Chitosan-molybdenum disulfide nanometer plugging agent and water-based drilling fluid

Abstract

The application relates to the field of oil field chemistry and discloses a chitosan-molybdenum disulfide nano plugging agent and a water-based drilling fluid, wherein the plugging agent used in the water-based drilling fluid is the chitosan-molybdenum disulfide nano plugging agent, the synthesis raw materials of the chitosan-molybdenum disulfide nano plugging agent include molybdenum disulfide and chitosan; and the water-based drilling fluid contains the chitosan-molybdenum disulfide nano plugging agent. The chitosan-molybdenum disulfide nano plugging agent has a particle size distribution of about 226-452 nm, can effectively plug the micro-nano size pores in a shale well wall, and can effectively stabilize the well wall and prevent collapse. The water-based drilling fluid has good performances in terms of rheological property, stability and plugging property under shale formation conditions.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of oil and gas drilling technology, and particularly relates to a chitosan-molybdenum disulfide nanometer plugging agent and a water-based drilling fluid containing the nanometer plugging agent. BACKGROUND

[0002] In the process of shale gas horizontal well drilling, the problem of wellbore instability has always been a technical problem in the field of oil drilling. Due to the development of shale formation fractures and strong water sensitivity, the filtration of drilling fluid may cause the hydration swelling of shale micro-pores and micro-nano cracks, and further cause complex problems such as wellbore collapse and lost circulation. Therefore, how to effectively inhibit the hydration swelling of shale clay, plug the formation cracks, prevent the drilling fluid or filtrate from entering the formation, and thus reduce the influence of hydration effect and capillary force on the shale wellbore, is the focus and difficulty of current drilling fluid research.

[0003] At present, oil-based drilling fluid and conventional plugging agents are generally used in shale gas wells at home and abroad to deal with the problem of wellbore instability. Oil-based drilling fluid can improve the wellbore stability and reduce the risk of wellbore collapse by increasing the capillary pressure of water-wet shale and preventing the invasion of drilling fluid into shale. In addition, oil-based drilling fluid also has obvious advantages in lubrication, anti-sticking and drag reduction, especially in the process of sliding drilling, which can reduce friction and improve drilling efficiency. However, oil-based drilling fluid also has the problems of reservoir pollution and permeability reduction, especially in low permeability oil and gas reservoirs, oil-based drilling fluid may change the wettability of the reservoir, resulting in a decrease in productivity. At the same time, the size of shale fractures is usually between microns and nanometers, and the particle size of conventional plugging agents is relatively large, which makes it difficult to effectively plug micro-nano cracks, resulting in the failure of fluid penetration channels to be completely blocked.

[0004] In view of these problems, a kind of high-efficiency plugging agent with nanometer size is developed, which can realize deep plugging of shale fractures in the water-based drilling fluid system, which is the key to solving the problem of wellbore stability in shale drilling. In recent years, nanometer plugging agents based on molybdenum disulfide have gradually attracted attention. Molybdenum disulfide has a layered structure, excellent lubricity, strong plugging ability and high temperature and high pressure resistance, and can form a dense nanometer barrier in the drilling fluid system to effectively plug micro-nano cracks. However, pure molybdenum disulfide nanomaterials have poor dispersibility in drilling fluid, making it difficult to achieve stable plugging.

[0005] In order to improve the dispersibility and plugging performance of molybdenum disulfide, the application provides a chitosan modified molybdenum disulfide nano plugging agent. Chitosan is a biodegradable amphoteric polymer, which has functional groups such as hydroxyl, amino or sulfonic acid groups on the surface, can improve the water solubility and dispersion stability of molybdenum disulfide nanosheet, and at the same time, enhance the plugging ability to the formation fracture. In addition, through the planetary ball milling method combined with ultrasonic stripping technology, the uniform stripping of molybdenum disulfide can be realized, and through the chemical modification of chitosan, the adaptability of molybdenum disulfide in water-based drilling fluid can be further optimized. The plugging agent can not only effectively reduce the filtration effect of the drilling fluid and reduce the hydration swelling of shale, but also improve the rheological stability and anti-pollution ability of the drilling fluid, so as to provide a safer and more efficient water-based drilling fluid system for shale drilling.

