Modified hexagonal boron nitride nanosheet nano plugging agent and water-based drilling fluid

Abstract

The invention relates to the field of oilfield chemistry, and discloses a modified hexagonal boron nitride nanosheet nanometer plugging agent and a water-based drilling fluid, and the plugging agent used by the water-based drilling fluid is the modified hexagonal boron nitride nanosheet nanometer plugging agent. The modified hexagonal boron nitride nanosheet nano plugging agent is mainly prepared from the following raw materials: hexagonal boron nitride and 1-methylacryloyl 3-propyl sulfonic acid imidazole inner salt; the water-based drilling fluid comprises the modified hexagonal boron nitride nanosheet nano plugging agent provided by the invention. The modified hexagonal boron nitride nanosheet disclosed by the invention is used as a nano blocking agent, the particle size of the nano blocking agent is approximately distributed between 56 nm and 198nm, and micro-nano-sized pores in a shale well wall can be effectively blocked, so that the well wall can be effectively stabilized, and collapse can be prevented; the water-based drilling fluid used in the invention has good rheological property, stability, plugging property and the like under the shale formation condition.

Description

Technical Field

[0001] The invention relates to the technical field of oil and gas field drilling, and in particular to a modified hexagonal boron nitride nanosheet nano-plugging agent, and a water-based drilling fluid containing the nano-plugging agent. Background Art

[0002] During the drilling of horizontal shale gas wells, wellbore instability is a key technical challenge. Due to the well-developed fractures and water sensitivity of shale formations, the percolation of water-based drilling fluids can cause hydration and expansion of micropores and micro-nanofractures, leading to wellbore collapse, lost circulation, and stuck pipe. Therefore, the key research focus is on how to effectively inhibit shale hydration, seal fractures, and reduce the risk of drilling fluid intrusion into the formation.

[0003] Oil-based drilling fluids are currently widely used in shale gas wells due to their ability to inhibit hydration and reduce wellbore instability. They also excel in lubrication, anti-sticking, and drag reduction. However, issues such as reservoir contamination, reduced permeability, and poor environmental performance limit their application. This is particularly true in low-permeability oil and gas formations, where oil-based drilling fluids can alter reservoir wettability and impact oil and gas production. Furthermore, the large particle size of conventional plugging agents makes it difficult to effectively seal micro- and nano-fractures, resulting in an inability to completely block permeation pathways.

[0004] To address these challenges, developing highly efficient nanoscale plugging agents capable of deeply sealing shale fractures in water-based drilling fluids is crucial for improving wellbore stability. In recent years, hexagonal boron nitride (h-BN), a layered material, has been recognized as an ideal nano-plugging agent due to its high strength, high-temperature stability, and lubricity. It can form a tight sealing layer within the wellbore and microfractures, reducing drilling fluid penetration and the risk of shale hydration and expansion. However, due to its poor dispersibility in drilling fluids, h-BN tends to aggregate and precipitate, compromising its plugging effectiveness.

[0005] To address this issue, the present invention proposes a modified hexagonal boron nitride nanosheet plugging agent. Through alkaline activation, surface-initiated grafting, and ionic modification, 1-methacryloyl-3-propylsulfonic acid imidazolium inner salt is introduced onto the hexagonal boron nitride surface, improving its dispersibility and stability in water-based drilling fluids. Furthermore, surface modification is performed using a Schlenk reaction system under nitrogen protection, and the agent is combined with a crosslinker, ligand, and catalyst to further enhance its chemical stability and high-temperature and salt resistance.

[0006] This plugging agent can form a highly effective plugging barrier within the wellbore wall and micro-nano fractures, effectively reducing drilling fluid intrusion into the formation, reducing shale hydration expansion, and improving wellbore stability. Furthermore, its surface functionalization improves compatibility with the drilling fluid system, reduces fluid loss, improves plugging effectiveness, and can replace some oil-based drilling fluid applications. By optimizing the water-based drilling fluid formula and combining it with a modified hexagonal boron nitride nano-plugging agent, a fluid loss reducer, an inhibitor, and a rheology modifier, the present invention ensures wellbore stability in high-temperature, high-pressure, and complex formation environments.

