An environmentally friendly high-temperature and saturated salt resistant thickener for water-based drilling fluid, and its preparation method and application

Abstract

The application provides an environment-friendly high-temperature-resistant and saturated-salt-resistant thickening agent for water-based drilling fluid and a preparation method and application thereof. The preparation method comprises the following steps: adding an olefin monomer into water, adding sodium alginate after adjusting the pH of the system to 7-8, stirring and dissolving to obtain water phase A; adding a cationic surfactant and a hydrophobic monomer into water, stirring uniformly to obtain water phase B; mixing and stirring water phase A and water phase B uniformly, adding a crosslinking agent, heating to a reaction temperature, and then adding an initiator to react; after the reaction is completed, filtering, washing, drying, and crushing to obtain the thickening agent. The olefin monomer and the hydrophobic monomer are used to graft copolymerize the sodium alginate, the temperature resistance and salt resistance of the sodium alginate are increased, and the sodium alginate still has good biodegradability and environmental friendliness. The thickening agent is an environment-friendly polymer thickening agent resistant to 200 DEG C high temperature, and the thickening agent overcomes the shortcomings of the existing water-based drilling fluid polymer thickening agent, such as insufficient environmental friendliness and high-temperature and high-salt stability.

Description

Technical Field

[0001] The invention relates to an environmentally friendly high-temperature and saturated salt resistant tackifier for water-based drilling fluid, a preparation method and application thereof, and belongs to the field of oilfield chemistry in the petroleum industry. Background Art

[0002] Oil and natural gas resources are closely linked to the development of the national economy. With the rapid growth of my country's economy, the demand for oil and other energy sources has steadily increased, and oil and gas development has gradually shifted from conventional formations to complex unconventional formations. The complex geological conditions of deep and ultra-deep formations have always been a focus of exploration and development. Drilling fluid systems and treatment agents that can adapt to high-temperature, high-pressure, and complex downhole conditions have become key technologies for ensuring the drilling and completion of deep and ultra-deep wells.

[0003] During drilling in deep and ultra-deep oil and gas reservoirs, submicron clay particles in the drilling fluid can easily invade reservoir pores and microfractures, blocking oil and gas pathways and damaging the reservoirs. Oil-based drilling fluids are typically used to address drilling challenges in water-sensitive formations and shale formations susceptible to hydration damage. However, the use of oil-based drilling fluids is often accompanied by numerous contamination issues, significantly limiting their use.

[0004] Because these drilling fluids contain no or very little clay particles, they avoid the problem of clay solids in the drilling fluid clogging reservoir oil and gas channels. This improves the mechanical penetration rate (ROP) during drilling, shortens the drilling and completion cycles, and provides a certain degree of protection for reservoir drilling and production. However, because these drilling fluids contain no clay or very low clay content, a viscosity enhancer must be added to address the problem of carrying and suspending cuttings during drilling.

[0005] Thickeners used to adjust the rheological properties of water-based drilling fluids are one of the core treatment agents for high-temperature drilling fluids. Currently, polymer-based thickeners are commonly used. The main thickening mechanism is that polymer molecules form a network structure through bridging to increase the viscosity of the drilling fluid. The temperature resistance of polymer-based thickeners is closely related to their molecular structure. Optimizing the molecular structure of the polymer can significantly improve the temperature resistance of the thickener. The main optimization methods are: (1) The primary structure of the molecule should select monomers with CC, CN, and CS bonds as the main chain; (2) The secondary structure should have a certain branched and bulk structure; (3) Select monomers with hydrolysis resistance and rigid groups.

