of up to saturation. The preparation process is environmentally friendly and does not produce three wastes.

[0025] 3. The sulfonate fluid loss additive prepared by the preparation method of the sulfonate fluid loss additive for low-viscosity drilling fluid of the present application has the following advantages:

[0026] (1) Low viscosity: By controlling the polymer molecular weight (50-100 million) and introducing a side chain structure, the viscosity of the fluid loss additive itself is effectively reduced, and the viscosity of the drilling fluid system is not increased;

[0027] (2) High temperature resistance: The introduction of sulfonic acid groups and ester bonds enhances the thermal stability of the polymer, enabling it to resist temperatures of 200℃ or higher;

[0028] (3) High salt resistance: The sulfonic acid group is not sensitive to salt and can resist salt up to saturation;

[0029] (4) Environmental friendliness: The preparation process does not produce three wastes, and the raw material utilization rate is high;

[0030] (5) Improved rheological properties: The product can effectively improve the rheological properties of the drilling fluid and prevent high-temperature thickening. DETAILED DESCRIPTION

[0031] Example 1

[0032] In this embodiment, the preparation method of the sulfonate fluid loss additive for low-viscosity drilling fluid includes the following steps:

[0033] Step (1), 8.29 kg of 2-acrylamido-2-methylpropanesulfonic acid (40 mol), 2.47 kg of sodium styrene sulfonate (12 mol) and 1.78 kg of acrylamide (25 mol) were added to 200 L of pure water and stirred to dissolve, to obtain a mixed dispersion A;

[0034] Step (2), the pH of the mixed solution A was adjusted to 7.5 using a 10wt% sodium hydroxide solution, then 14.51 kg of allyl polyethylene glycol ether (APEG-1000, polymerization degree n = 21, 15 mol) and 1.38 kg of diethyl maleate (8 mol) were added and mixed uniformly, to obtain a mixed dispersion B;

[0035] Step (3), nitrogen was introduced into the mixed dispersion B at a rate of 1 L / min to remove oxygen for 30 min, then an ammonium persulfate-sodium bisulfite initiator was added, and the temperature was raised to 70°C at a rate of 2°C / min under nitrogen protection to carry out the polymerization reaction, the reaction time was 5 h; the stirring rate during the whole process was 150 rpm; after the polymerization reaction was completed, a mixed dispersion C was obtained;

[0036] In this embodiment, the initiator was an ammonium persulfate aqueous solution (1.5 L) and a sodium bisulfite aqueous solution (1.4 L), the mass fraction of ammonium persulfate in the ammonium persulfate aqueous solution was 2wt%, and the mass fraction of sodium bisulfite in the sodium bisulfite aqueous solution was 2wt%; the initiator was added in the following way: the ammonium persulfate aqueous solution was added into the mixed dispersion B at one time and stirred to mix uniformly, and then the sodium bisulfite aqueous solution was slowly added dropwise (30 min for dropwise addition);

[0037] Step (4), the mixed dispersion C was placed in a 80°C vacuum drying oven for drying for 24 h, the dried solid product was crushed through a 40 mesh sieve, and the obtained white powder was a low-viscosity sulfonate filtrate reducer for drilling fluid, the relative molecular mass of which was 750,000; the sulfonate filtrate reducer was prepared into a 1wt% aqueous solution, and the dynamic viscosity thereof was measured to be 10 mPa·s.

[0038] Example 2

[0039] In this embodiment, the preparation method of the low-viscosity sulfonate filtrate reducer for drilling fluid included the following steps:

[0040] Step (1), 9.33 kg of 2-acrylamido-2-methylpropanesulfonic acid (45 mol), 2.06 kg of sodium styrene sulfonate (10 mol) and 1.56 kg of acrylamide (22 mol) were added to 200 L of pure water and stirred to dissolve, to obtain a mixed dispersion A;

[0041] Step (2), the pH of the mixed solution A was adjusted to 7.0 by using a 10wt% sodium hydroxide solution, then 17.70 kg of allyl polyethylene glycol ether (APEG-1000, degree of polymerization n = 21, 18 mol) and 0.86 kg of diethyl maleate (5 mol) were added and mixed uniformly to obtain a mixed dispersion B;

[0042] Step (3), nitrogen was introduced into the mixed dispersion B at a rate of 1 L / min to remove oxygen for 30 min, then an ammonium persulfate-sodium bisulfite initiator was added, and the temperature was raised to 75℃ at a rate of 2℃ / min under nitrogen protection to carry out the polymerization reaction, the reaction time was 4 h; the stirring rate during the whole process was 150 rpm; after the polymerization reaction was completed, a mixed dispersion C was obtained;

