Ionic liquid grafted modified starch-based filtration loss reducers, their preparation methods and applications

Abstract

This invention discloses an ionic liquid graft-modified starch-based filtration loss reducer, its preparation method, and its application. The filtration loss reducer comprises cross-linked starch and 50%–300% by weight of polymeric monomers of the cross-linked starch; wherein the cross-linked starch comprises starch and 0.1%–5% by weight of a cross-linking agent; the polymeric monomers are a composition of alkenylamide monomers, alkenyl sulfonic acid monomers, polymerizable imidazole salt ionic liquid monomers, and N-vinylpyrrolidone monomers. The embodiments of this invention improve the temperature resistance of the starch itself by using a cross-linking agent; improve the temperature resistance of the polymer by using sulfonic acid groups and pyrrolidone; and simultaneously introduce imidazole salt ionic liquids, which not only promote the dispersion of clay particles but also improve the quality of the filter cake, thereby reducing filtration loss.

Description

Technical Field

[0001] This invention relates to ionic liquid grafted modified starch-based filtration loss reducers, their preparation methods, and applications. Background Technology

[0002] Drilling fluid is one of the most commonly used chemicals in oilfields, and filtration reducers are commonly used additives in drilling fluids. Adding filtration reducers can form a thin and dense filter cake on the wellbore surface, reducing the loss of free water from the drilling fluid through the wellbore and protecting the wellbore. This safeguards the excellent performance of the drilling fluid and improves the safety and efficiency of drilling operations. Starch-based filtration reducers are the main natural polymeric filtration reducers. Due to their excellent salt and calcium resistance, ability to protect the oil reservoir from drilling fluid contamination, and biodegradability, they have attracted increasing attention from oilfield chemical researchers.

[0003] Generally, starch can be classified into pregelatinized starch, etherified starch, esterified starch, cross-linked starch, and grafted starch, depending on the modification method. However, as a drilling fluid treatment agent, the applicable temperature for modified starch in evaluating its filtration loss reduction performance is generally no more than 130℃. Summary of the Invention

[0004] To expand the selection of starch-based filtration loss reducers, this invention provides a graft-modified cross-linked starch-based filtration loss reducer with good temperature resistance, thermal stability, chemical stability, and solubility.

[0005] As one aspect of the present invention, there is a starch filtration loss reducer grafted with an ionic liquid, the filtration loss reducer comprising cross-linked starch and 50-300% by weight of a polymeric monomer of the cross-linked starch; the cross-linked starch comprising starch and 0.1-5% by weight of a cross-linking agent of the starch; the polymeric monomer comprising alkenylamide monomers, alkenyl sulfonic acid monomers, polymerizable imidazole salt ionic liquid monomers, and N-vinylpyrrolidone monomers.

[0006] Further, the mass ratio of the starch to the crosslinking agent is 1:(0.001~0.01).

[0007] Furthermore, the crosslinking agent is epichlorohydrin.

[0008] Furthermore, the mass ratio of the alkenylamide monomer, alkenyl sulfonic acid monomer, polymerizable imidazole salt ionic liquid monomer, and N-vinylpyrrolidone monomer is (20-60): (20-60): (10-20): (10-30).

[0009] Furthermore, the alkenylamide monomer is selected from one or more of acrylamide, methacrylamide, N,N-dimethylacrylamide, and N,N-diethylacrylamide.

[0010] Furthermore, the alkenyl sulfonic acid monomer is selected from one or more of 2-acrylamido-2-methylpropanesulfonic acid, sodium 2-acrylamido-2-methylpropanesulfonate, sodium allyl sulfonate, sodium styrene sulfonate, and sodium vinyl sulfonate.

[0011] Furthermore, the polymerizable imidazole salt ionic liquid monomer is selected from one or more of 1-vinyl-3-ethylimidazolium bromide, 1-vinyl-3-butylimidazolium bromide, and 1-allyl-3-butylimidazolium bromide.

[0012] In a specific embodiment, the filtration loss reducing agent also includes an initiator.

[0013] Further, the initiator is selected from one of azobisisobutyronitrile, azobisisovalerate, azobisisoheptanenitrile, azobisacrylonitrile, azobisisobutyramidine hydrochloride, azobisisobutyramidazolinium hydrochloride, azodimethyl N-2-hydroxybutylacrylamide, azobiscyclohexylformonitrile, dimethyl azobisisobutyrate, and azoisobutylcyanoformamide.

[0014] Furthermore, the mass of the initiator is 1% to 10% of the total mass of the cross-linked starch and the polymeric monomer.

[0015] As another aspect of the present invention, a method for preparing the above-mentioned ionic liquid grafted modified starch filtration reducer is provided, wherein the method uses polymerizable imidazole salt ionic liquid monomers and N-vinylpyrrolidone monomers simultaneously.

[0016] In a specific embodiment, the method for preparing a starch filtration reducer grafted with an ionic liquid uses acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, 1-vinyl-3-ethylimidazolium bromide and N-vinylpyrrolidone as polymerization monomers and azobisisobutyrazoline hydrochloride as an initiator.

[0017] Specifically, the method may include the following steps:

[0018] S1. Preparation of starch emulsion

[0019] Weigh out starch, add water and stir to dissolve it, prepare a colloidal solution, then add NaCl and mix well to obtain a starch emulsion;

[0020] S2, Preparation of cross-linked starch

[0021] Adjust the pH of the starch emulsion obtained in S1 to alkaline, add the crosslinking agent and react at room temperature, then adjust the pH of the reaction solution to neutral, filter, wash and dry to obtain crosslinked starch;

[0022] S3. Preparation of grafted modified cross-linked starch filtration loss reducer

[0023] The cross-linked starch and polymer monomers prepared in step S2 were added to water and dissolved completely. Under stirring, an initiator was added, and an inert gas was added to the system at room temperature. The system was then heated to react and a crude product of graft-modified cross-linked starch filtration loss reducer was obtained. After the temperature dropped, the product was filtered, washed, and vacuum dried to obtain a light yellow graft-modified cross-linked starch filtration loss reducer.

[0024] Furthermore, in S3, the reaction temperature is 50–80°C, and the reaction time is 5–10 h.

[0025] As another aspect of the present invention, it relates to the application of the above-mentioned ionic liquid grafted modified starch filtration reducer in oilfield drilling.

[0026] As another aspect of the invention, a drilling fluid is provided, comprising the above-mentioned ionic liquid grafted modified starch filtration reducer.

[0027] As another aspect of the invention, an oilfield drilling process is provided, which uses the aforementioned drilling fluid.

[0028] In the preparation of cross-linked starch, the cross-linking agent effectively improves the temperature resistance of the starch itself. Furthermore, the introduction of sulfonic acid groups and pyrrolidone into the filtration loss reducer molecule significantly enhances the polymer's temperature resistance. Additionally, the introduced imidazole salt ionic liquid possesses excellent thermal stability, chemical stability, and solubility, and can prevent the binding of cations such as calcium, magnesium, and sodium to clay, reducing the charge neutralization effect of these cations on the clay. This promotes the dispersion of clay particles, improves filter cake quality, and thus reduces filtration loss.

