A desulfonated low-viscosity high-shear strong-inhibiting water-based drilling fluid

Abstract

The present invention provides a desulfonated low-viscosity high-yield point strongly inhibitory water-based drilling fluid, belonging to the technical field of oilfield chemistry in oil and gas drilling engineering. By mass fraction, the raw materials of the desulfonated low-viscosity high-yield point strongly inhibitory water-based drilling fluid include: 100 parts of water, 0.5 - 1.0 part of pH regulator, 1 - 3 parts of lubricant, 0.5 - 0.7 part of yield point enhancer, 2 - 4 parts of filtration reducer, 2 - 4 parts of inhibitor, 5 - 15 parts of auxiliary inhibitor, 1 - 3 parts of dispersant, and barite; the number of parts of the barite is not limited, and it is weighted to the required density. The desulfonated low-viscosity high-yield point strongly inhibitory water-based drilling fluid of the present invention can effectively inhibit the swelling and dispersion of formation water-sensitive minerals in the high-temperature and water-sensitive formation environment, maintain wellbore stability, ensure wellbore cleaning, improve drilling efficiency, and is environmentally friendly and biodegradable, meeting the requirements of green, safe, and efficient drilling.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and gas drilling engineering and oilfield chemistry, and particularly relates to a desulfonated low-viscosity high-yield point strongly inhibitory water-based drilling fluid. Background Art

[0002] Drilling fluid plays a crucial role in the drilling process of resources such as oil and natural gas. Its main functions include carrying cuttings, cooling and lubricating the drill bit, maintaining wellbore stability, and balancing formation pressure. With the progress of drilling technology, the complexity of drilling environment, and the strict environmental protection requirements, the performance requirements for drilling fluid are also increasing day by day. Especially for the long horizontal well construction operations in high-temperature and water-sensitive formations, although conventional water-based drilling fluids have certain environmental protection advantages, their rheological properties, inhibitory properties, and temperature resistance are still insufficient.

[0003] As is well known, the plastic viscosity and yield point of drilling fluid are important indicators for evaluating its rheological properties. A low plastic viscosity helps to reduce the circulating pressure loss, lower the pumping energy consumption, and improve the drilling efficiency. A drilling fluid with a high yield point can still maintain a high suspension capacity under low-speed conditions, which helps to reduce the cutting settlement speed and ensure that the cuttings are effectively carried to the surface. Especially for the horizontal well drilling operations in long horizontal sections, achieving the rheological properties of low plastic viscosity and high yield point of drilling fluid is the key.

[0004] For water-sensitive formations, the inhibitory property of drilling fluid is crucial, which is related to the swelling and dispersion degree of water-sensitive minerals (such as shale, mudstone, etc.) in the formation. Insufficient inhibitory property will cause the formation rocks to absorb water and expand, disintegrate, trigger wellbore instability, and affect the smooth progress of drilling operations. Therefore, developing a drilling fluid with strong inhibitory property is of great significance for ensuring wellbore stability, improving drilling safety and efficiency.

[0005] At the same time, high-temperature conditions pose a major challenge to the drilling fluid to achieve the above rheological properties and inhibitory properties. Although the traditional sulfonation modification method can significantly improve the temperature resistance of drilling fluid materials, the introduced sulfonic acid groups make it difficult for polymer materials to degrade, resulting in difficulties in the subsequent treatment of waste and drill cuttings. Moreover, even if treated, sulfur-containing by-products will be generated, which is not conducive to ecological environment protection.

[0006] Based on this, researching and developing a desulfonated low-viscosity high-yield point strongly inhibitory water-based drilling fluid can not only solve the environmental protection problem, but also meet the performance requirements of the drilling fluid for shale water-sensitive formations and long horizontal wells, thereby improving drilling efficiency and safety, which is of great significance for realizing green, safe, and efficient drilling. Summary of the Invention

[0007] In view of this, the object of the present invention is to provide a desulfonated low-viscosity high-yield point strongly inhibitory water-based drilling fluid. The drilling fluid provided by the present invention can effectively inhibit the swelling and dispersion of formation water-sensitive minerals in a high-temperature and water-sensitive formation environment, maintain wellbore stability, ensure wellbore cleaning, improve drilling efficiency, and is environmentally friendly and biodegradable, meeting the requirements of green, safe, and efficient drilling.

[0008] To achieve the above object, the present invention provides the following technical solutions:

[0009] A desulfonated low-viscosity high-yield point strongly inhibitory water-based drilling fluid, by mass, the raw materials include: 100 parts of water, 0.5 - 1.0 part of pH regulator, 0.5 - 0.7 part of yield point enhancer, 2 - 4 parts of filtration reducer, 2 - 4 parts of inhibitor, 5 - 15 parts of auxiliary inhibitor, 1 - 3 parts of dispersant, 1 - 3 parts of lubricant, and barite; the amount of barite is not limited, and it is weighted to the required density.

[0010] The yield point enhancer is a mixture of 20 - 30 parts of scleroglucan, 20 - 30 parts of diutan gum, and 40 - 60 parts of welan gum.

[0011] In the present invention, the density of the desulfonated low-viscosity high-yield point strongly inhibitory water-based drilling fluid is 1.1 - 1.7 g / cm 3 .

[0012] The present invention discloses the following technical effects:

[0013] The desulfonated low-viscosity high-yield point strongly inhibitory water-based drilling fluid provided by the present invention can achieve the rheological characteristics of low viscosity and high yield point under the action of the yield point enhancer, that is, it has significant shear thinning behavior, maintains good fluidity and cuttings transport performance during normal drilling, and has the ability to suspend cuttings during the stop of circulation, avoiding the sticking caused by cuttings settlement during tripping. The desulfonated low-viscosity high-yield point strongly inhibitory water-based drilling fluid provided by the present invention also has excellent inhibitory performance, mainly achieving the hydration inhibition of clay through the following aspects: First, using the characteristics of the polyamine functional group of the inhibitor, it effectively adsorbs on the surface of clay particles to form a protective layer, preventing water molecules from entering the interlayer of clay, and at the same time further compressing the diffuse double layer under the action of cationic ammonium, thereby inhibiting clay hydration; second, combining with the large amount of cations provided by the auxiliary inhibitor to strengthen the electrostatic interaction, and using the intercalation effect of potassium ions to play an auxiliary inhibitory effect; third, through the adsorption and film-forming characteristics of the dispersant, it can synergistically enhance the hydration inhibition effect on clay. The desulfonated low-viscosity high-yield point strongly inhibitory water-based drilling fluid provided by the present invention adopts a desulfonated design, avoiding the problem of difficult degradation of traditional sulfonated polymers, making the drilling fluid more environmentally friendly, reducing the negative impact on the ecological environment, and meeting the requirements of green drilling.

[0014] The plastic viscosity to yield point ratio of the desulfurized low-viscosity high-shear-strength inhibition water-based drilling fluid of the present invention is > 1.0, the API filtration loss is < 3.5 mL, the extreme pressure friction coefficient is ≤ 0.08, the apparent viscosity increase rate after 20% contamination by sodium bentonite is < 11%, the shale rolling recovery rate is > 95%, the biodegradation index is > 25%, the sulfur content of the unweighted dry basis is 0. While meeting the safety operation requirements of long horizontal wells in high-temperature and water-sensitive formations, it also has significant environmental protection and biodegradable properties. Detailed Embodiments

[0015] The various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, characteristics, and implementation schemes of the present invention.