[0043] In this embodiment, the initiator was an ammonium persulfate aqueous solution (1.65 L) and a sodium bisulfite aqueous solution (1.5 L), the mass fraction of ammonium persulfate in the ammonium persulfate aqueous solution was 2wt%, and the mass fraction of sodium bisulfite in the sodium bisulfite aqueous solution was 2wt%; the initiator was added in the following way: the ammonium persulfate aqueous solution was added into the mixed dispersion B at one time and stirred to mix uniformly, and then the sodium bisulfite aqueous solution was slowly added dropwise (40 min for dropwise addition);

[0044] Step (4), the mixed dispersion C was placed in a vacuum drying oven at 80℃ and dried for 24 h, the solid product obtained by drying was crushed through a 40 mesh sieve, and the white powder obtained was a low-viscosity sulfonate filtrate reducer for drilling fluid, the relative molecular mass of which was 720,000; the sulfonate filtrate reducer was prepared into a 1wt% aqueous solution, and the dynamic viscosity thereof was measured to be 8 mPa·s.

[0045] The low-viscosity sulfonate filtrate reducers for drilling fluid prepared in Example 1 and Example 2 were added to a drilling fluid base slurry (which was mixed by using drilling fluid slurry preparation sodium bentonite and distilled water, and the mass fraction of the drilling fluid slurry preparation sodium bentonite was 4wt%), and the addition amount of the sulfonate filtrate reducer was 2.0wt% of the mass of the drilling fluid base slurry. The performance of the drilling fluid was tested according to the API standard, and a commercially available sulfomethyl phenolic resin filtrate reducer was used as a control (the amount was the same as that of the sulfonate filtrate reducer). The test conditions were: aging at a temperature of 200℃ for 16 h, saturated brine drilling fluid; the test results are shown in Table 1.

[0046] The "Example 1 group" represents a drilling fluid prepared by adding the low-viscosity drilling fluid sulfonate filtrate reducer prepared in Example 1 to a drilling fluid base paste; the "Example 2 group" represents a drilling fluid prepared by adding the low-viscosity drilling fluid sulfonate filtrate reducer prepared in Example 2 to a drilling fluid base paste; and the "control group" represents a drilling fluid prepared by adding a commercially available sulfomethyl phenolic resin filtrate reducer (product name: drilling fluid filtrate reducer sulfomethyl phenolic resin type 2, model SMP-2, manufacturer: Sichuan Shangzhideng New Material Technology Co., Ltd.) to a drilling fluid base paste.

[0047] Table 1

[0048]

[0049] As can be seen from the results in Table 1, the high-temperature high-pressure filtration amounts HTHP FL of the three groups of drilling fluids are all significantly reduced relative to the drilling fluid base paste, among which the high-temperature high-pressure filtration amount of the Example 2 group is the lowest, the Example 1 group and the Example 2 group are not much different, and the high-temperature high-pressure filtration amount of the control group is also lower than that of the drilling fluid base paste, but is significantly higher than those of the Example 1 group and the Example 2 group. As can be seen from the test results of the apparent viscosity AV and the plastic viscosity PV, the apparent viscosity and the plastic viscosity of the Example 1 group and the Example 2 group are not significantly increased compared with the drilling fluid base paste, while the apparent viscosity and the plastic viscosity of the control group are significantly increased. In addition, the test results of the yield point YP also show the same law as the apparent viscosity and the plastic viscosity, which indicates that the sulfonate filtrate reducer prepared by the preparation method of the present application basically does not increase the viscosity of the drilling fluid while maintaining excellent filtration reduction performance.

[0050] Obviously, the above examples are merely illustrative examples for the purpose of clarity, and are not intended to limit the embodiments. Based on the above description, other different forms of changes or variations can also be made by those of ordinary skill in the art. Here, it is not necessary and impossible to exhaust all the embodiments. The changes or variations derived therefrom are still within the protection scope of the claims of the present patent application.

Claims

1. A sulfonate filtrate reducer for low viscosity drilling fluids, characterized by, The low-viscosity drilling fluid sulfonate filtrate reducer is prepared by copolymerization of 2-acrylamido-2-methylpropane sulfonic acid, sodium styrene sulfonate, acrylamide, allyl polyethylene glycol ether and maleic acid diethyl ester; the mass ratio of 2-acrylamido-2-methylpropane sulfonic acid, sodium styrene sulfonate, acrylamide, allyl polyethylene glycol ether and maleic acid diethyl ester is (30-50):(10-20):(20-30):(5-15):(3-8); and the relative molecular mass of the low-viscosity drilling fluid sulfonate filtrate reducer is 500,000-1,000,000.

2. The method for preparing a sulfonate filtrate reducer for a low viscosity drilling fluid according to claim 1, characterized by, The mass ratio of 2-acrylamido-2-methylpropane sulfonic acid, sodium styrene sulfonate, acrylamide, allyl polyethylene glycol ether and maleic acid diethyl ester is 45:10:22:18:5; and the relative molecular mass of the low-viscosity drilling fluid sulfonate filtrate reducer is 720,000.