[0029] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention are realized and obtained in accordance with the structures particularly pointed out in the description and claims. Detailed Implementation

[0030] The literature "Preparation and Evaluation of a High-Temperature Resistant Cross-linked Starch Drilling Fluid Filtration Reducer" (Li Jiaqi, Yang Haitong, Ge Bing, et al., Special Oil and Gas Reservoirs, 2022) describes the synthesis of a high-temperature resistant cross-linked starch drilling fluid filtration reducer using corn starch as raw material and sodium trimetaphosphate as a cross-linking agent via a cross-linking reaction. When the mass fraction of cross-linked starch in the drilling fluid is 1.5%, it still exhibits good filtration reduction performance at 160℃, with an API filtration loss of 11.0 mL and a viscosity of 33.5 mPa·s. Compared with carboxymethyl starch filtration reducers, this filtration reducer shows significantly better high-temperature resistance and does not increase viscosity. However, the filtration performance of this product under high temperature and high pressure is not as expected.

[0031] The literature "Research and Application of Diesterified Starch Filtration Loss Reducer" (Zhang Kun, Ma Hong, Shu Ruhong, et al., Drilling Fluid & Completion Fluid, 2021, 38(02)) describes the synthesis of a diesterified starch filtration loss reducer, BZ-JLS, using acetic anhydride, sodium trimetaphosphate, and corn starch as raw materials through esterification modification. This product exhibits good dispersibility and filtration loss reduction effects. Indoor research results show that after aging at 150℃ for 16 hours, the filtration loss of the base slurry containing 1.5% BZ-JLS at room temperature and medium pressure is only 9.4 mL. However, this study only tested the filtration loss at room temperature and medium pressure; the filtration performance under high temperature and high pressure was not as expected.

[0032] Zhang Yaoyuan et al. synthesized a modified starch filtration reducer, St-AANDP, using acrylamide (AM), 2-acrylamido-2-methylpropanesulfonic acid (AMPS), dimethyl diallyl ammonium chloride (DMDAAC), N-vinylpyrrolidone (NVP), and potassium 2,5-dihydroxybenzenesulfonate (PDHBS) as monomers and horseradish peroxidase (HRP) as a catalyst via an enzymatic reaction method. After aging at 140℃ for 16.0 h, the filtration loss of drilling fluid with a dosage of 1.0% St-AANDP was only 5.2 mL at room temperature and 26.2 mL at high temperature and high pressure. They also revealed the mechanism by which the temperature resistance of the filtration reducer can be improved by introducing benzene rings into the molecular backbone to increase molecular rigidity (Zhang Yaoyuan, Ma Shuangzheng, Chen Jinding, et al. Preparation and performance of high temperature resistant modified starch filtration reducer, Drilling Fluids and Completion Fluids, 2019, 36(06)). However, this literature only measured the high-temperature and high-pressure filtration loss of the synthesized sample at 140℃, and the filtration performance at other higher temperatures (>140℃) was not as expected.

[0033] Chinese invention patent CN 111057160 discloses a method for preparing high amylose starch as a filtration loss reducer: first, high amylose corn starch is acidified with hydrochloric acid, and then modified with calcium-based bentonite to obtain modified amylose starch for filtration loss reduction, but the performance of the modified starch is not evaluated. Patent CN 111647109 uses N-vinyl-2-caprolactam, hydroxybutyl vinyl ether, acrylic acid, and maleic anhydride to graft copolymerize with starch to obtain a graft-modified filtration loss reducer, which has good viscosity and filtration loss reduction effects. After curing at 140℃ for 16 hours, its filtration loss reduction and viscosity reduction properties remain stable, showing good temperature resistance. However, the filtration loss reduction effect above 140℃ is not as expected. In patent CN... Paper 114163568 reports a method for preparing a modified starch filtration reducer containing ionic liquid segments. This filtration reducer is polymerized from partially degraded starch, alkenyl amide monomers, alkenyl sulfonic acid monomers, alkenyl imidazole monomers, and polyoxyethylene ether monomers. This filtration reducer exhibits good temperature and salt resistance at temperatures above 160℃. The introduction of ionic liquid segments enhances the cation shielding effect, preventing charge neutralization between cations and clay, thus improving its temperature and salt resistance. However, the synthesis of this filtration reducer requires the prior preparation of polyoxyethylene ether monomers using 3-alkoxy-2-acryloyl isocyanate, making the entire preparation process complex and cumbersome.

[0034] In summary, given that the existing technology could not meet the inventor's expectations, the inventor made this invention through further research and development.

[0035] The present invention will be further described below with reference to specific embodiments. The scope of protection of this application is not limited by the following embodiments.

[0036] In the preparation of starch-based filtration loss reducers, this invention improves the temperature resistance of starch by pre-preparing cross-linked starch with better thermal stability using a cross-linking agent. Subsequently, sulfonic acid groups and pyrrolidone are introduced to further improve the temperature resistance of the starch polymer. At the same time, imidazole salt ionic liquids with good thermal stability, chemical stability, and solubility are added to the raw materials. This not only prevents the binding of cations such as calcium, magnesium, and sodium with clay and reduces the charge neutralization effect of cations such as calcium, magnesium, and sodium on clay, but also promotes the dispersion of clay particles, improves the quality of the filter cake, and thus reduces filtration loss.

[0037] The main sources of materials involved in the following embodiments are shown in Table 1 below. Other materials not specified are all conventional commercially available products.

[0038] Table 1: Material Source Description

[0039]

[0040]

[0041] The Fann 500 high-temperature and high-pressure filtration analyzer used in this embodiment of the invention is from Beijing Koch Scientific Instruments Co., Ltd. (the agent); the bentonite used for drilling fluid testing conforms to the standard: SY / T 5490-2015 "Soil for Drilling Fluid Testing".

[0042] The inventors have optimized the preparation method of the grafted modified cross-linked starch filtration reducer through Examples 1 to 20 below.

[0043] Example 1

[0044] (1) Preparation of starch emulsion

[0045] Dissolve 50g of corn starch in water to prepare a 40% colloidal solution, add 6g of NaCl, mix well, and obtain a starch emulsion.

[0046] (2) Preparation of cross-linked starch

[0047] The pH of the starch emulsion prepared in step (1) was adjusted to 10.0 with 1 mol / L NaOH, and 0.1% by weight of epichlorohydrin was added. The mixture was reacted at 30°C for 3 h. The pH was adjusted to neutral with 2% dilute hydrochloric acid, filtered, and the filtrate was washed with water and ethanol, respectively. The filtrate was then dried to obtain cross-linked starch.

[0048] (3) Preparation of graft-modified cross-linked starch filtration loss reducer

[0049] Add 50g of cross-linked starch, 10g of acrylamide, 10g of 2-acrylamido-2-methylpropanesulfonic acid, 2.5g of 1-vinyl-3-ethylimidazolium bromide, and 2.5g of N-vinylpyrrolidone prepared in step (2) to 400mL of deionized water and dissolve them completely. Under stirring at 200r / min, add 0.15g of azobisisobutyrazoline hydrochloride (initiator), purge with nitrogen gas for 30min at room temperature to remove oxygen from the system, and then heat to 60℃ and react for 10h to obtain a light yellow viscous liquid, which is the crude product of graft-modified cross-linked starch filtration loss reducer.