[0007] Therefore, developing nano-plugging agents based on modified hexagonal boron nitride and optimizing their application in water-based drilling fluids have important engineering value in improving shale gas drilling wellbore stability, reducing reservoir pollution, and optimizing drilling fluid performance. It is an important breakthrough direction in shale gas drilling technology. Summary of the Invention

[0008] In order to solve the technical problem that conventional plugging agents in existing water-based drilling fluids are difficult to effectively plug nano-scale pores in mud shale formations, leading to problems such as well wall instability and well leakage, the present invention provides a modified hexagonal boron nitride nanosheet nano plugging agent. The plugging agent has a particle size of nanometer scale and can penetrate deep into shale microcracks and nanopores to form a dense barrier structure, thereby effectively inhibiting the penetration of drilling fluid and filtrate into the well wall, reducing hydration expansion, and achieving well wall stability. In addition, the present invention also proposes a water-based drilling fluid system based on the plugging agent, which has good plugging, inhibition and rheological properties, is suitable for replacing part of the oil-based drilling fluid, alleviates reservoir pollution, and meets the drilling needs in the complex environment of shale formations.

[0009] To achieve the above-mentioned purpose, the present invention provides a preparation method of a modified hexagonal boron nitride nanosheet plugging agent and a technical solution for its application in water-based drilling fluid. The plugging agent uses hexagonal boron nitride (h-BN) as the basic raw material, and is modified by alkaline activation, surface-initiated grafting and ionic liquid polymerization to improve its dispersion stability and plugging effect in a water-based system. The method comprises the following steps: (1) treating hexagonal boron nitride powder with an alkaline activator such as sodium hydroxide or potassium hydroxide, activating it at high temperature (200°C), and then ultrasonically dispersing, washing, purifying and drying to obtain activated hexagonal boron nitride nanosheets; (2) at low temperature (0°C), activating it with an aqueous solution of 0.1% ethanol and 0.1% ethanol. Water and toluene are used as solvents to mix nucleophilic reagents, catalysts and triethylamine, and then an acylating agent is added to react to synthesize a surface initiator; (3) under nitrogen protection, the activated BN nanosheets are reacted with the surface initiator in toluene to complete the surface initiated grafting modification; (4) then by polymerizing 1-methacryloyl-3-propylsulfonic acid imidazole salt, under the catalysis of a crosslinker, a ligand and cuprous bromide, the initiator is grafted onto hexagonal boron nitride by ionic liquid grafting polymerization, and finally a modified hexagonal boron nitride nanosheet plugging agent is obtained.

[0010] In step (1), the weight ratio of hexagonal boron nitride: alkaline activator: ultrapure water is 1: (7-9): (90-110); wherein, in step (2), the weight ratio of anhydrous toluene: nucleophile: catalyst: triethylamine: acylating agent is 100: (1.6-1.9): (0.4-0.8): (0.8-1.2): (1.4-1.6); wherein, in step (3), the activated hexagonal boron nitride nanoparticles are The weight ratio of the sheet: anhydrous toluene: surface initiator is 1: (20-30): (0.6-1); wherein, in step (4), the weight ratio of the initiator-grafted hexagonal boron nitride nanosheet: crosslinker, ligand and cuprous bromide: 1-propylsulfonic acid-3-methylimidazolium inner salt solution is 1: (4.7-5.3): (0.04-0.08): (0.025-0.035): (0.1-0.2): (45-65).

[0011] In step (1), the alkaline activator is selected from at least one of sodium hydroxide and potassium hydroxide; in step (2), the nucleophile is selected from one of 3-aminopropyltriethoxysilane, 3-aminopropyldimethylethoxysilane, and 3-aminopropyltriisopropoxysilane; the catalyst is selected from one of 4-dimethylaminopyridine, 2,6-di-tert-butylpyridine, and 4-pyrrolidinylpyridine; the acylating agent is selected from one of 2-bromoisobutyryl bromide, 2-chloroisobutyryl chloride, and 3-bromopropionyl bromide; in step (4), the cross-linking agent is selected from one of N,N-methylenebisacrylamide and N,N'-ethylenebisacrylamide; and the ligand is selected from one of 2,2'-bipyridine, 2,2'-biquinoline, and 2,6-bipyridylpyridine.

[0012] This modified plugging agent incorporates sulfonic acid imidazolium salt groups on its surface, resulting in excellent hydrophilicity, charge control capabilities, and adsorption to well walls, enabling efficient plugging at the nanoscale. During formulation optimization, hexagonal boron nitride, initiator, monomer solution, crosslinker, ligand, and catalyst were blended in specific mass ratios to form a stable, dense three-dimensional network structure, enhancing plugging durability and high-temperature salt stability.

