Ultrahigh-temperature-resistant water-based drilling fluid filtrate reducer as well as preparation method and application thereof

Abstract

The invention provides an ultrahigh-temperature-resistant water-based drilling fluid filtrate reducer as well as a preparation method and application thereof. The filtrate reducer is obtained by copolymerization of unsaturated monomers. In the molecular structure of the filtrate reducer, the main chain is a C-C bond, the side chain is a cyclic functional group with relatively strong rigidity, an amide group with strong adsorbability and a sulfonic acid group with strong hydrophilicity, the bond energy is relatively large, and the filtrate reducer is not easy to decompose and lose efficacy in an ultrahigh-temperature and high-salt calcium environment. Due to lattice substitution, the surfaces of the clay particles are negatively charged, and the filtrate reducer is adsorbed on the surfaces of the clay particles under the action of static electricity and hydrogen bonds to form a spatial network structure of the clay particles and filtrate reducer macromolecules, so that the hydration film thickness of the clay particles, Zeta potential and repulsive force among the clay particles are increased, the clay particles are not easy to coalesce, and the viscosity of the filtrate reducer is increased. Certain dispersity is kept in the drilling fluid, and clay particles with small particle size are formed, so that a compact and low-permeability filter cake is formed under the action of pressure difference, and the filter loss of the drilling fluid is effectively reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of oil exploration and development, and particularly relates to a high-temperature-resistant water-based drilling fluid filtrate reducer and its preparation method and application. Background Technique

[0002] With the gradual depletion of conventional oil and gas resources, unconventional oil and gas resources such as heavy oil, oil sands, shale oil, shale gas, and coalbed methane have increasingly become the focus of development. The deep and ultra-deep oil and gas resources in China are widely distributed and have large reserves, and will become the main backup energy source to alleviate the contradiction between energy supply and demand in China. The deep reservoirs in China (such as Tarim, Sichuan, Bohai Bay, etc.) generally have a depth exceeding 6000m, and the deepest is nearly 9000m, with a bottom hole temperature of 180 - 260°C. Ultra-deep wells have the characteristics of high temperature and pressure, complex geological conditions (mostly with salt gypsum layers), and multiple pressure systems in the same open hole section. During the drilling process, major safety accidents such as well collapse, stuck pipe, lost circulation, and blowout often occur due to the failure of the drilling fluid under ultra-high temperature conditions, resulting in high drilling costs and easy formation damage, which has a significant impact on the development of deep and ultra-deep oil and gas.

[0003] There have been reports on water-based drilling fluid filtrate reducers in the prior art. For example, Chinese Patent Document CN113549431A discloses a high-temperature-resistant water-based drilling fluid filtrate reducer with high inhibition and its preparation method. The filtrate reducer is made from raw materials with the following weight ratios: acrylic fiber, potassium hydroxide, lignite, sodium metabisulfite, formaldehyde, sodium acrylate, dimethyldiallylammonium chloride, potassium chloride, hydrogen peroxide, and water. Add acrylic fiber and potassium hydroxide to water and react at 85 - 100°C for 2 - 4h; then add lignite, sodium metabisulfite, formaldehyde, sodium acrylate, and potassium chloride, and react at 85 - 95°C for 1 - 3h; add hydrogen peroxide and dimethyldiallylammonium chloride and react for 20 - 50min. Cool down, take out the product, dry and crush it to obtain the filtrate reducer. It can resist high temperatures of 180°C, saturated brine, and seawater, can effectively reduce the filtration loss of drilling mud, thus solving the problems of mud temperature resistance and salt resistance in deep well and ultra-deep well drilling, and at the same time can inhibit the hydration swelling of clay, which is beneficial to the stability of shale formations. However, it only has filtrate reduction performance at a high temperature of 180°C and has great application limitations when the well temperature exceeds 180°C.

