High-temperature-resistant and saturated-salt-resistant filtrate reducer for drilling fluid and preparation method of high-temperature-resistant and saturated-salt-resistant filtrate reducer

Abstract

The invention discloses a high-temperature-resistant and saturated-salt-resistant filtrate reducer for drilling fluid and a preparation method thereof, and relates to the technical field of filtrate reducers. 2-acrylamido-2-methylpropanesulfonic acid is used as a core monomer, N-vinyl-2-pyrrolidone and acrylic acid monomers are added, a comb-shaped structure with a rigid main chain and a flexible side chain is formed, and the high-temperature-resistant and saturated-salt-resistant filtrate reducer is prepared. The main chain and the side chain have a synergistic effect, so that the high temperature resistance and the saturated salt resistance of the filtrate reducer are improved. Ferroferric oxide precipitates are generated on the surface of the mullite, and the high-temperature resistance of the whiskers can be improved by adding the ferroferric oxide, so that the high-temperature resistance of the filtrate reducer is improved. The polyvinyl alcohol modified mullite whisker and the blended material are subjected to polymerization reaction, the surface of polyvinyl alcohol is provided with hydroxyl, a barrier of a hydrophilic layer can be formed on the surface of the whisker, compression of saturated salt on a polymer is effectively blocked, the polymer is prevented from curling, and therefore the saturated salt resistance and the high-temperature resistance of the filtrate reducer are improved.

Description

Technical Field

[0001] This invention relates to the field of filtration loss reducing agents, specifically a high-temperature and saturated salt resistant filtration loss reducing agent for drilling fluids and its preparation method. Background Technology

[0002] As oil and gas drilling continues to deepen, the drilling depth becomes deeper and the formation temperature becomes higher, making drilling more and more difficult. In order to effectively solve the problem of wellbore stability in the process of drilling deep wells in complex formations, high-temperature resistant brine or saturated brine drilling fluids are often selected. However, most high-temperature resistant treatment agents are not salt resistant, and salt resistant treatment agents are not resistant to high temperatures.

[0003] To address the issues of high-temperature resistance and saturated salt resistance in drilling fluids, this invention provides a high-temperature and saturated salt resistant fluid loss reducer for drilling fluids and its preparation method. Summary of the Invention

[0004] The purpose of this invention is to provide a high-temperature and saturated salt resistant fluid reducer for drilling fluids and its preparation method, so as to solve the problems raised in the prior art.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A method for preparing a high-temperature resistant and saturated salt resistant filtration loss reducer for drilling fluids includes the following steps:

[0007] Step 1: Add sorbitan oleate to deionized water, heat to 55-60℃, stir evenly, add 2-acrylamido-2-methylpropanesulfonic acid, acrylic acid, N-vinyl-2-pyrrolidone, and N,N'-methylenebisacrylamide, stir evenly to obtain the blended material;

[0008] Step 2: Take polyvinyl alcohol modified mullite whiskers, add deionized water, ultrasonically disperse, stir for 3-6 hours, add the blended material, heat to 60-65℃, stir for 5-7 hours to obtain the modified material;

[0009] Step 3: Take the modified material, add sodium citrate and ammonium persulfate aqueous solution, stir magnetically, purge with nitrogen for 50-70 minutes, heat to 70-80℃, and react for 6-8 hours; add sodium hydroxide and isopropanol, stir thoroughly for 30-50 minutes, wash, dry, and pulverize to obtain a high-temperature and saturated salt resistant fluid loss reducer for drilling fluid.

[0010] A more optimized method for preparing the polyvinyl alcohol modified mullite whiskers is as follows: take dimethyl sulfoxide, add iron-modified mullite whiskers with surface epoxidation, ultrasonically disperse for 1-3 hours, add polyvinyl alcohol and potassium hydroxide, heat in an oil bath at 95-100℃ for 12-14 hours, filter, wash, and dry to obtain polyvinyl alcohol modified mullite whiskers.

[0011] In a more optimized manner, the mass ratio of the surface-epoxidized iron-modified mullite whiskers, polyvinyl alcohol, and potassium hydroxide is (5-7):(6-8):(0.4-0.6).

