High-temperature-resistant salt-tolerant filtrate reducer for water-based drilling fluid and preparation method of high-temperature-resistant salt-tolerant filtrate reducer

Abstract

The invention discloses a high-temperature-resistant salt-tolerant filtrate reducer for a water-based drilling fluid and a preparation method of the filtrate reducer, and belongs to the technical field of drilling fluids. The high-temperature-resistant salt-tolerant filtrate reducer for the water-based drilling fluid is prepared from the following raw materials in parts by mass: 24-30 parts of acrylamide, 14-20 parts of sodium p-styrenesulfonate, 5-15 parts of lauryl methacrylate, 4-10 parts of dimethyl diallyl ammonium chloride, 2-3 parts of a composite siloxane cross-linking agent, 1-2 parts of an initiator and 100 parts of deionized water. Through the synergistic effect of dynamic disulfide bond crosslinking, zwitterionic charge regulation and control and nanosheet layer physical plugging, compared with the prior art, the improvement range is remarkable, and the comprehensive performance reaches the industry leading level.

Description

Technical Field

[0001] The invention belongs to the technical field of drilling fluids, and in particular relates to a high temperature and salt resistant fluid loss reducer for water-based drilling fluids and a preparation method thereof. Background Art

[0002] As oil and gas exploration and development extend to deep formations, drilling depths continue to increase, and bottom hole temperatures and mineralization levels increase significantly. In high temperature (≥200°C) and high salt (NaCl content ≥30%) environments, fluid loss reducers in drilling fluids face problems such as molecular degradation, curling, and thickening, leading to uncontrolled fluid loss and deterioration of rheological properties, which seriously affect wellbore stability and drilling efficiency.

[0003] In the prior art, although a variety of high temperature and salt resistant fluid loss reducers have been developed, such as Chinese patent CN114773539B discloses a micro-crosslinked hydrophobic association viscosity-enhancing fluid loss reducer, which improves high temperature stability by introducing a composite siloxane crosslinker, this technology does not fully consider the adaptability of the zwitterionic structure to salt ions, resulting in insufficient fluid loss reduction performance under high salt conditions. In addition, Chinese patent CN106046251B adopts a tetrapolymer design, which has certain temperature and salt resistance, but the preparation process is complicated and the cost is high.

[0004] Therefore, developing a fluid loss reducer with excellent temperature and salt resistance, rheological stability and low cost has become a hot topic in current research. Summary of the invention

[0005] In view of the above problems existing in the prior art, the purpose of the present invention is to provide a high temperature and salt resistant fluid loss reducer for water-based drilling fluid and a preparation method thereof, so as to solve the problems that the existing fluid loss reducers are insufficiently stable and have poor fluid loss control effect in high temperature and high salt environments.

[0006] The purpose of the present invention can be achieved through the following technical solutions: A high temperature and salt resistant fluid loss reducer for water-based drilling fluid is prepared from the following raw materials in parts by weight: 24-30 parts of acrylamide; 14-20 parts of sodium styrene sulfonate; 5-15 parts of lauryl methacrylate; 4-10 parts of dimethyldiallylammonium chloride; 2-3 parts of composite siloxane crosslinking agent; 1-2 parts of initiator; 100 parts of deionized water.

[0007] Furthermore, the fluid loss reducer is prepared from the following raw materials in parts by mass: 25 parts of acrylamide; 15 parts of sodium styrene sulfonate; 8 parts of lauryl methacrylate; 7 parts of dimethyldiallylammonium chloride; 3 parts of composite siloxane crosslinking agent; 2 parts of initiator; 100 parts of deionized water.

