Modified styrene-butadiene latex, its preparation method and application

Abstract

This invention relates to the field of oil and gas drilling, specifically to a modified styrene-butadiene latex, its preparation method, and its applications. The modified styrene-butadiene latex has a core-shell structure, containing structural units A, B, C, and D. This modified styrene-butadiene latex possesses a hydrophobic core and a hydrophilic shell, making it suitable for both water-based and oil-based drilling fluid systems. It can evenly seal nano- and micron-sized pores and fractures in heterogeneous formations, reducing drilling fluid loss. The preparation process of this modified styrene-butadiene latex is simple and low-cost, making it suitable for industrial application.

Description

Technical Field

[0001] This invention relates to the field of oil and gas drilling, specifically to a modified styrene-butadiene latex, its preparation method, and its application. Background Technology

[0002] With global economic growth and the continuous development of human society, the world's energy demand is expected to continue to rise in the coming decades. Unconventional oil and gas resources such as shale gas, tight gas, and coalbed methane will become increasingly important for meeting energy supply needs. During unconventional oil and gas extraction, many heterogeneous formations contain numerous nano- to micron-sized pores and fractures. When drilling fluid plugging capabilities are inadequate or treatment agents are not effective in reducing filtration loss, fluid intrusion can easily cause "self-absorption," which typically leads to the extension of formation fractures to deeper layers. Free water thus penetrates even deeper. Furthermore, the high clay mineral content and strong hydration capacity of shale and mudstone result in severe hydration swelling upon contact with water. Therefore, both factors contribute to the wellbore instability problems commonly found in shale and mudstone formations.

[0003] As the working fluid that comes into most contact with the formation during the initial drilling process, drilling fluids often contain numerous plugging agents or filtration reducers to form a denser sealing layer on the wellbore and to further control the intrusion of free water into reservoir pores and fractures. These include conventional solid materials, polymer-based treatment agents, and nanoparticles. Typically, conventional solid materials such as bentonite, calcium carbonate, and barite are generally micron-sized, and the resulting sealing layer cannot effectively prevent water molecule intrusion. Natural polymers such as cellulose and starch have poor temperature resistance (below 120℃) and cannot be used in high-temperature deep wells. Materials such as asphalt and resin thicken at high temperatures, affecting the rheological parameters of the drilling fluid system, and are difficult to degrade and process, posing serious environmental problems. Polymer-based treatment agents typically exist in a linear or network structure in the system, exhibiting severe thickening at low temperatures and decomposition at high temperatures. Meanwhile, research shows that nanoparticles have poor dispersibility, with particles tending to aggregate, making it impossible to ensure balanced plugging of heterogeneous formations. Given the bottleneck issues encountered by the aforementioned drilling fluid treatment agents, there is an urgent need to develop new drilling fluid treatment agent materials with a wider range of applications. Summary of the Invention

[0004] The purpose of this invention is to solve the problems of insufficient nano-micron plugging ability and filtration loss reduction performance of drilling fluids in the prior art.

[0005] To achieve the above objectives, the present invention provides a modified styrene-butadiene latex, wherein the modified styrene-butadiene latex has a core-shell structure and contains structural unit A, structural unit B, structural unit C and structural unit D. Structural unit A is at least one of the structural units shown in formula (1), structural unit B is at least one of the structural units shown in formula (2), structural unit C is at least one of the structural units shown in formula (3), and structural unit D is at least one of the structural units shown in formula (4). The weight-average molecular weight of the modified styrene-butadiene latex is 20,000 to 25,000.

[0006]

[0007] Among them, R 1 R 2 R 3 R 6 Each is independently selected from H or C1-C4 alkyl groups;

[0008] R 4 R 5 R 7 R 8 Each is independently selected from H or C1-C6 alkyl groups;

[0009] M is selected from H or an alkali metal element.

[0010] Preferably, the R 4 The R 5 The R 7 The R 8 Each is independently selected from one of methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, and n-hexyl.

[0011] Preferably, M is selected from H, Na, and K.

[0012] Preferably, the average particle size of the rubber particles in the modified styrene-butadiene latex is 80 nm to 310 nm.

[0013] Preferably, the modified styrene-butadiene latex is in the form of an emulsion or a solid.