[0012] A more optimized method for preparing the surface-epoxidized iron-modified mullite whiskers includes the following steps:

[0013] S1: Take mullite whiskers, add deionized water, stir evenly, add ferric chloride hexahydrate and ferrous sulfate heptahydrate, ultrasonically disperse for 20-30 minutes, heat to 50-55℃, add sodium hydroxide solution dropwise, adjust the pH value to 11-12, wash and dry to obtain iron-modified mullite whiskers;

[0014] S2: Take 3-glycidyl etheroxypropyltrimethoxysilane, add it to an ethanol solution, stir well, add iron-modified mullite whiskers, react for 24-28 hours, wash, and dry to obtain iron-modified mullite whiskers with epoxidized surface.

[0015] More optimally, the mass ratio of the 3-glycidyl etheroxypropyltrimethoxysilane to the iron-modified mullite whiskers is (3-4):(50-60).

[0016] A more optimized method for preparing mullite whiskers is as follows: alumina and silicon dioxide are mixed evenly, ammonium metatungstate is added, the mixture is stirred evenly, and the mixture is ball-milled and heat-treated to obtain mullite whiskers.

[0017] Ideally, the ball milling time is 10–12 hours, the heat treatment time is 5–7 hours, and the heat treatment temperature is 1500–1520°C.

[0018] Compared with the prior art, the beneficial effects of the present invention are:

[0019] 1. This invention uses 2-acrylamido-2-methylpropanesulfonic acid as the core monomer, and adds N-vinyl-2-pyrrolidone and acrylic acid monomer to form a comb-like structure with a rigid main chain and flexible side chains. The rigid main chain provides high-temperature stability and avoids thermal degradation; the flexible side chains containing sulfonates maintain dispersion and avoid flocculation due to saturated brine; the synergistic effect of the main chain and side chains improves the high-temperature resistance and resistance to saturated salt of the filtration loss reducer.

[0020] 2. Mullite whiskers are hollow columnar structures with low density, high porosity, low thermal conductivity, and good high-temperature resistance. Polymerizing polyvinyl alcohol-modified mullite whiskers and blends together with monomers in situ can effectively improve the resistance of saturated salts to filtration loss reducers.

[0021] 3. Modify mullite whiskers with ferric chloride hexahydrate and ferrous sulfate heptahydrate to generate iron oxide precipitate on the surface of mullite. The addition of iron oxide can improve the high temperature resistance of the whiskers, thereby improving the high temperature resistance of the filtration loss reducer.

[0022] 4. By treating iron-modified mullite whiskers with 3-glycidyl etheroxypropyltrimethoxysilane, epoxy groups are grafted onto them, and hydroxyl groups are added to the surface of polyvinyl alcohol. The reaction between the epoxy groups and hydroxyl groups allows polyvinyl alcohol to be loaded onto the surface of the epoxidized iron-modified mullite whiskers, forming a hydrophilic barrier that effectively blocks the compression of the polymer by saturated salts and prevents the polymer from curling, thereby improving the anti-saturated salt performance of the filtration loss reducer. Detailed Implementation

[0023] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] The sources and types of substances involved in this invention are not specifically limited. Exemplary examples include: sorbitan oleate, catalog number 0037, provided by Xi'an Jinxiang Pharmaceutical Excipients Co., Ltd.; 2-acrylamido-2-methylpropanesulfonic acid, catalog number HXKJ2024, provided by Wuhan Huaxiang Kejie Biotechnology Co., Ltd.; acrylic acid, catalog number BXS01, provided by Jinan Shanhai Chemical Technology Co., Ltd.; N-vinyl-2-pyrrolidone, catalog number wkq-11993, provided by Sichuan Weikeqi Biotechnology Co., Ltd.; 3-glycidyl etheroxypropyltrimethoxysilane. The following products were supplied: Alkane (CCHM705116) by Beijing Naphthalene Biochemical Technology Co., Ltd.; Polyvinyl alcohol (363103) by Shanghai Lusen Bioengineering Co., Ltd.; Sodium citrate (PHR1416) by Zhejiang Yigao Biotechnology Co., Ltd.; Ammonium persulfate (M133-25G) by Beijing Shengke Boyuan Biotechnology Co., Ltd.; Silica (30nm particle size) by Beijing Deco Island Gold Technology Co., Ltd.; and Alumina (ALUNA-100C) by Hubei Huifu Nanomaterials Co., Ltd.