[0008] Furthermore, the composite siloxane crosslinking agent is prepared by the following steps: Add bis-[3-(triethoxysilyl)propyl]-disulfide and 3-mercaptopropyltrimethoxysilane to an ethanol / water mixed solvent, adjust the pH to 4.5-5.0 with acetic acid, heat the system to 50°C and stir for hydrolysis for 2 hours to obtain a siloxane oligomer, add sodium montmorillonite to the siloxane oligomer, ultrasonically disperse for 30 minutes, heat the system to 70-80°C, slowly dropwise add an ethanol solution of 3-aminophenylboronic acid, react for 3 hours, and then add glycidyl methacrylate, react at 80°C for 4 hours under nitrogen protection, collect the reaction solution and centrifuge, take the precipitate and dry it in vacuo at 60°C, grind it through a 200-mesh sieve to obtain a composite siloxane crosslinker.

[0009] Furthermore, the ethanol / water mixed solvent is prepared by mixing anhydrous ethanol and pure water in a volume ratio of 1:2.

[0010] Furthermore, the ethanol solution of 3-aminophenylboronic acid is prepared by stirring and mixing 3-aminophenylboronic acid and ethanol in a mass ratio of 1:5.

[0011] Furthermore, the mass ratio of the bis-[3-(triethoxysilyl)propyl]-disulfide, 3-mercaptopropyltrimethoxysilane, ethanol / water mixed solvent, sodium montmorillonite, ethanol solution of 3-aminophenylboric acid, and glycidyl methacrylate is 60:40-50:450:100-150:24-30:32-35.

[0012] Furthermore, the initiator is a mixture of ammonium persulfate and sodium bisulfite in a mass ratio of 1:1.

[0013] As a further embodiment of the present invention, a method for preparing a high temperature and salt resistant fluid loss reducer for water-based drilling fluid comprises the following steps: Weigh each raw material according to mass proportion, add deionized water into a reaction container, then add acrylamide, sodium styrene sulfonate, lauryl methacrylate and dimethyldiallylammonium chloride in turn, stir until completely dissolved, add composite siloxane crosslinker, continue stirring for 30 min, adjust the pH value of the system to 7-8 with sodium hydroxide solution, introduce nitrogen for 30 min, exhaust the air and heat to 60-80°C, add initiator, stir and react at constant temperature for 4-7 h, after the reaction is completed, cool to room temperature, and prepare a high temperature and salt resistant fluid loss reducer for water-based drilling fluid.

[0014] Beneficial effects of the present invention: The present invention provides a high temperature and salt resistant fluid loss reducer for water-based drilling fluid. After testing, the fluid loss reducer prepared by the present invention has high temperature resistance, salt resistance, calcium resistance and rheological stability. The analysis with reference to the test data is as follows: The dynamic disulfide cross-linked network significantly reduces the high-temperature and high-pressure filtration loss: the HTHP filtration loss of Example 5 of the present invention (salt water-based slurry) is 24.8 mL, which is 46.3% lower than that of Comparative Example 2 (no cross-linking agent, 46.2 mL), and 35.9% lower than that of Comparative Example 3 (ordinary silane KH-570, 38.7 mL); the HTHP filtration loss of Example 5 of the present invention (calcium water-based slurry) is 40.1 mL, which is 31.2% lower than that of Comparative Example 2 (58.3 mL), and 18.0% lower than that of Comparative Example 4 (unmodified montmorillonite, 48.9 mL).

[0015] Principle analysis: The dynamic disulfide bonds (SS) in the composite siloxane crosslinker prepared by the present invention undergo reversible fracture and recombination at high temperature (230°C). When microcracks are generated in the filter cake due to high temperature stress, the dynamic exchange of disulfide bonds can quickly repair the cracks (HTHP filter loss is reduced by more than 35%), while the integrity of the filter cake is quickly destroyed due to the lack of dynamic bonds of traditional linear crosslinkers (such as KH-570). In addition, the silicon-oxygen bonds (Si-O-Si) in the crosslinker provide a rigid skeleton, inhibiting the high-temperature curling of the molecular chain, and further reducing the filtrate penetration path.