[0006] The chitosan molybdenum disulfide nano plugging agent prepared by the application can be compatible with the water-based drilling fluid system, and the optimized nano plugging structure can realize more efficient micro-nano fracture plugging, reduce the damage of the drilling fluid to the reservoir, and replace part of the application demand of the oil-based drilling fluid. Therefore, developing a nano plugging agent based on chitosan molybdenum disulfide and applying it to a high-performance water-based drilling fluid to improve the wellbore stability and reduce the reservoir pollution is a key technical breakthrough direction in the field of shale gas drilling. SUMMARY

[0007] In view of the problem that the conventional plugging agent cannot effectively plug the micro-nano cracks in the shale, which leads to the instability of the wellbore, the application provides a chitosan molybdenum disulfide nano plugging agent, which has a nano particle size and can effectively plug the micron and nano cracks, preventing the drilling fluid and filtrate from entering the formation, thereby improving the wellbore stability. At the same time, a nano plugging water-based drilling fluid suitable for shale formation is developed to replace the oil-based drilling fluid, solving the key problems of wellbore instability and reservoir pollution.

[0008] To achieve the above-mentioned purposes, the technical solutions provided by the application are as follows: the application provides a chitosan molybdenum disulfide nano plugging agent, which is prepared by using molybdenum disulfide, chitosan and grinding aid as main raw materials through the planetary ball milling method combined with ultrasonic stripping treatment. The specific preparation steps are as follows:

[0009] S1, ball milling and stripping: the molybdenum disulfide raw powder, chitosan, grinding aid and ball milling medium are loaded into a agate jar according to a specific ratio (1:(1.5-3.5):(0.3-0.8):(90-110)), and after sealing, it is installed into a planetary ball mill, and the ball milling time is set to 12-24h, and the rotating speed is set to 300-600r / min, and mechanical stripping is carried out.

[0010] S2, ultrasonic dispersion and centrifugation: after the ball milling is completed, the obtained powder is ultrasonically treated for 1-2h (power 300W), and is fully dispersed in deionized water, and then high-speed centrifugation is carried out, and the three-fourth upper clear liquid is collected.

[0011] S3, purification and drying: the obtained supernatant is filtered by a filter membrane to remove excess ball milling aids, and finally the solid product is collected and dried at 60-70 DEG C under vacuum for 12-36h to obtain the chitosan molybdenum disulfide nanometer plugging agent.

[0012] The chitosan is one of carboxymethyl chitosan, sulfonated chitosan and quaternized chitosan; the ball milling aid is graphene; and the ball milling medium is one of agate beads, silicon carbide beads and zirconia beads.

[0013] The chitosan molybdenum disulfide nanometer plugging agent has the following characteristics:

[0014] Small particle size and strong plugging capacity: the double process of planetary ball milling and ultrasonic stripping reduces the thickness of molybdenum disulfide nanometer sheet, improves the nanometer plugging capacity, and can deeply plug micron and nanometer cracks.

[0015] Surface modification and good dispersion stability: the introduction of chitosan improves the dispersion of molybdenum disulfide nanometer sheet in a water-based system, and enhances the interaction with the well wall, thereby improving the plugging performance.

[0016] High plugging efficiency and hydration inhibition: the plugging agent can form a dense nanometer barrier in the shale cracks, reduce the risk of drilling fluid invasion into the formation, inhibit the hydration of shale, and stabilize the well wall.

[0017] Another object of the present application is to provide a water-based drilling fluid system, wherein the drilling fluid is added with the chitosan molybdenum disulfide nanometer plugging agent.

[0018] The drilling fluid is composed of the following components in parts by weight: 100 parts by weight of water, 4-7 parts by weight of bentonite, 0.3-0.6 parts by weight of sodium carbonate, 0.6-1.2 parts by weight of flow regulator, 6-10 parts by weight of filtrate reducer, 3-7 parts by weight of lubricant, 2-4 parts by weight of inhibitor, 0.5-0.7 parts by weight of pH regulator, 250-320 parts by weight of weighting agent, and 1-3 parts by weight of chitosan molybdenum disulfide nanometer plugging agent.

[0019] The bentonite is sodium-based bentonite, the flow regulator is carboxymethyl cellulose, the filtrate reducer is sulfonated asphalt, the lubricant is graphite, the inhibitor is polyamine, the pH regulator is sodium hydroxide, and the weighting agent is API barite.

[0020] The pH of the water-based drilling fluid of the present application is 8-10, and the density is 1.15-1.45 g / cm 3 .