[0004] Chinese patent document CN113150754A discloses a high-temperature and salt-resistant water-based drilling fluid filtrate reducer and its preparation method, which relates to the technical field of oilfield chemistry. The disclosed filtrate reducer is copolymerized from raw materials including acrylamide, N-vinylpyrrolidone, 2-acrylamido-2-methylpropanesulfonic acid, and zwitterionic monomers under the action of an initiator. The zwitterionic monomer is one or more of N,N-dimethyl-N-(3-sulfopropyl)-4-vinylbenzylammonium inner salt, N,N-diethyl-N-(3-sulfopropyl)-4-vinylbenzylammonium inner salt, N,N-dimethyl-N-(3-sulfobutyl)-4-vinylbenzylammonium inner salt, and N,N-diethyl-N-(3-sulfobutyl)-4-vinylbenzylammonium inner salt. The zwitterionic monomer in the filtrate reducer of the present invention contains equal amounts of quaternary ammonium cations and sulfonic acid groups, and in addition, there is a rigid benzene ring group, making the filtrate reducer of the present invention have good high-temperature and salt-resistant properties, with a high temperature resistance of up to 230 °C and a salt resistance of up to 36% saturated sodium chloride. However, it can only resist high temperatures of 230 °C, and has great application limitations when the well temperature exceeds 230 °C.

[0005] Chinese patent document CN108264587A discloses a high-temperature-resistant water-based drilling fluid filtrate reducer and its preparation method and application. The preparation method of the high-temperature-resistant water-based drilling fluid filtrate reducer includes the following steps: Add three monomers, styrene, maleic anhydride, and acrylamide, to a reaction kettle, stir and dissolve, and then heat up by introducing an inert gas. Then add an initiator and a crosslinking agent, and stir and react at a constant temperature to obtain a yellow-brown solid reactant. After cooling and drying, a yellow-brown solid powder is obtained; place the yellow-brown solid powder in an oil phase, stir and heat up, then add a sulfonating agent, and react at a constant temperature to obtain a yellow-brown viscous colloidal reactant. After cooling, it is neutralized with an alkali, washed with an organic solvent, and dried and pulverized to obtain a yellow-brown solid powder, which is the high-temperature-resistant water-based drilling fluid filtrate reducer. This filtrate reducer has the advantages of less waste in the synthesis process, less environmental pollution, a high temperature resistance of up to 200 °C, and good filtrate reduction performance. However, it only has good filtrate reduction performance in a well temperature environment below 200 °C, and also has application limitations. Summary of the Invention

[0006] The purpose of the present invention is to provide a high-temperature-resistant water-based drilling fluid filtrate reducer with a high temperature resistance of up to 260 °C, a salt resistance up to saturation, and a calcium resistance of 20,000 mg / L.

[0007] Another purpose of the present invention is to provide a preparation method of a high-temperature-resistant water-based drilling fluid filtrate reducer.

[0008] Another purpose of the present invention is to provide an application of a high-temperature-resistant water-based drilling fluid filtrate reducer, which fundamentally solves the problems of deterioration of the rheological and filtration properties of water-based drilling fluids in salt gypsum layers and high-temperature environments, and has good application prospects.

[0009] To this end, the technical solution provided by the present invention is as follows:

[0010] An ultra-high temperature resistant water-based drilling fluid filtrate reducer is obtained by copolymerization of unsaturated monomers, and the unsaturated monomers are amide monomers, sulfonic acid monomers, pyridine monomers and N-vinylcaprolactam, and the molar ratio of the amide monomers, sulfonic acid monomers, pyridine monomers and N-vinylcaprolactam is 4-8:1-3:1-3:1-3.

[0011] The amide monomers are acrylamide, N-vinyl-ε-caprolactam, N,N-dimethylacrylamide, N-(4-bromophenyl)prop-2-enamide, N-allyl-p-toluenesulfonamide, 2,2,2-trichloroacetamide allyl ester, prop-2-ene-1-sulfonamide, N-allyl-2-chloroacetamide, N-(allyloxy)-2-nitrobenzenesulfonamide, diene-3-amino-7-oxabicyclo[2.2.1]hept-5-ene-2-carboxamide or N-(3-allylpyridin-4-yl)pivalamide.

[0012] The sulfonic acid monomers are 2-acrylamido-2-methylpropane sulfonic acid, sodium vinyl sulfonate, dimethylamine vinyl sulfonate, allyl vinyl sulfonic acid, styrene sulfonic acid, methacrylic acid or allyl sulfonic acid.

