An ultra-low friction coefficient microemulsion water-based drilling fluid for tight gas long horizontal wells

Abstract

The present invention provides an ultra-low friction coefficient microemulsion water-based drilling fluid for use in long horizontal wells of tight gas reservoirs, belonging to the field of oilfield chemistry technology for oil and gas drilling projects. The drilling fluid comprises, by weight, 75-85 parts of an aqueous phase, 15-25 parts of an oil phase, 3-5 parts of an emulsifier, 1-2 parts of a cosurfactant, 0.5-1.0 parts of a pH adjuster, 0.3-0.5 parts of a viscosity enhancer, 0.5-0.7 parts of a coating agent, 3-5 parts of a fluid loss additive, 0.5-1.5 parts of a lubricant, and barite; the barite is not limited in number and is added to the desired density. The drilling fluid provided by the present invention combines environmental protection, an ultra-low friction coefficient, excellent wellbore cleaning performance, superior wellbore stability, and efficient plugging performance, enabling the green, safe, and efficient development of tight gas reservoirs.

Description

Technical Field

[0001] The present invention relates to the technical field of oilfield chemistry in oil and gas drilling engineering, and in particular to an ultra-low friction coefficient microemulsion water-based drilling fluid for tight gas long horizontal wells. Background Art

[0002] With the continued growth of global energy demand and the dwindling availability of conventional oil and gas resources, the development of unconventional tight gas resources has gradually become a research hotspot in the energy sector and an important direction for future development. Tight gas reservoirs generally exhibit low porosity, low permeability, and significant heterogeneity, making them challenging to exploit. To effectively develop these unconventional resources, long horizontal well technology has been widely used as a means to effectively increase single-well production and resource recovery. However, the drilling of long horizontal tight gas wells often faces technical challenges such as long well sections, complex and variable formation properties, poor wellbore stability, and high frictional resistance, posing numerous challenges to drilling fluid performance.

[0003] Currently, drilling fluid systems used for long horizontal tight gas wells primarily include water-based and oil-based drilling fluids, but each has its limitations. While water-based drilling fluids offer significant environmental advantages and excellent economics, they generally suffer from poor lubricity, inhibition, and wellbore stability. This can lead to high friction resistance, excessive torque, increased risk of wellbore collapse, and difficulty cleaning the wellbore, significantly reducing drilling efficiency. Oil-based drilling fluids offer superior lubricity and wellbore stability, but pose significant environmental pollution risks and difficult waste fluid disposal, hindering environmentally friendly development and limiting their application in unconventional tight gas reservoirs.

[0004] Therefore, the development of a new microemulsion water-based drilling fluid system that takes into account environmental protection, ultra-low friction coefficient, excellent wellbore cleaning performance, outstanding wellbore stability and efficient plugging performance can not only effectively reduce the friction resistance and collapse risk in the drilling construction of long horizontal wells in tight gas reservoirs, but also meet the requirements of environmental protection. It has important practical significance for promoting the green, safe and efficient development of tight gas reservoirs. Summary of the Invention

[0005] Based on the above, the present invention aims to provide an ultra-low friction microemulsion water-based drilling fluid for use in long horizontal tight gas wells. This drilling fluid combines environmental friendliness with ultra-low friction, excellent wellbore cleaning performance, superior wellbore stability, and efficient plugging performance, enabling the green, safe, and efficient development of tight gas reservoirs.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] One of the technical solutions of the present invention is an ultra-low friction coefficient microemulsion water-based drilling fluid for tight gas long horizontal wells, which comprises, by weight, 75-85 parts of an aqueous phase, 15-25 parts of an oil phase, 3-5 parts of an emulsifier, 1-2 parts of a cosurfactant, 0.5-1.0 parts of a pH adjuster, 0.3-0.5 parts of a viscosity enhancer, 0.5-0.7 parts of a coating agent, 3-5 parts of a fluid loss additive, 0.5-1.5 parts of a lubricant, and barite; the barite is not limited in number and is added until the desired density is achieved;

[0008] The cosurfactant is a mixture of 30 to 40 parts of isopropyl alcohol, 30 to 40 parts of ethoxylated glycerol and 20 to 40 parts of n-butanol, calculated by mass.

[0009] The coating agent is polyacrylamide nanoparticles.

[0010] In a preferred embodiment of the present invention, the aqueous phase is a mixture of 80-95 parts of water, 3-12 parts of sodium chloride and 2-8 parts of potassium chloride, calculated by mass.

[0011] The aqueous phase can inhibit the hydration and swelling of clay minerals (such as montmorillonite) through ion exchange, in which sodium chloride provides high ionic strength and potassium ions enhance the inhibition by intercalating between clay layers.

[0012] In a preferred embodiment of the present invention, the oil phase is a mixture of 20 to 40 parts by mass of trimethylolpropane ester and 60 to 80 parts by mass of polyalphaolefin.

[0013] Trimethylolpropane ester is both biodegradable and has excellent lubricity, while polyalphaolefin is heat-resistant, has low viscosity and excellent lubricity. The combination of the two can form a polar-nonpolar synergistic lubricating film, enhance the boundary lubrication effect, and significantly reduce the friction torque between the drill bit and the well wall.

[0014] In a preferred embodiment of the present invention, the emulsifier is a mixture of 80-90 parts of isomeric tridecyl alcohol polyoxyethylene ether 1308 and 10-20 parts of Span 80, calculated by weight.

[0015] Isotridecyl polyoxyethylene ether 1308 is a hydrophilic nonionic surfactant with excellent emulsification effect, reducing oil-water interfacial tension and stabilizing the microemulsion structure; Span 80 has strong oil solubility and helps form a stable oil phase core, improve oil droplet size and distribution, and enhance the stability of the microemulsion system; the combined use of the two can form a stable oil-in-water (O / W) microemulsion.