[0013] Another object of the present invention is to provide a water-based drilling fluid, to which the modified hexagonal boron nitride nanosheet nano-plugging agent of the present invention is added.

[0014] The drilling fluid is composed of 100 parts by weight of water, 3-6 parts by weight of sodium bentonite, 0.3-0.6 parts by weight of sodium carbonate, 0.04-0.08 parts by weight of KPAM, 0.1-0.5 parts by weight of LKY, 0.2-0.6 parts by weight of PAC-LV, 5-9 parts by weight of LSY-1, 3-7 parts by weight of DYEP, 3-7 parts by weight of UHIB, 0.3-0.7 parts by weight of calcium oxide, 100-230 parts by weight of barite, and 1-2 parts by weight of modified hexagonal boron nitride nanosheets. The drilling fluid density is 1.15-2.15 g / cm 3 .

[0015] The beneficial effects of the present invention are as follows: the particle size distribution of the modified hexagonal boron nitride nanosheet nano-plugging agent prepared by the present invention is between 56 and 198 nm, which can effectively plug the nano-level pores in the mud shale formation, thereby achieving the effect of stabilizing the well wall; the water-based drilling fluid used in the present invention has good performance in terms of rheology, stability and plugging properties under mud shale formation conditions.

[0016] In summary, the present invention effectively solves the problems of wellbore instability and insufficient sealing of nano-fractures in shale formations through material structure innovation and drilling fluid system optimization, providing reliable technical support for safe and efficient drilling in complex oil and gas reservoirs such as shale gas. DETAILED DESCRIPTION

[0017] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0018] The specific embodiments of the present invention are described in detail below. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention and are not used to limit the present invention.

[0019] Preparation Example 1: (1) 8 parts by weight of potassium hydroxide were placed in a mortar and ground for 30 minutes, and then 1 part by weight of hexagonal boron nitride was added and ground for 30 minutes. The powder was then transferred to a reactor and activated at 200°C. 100 parts by weight of ultrapure water was added and ultrasonically treated at 300W for 1 hour. After deionization washing until neutrality, separation and purification were performed, and drying was performed at 65°C for 24 hours to obtain activated hexagonal boron nitride nanosheets; (2) At 0°C, 100 parts by weight of anhydrous toluene, 1.8 parts by weight of 3-aminopropyltriethoxysilane, 0.6 parts by weight of 4-dimethylaminopyridine and 1 part by weight of triethylamine were added to a Schlenk flask in sequence. After mixing and stirring for 1 hour, 1.5 parts by weight of 2-bromoisobutyryl bromide was added to the above mixture and reacted for 4 hours. After the reaction was completed, the surface initiator was separated and purified; (3) Under nitrogen protection, 1 part by weight of The activated hexagonal boron nitride nanosheets were added to 25 parts by weight of anhydrous toluene, ultrasonically dispersed for 30 minutes, and then 0.8 parts by weight of the surface initiator prepared in step (2) was added at 300 rpm. The mixture was then reacted for 48 hours. After the reaction was completed, the initiator-grafted hexagonal boron nitride nanosheets were obtained by separation and purification. (4) Under nitrogen protection, 50 parts by weight of 1-propylsulfonic acid-3-methylimidazole inner salt solution (15% wt) was added to a Schlenk flask. Then, 1 part by weight of the initiator-grafted hexagonal boron nitride nanosheets prepared in step (3), 5 parts by weight of N,N-methylenebisacrylamide, 0.03 parts by weight of 2,2'-bipyridine and 0.15 parts by weight of cuprous bromide were added in sequence at 300 rpm. After the reaction was completed at room temperature for 24 hours, the mixture was separated and purified, and then dried at 65°C for 24 hours to obtain a modified hexagonal boron nitride nanosheet plugging agent (denoted as S1).

