Water-based drilling fluid and preparation method thereof

Abstract

The invention discloses a water-based drilling fluid and a preparation method thereof, and belongs to the technical field of drilling fluids. The water-based drilling fluid comprises the following raw materials in parts by weight: 100 parts of deionized water, 4-8 parts of bentonite, 1-3 parts of an inhibitor and 1-5 parts of a lubricant, 0.5-5 parts of a filtrate reducer, 5-40 parts of barite powder, 1-5 parts of a blocking agent and 0.5-1 part of sodium hydroxide; the lubricant is prepared by the following steps: reacting 4, 4 '-dihydroxy-3, 3'-diphenyldicarboxylic acid with tri (3-aminopropyl) amine to generate a hyperbranched intermediate, and reacting the hyperbranched intermediate with 1-octadecene. The drilling fluid prepared by the invention is excellent in lubricating property, reduces the abrasion of drilling tools such as drill rods and the like, and has good leaking stoppage performance at the same time.

Description

Technical Field

[0001] The invention relates to the technical field of drilling fluid, and in particular to a water-based drilling fluid and a preparation method thereof. Background Art

[0002] In recent years, with the decreasing reserves of shallow underground oil, the proportion of drilling complex process wells such as large displacement long horizontal section wells, directional wells, cluster wells and ultra-deep wells has continued to increase, and the lubricating performance of lubricants in ordinary water-based drilling fluid systems is difficult to meet the demand. Compared with oil-based drilling fluids, water-based drilling fluids have the advantages of environmental protection and low cost. They are the main drilling fluid system currently and in the future, but their lubricating performance is poor, which seriously restricts their promotion and use in complex structure wells such as large displacement wells and horizontal wells. By adding lubricants to water-based drilling fluids, the lubricating performance of the system can be significantly improved. Lubricant molecules can be adsorbed between the drill bit and the well wall, and between the drill bit and the casing, greatly reducing friction, torque and friction resistance.

[0003] The development of new high-performance water-based drilling fluid lubricants that can meet the requirements of wellbore stability, friction reduction and drag reduction in directional sections, and replace traditional lubricants such as emulsified paraffin, asphalt, diesel, and white oil, has become a key technical requirement for promoting efficient resource development.

[0004] A Chinese invention patent with publication number CN119161275A discloses a lubricant additive and a preparation method, a lubricant, a water-based drilling fluid and a preparation method. The lubricant additive uses a sulfonic acid amine group as an active adsorption group and can be stably adsorbed on a drill string, a casing and a mud cake; at the same time, it has two C16 flexible chains and can form a dense lubricating film to effectively reduce friction resistance, but its lubrication performance is poor. Summary of the invention

[0005] In view of the deficiencies in the prior art, the present invention aims to provide a water-based drilling fluid and a preparation method thereof.

[0006] A water-based drilling fluid comprises the following raw materials in parts by weight: Deionized water: 100 parts, Bentonite: 4-8 parts, Inhibitor: 1-3 parts, Lubricant: 1-5 parts, Fluid loss reducer: 0.5-5 parts, Barite powder: 5-40 parts, Blocking agent: 1-5 parts, Sodium hydroxide: 0.5-1 part; The lubricant is firstly prepared by reacting 4,4'-dihydroxy-3,3'-biphenyldicarboxylic acid and tris(3-aminopropyl)amine to generate a hyperbranched intermediate, which is then reacted with 1-octadecene.

[0007] The lubricant is prepared by the following method: M1: Under nitrogen protection, N-methylpyrrolidone, pyridine, triphenyl phosphite, 4,4'-dihydroxy-3,3'-biphenyldicarboxylic acid and tris(3-aminopropyl)amine were mixed evenly, heated to 100-150°C, reacted for 10-15h, and post-treated to obtain a hyperbranched intermediate; the reaction equation is as follows: It should be noted that the reaction equation for generating a hyperbranched intermediate below is only used to represent the reaction between the functional groups in this step.

[0008]

[0009] M2: Under nitrogen protection, N-methylpyrrolidone, triethylamine, hyperbranched intermediate and 1-octadecene are mixed evenly, heated to 80-90°C, reacted for 6-10 hours, and post-treated to obtain a lubricant; wherein, the amine group of the hyperbranched intermediate and the carbon-carbon double bond of 1-octadecene undergo Michael addition reaction under the catalysis of triethylamine to generate a lubricant.