[0016] The synergistic effect of zwitterions achieves ultra-low API filtration loss: the API filtration loss of Example 5 of the present invention (salt water-based slurry) is 2.4 mL, which is 72.4% lower than that of Comparative Example 2 (8.7 mL) and 61.9% lower than that of Comparative Example 3 (6.3 mL); the YP value of Example 5 of the present invention (salt water-based slurry) is 14.0 Pa, which is 169% higher than that of Comparative Example 2 (5.2 Pa) and 86.7% higher than that of Comparative Example 3 (7.5 Pa).

[0017] Principle analysis: The present invention forms a zwitterionic copolymer by introducing four monomers, namely acrylamide (AM), sodium styrene sulfonate (SSS), lauryl methacrylate (LMA) and dimethyldiallylammonium chloride (DMDAAC). AM provides amide groups to enhance thermal stability; SSS introduces sulfonic acid groups to improve salt resistance; the long hydrophobic chain ester structure of LMA improves rheological properties through hydrophobic association; the cationic group of DMDAAC and the anionic group of SSS form an inner salt structure to synergistically enhance salt resistance. Specifically, the inner salt structure of the zwitterionic copolymer (AM / SSS / DMDAAC) of the present invention forms a tight charge pair through electrostatic attraction of cation (DMDAAC)-anion (SSS) to resist the counterion shielding effect in a high-salt environment. In salt water-based slurry, the traditional fluid loss reducer (Comparative Example 3) causes clay particles to desorb due to charge shielding (YP value is only 7.5Pa), while the inner salt structure of the present invention maintains a high dynamic shear force (YP=14.0Pa), indicating that the density of the filter cake is significantly improved. At the same time, the sulfonic acid group (-SO 3 ⁻) has strong hydration capacity and can still be adsorbed on the clay surface under high salt conditions to reduce filtration loss.

[0018] The borate bond enhances the tolerance to calcium ions: the API filtration loss of Example 5 (calcium water-based slurry) of the present invention is 5.2 mL, which is 58.1% lower than that of Comparative Example 2 (12.4 mL) and 39.5% lower than that of Comparative Example 4 (unmodified montmorillonite, 8.6 mL); the YP value of Example 5 (calcium water-based slurry) of the present invention is 9.7 Pa, which is 155% higher than that of Comparative Example 2 (3.8 Pa) and 115% higher than that of Comparative Example 4 (4.5 Pa).

[0019] Principle analysis: The 3-aminophenylboronic acid modified montmorillonite in the composite siloxane crosslinker prepared by the present invention is bonded to Ca via a borate ester bond (BO). 2+ Competitive binding. In a calcium-contaminated environment (1.5% CaCl 2 ) in the conventional fluid loss additive (Comparative Example 4) due to Ca 2+ Bridging leads to polymer flocculation (YP value is only 4.5Pa), while the borate bond of the present invention preferentially combines with clay hydroxyl groups, reducing Ca 2+ The destruction of the polymer network maintains the stability of the filter cake structure (YP = 9.7Pa). At the same time, the intercalation effect of the montmorillonite nanosheets (Example 5) further blocks the Ca 2+ Diffusion, delaying the flocculation process.

[0020] The hydrophobic association and the nanosheet layer synergistically maintain the rheological properties of the drilling fluid: the AV of Example 5 of the present invention (salt water-based slurry) is 38.5 mPa·s, which is 71.1% higher than that of Comparative Example 2 (22.5 mPa·s) and 37.5% higher than that of Comparative Example 3 (28.0 mPa·s); the PV of Example 5 of the present invention (salt water-based slurry) is 24.0 mPa·s, which is 60% higher than that of Comparative Example 2 (15.0 mPa·s) and 41.2% higher than that of Comparative Example 4 (17.0 mPa·s).

[0021] Principle analysis: The hydrophobic long chain (C12) of lauryl methacrylate (LMA) of the present invention forms physical crosslinking points through hydrophobic association, and can still maintain a three-dimensional network (AV=38.5mPa·s) under high temperature and high salt conditions. The montmorillonite nanosheets (Example 5) are embedded in the polymer network, and the plastic viscosity (PV=24.0mPa·s) is increased by the friction resistance between the nanosheet layers. Compared with the unmodified montmorillonite (Comparative Example 4, PV=17.0mPa·s), the surface grafting (GMA) of the modified montmorillonite enhances the interface bonding between the nanosheets and the polymer, avoiding the deterioration of rheology caused by the aggregation of the nanosheets.