[0006] Chinese patent document CN114805678A discloses a drilling fluid thickener and its preparation method. The method involves quaternizing an unsaturated amino acid ester and a halogenated hydrocarbon to obtain a hydrophobic monomer, which is then polymerized with acrylamide, acrylic acid, and a sulfonic acid monomer to produce a 200°C temperature-resistant thickener. However, the use of unsaturated amino acid esters and halogenated hydrocarbons in the synthesis of this thickener results in low environmental performance. Chinese patent document CN114805680A discloses a method for preparing a temperature-resistant and salt-resistant thickener. The method uses an olefinic monomer, an anionic monomer, and a cationic monomer through emulsion polymerization to produce a 180°C temperature-resistant and 15% NaCl-resistant thickener. While the environmental performance of this thickener meets industry standards, it still requires a 4% base slurry during use, making it unsuitable for zero- or low-solids drilling fluid systems. Chinese patent CN115537190A provides a drilling fluid and its application. The drilling fluid comprises fucoidan, alginate, a vegetable oil lubricant, KCl, Na2CO3, and water. This fluid addresses the issues of existing solid-free drilling fluids, such as toxicity, non-degradable materials, poor suspension properties, and poor rock transport. However, the fucoidan and alginate used in this drilling fluid suffer from insufficient temperature and salt tolerance.

[0007] Therefore, the development of a non-toxic and biodegradable viscosifier suitable for drilling fluid systems with no / low soil phase is of great significance for drilling deep and ultra-deep oil and gas reservoirs. Summary of the Invention

[0008] In view of the shortcomings of the existing technology, especially the shortcomings of the existing thickeners for water-based drilling fluids with no or low solid phase: (1) insufficient environmental performance. my country has increasingly stringent requirements on the environmental performance of oilfield treatment agents, and the existing drilling fluid waste liquid is highly polluting and has high treatment costs; (2) insufficient resistance to high temperature and high salt. The existing environmentally friendly drilling fluid thickeners have certain deficiencies in their resistance to high temperature and salt, and the thickeners are easily ineffective under high temperature and high salt conditions. The present invention provides an environmentally friendly high temperature and saturated salt resistant thickener for water-based drilling fluids and its preparation method and application. The present invention uses olefin monomers and hydrophobic monomers to graft copolymerize natural high molecular weight polysaccharide polymer sodium alginate, thereby increasing the temperature and salt resistance of the natural high molecular weight polysaccharide sodium alginate, while still maintaining good biodegradability and environmental friendliness. The thickener of the present invention is an environmentally friendly polymer thickener that is resistant to high temperatures of 200°C, overcoming the shortcomings of existing water-based drilling fluid polymer thickeners in terms of environmental friendliness and high temperature and high salt stability.

[0009] The technical solutions of the present invention are as follows:

[0010] A method for preparing an environmentally friendly high-temperature and saturated salt resistant thickener for water-based drilling fluid comprises the following steps:

[0011] (1) Adding an olefin monomer to water, adjusting the pH of the system to 7-8, and then adding sodium alginate, stirring and dissolving to obtain aqueous phase A;

[0012] (2) adding a cationic surfactant and a hydrophobic monomer to water and stirring uniformly to obtain an aqueous phase B;

[0013] (3) Mixing and stirring the aqueous phase A and the aqueous phase B uniformly, adding a crosslinking agent, heating to the reaction temperature, and then adding an initiator to react; after the reaction is completed, filtering, washing, drying, and crushing to obtain an environmentally friendly high-temperature and anti-saturated salt thickener for water-based drilling fluid.

[0014] According to the present invention, preferably, the vinyl monomer in step (1) is a combination of monomer I and monomer II, the monomer I is acrylamide and / or acrylic acid, the monomer II is sodium styrene sulfonate and / or 2-acrylamide-2-methylpropanesulfonic acid, and the mass ratio of the monomer I to the monomer II is 1:0.3-1.5; and the ratio of the mass of the vinyl monomer to the volume of water is 0.1-1 g:1 mL.

[0015] Preferably, according to the present invention, in step (1), a NaOH aqueous solution with a mass fraction of 30 to 50% is used to adjust the pH of the system.

[0016] Preferably, according to the present invention, the mass ratio of the sodium alginate to the vinyl monomer in step (1) is 0.1 to 0.5:1; and the number average molecular weight of the sodium alginate is 20,000 to 30,000.

[0017] According to the present invention, preferably, the cationic surfactant in step (2) is one or a combination of cetyltrimethylammonium bromide and octadecyldimethylbenzylammonium chloride; and the mass ratio of the cationic surfactant to the hydrophobic monomer is 0.05 to 0.2:1.