[0013] The pyridine monomers are 4-vinylpyridine, 3-vinylpyridine, 2-vinylpyridine, 2-fluoro-4-vinylpyridine, 3-fluoro-5-vinylpyridine, 3-bromo-5-vinylpyridine, 4-chloro-2-vinylpyridine, 5-bromo-2-vinylpyridine, 6-vinylpyridinecarboxaldehyde, 2-methyl-6-vinylpyridine, 4-methyl-2-vinylpyridine, 2-methyl-5-enylpyridine, 1-(3-sulfopropyl)-2-vinylpyridine hydroxide inner salt or 1-methyl-2-vinylpyridine trifluoromethanesulfonate.

[0014] It is obtained by polymerization of unsaturated monomers N,N-dimethylacrylamide, 2-acrylamido-2-methylpropane sulfonic acid, 4-vinylpyridine and N-vinylcaprolactam.

[0015] A preparation method of an ultra-high temperature resistant water-based drilling fluid filtrate reducer includes the following steps:

[0016] Step 1) Dissolve the sulfonic acid monomers in an amount according to the formula in water, and adjust the pH value of the solution to neutral with a NaOH solution to obtain a sulfonic acid monomer solution;

[0017] Step 2) Add the amide monomers, pyridine monomers, N-vinylcaprolactam and the sulfonic acid monomer solution in an amount according to the formula into a reaction vessel filled with water;

[0018] Step 3) Under nitrogen protection and stirring conditions, an initiator is added to a container, and free radical polymerization reaction is carried out at 55 - 65 °C for 2 - 3 h;

[0019] Step 4) After the free radical polymerization reaction ends, the product is purified with a dialysis bag, then vacuum dried at 45 - 55 °C for 6 - 8 hours and pulverized to obtain the target product;

[0020] Among them, the total mass percentage of the amide monomer, sulfonic acid monomer solution, pyridine monomer and N - vinylcaprolactam is 20%, and the mass percentage of water is 80%; the dosage of the initiator is 0.05% of the mass of the target product.

[0021] The initiator is a mixture of ammonium persulfate and sodium bisulfite, and the mass ratio of the two is 1:1.

[0022] Application of an ultra - high - temperature resistant water - based drilling fluid filtrate reducer in the preparation of water - based drilling fluid.

[0023] The mass percentage of the filtrate reducer is 1 - 2%.

[0024] The beneficial effects of the present invention are as follows:

[0025] The ultra - high - temperature resistant water - based drilling fluid filtrate reducer provided by the present invention has a main chain of C - C bonds in its molecular structure, and side chains of rigid cyclic functional groups, strongly adsorptive amide groups and strongly hydrophilic sulfonic acid groups. Its bond energy is relatively large, and it is not easily decomposed and inactivated in ultra - high - temperature and high - salt calcium environments. Due to lattice substitution, the surface of clay particles is negatively charged. The filtrate reducer is adsorbed on the surface of clay particles under the action of electrostatic force and hydrogen bonds, forming a spatial network structure of clay particles and filtrate reducer macromolecules, increasing the hydration film thickness, Zeta potential (absolute value) of clay particles and the repulsion force between clay particles, making clay particles not easily coalesce, maintaining a certain degree of dispersion in the drilling fluid, forming clay particles with smaller particle sizes, and thus forming a dense and low - permeability filter cake under the action of pressure difference, effectively reducing the filtrate loss of the drilling fluid.

[0026] The ultra - high - temperature resistant water - based drilling fluid filtrate reducer of the present invention has excellent viscosity - increasing, salt - calcium resistance, ultra - high - temperature resistance and filtrate - reducing properties, and can be applied to ultra - high - temperature deep wells, ultra - deep wells and salt gypsum formations; experiments prove that the ultra - high - temperature resistant water - based drilling fluid filtrate reducer of the present invention can withstand a temperature of up to 260 °C, resist salt to saturation, and resist calcium of 20,000 mg / L.

[0027] The filtrate reducer of the ultra-high temperature resistant water-based drilling fluid of the present invention can be effectively adsorbed on the surface of clay particles under ultra-high temperature and high salt-calcium environment, increase the thickness of its hydration film, form a dense mud cake, reduce the permeability of the mud cake, and thus reduce the filtrate loss. It has good filtrate reduction performance when applied to deep wells, ultra-deep wells and salt gypsum formations. It has good viscoelasticity and shear dilution, which is beneficial to suspending and carrying cuttings, cleaning the wellbore and enhancing the stability of the wellbore. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is the thermogravimetric diagram of the ultra-high temperature resistant water-based drilling fluid filtrate reducer prepared in Example 2;

[0029] Figure 2 It is the infrared spectrum diagram of the ultra-high temperature resistant water-based drilling fluid filtrate reducer prepared in Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0030] The following specific embodiments illustrate the implementation manners of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification.