[0020] 2. Preparation of water-based drilling fluid: 2. Preparation of water-based drilling fluid: 100 parts by weight of tap water and 5 parts by weight of sodium bentonite were stirred at a stirring rate of 1000 r / min for 60 min, then 0.4 parts by weight of sodium carbonate were stirred at a stirring rate of 2000 r / min for 20 min and then allowed to stand for 24 h, then 0.06 parts by weight of KPAM were added and stirred at a stirring rate of 2000 r / min for 30 min, then 0.3 parts by weight of LKY were added and stirred at a stirring rate of 2000 r / min for 20 min, then 0.3 parts by weight of PAC-LV were added and stirred at a stirring rate of 2000 r / min for 10 min, then 7 parts by weight of LSY-1 were added and stirred at a stirring rate of 1000 r / min. r / min and stirred for 30 min, then added 5 parts by weight of DYEP and stirred at a stirring rate of 1000 r / min for 10 min, then added 5 parts by weight of UHIB and stirred at a stirring rate of 1000 r / min for 10 min, then added 0.5 parts by weight of calcium oxide and stirred at a stirring rate of 1000 r / min for 10 min, then added 180 parts by weight of barite and stirred at a stirring rate of 2000 r / min for 30 min, then added 1.5 parts by weight of modified hexagonal boron nitride nanosheet nano-plugging agent S1 and stirred at a stirring rate of 1000 r / min for 30 min to obtain a water-based drilling fluid (denoted as F1) with a density of 1.58 g / cm 3 .

[0021] Preparation Example 2: (1) 9 parts by weight of potassium hydroxide were placed in a mortar and ground for 30 minutes, and then 1 part by weight of hexagonal boron nitride was added and ground for 30 minutes. The powder was then transferred to a reactor and activated at 200°C. 110 parts by weight of ultrapure water was added and ultrasonically treated at 300W for 1 hour. After deionization washing until neutrality, separation and purification were performed, and drying was performed at 65°C for 24 hours to obtain activated hexagonal boron nitride nanosheets. (2) At 0°C, 100 parts by weight of anhydrous toluene, 1.9 parts by weight of 3-aminopropyltriethoxysilane, 0.8 parts by weight of 4-dimethylaminopyridine and 1.2 parts by weight of triethylamine were added to a Schlenk flask in sequence. After mixing and stirring for 1 hour, 1.6 parts by weight of 2-bromoisobutyryl bromide was added to the above mixture and reacted for 4 hours. After the reaction was completed, the surface initiator was separated and purified. (3) Under nitrogen protection, 1 part by weight of anhydrous toluene, 1.9 parts by weight of 3-aminopropyltriethoxysilane, 0.8 parts by weight of 4-dimethylaminopyridine and 1.2 parts by weight of triethylamine were added to the Schlenk flask in sequence. After mixing and stirring for 1 hour, 1.6 parts by weight of 2-bromoisobutyryl bromide was added to the above mixture and reacted for 4 hours. After the reaction was completed, the surface initiator was obtained by separation and purification. 1. Add 30 parts by weight of activated hexagonal boron nitride nanosheets to 30 parts by weight of anhydrous toluene, and ultrasonically disperse for 30 minutes. Then, add 1 part by weight of the surface initiator prepared in step (2) at 300 rpm, and then react for 48 hours. After the reaction is completed, separate and purify to obtain initiator-grafted hexagonal boron nitride nanosheets; (4) Under nitrogen protection, add 65 parts by weight of 1-propylsulfonic acid-3-methylimidazole inner salt solution (15% wt) into the Schlenk flask. Then, 1 part by weight of the initiator-grafted hexagonal boron nitride nanosheets prepared in step (3), 5.3 parts by weight of N,N-methylenebisacrylamide, 0.035 parts by weight of 2,2'-bipyridine and 0.2 parts by weight of cuprous bromide were added in sequence at 300 rpm. After reacting at room temperature for 24 hours, the mixture was separated and purified, and then dried at 65°C for 24 hours to obtain a modified hexagonal boron nitride nanosheet nanoblocking agent (denoted as S2).

[0022] 2. Preparation of water-based drilling fluid: 100 parts by weight of tap water and 6 parts by weight of sodium bentonite were stirred at a stirring rate of 1000 r / min for 60 min, then 0.6 parts by weight of sodium carbonate were stirred at a stirring rate of 2000 r / min for 20 min and then allowed to stand for 24 h, then 0.08 parts by weight of KPAM were added and stirred at a stirring rate of 2000 r / min for 30 min, then 0.5 parts by weight of LKY were added and stirred at a stirring rate of 2000 r / min for 20 min, then 0.6 parts by weight of PAC-LV were added and stirred at a stirring rate of 2000 r / min for 10 min, then 9 parts by weight of LSY-1 were added and stirred at a stirring rate of 1000 r / min. n stirring rate for 30 min, then add 7 parts by weight of DYEP and stir at a stirring rate of 1000 r / min for 10 min, then add 7 parts by weight of UHIB and stir at a stirring rate of 1000 r / min for 10 min, then add 0.7 parts by weight of calcium oxide and stir at a stirring rate of 1000 r / min for 10 min, then add 230 parts by weight of barite and stir at a stirring rate of 2000 r / min for 30 min, then add 2 parts by weight of modified hexagonal boron nitride nanosheet nano plugging agent S2 and stir at a stirring rate of 1000 r / min for 30 min to obtain a water-based drilling fluid (denoted as F1) with a density of 2.15 g / cm 3 .