[0016] It should be understood that the terms used in the present invention are only for describing specific embodiments and are not intended to limit the present invention. Additionally, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded from the range.

[0017] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. Although the present invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0018] Without departing from the scope or spirit of the present invention, various improvements and changes can be made to the specific embodiments of the present invention specification, which are obvious to those skilled in the art. Other embodiments obtained from the present invention specification are obvious to those skilled in the art. The present invention specification and examples are only exemplary.

[0019] Regarding the terms "comprising", "including", "having", "containing", etc. used herein, they are all open-ended terms, meaning including but not limited to.

[0020] The present invention provides a desulfonated low-viscosity high-shear-strength inhibition water-based drilling fluid. By mass, the raw materials include: 100 parts of water, 0.5 - 1.0 part of pH regulator, 0.5 - 0.7 part of shear enhancer, 2 - 4 parts of filtration reducer, 2 - 4 parts of inhibitor, 5 - 15 parts of auxiliary inhibitor, 1 - 3 parts of dispersant, 1 - 3 parts of lubricant, and barite; the amount of barite is not limited, and the density is increased to the required value.

[0021] In the present invention, the water is fresh water or seawater.

[0022] In some embodiments of the present invention, by mass, the pH regulator is a mixture of 40 - 60 parts of sodium hydroxide and 40 - 60 parts of sodium carbonate.

[0023] Sodium hydroxide can provide a strong alkaline environment for the system. On the one hand, it can prevent the drill tool from being corroded by acidic substances. On the other hand, all the constituent materials can play their maximum roles in an alkaline environment; sodium carbonate can react with high-valence mineral ions to form water-insoluble precipitates, avoiding the influence of these ions on the performance of other additive materials.

[0024] In some embodiments of the present invention, by mass, the shear enhancer is a mixture of 20 - 30 parts of scleroglucan, 20 - 30 parts of diutan gum, and 40 - 60 parts of welan gum.

[0025] Scleroglucan, diutan gum, and welan gum are all microbial polysaccharide polymers. When used in combination, they can significantly increase the dynamic shear force of the drilling fluid while controlling a relatively low viscosity, which is beneficial for suspending cuttings, improving the wellbore cleaning effect, and enhancing the drilling efficiency. These polysaccharide polymers are all prepared by microbial fermentation and have the characteristics of non-toxicity and biodegradability, which is beneficial for protecting the ecological environment.

[0026] In some embodiments of the present invention, by mass, the raw materials of the filtration reducer include: 15 - 25 parts of humic acid, 100 parts of water, 1 - 3 parts of chitosan, 1 - 3 parts of γ-methacryloyloxypropyltrimethoxysilane, 100 parts of ethanol aqueous solution containing acetic acid, 5 - 10 parts of acrylic acid, 10 - 20 parts of N-vinylpyrrolidone, 5 - 12 parts of dimethyldiallylammonium chloride, and 0.1 - 0.3 part of ammonium persulfate;

[0027] The preparation method of the filtration reducer includes the following steps:

[0028] Dissolve chitosan in the humic acid aqueous solution to obtain a humic acid-chitosan mixture;

[0029] Dissolve γ-methacryloyloxypropyltrimethoxysilane in the ethanol aqueous solution containing acetic acid, and then carry out a hydrolysis reaction to obtain a pre-hydrolyzed silane coupling agent;

[0030] Add the pre-hydrolyzed silane coupling agent to the fulvic acid-chitosan mixed solution for reaction to obtain an intermediate product;

[0031] Dissolve acrylic acid, N-vinylpyrrolidone, and dimethyldiallylammonium chloride in water, adjust the pH value to alkaline, then add the intermediate product under stirring conditions. Under the protection of an inert atmosphere, add ammonium persulfate to the reaction system for polymerization reaction 1 to obtain the filtrate reducer.

[0032] The present invention does not make special limitations on the preparation method of the fulvic acid aqueous solution, and the well-known technical means of those skilled in the art can be selected. For example: add fulvic acid to water and stir to dissolve. The present invention does not make special limitations on the way of dissolving chitosan in the fulvic acid aqueous solution, and the well-known technical means of those skilled in the art can be selected. For example: stir to dissolve.

[0033] In some embodiments of the present invention, in the ethanol aqueous solution containing acetic acid, the content of acetic acid is 1% v / v, and the content of ethanol is 85% v / v.

[0034] In some embodiments of the present invention, the temperature of the hydrolysis reaction is 40-50 °C, and the time is 3-5 h.

[0035] In some embodiments of the present invention, when adding the pre-hydrolyzed silane coupling agent to the fulvic acid-chitosan mixed solution for reaction, the temperature of the reaction is 60-70 °C, and the time is 10-20 h. After the reaction, it also includes cooling to room temperature, removing the solvent by centrifugation, washing with absolute ethanol, and vacuum drying.

[0036] In some embodiments of the present invention, adjusting the pH value to alkaline means adjusting pH = 7-8. The present invention does not make special limitations on the alkali solution used to adjust the pH to alkaline, and the alkali solution well-known to those skilled in the art can be selected. For example: 0.1 mol / L sodium hydroxide aqueous solution.

[0037] In some embodiments of the present invention, the reaction temperature of the polymerization reaction 1 is 65-75 °C, and the time is 3-5 h; after the polymerization reaction 1, it also includes cooling to room temperature, washing with deionized water, followed by vacuum filtration and vacuum drying.

[0038] The filtrate reducer provided by the present invention is a compound modified product of natural polymers fulvic acid and chitosan. The abundant carboxyl groups and phenolic hydroxyl groups in fulvic acid can form a strong adsorption with the minerals or drill cuttings on the wellbore wall, which helps to form a dense protective film on the wellbore surface and reduce the penetration of drilling fluid; the addition of chitosan is beneficial to enrich the network structure and increase the filtrate viscosity, thereby further reducing the filtrate penetration rate. Through the cross-linking effect of the silane coupling agent, on the one hand, these two natural polymers can be connected to enhance the network structure coverage, and on the other hand, functional groups can be introduced through graft copolymerization to improve the water-soluble dispersion and temperature and salt resistance performance. For example, the introduction of acrylic acid is beneficial to improve the carboxyl distribution, thereby improving the water-soluble dispersion; the introduction of N-vinylpyrrolidone can maintain the polymer structure stability at high temperatures by utilizing the rigid structure of its five-membered ring; in addition, dimethyldiallylammonium chloride provides cations, which helps to improve the salt resistance stability.

[0039] In some embodiments of the present invention, by mass, the inhibitor is a mixture of 70-80 parts of polyethyleneimine graft copolymer and 20-30 parts of hexamethylenediamine.

[0040] The inhibitor provided by the present invention is a compound product of macromolecular polyethyleneimine graft copolymer and small molecule hexamethylenediamine. The polyethyleneimine graft copolymer contains ether bonds, amide groups, carboxyl groups and cationic ammonium, etc., showing extremely strong hydrophilicity and adsorption, and can adsorb on the surface of clay particles, playing a role in inhibiting the hydration and dispersion of clay; the cationic ammonium therein can neutralize the negative charge on the clay surface and compress the diffusion double layer, thereby inhibiting the hydration and swelling of clay. In addition, due to the relatively small molecular weight of hexamethylenediamine, it can be evenly adsorbed on the surface of clay particles. On the one hand, by using the characteristic that the terminal amino functional group is positively charged after protonation in the solution, it enters the clay interlayer under the drive of the chemical potential difference and prevents the separation of clay platelets under the electrostatic interaction, playing a role in strengthening the inhibition.