[0014] A second aspect of the present invention provides a method for preparing the modified styrene-butadiene latex provided in the first aspect, comprising the following steps:

[0015] (1) Mixing monomer A' and monomer B' yields solution I; and

[0016] In an aqueous solvent, monomers C' and D' are mixed and the pH is adjusted to 7-9 to obtain solution II;

[0017] (2) Mix solution I and a portion of solution II and heat to a target temperature I to obtain a first intermediate system; the target temperature I is 25℃-60℃.

[0018] (3) Initiator I is mixed with the first intermediate system and heated to the target temperature II to obtain the second intermediate system; the target temperature II is 60℃-82℃ and the target temperature II is higher than the target temperature I;

[0019] (4) The remaining solution II and initiator II are mixed with the second intermediate system and subjected to constant temperature treatment to obtain the modified styrene-butadiene latex;

[0020] Wherein, monomer A' is selected from at least one of the monomers shown in formula (I), monomer B' is selected from at least one of the monomers shown in formula (II), monomer C' is selected from at least one of the monomers shown in formula (II), and monomer D' is selected from at least one of the monomers shown in formula (IV). The amounts of monomer A', monomer B', monomer C', and monomer D' are such that the weight-average molecular weight of the obtained modified styrene-butadiene latex is 20,000 to 25,000.

[0021] The monomers A', B', C', and D' respectively make the modified styrene-butadiene latex contain structural units A, B, C, and D, respectively. Structural unit A is at least one of the structural units shown in formula (1), structural unit B is at least one of the structural units shown in formula (2), structural unit C is at least one of the structural units shown in formula (3), and structural unit D is at least one of the structural units shown in formula (4).

[0022]

[0023]

[0024] The definitions of R1, R2, R3, R4, R5, R6, R7, R8, and M are the same as those in the modified styrene-butadiene latex provided in the first aspect of this invention.

[0025] Preferably, the molar ratio of monomer A', monomer B', monomer C' and monomer D' is 1:(0.5-1.20):(0.04-0.08):(0.05-0.20).

[0026] Preferably, the amount of the aqueous solvent used is 40wt%-70wt%, based on the total mass of monomer A', monomer B', monomer C', monomer D' and the aqueous solvent.

[0027] Preferably, the weight ratio of the amount of solution II used in step (2) to the amount of solution II used in step (4) is 1:(0.5-2).

[0028] Preferably, the target temperature I is 50℃-55℃, and the target temperature II is 70℃-75℃.

[0029] Preferably, in step (2), the heating rate to the target temperature I is 0.5℃ / min-2℃ / min;

[0030] In step (3), the heating rate to the target temperature II is 0.5℃ / min-2℃ / min.

[0031] Preferably, in step (4), the temperature of the constant temperature treatment is 70℃-80℃, and the treatment time is 3h-8h.

[0032] Preferably, the initiator I and the initiator II may be the same or different, and each is independently selected from at least one of potassium persulfate, ammonium persulfate, and sodium persulfate.

[0033] A third aspect of the present invention provides a drilling fluid containing modified styrene-butadiene latex, wherein the content of the modified styrene-butadiene latex is 1wt%-4wt% based on the total mass of the drilling fluid;

[0034] The modified styrene-butadiene latex is the modified styrene-butadiene latex provided in the first aspect of the present invention.

[0035] Preferably, the drilling fluid is a water-based drilling fluid, which further contains bentonite and additive A, wherein additive A is selected from at least one of sodium carbonate, filtration loss reducer, inhibitor, plugging agent, and weighting agent.

[0036] Preferably, based on the total mass of the water-based drilling fluid, the bentonite content is 1wt%-5wt%, the sodium carbonate content is 0.2wt%-0.5wt%, the filtration loss reducer content is 0.7wt%-1.7wt%, the inhibitor content is 1wt%-10wt%, the plugging agent content is 3wt%-10wt%, and the weighting agent makes the density of the water-based drilling fluid 1.2 g / cm³. 3 -1.8g / cm 3 The remainder is water.

[0037] Preferably, the filtration loss reducer is a combination of xanthan gum and polyanionic cellulose, wherein, based on the total mass of the water-based drilling fluid, the content of xanthan gum is 0.1wt%-0.5wt%, and the content of polyanionic cellulose is 0.6wt%-1.2wt%.

[0038] Preferably, the sealing agent is a combination of asphalt and calcium carbonate, wherein, based on the total mass of the water-based drilling fluid, the asphalt content is 1wt%-4wt% and the calcium carbonate content is 2wt%-6wt%.