[0023] Preparation Example 3: (1) Place 7 parts by weight of potassium hydroxide in a mortar and grind for 30 minutes, then add 1 part by weight of hexagonal boron nitride and grind for 30 minutes, transfer the powder to a reactor, activate it at 200°C, add 90 parts by weight of ultrapure water and ultrasonically treat it at 300W for 1 hour, use deionized water to wash it until it is neutral, separate and purify it, and dry it at 65°C for 24 hours to obtain activated hexagonal boron nitride nanosheets; (2) At 0°C, add 100 parts by weight of anhydrous toluene, 1.6 parts by weight of 3-aminopropyltriethoxysilane, 0.4 parts by weight of 4-dimethylaminopyridine and 0.8 parts by weight of triethylamine to a Schlenk flask in sequence, mix and stir for 1 hour, then add 1.4 parts by weight of 2-bromoisobutyryl bromide to the above mixture and react for 4 hours. After the reaction is completed, separate and purify it to obtain a surface initiator; (3) Under nitrogen protection, add 1 part by weight of The activated hexagonal boron nitride nanosheets were added to 20 parts by weight of anhydrous toluene, and ultrasonically dispersed for 30 minutes. Then, 0.6 parts by weight of the surface initiator prepared in step (2) was added at 300 rpm, and the mixture was reacted for 48 hours. After the reaction was completed, the initiator-grafted hexagonal boron nitride nanosheets were obtained by separation and purification. (4) Under nitrogen protection, 45 parts by weight of 1-propylsulfonic acid-3-methylimidazolium salt solution (15% wt) was added to the Schlenk flask. Then, 1 part by weight of the initiator-grafted hexagonal boron nitride nanosheets prepared in step (3), 4.7 parts by weight of N,N-methylenebisacrylamide, 0.025 parts by weight of 2,2'-bipyridine and 0.1 parts by weight of cuprous bromide were added in sequence at 300 rpm. After reacting at room temperature for 24 hours, the mixture was separated and purified, and then dried at 65°C for 24 hours to obtain a modified hexagonal boron nitride nanosheet nanoblocking agent (denoted as S3).

[0024] 2. Preparation of water-based drilling fluid: 100 parts by weight of tap water and 3 parts by weight of sodium bentonite were stirred at a stirring rate of 1000 r / min for 60 min, then 0.3 parts by weight of sodium carbonate were stirred at a stirring rate of 2000 r / min for 20 min and then allowed to stand for 24 h, then 0.04 parts by weight of KPAM were added and stirred at a stirring rate of 2000 r / min for 30 min, then 0.1 parts by weight of LKY were added and stirred at a stirring rate of 2000 r / min for 20 min, then 0.2 parts by weight of PAC-LV were added and stirred at a stirring rate of 2000 r / min for 10 min, then 5 parts by weight of LSY-1 were added and stirred at a stirring rate of 1000 r / min. n stirring rate for 30 min, then add 3 parts by weight of DYEP and stir at a stirring rate of 1000 r / min for 10 min, then add 3 parts by weight of UHIB and stir at a stirring rate of 1000 r / min for 10 min, then add 0.3 parts by weight of calcium oxide and stir at a stirring rate of 1000 r / min for 10 min, then add 100 parts by weight of barite and stir at a stirring rate of 2000 r / min for 30 min, then add 1 part by weight of modified hexagonal boron nitride nanosheet nano plugging agent S3 and stir at a stirring rate of 1000 r / min for 30 min to obtain a water-based drilling fluid (denoted as F3) with a density of 1.15 g / cm 3 .