[0022] In summary, the present invention has a significant improvement over the prior art through the synergistic effect of dynamic disulfide bond cross-linking, zwitterionic charge regulation and nanosheet physical blocking, and its comprehensive performance has reached the industry-leading level. DETAILED DESCRIPTION

[0023] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0024] Example 1

[0025] Preparation of composite siloxane crosslinker: 60 parts (mass parts, the same below) of bis-[3-(triethoxysilyl)propyl]-disulfide and 40 parts of 3-mercaptopropyltrimethoxysilane were added to 450 parts of ethanol / water mixed solvent (anhydrous ethanol and pure water were mixed in a volume ratio of 1:2), and then the pH was adjusted to 4.5 with acetic acid. The system was heated to 50°C and stirred for hydrolysis for 2 hours to generate siloxane oligomers containing -SH and -SS-. Then 100 parts of sodium montmorillonite were added to the siloxane oligomers, and ultrasonic dispersion (power 300W, 30min) was carried out, and then the temperature was raised to 70°C, and 24 parts of 3-aminophenylboronic acid were slowly added dropwise. An ethanol solution (mass ratio of 3-aminophenylboronic acid to ethanol is 1:5) was added to react for 3 hours, and 3-aminophenylboronic acid was grafted onto the surface of sodium montmorillonite through a thiol-boric ester click reaction. After completion, 32 parts of glycidyl methacrylate were added thereto, and the mixture was reacted at 80°C for 4 hours under nitrogen protection to allow the epoxy group of glycidyl methacrylate to react with the amino group on the surface of sodium montmorillonite to introduce a polymerizable double bond. After completion, the reaction solution was collected and centrifuged (8000rpm, 10min), and the precipitate was vacuum dried at 60°C and ground through a 200-mesh sieve to obtain a composite siloxane crosslinker.

[0026] Example 2

[0027] Preparation of composite siloxane crosslinker: 60 parts (mass parts, the same below) of bis-[3-(triethoxysilyl)propyl]-disulfide and 45 parts of 3-mercaptopropyltrimethoxysilane were added to 450 parts of ethanol / water mixed solvent (anhydrous ethanol and pure water were mixed in a volume ratio of 1:2), and then the pH was adjusted to 5.0 with acetic acid. The system was heated to 50°C and stirred for hydrolysis for 2 hours to generate siloxane oligomers containing -SH and -SS-. Then 120 parts of sodium montmorillonite were added to the siloxane oligomers, and ultrasonic dispersion (power 300W, 30min) was carried out and then the temperature was raised to 75°C, and 30 parts of 3-aminophenylboronic acid were slowly added dropwise. An ethanol solution (mass ratio of 3-aminophenylboronic acid to ethanol is 1:5) was added to react for 3 hours, and 3-aminophenylboronic acid was grafted onto the surface of sodium montmorillonite through a thiol-boric ester click reaction. After completion, 35 parts of glycidyl methacrylate were added thereto, and the mixture was reacted at 80°C for 4 hours under nitrogen protection to allow the epoxy group of glycidyl methacrylate to react with the amino group on the surface of sodium montmorillonite to introduce a polymerizable double bond. After completion, the reaction solution was collected and centrifuged (8000rpm, 10min), and the precipitate was vacuum dried at 60°C and ground through a 200-mesh sieve to obtain a composite siloxane crosslinker.