[0010] In step M1, the molar ratio of pyridine, triphenyl phosphite, 4,4'-dihydroxy-3,3'-biphenyldicarboxylic acid and tris(3-aminopropyl)amine is (4-6):(2-3):1:(1-1.3).

[0011] In step M2, the triethylamine, the hyperbranched intermediate and 1-octadecene are uniformly mixed and fed in a mass ratio of (2-3):10:(5-10).

[0012] The plugging agent is prepared by the following method: N1: Under nitrogen protection, N-methyl-2-pyrrolidone, 10-undecenoic acid, and N, N-carbonyldiimidazole are stirred and mixed uniformly for activation, and then the activated 10-undecenoic acid reacts with 2,2'-bissulfonic acid benzidine to obtain an amide monomer; the reaction equation is as follows:

[0013] N2: Stir and mix deionized water, amide monomer and 2-acrylamide-2-methylpropane sulfonic acid evenly, adjust the pH to neutral with sodium hydroxide solution, add acrylamide, raise the temperature to 60°C, and add ammonium persulfate to react (using 2-acrylamide-2-methylpropane sulfonic acid, acrylamide and amide monomer as monomer free radical polymerization) to obtain a plugging agent.

[0014] The inhibitor is one of white asphalt and polyethylene glycol.

[0015] The fluid loss reducer is one of sodium carboxymethyl cellulose and sulfomethyl phenolic resin.

[0016] A method for preparing a water-based drilling fluid comprises the following steps: S1: Weigh by weight: deionized water: 100 parts; bentonite: 4-8 parts; inhibitor: 1-3 parts; lubricant: 1-5 parts; fluid loss reducer: 0.5-5 parts; barite powder: 5-40 parts; plugging agent: 1-5 parts; sodium hydroxide: 0.5-1 part; S2: Mix deionized water and bentonite to form a uniform base slurry, add inhibitor, lubricant, fluid loss reducer, plugging agent and sodium hydroxide in sequence under stirring, stir thoroughly for 0.5-1h, add barite powder and stir for 20-30min to obtain water-based drilling fluid.

[0017] Due to the adoption of the above technical solution, the beneficial effects of the present invention include: (1) The present invention generates a hyperbranched intermediate by reacting 4,4'-dihydroxy-3,3'-biphenyldicarboxylic acid and tris(3-aminopropyl)amine, and then reacts with 1-octadecene to prepare a lubricant. The hyperbranched structure of the lubricant isolates the drilling tool from the well wall through multi-point adsorption, thereby improving the lubrication effect. In addition, the long carbon chain molecules are densely distributed on the friction surface and extend vertically to form a "molecular brush", further improving the boundary lubrication ability.

[0018] (2) The present invention prepares a plugging agent by reacting 2,2'-disulfonic acid benzidine with 10-undecenoic acid to generate an amide monomer, which is then reacted with acrylamide and 2-acrylamido-2-methylpropanesulfonic acid. The plugging agent utilizes the rigid structure of the benzene ring and the hydration of the sulfonic acid group to improve the high temperature resistance and plugging ability of the plugging agent. DETAILED DESCRIPTION

[0019] The invention will be further described below in conjunction with the embodiments, but the invention is not limited to these embodiments.

[0020] Example 1 Preparation of lubricant M1: Under nitrogen protection, 1000 ml of N-methylpyrrolidone, 4 mol of pyridine, 2 mol of triphenyl phosphite, 1 mol of 4,4'-dihydroxy-3,3'-biphenyldicarboxylic acid and 1 mol of tris(3-aminopropyl)amine were added to the reaction bottle in sequence, stirred and mixed evenly, heated to 100°C, reacted for 15 h, cooled to room temperature, added 500 ml of deionized water to precipitate solids, filtered, washed with 300 ml of deionized water, and dried under vacuum at 50°C for 24 h to obtain a hyperbranched intermediate; M2: Under nitrogen protection, 800 ml of N-methylpyrrolidone, 20 g of triethylamine, 100 g of hyperbranched intermediate and 50 g of 1-octadecene were added to the reaction bottle in sequence, stirred and mixed evenly, heated to 80°C, reacted for 10 h, cooled to room temperature, and the reaction solution was distilled at 70°C under reduced pressure for 3 h. 300 ml of deionized water was added to precipitate the solid, stirred for 30 min, filtered, washed with 300 ml of deionized water, and dried in vacuo at 60°C for 24 h to obtain a lubricant.