[0050] After the temperature drops, the mixture is filtered, washed with ethanol and ether, and the filtered product is vacuum dried at 70°C for 20 hours to obtain a light yellow grafted modified cross-linked starch filtration reducer.

[0051] Example 2

[0052] (1) Preparation of starch emulsion

[0053] Dissolve 50g of corn starch in water to prepare a 40% colloidal solution, add 6g of NaCl, mix well, and obtain a starch emulsion.

[0054] (2) Preparation of cross-linked starch

[0055] The pH of the starch emulsion prepared in step (1) was adjusted to 10.0 with 1 mol / L NaOH, and 0.1% by weight of epichlorohydrin was added. The mixture was reacted at 30°C for 3 h. The pH was adjusted to neutral with 2% dilute hydrochloric acid, filtered, and the filtrate was washed with water and ethanol, respectively. The filtrate was then dried to obtain cross-linked starch.

[0056] (3) Preparation of graft-modified cross-linked starch filtration loss reducer

[0057] Add 50g of cross-linked starch, 20g of acrylamide, 20g of 2-acrylamido-2-methylpropanesulfonic acid, 5g of 1-vinyl-3-ethylimidazolium bromide, and 5g of N-vinylpyrrolidone prepared in step (2) to 500mL of deionized water and dissolve them completely. Under stirring at 200r / min, add 0.15g of azobisisobutyrazoline hydrochloride (initiator), purge with nitrogen gas for 30min at room temperature to remove oxygen from the system, and then heat to 60℃ and react for 10h to obtain a light yellow viscous liquid, which is the crude product of graft-modified cross-linked starch filtration loss reducer.

[0058] After the temperature drops, the mixture is filtered, washed with ethanol and ether, and the filtered product is vacuum dried at 70°C for 20 hours to obtain a light yellow grafted modified cross-linked starch filtration reducer.

[0059] Example 3

[0060] (1) Preparation of starch emulsion

[0061] Dissolve 50g of corn starch in water to prepare a 40% colloidal solution, add 6g of NaCl, mix well, and obtain a starch emulsion.

[0062] (2) Preparation of cross-linked starch

[0063] The pH of the starch emulsion prepared in step (1) was adjusted to 10.0 with 1 mol / L NaOH, and 0.1% by weight of epichlorohydrin was added. The mixture was reacted at 30°C for 3 h. The pH was adjusted to neutral with 2% dilute hydrochloric acid, filtered, and the filtrate was washed with water and ethanol, respectively. The filtrate was then dried to obtain cross-linked starch.

[0064] (3) Preparation of graft-modified cross-linked starch filtration loss reducer

[0065] Add 50g of cross-linked starch, 30g of acrylamide, 30g of 2-acrylamido-2-methylpropanesulfonic acid, 7.5g of 1-vinyl-3-ethylimidazolium bromide, and 7.5g of N-vinylpyrrolidone prepared in step (2) to 650mL of deionized water and dissolve them completely. Under stirring at 200r / min, add 0.15g of azobisisobutyronitrile (initiator), purge with nitrogen gas for 30min at room temperature to remove oxygen from the system, and then heat to 60℃ and react for 10h to obtain a light yellow viscous liquid, which is the crude product of graft-modified cross-linked starch filtration loss reducer.

[0066] After the temperature drops, the mixture is filtered, washed with ethanol and ether, and the filtered product is vacuum dried at 70°C for 20 hours to obtain a light yellow grafted modified cross-linked starch filtration reducer.

[0067] Example 4

[0068] (1) Preparation of starch emulsion

[0069] Dissolve 50g of corn starch in water to prepare a 40% colloidal solution, add 6g of NaCl, mix well, and obtain a starch emulsion.

[0070] (2) Preparation of cross-linked starch

[0071] The pH of the starch emulsion prepared in step (1) was adjusted to 10.0 with 1 mol / L NaOH, and 0.1% by weight of epichlorohydrin was added. The mixture was reacted at 30°C for 3 h. The pH was adjusted to neutral with 2% dilute hydrochloric acid, filtered, and the filtrate was washed with water and ethanol, respectively. The filtrate was then dried to obtain cross-linked starch.

[0072] (3) Preparation of graft-modified cross-linked starch filtration loss reducer

[0073] Add 50g of cross-linked starch, 40g of acrylamide, 40g of 2-acrylamido-2-methylpropanesulfonic acid, 10g of 1-vinyl-3-ethylimidazolium bromide, and 10g of N-vinylpyrrolidone prepared in step (2) to 1000mL of deionized water and dissolve them completely. Under stirring at 200r / min, add 0.3g of azobisisobutylamidine hydrochloride (initiator), purge with nitrogen gas for 30min at room temperature to remove oxygen from the system, and then heat to 70℃ and react for 6h to obtain a light yellow viscous liquid, which is the crude product of grafted modified cross-linked starch filtration loss reducer.

[0074] After the temperature drops, the mixture is filtered, washed with ethanol and ether, and the filtered product is vacuum dried at 70°C for 20 hours to obtain a light yellow grafted modified cross-linked starch filtration reducer.

[0075] Example 5

[0076] (1) Preparation of starch emulsion

[0077] Dissolve 50g of corn starch in water to prepare a 40% colloidal solution, add 6g of NaCl, mix well, and obtain a starch emulsion.

[0078] (2) Preparation of cross-linked starch

[0079] The pH of the starch emulsion prepared in step (1) was adjusted to 10.0 with 1 mol / L NaOH, and 0.1% by weight of epichlorohydrin was added. The mixture was reacted at 30°C for 3 h. The pH was adjusted to neutral with 2% dilute hydrochloric acid, filtered, and the filtrate was washed with water and ethanol, respectively. The filtrate was then dried to obtain cross-linked starch.

[0080] (3) Preparation of graft-modified cross-linked starch filtration loss reducer

[0081] Add 50g of cross-linked starch, 60g of acrylamide, 60g of 2-acrylamido-2-methylpropanesulfonic acid, 15g of 1-vinyl-3-ethylimidazolium bromide, and 15g of N-vinylpyrrolidone prepared in step (2) to 1200mL of deionized water and dissolve them completely. Under stirring at 200r / min, add 0.4g of dimethyl azobisisobutyrate (initiator), purge with nitrogen gas for 30min at room temperature to remove oxygen from the system, and then heat to 80℃ and react for 5h to obtain a light yellow viscous liquid, which is the crude product of graft-modified cross-linked starch filtration loss reducer.

[0082] After the temperature drops, the mixture is filtered, washed with ethanol and ether, and the filtered product is vacuum dried at 70°C for 20 hours to obtain a light yellow grafted modified cross-linked starch filtration reducer.

[0083] Example 6

[0084] (1) Preparation of starch emulsion

[0085] Dissolve 50g of corn starch in water to prepare a 40% colloidal solution, add 6g of NaCl, mix well, and obtain a starch emulsion.

[0086] (2) Preparation of cross-linked starch

[0087] The pH of the starch emulsion prepared in step (1) was adjusted to 10.0 with 1 mol / L NaOH, and 0.5% by weight of epichlorohydrin was added. The mixture was reacted at 30°C for 3 h. The pH was adjusted to neutral with 2% dilute hydrochloric acid, filtered, and the filtrate was washed with water and ethanol, respectively. The filtrate was then dried to obtain cross-linked starch.