[0025] Example 1: A high-temperature and saturated salt resistant fluid reducer for drilling fluids and its preparation method:

[0026] Step 1: (1) Take 2g of sorbitan oleate and add it to 150mL of deionized water. Heat the water to 58℃ and stir until homogeneous. Add 25.4g of 2-acrylamido-2-methylpropanesulfonic acid, 6.73g of acrylic acid, 37g of N-vinyl-2-pyrrolidone, and 0.35g of N,N'-methylenebisacrylamide. Stir until homogeneous to obtain the blended material.

[0027] Step 2: (1) Take 5.9g of alumina and 3.9g of silicon dioxide, mix them evenly, add 0.2g of ammonium metatungstate, stir evenly, ball mill and mix for 10h, heat treat at 30MPa and 1500℃ for 5h to obtain mullite whiskers;

[0028] (2) Take 5g of mullite whiskers, add 100mL of deionized water, stir evenly, add 2.5g of ferric chloride hexahydrate and 1.2g of ferrous sulfate heptahydrate, sonicate for 25min, heat to 53℃, add 5mol / L sodium hydroxide, adjust the pH value to 11, wash and dry to obtain iron-modified mullite whiskers.

[0029] (3) Take 0.3g of 3-glycidyl etheroxypropyltrimethoxysilane, add 100mL of 10% ethanol solution, stir evenly, add 5g of iron-modified mullite whiskers, react at 40℃ for 24h, wash and dry to obtain surface epoxidized iron-modified mullite whiskers; take 100mL of dimethyl sulfoxide, add 3g of surface epoxidized iron-modified mullite whiskers, ultrasonically disperse for 1h, add 3.5g of polyvinyl alcohol and 0.5g of catalyst potassium hydroxide, heat in an oil bath at 95℃ for 12h, filter, wash and dry to obtain polyvinyl alcohol-modified mullite whiskers;

[0030] (4) Take 5g of polyvinyl alcohol modified mullite whiskers, add 100mL of deionized water, ultrasonically disperse, stir for 3h, add 50mL of the blended material, heat to 62℃, stir for 5h, and obtain the modified material.

[0031] Step 3: Take 50 mL of the modified material, add 3.14 g of sodium citrate as a complexing agent, add 0.4 mL of 3% ammonium persulfate aqueous solution, stir magnetically, purge with nitrogen for 50 min, heat to 70 °C, and react for 6 h; add 3.3 g of sodium hydroxide and 5 mL of isopropanol, stir thoroughly for 30 min, wash with anhydrous ethanol to obtain the precipitate, dry at 110 °C and pulverize to obtain a high-temperature resistant and saturated salt resistant filtration loss reducer for drilling fluid.

[0032] Example 2: A high-temperature resistant and saturated salt resistant fluid reducer for drilling fluids and its preparation method:

[0033] Step 1: (1) Take 2g of sorbitan oleate and add it to 150mL of deionized water. Heat the water to 60℃ and stir until homogeneous. Add 25.4g of 2-acrylamido-2-methylpropanesulfonic acid, 6.73g of acrylic acid, 37g of N-vinyl-2-pyrrolidone, and 0.35g of N,N'-methylenebisacrylamide. Stir until homogeneous to obtain the blended material.

[0034] Step 2: (1) Take 5.9g of alumina and 3.9g of silicon dioxide, mix them evenly, add 0.2g of ammonium metatungstate, stir evenly, ball mill and mix for 12h, heat treat at 40MPa and 1520℃ for 7h to obtain mullite whiskers.