[0041] In some embodiments of the present invention, by mass, the raw materials of the polyethyleneimine graft copolymer include: 100 parts of water, 40-60 parts of polyethyleneimine, 10-20 parts of maleic anhydride, 15-25 parts of dimethyldiallylammonium chloride and 0.6-0.8 parts of potassium persulfate.

[0042] In some embodiments of the present invention, the preparation method of the polyethyleneimine graft copolymer includes the following steps:

[0043] Perform an amidation reaction on polyethyleneimine and maleic anhydride;

[0044] After the amidation reaction is completed, add water and dimethyldiallylammonium chloride to the reaction system, and under an inert atmosphere, add potassium persulfate to carry out polymerization reaction 2 to obtain the polyethyleneimine graft copolymer.

[0045] In some embodiments of the present invention, polyethyleneimine and maleic anhydride are subjected to amidation reaction, specifically: polyethyleneimine is heated in a water bath to 65 - 75 °C under stirring conditions, nitrogen is passed through to remove oxygen, and then maleic anhydride is slowly added for amidation reaction; the temperature of the amidation reaction is 70 - 80 °C, and the time is 3 - 5 h.

[0046] In some embodiments of the present invention, the temperature of the polymerization reaction 2 is 60 - 70 °C, and the time is 2 - 4 h.

[0047] In some embodiments of the present invention, by mass, the auxiliary inhibitor is a mixture of 10 - 20 parts of sodium chloride, 20 - 30 parts of potassium chloride, 30 - 40 parts of sodium formate, and 20 - 30 parts of potassium formate.

[0048] Sodium chloride and potassium chloride respectively provide sodium and potassium cations, which can assist in enhancing the inhibition of the drilling fluid. Especially potassium ions, because they can embed between clay layers, thus effectively inhibiting clay swelling. In addition to providing sodium and potassium cations, sodium formate and potassium formate can also provide formate anions. Because they have a free radical scavenging function, they can effectively improve the oxidation degradation resistance of the viscosifier, thereby improving the thermal stability.

[0049] In some embodiments of the present invention, by mass, the raw materials of the dispersant include: 100 parts of water, 20 - 30 parts of ethanolamine, 20 - 30 parts of itaconic anhydride, 3 - 5 parts of vinylphosphonic acid, 3 - 5 parts of N - vinylpyrrolidone, and 0.5 - 1.0 part of ammonium persulfate;

[0050] The preparation method of the dispersant includes the following steps:

[0051] Ethanolamine and itaconic anhydride are subjected to amidation reaction;

[0052] After the amidation reaction is completed, water, vinylphosphonic acid, and N - vinylpyrrolidone are added to the reaction system. Under an inert atmosphere, potassium persulfate is added for polymerization reaction 3 to obtain the dispersant.

[0053] In some embodiments of the present invention, the amidation reaction of ethanolamine and itaconic anhydride is specifically: ethanolamine is heated in a water bath to 70 - 75 °C under stirring conditions, nitrogen is passed through to remove oxygen, and then itaconic anhydride is slowly added for amidation reaction; the temperature of the amidation reaction is 80 - 90 °C, and the time is 2 - 4 h.

[0054] In some embodiments of the present invention, the temperature of the polymerization reaction 3 is 70 - 80 °C, and the time is 2 - 3 h.

[0055] The dispersant provided by the present invention contains a large number of functional groups such as carboxyl groups, hydroxyl groups, phosphonic acid groups, amide groups, and pyrrolidone rings. On the one hand, through the strong hydrophilicity and adsorption of polar groups such as hydroxyl groups, amide groups, and pyrrolidone rings, as well as the electrostatic repulsion of carboxyl groups and phosphonic acid groups, the aggregation of solid-phase particles such as cuttings and barite in the drilling fluid can be effectively prevented, and the uniform dispersion of the particles can be maintained through steric hindrance effects, thereby reducing the sedimentation risk of solid-phase particles and being beneficial to wellbore cleaning. On the other hand, the phosphonic acid groups, carboxyl groups, and amide groups in the dispersant form a stable protective layer by means of cation complexation, surface adsorption, and hydrogen bond binding with the cations in clay minerals, preventing water molecules from entering the interlayer of the clay, thereby inhibiting the water absorption swelling and dispersion of the clay, assisting in improving the inhibition performance of the drilling fluid, and avoiding problems such as thickening of the drilling fluid or wellbore instability caused by the hydration of cuttings with high clay content or wellbore rock. In addition, the introduction of phosphonic acid groups also endows the dispersant with the function of chelating divalent cations such as calcium and magnesium, which can effectively enhance the calcium and magnesium ion pollution resistance performance of the drilling fluid.

[0056] In some embodiments of the present invention, by mass, the lubricant is a mixture of 40 - 45 parts of polyethylene glycol borate, 45 - 50 parts of fatty alcohol polyoxyethylene ether, and 5 - 15 parts of nano silicon nitride.

[0057] Polyethylene glycol borate forms a stable lubricating film between the drill string and the wellbore wall, reducing metal contact and lowering the friction coefficient; fatty alcohol polyoxyethylene ether, as a surfactant, plays roles such as reducing the surface tension and enhancing the uniformity and stability of the lubricating film; nano silicon nitride acts as a solid lubricant, filling in small unevennesses, reducing friction, and improving the anti-wear ability of the lubricating film. The components work synergistically to further enhance the comprehensive performance of the lubricant and exhibit excellent lubricating effects under complex drilling conditions.

[0058] The desulfonated low-viscosity high-yield stress inhibition water-based drilling fluid provided by the present invention can be prepared by using a conventional preparation method.

[0059] The technical solutions of the present invention, unless otherwise specified, are all conventional solutions in the art, and the reagents or raw materials used, unless otherwise specified, are all purchased from commercial channels or have been made public.

[0060] To better understand the present invention, the content of the present invention will be further clarified below in conjunction with embodiments, but the content of the present invention is not limited to the following embodiments only. Example 1

[0061] A desulfonated low-viscosity high-yield stress inhibition water-based drilling fluid, by mass, the raw materials are as follows:

[0062] Fresh water: 100 parts

[0063] pH regulator: 0.5 part

[0064] Cutting agent: 0.5 parts

[0065] Fluid loss reducer: 2 parts

[0066] Inhibitor: 2 parts

[0067] Auxiliary inhibitor: 5 parts

[0068] Dispersant: 1 part

[0069] Lubricant: 1 part

[0070] Barite: Add weight to the drilling fluid density of 1.1g / cm 3

[0071] The pH adjuster is a mixture of 40 parts by mass of sodium hydroxide and 60 parts by mass of sodium carbonate.

[0072] The cutting agent is a mixture of 20 parts of sclerotium gum, 20 parts of diutan gum and 60 parts of welan gum by weight.

[0073] The raw materials of the fluid loss reducer are as follows: 15 parts of fulvic acid, 100 parts of deionized water, 1 part of chitosan, 1 part of γ-methacryloxypropyltrimethoxysilane, 100 parts of 85% ethanol aqueous solution (1% acetic acid), 5 parts of acrylic acid, 10 parts of N-vinyl pyrrolidone, 5 parts of dimethyldiallylammonium chloride and 0.1 parts of ammonium persulfate by mass.