[0088] (3) Preparation of graft-modified cross-linked starch filtration loss reducer

[0089] Take 50g of cross-linked starch from step (2), and separately take 10g of methacrylamide, 10g of sodium 2-acrylamido-2-methylpropanesulfonate, 2.5g of 1-allyl-3-butylimidazolium bromide, and 2.5g of N-vinylpyrrolidone. Add them to 400mL of deionized water and dissolve them completely. Under stirring at 200r / min, add 0.15g of azobisisobutyrazoline hydrochloride (initiator). At room temperature, purge with nitrogen for 30min to remove oxygen from the system. Then, heat to 80℃ and react for 10h to obtain a light yellow viscous liquid, which is the crude product of grafted modified cross-linked starch filtration loss reducer.

[0090] After the temperature drops, the mixture is filtered, washed with ethanol and ether, and the filtered product is vacuum dried at 70°C for 20 hours to obtain a light yellow grafted modified cross-linked starch filtration reducer.

[0091] Example 7

[0092] (1) Preparation of starch emulsion

[0093] Dissolve 50g of corn starch in water to prepare a 40% colloidal solution, add 6g of NaCl, mix well, and obtain a starch emulsion.

[0094] (2) Preparation of cross-linked starch

[0095] The pH of the starch emulsion prepared in step (1) was adjusted to 10.0 with 1 mol / L NaOH, and epichlorohydrin at 1% of the weight of the starch used was added. The mixture was reacted at 30°C for 3 h. The pH was adjusted to neutral with 2% dilute hydrochloric acid, filtered, and the filtrate was washed with water and ethanol, respectively. The filtrate was then dried to obtain cross-linked starch.

[0096] (3) Preparation of graft-modified cross-linked starch filtration loss reducer

[0097] Take 50g of cross-linked starch from step (2), and separately take 15g of N,N-dimethylacrylamide, 15g of sodium styrene sulfonate, 10g of 1-vinyl-3-ethylimidazolium bromide, and 10g of N-vinylpyrrolidone. Add them to 500mL of deionized water and dissolve them completely. Under stirring at 200r / min, add 0.1g of azobisisobutyronitrile (initiator), and purge with nitrogen gas for 30min at room temperature to remove oxygen from the system. Then, heat to 50℃ and react for 10h to obtain a light yellow viscous liquid, which is the crude product of grafted modified cross-linked starch filtration loss reducer.

[0098] After the temperature drops, the mixture is filtered, washed with ethanol and ether, and the filtered product is vacuum dried at 70°C for 20 hours to obtain a light yellow grafted modified cross-linked starch filtration reducer.

[0099] Example 8

[0100] (1) Preparation of starch emulsion

[0101] Dissolve 50g of corn starch in water to prepare a 40% colloidal solution, add 6g of NaCl, mix well, and obtain a starch emulsion.

[0102] (2) Preparation of cross-linked starch

[0103] The pH of the starch emulsion prepared in step (1) was adjusted to 10.0 with 1 mol / L NaOH, and epichlorohydrin at 3% of the weight of the starch used was added. The mixture was reacted at 30°C for 3 h. The pH was adjusted to neutral with 2% dilute hydrochloric acid, filtered, and the filtrate was washed with water and ethanol, respectively. The filtrate was then dried to obtain cross-linked starch.

[0104] (3) Preparation of graft-modified cross-linked starch filtration loss reducer

[0105] Add 50g of cross-linked starch, 10g of acrylamide, 30g of sodium vinyl sulfonate, 5g of 1-vinyl-3-butylimidazolium bromide, and 5g of N-vinylpyrrolidone prepared in step (2) to 500mL of deionized water and dissolve them completely. Under stirring at 200r / min, add 0.5g of azobisisobutyronitrile (initiator), purge with nitrogen gas for 30min at room temperature to remove oxygen from the system, and then heat to 60℃ and react for 8h to obtain a light yellow viscous liquid, which is the crude product of graft-modified cross-linked starch filtration loss reducer.

[0106] After the temperature drops, the mixture is filtered, washed with ethanol and ether, and the filtered product is vacuum dried at 70°C for 20 hours to obtain a light yellow grafted modified cross-linked starch filtration reducer.

[0107] Example 9

[0108] (1) Preparation of starch emulsion

[0109] Dissolve 50g of corn starch in water to prepare a 40% colloidal solution, add 6g of NaCl, mix well, and obtain a starch emulsion.

[0110] (2) Preparation of cross-linked starch

[0111] The pH of the starch emulsion prepared in step (1) was adjusted to 10.0 with 1 mol / L NaOH, and epichlorohydrin at 5% of the weight of the starch used was added. The mixture was reacted at 30°C for 3 h. The pH was adjusted to neutral with 2% dilute hydrochloric acid, filtered, and the filtrate was washed with water and ethanol, respectively. The filtrate was then dried to obtain cross-linked starch.

[0112] (3) Preparation of graft-modified cross-linked starch filtration loss reducer

[0113] Take 50g of cross-linked starch from step (2), and separately take 30g of N,N-diethylacrylamide, 10g of 2-acrylamido-2-methylpropanesulfonic acid, 5g of 1-vinyl-3-ethylimidazolium bromide, and 5g of N-vinylpyrrolidone. Add them to 500mL of deionized water and dissolve them completely. Under stirring at 200r / min, add 1g of the initiator azobisisobutyrazoline hydrochloride. Purge the system with nitrogen gas for 30min at room temperature to remove oxygen. Then raise the temperature to 50℃ and react for 8h to obtain a light yellow viscous liquid, which is the crude product of graft-modified cross-linked starch filtration loss reducer.

[0114] After the temperature drops, the mixture is filtered, washed with ethanol and ether, and the filtered product is vacuum dried at 70°C for 20 hours to obtain a light yellow grafted modified cross-linked starch filtration reducer.

[0115] Example 10

[0116] (1) Preparation of starch emulsion

[0117] Dissolve 50g of corn starch in water to prepare a 40% colloidal solution, add 6g of NaCl, mix well, and obtain a starch emulsion.

[0118] (2) Preparation of cross-linked starch

[0119] The pH of the starch emulsion prepared in step (1) was adjusted to 10.0 with 1 mol / L NaOH, and 0.1% by weight of epichlorohydrin was added. The mixture was reacted at 30°C for 3 h. The pH was adjusted to neutral with 2% dilute hydrochloric acid, filtered, and the filtrate was washed with water and ethanol, respectively. The filtrate was then dried to obtain cross-linked starch.

[0120] (3) Preparation of graft-modified cross-linked starch filtration loss reducer

[0121] Add 50g of cross-linked starch, 20g of acrylamide, 20g of sodium allyl sulfonate, 5g of 1-vinyl-3-ethylimidazolium bromide, and 5g of N-vinylpyrrolidone prepared in step (2) to 500mL of deionized water and dissolve them completely. Under stirring at 200r / min, add 5g of azobisisobutyrazoline hydrochloride (initiator), purge with nitrogen gas for 30min at room temperature to remove oxygen from the system, and then heat to 60℃ and react for 10h to obtain a light yellow viscous liquid, which is the crude product of graft-modified cross-linked starch filtration loss reducer.

[0122] After the temperature drops, the mixture is filtered, washed with ethanol and ether, and the filtered product is vacuum dried at 70°C for 20 hours to obtain a light yellow grafted modified cross-linked starch filtration reducer.