[0025] Comparative Example 1: (1) 5 parts by weight of potassium hydroxide were placed in a mortar and ground for 30 minutes, and then 1 part by weight of hexagonal boron nitride was added and ground for 30 minutes. The powder was then transferred to a reactor and activated at 200°C. After that, 70 parts by weight of ultrapure water was added and ultrasonically treated at 300W for 1 hour. After deionization washing until neutrality, separation and purification were performed, and drying was performed at 65°C for 24 hours to obtain activated hexagonal boron nitride nanosheets; (2) At 0°C, 100 parts by weight of anhydrous toluene, 1.2 parts by weight of 3-aminopropyltriethoxysilane, 0.2 parts by weight of 4-dimethylaminopyridine and 0.5 parts by weight of triethylamine were added to a Schlenk flask in sequence. After mixing and stirring for 1 hour, 1.1 parts by weight of 2-bromoisobutyryl bromide was added to the above mixture and reacted for 4 hours. After the reaction was completed, the surface initiator was separated and purified; (3) Under nitrogen protection, 1 part by weight of The activated hexagonal boron nitride nanosheets were added to 15 parts by weight of anhydrous toluene, and ultrasonically dispersed for 30 minutes. Then, 0.4 parts by weight of the surface initiator prepared in step (2) was added at 300 rpm, and the mixture was reacted for 48 hours. After the reaction was completed, the initiator-grafted hexagonal boron nitride nanosheets were obtained by separation and purification. (4) Under nitrogen protection, 40 parts by weight of 1-propylsulfonic acid-3-methylimidazolium salt solution (15% wt) was added to the Schlenk flask. Then, 1 part by weight of the initiator-grafted hexagonal boron nitride nanosheets prepared in step (3), 4.2 parts by weight of N,N-methylenebisacrylamide, 0.02 parts by weight of 2,2'-bipyridine and 0.08 parts by weight of cuprous bromide were added in sequence at 300 rpm. After reacting at room temperature for 24 hours, the mixture was separated and purified, and then dried at 65°C for 24 hours to obtain a modified hexagonal boron nitride nanosheet plugging agent (denoted as D1).

[0026] 2. Preparation of water-based drilling fluid: Prepared according to the method of Preparation Example 1, except that 1.5 parts by weight of modified hexagonal boron nitride nanosheet nanoblocking agent D1 (respectively referred to as DF1) was added.

[0027] Comparative Example 2: Prepared according to the method of Example 1.

[0028] 2. Preparation of water-based drilling fluid: 100 parts by weight of tap water and 2 parts by weight of sodium bentonite were stirred at a stirring rate of 1000 r / min for 60 min, then 0.2 parts by weight of sodium carbonate were stirred at a stirring rate of 2000 r / min for 20 min and allowed to stand for 24 h, then 0.03 parts by weight of KPAM were added and stirred at a stirring rate of 2000 r / min for 30 min, then 0.05 parts by weight of LKY were added and stirred at a stirring rate of 2000 r / min for 20 min, then 0.18 parts by weight of PAC-LV were added and stirred at a stirring rate of 2000 r / min for 10 min, then 4 parts by weight of LSY-1 were added and stirred at 10 00r / min and stirred for 30min, then 2 parts by weight of DYEP was added and stirred at a stirring rate of 1000r / min for 10min, then 2 parts by weight of UHIB was added and stirred at a stirring rate of 1000r / min for 10min, then 0.2 parts by weight of calcium oxide was added and stirred at a stirring rate of 1000r / min for 10min, then 100 parts by weight of barite was added and stirred at a stirring rate of 2000r / min for 30min, then 1 part by weight of modified hexagonal boron nitride nanosheet nanoplugging agent S1 was added and stirred at a stirring rate of 1000r / min for 30min to obtain a water-based drilling fluid (denoted as DF2).

[0029] 1. Basic performance test of water-based drilling fluid.

[0030] The basic properties of the drilling fluids F1-F3 prepared in Preparation Examples 1-3 and the water-based drilling fluids DF1 and DF2 prepared in Comparative Examples 1 and 2 were tested. The results are shown in Table 1.

[0031] Apparent viscosity (AV, mPa•s), plastic viscosity (PV, mPa•s), and dynamic shear force (YP, Pa) were measured using a six-speed rotary viscometer in accordance with the method specified in GB / T29170-2012; high-temperature and high-pressure filtration loss (HTHP, mL) was measured using a high-temperature and high-pressure filter loss meter in accordance with the method specified in GB / T29170-2012; medium-pressure filtration loss (API, mL) was measured using a medium-pressure filter loss meter in accordance with the method specified in GB / T29170-2012.