[0028] Example 3

[0029] Preparation of composite siloxane crosslinker: 60 parts (mass parts, the same below) of bis-[3-(triethoxysilyl)propyl]-disulfide and 50 parts of 3-mercaptopropyltrimethoxysilane were added to 450 parts of ethanol / water mixed solvent (anhydrous ethanol and pure water were mixed in a volume ratio of 1:2), and then the pH was adjusted to 5.0 with acetic acid. The system was heated to 50°C and stirred for hydrolysis for 2 hours to generate siloxane oligomers containing -SH and -SS-. Then 150 parts of sodium montmorillonite were added to the siloxane oligomers, and ultrasonic dispersion (power 300W, 30min) was carried out and then the temperature was raised to 80°C, and 30 parts of 3-aminophenylboronic acid were slowly added dropwise. An ethanol solution (mass ratio of 3-aminophenylboronic acid to ethanol is 1:5) was added to react for 3 hours, and 3-aminophenylboronic acid was grafted onto the surface of sodium montmorillonite through a thiol-boric ester click reaction. After completion, 35 parts of glycidyl methacrylate were added thereto, and the mixture was reacted at 80°C for 4 hours under nitrogen protection to allow the epoxy group of glycidyl methacrylate to react with the amino group on the surface of sodium montmorillonite to introduce a polymerizable double bond. After completion, the reaction solution was collected and centrifuged (8000rpm, 10min), and the precipitate was vacuum dried at 60°C and ground through a 200-mesh sieve to obtain a composite siloxane crosslinker.

[0030] Comparative Example 1 Comparative Example 1 is the control group of Example 2, except that the modification process of the sodium montmorillonite in Example 2 is removed. The specific preparation process of the composite siloxane crosslinking agent is as follows: 60 parts (mass parts, the same below) of bis-[3-(triethoxysilyl)propyl]-disulfide and 45 parts of 3-mercaptopropyltrimethoxysilane were added to 450 parts of an ethanol / water mixed solvent (anhydrous ethanol and pure water were mixed in a volume ratio of 1:2), and the pH was adjusted to 5.0 with acetic acid. The system was heated to 50°C and stirred for hydrolysis for 2 hours to generate a siloxane oligomer containing -SH and -SS-. Then, 120 parts of sodium montmorillonite were added to the siloxane oligomer, and the temperature was raised to 75°C after ultrasonic dispersion (power 300W, 30min), and the reaction was carried out for 3 hours. After completion, the reaction solution was collected and centrifuged (8000rpm, 10min), and the precipitate was vacuum dried at 60°C and ground through a 200-mesh sieve to obtain a composite siloxane crosslinker.

[0031] Example 4

[0032] A high temperature and salt resistant fluid loss reducer for water-based drilling fluid: First, the above-mentioned high temperature and salt resistant fluid loss reducer is prepared from the following raw materials in parts by weight: 24 parts of acrylamide; 14 parts of sodium styrene sulfonate; 5 parts of lauryl methacrylate; 4 parts of dimethyldiallylammonium chloride; 2 parts of the composite siloxane crosslinking agent prepared in Example 1; 1 part of initiator; 100 parts of deionized water; The initiator is a mixture of ammonium persulfate and sodium bisulfite in a mass ratio of 1:1.

[0033] Then, the preparation process of the above-mentioned high temperature and salt resistant fluid loss reducer is as follows: First, weigh each raw material according to the mass fraction, add deionized water into a reaction container, and then add acrylamide, sodium styrene sulfonate, lauryl methacrylate and dimethyldiallylammonium chloride in turn, stir until completely dissolved, add the composite siloxane crosslinker prepared in Example 1, continue stirring for 30 minutes, adjust the pH of the system to 7 with sodium hydroxide solution, pass nitrogen for 30 minutes, exhaust the air and heat to 60°C, add initiator, stir and react at constant temperature for 4 hours, and after the reaction is completed, cool to room temperature to obtain a high temperature and salt-resistant fluid loss reducer for water-based drilling fluid.

[0034] Example 5

[0035] A high temperature and salt resistant fluid loss reducer for water-based drilling fluid: First, the above-mentioned high temperature and salt resistant fluid loss reducer is prepared from the following raw materials in parts by weight: 25 parts of acrylamide; 15 parts of sodium styrene sulfonate; 8 parts of lauryl methacrylate; 7 parts of dimethyldiallylammonium chloride; 3 parts of the composite siloxane crosslinking agent prepared in Example 2; 2 parts of initiator; 100 parts of deionized water; The initiator is a mixture of ammonium persulfate and sodium bisulfite in a mass ratio of 1:1.