3. A method for preparing a sulfonate filtrate reducer for a low viscosity drilling fluid, characterized by, The method comprises the following steps: Step (1), 2-acrylamido-2-methylpropane sulfonic acid, sodium styrene sulfonate and acrylamide are added into water and stirred and dissolved to obtain a mixed dispersion A; Step (2), the pH of the mixed solution A is adjusted to neutral or weak alkaline, then allyl polyethylene glycol ether and maleic acid diethyl ester are added and uniformly mixed to obtain a mixed dispersion B; Step (3), after oxygen is removed from the mixed dispersion B by blowing nitrogen, an initiator is added, and the polymerization reaction is carried out under the protection of nitrogen by heating; after the polymerization reaction is completed, a mixed dispersion C is obtained; Step (4), the mixed dispersion C is dried in a vacuum drying box, the solid product obtained by drying is crushed and sieved, and thus the low-viscosity drilling fluid sulfonate filtrate reducer according to claim 1 or 2 is prepared.

4. The method of claim 3, wherein the sulfonate fluid loss additive is prepared by the steps of: (a) mixing a sulfonated aromatic compound with an aldehyde compound to form a mixture; (b) adding a base to the mixture to form a reaction mixture; (c) adding a reducing agent to the reaction mixture to form a product; and (d) recovering the product. In step (1), the stirring and dissolving time is 20-30 min; and in the mixed dispersion A, the mass concentration of acrylamide is 0.10-0.15 mol / L.

5. The method of claim 3, wherein the sulfonate fluid loss additive is prepared by the steps of: (a) mixing a sulfonated aromatic compound with an aldehyde compound to form a mixture; (b) adding a base to the mixture to form a reaction mixture; (c) adding a reducing agent to the reaction mixture to form a product; and (d) recovering the product. In step (2), the pH of the mixed solution A is adjusted to 7-8 by using a sodium hydroxide solution with a mass fraction of 8-15 wt%; and the polymerization degree n of the allyl polyethylene glycol ether is 20-50.

6. The method for preparing the low-viscosity drilling fluid sulfonate filtration reducer according to claim 3, characterized in that, In step (3), the flow rate of the nitrogen gas blown is 1-5 L / min, and the nitrogen gas oxygen removal time is 20-40 min.

7. The method of claim 3, wherein the sulfonate fluid loss additive is prepared by the steps of: (a) mixing a sulfonated aromatic compound with an aldehyde compound to form a mixture; (b) adding a base to the mixture to form a reaction mixture; (c) adding a reducing agent to the reaction mixture to form a product; and (d) recovering the product. In step (3), the initiator is an aqueous ammonium persulfate solution and an aqueous sodium bisulfite solution; the mass fraction of ammonium persulfate in the aqueous ammonium persulfate solution is 1-3 wt%, and the mass fraction of sodium bisulfite in the aqueous sodium bisulfite solution is 1-3 wt%; the mass ratio of ammonium persulfate to sodium bisulfite is 1:(1.8-2.2); the total mass of ammonium persulfate and sodium bisulfite is 0.1-0.3 wt% of the total mass of 2-acrylamido-2-methylpropane sulfonic acid, sodium styrene sulfonate and acrylamide, acrylamide, allyl polyethylene glycol ether and maleic acid diethyl ester; and the initiator is added in the following manner: the aqueous ammonium persulfate solution is added into the mixed dispersion B at one time, the aqueous sodium bisulfite solution is added dropwise after the mixed dispersion B is stirred and uniformly mixed, and the aqueous sodium bisulfite solution is added dropwise for 30-60 min.

8. The method of claim 3, wherein the sulfonate fluid loss additive is prepared by the steps of: (a) mixing a sulfonated aromatic compound with an aldehyde compound to form a mixture; (b) adding a base to the mixture to form a reaction mixture; (c) adding a reducing agent to the reaction mixture to form a product; and (d) recovering the product. In step (3), the aqueous solution polymerization reaction is carried out at a temperature of 70-80°C, with a stirring speed of 100-200 rpm, and a reaction time of 4-6 h.

9. The method of claim 3, wherein the sulfonate fluid loss additive is prepared by the steps of: (a) mixing a sulfonated aromatic compound with an aldehyde compound to form a mixture; (b) adding a base to the mixture to form a reaction mixture; (c) adding a reducing agent to the reaction mixture to form a product; and (d) recovering the product. In step (4), the drying is carried out at a temperature of 70-90°C for 16-32 h, and the solid product is ground to 40 mesh.

10. Use of a sulfonate fluid loss additive for a low viscosity drilling fluid, characterized in that, The low-viscosity sulfonate filtrate reducer of claims 1 or 2 is used in a drilling fluid for deep or ultra-deep wells.

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