[0031] The exemplary implementation manners of the present invention are introduced with reference to the accompanying drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. These embodiments are provided to disclose the present invention in detail and completely, and to fully convey the scope of the present invention to those skilled in the art. The terms in the exemplary implementation manners shown in the drawings are not limitations on the present invention.

[0032] Unless otherwise specified, the terms (including scientific and technical terms) used herein have the ordinary meaning understood by those skilled in the art. In addition, it can be understood that the terms defined in the commonly used dictionary should be understood as having a meaning consistent with the context of their related fields, and should not be understood as idealized or overly formal meanings.

[0033] Example 1

[0034] This example provides a filtrate reducer for ultra-high temperature resistant water-based drilling fluid, which is obtained by copolymerization of unsaturated monomers. The unsaturated monomers are amide monomers, sulfonic acid monomers, pyridine monomers and N-vinylcaprolactam, and the molar ratio of the amide monomers, sulfonic acid monomers, pyridine monomers and N-vinylcaprolactam is 4-8:1-3:1-3:1-3.

[0035] The amide monomers are acrylamide, N-vinyl-ε-caprolactam, N,N-dimethylacrylamide, N-(4-bromophenyl)prop-2-enamide, N-allyl-p-toluenesulfonamide, allyl 2,2,2-trichloroacetate, prop-2-ene-1-sulfonamide, N-allyl-2-chloroacetamide, N-(allyloxy)-2-nitrobenzenesulfonamide, diene-3-amino-7-oxabicyclo[2.2.1]hept-5-ene-2-carboxamide or N-(3-allylpyridin-4-yl)pivalamide.

[0036] The sulfonic acid monomers are 2-acrylamido-2-methylpropane sulfonic acid, sodium vinyl sulfonate, dimethylamine vinyl sulfonate, allyl vinyl sulfonic acid, styrene sulfonic acid, methacrylic acid or allyl sulfonic acid.

[0037] The pyridine monomers are 4-vinylpyridine, 3-vinylpyridine, 2-vinylpyridine, 2-fluoro-4-vinylpyridine, 3-fluoro-5-vinylpyridine, 3-bromo-5-vinylpyridine, 4-chloro-2-vinylpyridine, 5-bromo-2-vinylpyridine, 6-vinylpyridinecarboxaldehyde, 2-methyl-6-vinylpyridine, 4-methyl-2-vinylpyridine, 2-methyl-5-enylpyridine, 1-(3-sulfopropyl)-2-vinylpyridine hydroxide inner salt or 1-methyl-2-vinylpyridine trifluoromethanesulfonate.

[0038] The high-temperature resistant water-based drilling fluid filtrate reducer provided by the present invention has a main chain of C-C bonds in its molecular structure, and side chains of rigid cyclic functional groups, strongly adsorptive amide groups and strongly hydrophilic sulfonic acid groups. Its bond energy is relatively large and it is not easily decomposed and inactivated in high-temperature and high-salt calcium environments.

[0039] Example 2

[0040] On the basis of Example 1, this example provides a high-temperature resistant water-based drilling fluid filtrate reducer, which is obtained by polymerizing unsaturated monomers with the following molar ratios: the molar ratio of N,N-dimethylacrylamide, 2-acrylamido-2-methylpropane sulfonic acid, 4-vinylpyridine, and N-vinylcaprolactam is 6:2:1:1.

[0041] Preparation process:

[0042] (1) Weigh the formula amount of 2-acrylamido-2-methylpropane sulfonic acid and dissolve it in water, and use 20wt% NaOH solution to adjust the pH value of the solution to a neutral environment;

[0043] (2) Add 20 g in total of N,N-dimethylacrylamide, the 2-acrylamido-2-methylpropane sulfonic acid solution in (1), 4-vinylpyridine and N-vinylcaprolactam (molar ratio of 6:2:1:1) to a three-necked flask containing 80 g of pure water;

[0044] (3) Under nitrogen protection and at a stirring speed of 500 rpm, 0.025 g of ammonium persulfate and 0.025 g of sodium bisulfite as initiators were dispersed in the mixed solution in (2) above for 0.5 h, and then heated to 60 °C for free radical polymerization reaction;

[0045] (4) After the free radical polymerization reaction was completed, the product was purified with an MD44 dialysis bag (molecular cut-off of 8000 - 14000) for 24 h, then dried and pulverized at 50 °C to obtain the target product.