[0036] Then, the preparation process of the above-mentioned high temperature and salt resistant fluid loss reducer is as follows: First, weigh each raw material according to the mass fraction, add deionized water into the reaction container, and then add acrylamide, sodium styrene sulfonate, lauryl methacrylate and dimethyldiallylammonium chloride in turn, stir until completely dissolved, add the composite siloxane crosslinker prepared in Example 2, continue stirring for 30 minutes, adjust the pH of the system to 7.5 with sodium hydroxide solution, pass nitrogen for 30 minutes, exhaust the air and heat to 70°C, add initiator, stir and react at constant temperature for 7 hours, and after the reaction is completed, cool to room temperature to obtain a high temperature and salt-resistant fluid loss reducer for water-based drilling fluid.

[0037] Example 6

[0038] A high temperature and salt resistant fluid loss reducer for water-based drilling fluid: First, the above-mentioned high temperature and salt resistant fluid loss reducer is prepared from the following raw materials in parts by weight: 30 parts of acrylamide; 20 parts of sodium styrene sulfonate; 15 parts of lauryl methacrylate; 10 parts of dimethyldiallylammonium chloride; 3 parts of the composite siloxane crosslinking agent prepared in Example 3; 2 parts of initiator; 100 parts of deionized water; The initiator is a mixture of ammonium persulfate and sodium bisulfite in a mass ratio of 1:1.

[0039] Then, the preparation process of the above-mentioned high temperature and salt resistant fluid loss reducer is as follows: First, weigh each raw material according to the mass fraction, add deionized water into the reaction container, and then add acrylamide, sodium styrene sulfonate, lauryl methacrylate and dimethyldiallylammonium chloride in turn, stir until completely dissolved, add the composite siloxane crosslinker prepared in Example 3, continue stirring for 30 minutes, adjust the pH of the system to 8 with sodium hydroxide solution, pass nitrogen for 30 minutes, exhaust the air and heat to 80°C, add initiator, stir and react at constant temperature for 7 hours, and after the reaction is completed, cool to room temperature to obtain a high temperature and salt-resistant fluid loss reducer for water-based drilling fluid.

[0040] Comparative Example 2 Comparative Example 2 is the control group of Example 5, in which the composite siloxane crosslinker prepared in Example 2 in Example 5 is removed, and the remaining raw materials, raw material amounts and preparation steps remain unchanged, and finally a high temperature and salt resistant fluid loss reducer for water-based drilling fluid is obtained.

[0041] Comparative Example 3 Comparative Example 3 is the control group of Example 5, in which the composite siloxane crosslinker prepared in Example 2 in Example 5 is replaced with the silane coupling agent KH-570, and the remaining raw materials, raw material amounts and preparation steps remain unchanged, and finally a high temperature and salt resistant fluid loss reducer for water-based drilling fluid is obtained.

[0042] Comparative Example 4 Comparative Example 4 is the control group of Example 5, in which the composite siloxane crosslinker prepared in Example 2 in Example 5 is replaced by the composite siloxane crosslinker prepared in Comparative Example 1, and the remaining raw materials, raw material amounts and preparation steps remain unchanged, and finally a high temperature and salt-resistant fluid loss reducer for water-based drilling fluid is obtained.

[0043] The performance test of the fluid loss reducers prepared in Examples 4 to 6 and Comparative Examples 2 to 4 was performed. The performance test process is as follows, and the test results are shown in Table 1: (1) Base slurry preparation: Fresh water base slurry: 500mL water + 20g sodium bentonite + 1.0g anhydrous sodium carbonate, stir at high speed for 30min, seal and cure for 24h.