[0039] Preferably, the drilling fluid is an oil-based drilling fluid, which further contains base oil, a brine phase, and additive B, wherein additive B is selected from at least one of emulsifiers, wetting agents, lipophilic colloids, and weighting agents.

[0040] Preferably, in the oil-based drilling fluid, based on the total mass of the oil-based drilling fluid, the content of the emulsifier is 3wt%-10wt%, the content of the wetting agent is 0.5wt%-3wt%, the content of the oleophilic colloid is 1wt%-2wt%, and the content of the weighting agent is such that the density of the oil-based drilling fluid is 1.0 g / cm³. 3 -2.0g / cm 3 The remainder consists of the base oil and the brine phase, and the volume ratio of the base oil to the brine phase is (1-9):1.

[0041] Preferably, the emulsifier is a combination of organic fatty acids and fatty acid amides, wherein, based on the total mass of the water-based drilling fluid, the content of the organic fatty acids is 2wt%-6wt% and the content of the fatty acid amides is 1wt%-4wt%.

[0042] The fourth aspect of the present invention provides the application of the drilling fluid provided in the third aspect of the present invention in the field of oil and gas drilling.

[0043] This invention provides a modified styrene-butadiene latex, its preparation method, and its application. The modified styrene-butadiene latex has a hydrophobic core and a hydrophilic shell, and is suitable for both water-based and oil-based drilling fluid systems. It can evenly seal nano-micron pores and fractures in heterogeneous formations, reducing drilling fluid filtration loss. The preparation process of this modified styrene-butadiene latex is simple and low-cost, and it can be industrially applied. Attached Figure Description

[0044] Figure 1 This is a transmission electron microscope image of the modified styrene-butadiene latex provided in Example 1 of the present invention;

[0045] Figure 2 This is the thermogravimetric analysis spectrum of the modified styrene-butadiene latex provided in Example 1 of the present invention;

[0046] Figure 3 This is the 1H NMR spectrum of the modified styrene-butadiene latex provided in Example 1 of this invention. Detailed Implementation

[0047] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0048] As mentioned above, the first aspect of the present invention provides a modified styrene-butadiene latex, wherein the modified styrene-butadiene latex has a core-shell structure and contains structural unit A, structural unit B, structural unit C and structural unit D, wherein structural unit A is at least one of the structural units shown in formula (1), structural unit B is at least one of the structural units shown in formula (2), structural unit C is at least one of the structural units shown in formula (3), structural unit D is at least one of the structural units shown in formula (4), and the weight-average molecular weight of the modified styrene-butadiene latex is 20,000-25,000;

[0049]

[0050] Among them, R 1 R 2 R 3 R 6 Each is independently selected from H or C1-C4 alkyl groups;

[0051] R 4 R 5 R 7 R 8 Each is independently selected from H or C1-C6 alkyl groups;

[0052] M is selected from H or an alkali metal element.

[0053] The modified styrene-butadiene latex provided by this invention has a hydrophobic core and a hydrophilic shell. Through the combined action of structural units A, B, C and D, it plays a role in sealing and reducing filtration loss in drilling fluids, synergistically sealing heterogeneous formations and preventing water molecules from self-absorbing and penetrating. Furthermore, because it has an amphiphilic structure, it can be used in both water-based and oil-based drilling fluid systems, and has very practical application value and broad prospects.

[0054] For example, Figure 1 The images shown are transmission electron microscope (TEM) images of the modified styrene-butadiene latex particles prepared in Example 1 of this invention. Figure 1 It is evident that the modified styrene-butadiene latex provided by this invention has a special core-shell structure.

[0055] In this invention, the modified styrene-butadiene latex can be considered as a modified styrene-butadiene latex with a core structure consisting of structural unit A shown in formula (1) and structural unit B shown in formula (2) as the "core", and structural unit B shown in formula (2), structural unit C shown in formula (3), and structural unit D shown in formula (4) as the "shell".

[0056] Furthermore, the molecular structure of the modified styrene-butadiene latex has multiple synergistic functions in specific applications. The benzene ring structure provided by structural unit A in formula (1) serves as a rigid group, which can enhance the strength of the molecular chain segments. Under high temperatures, the molecular chain is not easily twisted or broken, ensuring its thermal stability. At the same time, the hard core particles formed can seal and fill the nano-micro pores of the formation, preventing the intrusion of fluids and solid particles. The hydrophobic group provided by structural unit B in formula (2) is distributed in the shell to form a hydrophobic layer, effectively reducing the contact between clay and water, thereby avoiding hydration swelling. The sulfonic acid group provided by structural unit C in formula (3), as an anionic strong hydration group, can enhance the thickness of the hydration film and improve its temperature and salt resistance to a certain extent. The amide group provided by structural unit in formula (4) can provide hydrogen bond donors and acceptors to combine with oxygen atoms to form strong hydrogen bonds, generating strong adsorption with formation rocks and well walls. Therefore, the modified styrene-butadiene latex provided by this invention can achieve the above-mentioned application effects in drilling fluids under the combined action of the groups provided by each structural unit.