[0018] According to the preferred embodiment of the present invention, the hydrophobic monomer in step (2) is isooctyl acrylate, methyl 3-methyl-3-butenoate or methyl 3-methoxyacrylate; and the ratio of the mass of the hydrophobic monomer to the volume of water is 2-8 g:50 mL.

[0019] Preferably, according to the present invention, the mass ratio of the hydrophobic monomer in the aqueous phase B to the sodium alginate in the aqueous phase A in step (3) is 0.5 to 1:1.

[0020] According to the preferred embodiment of the present invention, the cross-linking agent in step (3) is one or a combination of two or more of divinylbenzene, diallyldiphenylsilane or N,N-dimethylbisacrylamide; the mass of the cross-linking agent is 0.1 to 0.5% of the total mass of the vinyl monomer, sodium alginate and hydrophobic monomer.

[0021] According to the application, preferably, the initiator in step (3) is ammonium persulfate, potassium persulfate or azobisisobutyronitrile; the mass of the initiator is 0.05-0.3% of the total mass of the olefin monomer, sodium alginate and the hydrophobic monomer.

[0022] According to the application, preferably, the reaction temperature in step (3) is 45-55 DEG C; the reaction time is 4-6 h.

[0023] According to the application, preferably, the washing in step (3) is washing 3-5 times with water; the drying is drying at 70-85 DEG C for 8-12 h.

[0024] The application further provides an environment-friendly high-temperature-resistant and saturated-salt-resistant viscosifier for water-based drilling fluid, which is prepared by the above preparation method.

[0025] According to the application, the above environment-friendly high-temperature-resistant and saturated-salt-resistant viscosifier is applied to a water-based drilling fluid with no / low solid phase.

[0026] The technical features and advantages of the application are as follows:

[0027] 1. The viscosifier has excellent temperature resistance and salt resistance, and still has stable performance under the condition of 200 DEG C high temperature and saturated salt addition.

[0028] 2. The viscosifier has good environment-friendly performance, the raw material used in the application is natural high-molecular polysaccharide polymer alginate, EC50 is greater than 30000 ppm, BOD5 / CODCr is greater than 25%, and the viscosifier is non-toxic and easy to be biodegraded.

[0029] 3. The viscosifier is grafted on natural high-molecular polysaccharide polymer sodium alginate, and the sodium alginate has good biocompatibility and degradability, contains a large amount of -COO- and has certain adhesion, and when pH increases, the hydrophilicity of the sodium alginate increases, the molecular chain is stretched, the steric hindrance is large, the flow resistance of free water in the drilling fluid is increased, and the viscosity of the system is increased.

[0030] 4. The viscosifier is introduced with long-chain hydrophobic monomers with a specific length in the synthesis process, the polar hydrophobic chain makes the macromolecular chain of the viscosifier in a stretched state, the hydrophobic association between molecules makes the macromolecular chain physically crosslinked to form a spatial network structure with certain strength, so that the viscosifier has strong thickening capacity, and the hydrophobic long chain also increases the thermal stability of the viscosifier.

[0031] 5. A small amount of cross-linking agent is added during the synthesis process of the tackifier of the present invention, which can cause mild cross-linking between olefinic monomers, increase the degree of polymerization of the molecular chain, and also enhance the structural strength of the molecule, enhance the temperature resistance and tackifying effect of the molecule. DETAILED DESCRIPTION

[0032] The present invention will be further described below with reference to specific examples, but is not limited thereto.

[0033] The raw materials used in the examples are all conventional raw materials and can be obtained commercially; the methods described are all based on existing technologies unless otherwise specified.

[0034] The number average molecular weight of the sodium alginate used in the examples is 25,000.