[0021] The technical advantages of the present application: the particle size distribution of the chitosan molybdenum disulfide nano plugging agent is between 226-452nm, which can plug nanoscale cracks, reduce drilling fluid invasion and reduce the risk of hydration expansion; the pH range of the drilling fluid is 8-10, and the density can be adjusted to 1.15-1.45g / cm 3 The present application can be applied to different types of shale gas layers, and provides a chitosan molybdenum disulfide-based nano plugging agent and its application in water-based drilling fluid. The plugging agent has excellent performance in micro-nano crack plugging, wellbore stability and reservoir protection, and can be widely applied in the field of shale gas drilling, improve drilling efficiency, reduce the risk of wellbore instability, and has broad application prospects. DETAILED DESCRIPTION

[0022] The endpoints of the ranges and any values disclosed herein are not limited to the precise values recited as the exact dimensions are not considered critical for the present application. The endpoints of the ranges and the individual values are not to be understood as limited to the precise values recited as the exact dimensions are not considered critical for the present application. The ranges disclosed herein are understood to include all values from and between the recited ranges.

[0023] The specific embodiments of the present application are described in detail below, and it should be understood that the specific embodiments described herein are only used to illustrate and explain the present application, and are not used to limit the present application.

[0024] Preparation Example 1: 1. Preparation of chitosan molybdenum disulfide nano plugging agent: 1 part by weight of molybdenum disulfide raw powder, 2 parts by weight of carboxymethyl chitosan, 0.5 parts by weight of graphene and 100 parts by weight of agate beads are loaded into an agate jar; the agate jar is sealed and installed on a planetary ball mill, the ball milling time is set to 16h and the rotation speed is set to 450r / min, and the planetary ball mill is started; after the end, the powder is ultrasonically treated at 300W for 1.5h to make it fully dispersed in deionized water, the upper clear liquid is taken after centrifugation, and after filtration, it is dried at 65℃ for 24h to obtain a chitosan molybdenum disulfide nano plugging agent (denoted as S1).

[0025] 2. Preparation of water-based drilling fluid: 100 parts by weight of tap water and 5.5 parts by weight of bentonite are stirred at a stirring rate of 1000 r / min for 60 min, then 0.4 parts by weight of sodium carbonate is stirred at a stirring rate of 2000 r / min for 20 min, and then left to stand for 24 h, then 0.9 parts by weight of flow regulator is added and stirred at a stirring rate of 2000 r / min for 30 min, then 8 parts by weight of filtrate reducer is added and stirred at a stirring rate of 2000 r / min for 20 min, then 5 parts by weight of lubricant is added and stirred at a stirring rate of 2000 r / min for 10 min, then 3 parts by weight of inhibitor is added and stirred at a stirring rate of 1000 r / min for 10 min, then 0.6 parts by weight of pH regulator is added and stirred at a stirring rate of 2000 r / min for 10 min, then 280 parts by weight of pH weighting agent is added and stirred at a stirring rate of 2000 r / min for 30 min, then 2 parts by weight of chitosan molybdenum disulfide nano plugging agent S1 is added and stirred at a stirring rate of 2000 r / min for 30 min, to obtain a high-performance plugging and anti-sloughing water-based drilling fluid (denoted as F1), the pH of the drilling fluid is 9, the density is 1.30 g / cm 3 .

[0026] Preparation Example 2: 1. Preparation of chitosan molybdenum disulfide nano plugging agent: 1 part by weight of molybdenum disulfide raw powder, 1.5 parts by weight of carboxymethyl chitosan, 0.3 parts by weight of graphene and 90 parts by weight of agate beads are loaded into an agate jar; the agate jar is sealed and installed on a planetary ball mill, the ball milling time is set to 12 h and the rotation speed is set to 300 r / min, and the planetary ball mill is started; after the end, the powder is ultrasonically treated at 300 W for 1 h to make it fully dispersed in deionized water, the upper clear liquid is taken after centrifugation, and after filtration, it is dried at 60°C for 12 h to obtain a chitosan molybdenum disulfide nano plugging agent (denoted as S2).