[0057] When the above-mentioned modified styrene-butadiene latex is added to the drilling fluid system, it has excellent nano-micro plugging ability, filtration loss reduction effect and temperature resistance. It can be further applied in high-temperature drilling fluid systems, which is beneficial for high-temperature deep well drilling, and ensures less intrusion of free water, thereby maintaining wellbore stability and reservoir protection.

[0058] According to some preferred embodiments of the present invention, the R 4 The R 5 The R 7 The R 8 Each is independently selected from one of methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, and n-hexyl.

[0059] According to some preferred embodiments of the present invention, M is selected from H, Na, and K.

[0060] According to some preferred embodiments of the present invention, the average particle size of the modified styrene-butadiene latex is 80 nm to 310 nm. Styrene-butadiene latex with an average particle size within this range can better uniformly seal nano- and micron-sized pores and fractures in heterogeneous formations, thereby reducing drilling fluid loss.

[0061] According to some preferred embodiments of the present invention, the modified styrene-butadiene latex is in the form of an emulsion or a solid.

[0062] A second aspect of the present invention provides a method for preparing the modified styrene-butadiene latex provided in the first aspect, comprising the following steps:

[0063] (1) Mixing monomer A' and monomer B' yields solution I; and

[0064] In an aqueous solvent, monomers C' and D' are mixed and the pH is adjusted to 7-9 to obtain solution II;

[0065] (2) Mix solution I and a portion of solution II and heat to a target temperature I to obtain a first intermediate system; the target temperature I is 25℃-60℃.

[0066] (3) Initiator I is mixed with the first intermediate system and heated to the target temperature II to obtain the second intermediate system; the target temperature II is 60℃-82℃ and the target temperature II is higher than the target temperature I;

[0067] (4) The remaining solution II and initiator II are mixed with the second intermediate system and subjected to constant temperature treatment to obtain the modified styrene-butadiene latex;

[0068] Wherein, monomer A' is selected from at least one of the monomers shown in formula (I), monomer B' is selected from at least one of the monomers shown in formula (II), monomer C' is selected from at least one of the monomers shown in formula (II), and monomer D' is selected from at least one of the monomers shown in formula (IV). The amounts of monomer A', monomer B', monomer C', and monomer D' are such that the weight-average molecular weight of the obtained modified styrene-butadiene latex is 20,000 to 25,000.

[0069] The monomers A', B', C', and D' respectively make the modified styrene-butadiene latex contain structural units A, B, C, and D, respectively. Structural unit A is at least one of the structural units shown in formula (1), structural unit B is at least one of the structural units shown in formula (2), structural unit C is at least one of the structural units shown in formula (3), and structural unit D is at least one of the structural units shown in formula (4).

[0070]

[0071] The definitions of R1, R2, R3, R4, R5, R6, R7, R8, and M are the same as those in the modified styrene-butadiene latex provided in the first aspect of this invention.

[0072] In the preparation method described in the second aspect of the present invention, the relevant definitions and types of substituents in the monomers with the structure shown in formula (I), the monomers with the structure shown in formula (III), the monomers with the structure shown in formula (III), and the monomers with the structure shown in formula (IV) are the same as the relevant definitions and types of substituents mentioned above in the present invention. The present invention will not repeat them here, and those skilled in the art should not understand them as limitations on the technical solutions of the present invention.

[0073] It should be understood that the modified styrene-butadiene latex prepared by the above method usually refers to the direct product prepared by the above method without purification. Although such product may be a mixture of multiple polymers, this invention also includes such cases within the scope of this invention.

[0074] In this invention, monomers A', B', C', and D' can be obtained commercially or synthesized using known methods in the field of organic synthesis based on the structural formula provided by this invention.