[0074] The preparation method of the above-mentioned fluid loss reducing agent is:

[0075] First, dissolve fulvic acid in deionized water, stir for 30 minutes, then add chitosan, continue stirring for 1 hour, and transfer the fulvic acid-chitosan mixture to a four-necked round-bottom flask. Then dissolve γ-methacryloxypropyltrimethoxysilane in an 85% ethanol aqueous solution containing 1% acetic acid, then slowly heat to 40°C under stirring conditions, and hydrolyze for 3 hours; then slowly add the pre-hydrolyzed silane coupling agent to the fulvic acid-chitosan mixture, continue stirring and heat to 60°C, stop heating after 10 hours of reaction, and cool to room temperature; remove the solvent by centrifugation, wash with anhydrous ethanol several times, and then vacuum dry to obtain the intermediate product;

[0076] Secondly, acrylic acid, N-vinylpyrrolidone, and dimethyldiallylammonium chloride were pre-dissolved in deionized water, and the pH was adjusted to 7 with 0.1 mol / L aqueous sodium hydroxide solution. After stirring for 10 min, the mixed solution was transferred to a four-necked round-bottom flask. Then, under stirring conditions, the intermediate product obtained in the previous step was added thereto, nitrogen was passed through to remove oxygen, the temperature was raised to 65 °C, and ammonium persulfate was dissolved in deionized water and then added dropwise thereto to initiate polymerization reaction 1. After 3 h, the reaction was stopped and cooled to room temperature. Finally, it was washed with deionized water multiple times, followed by vacuum filtration, vacuum drying, and pulverization. The resulting product was the filtrate reducer.

[0077] By mass fraction, the inhibitor is a mixture of 70 parts of polyethyleneimine graft copolymer and 30 parts of hexamethylenediamine;

[0078] The raw materials of the polyethyleneimine graft copolymer are: 100 parts of deionized water, 40 parts of polyethyleneimine, 10 parts of maleic anhydride, 15 parts of dimethyldiallylammonium chloride, and 0.6 parts of potassium persulfate;

[0079] The preparation method of the above-mentioned polyethyleneimine graft copolymer is as follows:

[0080] First, polyethyleneimine was added to a four-necked flask, and the temperature was raised to 65 °C in a water bath under stirring conditions. Nitrogen was passed through to remove oxygen, and then maleic anhydride was slowly added for amidation reaction. The reaction temperature was controlled at 70 °C, and the reaction time was 3 h to obtain an intermediate product;

[0081] Secondly, the flask containing the above intermediate product was cooled to room temperature, and then deionized water and dimethyldiallylammonium chloride were slowly added thereto, stirred for 30 min, nitrogen was passed through to remove oxygen, and then potassium persulfate was added to initiate polymerization reaction 2. The reaction temperature was controlled at 60 °C, and the reaction time was 2 h. Finally, the obtained product was the polyethyleneimine graft copolymer.

[0082] By mass fraction, the auxiliary inhibitor is a mixture of 10 parts of sodium chloride, 20 parts of potassium chloride, 40 parts of sodium formate, and 30 parts of potassium formate.

[0083] By mass fraction, the raw materials of the dispersant are: 100 parts of deionized water, 20 parts of ethanolamine, 20 parts of itaconic anhydride, 3 parts of vinylphosphonic acid, 3 parts of N-vinylpyrrolidone, and 0.5 parts of ammonium persulfate;

[0084] The preparation method of the above dispersant is as follows:

[0085] First, ethanolamine was added to a four-necked flask, and the temperature was raised to 70 °C in a water bath under stirring conditions. Nitrogen was passed through to remove oxygen, and then itaconic anhydride was slowly added for amidation reaction. The reaction temperature was controlled at 80 °C, and the reaction time was 2 h to obtain an intermediate product;

[0086] Secondly, the flask containing the intermediate product was cooled to room temperature, and deionized water, vinylphosphonic acid and N-vinylpyrrolidone were slowly added thereto, stirred for 20 minutes, and nitrogen was passed to deoxygenate. Subsequently, ammonium persulfate was added to initiate the polymerization reaction 3, and the reaction temperature was controlled at 70°C and the reaction time was 2 hours. Finally, the product obtained was the dispersant.

[0087] The lubricant is a mixture of 40 parts of polyethylene glycol borate, 45 parts of fatty alcohol polyoxyethylene ether and 15 parts of nano silicon nitride by weight.

[0088] The drilling fluid density provided in this embodiment is 1.1 g / cm 3 , the hot rolling temperature of the drilling fluid is 30℃. Example 2

[0089] A desulfonated low-viscosity high-shear strength inhibited water-based drilling fluid, the raw materials of which are as follows by weight:

[0090] Seawater: 100 parts

[0091] pH adjuster: 1.0 part

[0092] Cutting agent: 0.7 parts

[0093] Fluid loss reducer: 4 parts

[0094] Inhibitor: 4 parts

[0095] Auxiliary inhibitor: 15 parts

[0096] Dispersant: 3 parts

[0097] Lubricant: 3 parts

[0098] Barite: Add weight to the drilling fluid density of 1.3g / cm 3

[0099] The pH adjuster is a mixture of 60 parts by mass of sodium hydroxide and 40 parts by mass of sodium carbonate.

[0100] The cutting agent is a mixture of 30 parts of sclerotium gum, 30 parts of diutan gum and 40 parts of welan gum by weight.

[0101] The raw materials of the fluid loss reducer are, by mass, 25 parts of fulvic acid, 100 parts of deionized water, 3 parts of chitosan, 3 parts of γ-methacryloxypropyltrimethoxysilane, 100 parts of 85% ethanol aqueous solution (1% acetic acid), 10 parts of acrylic acid, 20 parts of N-vinyl pyrrolidone, 12 parts of dimethyldiallylammonium chloride and 0.3 parts of ammonium persulfate.

[0102] The preparation method of the above-mentioned fluid loss reducing agent is:

[0103] First, dissolve fulvic acid in deionized water. After stirring for 60 min, continue to add chitosan. After continuous stirring for 2 h, transfer the fulvic acid-chitosan mixture to a four-necked round-bottom flask. Then, dissolve γ-methacryloxypropyltrimethoxysilane in an 85% ethanol aqueous solution containing 1% acetic acid, and then slowly heat it to 50 °C under stirring conditions for a hydrolysis reaction for 5 h. Subsequently, slowly add the pre-hydrolyzed silane coupling agent to the fulvic acid-chitosan mixture, continuously stir and heat it to 70 °C. After reacting for 20 h, stop heating and cool it to room temperature. Remove the solvent by centrifugation, wash it with absolute ethanol multiple times, and then obtain the intermediate product through vacuum drying;

[0104] Secondly, pre-dissolve acrylic acid, N-vinylpyrrolidone, and dimethyldiallylammonium chloride in deionized water, adjust its pH to 8 with a 0.1 mol / L sodium hydroxide aqueous solution, stir for 30 min, and then transfer the mixed solution to a four-necked round-bottom flask. Then, add the intermediate product obtained in the previous step to it under stirring conditions, deoxygenate by passing nitrogen, heat it to 75 °C, and dissolve ammonium persulfate in deionized water and then dropwise add it thereto to initiate the polymerization reaction 1, which lasts for 5 h. After that, stop the reaction and cool it to room temperature. Finally, wash it with deionized water multiple times, then perform vacuum filtration, vacuum drying, and pulverization. The obtained product is the filtrate reducer.