[0046] The molecular structural formula of the target product is as follows:

[0047]

[0048] Among them, a, b, c, and d are all 100 - 2000, and the relative molecular mass of the filtration loss reducer ranges from 200,000 to 1,000,000.

[0049] Thermogravimetric analysis:

[0050] In a TA Instruments SDT-Q600 thermogravimetric analyzer, an aluminum crucible was used, and the nitrogen purge flow rate was 50 mL·min -1 , and thermogravimetric (TGA) analysis was performed on the filtration loss reducer for ultra-high temperature water-based drilling fluid obtained in this example. The initial temperature was 40 °C, and the final temperature was 700 °C.

[0051] As Figure 1 shown, the weight loss process of the filtration loss reducer is divided into three parts. The first part is from 40 to 301 °C, and the TG curve is relatively flat, with a mass loss of 8.45%. The mass loss in this stage is mainly because the filtration loss reducer contains a large number of hydrophilic groups that adsorb free water in the air. When the temperature rises, the volatilization of free water leads to partial mass loss of the filtration loss reducer. The second part has a weight loss temperature range of 301 - 427.6 °C, and the TG curve drops sharply, with a weight loss ratio of 64.45%. The mass loss in this stage is mainly because the amide groups and sulfonic acid groups in the molecular chain of the filtration loss reducer begin to decompose when heated, and the molecular side chains are disconnected from the main chain, resulting in partial mass loss of the product. The last stage is after 427.6 °C. In this stage, the main chain and side chains are completely separated, the thermal degradation of the side chains is completed, and the C-C bonds of the main chain also begin to break, and the polymer filtration loss reducer is thermally decomposed as a whole. Generally speaking, the thermal decomposition of the filtration loss reducer starts after 301 °C, indicating its good thermal stability.

[0052] Infrared spectrum determination:

[0053] The filtration reducer for ultra-high temperature water-based drilling fluid prepared in this example was mixed evenly with potassium bromide in a certain proportion and then pressed into thin slices under a pressure of 2 MPa for 5 - 10 minutes. Using an IRTRacer-100 infrared series spectrophotometer, the absorption spectrum in the infrared region was obtained in the wavenumber range of 400 - 4000 cm-1.

[0054] As Figure 2 shown, the sharp peak at a wavelength of 2940 cm -1 is the stretching vibration peak of methylene on the product molecular chain. The peak at a wavelength of 1630 cm -1 is the vibration absorption peak of the C=O bond of the tertiary amino group in N,N-dimethylacrylamide. At a wavelength of 1550 cm -1 and 771 cm -1 , the vibration absorption peaks are caused by the vibration of the pyridine group in the 4-vinylpyridine molecular chain. The peak at a wavelength of 1350 cm -1 is the absorption vibration peak of the C-N bond in N-vinylcaprolactam. The absorption vibration peaks at wavelengths of 1186 cm -1 and 1040 cm -1 are the stretching vibrations of the sulfonic acid group on 2-acrylamido-2-methylpropanesulfonic acid. The peak at 623 cm -1 is the absorption peak of the C-S bond on 2-acrylamido-2-methylpropanesulfonic acid. In addition, the FT-IR results also show that there is no unsaturated bond C=C in the molecular chain, indicating that there are no unreacted monomers in the target product. In summary, the target product in this example has been successfully prepared.

[0055] Example 3

[0056] Based on Example 1, this example provides a filtration reducer for ultra-high temperature water-based drilling fluid, which is polymerized from unsaturated monomers with the following molar ratios: the molar ratio of N,N-dimethylacrylamide, 2-acrylamido-2-methylpropanesulfonic acid, 4-vinylpyridine, and N-vinylcaprolactam is 7:1:1:1.

[0057] The preparation process is the same as that in Example 2.