[0032] The instruments used are: six-speed rotational viscometer manufactured by Qingdao Chuangmeng Instrument Co., Ltd., model 1100; medium-pressure filter loss meter manufactured by Qingdao Chuangmeng Instrument Co., Ltd., model 1202; high-temperature and high-pressure filter loss meter manufactured by Qingdao Chuangmeng Instrument Co., Ltd., model GGS42-2.

[0033] Table 1 Basic performance test table of water-based drilling fluid; As shown in Table 1, the basic performance test table of water-based drilling fluids prepared in Examples F1, F2, and F3 all exhibit dynamic-to-plastic ratios within the range of 0.36–0.48. At this point, the drilling fluids exhibit a flat laminar flow pattern within the annulus, exhibit strong rock-carrying capacity at low viscosity, and exhibit minimal scouring of the wellbore, demonstrating excellent rheological properties. Comparative Example DF1, while using the same drilling fluid formulation as F1, lacks the modified hexagonal boron nitride nanosheet plugging agent prepared using the claimed process. This significantly reduces fluid loss performance, with HTHP fluid loss reaching 8.6 mL, significantly exceeding F1's 4.4 mL. API fluid loss also increases to 3.80 mL, demonstrating the crucial influence of the modification process on plugging performance. In contrast, while DF2 utilizes the same modified nanoplugging agent as F1, its drilling fluid system is not formulated according to the claimed method, resulting in a dynamic-to-plastic ratio of only 0.15, far below the ideal shear-thinning range and exhibiting poor rheological properties. The above comparison shows that excellent rheological properties and fluid loss control performance can only be achieved when the modified plugging agent and scientific drilling fluid system are jointly optimized.

[0034] 2. Test of the plugging performance of modified hexagonal boron nitride nanosheet nanoplugging agent.

[0035] This experiment used outcrop cores to simulate the permeability characteristics of nanofractures in formations. The plugging performance of a modified hexagonal boron nitride nanosheet plugging agent was evaluated by measuring the average fluid flow rate in the cores and calculating the core permeability based on Darcy's law. Initial permeability was measured using clean water. After adding different plugging agents to the water, the post-plugging permeability was measured. The permeability formula is K = QμL / (AΔP). The plugging efficiency of the plugging agent on the outcrop core was calculated using the formula: (initial permeability - post-plugging permeability) / initial permeability × 100%. The plugging performance was evaluated. The final results are shown in Table 2.

[0036] Table 2. Test data of plugging efficiency of modified hexagonal boron nitride nanosheets nano plugging agent; From the plugging rate test data table of modified hexagonal boron nitride nanosheets and nano plugging agents in Table 2, it can be seen that the modified hexagonal boron nitride nano plugging agents obtained by different preparation methods show significant differences in plugging performance. Among them, the plugging rate of the comparative example D1 plugging agent at each dosage level is significantly lower than that of Examples S1, S2 and S3. Taking 2% dosage as an example, the plugging rate of D1 is only 70.12%, while the plugging rates of S1, S2 and S3 are as high as 90.08%, 89.60% and 86.85% respectively. The fundamental reason is that D1 is not modified according to the method of the present invention, and the surface initiator grafting step is not introduced during the preparation process, and the effective regulation of the surface chemical structure of the hexagonal boron nitride sheet is not achieved, resulting in poor sheet dispersion, small specific surface area, and difficulty in fully spreading and embedding in core fractures, making it difficult to form a stable and dense plugging structure.