[0105] By mass fraction, the inhibitor is a mixture of 80 parts of polyethyleneimine graft copolymer and 20 parts of hexamethylenediamine;

[0106] The raw materials of the polyethyleneimine graft copolymer are: 100 parts of deionized water, 60 parts of polyethyleneimine, 20 parts of maleic anhydride, 25 parts of dimethyldiallylammonium chloride, and 0.8 part of potassium persulfate;

[0107] The preparation method of the above-mentioned polyethyleneimine graft copolymer is as follows:

[0108] First, add polyethyleneimine to a four-necked flask, heat it to 75 °C in a water bath under stirring conditions, deoxygenate by passing nitrogen, and then slowly add maleic anhydride for an amidation reaction, control the reaction temperature at 80 °C, and the reaction time is 5 h to obtain an intermediate product;

[0109] Secondly, cool the flask containing the above intermediate product to room temperature, then slowly add deionized water and dimethyldiallylammonium chloride to it, stir for 60 min, deoxygenate by passing nitrogen, then add potassium persulfate to initiate the polymerization reaction 2, and control the reaction temperature at 70 °C and the reaction time at 4 h. Finally, the obtained product is the polyethyleneimine graft copolymer.

[0110] By mass fraction, the auxiliary inhibitor is a mixture of 20 parts of sodium chloride, 30 parts of potassium chloride, 30 parts of sodium formate, and 20 parts of potassium formate.

[0111] The raw materials of the dispersant are, by weight, 100 parts of deionized water, 30 parts of ethanolamine, 30 parts of itaconic anhydride, 5 parts of vinylphosphonic acid, 5 parts of N-vinylpyrrolidone and 1.0 part of ammonium persulfate.

[0112] The preparation method of the above dispersant is:

[0113] First, ethanolamine was added to a four-necked flask, and the temperature was raised to 75°C in a water bath under stirring conditions, and nitrogen was passed to deoxygenate, and then itaconic anhydride was slowly added to carry out an amidation reaction, and the reaction temperature was controlled at 90°C and the reaction time was 4 hours to obtain an intermediate product;

[0114] Secondly, the flask containing the intermediate product was cooled to room temperature, and deionized water, vinylphosphonic acid and N-vinylpyrrolidone were slowly added thereto, stirred for 30 minutes, and nitrogen was passed to deoxygenate. Then, ammonium persulfate was added to initiate the polymerization reaction 3, and the reaction temperature was controlled at 80°C and the reaction time was 3 hours. Finally, the product obtained was the dispersant.

[0115] The lubricant is a mixture of 45 parts of polyethylene glycol borate, 50 parts of fatty alcohol polyoxyethylene ether and 5 parts of nano silicon nitride by weight.

[0116] The drilling fluid density prepared in this example is 1.3 g / cm 3 , the hot rolling temperature of the drilling fluid is 60℃. Example 3

[0117] A desulfonated low-viscosity high-shear strength inhibited water-based drilling fluid, the raw materials of which are as follows by weight:

[0118] Fresh water: 100 parts

[0119] pH adjuster: 0.75 parts

[0120] Cutting agent: 0.6 parts

[0121] Fluid loss reducer: 3 parts

[0122] Inhibitor: 3 parts

[0123] Auxiliary inhibitor: 10 parts

[0124] Dispersant: 2 parts

[0125] Lubricant: 2 parts

[0126] Barite: Add weight to the drilling fluid density of 1.5g / cm 3

[0127] Wherein, the pH adjuster is a mixture of 50 parts of sodium hydroxide and 50 parts of sodium carbonate by mass.

[0128] By mass fraction, the thickening agent is a mixture of 25 parts of scleroglucan, 25 parts of dextran and 50 parts of welan gum.

[0129] By mass fraction, the raw materials of the fluid loss reducer are: 20 parts of humic acid, 100 parts of deionized water, 2 parts of chitosan, 2 parts of γ-methacryloxypropyltrimethoxysilane, 100 parts of 85% ethanol aqueous solution (1% acetic acid), 7.5 parts of acrylic acid, 15 parts of N-vinylpyrrolidone, 8.5 parts of dimethyldiallylammonium chloride and 0.2 part of ammonium persulfate;

[0130] The preparation method of the above fluid loss reducer is as follows:

[0131] First, dissolve humic acid in deionized water, stir for 45 min and then continue to add chitosan. After continuous stirring for 1.5 h, transfer the humic acid-chitosan mixture to a four-necked round-bottom flask. Then dissolve γ-methacryloxypropyltrimethoxysilane in 85% ethanol aqueous solution containing 1% acetic acid, and then slowly heat up to 45 °C under stirring conditions for hydrolysis reaction for 4 h; subsequently, slowly add the pre-hydrolyzed silane coupling agent to the humic acid-chitosan mixture, continuously stir and heat up to 65 °C, stop heating after reacting for 15 h, and cool to room temperature; remove the solvent by centrifugation, wash with absolute ethanol for several times, and then vacuum dry to obtain the intermediate product;

[0132] Second, dissolve acrylic acid, N-vinylpyrrolidone and dimethyldiallylammonium chloride in deionized water in advance, adjust its pH to 7.5 with 0.1 mol / L sodium hydroxide aqueous solution, stir for 20 min, and then transfer the mixed solution to a four-necked round-bottom flask; then, add the intermediate product obtained in the previous step thereto under stirring conditions, deoxygenate by passing nitrogen, heat up to 70 °C, and dissolve ammonium persulfate in deionized water and then dropwise add it thereto to initiate the polymerization reaction 1, continue for 4 h, stop the reaction, and cool to room temperature; finally, wash with deionized water for several times, then perform vacuum filtration, vacuum drying and pulverization, and the obtained product is the fluid loss reducer.

[0133] By mass fraction, the inhibitor is a mixture of 75 parts of polyethyleneimine graft copolymer and 25 parts of hexamethylenediamine;

[0134] By mass fraction, the raw materials of the polyethyleneimine graft copolymer are: 100 parts of deionized water, 50 parts of polyethyleneimine, 15 parts of maleic anhydride, 20 parts of dimethyldiallylammonium chloride and 0.7 part of potassium persulfate;

[0135] The preparation method of the above polyethyleneimine graft copolymer is as follows:

[0136] First, add polyethyleneimine into a four-necked flask, heat it up to 70 °C in a water bath under stirring conditions, purge with nitrogen to remove oxygen, and then slowly add maleic anhydride for amidation reaction. Control the reaction temperature at 75 °C and the reaction time at 4 h to obtain an intermediate product.

[0137] Secondly, cool the flask containing the above intermediate product to room temperature, then slowly add deionized water and dimethyldiallylammonium chloride to it, stir for 45 min, purge with nitrogen to remove oxygen, and then add potassium persulfate to initiate polymerization reaction 2. Control the reaction temperature at 65 °C and the reaction time at 3 h. Finally, the obtained product is the polyethyleneimine graft copolymer.

[0138] By mass fraction, the auxiliary inhibitor is a mixture of 15 parts of sodium chloride, 25 parts of potassium chloride, 35 parts of sodium formate, and 25 parts of potassium formate.