[0123] Example 11

[0124] (1) Preparation of starch emulsion

[0125] Dissolve 50g of corn starch in water to prepare a 40% colloidal solution, add 6g of NaCl, mix well, and obtain a starch emulsion.

[0126] (2) Preparation of cross-linked starch

[0127] The pH of the starch emulsion prepared in step (1) was adjusted to 10.0 with 1 mol / L NaOH, and 0.1% by weight of epichlorohydrin was added. The mixture was reacted at 30°C for 3 h. The pH was adjusted to neutral with 2% dilute hydrochloric acid, filtered, and the filtrate was washed with water and ethanol, respectively. The filtrate was then dried to obtain cross-linked starch.

[0128] (3) Preparation of graft-modified cross-linked starch filtration loss reducer

[0129] Add 50g of cross-linked starch, 20g of acrylamide, 20g of 2-acrylamido-2-methylpropanesulfonic acid, 5g of 1-vinyl-3-ethylimidazolium bromide, and 5g of N-vinylpyrrolidone prepared in step (2) to 500mL of deionized water and dissolve them completely. Under stirring at 200r / min, add 2.5g of azobisisobutyrazoline hydrochloride (initiator), purge with nitrogen gas for 30min at room temperature to remove oxygen from the system, and then heat to 80℃ and react for 5h to obtain a light yellow viscous liquid, which is the crude product of graft-modified cross-linked starch filtration loss reducer.

[0130] After the temperature drops, the mixture is filtered, washed with ethanol and ether, and the filtered product is vacuum dried at 70°C for 20 hours to obtain a light yellow grafted modified cross-linked starch filtration reducer.

[0131] Example 12

[0132] (1) Preparation of starch emulsion

[0133] Dissolve 50g of corn starch in water to prepare a 40% colloidal solution, add 6g of NaCl, mix well, and obtain a starch emulsion.

[0134] (2) Preparation of cross-linked starch

[0135] The pH of the starch emulsion prepared in step (1) was adjusted to 10.0 with 1 mol / L NaOH, and 0.1% by weight of epichlorohydrin was added. The mixture was reacted at 30°C for 3 h. The pH was adjusted to neutral with 2% dilute hydrochloric acid, filtered, and the filtrate was washed with water and ethanol, respectively. The filtrate was then dried to obtain cross-linked starch.

[0136] (3) Preparation of graft-modified cross-linked starch filtration loss reducer

[0137] Add 50g of the cross-linked starch prepared in step (2), 30g of alkenylamide monomers (including 10g of acrylamide and 20g of N,N-dimethylacrylamide), 30g of 2-acrylamido-2-methylpropanesulfonic acid, 7.5g of 1-vinyl-3-ethylimidazolium bromide, and 7.5g of N-vinylpyrrolidone to 650mL of deionized water and dissolve them completely. Under stirring at 200r / min, add 0.15g of azobisisobutyronitrile (initiator), purge with nitrogen gas for 30min at room temperature to remove oxygen from the system, and then heat to 60℃ and react for 10h to obtain a light yellow viscous liquid, which is the crude product of the grafted modified cross-linked starch filtration loss reducer.

[0138] After the temperature drops, the mixture is filtered, washed with ethanol and ether, and the filtered product is vacuum dried at 70°C for 20 hours to obtain a light yellow grafted modified cross-linked starch filtration reducer.

[0139] Example 13

[0140] (1) Preparation of starch emulsion

[0141] Dissolve 50g of corn starch in water to prepare a 40% colloidal solution, add 6g of NaCl, mix well, and obtain a starch emulsion.

[0142] (2) Preparation of cross-linked starch

[0143] The pH of the starch emulsion prepared in step (1) was adjusted to 10.0 with 1 mol / L NaOH, and 0.1% by weight of epichlorohydrin was added. The mixture was reacted at 30°C for 3 h. The pH was adjusted to neutral with 2% dilute hydrochloric acid, filtered, and the filtrate was washed with water and ethanol, respectively. The filtrate was then dried to obtain cross-linked starch.

[0144] (3) Preparation of graft-modified cross-linked starch filtration loss reducer

[0145] Add 50g of the cross-linked starch prepared in step (2), 20g of alkenylamide monomers (including 10g of methacrylamide and 10g of N,N-dimethylacrylamide), 20g of 2-acrylamido-2-methylpropanesulfonic acid, 5g of 1-vinyl-3-ethylimidazolium bromide, and 5g of N-vinylpyrrolidone to 500mL of deionized water and dissolve them completely. Under stirring at 200r / min, add 0.15g of azobisisobutyronitrile (initiator), purge with nitrogen gas for 30min at room temperature to remove oxygen from the system, and then heat to 60℃ and react for 6h to obtain a light yellow viscous liquid, which is the crude product of the grafted modified cross-linked starch filtration loss reducer.

[0146] After the temperature drops, the mixture is filtered, washed with ethanol and ether, and the filtered product is vacuum dried at 70°C for 20 hours to obtain a light yellow grafted modified cross-linked starch filtration reducer.

[0147] Example 14

[0148] (1) Preparation of starch emulsion

[0149] Dissolve 50g of corn starch in water to prepare a 40% colloidal solution, add 6g of NaCl, mix well, and obtain a starch emulsion.

[0150] (2) Preparation of cross-linked starch

[0151] The pH of the starch emulsion prepared in step (1) was adjusted to 10.0 with 1 mol / L NaOH, and 0.1% by weight of epichlorohydrin was added. The mixture was reacted at 30°C for 3 h. The pH was adjusted to neutral with 2% dilute hydrochloric acid, filtered, and the filtrate was washed with water and ethanol, respectively. The filtrate was then dried to obtain cross-linked starch.

[0152] (3) Preparation of graft-modified cross-linked starch filtration loss reducer

[0153] Add 50g of the cross-linked starch prepared in step (2), 20g of alkenylamide monomers (including 10g of acrylamide and 10g of N,N-diethylacrylamide), 40g of 2-acrylamido-2-methylpropanesulfonic acid, 7.5g of 1-vinyl-3-ethylimidazolium bromide, and 7.5g of N-vinylpyrrolidone to 650mL of deionized water and dissolve them completely. Under stirring at 200r / min, add 0.15g of azobisisobutyronitrile (initiator), purge with nitrogen gas for 30min at room temperature to remove oxygen from the system, and then heat to 60℃ and react for 6.5h to obtain a light yellow viscous liquid, which is the crude product of the grafted modified cross-linked starch filtration loss reducer.

[0154] After the temperature drops, the mixture is filtered, washed with ethanol and ether, and the filtered product is vacuum dried at 70°C for 20 hours to obtain a light yellow grafted modified cross-linked starch filtration reducer.

[0155] Example 15

[0156] (1) Preparation of starch emulsion

[0157] Dissolve 50g of corn starch in water to prepare a 40% colloidal solution, add 6g of NaCl, mix well, and obtain a starch emulsion.

[0158] (2) Preparation of cross-linked starch

[0159] The pH of the starch emulsion prepared in step (1) was adjusted to 10.0 with 1 mol / L NaOH, and 0.1% by weight of epichlorohydrin was added. The mixture was reacted at 30°C for 3 h. The pH was adjusted to neutral with 2% dilute hydrochloric acid, filtered, and the filtrate was washed with water and ethanol, respectively. The filtrate was then dried to obtain cross-linked starch.