[0037] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as a preferred embodiment as above, it is not intended to limit the present invention. Any technician familiar with this profession can make some changes or modifications to equivalent embodiments of the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A modified hexagonal boron nitride nanosheet nano plugging agent, characterized in that: The raw materials for preparing the modified hexagonal boron nitride nanosheet nanoblocking agent mainly include hexagonal boron nitride and 1-methacryloyl 3-propyl sulfonic acid imidazole inner salt, and the preparation steps are as follows: (1) placing the alkaline activator in a mortar and grinding for 30 minutes, then adding hexagonal boron nitride and grinding for 30 minutes, transferring the powder to a reactor, performing activation treatment at 200°C, adding ultrapure water and ultrasonic treatment at 300W for 1 hour, washing with deionization until neutral, separating and purifying, and drying at 65°C for 24 hours to obtain activated hexagonal boron nitride nanosheets; (2) adding anhydrous toluene, nucleophilic reagent, catalyst and triethylamine to a Schlenk flask in sequence at 0°C, mixing and stirring for 1 hour, adding the acylating reagent to the above-mentioned mixture and reacting for 4 hours, and the reaction is completed. After completion, the surface initiator was obtained by separation and purification; (3) under nitrogen protection, the activated hexagonal boron nitride nanosheets were added to anhydrous toluene, ultrasonically dispersed for 30 minutes, and then the surface initiator prepared in step (2) was added at 300 rpm, followed by reaction for 48 hours. After the reaction was completed, the initiator-grafted hexagonal boron nitride nanosheets were obtained by separation and purification; (4) under nitrogen protection, 1-propylsulfonic acid-3-methylimidazolium salt solution (15% wt) was added to the Schlenk flask, and the initiator-grafted hexagonal boron nitride nanosheets, crosslinking agent, ligand and cuprous bromide prepared in step (3) were added in sequence at 300 rpm. After the reaction was completed at room temperature for 24 hours, the surface initiator was separated and purified, and then dried at 65°C for 24 hours to obtain the modified hexagonal boron nitride nanosheet nanoblocking agent.

2. The modified hexagonal boron nitride nanosheet nano-blocking agent according to claim 1, characterized in that: The weight ratio of the hexagonal boron nitride: alkaline activator: ultrapure water is 1: (7-9): (90-110); wherein, in step (2), the weight ratio of the anhydrous toluene: nucleophile: catalyst: triethylamine: acylating agent is 100: (1.6-1.9): (0.4-0.8): (0.8-1.2): (1.4-1.6); wherein, in step (3), the weight ratio of the activated hexagonal boron nitride nanosheets: anhydrous toluene: surface initiator is 1: (20-30): (0.6-1); wherein, in step (4), the weight ratio of the initiator-grafted hexagonal boron nitride nanosheets: crosslinker, ligand and cuprous bromide: 1-propylsulfonic acid-3-methylimidazolium inner salt solution is 1: (4.7-5.3): (0.025-0.035): (0.1-0.2): (45-65).

3. The modified hexagonal boron nitride nanosheet nano-blocking agent according to any one of claims 1-2, characterized in that: In step (1), the alkaline activator is selected from at least one of sodium hydroxide and potassium hydroxide; in step (2), the nucleophile is selected from one of 3-aminopropyltriethoxysilane, 3-aminopropyldimethylethoxysilane, and 3-aminopropyltriisopropoxysilane; the catalyst is selected from one of 4-dimethylaminopyridine, 2,6-di-tert-butylpyridine, and 4-pyrrolidinylpyridine; the acylating agent is selected from one of 2-bromoisobutyryl bromide, 2-chloroisobutyryl chloride, and 3-bromopropionyl bromide; in step (4), the cross-linking agent is selected from one of N,N-methylenebisacrylamide and N,N'-ethylenebisacrylamide; and the ligand is selected from one of 2,2'-bipyridine, 2,2'-biquinoline, and 2,6-bipyridylpyridine.

4. A water-based drilling fluid, characterized in that: The drilling fluid is added with the modified hexagonal boron nitride nanosheet nano plugging agent according to claims 1-3.

5. The water-based drilling fluid according to claim 4, characterized in that: The drilling fluid comprises the following components: water, sodium bentonite, sodium carbonate, coating agent KPAM, free water complexing agent LKY, flow pattern regulator PAC-LV, fluid loss reducer LSY-1, lubricant DYEP, inhibitor UHIB, calcium oxide, barite, and modified hexagonal boron nitride nanosheet nano-plugging agent.

6. The water-based drilling fluid according to claim 5, characterized in that: Based on 100 parts by weight of water, the amount of the sodium bentonite is 3-6 parts by weight, the amount of the sodium carbonate is 0.3-0.6 parts by weight, the amount of the KPAM is 0.04-0.08 parts by weight, the amount of the LKY is 0.1-0.5 parts by weight, the amount of the PAC-LV is 0.2-0.6 parts by weight, the amount of the LSY-1 is 5-9 parts by weight, the amount of the DYEP is 3-7 parts by weight, the amount of the UHIB is 3-7 parts by weight, the amount of the calcium oxide is 0.3-0.7 parts by weight, the amount of the barite is 100-230 parts by weight, the amount of the modified hexagonal boron nitride nanosheet nano plugging agent is 1-2 parts by weight, and the drilling fluid density is 1.15-2.15 g / cm 3 .

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