[0021] Example 2 Preparation of lubricant M1: Under nitrogen protection, 1000 ml of N-methylpyrrolidone, 5 mol of pyridine, 2.6 mol of triphenyl phosphite, 1 mol of 4,4'-dihydroxy-3,3'-biphenyldicarboxylic acid and 1.2 mol of tris(3-aminopropyl)amine were added to the reaction bottle in sequence, stirred and mixed evenly, heated to 120°C, reacted for 13 h, cooled to room temperature, added 500 ml of deionized water to precipitate solids, filtered, washed with 300 ml of deionized water, and dried under vacuum at 50°C for 24 h to obtain a hyperbranched intermediate; M2: Under nitrogen protection, 800 ml of N-methylpyrrolidone, 25 g of triethylamine, 100 g of hyperbranched intermediate and 80 g of 1-octadecene were added to the reaction bottle in sequence, stirred and mixed evenly, heated to 85°C, reacted for 8 hours, cooled to room temperature, and the reaction solution was distilled at 70°C under reduced pressure for 3 hours. 300 ml of deionized water was added to precipitate the solid, stirred for 30 minutes, filtered, washed with 300 ml of deionized water, and dried in vacuo at 60°C for 24 hours to obtain a lubricant.

[0022] Example 3 Preparation of lubricant M1: Under nitrogen protection, 1000 ml of N-methylpyrrolidone, 6 mol of pyridine, 3 mol of triphenyl phosphite, 1 mol of 4,4'-dihydroxy-3,3'-biphenyldicarboxylic acid and 1.3 mol of tris(3-aminopropyl)amine were added to the reaction bottle in sequence, stirred and mixed evenly, heated to 150°C, reacted for 10 h, cooled to room temperature, added 500 ml of deionized water to precipitate solids, filtered, washed with 300 ml of deionized water, and dried under vacuum at 50°C for 24 h to obtain a hyperbranched intermediate; M2: Under nitrogen protection, 800 ml of N-methylpyrrolidone, 30 g of triethylamine, 100 g of hyperbranched intermediate and 100 g of 1-octadecene were added to the reaction bottle in sequence, stirred and mixed evenly, heated to 90°C, reacted for 6 h, cooled to room temperature, the reaction solution was distilled at 70°C under reduced pressure for 3 h, 300 ml of deionized water was added to precipitate solid, stirred for 30 min, filtered, washed with 300 ml of deionized water, and dried in vacuo at 60°C for 24 h to obtain a lubricant.

[0023] Example 4 Preparation of plugging agent N1: Under nitrogen protection, 1000 ml of N-methyl-2-pyrrolidone, 2 mol of 10-undecenoic acid and 2.5 mol of N,N-carbonyldiimidazole were mixed evenly, stirred and activated for 1.5 h, heated to 50 °C, 1 mol of 2,2'-bissulfonic acid benzidine was added to react for 6 h, cooled to room temperature, 400 ml of deionized water was added to precipitate the solid, filtered, washed with deionized water twice (300 ml each time), and vacuum dried at 60 °C for 24 h to obtain an amide monomer; its hydrogen nuclear magnetic resonance spectrum data are as follows: 1 H NMR (500 MHz, Chloroform-d) δ 10.47 (s, 2H), 9.32 (s, 2H), 8.09 (d, J=2.1 Hz, 2H), 7.93 (d,J=8.2 Hz, 2H), 7.53 (dd, J=8.2, 2.1 Hz, 2H), 5.77 (ddt, J=17.1, 10.3, 6.8 Hz,2H), 5.17-5.10 (m, 2H), 4.99-4.91 (m, 2H), 2.33 (t, J=8.3 Hz, 4H), 2.03 (tdt,J=8.0, 6.8, 1.4 Hz, 4H), 1.74-1.64 (m, 4H), 1.40-1.30 (m, 8H), 1.28 (qt, J=4.0, 2.1 Hz, 12H).