[0160] (3) Preparation of graft-modified cross-linked starch filtration loss reducer

[0161] Add 50g of cross-linked starch, 30g of acrylamide, 30g of 2-acrylamido-2-methylpropanesulfonic acid, 7.5g of alkenyl imidazole monomethylolpropane (including 3.75g of 1-vinyl-3-ethylimidazolium bromide and 3.75g of 1-vinyl-3-butylimidazolium bromide), and 7.5g of N-vinylpyrrolidone to 650mL of deionized water and dissolve them completely. Under stirring at 200r / min, add 0.15g of azobisisobutyronitrile (initiator), purge with nitrogen gas for 30min at room temperature to remove oxygen from the system, and then heat to 60℃ and react for 10h to obtain a light yellow viscous liquid, which is the crude product of graft-modified cross-linked starch filtration loss reducer.

[0162] After the temperature drops, the mixture is filtered, washed with ethanol and ether, and the filtered product is vacuum dried at 70°C for 20 hours to obtain a light yellow grafted modified cross-linked starch filtration reducer.

[0163] Example 16

[0164] (1) Preparation of starch emulsion

[0165] Dissolve 50g of corn starch in water to prepare a 40% colloidal solution, add 6g of NaCl, mix well, and obtain a starch emulsion.

[0166] (2) Preparation of cross-linked starch

[0167] The pH of the starch emulsion prepared in step (1) was adjusted to 10.0 with 1 mol / L NaOH, and 0.1% by weight of epichlorohydrin was added. The mixture was reacted at 30°C for 3 h. The pH was adjusted to neutral with 2% dilute hydrochloric acid, filtered, and the filtrate was washed with water and ethanol, respectively. The filtrate was then dried to obtain cross-linked starch.

[0168] (3) Preparation of graft-modified cross-linked starch filtration loss reducer

[0169] Add 50g of cross-linked starch, 20g of acrylamide, 20g of 2-acrylamido-2-methylpropanesulfonic acid, 5g of alkenyl imidazole monomers (including 2.5g of 1-allyl-3-butylimidazolium bromide and 2.5g of 1-vinyl-3-ethylimidazolium bromide), and 5g of N-vinylpyrrolidone to 500mL of deionized water and dissolve them completely. Under stirring at 200r / min, add 0.15g of azobisisobutyronitrile (initiator), purge with nitrogen gas for 30min at room temperature to remove oxygen from the system, and then heat to 60℃ and react for 8h to obtain a light yellow viscous liquid, which is the crude product of graft-modified cross-linked starch filtration loss reducer.

[0170] After the temperature drops, the mixture is filtered, washed with ethanol and ether, and the filtered product is vacuum dried at 70°C for 20 hours to obtain a light yellow grafted modified cross-linked starch filtration reducer.

[0171] Example 17

[0172] (1) Preparation of starch emulsion

[0173] Dissolve 50g of corn starch in water to prepare a 40% colloidal solution, add 6g of NaCl, mix well, and obtain a starch emulsion.

[0174] (2) Preparation of cross-linked starch

[0175] The pH of the starch emulsion prepared in step (1) was adjusted to 10.0 with 1 mol / L NaOH, and 0.1% epichlorohydrin (by weight of the starch used) was added. The mixture was reacted at 30°C for 3 h. The pH was adjusted to neutral with 2% dilute hydrochloric acid, filtered, and the filtrate was washed with water and ethanol, respectively. The filtrate was then dried to obtain cross-linked starch.

[0176] (3) Preparation of graft-modified cross-linked starch filtration loss reducer

[0177] Add 50g of the cross-linked starch prepared in step (2), 20g of alkenylamide monomer (10g of N,N-dimethylacrylamide and 10g of N,N-diethylacrylamide), 20g of 2-acrylamido-2-methylpropanesulfonic acid, 5g of 1-vinyl-3-ethylimidazolium bromide, and 5g of N-vinylpyrrolidone to 500mL of deionized water and dissolve them completely. Under stirring at 200r / min, add 0.15g of azobisisobutyronitrile (initiator), purge with nitrogen gas for 30min at room temperature to remove oxygen from the system, and then heat to 60℃ and react for 7h to obtain a light yellow viscous liquid, which is the crude product of the grafted modified cross-linked starch filtration loss reducer.

[0178] After the temperature drops, the mixture is filtered, washed with ethanol and ether, and the filtered product is vacuum dried at 70°C for 20 hours to obtain a light yellow grafted modified cross-linked starch filtration reducer.

[0179] Example 18

[0180] (1) Preparation of starch emulsion

[0181] Dissolve 50g of corn starch in water to prepare a 40% colloidal solution, add 6g of NaCl, mix well, and obtain a starch emulsion.

[0182] (2) Preparation of cross-linked starch

[0183] The pH of the starch emulsion prepared in step (1) was adjusted to 10.0 with 1 mol / L NaOH, and 0.1% epichlorohydrin (by weight of starch) was added. The mixture was reacted at 30°C for 3 h. The pH was adjusted to neutral with 2% dilute hydrochloric acid, filtered, and the filtrate was washed with water and ethanol, respectively. The filtrate was then dried to obtain cross-linked starch.

[0184] (3) Preparation of graft-modified cross-linked starch filtration loss reducer

[0185] Add 50g of cross-linked starch, 40g of acrylamide, 20g of allyl sulfonic acid monomers (including 10g of 2-acrylamido-2-methylpropanesulfonic acid and 10g of sodium allyl sulfonate), 7.5g of 1-vinyl-3-ethylimidazolium bromide, and 7.5g of N-vinylpyrrolidone to 650mL of deionized water and dissolve them completely. Under stirring at 200r / min, add 0.15g of azobisisobutyronitrile (initiator), purge with nitrogen gas for 30min at room temperature to remove oxygen from the system, and then heat to 60℃ and react for 8h to obtain a light yellow viscous liquid, which is the crude product of graft-modified cross-linked starch filtration loss reducer.

[0186] After the temperature drops, the mixture is filtered, washed with ethanol and ether, and the filtered product is vacuum dried at 70°C for 20 hours to obtain a light yellow grafted modified cross-linked starch filtration reducer.

[0187] Example 19

[0188] (1) Preparation of starch emulsion

[0189] Dissolve 50g of corn starch in water to prepare a 40% colloidal solution, add 6g of NaCl, mix well, and obtain a starch emulsion.

[0190] (2) Preparation of cross-linked starch

[0191] The pH of the starch emulsion prepared in step (1) was adjusted to 10.0 with 1 mol / L NaOH, and 0.1% epichlorohydrin by weight of starch was added. The mixture was reacted at 30°C for 3 h. The pH was adjusted to neutral with 2% dilute hydrochloric acid, filtered, and the filtrate was washed with water and ethanol, respectively. The filtrate was then dried to obtain cross-linked starch.