[0035] Example 1

[0036] A method for preparing an environmentally friendly high-temperature and saturated salt resistant thickener for water-based drilling fluid comprises the following steps:

[0037] (1) Add 15 g of acrylamide and 10 g of 2-acrylamido-2-methylpropanesulfonic acid to 50 mL of distilled water, adjust the pH of the system to 8 with a 40% aqueous solution of NaOH, add 5 g of sodium alginate to the solution, and continue stirring until it is completely dissolved to prepare aqueous phase A;

[0038] (2) Add 0.3 g of hexadecyltrimethylammonium bromide to 50 mL of distilled water, continue stirring, slowly add 3 g of isooctyl acrylate, and stir evenly to prepare aqueous phase B;

[0039] (3) The aqueous phase A obtained in step (1) and the aqueous phase B obtained in step (2) were mixed and stirred uniformly, 0.05 g of a cross-linking agent N,N-methylenebisacrylamide was added, and then heated to 45°C, 0.03 g of an initiator ammonium persulfate was added, and the mixture was continuously stirred and nitrogen was introduced for 30 minutes, and then reacted at 45°C for 4 hours; after the reaction was completed, the mixture was filtered, and the obtained product was washed with distilled water 3 times. The obtained precipitate was dried at 70°C for 10 hours, and then crushed to obtain an environmentally friendly high-temperature and anti-saturated salt thickener for water-based drilling fluid.

[0040] Example 2

[0041] A method for preparing an environmentally friendly high-temperature and saturated salt resistant thickener for water-based drilling fluid comprises the following steps:

[0042] (1) Add 10 g of acrylamide, 8 g of 2-acrylamido-2-methylpropanesulfonic acid, and 5 g of sodium styrenesulfonate to 50 mL of distilled water, adjust the pH of the system to 7 with a 40% aqueous solution of NaOH, add 5 g of sodium alginate to the solution, and continue stirring until it is completely dissolved to prepare aqueous phase A;

[0043] (2) Add 0.4 g of hexadecyltrimethylammonium bromide to 50 mL of distilled water, continue stirring, and slowly add 4 g of methyl 3-methyl-3-butenoate and stir evenly to prepare aqueous phase B;

[0044] (3) The aqueous phase A obtained in step (1) and the aqueous phase B obtained in step (2) were mixed and stirred uniformly, 0.07 g of a cross-linking agent, divinylbenzene, were added, and then heated to 50° C., 0.05 g of an initiator, potassium persulfate, was added, and the mixture was continuously stirred and nitrogen was introduced for 30 minutes, and then reacted at 50° C. for 5 hours; after the reaction was completed, the mixture was filtered, and the obtained product was washed 3 times with distilled water. The obtained precipitate was dried at 80° C. for 10 hours, and then crushed to obtain an environmentally friendly high-temperature and anti-saturated salt thickener for water-based drilling fluid.

[0045] Example 3

[0046] A method for preparing an environmentally friendly high-temperature and saturated salt resistant thickener for water-based drilling fluid comprises the following steps:

[0047] (1) Add 10 g of acrylic acid and 5 g of sodium styrene sulfonate to 50 mL of distilled water, adjust the pH of the system to 8 with a 40% aqueous solution of NaOH, add 5 g of sodium alginate to the solution, and continue stirring until it is completely dissolved to prepare aqueous phase A;

[0048] (2) Add 0.4 g of hexadecyltrimethylammonium bromide to 50 mL of distilled water, continue stirring, and slowly add 3 g of methyl 3-methoxyacrylate and stir evenly to prepare aqueous phase B;

[0049] (3) The aqueous phase A obtained in step (1) and the aqueous phase B obtained in step (2) were mixed and stirred uniformly, 0.08 g of a cross-linking agent N,N-methylenebisacrylamide was added, and then heated to 50° C., 0.03 g of an initiator potassium persulfate was added, and the mixture was continuously stirred and nitrogen was introduced for 30 minutes, and then reacted at 50° C. for 6 hours; after the reaction was completed, the mixture was filtered, and the obtained product was washed with distilled water 3 times. The obtained precipitate was dried at 75° C. for 12 hours, and then crushed to obtain an environmentally friendly high-temperature and anti-saturated salt thickener for water-based drilling fluid.

[0050] Example 4

[0051] A method for preparing an environmentally friendly high-temperature and saturated salt-resistant thickener for water-based drilling fluid is as described in Example 1, except that 8 g of acrylic acid and 4 g of sodium styrene sulfonate are added in step (1).

[0052] Example 5

[0053] A method for preparing an environmentally friendly high-temperature and saturated salt-resistant thickener for water-based drilling fluid is as described in Example 1, except that the amount of cross-linking agent added in step (3) is 0.1 g.