[0024] N2: 800 ml of deionized water, 0.1 mol of amide monomer and 0.4 mol of 2-acrylamido-2-methylpropanesulfonic acid were added to the reaction bottle in sequence, and the mixture was stirred evenly. The pH was adjusted to 7 with 10 wt% sodium hydroxide solution, 1 mol of acrylamide was added, the temperature was raised to 60 °C, and the mixture was stirred for 1 h. 0.05 mol of ammonium persulfate was added, and the mixture was reacted for 3 h. The mixture was cooled to room temperature, and 500 ml of anhydrous ethanol was added dropwise to precipitate crystals. The crystals were filtered and dried under vacuum at 50 °C for 24 h to obtain a plugging agent.

[0025] Example 5 Preparation of water-based drilling fluid S1: Weigh by weight: deionized water: 100 parts; bentonite: 4 parts; white asphalt: 1 part; lubricant (prepared in Example 1): 1 part; sodium carboxymethyl cellulose: 0.5 parts; barite powder: 5 parts; plugging agent (prepared in Example 4): 1 part; sodium hydroxide: 0.5 parts; S2: Deionized water and bentonite are mixed and stirred to form a uniform base slurry. White asphalt, lubricant, sodium carboxymethyl cellulose, plugging agent and sodium hydroxide are added in sequence under stirring. The mixture is fully stirred for 0.5 h. Barite powder is added and stirred for 20 min to obtain an improved anti-collapse drilling fluid.

[0026] Example 6 Preparation of water-based drilling fluid S1: Weigh by weight: deionized water: 100 parts; bentonite: 6 parts; white asphalt: 2 parts; lubricant (prepared in Example 2): 3.6 parts; sulfomethylphenolic resin: 4 parts; barite powder: 32 parts; plugging agent (prepared in Example 4): 4.2 parts; sodium hydroxide: 0.6 parts; S2: Deionized water and bentonite are mixed and stirred to form a uniform base slurry. White asphalt, lubricant, sulfomethyl phenolic resin, plugging agent and sodium hydroxide are added in sequence under stirring. The mixture is stirred for 1 hour. Barite powder is added and stirred for 30 minutes to obtain an improved anti-collapse drilling fluid.

[0027] Example 7 Preparation of water-based drilling fluid S1: Weigh by weight: deionized water: 100 parts; bentonite: 8 parts; polyethylene glycol: 3 parts; lubricant (prepared in Example 3): 5 parts; sulfomethylphenolic resin: 5 parts; barite powder: 40 parts; plugging agent (prepared in Example 4): 5 parts; sodium hydroxide: 1 part; S2: Deionized water and bentonite are mixed and stirred to form a uniform base slurry. Polyethylene glycol, lubricant, sulfomethylphenolic resin, plugging agent and sodium hydroxide are added in sequence under stirring. The mixture is stirred for 1 hour. Barite powder is added and stirred for 30 minutes to obtain an improved anti-collapse drilling fluid.

[0028] Comparative Example 1 The preparation method of the water-based drilling fluid is substantially the same as that of Example 6, except that the lubricant (prepared in Example 2) is replaced with an equal mass of the hyperbranched intermediate (prepared in Example 2).

[0029] Comparative Example 2 The preparation method of the water-based drilling fluid is substantially the same as that of Example 6, except that the lubricant (prepared in Example 2) is replaced with a lubricant of equal mass prepared by the following method: M1: Under nitrogen protection, 1000 ml of N-methylpyrrolidone, 5 mol of pyridine, 2.6 mol of triphenyl phosphite, 1 mol of 4,5-dihydroxyoctanedioic acid and 1.2 mol of tris(3-aminopropyl)amine were added to the reaction bottle in sequence, stirred and mixed evenly, heated to 120°C, reacted for 13 h, cooled to room temperature, added 500 ml of deionized water to precipitate solids, filtered, washed with 300 ml of deionized water, and dried under vacuum at 50°C for 24 h to obtain a hyperbranched intermediate; M2: Under nitrogen protection, 800 ml of N-methylpyrrolidone, 25 g of triethylamine, 100 g of hyperbranched intermediate and 80 g of 1-octadecene were added to the reaction bottle in sequence, stirred and mixed evenly, heated to 85°C, reacted for 8 hours, cooled to room temperature, and the reaction solution was distilled at 70°C under reduced pressure for 3 hours. 300 ml of deionized water was added to precipitate the solid, stirred for 30 minutes, filtered, washed with 300 ml of deionized water, and dried in vacuo at 60°C for 24 hours to obtain a lubricant.