[0192] (3) Preparation of graft-modified cross-linked starch filtration loss reducer

[0193] Add 50g of cross-linked starch, 20g of acrylamide, 20g of allyl sulfonic acid monomers (including 10g of sodium 2-acrylamido-2-methylpropanesulfonate and 10g of sodium styrene sulfonate), 5g of 1-vinyl-3-ethylimidazolium bromide, and 5g of N-vinylpyrrolidone to 500mL of deionized water and dissolve them completely. Under stirring at 200r / min, add 0.15g of azobisisobutyronitrile (initiator), purge with nitrogen gas for 30min at room temperature to remove oxygen from the system, and then heat to 60℃ and react for 10h to obtain a light yellow viscous liquid, which is the crude product of graft-modified cross-linked starch filtration loss reducer.

[0194] After the temperature drops, the mixture is filtered, washed with ethanol and ether, and the filtered product is vacuum dried at 70°C for 20 hours to obtain a light yellow grafted modified cross-linked starch filtration reducer.

[0195] Example 20

[0196] (1) Preparation of starch emulsion

[0197] Dissolve 50g of corn starch in water to prepare a 40% colloidal solution, add 6g of NaCl, mix well, and obtain a starch emulsion.

[0198] (2) Preparation of cross-linked starch

[0199] The pH of the starch emulsion prepared in step (1) was adjusted to 10.0 with 1 mol / L NaOH, and 0.1% epichlorohydrin by weight of starch was added. The mixture was reacted at 30°C for 3 h. The pH was adjusted to neutral with 2% dilute hydrochloric acid, filtered, and the filtrate was washed with water and ethanol, respectively. The filtrate was then dried to obtain cross-linked starch.

[0200] (3) Preparation of graft-modified cross-linked starch filtration loss reducer

[0201] Add 50g of cross-linked starch, 20g of acrylamide, 20g of allyl sulfonic acid polymerizable monomers (including 10g of sodium vinyl sulfonate and 10g of sodium allyl sulfonate), 5g of 1-vinyl-3-ethylimidazolium bromide, and 5g of N-vinylpyrrolidone to 500mL of deionized water and dissolve them completely. Under stirring at 200r / min, add 0.15g of azobisisobutyronitrile (initiator), purge with nitrogen gas for 30min at room temperature to remove oxygen from the system, and then heat to 60℃ and react for 9h to obtain a light yellow viscous liquid, which is the crude product of graft-modified cross-linked starch filtration loss reducer.

[0202] After the temperature drops, the mixture is filtered, washed with ethanol and ether, and the filtered product is vacuum dried at 70°C for 20 hours to obtain a light yellow grafted modified cross-linked starch filtration reducer.

[0203] The following experiments, which showed results that were not as expected during the development of this invention, are recorded here as comparative examples.

[0204] Comparative Example 1

[0205] The difference between Comparative Example 1 and Example 1 is that the monomers used do not include polymerizable imidazole salt ionic liquid monomers.

[0206] Comparative Example 2

[0207] The difference between Comparative Example 2 and Example 2 is that the monomers used do not include polymerizable imidazole salt ionic liquid monomers.

[0208] Comparative Example 3

[0209] The difference between Comparative Example 3 and Example 3 is that the monomers used do not include polymerizable imidazole salt ionic liquid monomers.

[0210] Comparative Example 4

[0211] The difference between Comparative Example 4 and Example 1 is that the polymerization monomers used do not include N-vinylpyrrolidone monomers.

[0212] Comparative Example 5

[0213] The difference between Comparative Example 5 and Example 2 is that the polymerization monomers used do not include N-vinylpyrrolidone monomers.

[0214] Comparative Example 6

[0215] The difference between Comparative Example 6 and Example 3 is that the polymerization monomers used do not include N-vinylpyrrolidone monomers.

[0216] Comparative Example 7

[0217] The difference between Comparative Example 7 and Example 1 is that neither polymerizable imidazole salt ionic liquid monomers nor N-vinylpyrrolidone monomers were used in the polymerization monomers used.

[0218] Comparative Example 8

[0219] The difference between Comparative Example 8 and Example 2 is that neither polymerizable imidazole salt ionic liquid monomers nor N-vinylpyrrolidone monomers were used in the polymerization monomers used.

[0220] Comparative Example 9

[0221] The difference between Comparative Example 9 and Example 3 is that neither polymerizable imidazole salt ionic liquid monomers nor N-vinylpyrrolidone monomers were used in the polymerization monomers used.

[0222] Performance testing

[0223] The filtration loss reducers prepared in Examples 1-20 and Comparative Examples 1-9 were applied to oilfield drilling processes to produce a drilling fluid. The following performance tests were then conducted, and the results were recorded in a table.

[0224] 1. Evaluation of the temperature and salt resistance properties of the filtration loss reducer

[0225] (1) Testing in freshwater-based slurry

[0226] The test can be conducted in accordance with the relevant standards in SYT 5241-91 "Evaluation Procedure for Filtration Loss Control Agents for Water Turbine Drilling Fluids". Specific steps include:

[0227] Freshwater-based slurry: Dissolve 0.8g Na2CO3 in 400mL of deionized water by stirring. Add 16.0g of bentonite for drilling fluid test slurry preparation while stirring continuously. Continue stirring for 20min at a speed of (11000±300)rpm / min, taking care to scrape off the bentonite adhering to the container wall during this period. Cure in a sealed container for at least 24 hours.

[0228] Filtration loss reducer-freshwater drilling fluid system: Weigh 20.0g of the filtration loss reducer prepared in Examples 1-20 and Comparative Examples 1-9 respectively, add each to 400mL of freshwater-based slurry, stir and mix well, and cure in a sealed container for more than 24 hours.

[0229] The cured filtration loss reducer-freshwater drilling fluid system was stirred for 10 minutes at (11000±300) rpm / min, then poured into an aging tank and hot-rolled in a roller furnace at 120℃, 150℃, and 180℃ for 16 hours respectively. The high-temperature and high-pressure filtration loss (FL) was then measured using a high-temperature and high-pressure filtration loss meter. HTHP The results are shown in Table 2 below.

[0230] Table 2: Filtration Loss in High-Temperature and High-Pressure Systems of Filtration Loss Control Agent-Freshwater Drilling Fluid (FL) HTHP (Unit: mL)

[0231]

[0232]

[0233] (2) Testing in 20% brine-based slurry

[0234] The test can be conducted in accordance with the relevant standards in SYT 5241-9 "Evaluation Procedure for Filtration Loss Control Agents for Water Turbine Drilling Fluids". Specific steps include:

[0235] Freshwater-based slurry: Dissolve 400 mL of deionized water, 0.8 g of Na2CO3, and 80 g of NaCl by stirring. While stirring continuously, add 16.0 g of bentonite for drilling fluid test slurry preparation. Continue stirring for 20 min at a speed of (11000±300) rpm / min, taking care to scrape off the bentonite adhering to the container wall during this period. Cure in a sealed container for at least 24 hours.

[0236] Filtration loss reducer-20% brine drilling fluid system: Weigh 20.0g of the filtration loss reducer prepared in Examples 1-20 and Comparative Examples 1-9 respectively, add each to 400mL of fresh water-based slurry, stir and mix well, and cure in a sealed container for more than 24 hours.

[0237] The cured filtration loss reducer-20% brine drilling fluid system was stirred for 10 minutes at (11000±300) rpm / min, then poured into an aging tank and hot-rolled in a roller furnace at 120℃, 150℃, and 180℃ for 16 hours respectively. The high-temperature and high-pressure filtration loss (FL) was then measured using a high-temperature and high-pressure filtration loss meter. HTHP The results are shown in Table 3 below.