[0044] Salt water base slurry: 500mL fresh water base slurry + 150g NaCl, stir at high speed for 30min, seal and maintain for 24h.

[0045] Calcium water-based slurry: 500mL fresh water-based slurry + 7.5gCaCl 2 , stir at high speed for 30 minutes, and seal and cure for 24 hours.

[0046] (2) Performance test method: API filtration loss: According to GB / T16783.1-2014 standard, the filtration loss reducers prepared in Examples 4 to 6 and Comparative Examples 2 to 4 were added to the brine / calcium water-based slurry at an amount of 3.5%, stirred at high speed for 30 minutes, aged at 230°C for 16 hours, and the API filtration loss was measured using a medium pressure filter loss meter.

[0047] High temperature and high pressure fluid loss (HTHP): Under the conditions of 230℃ and 3.5MPa, a high temperature and high pressure fluid loss instrument is used to measure the fluid loss of the aged base slurry.

[0048] Rheological properties: The apparent viscosity (AV), plastic viscosity (PV) and dynamic shear force (YP) of the aged slurry were measured using a six-speed rotational viscometer.

[0049] Table 1 Test results project API Filtrate Loss (mL) HTHP Filtrate Loss (mL) AV(mPa·s) PV (mPa·s) YP(Pa) Example 4 (Salt Water-Based Slurry) 3.6 30.0 32.0 21.0 11.0 Example 4 (calcium water-based slurry) 6.8 45.2 25.0 18.0 7.0 Example 5 (Salt Water-Based Slurry) 2.4 24.8 38.5 24.0 14.0 Example 5 (calcium water-based slurry) 5.2 40.1 30.2 20.5 9.7 Example 6 (Salt Water-Based Slurry) 3.2 28.5 35.0 22.0 12.5 Example 6 (Calcium water-based slurry) 6.5 43.8 27.8 19.0 8.3 Comparative Example 2 (Salt Water-Based Slurry) 8.7 46.2 22.5 15.0 5.2 Comparative Example 2 (calcium water-based slurry) 12.4 58.3 18.3 12.0 3.8 Comparative Example 3 (Salt Water-Based Slurry) 6.3 38.7 28.0 18.5 7.5 Comparative Example 3 (calcium water-based slurry) 9.8 50.2 22.0 15.5 4.2 Comparative Example 4 (Salt Water-Based Slurry) 5.1 35.4 26.5 17.0 6.8 Comparative Example 4 (calcium water-based slurry) 8.6 48.9 20.5 14.0 4.5 From the data in Table 1, we can get: Example 5 (optimal): Due to the use of a dynamic disulfide crosslinker and pH-responsive montmorillonite, the API filtration loss was the lowest (saltwater-based slurry; 2.4 mL) and the YP value was the highest (saltwater-based slurry; 14.0 Pa), indicating that the filter cake had the best compactness; Comparative Example 2 (without cross-linking agent): The molecular chain has no cross-linking network, and curls up severely at high temperature. The API filtration loss of the salt water-based slurry increases by 262% (8.7 mL), and the YP value of the salt water-based slurry decreases by 63%; Comparative Example 3 (ordinary silane): lacks dynamic self-repairing ability, and the filtration loss of saltwater-based slurry HTHP (38.7 mL) is 56% higher than that of Example 5, proving the key role of disulfide bond reorganization in the integrity of the filter cake; Comparative Example 4 (unmodified montmorillonite): Due to the lack of borate bond clay bonding, the calcium water-based slurry filtration loss (8.6 mL) was 65% higher than that of Example 5 (5.2 mL), verifying the necessity of pH response design.

[0050] Summarize: Dynamic disulfide bonds dominate high temperature stability: The API filtration loss of Comparative Example 2 (without cross-linking agent) is higher than that of Example 5, proving the key role of the cross-linking network in inhibiting the thermal motion of the molecular chain; Borate-pH responsiveness improves calcium resistance: The YP value of Example 5 in calcium water-based slurry (9.7 Pa) is 116% higher than that of Comparative Example 4 (4.5 Pa), indicating that the modified montmorillonite enhances clay bonding through borate bonds; Nanosheets reduce permeability: The HTHP fluid loss of Example 5 (24.8 mL) is 36% lower than that of Comparative Example 3 (38.7 mL).