[0030] Comparative Example 3 The preparation method of the water-based drilling fluid is substantially the same as that of Example 6, except that the lubricant (prepared in Example 2) is replaced with a lubricant of equal mass prepared by the following method: M1: Under nitrogen protection, 1000 ml of N-methylpyrrolidone, 5 mol of pyridine, 2.6 mol of triphenyl phosphite, 1 mol of 4,4'-dihydroxy-3,3'-biphenyldicarboxylic acid and 1.2 mol of tris(3-aminopropyl)amine were added to the reaction bottle in sequence, stirred and mixed evenly, heated to 120°C, reacted for 13 h, cooled to room temperature, added 500 ml of deionized water to precipitate solids, filtered, washed with 300 ml of deionized water, and dried under vacuum at 50°C for 24 h to obtain a hyperbranched intermediate; M2: Under nitrogen protection, 800 ml of N-methylpyrrolidone, 25 g of triethylamine, 100 g of hyperbranched intermediate and 80 g of octadecyl acrylate were added to the reaction bottle in sequence, stirred and mixed evenly, heated to 85°C, reacted for 8 hours, cooled to room temperature, and the reaction solution was distilled at 70°C under reduced pressure for 3 hours. 300 ml of deionized water was added to precipitate the solid, stirred for 30 minutes, filtered, washed with 300 ml of deionized water, and dried in vacuo at 60°C for 24 hours to obtain a lubricant.

[0031] Comparative Example 4 The preparation method of the water-based drilling fluid is basically the same as that of Example 6, except that the plugging agent (prepared in Example 4) is replaced with an equal mass of plugging agent prepared by the following method: 800 ml of deionized water, 0.1 mol of N,N-methylenebisacrylamide and 0.4 mol of 2-acrylamido-2-methylpropanesulfonic acid were added to the reaction bottle in sequence, and the mixture was stirred and mixed evenly. The pH was adjusted to 7 with 10 wt% sodium hydroxide solution, 1 mol of acrylamide was added, the temperature was raised to 60 ° C, and the mixture was stirred for 1 h. 0.05 mol of ammonium persulfate was added, and the mixture was reacted for 3 h. The mixture was cooled to room temperature, 500 ml of anhydrous ethanol was added dropwise to precipitate crystals, and the crystals were filtered and dried in a vacuum at 50 ° C for 24 h to obtain a plugging agent.

[0032] Comparative Example 5 The preparation method of the water-based drilling fluid is basically the same as that of Example 6, except that the plugging agent (prepared in Example 4) is replaced with an equal mass of plugging agent prepared by the following method: The preparation method of the plugging agent is substantially the same as that of Example 4, except that the 10-undecenoic acid in step N1 is replaced by an equimolar amount of acrylic acid.

[0033] Comparative Example 6 The preparation method of the water-based drilling fluid is basically the same as that of Example 6, except that the plugging agent (prepared in Example 4) is replaced with an equal mass of plugging agent prepared by the following method: The preparation method of the plugging agent is substantially the same as that of Example 4, except that the 2,2'-bissulfonic acid benzidine in step N1 is replaced by an equal molar amount of 4,4'-diaminobiphenyl.

[0034] The bentonite model used in the examples and comparative examples of the present application is SUPBENT-LD, purchased from Hangzhou Xihe Chemical Co., Ltd.; the model of white asphalt is LATISEAL®, purchased from Shak (Tianjin) Petroleum Technology Service Co., Ltd.; the molecular weight of polyethylene glycol is 20,000; the model of sodium carboxymethyl cellulose is PAC-HV, purchased from Shandong Weifang Lite Composite Materials Co., Ltd.; the model of sulfomethyl phenolic resin is SMP-II, purchased from Henan Jinma Petroleum Technology Co., Ltd.; the model of barite powder is BARITE4.3, purchased from Shak (Tianjin) Petroleum Technology Service Co., Ltd.; the English name of 4,5-dihydroxy-octanedioic acid is 4,5-dihydroxy-octanedioic acid, CAS: 102812-69-1.