[0035] (2) Take 5g of mullite whiskers, add 100mL of deionized water, stir evenly, add 2.5g of ferric chloride hexahydrate and 1.2g of ferrous sulfate heptahydrate, sonicate for 30min, heat to 55℃, add 5mol / L sodium hydroxide, adjust the pH value to 12, wash and dry to obtain iron-modified mullite whiskers.

[0036] (3) Take 0.4g of 3-glycidyl etheroxypropyltrimethoxysilane, add 100mL of 10% ethanol solution, stir evenly, add 5.7g of iron-modified mullite whiskers, react at 60℃ for 28h, wash and dry to obtain surface epoxidized iron-modified mullite whiskers; take 100mL of dimethyl sulfoxide, add 3.5g of surface epoxidized iron-modified mullite whiskers, ultrasonically disperse for 3h, add 4g of polyvinyl alcohol and 0.5g of catalyst potassium hydroxide, heat in an oil bath at 100℃ for 14h, filter, wash and dry to obtain polyvinyl alcohol-modified mullite whiskers;

[0037] (4) Take 5g of polyvinyl alcohol modified mullite whiskers, add 100mL of deionized water, ultrasonically disperse, stir for 6h, add 50mL of the blended material, heat to 65℃, stir for 7h, and obtain the modified material.

[0038] Step 3: Take 50 mL of the modified material, add 3.14 g of sodium citrate as a complexing agent, add 0.4 mL of 3% ammonium persulfate aqueous solution, stir magnetically, purge with nitrogen for 70 min, heat to 80 °C, and react for 8 h; add 3.3 g of sodium hydroxide and 5 mL of isopropanol, stir thoroughly for 50 min, wash with anhydrous ethanol to obtain the precipitate, dry at 130 °C and pulverize to obtain a high-temperature resistant and saturated salt resistant filtration loss reducer for drilling fluid.

[0039] Example 3: A high-temperature resistant and saturated salt resistant fluid reducer for drilling fluids and its preparation method:

[0040] Step 1: (1) Take 2g of sorbitan oleate and add it to 150mL of deionized water. Heat the water to 55℃ and stir until homogeneous. Add 25.4g of 2-acrylamido-2-methylpropanesulfonic acid, 6.73g of acrylic acid, 37g of N-vinyl-2-pyrrolidone, and 0.35g of N,N'-methylenebisacrylamide. Stir until homogeneous to obtain the blended material.

[0041] Step 2: (1) Take 5.9g of alumina and 3.9g of silicon dioxide, mix them evenly, add 0.2g of ammonium metatungstate, stir evenly, ball mill and mix for 11h, heat treat at 35MPa and 1510℃ for 5h to obtain mullite whiskers;

[0042] (2) Take 5g of mullite whiskers, add 100mL of deionized water, stir evenly, add 2.5g of ferric chloride hexahydrate and 1.2g of ferrous sulfate heptahydrate, sonicate for 20min, heat to 50℃, add 5mol / L sodium hydroxide, adjust the pH value to 11, wash and dry to obtain iron-modified mullite whiskers.

[0043] (3) Take 0.4g of 3-glycidyl etheroxypropyltrimethoxysilane, add 100mL of 10% ethanol solution, stir evenly, add 6g of iron-modified mullite whiskers, react at 50℃ for 25h, wash and dry to obtain iron-modified mullite whiskers with surface epoxidation; take 100mL of dimethyl sulfoxide, add 2.5g of iron-modified mullite whiskers with surface epoxidation, ultrasonically disperse for 2h, add 3g of polyvinyl alcohol and 0.2g of catalyst potassium hydroxide, heat in an oil bath at 97℃ for 13h, filter, wash and dry to obtain polyvinyl alcohol-modified mullite whiskers;

[0044] (4) Take 5g of polyvinyl alcohol modified mullite whiskers, add 100mL of deionized water, ultrasonically disperse, stir for 4h, add 50mL of the blended material, heat to 60℃, stir for 6h, and obtain the modified material.