[0016] Isopropyl alcohol and n-butanol can effectively regulate the properties of the interfacial layer and enhance the self-emulsification ability of the system; ethoxylated glycerol increases the thickness of the interfacial layer and maintains the stability of the microemulsion; the combined use of the three can further reduce the interfacial tension and improve the microemulsion formation rate and stability.

[0017] In a preferred embodiment of the present invention, the pH adjuster is one or more of diethanolamine, triethanolamine and triisopropanolamine.

[0018] In a preferred embodiment of the present invention, the pH adjuster is diethanolamine.

[0019] In a preferred embodiment of the present invention, the raw materials of the viscosity enhancer include, by weight: 5 to 10 parts of nano-calcium carbonate, 200 parts of ethanol aqueous solution, 0.5 to 0.7 parts of γ-aminopropyltriethoxysilane, 0.8 to 1.5 parts of dimethicone, 300 parts of water, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and N-hydroxysuccinimide; the total weight of the 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and N-hydroxysuccinimide is 0.10 to 0.15 parts, and the molar ratio of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide to N-hydroxysuccinimide is 1:1;

[0020] The preparation method of the tackifier comprises the following steps:

[0021] Dispersing nano-calcium carbonate in an ethanol aqueous solution, and then adding γ-aminopropyltriethoxysilane to the dispersion under stirring conditions to carry out reaction 1 to obtain amino-treated nano-calcium carbonate;

[0022] Dissolving diutan gum in water and adjusting the pH to acidic, then adding 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and N-hydroxysuccinimide to carry out reaction 2 to obtain an activated diutan gum solution;

[0023] Under an inert atmosphere, the amino-modified nano-calcium carbonate is added to the activated diutan gum solution to carry out reaction 3 to obtain the viscosity-increasing agent.

[0024] In the present invention, the concentration of ethanol in the ethanol aqueous solution is 88% v / v; the temperature of the reaction 1 is 60-70° C., and the time is 8-12 hours; after the reaction 1 is completed, the process further includes collecting the precipitate, washing the precipitate, and drying the precipitate.

[0025] In the present invention, the pH is 6, and the reagent for adjusting the pH is 2-morpholineethanesulfonic acid; and the reaction 2 is: stirring the reaction at room temperature for 30 to 60 minutes.

[0026] In the present invention, the temperature of reaction 3 is 50-60° C. and the time is 10-16 h. After reaction 3 is completed, the steps of dialyzing the obtained reaction solution (molecular weight cut-off 8000 Da) to remove unreacted reagents and freeze-drying are also included.

[0027] The viscosity enhancer in the present invention is a nano-calcium carbonate-dinobutane grafted complex. This nano-calcium carbonate-dinobutane grafted complex can simultaneously achieve multiple functions in microemulsion water-based drilling fluids, including improving rheology, enhancing plugging, stabilizing the wellbore, and improving lubrication. As a high-molecular-weight polysaccharide, dinobutane naturally imparts high shear force and viscosity to the system. In horizontal sections and large-displacement wellbores, it can significantly improve sand / rock-carrying capacity, preventing wellbore sand settling or mud cake accumulation. After being grafted with nano-calcium carbonate, its molecular chains more easily form a spatial network structure in the aqueous phase, resulting in more pronounced viscosity enhancement and thixotropic effects, ensuring both sand suspension performance and facilitating wellbore cleaning. Furthermore, rigid nano-scale calcium carbonate can form mechanical bridges at wellbore pores or microcracks, synergistically constructing a dense filter cake with the high-molecular-weight polysaccharide chains, inhibiting formation hydration and collapse and effectively reducing filtration loss. When used in conjunction with the microemulsion lubricating component, it can also help reduce the frictional contact between the well wall and the drill bit, helping to control torque and frictional resistance; while nano-calcium carbonate can dissolve during acidification, and the polysaccharide matrix will dissociate or migrate accordingly, facilitating subsequent unblocking and increasing production capacity.

[0028] Polyacrylamide nanospheres have multiple functions in microemulsion water-based drilling fluids, including coating, sealing, improving rheology and reducing friction. First, they can form effective physical bridges at the pores or microcracks of the well wall, and work together with other solid phases or fluid loss reducers in the microemulsion to build a dense filter cake, preventing excessive intrusion of drilling fluid into the formation and inhibiting well wall collapse. Their polymer skeleton and internal cross-linked structure enable the microspheres to remain elastic and compressible when subjected to shear or collision. They can adsorb on the formation surface and, together with the surfactants in the drilling fluid, enhance the coating effect and reduce the hydration and shedding of clay particles. At the same time, because the microspheres contain polyacrylamide chain segments on their surface, they can fully combine with the water phase, increase the liquid phase viscosity and sand-carrying capacity, and prevent the deposition of rock cuttings. Under the joint action of the microemulsion, these microspheres can form a certain lubricating barrier or "friction-reducing layer" on the well wall or drill bit surface, helping to further reduce contact friction and control torque and friction.