[0139] By mass fraction, the raw materials of the dispersant are: 100 parts of deionized water, 25 parts of ethanolamine, 25 parts of itaconic anhydride, 4 parts of vinylphosphonic acid, 4 parts of N-vinylpyrrolidone, and 0.75 parts of ammonium persulfate;

[0140] The preparation method of the dispersant is as follows:

[0141] First, add ethanolamine into a four-necked flask, heat it up to 72 °C in a water bath under stirring conditions, purge with nitrogen to remove oxygen, and then slowly add itaconic anhydride for amidation reaction. Control the reaction temperature at 85 °C and the reaction time at 3 h to obtain an intermediate product.

[0142] Secondly, cool the flask containing the above intermediate product to room temperature, then slowly add deionized water, vinylphosphonic acid, and N-vinylpyrrolidone to it, stir for 25 min, purge with nitrogen to remove oxygen, and then add ammonium persulfate to initiate polymerization reaction 3. Control the reaction temperature at 75 °C and the reaction time at 2.5 h. Finally, the obtained product is the dispersant.

[0143] By mass fraction, the lubricant is a mixture of 42.5 parts by mass of polyethylene glycol borate, 47.5 parts by mass of fatty alcohol polyoxyethylene ether, and 7.5 parts by mass of nano silicon nitride.

[0144] The density of the drilling fluid prepared in this example is 1.5 g / cm 3 , and the thermal rolling temperature of the drilling fluid is 90 °C. Example 4

[0145] A desulfonated low-viscosity high-shear-strength inhibition water-based drilling fluid, by mass fraction, the raw materials are as follows:

[0146] Fresh water: 100 parts

[0147] pH regulator: 1.0 part

[0148] Viscosity increasing agent: 0.5 part

[0149] Fluid loss reducer: 3.5 parts

[0150] Inhibitor: 3 parts

[0151] Auxiliary inhibitor: 5 parts

[0152] Dispersant: 3 parts

[0153] Lubricant: 3 parts

[0154] Barite: Add weight to the drilling fluid density of 1.7g / cm 3

[0155] Wherein, the pH adjuster is a mixture of 40 parts of sodium hydroxide and 60 parts of sodium carbonate by mass.

[0156] The cutting agent is a mixture of 30 parts of sclerotium gum, 20 parts of diutan gum and 50 parts of welan gum by weight.

[0157] The raw materials of the fluid loss reducer are as follows: 18 parts of fulvic acid, 100 parts of deionized water, 1.5 parts of chitosan, 2 parts of γ-methacryloxypropyltrimethoxysilane, 100 parts of 85% ethanol aqueous solution (1% acetic acid), 6 parts of acrylic acid, 12 parts of N-vinyl pyrrolidone, 6 parts of dimethyldiallylammonium chloride and 0.1 parts of ammonium persulfate by mass.

[0158] The preparation method of the above-mentioned fluid loss reducing agent is:

[0159] First, dissolve fulvic acid in deionized water, stir for 40 minutes, then add chitosan, continue stirring for 1 hour, and transfer the fulvic acid-chitosan mixture to a four-necked round-bottom flask. Then dissolve γ-methacryloxypropyltrimethoxysilane in 85% ethanol aqueous solution containing 1% acetic acid, then slowly heat to 42°C under stirring conditions, and hydrolyze for 3.5 hours; then slowly add the pre-hydrolyzed silane coupling agent to the fulvic acid-chitosan mixture, continue stirring and heat to 63°C, stop heating after 12 hours of reaction, and cool to room temperature; remove the solvent by centrifugation, wash with anhydrous ethanol several times, and then vacuum dry to obtain the intermediate product;

[0160] Secondly, acrylic acid, N-vinylpyrrolidone and dimethyldiallylammonium chloride were pre-dissolved in deionized water, and the pH was adjusted to 7 with 0.1 mol / L sodium hydroxide aqueous solution. After stirring for 16 min, the mixed solution was transferred to a four-necked round-bottom flask. Then, under stirring conditions, the intermediate product obtained in the previous step was added thereto, nitrogen was passed through to remove oxygen, the temperature was raised to 68 °C, and ammonium persulfate was dissolved in deionized water and then added dropwise thereto to initiate the polymerization reaction 1. After 3.5 h, the reaction was stopped and cooled to room temperature. Finally, it was washed with deionized water multiple times and then subjected to vacuum filtration, vacuum drying and pulverization, and the obtained product was the filtration reducer.

[0161] By mass, the inhibitor is a mixture of 72 parts of polyethyleneimine graft copolymer and 28 parts of hexamethylenediamine;

[0162] By mass, the raw materials of the polyethyleneimine graft copolymer are: 100 parts of deionized water, 55 parts of polyethyleneimine, 18 parts of maleic anhydride, 15 parts of dimethyldiallylammonium chloride and 0.6 part of potassium persulfate;

[0163] The preparation method of the above-mentioned polyethyleneimine graft copolymer is as follows:

[0164] First, polyethyleneimine was added to a four-necked flask, and the temperature was raised to 68 °C in a water bath under stirring conditions. Nitrogen was passed through to remove oxygen, and then maleic anhydride was slowly added for amidation reaction. The reaction temperature was controlled at 76 °C and the reaction time was 5 h to obtain an intermediate product;

[0165] Secondly, the flask containing the above intermediate product was cooled to room temperature, and then deionized water and dimethyldiallylammonium chloride were slowly added thereto, stirred for 40 min, nitrogen was passed through to remove oxygen, and then potassium persulfate was added to initiate the polymerization reaction 2. The reaction temperature was controlled at 66 °C and the reaction time was 2 h. Finally, the obtained product was the polyethyleneimine graft copolymer.

[0166] By mass, the auxiliary inhibitor is a mixture of 20 parts of sodium chloride, 20 parts of potassium chloride, 35 parts of sodium formate and 25 parts of potassium formate.

[0167] By mass, the raw materials of the dispersant are: 100 parts of deionized water, 26 parts of ethanolamine, 30 parts of itaconic anhydride, 3 parts of vinylphosphonic acid, 5 parts of N-vinylpyrrolidone and 0.8 part of ammonium persulfate;

[0168] The preparation method of the above dispersant is as follows:

[0169] First, ethanolamine was added to a four-necked flask, and the temperature was raised to 73 °C in a water bath under stirring conditions. Nitrogen was passed through to remove oxygen, and then itaconic anhydride was slowly added for amidation reaction. The reaction temperature was controlled at 86 °C and the reaction time was 3.5 h to obtain an intermediate product;

[0170] Secondly, the flask containing the intermediate product was cooled to room temperature, and deionized water, vinylphosphonic acid and N-vinylpyrrolidone were slowly added thereto, stirred for 28 minutes, and nitrogen was passed to deoxygenate. Subsequently, ammonium persulfate was added to initiate the polymerization reaction 3, and the reaction temperature was controlled at 76°C. The reaction time was 2 hours, and the final product was the dispersant.

[0171] The lubricant is a mixture of 40 parts of polyethylene glycol borate, 50 parts of fatty alcohol polyoxyethylene ether and 10 parts of nano silicon nitride by weight.

[0172] The drilling fluid density prepared in this example is 1.7 g / cm 3 , the hot rolling temperature of the drilling fluid is 120℃. Example 5

[0173] A desulfonated low-viscosity high-shear strength inhibited water-based drilling fluid, the raw materials of which are as follows by weight:

[0174] Fresh water: 100 parts

[0175] pH adjuster: 0.8 parts

[0176] Cutting agent: 0.6 parts

[0177] Fluid loss reducer: 4 parts

[0178] Inhibitor: 4 parts

[0179] Auxiliary inhibitor: 15 parts

[0180] Dispersant: 2 parts

[0181] Lubricant: 3 parts

[0182] Barite: Add weight to the drilling fluid density of 1.7g / cm 3

[0183] Wherein, the pH adjuster is a mixture of 50 parts of sodium hydroxide and 50 parts of sodium carbonate by mass.