[0027] 2. Preparation of water-based drilling fluid: 100 parts by weight of tap water was stirred with 4 parts by weight of bentonite at a stirring rate of 1000 r / min for 60 min, then 0.3 parts by weight of sodium carbonate was stirred at a stirring rate of 2000 r / min for 20 min and then left to stand for 24 h, then 0.6 parts by weight of flow regulator was added and stirred at a stirring rate of 2000 r / min for 30 min, then 6 parts by weight of filtrate reducer was added and stirred at a stirring rate of 2000 r / min for 20 min, then 3 parts by weight of lubricant was added and stirred at a stirring rate of 2000 r / min for 10 min, then 2 parts by weight of inhibitor was added and stirred at a stirring rate of 1000 r / min for 10 min, then 0.5 parts by weight of pH regulator was added and stirred at a stirring rate of 2000 r / min for 10 min, then 250 parts by weight of pH weighting agent was added and stirred at a stirring rate of 2000 r / min for 30 min, then 1 part by weight of chitosan molybdenum disulfide nano plugging agent S2 was added and stirred at a stirring rate of 2000 r / min for 30 min, to obtain a high-performance plugging and anti-sloughing water-based drilling fluid (denoted as F2), the pH of the drilling fluid is 8, the density is 1.15 g / cm 3 .

[0028] Preparation Example 3: 1. Preparation of chitosan molybdenum disulfide nano plugging agent: 1 part by weight of molybdenum disulfide raw powder, 3.5 parts by weight of carboxymethyl chitosan, 0.8 parts by weight of graphene and 110 parts by weight of agate beads were loaded into an agate jar; the agate jar was sealed and installed on a planetary ball mill, the ball milling time was set to 24 h and the rotation speed was set to 450 r / min, and the planetary ball mill was started; after the end, the powder was ultrasonically treated at 300 W for 2 h to make it fully dispersed in deionized water, the upper clear liquid was taken after centrifugation, and after filtration, it was dried at 70°C for 36 h to obtain a chitosan molybdenum disulfide nano plugging agent (denoted as S3).

[0029] 2. Preparation of water-based drilling fluid: 100 parts by weight of tap water was stirred with 7 parts by weight of bentonite at a stirring rate of 1000 r / min for 60 min, then 0.6 parts by weight of sodium carbonate was stirred at a stirring rate of 2000 r / min for 20 min and then left to stand for 24 h, then 1.2 parts by weight of flow regulator was added and stirred at a stirring rate of 2000 r / min for 30 min, then 10 parts by weight of filtrate reducer was added and stirred at a stirring rate of 2000 r / min for 20 min, then 7 parts by weight of lubricant was added and stirred at a stirring rate of 2000 r / min for 10 min, then 4 parts by weight of inhibitor was added and stirred at a stirring rate of 1000 r / min for 10 min, then 0.7 parts by weight of pH regulator was added and stirred at a stirring rate of 2000 r / min for 10 min, then 320 parts by weight of pH weighting agent was added and stirred at a stirring rate of 2000 r / min for 30 min, then 3 parts by weight of chitosan molybdenum disulfide nano plugging agent S3 was added and stirred at a stirring rate of 2000 r / min for 30 min, to obtain a high-performance plugging and anti-sloughing water-based drilling fluid (denoted as F3), the pH of the drilling fluid is 10, the density is 1.45 g / cm 3 .

[0030] Comparative Example 1: 1. Preparation of chitosan molybdenum disulfide nano plugging agent: 1 part by weight of molybdenum disulfide raw powder, 1 part by weight of carboxymethyl chitosan, 0.1 part by weight of graphene and 50 parts by weight of agate beads were loaded into an agate jar; the agate jar was sealed and installed on a planetary ball mill, the ball milling time was set to 6 h and the rotation speed was set to 100 r / min, and the planetary ball mill was started; after the end, the powder was ultrasonically treated at 300 W for 0.5 h to make it fully dispersed in deionized water, the upper clear liquid was taken after centrifugation, and after filtration, it was dried at 50°C for 6 h to obtain a chitosan molybdenum disulfide nano plugging agent (denoted as D1).

[0031] 2. Preparation of water-based drilling fluid: prepared according to the method of Preparation Example 1, the difference is that 2 parts by weight of chitosan molybdenum disulfide nano plugging agent D1 (denoted as DF1, respectively) is added.

[0032] Comparative Example 2: 1. Preparation of chitosan molybdenum disulfide nano plugging agent: prepared according to the method of Example 1.