[0075] According to some preferred embodiments of the present invention, the molar ratio of monomer A', monomer B', monomer C', and monomer D' is 1:(0.5-1.20):(0.04-0.08):(0.05-0.20). In this preferred case, the modified styrene-butadiene latex obtained has better blocking performance and filtration loss reduction performance, and higher raw material utilization rate.

[0076] In this invention, it should be noted that the monomer is almost completely converted into the corresponding structural unit contained in the polymer, and the amount of the monomer can be consistent with the content of the corresponding structural unit contained in the polymer.

[0077] In step (1), according to some preferred embodiments of the present invention, the pH of the mixture of monomer C' and monomer D' is adjusted to 7-9, such that the polymerization reaction between monomer A', monomer B', monomer C', and monomer D' is carried out under alkaline conditions. Preferably, the pH of this alkaline condition is 7-7.5. The present invention does not have any particular requirements for the reagents used to adjust the pH, and it can be adjusted by various alkaline compounds conventionally used in the art. Examples of such alkaline compounds include one or more of lithium hydroxide, sodium hydroxide, potassium hydroxide, potassium carbonate, sodium carbonate, sodium bicarbonate, and their respective aqueous solutions (e.g., at a concentration of 1 wt%-10 wt%).

[0078] According to some preferred embodiments of the present invention, the amount of the aqueous solvent is 40wt%-70wt%, based on the total mass of monomer A', monomer B', monomer C', monomer D', and the aqueous solvent. It should be understood that the aqueous solvent can be water alone, or a mixture of water and some solvents that do not affect the reaction of the present invention; water is preferred.

[0079] According to some preferred embodiments of the present invention, the weight ratio of the amount of solution II in step (2) to the amount of solution II in step (4) is 1:(0.5-2). The portion of solution II added in step (2) allows the mixture of solution I and solution II to undergo a slow polymerization reaction under the initiation of initiator I, gradually forming the core in the core-shell structure; the remaining solution II added in step (3) allows the mixture of solution I and solution II to undergo a full polymerization reaction, grafting and coating the inner shell to form a polymer outer shell. In this preferred case, the modified styrene-butadiene latex obtained has a good core morphology and good outer shell coating properties, and the overall particle morphology of the modified styrene-butadiene latex obtained is excellent.

[0080] According to some preferred embodiments of the present invention, in step (2), the target temperature I is 50℃-55℃, and in step (3), the target temperature II is 70℃-75℃. At the target temperature I, initiator I is added to initiate the polymerization of monomer A' and monomer B', completing the formation of the core in the core-shell structure. Then, the temperature is raised to the target temperature II, and initiator II is added, so that the structural unit B formed by monomer C', monomer D' and monomer B' polymerizes to form the outer shell in the core-shell structure, which covers the core, forming a stable core-shell structure.

[0081] According to some preferred embodiments of the present invention, in step (2), the heating rate to the target temperature I is 0.5℃ / min-2℃ / min; in step (3), the heating rate to the target temperature II is 0.5℃ / min-2℃ / min. In this preferred case, the modified styrene-butadiene latex obtained can better form a core-shell structure, and the particle morphology of the modified styrene-butadiene latex obtained is better.

[0082] According to some preferred embodiments of the present invention, in step (4), the temperature of the isothermal treatment is 70℃-80℃, and the treatment time is 3h-8h. In this preferred case, monomers A', B', C', and D' can fully polymerize, resulting in a high yield of modified styrene-butadiene latex, and the modified styrene-butadiene latex can better form a core-shell structure, resulting in better particle morphology of the modified styrene-butadiene latex.

[0083] According to some preferred embodiments of the present invention, the initiator I and the initiator II may be the same or different, and each is independently selected from at least one of potassium persulfate, ammonium persulfate, and sodium persulfate.

[0084] According to some preferred embodiments of the present invention, steps (2), (3), and (4) are carried out under stirring conditions, preferably with a stirring rate of 100 rpm to 400 rpm.

[0085] According to some preferred embodiments of the present invention, steps (2), (3), and (4) are performed under a protective atmosphere, wherein the protective gas in the protective atmosphere includes one or more of nitrogen, helium, neon, and argon.

[0086] It should be noted that, in addition to directly obtaining modified styrene-butadiene latex in liquid form, the present invention can also obtain modified styrene-butadiene latex in solid form. The method for obtaining solid modified styrene-butadiene latex further includes:

[0087] (5) The modified styrene-butadiene latex obtained in step (4) is dried to obtain a solid modified styrene-butadiene latex.