[0045] Step 3: Take 50 mL of the modified material, add 3.14 g of sodium citrate as a complexing agent, add 0.4 mL of 3% ammonium persulfate aqueous solution, stir magnetically, purge with nitrogen for 60 min, heat to 80 °C, and react for 7 h; add 3.3 g of sodium hydroxide and 5 mL of isopropanol, stir thoroughly for 40 min, wash with anhydrous ethanol to obtain the precipitate, dry at 120 °C and pulverize to obtain a high-temperature resistant and saturated salt resistant filtration loss reducer for drilling fluid.

[0046] Comparative Example 1: No iron modification was performed on the mullite whiskers; all other procedures were the same as in Example 1. The specific operations are as follows:

[0047] Step 1: (1) Take 2g of sorbitan oleate and add it to 150mL of deionized water. Heat the water to 58℃ and stir until homogeneous. Add 25.4g of 2-acrylamido-2-methylpropanesulfonic acid, 6.73g of acrylic acid, 37g of N-vinyl-2-pyrrolidone, and 0.35g of N,N'-methylenebisacrylamide. Stir until homogeneous to obtain the blended material.

[0048] Step 2: (1) Take 5.9g of alumina and 3.9g of silicon dioxide, mix them evenly, add 0.2g of ammonium metatungstate, stir evenly, ball mill and mix for 10h, heat treat at 30MPa and 1500℃ for 5h to obtain mullite whiskers;

[0049] (2) Take 0.3g of 3-glycidyl etheroxypropyltrimethoxysilane, add 100mL of 10% ethanol solution, stir evenly, add 5g of mullite whiskers, react at 40℃ for 24h, wash and dry to obtain surface epoxidized mullite whiskers; take 100mL of dimethyl sulfoxide, add 3g of surface epoxidized mullite whiskers, ultrasonically disperse for 1h, add 3.5g of polyvinyl alcohol and 0.5g of catalyst potassium hydroxide, heat in an oil bath at 95℃ for 12h, filter, wash and dry to obtain polyvinyl alcohol modified mullite whiskers;

[0050] (3) Take 5g of polyvinyl alcohol modified mullite whiskers, add 100mL of deionized water, ultrasonically disperse, stir for 3h, add 50mL of the blended material, heat to 62℃, stir for 5h, and obtain the modified material.

[0051] Comparative Example 2: Polyvinyl alcohol was not added; all other procedures were the same as in Example 1. The specific operations are as follows:

[0052] Step 1: (1) Take 2g of sorbitan oleate and add it to 150mL of deionized water. Heat the water to 58℃ and stir until homogeneous. Add 25.4g of 2-acrylamido-2-methylpropanesulfonic acid, 6.73g of acrylic acid, 37g of N-vinyl-2-pyrrolidone, and 0.35g of N,N'-methylenebisacrylamide. Stir until homogeneous to obtain the blended material.

[0053] Step 2: (1) Take 5.9g of alumina and 3.9g of silicon dioxide, mix them evenly, add 0.2g of ammonium metatungstate, stir evenly, ball mill and mix for 10h, heat treat at 30MPa and 1500℃ for 5h to obtain mullite whiskers;

[0054] (2) Take 5g of mullite whiskers, add 100mL of deionized water, stir evenly, add 2.5g of ferric chloride hexahydrate and 1.2g of ferrous sulfate heptahydrate, sonicate for 25min, heat to 53℃, add 5mol / L sodium hydroxide, adjust the pH value to 11, wash and dry to obtain iron-modified mullite whiskers.

[0055] (3) Take 5g of iron-modified mullite whiskers, add 100mL of deionized water, ultrasonically disperse, stir for 3h, add 50mL of the blended material, stir for 5h, and obtain the modified material.

[0056] Comparative Example 3: The mullite whiskers without iron modification were subjected to epoxidation treatment; the rest of the procedure was the same as in Example 1. The specific operation is as follows:

[0057] Step 1: (1) Take 2g of sorbitan oleate and add it to 150mL of deionized water. Heat the water to 58℃ and stir until homogeneous. Add 25.4g of 2-acrylamido-2-methylpropanesulfonic acid, 6.73g of acrylic acid, 37g of N-vinyl-2-pyrrolidone, and 0.35g of N,N'-methylenebisacrylamide. Stir until homogeneous to obtain the blended material.