[0029] The polyacrylamide nanospheres used in the present invention can be commercially available polyacrylamide nanospheres or prepared using methods well known to those skilled in the art. For example, a method for preparing polyacrylamide nanospheres (which is not significantly different from the method for preparing commercially available polyacrylamide nanospheres) includes the following steps:

[0030] Step 1: Add 80-100 parts by mass of isooctane, 3-5 parts by mass of Span 80, and 1-3 parts by mass of isopropanol into a three-necked flask, and stir at room temperature for 2-3 hours to obtain an oil phase;

[0031] Step 2: dissolving 10-15 parts by mass of acrylamide and 0.05-0.1 parts by mass of N,N'-methylenebisacrylamide in 30 parts by mass of deionized water, and stirring at room temperature for 30-60 minutes to obtain a monomer solution;

[0032] Step 3: During the stirring process, the monomer solution obtained in step 2 is slowly added to the oil phase of step 1, and 0.08-0.12 parts by mass of ammonium persulfate as an initiator is added, nitrogen is passed through to deoxygenate, and then the temperature is raised to 55-65°C and the reaction is kept at this temperature for 4-6 hours;

[0033] Step 4: After the reaction in step 3 is completed, the mixture is cooled to room temperature, ethanol is added to break the emulsion, the microspheres are collected by centrifugation, and the mixture is washed with ethanol for 2 to 3 times and dried in vacuo to obtain the product, which is polyacrylamide nanospheres.

[0034] In a preferred embodiment of the present invention, the fluid loss additive is a mixture of 5 to 15 parts of polyanionic cellulose, 20 to 30 parts of carboxymethyl starch, and 55 to 75 parts of ultrafine calcium carbonate. The mesh size of the ultrafine calcium carbonate is 3800 mesh.

[0035] On the one hand, polyanionic cellulose and carboxymethyl starch can further strengthen the spatial network structure of the drilling fluid and reduce the viscosity of the filtrate. On the other hand, they can also be adsorbed on the well wall surface to participate in the formation of mud cake; ultrafine calcium carbonate particles can fill the network micropores, further reducing filtration loss and strengthening plugging.

[0036] In a preferred embodiment of the present invention, the lubricant is a mixture of 30 to 40 parts by mass of boron nitride nanosheets, 20 to 30 parts by mass of hydroxylated graphene, and 30 to 50 parts by mass of fluorinated molybdenum disulfide.

[0037] Boron nitride nanosheets have a layered structure and ultra-low friction properties, forming an effective lubricating film; hydroxylated graphene is a graphene derivative with excellent lubrication properties and hydrophilicity, making it highly compatible with the system; fluorinated molybdenum disulfide has excellent chemical inertness, thermal stability and lubricity, further enhancing the strength of the lubricating film.

[0038] A second aspect of the present invention provides a method for preparing the ultra-low friction coefficient microemulsion water-based drilling fluid for tight gas long horizontal wells, comprising the following steps:

[0039] Step 1. adding a mixed solution of an oil phase, an emulsifier, and a cosurfactant to the aqueous phase under stirring, followed by high-pressure homogenization to obtain an oil-in-water microemulsion;

[0040] Step 2. Under stirring conditions, adding a pH regulator, a fluid loss reducer, a lubricant, a coating agent, a tackifier and barite to the oil-in-water microemulsion, and stirring evenly to obtain the ultra-low friction coefficient microemulsion water-based drilling fluid.

[0041] The present invention discloses the following technical effects:

[0042] The present invention, through the synergistic effect of the microemulsion system and the multifunctional additive, can significantly reduce friction resistance, improve wellbore cleaning, enhance the plugging effect and stabilize the well wall, meeting the needs of long horizontal well drilling construction in tight gas. The nanoscale, uniformly distributed oil droplets in the microemulsion effectively reduce interfacial friction between the drill string and the wellbore wall. They synergize with the nano-lubricating particles to form a multi-layered, composite lubricating film on the wellbore surface, significantly reducing friction and torque during long horizontal drilling. The cross-linking network of the polymer materials in the fluid loss additive and the pore-filling effect of the ultrafine particles create a dense filter cake with extremely low permeability, effectively preventing drilling fluid filtrate from invading the formation and reducing the risk of hydration, expansion, and collapse of the surrounding rock. Furthermore, the nanoscale and elastic deformation capacity of the coating agent allow it to rapidly penetrate and fill microcracks and pores in the formation, forming a stable physical bridging layer. This layer then adsorbs onto the wellbore surface to form a continuous protective film, effectively inhibiting the propagation of formation cracks and wellbore instability. Furthermore, the synergistic effect of the spatial network structure of the polymer polysaccharide chains in the viscosity enhancer and the rigid nanoparticles allows the viscosity enhancer to maintain excellent viscosity-increasing and thixotropic properties even under high-temperature and high-salinity conditions, ensuring efficient suspension and transport of cuttings, preventing sand settling and mudcake accumulation in horizontal sections, and maintaining a clean and unobstructed wellbore. The synergistic effect of the above-mentioned multiple components enables the drilling fluid of the present invention to have excellent lubrication and friction reduction properties, efficient well wall protection and plugging capabilities, and outstanding wellbore purification effect, and is particularly suitable for green, safe and efficient drilling operations in long horizontal wells of tight gas. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0044] Figure 1 This is the particle size distribution diagram of the oil-in-water microemulsion prepared in Example 1;

[0045] Figure 2 This is the particle size distribution diagram of the oil-in-water microemulsion prepared in Example 2;

[0046] Figure 3 This is the particle size distribution diagram of the oil-in-water microemulsion prepared in Example 3;

[0047] Figure 4 This is the particle size distribution diagram of the oil-in-water microemulsion prepared in Example 4. DETAILED DESCRIPTION

[0048] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0049] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. The intermediate value within any stated value or stated range, and each smaller range between any other stated value or intermediate value within the stated range, is also encompassed within the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0050] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice 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 associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0051] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be exemplary only.

[0052] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0053] Room temperature in the present invention means a temperature of 25-35°C.