[0035] The water-based drilling fluids prepared in Examples 5-7 and Comparative Examples 1-6 of the present application were subjected to an aging test: the drilling fluids were placed in a roller heating furnace and aged at 180° C. for 16 hours, and then taken out and cooled to room temperature.

[0036] The water-based drilling fluids prepared in Examples 5-7 of the present application and Comparative Examples 1-6 and the aged water-based drilling fluids were tested for lubrication coefficient according to the SY / T 6094-1994 drilling fluid lubricant evaluation procedure (torque arm applies 150 psi pressure, and the rotation speed is maintained at 60 r / min). The experimental results were compared with the lubrication coefficient of the drilling fluid without adding lubricant to obtain the lubrication coefficient reduction rate. The test results are shown in Table 1.

[0037] The improved anti-collapse drilling fluids prepared in Examples 5-7 and Comparative Examples 1-6 of the present application were tested for filtration loss (FL) according to GB / T 16783.1-2006. API / ml), high temperature and high pressure filtration loss (FL HTHP / ml, 200℃×16h) test, the test results are shown in Table 1.

[0038] Table 1 Performance test data table

[0039] It can be seen from the data of Examples 5, 6 and 7 in Table 1 that the water-based drilling fluid prepared in the present invention has excellent lubrication and plugging properties.

[0040] The lubricant prepared in the present application is a hyperbranched lubricant with a long-chain alkyl group, the molecular chain of which is relatively long, the intermolecular van der Waals force is relatively strong, and it is easy to form a tightly arranged lubricating film, which is adsorbed on the friction surface through the polar end group, thereby reducing the friction coefficient. Under the action of shear force, the long-chain molecules of the lubricant tend to be arranged in parallel to form a layered structure, and the molecular layers slide through weak interaction forces, significantly reducing the friction coefficient. The entanglement between long-chain alkyl molecules can enhance the viscosity of the lubricant, and a thicker oil film can be formed under high pressure (fluid dynamic lubrication effect), avoiding metal contact under boundary lubrication conditions. In addition, the long-chain structure has a high thermal stability, is not easy to break or oxidatively decompose at high temperatures, and can maintain the continuity of the lubricating film. However, the lubricant of Comparative Example 1 does not introduce a long-chain alkyl group, so the lubrication performance is relatively low.

[0041] The lubricant used in Comparative Example 2 is a lubricant synthesized by replacing 4,4'-dihydroxy-3,3'-biphenyl dicarboxylic acid with 4,5-dihydroxyoctanedioic acid, and its lubricating performance and lubricating performance after high temperature aging are relatively poor. The benzene ring in the lubricant used in this application has a conjugated effect, which can enhance the acidity of the hydroxyl group and make it easy to dissociate H + Negatively charged active sites are formed to enhance the adsorption capacity, and the benzene ring structure imparts high thermal stability, maintaining adsorption performance at high temperatures. However, the hydroxyl group in 4,5-dihydroxyoctanedioic acid used in Comparative Example 2 is easily decomposed by heat, and the adsorption capacity decreases significantly with increasing temperature, thereby affecting its lubrication performance.

[0042] The lubricant used in Comparative Example 3 is octadecyl acrylate instead of 1-octadecene synthetic lubricant. The ester group in octadecyl acrylate is prone to hydrolysis or oxidation reaction under high temperature conditions, which destroys the integrity of the lubricating film and affects the lubrication effect.

[0043] The benzene ring in the plugging agent prepared in the present application can enhance the pressure bearing strength of the plugging agent as a rigid structure and improve its high temperature resistance. The sulfonic acid group on the benzene ring can absorb water and swell, and can adapt to the size and shape of the formation through deformation, thereby enhancing the plugging ability; the introduction of long-chain alkyl groups increases the flexibility of the plugging agent, plugs leakage channels of different shapes, thereby reducing leakage; the amide monomer has two double bonds, and the plugging agent obtained after its participation in polymerization can form a network structure rather than a linear structure. The network structure can provide a certain elasticity, so that it can adapt to the deformation and pressure changes of the formation, and dynamically adjust the integrity of the plugging layer, thereby maintaining efficient plugging performance in complex formations; the introduction of acrylamide enhances its adsorption capacity and improves its binding force with clay particles; the introduction of 2-acrylamide-2-methylpropanesulfonic acid further enhances its hydration effect and improves its plugging effect on pores and cracks.