[0051] It should be noted that, in this article, terms such as "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or equipment that includes a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such process, method, article or equipment.

[0052] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the invention, and the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A high temperature and salt resistant fluid loss reducer for water-based drilling fluid, characterized in that: It is prepared from the following raw materials in parts by weight: 24-30 parts of acrylamide; 14-20 parts of sodium styrene sulfonate; 5-15 parts of lauryl methacrylate; 4-10 parts of dimethyldiallylammonium chloride; 2-3 parts of composite siloxane crosslinking agent; 1-2 parts of initiator; 100 parts of deionized water.

2. The high temperature and salt resistant fluid loss reducer for water-based drilling fluid according to claim 1, characterized in that: The fluid loss reducer is prepared from the following raw materials in parts by mass: 25 parts of acrylamide; 15 parts of sodium styrene sulfonate; 8 parts of lauryl methacrylate; 7 parts of dimethyldiallylammonium chloride; 3 parts of composite siloxane crosslinking agent; 2 parts of initiator; 100 parts of deionized water.

3. The high temperature and salt resistant fluid loss reducer for water-based drilling fluid according to claim 1, characterized in that: The composite siloxane crosslinking agent is prepared by the following steps: Add bis-[3-(triethoxysilyl)propyl]-disulfide and 3-mercaptopropyltrimethoxysilane to an ethanol / water mixed solvent, adjust the pH to 4.5-5.0 with acetic acid, heat the system to 50°C and stir for hydrolysis for 2 hours to obtain a siloxane oligomer, add sodium montmorillonite to the siloxane oligomer, ultrasonically disperse for 30 minutes, heat the system to 70-80°C, slowly dropwise add an ethanol solution of 3-aminophenylboronic acid, react for 3 hours, and then add glycidyl methacrylate, react at 80°C for 4 hours under nitrogen protection, collect the reaction solution and centrifuge, take the precipitate and dry it in vacuo at 60°C, grind it through a 200-mesh sieve to obtain a composite siloxane crosslinker.

4. The high temperature and salt resistant fluid loss reducer for water-based drilling fluid according to claim 3, characterized in that: The ethanol / water mixed solvent is prepared by mixing anhydrous ethanol and pure water in a volume ratio of 1:

2.

5. The high temperature and salt resistant fluid loss reducer for water-based drilling fluid according to claim 3, characterized in that: The ethanol solution of 3-aminophenylboronic acid is prepared by stirring and mixing 3-aminophenylboronic acid and ethanol in a mass ratio of 1:

5.

6. The high temperature and salt resistant fluid loss reducer for water-based drilling fluid according to claim 3, characterized in that: The mass ratio of the bis-[3-(triethoxysilyl)propyl]-disulfide, 3-mercaptopropyltrimethoxysilane, ethanol / water mixed solvent, sodium montmorillonite, ethanol solution of 3-aminophenylboric acid, and glycidyl methacrylate is 60:40-50:450:100-150:24-30:32-35.

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

1.

8. The method for preparing a high temperature and salt resistant fluid loss reducer for water-based drilling fluid according to any one of claims 1 to 7, characterized in that: The following steps are involved: Weigh each raw material according to mass proportion, add deionized water into a reaction container, then add acrylamide, sodium styrene sulfonate, lauryl methacrylate and dimethyldiallylammonium chloride in turn, stir until completely dissolved, add composite siloxane crosslinker, continue stirring for 30 min, adjust the pH value of the system to 7-8 with sodium hydroxide solution, introduce nitrogen for 30 min, exhaust the air and heat to 60-80°C, add initiator, stir and react at constant temperature for 4-7 h, after the reaction is completed, cool to room temperature, and prepare a high temperature and salt resistant fluid loss reducer for water-based drilling fluid.