[0058] Step 2: (1) Take 5.9g of alumina and 3.9g of silicon dioxide, mix them evenly, add 0.2g of ammonium metatungstate, stir evenly, ball mill and mix for 10h, heat treat at 30MPa and 1500℃ for 5h to obtain mullite whiskers;

[0059] (2) Take 5g of mullite whiskers, add 100mL of deionized water, stir evenly, add 2.5g of ferric chloride hexahydrate and 1.2g of ferrous sulfate heptahydrate, sonicate for 25min, heat to 53℃, add 5mol / L sodium hydroxide, adjust the pH value to 11, wash and dry to obtain iron-modified mullite whiskers.

[0060] (3) Take 100 mL of dimethyl sulfoxide, add 3 g of iron-modified mullite whiskers, ultrasonically disperse for 1 h, add 3.5 g of polyvinyl alcohol and 0.5 g of catalyst potassium hydroxide, heat in an oil bath at 95 °C for 12 h, filter, wash and dry to obtain polyvinyl alcohol-modified mullite whiskers.

[0061] (4) Take 5g of polyvinyl alcohol modified mullite whiskers, add 100mL of deionized water, ultrasonically disperse, stir for 3h, add 50mL of the blended material, heat to 62℃, stir for 5h, and obtain the modified material.

[0062] experiment:

[0063] 1. Measure the drying loss:

[0064] Weigh 3g of the filtration loss reducing agent prepared in Examples 1-3 and Comparative Examples 1-3 respectively, place them in a constant temperature drying oven, dry them at 105℃ for 2h, weigh them, calculate the drying loss according to the formula, record the data, and the results are shown in Table 1 below;

[0065] 2. Measure the apparent viscosity and filtration loss at 180°C:

[0066] Take 350 mL of deionized water, add 0.74 g of anhydrous sodium carbonate, 21.0 g of bentonite and 21.0 g of evaluation soil, stir at high speed for 20 min, and cure in a sealed container at 25 °C for 24 h. Add 8.75 g of the filtration loss reducer prepared in Examples 1-3 and Comparative Examples 1-3, stir at high speed for 10 min, add 20% sodium oxide and 10 mL of 40% sodium hydroxide solution, stir at high speed for 30 min, place in a curing vessel, and roll at 25 °C and 180 °C for 16 h respectively. Test the apparent viscosity of the drilling fluid and the filtration loss at 180 °C. The results are shown in Table 1 below.

[0067] Table 1

[0068]

[0069]

[0070] Conclusion: As can be seen from the above data, after aging in saturated brine at 180°C, the API filtration loss and HTHP filtration loss of the filtration loss agent prepared in the examples are both at very low levels, indicating that the filtration loss agent prepared in the examples has good resistance to high temperature and saturated salt.

[0071] Comparing Comparative Example 1 and Example 1, which do not modify mullite whiskers with iron, it can be seen that Example 1 of the present invention uses ferric chloride hexahydrate and ferrous sulfate heptahydrate to modify mullite whiskers, generating iron oxide precipitate on the surface of mullite. The addition of iron oxide can improve the high temperature resistance of the whiskers, thereby improving the high temperature resistance of the filtration loss reducer.

[0072] Comparing Comparative Example 2 and Example 1 without polyvinyl alcohol, it can be seen that the polyvinyl alcohol has hydroxyl groups on its surface, forming a hydrophilic barrier on the surface of the mullite whiskers. This effectively blocks the compression of the polymer by saturated salts and prevents the polymer from curling, thereby improving the saturated salt resistance of the filtration loss reducer.

[0073] A comparison of Comparative Example 3 and Example 1, where no iron-modified mullite whiskers underwent epoxidation treatment, reveals that treating the iron-modified mullite whiskers with 3-glycidyl etheroxypropyltrimethoxysilane grafts epoxy groups onto them. The polyvinyl alcohol (PVA) surface contains hydroxyl groups, and the reaction between the epoxy and hydroxyl groups allows PVA to be loaded onto the surface of the epoxidized iron-modified mullite whiskers, forming a hydrophilic barrier that effectively blocks the compression of the polymer by saturated salts and prevents polymer curling. This improves the resistance of the filtration loss reducer to saturated salts. In Comparative Example 3, where the iron-modified mullite whiskers were not epoxidized, the loading effect of PVA was poor, resulting in a decrease in the performance of the filtration loss reducer.