[0054] In the present invention, the preparation method of the tackifier is as follows:

[0055] Step 1: Disperse 5-10 parts by weight of nano-calcium carbonate in 200 parts by weight of 88% v / v ethanol aqueous solution. After ultrasonic treatment for 30-60 minutes, transfer the suspension to a three-necked round-bottom flask. Then, heat to 60-70°C and slowly add 0.5-0.7 parts by weight of γ-aminopropyltriethoxysilane dropwise while stirring. After reacting for 8-12 hours, stop heating and cool to room temperature. Centrifuge and collect the precipitate, wash it 2-3 times with anhydrous ethanol, and vacuum dry it to obtain amino-nano-calcium carbonate.

[0056] Step 2: Dissolve 0.8-1.5 parts by mass of diutanol in 300 parts by mass of deionized water, adjust the pH to 6.0 with 2-morpholineethanesulfonic acid, then add 0.10-0.15 parts by mass of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and N-hydroxysuccinimide in a total amount and a molar ratio of 1:1, and stir at room temperature for 30-60 minutes to obtain an activated diutanol solution.

[0057] Step 3: Transfer the activated diutanol solution obtained in step 2 to a three-necked round-bottom flask, deoxygenate with nitrogen, and slowly add the amino-nano calcium carbonate obtained in step 1 under stirring. Heat to 50-60°C and react for 10-16 hours. Stop heating and cool to room temperature. Remove unreacted reagents by dialysis (molecular weight cut-off 8000 Da), and freeze-dry to obtain the viscosity enhancer.

[0058] The method for preparing an ultra-low friction coefficient microemulsion water-based drilling fluid for a tight gas long horizontal well of the present invention comprises the following steps:

[0059] The oil phase was premixed with the emulsifier and cosurfactant at 50-60°C and stirred at 500-1000 rpm for 30-60 minutes to obtain mixed solution 1. The aqueous phase was preheated to 50-60°C and then added dropwise to the aqueous phase at a stirring speed of 3000-5000 rpm for 5-10 minutes. The stirring speed was then increased to 12000-15000 rpm and maintained for 5-10 minutes. The mixture was further homogenized using a high-pressure homogenizer (50-100 MPa, three cycles) to obtain an oil-in-water microemulsion. Subsequently, the stirring speed was set at 8000-12000 rpm, and a pH adjuster, fluid loss control agent, lubricant, coating agent, and viscosity enhancer were added sequentially, with a 10-minute interval between each addition. Finally, barite was added and stirred for 30-60 minutes to obtain the drilling fluid.

[0060] Unless otherwise specified, the technical solutions described in the present invention are all conventional solutions in the field, and the reagents or raw materials used, unless otherwise specified, are purchased from commercial channels or have been disclosed.

[0061] In the embodiment of the present invention, the preparation method of the coating agent (polyacrylamide nanospheres) is as follows:

[0062] Step 1: Add 80 parts by mass of isooctane, 3 parts by mass of Span 80 and 1 part by mass of isopropanol into a three-necked flask and stir at room temperature for 2 hours to obtain an oil phase;

[0063] Step 2: dissolving 10 parts by mass of acrylamide and 0.05 parts by mass of N,N'-methylenebisacrylamide in 30 parts by mass of deionized water, and stirring at room temperature for 30 minutes to obtain a monomer solution;

[0064] Step 3: During the stirring process, the monomer solution obtained in step 2 was slowly added to the oil phase of step 1, and 0.08 parts by mass of initiator ammonium persulfate was added, nitrogen was passed through to deoxygenate, and then the temperature was raised to 55°C and the reaction was kept at this temperature for 4 hours;

[0065] Step 4: After the reaction in step 3 is completed, the mixture is cooled to room temperature, ethanol is added to break the emulsion, the microspheres are collected by centrifugation, and the microspheres are washed twice with ethanol and dried under vacuum to obtain the coating agent.

[0066] In order to better understand the present invention, the content of the present invention is further illustrated below in conjunction with the examples, but the content of the present invention is not limited to the following examples.

[0067] Example 1:

[0068] An ultra-low friction coefficient microemulsion water-based drilling fluid for tight gas long horizontal wells, the raw materials are as follows, calculated by weight:

[0069] Water phase: 75 parts

[0070] Oil phase: 25 parts

[0071] Emulsifier: 3 parts

[0072] Co-surfactant: 1 part

[0073] pH adjuster: 0.5 parts

[0074] Tackifier: 0.3 parts

[0075] Coating agent: 0.5 parts

[0076] Fluid loss additive: 3 parts

[0077] Lubricant: 0.5 parts

[0078] Barite: Add weight to the drilling fluid density of 1.10g / cm 3 .

[0079] The aqueous phase is a mixture of 95 parts of water, 3 parts of sodium chloride and 2 parts of potassium chloride by mass.

[0080] The oil phase is a mixture of 20 parts of trimethylolpropane ester and 80 parts of polyalphaolefin by mass.

[0081] The emulsifier is a mixture of 80 parts of isomeric tridecanol polyoxyethylene ether 1308 and 20 parts of Span 80, calculated by mass.

[0082] The co-surfactant is a mixture of 30 parts of isopropyl alcohol, 30 parts of ethoxylated glycerol and 40 parts of n-butanol, calculated by mass.

[0083] The pH adjuster is diethanolamine.

[0084] The tackifier is dimethicone grafted with nano-calcium carbonate, and the preparation method is as follows:

[0085] Step 1: Disperse 5 parts by mass of nano-calcium carbonate in 200 parts by mass of 88% v / v ethanol-water solution. After ultrasonic treatment for 30 minutes, transfer the suspension to a three-necked round-bottom flask. Then, heat to 60°C and dropwise add 0.5 parts by mass of γ-aminopropyltriethoxysilane while stirring. After reacting for 8 hours, stop heating and cool to room temperature. Centrifuge and collect the precipitate, wash twice with anhydrous ethanol, and vacuum dry to obtain amino-nano-calcium carbonate.