[0033] 2. Preparation of water-based drilling fluid: 100 parts by weight of tap water was stirred with 8 parts by weight of bentonite at a stirring rate of 1000 r / min for 60 min, then 0.8 parts by weight of sodium carbonate was stirred at a stirring rate of 2000 r / min for 20 min and then left to stand for 24 h, then 1.5 parts by weight of flow regulator was added and stirred at a stirring rate of 2000 r / min for 30 min, then 12 parts by weight of filtrate reducer was added and stirred at a stirring rate of 2000 r / min for 20 min, then 8 parts by weight of lubricant was added and stirred at a stirring rate of 2000 r / min for 10 min, then 5 parts by weight of inhibitor was added and stirred at a stirring rate of 1000 r / min for 10 min, then 0.9 parts by weight of pH regulator was added and stirred at a stirring rate of 2000 r / min for 10 min, then 350 parts by weight of pH weighting agent was added and stirred at a stirring rate of 2000 r / min for 30 min, then 2 parts by weight of chitosan molybdenum disulfide nano plugging agent S1 was added and stirred at a stirring rate of 2000 r / min for 30 min, to obtain a high-performance plugging and anti-sloughing water-based drilling fluid (denoted as DF2).

[0034] 1. Basic performance test of water-based drilling fluid.

[0035] The water-based drilling fluids F1-F3 prepared in Preparation Examples 1-3 and the water-based drilling fluids DF1, DF2 prepared in Comparative Examples 1, 2 were subjected to basic performance test of drilling fluid, and the results are shown in Table 1.

[0036] The apparent viscosity (AV, mPa·s), plastic viscosity (PV, mPa·s) and dynamic shear force (YP, Pa) were measured by a six-speed rotational viscometer according to the method specified in GB / T29170-2012; the high temperature and high pressure filtration loss (HTHP, mL) was measured by a high temperature and high pressure filtration instrument according to the method specified in GB / T29170-2012; and the medium pressure filtration loss (API, mL) was measured by a medium pressure filtration instrument according to the method specified in GB / T29170-2012.

[0037] The instruments used were: the manufacturer of the six-speed rotational viscometer was Qingdao Chuangmei Instrument Co., Ltd., model 1100; the manufacturer of the medium pressure filtration instrument was Qingdao Chuangmei Instrument Co., Ltd., model 1202; and the manufacturer of the high temperature and high pressure filtration instrument was Qingdao Chuangmei Instrument Co., Ltd., model GGS42-2.

[0038] Table 1: Basic performance test table of water-based drilling fluid;

[0039]

[0040] From the water-based drilling fluid basic performance test table in Table 1, the YP / PV values of the chitosan molybdenum disulfide nano plugging agent (F1, F2, F3) in the water-based drilling fluid are 0.39, 0.35 and 0.38 respectively, indicating that it has good shear thinning characteristics, so that the drilling fluid can maintain stable rheological properties under different shear rates; in comparison, the dynamic plastic ratio of the drilling fluid DF2 of the comparative example is only 0.17, far below the normal range, indicating that it has poor shear thinning ability, which may lead to reduced fluidity of the drilling fluid under high shear rate, affecting the rock carrying capacity. Although the dynamic plastic ratio (0.42) of DF1 is within the normal range, its API filtration loss (8.6 mL) and HTHP filtration loss (16.2 mL) are significantly higher than those of F1-F3, indicating that it has poor plugging performance and is prone to cause drilling fluid invasion into the formation; in summary, the chitosan molybdenum disulfide plugging agent of the application optimizes the plugging effect while ensuring good shear thinning performance of the drilling fluid, improves the wellbore stability, and is suitable for drilling operations in complex formations and high temperature and high pressure environments.

[0041] 2. Plugging performance test of chitosan molybdenum disulfide nano plugging agent.

[0042] In this experiment, the outcrop core was used to simulate the permeability of the nano fracture in the formation, the average flow rate of the fluid in the core was measured, and the permeability of the core was calculated according to Darcy's law to evaluate the plugging performance of the chitosan molybdenum disulfide nano plugging agent. In the experiment, the initial permeability was determined by clear water, then different plugging agents were added in the clear water, and the permeability after plugging was measured. The permeability formula is: K=QμL / (AΔP), and the plugging rate formula is: (initial permeability-plugged permeability) / initial permeability*100%, to calculate the plugging rate of the plugging agent to the outcrop core, evaluate its plugging performance, and the final result is shown in Table 2.