[0074] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

Claims

1. A method for preparing a high-temperature resistant and saturated salt resistant filtration loss reducer for drilling fluids, characterized in that: Includes the following steps: Step 1: Add sorbitan oleate to deionized water, heat to 55-60℃, stir evenly, add 2-acrylamido-2-methylpropanesulfonic acid, acrylic acid, N-vinyl-2-pyrrolidone, and N,N'-methylenebisacrylamide, stir evenly to obtain the blended material; Step 2: Take polyvinyl alcohol modified mullite whiskers, add deionized water, ultrasonically disperse, stir for 3-6 hours, add the blended material, heat to 60-65℃, stir for 5-7 hours to obtain the modified material; Step 3: Take the modified material, add sodium citrate and ammonium persulfate aqueous solution, stir magnetically, purge with nitrogen for 50-70 minutes, heat to 70-80℃, and react for 6-8 hours; add sodium hydroxide and isopropanol, stir thoroughly for 30-50 minutes, wash, dry, and pulverize to obtain a high-temperature and saturated salt resistant fluid loss reducer for drilling fluid.

2. The method for preparing a high-temperature resistant and saturated salt resistant filtration loss reducer for drilling fluid according to claim 1, characterized in that: The method for preparing the polyvinyl alcohol modified mullite whiskers is as follows: take dimethyl sulfoxide, add iron-modified mullite whiskers with surface epoxidation, ultrasonically disperse for 1-3 hours, add polyvinyl alcohol and potassium hydroxide, heat in an oil bath at 95-100℃ for 12-14 hours, filter, wash and dry to obtain polyvinyl alcohol modified mullite whiskers.

3. The method for preparing a high-temperature resistant and saturated salt resistant filtration reducer for drilling fluids according to claim 2, characterized in that: The mass ratio of the surface-epoxidized iron-modified mullite whiskers, polyvinyl alcohol, and potassium hydroxide is (5-7):(6-8):(0.4-0.6).

4. The method for preparing a high-temperature resistant and saturated salt resistant filtration loss reducer for drilling fluid according to claim 3, characterized in that: The preparation method of the iron-modified mullite whiskers with surface epoxidation is as follows: Includes the following steps: S1: Take mullite whiskers, add deionized water, stir evenly, add ferric chloride hexahydrate and ferrous sulfate heptahydrate, ultrasonically disperse for 20-30 minutes, heat to 50-55℃, add sodium hydroxide solution dropwise, adjust the pH value to 11-12, wash and dry to obtain iron-modified mullite whiskers; S2: Take 3-glycidyl etheroxypropyltrimethoxysilane, add it to an ethanol solution, stir well, add iron-modified mullite whiskers, react for 24-28 hours, wash, and dry to obtain iron-modified mullite whiskers with epoxidized surface.

5. The method for preparing a high-temperature resistant and saturated salt resistant filtration loss reducer for drilling fluid according to claim 4, characterized in that: The mass ratio of the 3-glycidyl etheroxypropyltrimethoxysilane to the iron-modified mullite whiskers is (3-4):(50-60).

6. The method for preparing a high-temperature resistant and saturated salt resistant filtration loss reducer for drilling fluid according to claim 4, characterized in that: The preparation method of the mullite whiskers is as follows: take alumina and silicon dioxide, mix them evenly, add ammonium metatungstate, stir evenly, ball mill and heat treat to obtain mullite whiskers.

7. The method for preparing a high-temperature resistant and saturated salt resistant filtration loss reducer for drilling fluids according to claim 6, characterized in that: The ball milling time is 10-12 hours, the heat treatment time is 5-7 hours, and the heat treatment temperature is 1500-1520℃.

8. The high-temperature resistant and saturated salt filtration reducer for drilling fluid prepared by the method according to any one of claims 1 to 7.

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