[0054] Comparative Example 1

[0055] A method for preparing a water-based drilling fluid viscosity enhancer is as described in Example 1, except that in step (1), the olefinic monomer contains only 25 g of acrylamide.

[0056] Comparative Example 2

[0057] A method for preparing a viscosifier for water-based drilling fluid is as described in Example 1, except that no hydrophobic monomer is added in step (2).

[0058] Comparative Example 3

[0059] A method for preparing a viscosifier for water-based drilling fluid is as described in Example 1, except that no cross-linking agent is added in step (3).

[0060] Comparative Example 4

[0061] A method for preparing a viscosifier for water-based drilling fluid is as described in Example 1, except that the amount of the hydrophobic monomer in step (2) is 8 g.

[0062] Comparative Example 5

[0063] A method for preparing a water-based drilling fluid viscosity enhancer is as described in Example 1, except that in step (1), the olefin monomer contains only 25 g of sodium styrene sulfonate.

[0064] Comparative Example 6

[0065] A method for preparing a viscosity enhancer for water-based drilling fluid is as described in Example 1, except that the hydrophobic monomer added in step (2) is octadecyl methacrylate.

[0066] Comparative Example 7

[0067] A method for preparing a tackifier for water-based drilling fluid is as described in Example 1, except that the amount of cross-linking agent added in step (3) is 0.2 g.

[0068] Test example

[0069] The prepared tackifier was evaluated for its performance as follows:

[0070] (1) Effect of viscosifier on drilling fluid rheological parameters

[0071] The prepared tackifier was tested for rheological parameters (apparent viscosity, plastic viscosity, dynamic shear force) according to the American Petroleum Institute (API) standard (API RP 13B-1, 2009).

[0072] A 1% (mass fraction) aqueous solution of the thickener was added to deionized water. The apparent viscosity, plastic viscosity, and dynamic shear force of this aqueous solution were then tested at room temperature. The post-aging apparent viscosity, plastic viscosity, and dynamic shear force were also measured at room temperature after aging at 180°C for 16 hours. The results are shown in Table 1.

[0073] Table 1

[0074]

[0075] As shown in Table 1, it can be seen from the embodiments and comparative example data that vinyl monomers, hydrophobic monomers, cross-linking agent play synergistic effects in polymer molecules, and the disappearance of any monomer all can reduce the polymer tackifier performance of synthesis.Can be found by embodiment 1 and comparative example 1, introducing and containing sulfonate vinyl monomers can increase the temperature resistance of polymer.Can be found by embodiment 1 and embodiment 2, sodium styrene sulfonate can strengthen molecular chain rigidity because it contains phenyl ring, makes the spatial structure formed by polymer difficult for deformation and curling up at high temperature, and tackifying effect is better.Can be seen by comparative example 2 and comparative example 4, it is larger to tackifier performance impact with or without hydrophobicity, long-chain hydrophobic monomer can make tackifier macromolecular chain become extended state in polymer, and intermolecular hydrophobic association makes macromolecular chain physical cross-linking form the spatial network structure with certain intensity, thereby tackifier can be made to have very strong tackifying ability, can be seen by comparative example 6, long-chain hydrophobic monomer is obvious to tackifying effect, but also reduces polymer temperature resistance, easily loses efficacy at high temperature. By comparing Example 1 with Example 5, it can be found that increasing the amount of cross-linking agent can more easily make the cross-linked structure between the vinyl monomers exist, which improves the stability of the tackifier structure in water and the ability to resist high-temperature decomposition. Comparative Example 3 does not add a cross-linking agent, and performance decreases significantly at high temperatures. By Comparative Example 7, it can be seen that increasing the amount of cross-linking agent strengthens the molecular spatial structure, increases temperature resistance, and increases the temperature resistance of the polymer. However, since the polymer is reticulated, the chain molecule length is reduced, and the viscosity increase is not obvious. By Comparative Example 5, it can be seen that only using sodium styrene sulfonate, the tackifying effect of the polymer is poor.