[0238] Filtration loss under high temperature and high pressure (FLHTHP) in a 20% brine drilling fluid system with filtration loss reducer (unit: mL)

[0239]

[0240]

[0241] The above test results show that the grafted modified starch filtration reducer prepared in Examples 1-20 exhibits a decrease in FLOPs in both freshwater-based and 20% brine-based slurries with increasing aging temperature. HTHP The levels also increased, all exhibiting certain resistance to temperature and salt. Under the same test conditions, the modified starch filtration loss reducer produced significantly greater filtration loss in brine-based slurry than in freshwater-based slurry. This indicates that under the influence of a large amount of salt, the molecular chains of the filtration loss reducer are less likely to extend under the influence of cations, and the interaction with bentonite also deteriorates.

[0242] Compared with the products prepared in Comparative Examples 1-9, the products prepared in Examples 1-20 showed an overall increasing trend in filtration loss with increasing temperature, but without a sharp increase. Based on the above experimental results, the inventors speculate that in the experiments of Examples 1-20, hydration monomers (N-vinylpyrrolidone monomers) and polymerizable cationic monomers (polymerizable imidazole salt ionic liquid monomers) were introduced simultaneously. The two types of monomers may have produced a synergistic effect, forming a hydration film on the surface of clay particles, increasing the dispersion ability of clay particles in the entire drilling fluid system. At the same time, the polymerizable cationic monomers can adsorb onto the surface of clay, preventing the cations in the brine from interacting with the clay and promoting the dispersion of clay particles, thereby improving the temperature and salt resistance of the filtration loss reducer.

[0243] In Examples 1-20, the sample obtained in Example 3 showed outstanding performance in both freshwater-based and brine-based slurries.

[0244] By comparing Examples 1-5, it can be seen that the filtration performance first increases and then decreases as the starch content decreases. We can infer that the cross-linked modified starch still exhibits easy decomposition at higher temperatures, so reducing the starch content can improve the filtration performance. The decrease in starch content reduces the ether bonds provided by starch in the filtration reducer molecule, thus weakening the interaction between the filtration reducer and clay and water. As the starch content increases, the filtration performance first strengthens and then weakens. Therefore, we further controlled the mass ratio of cross-linked starch to polymer monomers to approximately 1:1.25.

[0245] Examples 7 and 9 show that at lower reaction temperatures, the filtration loss reduction performance of the sample can be improved by appropriately extending the reaction time.

[0246] By reviewing relevant literature and examining the performance of samples from Examples 1-20, it can be seen that in Examples 6, 7, 8, and 9, the filtration loss reduction performance of the products did not significantly improve with the increase in the amount of crosslinking agent used. Therefore, considering the overall economic benefits, reaction process, and cost, we recommend further controlling the amount of crosslinking agent to between 0.001 and 0.1% of the starch mass.

[0247] The above are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. All modifications or applications made in accordance with the above embodiments are within the scope of protection of this technical solution.

[0248] Although specific embodiments of the invention have been described in detail, those skilled in the art will understand that various modifications and substitutions can be made to those details based on all the teachings disclosed, and all such changes are within the scope of protection of this invention. The full scope of this invention is given by the appended claims and any equivalents thereof.

Claims

1. An ionic liquid grafted modified starch fluid loss additive characterized in that, The preparation raw material of the fluid loss additive comprises crosslinked starch and 50-300% of the mass of the crosslinked starch of polymerized monomers; the crosslinked starch comprises starch and 0.1-5% of the mass of the starch of epichlorohydrin; and the polymerized monomers comprise alkenyl amide monomers, alkenyl sulfonic acid monomers, polymerizable imidazole salt ionic liquid monomers and N-vinyl pyrrolidone monomers in a mass ratio of (20-60):(20-60):(10-20):(10-30). The alkenyl amide monomers are selected from one or more of acrylamide, methacrylamide, N,N-dimethyl acrylamide and N,N-diethyl acrylamide; the alkenyl sulfonic acid monomers are selected from one or more of 2-acrylamido-2-methylpropanesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid sodium, allyl sulfonic acid sodium, styrene sulfonic acid sodium and vinyl sulfonic acid sodium; and the polymerizable imidazole salt ionic liquid monomers are selected from one or more of 1-vinyl-3-ethyl imidazole bromide, 1-vinyl-3-butyl imidazole bromide and 1-allyl-3-butyl imidazole bromide.

2. The ionic liquid grafted modified starch fluid loss additive of claim 1, wherein, The mass ratio of the starch to the epichlorohydrin is 1:(0.001-0.01).

3. The ionic liquid grafted modified starch fluid loss additive of claim 1, wherein, The preparation raw material of the fluid loss additive further comprises an initiator.

4. The ionic liquid grafted modified starch fluid loss additive of claim 3, wherein, The initiator is selected from one of azobisisobutyronitrile, azobisisopentyl nitrile, azobisisoheptyl nitrile, azobis(cyanovaleric acid), azobis(isobutylamidine hydrochloride), azobis(isobutylimidazole hydrochloride), azobis(dimethyl N-2-hydroxybutyl acrylamide), azobis(cyclohexyl cyanide), azobis(dimethyl isobutyrate) and azoisobutyryl cyanamide.

5. The ionic liquid grafted modified starch fluid loss additive of claim 4, wherein, The mass of the initiator is 1%-10% of the total mass of the crosslinked starch and the polymerized monomers.

6. The method of preparing an ionic liquid grafted modified starch fluid loss additive according to any one of claims 1 to 5, characterized in that, The method comprises the following steps: S1, preparation of a starch emulsion The starch is weighed, stirred and dissolved in water to prepare a colloidal solution, and then NaCl is added and uniformly mixed to prepare the starch emulsion; S2, preparation of crosslinked starch The pH value of the starch emulsion prepared in S1 is adjusted to be alkaline, epichlorohydrin is added and reacted at room temperature, the pH value of the reaction solution is then adjusted to be neutral, and the crosslinked starch is obtained after filtration, washing and drying; S3, preparation of the graft-modified crosslinked starch fluid loss additive The crosslinked starch and the polymerized monomers prepared in S2 are sequentially added to water and fully dissolved, and then the initiator is added under stirring, and inert gas is added to the system at room temperature, and the reaction is carried out after heating to obtain the crude product of the graft-modified crosslinked starch fluid loss additive; after the temperature is reduced, the product is filtered, washed and vacuum dried to obtain the light yellow graft-modified crosslinked starch fluid loss additive.

7. The method of preparing an ionic liquid grafted modified starch fluid loss additive according to claim 6, wherein, In S3, the reaction temperature is 50-80°C, and the reaction time is 5-10h.

8. Application of the graft-modified starch fluid loss additive prepared by the method of any one of claims 1-5 or 6-7 in oilfield drilling.

9. A drilling fluid, characterized by, The drilling fluid contains the ionic liquid grafted modified starch fluid loss additive as claimed in any one of claims 1 to 5 or the ionic liquid grafted modified starch fluid loss additive prepared by the method as claimed in any one of claims 6 to 7.

10. An oilfield drilling process characterized by, The drilling process uses the drilling fluid as claimed in claim 9.

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