[0086] Step 2: Dissolve 0.8 parts by mass of diutanol in 300 parts by mass of deionized water, adjust the pH to 6.0 with 2-morpholineethanesulfonic acid, then add 0.10 parts by mass of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and N-hydroxysuccinimide in a molar ratio of 1:1, and stir at room temperature for 30 minutes to obtain an activated diutanol solution.

[0087] Step 3: The activated diutan gum solution obtained in step 2 was transferred to a three-necked round-bottom flask, deoxygenated with nitrogen, and the amino-nano calcium carbonate obtained in step 1 was slowly added under stirring. The temperature was raised to 50°C and the reaction was continued for 10 hours. The heating was stopped and the solution was cooled to room temperature. The unreacted reagent was removed by dialysis (molecular weight cut-off 8000 Da), and the grafted product obtained by freeze-drying was the thickener.

[0088] The coating agent is polyacrylamide nanoparticles.

[0089] The fluid loss additive is a mixture of 5 parts of polyanionic cellulose, 20 parts of carboxymethyl starch and 75 parts of ultrafine calcium carbonate (3800 mesh) by mass.

[0090] The lubricant is a mixture of 30 parts by mass of boron nitride nanosheets, 20 parts by mass of hydroxylated graphene, and 50 parts by mass of fluorinated molybdenum disulfide.

[0091] The preparation steps of the drilling fluid are as follows:

[0092] First, the oil phase was premixed with the emulsifier and the cosurfactant at 50°C and stirred at 500 rpm for 30 min to obtain a mixed solution 1; the aqueous phase was preheated to 50°C, and then the mixed solution 1 was added dropwise to the aqueous phase at a stirring speed of 3000 rpm for 5 min; the stirring speed was then increased to 12000 rpm and maintained for 5 min; and the mixture was further homogenized by a high-pressure homogenizer (pressure 50 MPa, cycle 3 times) to obtain an oil-in-water microemulsion (the average particle size of the oil-in-water microemulsion was 61.4 nm, as shown in FIG. Figure 1Then, the stirring speed was set at 8000 rpm, and the pH regulator, fluid loss reducer, lubricant, coating agent, and viscosity enhancer were added in sequence, with an interval of 10 minutes between each addition of each material. Finally, barite was added, and the stirring was continued for 30 minutes to obtain the drilling fluid.

[0093] The density of the drilling fluid in this embodiment is 1.10 g / cm 3 , the hot rolling temperature of the drilling fluid is 60℃.

[0094] Example 2:

[0095] An ultra-low friction coefficient microemulsion water-based drilling fluid for tight gas long horizontal wells, the raw materials are as follows, calculated by weight:

[0096] Water phase: 85 parts

[0097] Oil phase: 15 parts

[0098] Emulsifier: 5 parts

[0099] Co-surfactant: 2 parts

[0100] pH adjuster: 1.0 part

[0101] Tackifier: 0.5 parts

[0102] Coating agent: 0.7 parts

[0103] Fluid loss additive: 5 parts

[0104] Lubricant: 1.5 parts

[0105] Barite: Add weight to the drilling fluid density of 1.20g / cm 3 .

[0106] The aqueous phase is a mixture of 80 parts of water, 12 parts of sodium chloride and 8 parts of potassium chloride by mass.

[0107] The oil phase is a mixture of 40 parts of trimethylolpropane ester and 60 parts of polyalphaolefin, calculated by mass.

[0108] The emulsifier is a mixture of 90 parts of isomeric tridecanol polyoxyethylene ether 1308 and 10 parts of Span 80, calculated by mass.

[0109] The co-surfactant is a mixture of 40 parts of isopropyl alcohol, 40 parts of ethoxylated glycerol and 20 parts of n-butanol, calculated by mass.

[0110] The pH adjuster is diethanolamine.

[0111] The tackifier is dimethicone grafted with nano-calcium carbonate, and the preparation method is as follows:

[0112] Step 1: Disperse 10 parts by mass of nano-calcium carbonate in 200 parts by mass of 88% ethanol aqueous solution. After ultrasonic treatment for 60 minutes, transfer the suspension to a three-necked round-bottom flask. Then, heat to 70°C and slowly add 0.7 parts by mass of γ-aminopropyltriethoxysilane dropwise while stirring. After reacting for 12 hours, stop heating and cool to room temperature. Centrifuge and collect the precipitate, wash three times with anhydrous ethanol, and vacuum dry to obtain amino-nano-calcium carbonate.

[0113] Step 2: Dissolve 1.5 parts by mass of diutanol in 300 parts by mass of deionized water, adjust the pH to 6.0 with 2-morpholineethanesulfonic acid, then add 0.15 parts by mass of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and N-hydroxysuccinimide in a molar ratio of 1:1, and stir at room temperature for 60 minutes to obtain an activated diutanol solution.

[0114] Step 3: The activated diutan gum solution obtained in step 2 was transferred to a three-necked round-bottom flask, deoxygenated with nitrogen, and the amino-nano calcium carbonate obtained in step 1 was slowly added under stirring. The temperature was raised to 60°C and the reaction was carried out for 16 hours. After that, the heating was stopped and the solution was cooled to room temperature. The unreacted reagent was removed by dialysis (molecular weight cut-off 8000 Da), and the grafted product obtained by freeze-drying was the thickener.

[0115] The coating agent is polyacrylamide nanoparticles.

[0116] The fluid loss additive is a mixture of 15 parts of polyanionic cellulose, 30 parts of carboxymethyl starch and 55 parts of ultrafine calcium carbonate (3800 mesh) by mass.