[0058] Example 4

[0059] Based on Example 1, this example provides a filtration reducer for ultra-high temperature water-based drilling fluid, which is polymerized from unsaturated monomers with the following molar ratios: the molar ratio of N,N-dimethylacrylamide, 2-acrylamido-2-methylpropanesulfonic acid, 4-vinylpyridine, and N-vinylcaprolactam is 5:3:1:1.

[0060] The preparation process is the same as that in Example 2.

[0061] Example 5

[0062] On the basis of Example 1, this example provides a filtration reducer for ultra-high temperature water-based drilling fluid, which is obtained by polymerizing unsaturated monomers with the following molar ratios: the molar ratio of N,N-dimethylacrylamide, 2-acrylamido-2-methylpropanesulfonic acid, 4-vinylpyridine, and N-vinylcaprolactam is 4:4:1:1.

[0063] The preparation process is the same as that of Example 2.

[0064] Example 6

[0065] On the basis of Example 1, this example provides a filtration reducer for ultra-high temperature water-based drilling fluid, which is obtained by polymerizing unsaturated monomers with the following molar ratios: the molar ratio of N,N-dimethylacrylamide, 2-acrylamido-2-methylpropanesulfonic acid, 4-vinylpyridine, and N-vinylcaprolactam is 3:5:1:1.

[0066] The preparation process is the same as that of Example 2.

[0067] Comparative Example

[0068] The molar ratio of unsaturated monomers N,N-dimethylacrylamide, 4-vinylpyridine, and N-vinylcaprolactam is 6:2:2, the total mass is 20 g, and pure water is 80 g. The preparation method is as follows:

[0069] (1) Add 20 g in total of N,N-dimethylacrylamide, 4-vinylpyridine, and N-vinylcaprolactam (molar ratio 6:2:2) to a three-necked flask containing 80 g of pure water;

[0070] (2) Under nitrogen protection and at a stirring speed of 500 rpm, disperse 0.05 g of ammonium persulfate and 0.05 g of sodium bisulfite as initiators in the mixed solution in (2) for 0.5 hour, and heat to 60 °C for free radical polymerization reaction;

[0071] (3) After the free radical polymerization reaction, use an MD44 dialysis bag (molecular cut-off of 8000 - 14000) to purify the product for 24 h, then dry and crush it at 50 °C to obtain the target product.

[0072] Performance Test

[0073] Evaluate the performance of the filtration reducer for ultra-high temperature water-based drilling fluid prepared in Example 2 and the polymer prepared in the comparative example:

[0074] 1. Rheological property test

[0075] Preparation of water-based slurry: Add 400 mL of distilled water to a high-speed stirrer cup, and add 16 g of bentonite and 0.56 g of Na 2 CO 3Stir at high speed for 20 min, stop twice during this period to scrape off the clay adhering to the cup wall, and cure in a sealed container for 24 h.

[0076] Add the filtrate reducer prepared in Example 2 and the polymer of the comparative example to the prepared fresh water base mud at mass concentrations of 0%, 0.5%, 1.0%, 1.5% and 2.0% respectively, and use an SD medium-pressure filtrate loss instrument, a ZNN-D6 rotational viscometer, and a GGS42-2 high-temperature and high-pressure water loss instrument to measure the rheological properties of the drilling fluid before and after aging at 260 °C.

[0077] 2. Filtrate loss performance test

[0078] Add the filtrate reducer prepared in Example 2 to the prepared fresh water base mud at mass concentrations of 0%, 0.5%, 1.0%, 1.5% and 2.0% respectively and mix evenly. For the API low-temperature and low-pressure filtrate loss experiment, under a constant pressure of 100 psi and at an ambient temperature (25 °C), conduct the filtrate loss performance test before and after aging according to the drilling fluid test standard of GB / T 16783-2014.

[0079] 3. Salt resistance performance test

[0080] Add 2.0% of the filtrate reducer prepared in Example 2 to the prepared fresh water base mud. After stirring at high speed for 20 min, add 5%, 10%, 20% and 35% of different concentrations of NaCl respectively, and measure the rheological and filtrate loss properties of the drilling fluid before and after aging. Conduct the determination of the rheological and filtrate loss properties of the drilling fluid according to the standard of GB / T 16783-2014.

[0081] 4. Calcium resistance performance test

[0082] Add 2.0% of the filtrate reducer prepared in Example 2 to the prepared fresh water base mud. After stirring at high speed for 20 min, add 0.5%, 1.0% and 2.0% of different concentrations of calcium chloride respectively, and measure the rheological and filtrate loss properties of the drilling fluid before and after aging.