[0076] (2) Test of temperature and salt resistance of thickener

[0077] The viscosifiers prepared in the Examples and Comparative Examples were added to a saturated NaCl aqueous solution to obtain a 1% by mass saline solution. The apparent viscosity, plastic viscosity, and dynamic shear force of the saline solution were then tested at room temperature. The post-aging apparent viscosity, plastic viscosity, and dynamic shear force were also measured at room temperature after aging at 180°C for 16 hours. The results are shown in Table 2.

[0078] Table 2

[0079]

[0080]

[0081] By embodiment and comparative example data change can be seen, although the embodiment of the present invention performance declines after adding saturated brine, but still can keep stable within the specific limits, but comparative example data fluctuation is obvious, performance decline is rapid, illustrate that olefin monomer, hydrophobic monomer, cross-linking agent play synergistic effect in polymer molecule in environment-friendly anti-temperature anti-saturated salt tackifier building-up process of the present invention, and the disappearance of any monomer all can reduce the polymer tackifier performance synthesized.Can be found by embodiment 1 and comparative example 1, in polymer, introduce sulfonate radical not only strengthens the temperature resistance of polymer, its salt resistance has also been improved, by embodiment 2 and embodiment 3 can be known, sodium styrene sulfonate, with its rigid molecular structure, can strengthen the salt resistance of polymer, phenyl ring strengthens the rigid strength of polymer molecule side chain, molecule is difficult for curling up, deformation under high temperature and high salt environment, still can stretch in water and form structure and increase solution viscosity.Can be found by embodiment 5 and comparative example 3, the use of cross-linking agent can make slightly cross-linked between olefin monomer, can increase the degree of polymerization of molecular chain, also strengthen the structural strength of molecule, strengthen temperature resistance and tackifying effect of molecule.

[0082] (3) Viscosity enhancement in low solids drilling fluids

[0083] To prepare a 2% low-solids base slurry, 8g of bentonite and 0.32g of NaCO were slowly added to 400mL of distilled water while stirring. The mixture was then hydrated at room temperature for 24 hours to create a 2% low-solids base slurry. NaCl was then added to saturation. A 2% viscosity enhancer was added to this low-solids saturated salt system. The apparent viscosity, plastic viscosity, and dynamic shear force of this low-solids system were then tested at room temperature. The post-aging apparent viscosity, plastic viscosity, and dynamic shear force were also measured at room temperature after aging at 200°C for 16 hours. The results are shown in Table 3.

[0084] Table 3

[0085]

[0086] In low-solid drilling fluid, clay particles are negatively charged. The negatively charged groups in the thickener of the present invention enhance the dispersibility of the clay particles through electrostatic repulsion. At the same time, the thickener of the present invention dissolves well in a low-solid saturated salt system. The hydrophilic groups, carboxyl and hydroxyl, ensure the stretching of the long polymer chain, and the steric hindrance is large, which advantageously increases the viscosity of the system. The temperature-resistant sulfonate group gives the polymer good temperature resistance. At the same time, the polymer thickener is slightly cross-linked, which synergistically increases the temperature resistance of the grafted polymer thickener.

[0087] (4) Environmental performance test

[0088] The environmental performance of the material is rated according to the CNPC standard "Q / SY 111-2007 Oilfield Chemicals and Drilling Fluids Biological Toxicity Classification and Detection Method Luminescent Bacteria Method". The biotoxicity of the thickener is tested by luminescent bacteria, and the concentration of the substance to be evaluated when the luminescent ability of the luminescent bacteria is reduced by half is EC 50 As the evaluation index, EC 50 A value greater than 25,000 indicates that the thickener is non-toxic. By testing the chemical oxygen demand (CODCr) and biological oxygen demand (BOD5) values ​​of the thickener, the BOD5 / CODCr ratio is calculated. The larger the BOD / COD value, the better the biodegradability of the thickener. The results are shown in Table 4.

[0089] Table 4

[0090] Sample <![CDATA[EC 50 (mg / L)]]> Biodegradability rating Example 1 59145 readily degradable Example 2 53562 readily degradable Example 3 57754 readily degradable Example 4 48952 readily degradable Example 5 47845 readily degradable

[0091] As shown in Table 4, the EC of each embodiment product 50 >25000ppm, easily biodegradable, indicating that it is non-toxic, easily biodegradable, and has good environmental performance.