[0044] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. However, any equivalent changes, modifications and evolutions made by ordinary technicians in the field without departing from the scope of the technical solution of the present invention by using the technical content disclosed above are all equivalent embodiments of the present invention. At the same time, any equivalent changes, modifications and evolutions made to the above embodiments based on the essential technology of the present invention are still within the protection scope of the technical solution of the present invention.

Claims

1. A water-based drilling fluid, characterized in that: The invention comprises the following raw materials in parts by weight: Deionized water: 100 parts, Bentonite: 4-8 parts, Inhibitor: 1-3 parts, Lubricant: 1-5 parts, Fluid loss reducer: 0.5-5 parts, Barite powder: 5-40 parts, Blocking agent: 1-5 parts, Sodium hydroxide: 0.5-1 part; The lubricant is firstly prepared by reacting 4,4'-dihydroxy-3,3'-biphenyldicarboxylic acid and tris(3-aminopropyl)amine to generate a hyperbranched intermediate, which is then reacted with 1-octadecene.

2. A water-based drilling fluid according to claim 1, characterized in that: The lubricant is prepared by the following method: M1: Under nitrogen protection, N-methylpyrrolidone, pyridine, triphenyl phosphite, 4,4'-dihydroxy-3,3'-biphenyldicarboxylic acid and tris(3-aminopropyl)amine were mixed uniformly, heated to 100-150°C, reacted for 10-15h, and post-treated to obtain a hyperbranched intermediate; M2: Under nitrogen protection, N-methylpyrrolidone, triethylamine, hyperbranched intermediate and 1-octadecene are mixed uniformly, heated to 80-90°C, reacted for 6-10 hours, and post-treated to obtain a lubricant.

3. A water-based drilling fluid according to claim 2, characterized in that: In step M1, the molar ratio of pyridine, triphenyl phosphite, 4,4'-dihydroxy-3,3'-biphenyldicarboxylic acid and tris(3-aminopropyl)amine is (4-6):(2-3):1:(1-1.3).

4. A water-based drilling fluid according to claim 2, characterized in that: In step M2, the triethylamine, the hyperbranched intermediate and 1-octadecene are uniformly mixed and fed in a mass ratio of (2-3):10:(5-10).

5. The water-based drilling fluid according to claim 1, characterized in that: The plugging agent is prepared by the following method: N1: Under nitrogen protection, N-methyl-2-pyrrolidone, 10-undecenoic acid, and N, N-carbonyldiimidazole are stirred and mixed uniformly for activation, and then the activated 10-undecenoic acid is reacted with 2,2'-bissulfonic acid benzidine to obtain an amide monomer; N2: Deionized water, amide monomer, and 2-acrylamide-2-methylpropanesulfonic acid are stirred and mixed evenly, the pH is adjusted to neutral with sodium hydroxide solution, acrylamide is added, the temperature is raised to 60° C., and ammonium persulfate is added to react to obtain a plugging agent.

6. A water-based drilling fluid according to claim 1, characterized in that: The inhibitor is one of white asphalt and polyethylene glycol.

7. A water-based drilling fluid according to claim 1, characterized in that: The fluid loss reducer is one of sodium carboxymethyl cellulose and sulfomethyl phenolic resin.

8. A method for preparing a water-based drilling fluid according to any one of claims 1 to 7, characterized in that: The following steps are involved: S1: Weigh by weight: deionized water: 100 parts, bentonite: 4-8 parts, inhibitor: 1-3 parts, lubricant: 1-5 parts, fluid loss reducer: 0.5-5 parts, barite powder: 5-40 parts, plugging agent: 1-5 parts, sodium hydroxide: 0.5-1 parts; S2: Mix deionized water and bentonite to form a uniform base slurry, add inhibitor, lubricant, fluid loss reducer, plugging agent and sodium hydroxide in sequence under stirring, stir thoroughly for 0.5-1h, add barite powder and stir for 20-30min to obtain water-based drilling fluid.

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