[0117] The lubricant is a mixture of 40 parts by mass of boron nitride nanosheets, 30 parts by mass of hydroxylated graphene, and 30 parts by mass of fluorinated molybdenum disulfide.

[0118] The preparation steps of the drilling fluid are as follows:

[0119] The oil phase was premixed with the emulsifier and cosurfactant at 60°C and stirred at 1000 rpm for 60 min to obtain a mixed solution 1. The aqueous phase was preheated to 60°C and then the mixed solution 1 was added dropwise to the aqueous phase at a stirring speed of 5000 rpm for 10 min. The stirring speed was then increased to 15000 rpm and maintained for 10 min. The mixture was further homogenized by a high-pressure homogenizer (pressure 100 MPa, 3 cycles) to obtain an oil-in-water microemulsion (the average particle size of the oil-in-water microemulsion was 53.5 nm, as shown in FIG. Figure 2 Then, the stirring speed was set to 12,000 rpm, and the pH regulator, fluid loss additive, lubricant, coating agent, and viscosity enhancer were added in sequence, with an interval of 10 minutes between each addition of each material. Finally, barite was added, and the stirring was continued for 60 minutes to obtain the drilling fluid.

[0120] The density of the drilling fluid in this embodiment is 1.20 g / cm 3 , the hot rolling temperature of the drilling fluid is 80℃.

[0121] Example 3:

[0122] An ultra-low friction coefficient microemulsion water-based drilling fluid for tight gas long horizontal wells, the raw materials are as follows, calculated by weight:

[0123] Water phase: 80 parts

[0124] Oil phase: 20 parts

[0125] Emulsifier: 4 parts

[0126] Co-surfactant: 1.5 parts

[0127] pH adjuster: 0.75 parts

[0128] Tackifier: 0.4 parts

[0129] Coating agent: 0.6 parts

[0130] Fluid loss additive: 4 parts

[0131] Lubricant: 1 part

[0132] Barite: Add weight to the drilling fluid density of 1.30g / cm 3 .

[0133] The aqueous phase is a mixture of 88 parts of water, 8 parts of sodium chloride and 4 parts of potassium chloride, calculated by mass.

[0134] The oil phase is a mixture of 30 parts of trimethylolpropane ester and 70 parts of polyalphaolefin by mass.

[0135] The emulsifier is a mixture of 85 parts of isomeric tridecanol polyoxyethylene ether 1308 and 15 parts of Span 80, calculated by mass.

[0136] The co-surfactant is a mixture of 35 parts of isopropyl alcohol, 35 parts of ethoxylated glycerol and 30 parts of n-butanol, calculated by mass.

[0137] The pH regulator is diethanolamine;

[0138] The tackifier is dimethicone grafted with nano-calcium carbonate, and the preparation method is as follows:

[0139] Step 1: Disperse 7.5 parts by mass of nano-calcium carbonate in 200 parts by mass of 88% v / v ethanol-water solution. After ultrasonic treatment for 45 minutes, transfer the suspension to a three-necked round-bottom flask. Then, heat to 65°C and slowly add 0.6 parts by mass of γ-aminopropyltriethoxysilane dropwise with stirring. After reacting for 10 hours, stop heating and cool to room temperature. Centrifuge and collect the precipitate, wash three times with anhydrous ethanol, and vacuum dry to obtain amino-nano-calcium carbonate.

[0140] Step 2: Dissolve 1.1 parts by mass of diutanol in 300 parts by mass of deionized water, adjust the pH to 6.0 with 2-morpholineethanesulfonic acid, then add 0.12 parts by mass of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and N-hydroxysuccinimide in a molar ratio of 1:1, and stir at room temperature for 45 minutes to obtain an activated diutanol solution.

[0141] Step 3: The activated diutan gum solution obtained in step 2 was transferred to a three-necked round-bottom flask, deoxygenated with nitrogen, and the amino-nano calcium carbonate obtained in step 1 was slowly added under stirring. The temperature was raised to 55°C and the reaction was continued for 13 hours. The heating was stopped and the solution was cooled to room temperature. The unreacted reagent was removed by dialysis (molecular weight cut-off 8000 Da), and the grafted product obtained by freeze-drying was the thickener.

[0142] The coating agent is polyacrylamide nanoparticles.

[0143] The fluid loss additive is a mixture of 10 parts of polyanionic cellulose, 25 parts of carboxymethyl starch and 65 parts of ultrafine calcium carbonate (3800 mesh) by mass.

[0144] The lubricant is a mixture of 35 parts of boron nitride nanosheets, 25 parts of hydroxylated graphene, and 40 parts of fluorinated molybdenum disulfide, by mass.

[0145] The preparation steps of the drilling fluid are as follows:

[0146] The oil phase was premixed with the emulsifier and cosurfactant at 55°C and stirred at 700 rpm for 45 min to obtain a mixed solution 1. The aqueous phase was preheated to 55°C and then the mixed solution 1 was added dropwise to the aqueous phase at a stirring speed of 4000 rpm for 7 min. The stirring speed was then increased to 13000 rpm and maintained for 7 min. The mixture was further homogenized by a high-pressure homogenizer (pressure 75 MPa, 3 cycles) to obtain an oil-in-water microemulsion (the average particle size of the oil-in-water microemulsion was 58.2 nm, as shown in FIG. Figure 3 Then, the stirring speed was set to 10,000 rpm, and the pH regulator, fluid loss additive, lubricant, coating agent, and viscosity enhancer were added in sequence, with an interval of 10 minutes between each addition of each material. Finally, barite was added, and the stirring was continued for 45 minutes to obtain the drilling fluid.