[0184] The cutting agent is a mixture of 25 parts of sclerotium gum, 30 parts of diutan gum and 45 parts of welan gum by weight.

[0185] The raw materials of the fluid loss reducer are as follows: 25 parts of fulvic acid, 100 parts of deionized water, 1 part of chitosan, 2 parts of γ-methacryloxypropyltrimethoxysilane, 100 parts of 85% ethanol aqueous solution (1% acetic acid), 8 parts of acrylic acid, 16 parts of N-vinyl pyrrolidone, 10 parts of dimethyldiallylammonium chloride and 0.2 parts of ammonium persulfate by mass.

[0186] The preparation method of the above-mentioned fluid loss reducing agent is:

[0187] First, dissolve fulvic acid in deionized water. After stirring for 50 min, continue to add chitosan. After continuously stirring for 2 h, transfer the fulvic acid-chitosan mixture to a four-necked round-bottom flask. Then, dissolve γ-methacryloxypropyltrimethoxysilane in an 85% ethanol aqueous solution containing 1% acetic acid. Then, slowly heat it to 48 °C under stirring conditions and carry out a hydrolysis reaction for 5 h. Subsequently, slowly add the pre-hydrolyzed silane coupling agent to the fulvic acid-chitosan mixture, continuously stir and heat it to 66 °C. After reacting for 18 h, stop heating and cool it to room temperature. Remove the solvent by centrifugation, wash it with anhydrous ethanol multiple times, and then obtain the intermediate product through vacuum drying.

[0188] Secondly, pre-dissolve acrylic acid, N-vinylpyrrolidone, and dimethyldiallylammonium chloride in deionized water, adjust its pH to 8 with a 0.1 mol / L sodium hydroxide aqueous solution, and after stirring for 18 min, transfer the mixed solution to a four-necked round-bottom flask. Then, add the intermediate product obtained in the previous step thereto under stirring conditions, remove oxygen by passing nitrogen, heat it to 72 °C, and dissolve ammonium persulfate in deionized water and then dropwise add it thereto to initiate polymerization reaction 1, which lasts for 4 h. Then, stop the reaction and cool it to room temperature. Finally, wash it with deionized water multiple times, followed by vacuum filtration, vacuum drying, and pulverization. The obtained product is the filtration reducer.

[0189] By mass, the inhibitor is a mixture of 78 parts of polyethyleneimine graft copolymer and 22 parts of hexamethylenediamine.

[0190] By mass, the raw materials of the polyethyleneimine graft copolymer are: 100 parts of deionized water, 50 parts of polyethyleneimine, 16 parts of maleic anhydride, 16 parts of dimethyldiallylammonium chloride, and 0.7 parts of potassium persulfate.

[0191] The preparation method of the above-mentioned polyethyleneimine graft copolymer is as follows:

[0192] First, add polyethyleneimine to a four-necked flask, heat it to 70 °C in a water bath under stirring conditions, remove oxygen by passing nitrogen, and then slowly add maleic anhydride for an amidation reaction. Control the reaction temperature at 70 °C and the reaction time at 5 h to obtain an intermediate product.

[0193] Secondly, cool the flask containing the above intermediate product to room temperature, then slowly add deionized water and dimethyldiallylammonium chloride thereto, stir for 30 min, remove oxygen by passing nitrogen, then add potassium persulfate to initiate polymerization reaction 2, and control the reaction temperature at 65 °C and the reaction time at 2 h. Finally, the obtained product is the polyethyleneimine graft copolymer.

[0194] By mass, the auxiliary inhibitor is a mixture of 15 parts of sodium chloride, 30 parts of potassium chloride, 35 parts of sodium formate, and 20 parts of potassium formate.

[0195] By mass fraction, the raw materials of the dispersant are: 100 parts of deionized water, 20 parts of ethanolamine, 30 parts of itaconic anhydride, 5 parts of vinylphosphonic acid, 3 parts of N-vinylpyrrolidone, and 0.6 parts of ammonium persulfate;

[0196] The preparation method of the dispersant is as follows:

[0197] First, add ethanolamine to a four-necked flask, heat it up to 70 °C in a water bath under stirring conditions, purge with nitrogen to remove oxygen, and then slowly add itaconic anhydride for amidation reaction, control the reaction temperature at 80 °C, and the reaction time is 4 h to obtain an intermediate product;

[0198] Second, cool the flask containing the above intermediate product to room temperature, then slowly add deionized water, vinylphosphonic acid, and N-vinylpyrrolidone to it, stir for 30 min, purge with nitrogen to remove oxygen, then add ammonium persulfate to initiate polymerization reaction 3, and control the reaction temperature at 80 °C, the reaction time is 2 h, and finally the obtained product is the dispersant.

[0199] By mass fraction, the lubricant is a mixture of 40 parts of polyethylene glycol borate, 45 parts of fatty alcohol polyoxyethylene ether, and 15 parts of nano-silicon nitride.

[0200] The density of the drilling fluid prepared in this example is 1.7 g / cm 3 , and the hot rolling temperature of the drilling fluid is 150 °C. Comparative Example 1

[0201] The commonly used polysulfonate water-based drilling fluid on site, with the composition of 100 parts of fresh water, 3 parts of bentonite, 1.0 part of pH regulator (the mass ratio of sodium hydroxide to sodium carbonate is 1:1), 5 parts of potassium chloride, 0.5 part of zwitterionic polymer strong coating agent, 0.6 part of low-viscosity carboxymethyl cellulose, 3 parts of sulfonated lignite resin, 3 parts of sulfonated asphalt, 3 parts of sulfonated phenolic resin, 3 parts of modified vegetable oil, and barite is weighted to a density of 1.7 g / cm 3 . The hot rolling temperature of the drilling fluid obtained in this comparative example is 150 °C.

[0202] The drilling fluids obtained in the above examples and comparative examples were evaluated according to GB / T 16783.1-2014 "Petroleum and natural gas industries - Drilling fluids - Field testing - Part 1: Water-based drilling fluids", and the biodegradability and sulfur content tests were carried out with reference to SY / T 7467—2020 "Technical specification for evaluation of environmental protection performance of drilling fluids" and SN / T 3005-2011 "Determination method of carbon, hydrogen, nitrogen, and sulfur contents in organic chemicals by elemental analyzer", and the results are shown in Table 1.