[0083] 5. High-temperature resistance performance test

[0084] Place the above-prepared drilling fluid in a roller heating furnace and roll and age it at a set high temperature for 16 h, and then conduct the determination of the rheological and filtrate loss properties of the drilling fluid according to the standard of GB / T 16783-2014.

[0085] The experimental results are shown in Table 1:

[0086] Table 1 Influence of filtrate reducer on the performance of water-based drilling fluid

[0087]

[0088] Note: FL HTHPThe experimental temperature is 150°C

[0089] As can be seen from Table 1, as the dosage of the filtrate reducer increases, the apparent viscosity, plastic viscosity and shear force of the drilling fluid all increase. When the concentration of the filtrate reducer is 2.0%, the FLAPI of the drilling fluid before aging at 260°C is only 4.4 mL, the FLAPI after aging is only 6.0 mL, and the FLHTHP is only 24 mL. This indicates that the filtrate reducer still has good filtrate reduction effect even under ultra-high temperature conditions. This is because the filtrate reducer is adsorbed on the surface of clay particles under the action of electrostatic adsorption and hydrogen bonds, forming a spatial network structure of clay particles and product macromolecules. The bridging effect of the molecular chains makes the clay particles not easily coalesce, maintaining a certain degree of dispersion in the drilling fluid, forming fine clay particles, thus forming a dense filter cake and reducing the filtrate loss of the drilling fluid. After high-temperature aging, due to the strong rigidity of the molecular chains of the filtrate reducer, it is not easily degraded at high temperatures. In addition, the amide groups have a strong adsorption effect on clay particles, keeping the clay particles still having a certain degree of dispersion and not easily coalescing even in a high-temperature environment, ensuring the filtrate reduction performance of the filtrate reducer.

[0090] Table 2 Influence of NaCl on the Performance of Water-Based Drilling Fluid Containing Filtrate Reducer

[0091]

[0092] As can be seen from Table 2, as the salt content increases, the viscosity and shear force of the drilling fluid gradually decrease, and the filtrate loss gradually increases. However, when the NaCl content reaches saturation, the FL of the drilling fluid API is only 7.8 mL. This is because the molecular chains of the filtrate reducer are relatively rigid and are not easily desorbed due to salt invasion. At the same time, there are a large number of sulfonic acid groups on the side chains of the molecular chains, with large bond energy and being insensitive to salt and calcium, thus enabling the filtrate reducer to have good temperature resistance and salt tolerance, ensuring the rheological and filtrate loss performance of the water-based drilling fluid.

[0093] Table 3 Influence of CaCl 2 on the Performance of Water-Based Drilling Fluid Containing Filtrate Reducer

[0094]

[0095] As can be seen from Table 3, as the calcium ion concentration increases, the viscosity of the water-based drilling fluid gradually decreases, and the filtrate loss slightly increases. However, when the calcium ion concentration is 20,000 mg / L, the FL of the drilling fluid APIIt is only 6.4 mL, and the FLAPI after aging at 180 °C is 14.4 mL. This is because the molecular chain of the fluid loss reducer can shield the influence of salt and calcium on clay particles, keep the clay particles in a dispersed state without agglomeration, contribute to improving the overall stability of the colloid, reduce the penetration volume in a high-temperature and high-calcium environment, and thus keep the drilling fluid with a low fluid loss volume.

[0096] Table 4 Influence of the fluid loss reducer of the comparative example on the performance of the water-based drilling fluid

[0097]

[0098] Note: The experiment temperature of FL HTHP is 150 °C

[0099] It can be seen from the experimental results in Table 4 that as the dosage of the synthesized fluid loss reducer in the comparative example increases, the viscosity of the drilling fluid increases and the fluid loss volume decreases. However, compared with the fluid loss reducer in Example 1, when its dosage reaches 2%, the fluid loss volumes of the drilling fluid before and after aging are as high as 10.4 and 22.4 mL respectively, and the high-temperature and high-pressure fluid loss volume is as high as 42 mL, and the fluid loss reduction performance is insufficient.

[0100] The above examples are only illustrative of the present invention and do not constitute a limitation on the protection scope of the present invention. Any design identical or similar to the present invention falls within the protection scope of the present invention.