[0147] The drilling fluid density in this embodiment is 1.30 g / cm 3 , the hot rolling temperature of the drilling fluid is 100℃.

[0148] Example 4:

[0149] An ultra-low friction coefficient microemulsion water-based drilling fluid for tight gas long horizontal wells, the raw materials are as follows, calculated by weight:

[0150] Water phase: 82 parts

[0151] Oil phase: 18 parts

[0152] Emulsifier: 5 parts

[0153] Co-surfactant: 1 part

[0154] pH adjuster: 0.8 parts

[0155] Tackifier: 0.3 parts

[0156] Coating agent: 0.5 parts

[0157] Fluid loss additive: 5 parts

[0158] Lubricant: 1 part

[0159] Barite: Add weight to the drilling fluid density of 1.30g / cm 3 .

[0160] The aqueous phase is a mixture of 85 parts of water, 10 parts of sodium chloride and 5 parts of potassium chloride, calculated by mass.

[0161] The oil phase is a mixture of 30 parts of trimethylolpropane ester and 70 parts of polyalphaolefin by mass.

[0162] The emulsifier is a mixture of 88 parts of isomeric tridecanol polyoxyethylene ether 1308 and 12 parts of Span 80, calculated by mass.

[0163] The co-surfactant is a mixture of 35 parts of isopropyl alcohol, 40 parts of ethoxylated glycerol and 25 parts of n-butanol, calculated by mass.

[0164] The pH adjuster is diethanolamine.

[0165] The tackifier is dimethicone grafted with nano-calcium carbonate, and the preparation method is as follows:

[0166] Step 1: Disperse 8 parts by mass of nano-calcium carbonate in 200 parts by mass of 88% ethanol aqueous solution. After ultrasonic treatment for 50 minutes, transfer the suspension to a three-necked round-bottom flask. Then, heat to 66°C and dropwise add 0.6 parts by mass of γ-aminopropyltriethoxysilane under stirring. After reacting for 9 hours, stop heating and cool to room temperature. Centrifuge and collect the precipitate, wash three times with anhydrous ethanol, and vacuum dry to obtain amino-nano-calcium carbonate.

[0167] Step 2: Dissolve 0.9 parts by mass of diutanol in 300 parts by mass of deionized water, adjust the pH to 6.0 with 2-morpholineethanesulfonic acid, then add 0.12 parts by mass of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and N-hydroxysuccinimide in a molar ratio of 1:1, and stir at room temperature for 40 minutes to obtain an activated diutanol solution.

[0168] Step 3: The activated diutan gum solution obtained in step 2 was transferred to a three-necked round-bottom flask, deoxygenated with nitrogen, and the amino-nano calcium carbonate obtained in step 1 was slowly added under stirring. The temperature was raised to 60°C and the reaction was continued for 12 hours. The heating was stopped and the solution was cooled to room temperature. The unreacted reagent was removed by dialysis (molecular weight cut-off 8000 Da), and the grafted product obtained by freeze-drying was the thickener.

[0169] The coating agent is polyacrylamide nanoparticles.

[0170] The fluid loss additive is a mixture of 6 parts of polyanionic cellulose, 30 parts of carboxymethyl starch and 64 parts of ultrafine calcium carbonate (3800 mesh) by mass.

[0171] The lubricant is a mixture of 40 parts by mass of boron nitride nanosheets, 20 parts by mass of hydroxylated graphene, and 40 parts by mass of fluorinated molybdenum disulfide.

[0172] The preparation steps of the drilling fluid are as follows:

[0173] The oil phase was premixed with the emulsifier and cosurfactant at 60°C and stirred at 1000 rpm for 40 min to obtain a mixed solution 1. The aqueous phase was preheated to 60°C and then the mixed solution 1 was added dropwise to the aqueous phase at a stirring speed of 4000 rpm for 10 min. The stirring speed was then increased to 15000 rpm and maintained for 10 min. The mixture was further homogenized by a high-pressure homogenizer (pressure 80 MPa, 3 cycles) to obtain an oil-in-water microemulsion (the average particle size of the oil-in-water microemulsion was 56.3 nm, as shown in FIG. Figure 4 Then, the stirring speed was set to 11,000 rpm, and the pH regulator, fluid loss additive, lubricant, coating agent, and viscosity enhancer were added in sequence, with an interval of 10 minutes between each addition of each material. Finally, barite was added, and the stirring was continued for 40 minutes to obtain the drilling fluid.

[0174] The drilling fluid density in this embodiment is 1.30 g / cm 3 , the hot rolling temperature of the drilling fluid is 100℃.

[0175] The drilling fluids obtained in Examples 1-4 were tested for rheological properties, plugging and filtration reduction properties, inhibition properties, and lubrication properties in accordance with GB / T 29170-2012 "Laboratory Testing of Drilling Fluids in the Petroleum and Natural Gas Industry" and SY / T 6094-1994 "Evaluation Procedure for Lubricants for Drilling Fluids." The results are shown in Tables 1 and 2.