[0203] Table 1 Comprehensive performance of drilling fluids

[0204] ,

[0205] Note: ρ: density of drilling fluid, g / cm 3

[0206] T: aging temperature of drilling fluid, °C

[0207] AV: apparent viscosity of drilling fluid, mPa·s

[0208] PV: plastic viscosity of drilling fluid, mPa·s

[0209] YP: yield point of drilling fluid, Pa

[0210] YP / PV: yield point / plastic viscosity ratio, Pa / mPa·s

[0211] Φ3: reading at 3 revolutions of a six-speed rotational viscometer, dimensionless

[0212] API: medium-pressure filtration loss of drilling fluid (0.7 MPa, room temperature, 30 min), mL

[0213] EP: extreme pressure friction coefficient, dimensionless

[0214] η: rate of increase in apparent viscosity after contamination with 20% sodium-based bentonite, %

[0215] θ: rolling recovery rate of shale, %

[0216] δ: dry basis sulfur content of unweighted drilling fluid, %

[0217] BI: biodegradation index of drilling fluid, %

[0218] It can be seen from Examples 1 to 5 that the desulfonated low-viscosity high-shear strong-inhibiting water-based drilling fluid has a density of 1.1 to 1.7 g / cm 3In the range of 30 to 150°C for the aging temperature, it has good low-viscosity high-shear rheological properties, filtration loss control properties, lubrication properties, inhibition properties, and environmental-friendly biodegradability. It can be seen from Example 5 and Comparative Example 1 that, compared with the commonly used polysulfonate water-based drilling fluid in the field, the desulfonated low-viscosity high-shear strong inhibition water-based drilling fluid has significantly lower plastic viscosity and higher dynamic shear force, and the dynamic-plastic ratio > 1.0 Pa / mPa·s, showing better suspension and rock-carrying performance, and better lubrication performance, with the extreme pressure friction coefficient < 0.1, being more suitable for horizontal well drilling operations. In terms of inhibition, after being contaminated by 20% sodium bentonite, the desulfonated low-viscosity high-shear strong inhibition water-based drilling fluid has a more stable viscosity, and the apparent viscosity increase rate < 11%, while the apparent viscosity increase rate of the polysulfonate water-based drilling fluid exceeds 45%, showing obvious thickening. In addition, the biodegradation index of the desulfonated low-viscosity high-shear strong inhibition water-based drilling fluid is much higher than 5%, having excellent biodegradability, and the dry basis sulfur content is 0 without considering barite, being environmentally friendly to the ecological environment; while the biodegradation index of the polysulfonate water-based drilling fluid under the same conditions < 5%, with poor biodegradability, and the dry basis sulfur content reaches 4.07% without considering barite. Even after waste treatment, it will produce toxic and harmful sulfur-containing by-products, which is not conducive to environmental protection.

[0219] For the 5 groups of examples of the desulfonated low-viscosity high-shear strong inhibition water-based drilling fluid of the present invention, after aging at different densities and different temperatures: it has excellent rheological properties, low plastic viscosity, and the dynamic-plastic ratio is higher than 1.0, showing significant suspension and rock-carrying performance; the API filtration loss is low, all not exceeding 3.5 mL; the extreme pressure friction coefficient is significantly lower than 0.1, with excellent lubrication performance, which is beneficial to reducing the frictional torque and is suitable for horizontal well operations; the apparent viscosity increase rate after being contaminated by 20% sodium bentonite is lower than 11%, and the shale rolling recovery rate is higher than 95%, showing a significant inhibition effect on the hydration of clay; at the same time, the biodegradation index is greater than 25%, and the dry basis sulfur content without weighting is 0, having significant environmental-friendly biodegradability and being harmless to the ecological environment.

[0220] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art in this technical field, without departing from the principle of the present invention, several improvements and refinements can still be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A desulfonated low-viscosity high-shear strong-inhibiting water-based drilling fluid, characterized in that, By mass parts, the raw materials include: 100 parts of water, 0.5 - 1.0 part of pH regulator, 0.5 - 0.7 part of viscosifier, 2 - 4 parts of fluid loss reducer, 2 - 4 parts of inhibitor, 5 - 15 parts of auxiliary inhibitor, 1 - 3 parts of dispersant, 1 - 3 parts of lubricant and barite; the amount of barite is not limited, and it is weighted to the required density; The viscosifier is a mixture of 20 - 30 parts of scleroglucan, 20 - 30 parts of dextran and 40 - 60 parts of welan gum; By mass parts, the inhibitor is a mixture of 70 - 80 parts of polyethyleneimine graft copolymer and 20 - 30 parts of hexamethylenediamine; By mass parts, the raw materials of the polyethyleneimine graft copolymer include: 100 parts of water, 40 - 60 parts of polyethyleneimine, 10 - 20 parts of maleic anhydride, 15 - 25 parts of dimethyldiallylammonium chloride and 0.6 - 0.8 part of potassium persulfate; The preparation method of the polyethyleneimine graft copolymer includes the following steps: Carry out amidation reaction on polyethyleneimine and maleic anhydride; After the amidation reaction is completed, add water and dimethyldiallylammonium chloride to the reaction system, and under an inert atmosphere, add potassium persulfate to carry out polymerization reaction 2 to obtain the polyethyleneimine graft copolymer; By mass parts, the auxiliary inhibitor is a mixture of 10 - 20 parts of sodium chloride, 20 - 30 parts of potassium chloride, 30 - 40 parts of sodium formate and 20 - 30 parts of potassium formate; The raw materials of the dispersant include: 100 parts of water, 20 - 30 parts of ethanolamine, 20 - 30 parts of itaconic anhydride, 3 - 5 parts of vinylphosphonic acid, 3 - 5 parts of N - vinylpyrrolidone and 0.5 - 1.0 part of ammonium persulfate; The preparation method of the dispersant includes the following steps: Carry out amidation reaction on ethanolamine and itaconic anhydride; After the amidation reaction is completed, add water, vinylphosphonic acid and N - vinylpyrrolidone to the reaction system, and under an inert atmosphere, add potassium persulfate to carry out polymerization reaction 3 to obtain the dispersant.

2. The desulfonated low-viscosity high-shear strong-inhibiting water-based drilling fluid according to claim 1, wherein By mass parts, the pH regulator is a mixture of 40 - 60 parts of sodium hydroxide and 40 - 60 parts of sodium carbonate.

3. The desulfonated low-viscosity high-shear-strength inhibition water-based drilling fluid according to claim 1, wherein By mass parts, the raw materials of the fluid loss reducer include: 15 - 25 parts of fulvic acid, 100 parts of water, 1 - 3 parts of chitosan, 1 - 3 parts of γ - methacryloyloxypropyltrimethoxysilane, 100 parts of ethanol aqueous solution containing acetic acid, 5 - 10 parts of acrylic acid, 10 - 20 parts of N - vinylpyrrolidone, 5 - 12 parts of dimethyldiallylammonium chloride and 0.1 - 0.3 part of ammonium persulfate; The preparation method of the fluid loss reducer includes the following steps: Dissolve chitosan in the fulvic acid aqueous solution to obtain a fulvic acid - chitosan mixed solution; Dissolve γ - methacryloyloxypropyltrimethoxysilane in the ethanol aqueous solution containing acetic acid, and then carry out hydrolysis reaction to obtain a pre - hydrolyzed silane coupling agent; Add the pre - hydrolyzed silane coupling agent to the fulvic acid - chitosan mixed solution for reaction to obtain an intermediate product; Dissolve acrylic acid, N-vinyl pyrrolidone and dimethyldiallylammonium chloride in water, adjust the pH value to alkaline, then add the intermediate product under stirring conditions, and add ammonium persulfate to the reaction system under the protection of an inert atmosphere for polymerization reaction 1 to obtain the filtrate reducer.

4. The desulfonated low-viscosity high-shear strong-inhibiting water-based drilling fluid according to claim 1, wherein By mass, the lubricant is a mixture of 40 - 45 parts of polyethylene glycol borate, 45 - 50 parts of fatty alcohol polyoxyethylene ether and 5 - 15 parts of nano silicon nitride.