Claims

1. A fluid loss reducer for ultra-high temperature resistant water-based drilling fluid, characterized in that: The unsaturated monomers are obtained by copolymerization reaction. The unsaturated monomers are amide monomers, sulfonic acid monomers, pyridine monomers and N-vinyl caprolactam. The molar ratio of the amide monomers, sulfonic acid monomers, pyridine monomers and N-vinyl caprolactam is 4-8:1-3:1-3:1-3.

2. The ultra-high temperature resistant water-based drilling fluid fluid loss reducer according to claim 1, characterized in that: The amide monomer is acrylamide, N-vinyl-ε-caprolactam, N,N-dimethylacrylamide, N-(4-bromophenyl)prop-2-eneamide, N-allyl p-toluenesulfonamide, 2,2,2-trichloroacetamide allyl ester, prop-2-ene-1-sulfonamide, N-allyl-2-chloroacetamide, N-(allyloxy)-2-nitrobenzenesulfonamide, diene-3-amino-7-oxabicyclo[2.2.1]hept-5-ene-2-carboxylic acid amide or N-(3-allylpyridin-4-yl)pivalamide.

3. The ultra-high temperature resistant water-based drilling fluid fluid loss reducer according to claim 1, characterized in that: The sulfonic acid monomer is 2-acrylamide-2-methylpropanesulfonic acid, sodium vinyl sulfonate, dimethylamine vinylsulfonate, allyl vinylsulfonic acid, styrenesulfonic acid, methacrylic acid or allylsulfonic acid.

4. The ultra-high temperature resistant water-based drilling fluid fluid loss reducer according to claim 1, characterized in that: The pyridine monomer is 4-vinylpyridine, 3-vinylpyridine, 2-vinylpyridine, 2-fluoro-4-vinylpyridine, 3-fluoro-5-vinylpyridine, 3-bromo-5-vinylpyridine, 4-chloro-2-vinylpyridine, 5-bromo-2-vinylpyridine, 6-vinylpyridinecarboxaldehyde, 2-methyl-6-vinylpyridine, 4-methyl-2-vinylpyridine, 2-methyl-5-enylpyridine, 1-(3-sulfopropyl)-2-vinylpyridine hydroxide inner salt or 1-methyl-2-vinylpyridine trifluoromethylsulfonate.

5. The ultra-high temperature resistant water-based drilling fluid fluid loss reducer according to claim 1, characterized in that: The product is obtained by polymerization reaction of unsaturated monomers N,N-dimethylacrylamide, 2-acrylamide-2-methylpropanesulfonic acid, 4-vinylpyridine and N-vinylcaprolactam.

6. The method for preparing a super-high temperature resistant water-based drilling fluid fluid loss reducer according to claim 1, characterized in that: The following steps are involved: Step 1) dissolving a formulated amount of sulfonic acid monomer in water, and adjusting the pH value of the solution to neutral with a NaOH solution to obtain a sulfonic acid monomer solution; Step 2) adding the formulated amounts of amide monomers, pyridine monomers, N-vinyl caprolactam and sulfonic acid monomer solutions into a reaction container filled with water; Step 3) under nitrogen protection and stirring conditions, adding an initiator into a container, and performing a free radical polymerization reaction at 55-65° C. for 2-3 hours; Step 4) After the free radical polymerization reaction is completed, the product is purified using a dialysis bag, dried under vacuum at 45-55° C. for 6-8 hours, and then crushed to obtain the target product; The total mass percentage of amide monomers, sulfonic acid monomer solution, pyridine monomers and N-vinyl caprolactam is 20%, the mass percentage of water is 80%; and the amount of initiator used is 0.05% of the mass of the target product.

7. The method for preparing a super-high temperature resistant water-based drilling fluid fluid loss reducer according to claim 6, characterized in that: The initiator is a mixture of ammonium persulfate and sodium bisulfite, and the mass ratio of the two is 1:

1.

8. Use of the ultra-high temperature resistant water-based drilling fluid fluid loss reducer according to claim 1 in the preparation of water-based drilling fluid.

9. The use of the ultra-high temperature resistant water-based drilling fluid fluid loss reducer according to claim 1 in the preparation of water-based drilling fluid, characterized in that: The mass percentage of the fluid loss reducer is 1-2%.

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