[0043] Table 2 Plugging rate test data of chitosan molybdenum disulfide nano plugging agent,

[0044]

[0045] From the data in Table 2, it can be seen that the chitosan-molybdenum disulfide nanometer plugging agent (S1, S2, S3) of the present application exhibits good plugging performance at different concentrations, and the plugging rate shows the trend of S1>S3>S2>D1. Specifically, at an addition amount of 1%, the plugging rates of S1, S2 and S3 are 80.04%, 71.79% and 74.95% respectively, which are much higher than that of the comparative example D1 (44.21%), indicating that the plugging agent of the present application can effectively reduce the formation permeability and improve the plugging effect. When the addition amount of the plugging agent is increased to 2%, the plugging rates of S1, S2 and S3 are further increased to 84.91%, 84.91% and 79.92% respectively, which are more than 30% higher than that of D1 (54.81%). At an addition amount of 3%, the plugging rates of S1, S2 and S3 are 92.43%, 87.98% and 85.12% respectively, which are much better than that of D1 (60.70%), indicating that the increase of the concentration of the plugging agent helps to improve the plugging capacity, and S1 still maintains the highest plugging rate. This result shows that the plugging effect of the chitosan-molybdenum disulfide nanometer plugging agent is obviously better than that of the chitosan-molybdenum disulfide nanometer plugging agent prepared without following the limitations in the claims (D1), and S1 has the best plugging performance, and the plugging rate is significantly improved with the increase of the concentration, which is suitable for the drilling fluid system of different complex formations.

[0046] The above is only a preferred embodiment of the present application, and does not limit the present application in any form. Although the present application has been disclosed as above with a preferred embodiment, it is not intended to limit the present application. Any person skilled in the art can make some changes or modifications to the above disclosed technical content to obtain equivalent embodiments with equivalent changes, without departing from the technical solution of the present application. Any simple modification, equivalent change and modification of the above embodiments based on the technical essence of the present application are still within the scope of the technical solution of the present application.

Claims

1. A chitosan-molybdenum disulfide nano-blocking agent, characterized in that, The chitosan-molybdenum disulfide nano-blocking agent is synthesized from molybdenum disulfide and chitosan, and is prepared by the following steps: Molybdenum disulfide raw powder, chitosan, grinding aid, and milling media are loaded into an agate jar; the agate jar is sealed and installed on a planetary ball mill, the milling time and speed are set, and the planetary ball mill is turned on; after completion, the powder is ultrasonically treated to fully disperse it in deionized water, centrifuged, and the supernatant is collected, filtered, and dried to obtain the chitosan-molybdenum disulfide nano-blocking agent; in the above steps, the grinding aid is graphene; the weight ratio of molybdenum disulfide raw powder: chitosan: grinding aid: milling media is 1:(1.5-3.5):(0.3-0.8):(90-110).

2. The chitosan-molybdenum disulfide nano-blocking agent according to claim 1, characterized in that, The chitosan is one of carboxymethyl chitosan, sulfonated chitosan, or quaternized chitosan; the milling media is one of agate beads, silicon carbide beads, or zirconium oxide beads.

3. The chitosan molybdenum disulfide nano-blocking agent according to any one of claims 1-2, wherein, The ball milling time is 12-24 hours, the ball milling speed is 300-600 r / min, and the ultrasonic treatment conditions include: time of 1-2 hours, power of 300W; drying temperature of 60-70℃, and drying time of 12-36 hours.

4. A water-based drilling fluid, characterized in that, The drilling fluid contains the chitosan molybdenum disulfide nano-plugging agent as described in any one of claims 1-3.

5. The water-based drilling fluid according to claim 4, characterized in that, The drilling fluid comprises the following components: water, bentonite, sodium carbonate, flow pattern modifier, filtration loss reducer, lubricant, inhibitor, pH adjuster, weighting agent, and chitosan molybdenum disulfide nano-plugging agent.

6. The water-based drilling fluid according to claim 5, characterized in that, The bentonite is sodium-based bentonite, the flow pattern regulator is carboxymethyl cellulose, the filtration loss reducer is sulfonated asphalt, the lubricant is graphite, the inhibitor is polyamine, the pH adjuster is sodium hydroxide, and the weighting agent is API barite.

7. The water-based drilling fluid according to claim 6, characterized in that, The pH of the water-based drilling fluid is 8-10.

8. The water-based drilling fluid according to claim 6, characterized in that, The density of the water-based drilling fluid is 1.15-1.45 g / cm³. 3 .

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