[0092] In summary, the environmentally friendly high-temperature and saturated salt-resistant tackifier of the present invention has excellent performance, can meet existing drilling needs and comply with environmental protection requirements.

Claims

1. A method for preparing an environmentally friendly high-temperature and saturated salt resistant thickener for water-based drilling fluid, comprising the following steps: (1) Adding an olefin monomer to water, adjusting the pH of the system to 7-8, and then adding sodium alginate, stirring and dissolving to obtain an aqueous phase A; the olefin monomer is a combination of monomer I and monomer II, the monomer I is acrylamide and / or acrylic acid, and the monomer II is sodium styrene sulfonate and / or 2-acrylamide-2-methylpropane sulfonic acid; (2) adding a cationic surfactant and a hydrophobic monomer to water and stirring uniformly to obtain an aqueous phase B; the hydrophobic monomer is isooctyl acrylate, methyl 3-methyl-3-butenoate or methyl 3-methoxyacrylate; (3) Mixing and stirring the aqueous phase A and the aqueous phase B uniformly, adding a crosslinking agent, heating to the reaction temperature, and then adding an initiator to react; after the reaction is completed, filtering, washing, drying, and crushing to obtain an environmentally friendly high-temperature and anti-saturated salt thickener for water-based drilling fluid.

2. The method for preparing the environmentally friendly high temperature and saturated salt resistant thickener for water-based drilling fluid according to claim 1, wherein: The mass ratio of monomer I to monomer II in step (1) is 1:0.3-1.5; the mass ratio of the olefin monomer to the volume of water is 0.1-1 g:1 mL.

3. The method for preparing the environmentally friendly high temperature and saturated salt resistant thickener for water-based drilling fluid according to claim 1, wherein: In step (1), a 30-50% by mass NaOH aqueous solution is used to adjust the pH of the system; The mass ratio of the sodium alginate to the olefin monomer is 0.1-0.5:1; and the number average molecular weight of the sodium alginate is 20,000-30,000.

4. The method for preparing the environmentally friendly high temperature and saturated salt resistant thickener for water-based drilling fluid according to claim 1, characterized in that: The cationic surfactant in step (2) is one or a combination of hexadecyltrimethylammonium bromide and octadecyldimethylbenzylammonium chloride; the mass ratio of the cationic surfactant to the hydrophobic monomer is 0.05-0.2:

1.

5. The method for preparing the environmentally friendly high temperature and saturated salt resistant thickener for water-based drilling fluid according to claim 1, characterized in that: The ratio of the mass of the hydrophobic monomer to the volume of water in step (2) is 2-8 g:50 mL.

6. The method for preparing the environmentally friendly high temperature and saturated salt resistant thickener for water-based drilling fluid according to claim 1, characterized in that: The mass ratio of the hydrophobic monomer in the aqueous phase B to the sodium alginate in the aqueous phase A in step (3) is 0.5-1:

1.

7. The method for preparing the environmentally friendly high temperature and saturated salt resistant thickener for water-based drilling fluid according to claim 1, characterized in that: The cross-linking agent in step (3) is one or a combination of two or more of divinylbenzene, diallyldiphenylsilane or N,N-dimethylbisacrylamide; the mass of the cross-linking agent is 0.1-0.5% of the total mass of the vinyl monomer, sodium alginate and hydrophobic monomer; The initiator is ammonium persulfate, potassium persulfate or azobisisobutyronitrile; the mass of the initiator is 0.05-0.3% of the total mass of the vinyl monomer, sodium alginate and hydrophobic monomer.

8. The method for preparing the environmentally friendly high temperature and saturated salt resistant thickener for water-based drilling fluid according to claim 1, characterized in that: The reaction temperature in step (3) is 45-55°C; the reaction time is 4-6 hours; the washing is performed by washing with water 3-5 times; and the drying is performed at 70-85°C for 8-12 hours.

9. An environmentally friendly high temperature and saturated salt resistant thickener for water-based drilling fluid, characterized in that: The preparation method according to claim 1 is used for preparation.

10. Use of the environmentally friendly high-temperature and saturated salt resistant viscosifier for water-based drilling fluid according to claim 1 in zero-solids / low-solids water-based drilling fluid.

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