[0176] Table 1 Drilling fluid rheology and plugging and filtration reduction performance

[0177] ,

[0178] Table 2 Drilling fluid inhibition and lubrication properties

[0179] ,

[0180] Note: In Table 1 and Table 2:

[0181] ρ: drilling fluid density, g / cm 3

[0182] T: drilling fluid aging temperature, °C

[0183] AV: drilling fluid apparent viscosity, mPa·s

[0184] PV: drilling fluid plastic viscosity, mPa·s

[0185] YP: Drilling fluid dynamic shear force, Pa

[0186] YP / PV: dynamic plastic ratio, Pa / mPa·s

[0187] Φ6: Six-speed rotary viscometer 6-turn reading, dimensionless

[0188] Φ3: Six-speed rotary viscometer 3-turn reading, dimensionless

[0189] API: Drilling fluid medium pressure loss (0.7 MPa, room temperature, 30 min), mL

[0190] PPT: Drilling fluid filtration loss (6.9 MPa, T, 30 min), mL

[0191] W1: Apparent viscosity increase rate after 10% sodium bentonite contamination, %

[0192] W2: Apparent viscosity increase rate after 20% sodium bentonite contamination, %

[0193] θ: Mudstone rolling recovery rate, %

[0194] γ: linear expansion rate of clay, %

[0195] EP: Extreme pressure friction coefficient, dimensionless

[0196] CF: Four-ball friction coefficient (147N, 120rpm, 30min), dimensionless

[0197] D: Four-ball wear spot diameter, mm

[0198] Data from four sets of examples of the ultra-low friction coefficient microemulsion water-based drilling fluid for long horizontal wells of tight gas production disclosed herein show that the drilling fluid has a moderate and stable pH value, excellent rheological properties, low plastic viscosity, and a dynamic-plastic ratio greater than 0.9, exhibiting significant shear-thinning properties and good sand suspension and sand-carrying potential. The fluid also exhibits excellent plugging and filtration loss reduction performance, with API and PPT filtration losses less than 5.0 mL and 10.0 mL, respectively, indicating that the formed mud cake has good density. The fluid also has a high inferior solid phase capacity limit, with the apparent viscosity increase rate after contamination with 20% sodium bentonite not exceeding 10%. The fluid also exhibits significant clay hydration inhibition, with a mudstone rolling recovery rate greater than 99% and a linear expansion rate less than 6%. The fluid also exhibits excellent friction and drag reduction performance, with both the extreme pressure friction coefficient and the four-ball friction coefficient less than 0.06. Furthermore, the fluid exhibits low wear, with a wear spot diameter not exceeding 0.4 mm, making it suitable for long horizontal well drilling operations.

[0199] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. An ultra-low friction coefficient microemulsion water-based drilling fluid for tight gas long horizontal wells, characterized in that: The raw materials include, by mass, 75-85 parts of aqueous phase, 15-25 parts of oil phase, 3-5 parts of emulsifier, 1-2 parts of co-surfactant, 0.5-1.0 parts of pH adjuster, 0.3-0.5 parts of viscosity enhancer, 0.5-0.7 parts of coating agent, 3-5 parts of fluid loss reducer, 0.5-1.5 parts of lubricant and barite; the barite is not limited in number and is added until the required density is reached; The cosurfactant is a mixture of 30-40 parts of isopropyl alcohol, 30-40 parts of ethoxylated glycerol and 20-40 parts of n-butanol; The coating agent is polyacrylamide nanoparticles; The raw materials of the viscosity enhancer include: 5-10 parts of nano-calcium carbonate, 200 parts of ethanol aqueous solution, 0.5-0.7 parts of γ-aminopropyltriethoxysilane, 0.8-1.5 parts of dimethicone, 300 parts of water, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and N-hydroxysuccinimide; the total mass fraction of the 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and N-hydroxysuccinimide is 0.10-0.15 parts, and the molar ratio of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide to N-hydroxysuccinimide is 1:1; The preparation method of the tackifier comprises the following steps: Dispersing nano-calcium carbonate in an ethanol aqueous solution, and then adding γ-aminopropyltriethoxysilane to the dispersion under stirring conditions to carry out reaction 1 to obtain amino-treated nano-calcium carbonate; Dissolving diutan gum in water and adjusting the pH to acidic, then adding 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and N-hydroxysuccinimide to carry out reaction 2 to obtain an activated diutan gum solution; Under an inert atmosphere, adding the amino-modified nano-calcium carbonate to the activated diutan gum solution to carry out reaction 3 to obtain the viscosity-increasing agent; The oil phase is a mixture of 20 to 40 parts of trimethylolpropane ester and 60 to 80 parts of polyalphaolefin in parts by mass; The emulsifier is a mixture of 80-90 parts of isomeric tridecanol polyoxyethylene ether 1308 and 10-20 parts of Span 80 in parts by mass; The fluid loss reducer is a mixture of 5 to 15 parts of polyanionic cellulose, 20 to 30 parts of carboxymethyl starch and 55 to 75 parts of ultrafine calcium carbonate in parts by mass; The lubricant is a mixture of 30 to 40 parts of boron nitride nanosheets, 20 to 30 parts of hydroxylated graphene and 30 to 50 parts of fluorinated molybdenum disulfide, calculated by mass.

2. The ultra-low friction coefficient microemulsion water-based drilling fluid for tight gas long horizontal wells according to claim 1, characterized in that: The aqueous phase is a mixture of 80 to 95 parts of water, 3 to 12 parts of sodium chloride and 2 to 8 parts of potassium chloride, calculated by mass.

3. The ultra-low friction coefficient microemulsion water-based drilling fluid for tight gas long horizontal wells according to claim 1, characterized in that: The pH regulator is one or more of diethanolamine, triethanolamine and triisopropanolamine.

4. A method for preparing an ultra-low friction coefficient microemulsion water-based drilling fluid for tight gas long horizontal wells according to any one of claims 1 to 3, characterized in that: The following steps are involved: Step 1. adding a mixed solution of an oil phase, an emulsifier, and a cosurfactant to the aqueous phase under stirring, followed by high-pressure homogenization to obtain an oil-in-water microemulsion; Step 2. Under stirring conditions, adding a pH regulator, a fluid loss reducer, a lubricant, a coating agent, a tackifier and barite to the oil-in-water microemulsion, and stirring evenly to obtain the ultra-low friction coefficient microemulsion water-based drilling fluid.

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