[0088] According to some more preferred embodiments of the present invention, the drying temperature of the drying process is 75℃-90℃, and the drying time is 24h-72h.

[0089] It should be noted that the present invention does not particularly limit the specific method of drying treatment, and various conventional drying methods in the art can be used, such as oven drying, freeze drying, supercritical drying and spray drying.

[0090] Although the present invention is not particularly limited, the product can be considered as one or a mixture of several of the modified styrene-butadiene latexes described above. It should be understood that the modified styrene-butadiene latex prepared by the above method generally refers to the direct product of the above method without purification (or only after the drying process described above), although such a product may be a mixture of multiple polymers, and this invention also includes such cases within its scope.

[0091] A third aspect of the present invention provides a drilling fluid containing modified styrene-butadiene latex, wherein the content of the modified styrene-butadiene latex is 1wt%-4wt% based on the total mass of the drilling fluid;

[0092] The modified styrene-butadiene latex is the modified styrene-butadiene latex provided in the first aspect of the present invention.

[0093] Adding the modified styrene-butadiene latex to a water-based drilling fluid system results in a system that exhibits good plugging ability and low filtration loss at high temperatures, making it suitable to a certain extent for oil and gas drilling operations with high temperature and pressure requirements and stringent environmental regulations. This invention does not impose any particular limitation on the amount of modified styrene-butadiene latex added to the water-based drilling fluid system; commonly used water-based drilling fluid plugging agents or filtration loss reducers can be used, and adjustments can be made according to different needs. Preferably, the amount of modified styrene-butadiene latex added is 1wt%-4wt% based on the total mass of the water-based drilling fluid, more preferably 1wt%-3wt%. Water-based drilling fluids within this preferred range exhibit better plugging performance and lower filtration loss.

[0094] It should be noted that the present invention does not have any particular limitation on the above-mentioned water-based drilling fluid system, and conventional water-based drilling fluid systems in the art can be used.

[0095] According to some preferred embodiments of the present invention, the drilling fluid is a water-based drilling fluid, which further contains bentonite and additive A, wherein additive A is selected from at least one of sodium carbonate, filtration loss reducer, inhibitor, plugging agent, and weighting agent.

[0096] According to some preferred embodiments of the present invention, based on the total mass of the water-based drilling fluid, the bentonite content is 1wt%-5wt%, the sodium carbonate content is 0.2wt%-0.5wt%, the filtration loss reducer content is 0.7wt%-1.7wt%, the inhibitor content is 1wt%-10wt%, the plugging agent content is 3wt%-10wt%, and the weighting agent content results in a water-based drilling fluid density of 1.2 g / cm³. 3 -1.8g / cm 3 The remainder is water.

[0097] According to some preferred embodiments of the present invention, the bentonite refers to clay with montmorillonite as the main mineral component, which imparts viscosity and shear strength and filtration and wall-building properties to the drilling fluid. The bentonite described in the present invention is sodium-based bentonite and / or calcium-based bentonite, preferably sodium-based bentonite. More preferably, based on the total mass of the water-based drilling fluid, the content of sodium-based bentonite is 2wt%-4wt%.

[0098] According to some preferred embodiments of the present invention, the filtration loss reducer is mainly a natural polymer material used to increase the viscosity and shear force of water-based drilling fluid while reducing the filtration loss of water-based drilling fluid. In the present invention, the filtration loss reducer is a combination of xanthan gum and polyanionic cellulose, wherein, based on the total mass of the water-based drilling fluid, the content of xanthan gum is 0.1wt%-0.5wt%, and the content of polyanionic cellulose is 0.6wt%-1.2wt%.

[0099] According to some preferred embodiments of the present invention, the inhibitor is one or a combination of sodium chloride and potassium chloride. According to some more preferred embodiments of the present invention, the inhibitor is preferably 5 wt%-7 wt% potassium chloride, based on the total mass of the water-based drilling fluid. In this preferred embodiment, the inhibitor can reduce the drilling fluid osmotic pressure and clay interlayer spacing, prevent clay hydration swelling, and thereby improve wellbore stability.

[0100] According to some preferred embodiments of the present invention, the plugging agent is a combination of asphalt and calcium carbonate, wherein, based on the total mass of the water-based drilling fluid, the asphalt content is 1wt%-4wt% and the calcium carbonate content is 2wt%-6wt%. In this preferred embodiment, the plugging agent can seal pore throats through particle size matching, improve the pressure-bearing capacity of the sealing layer, prevent solid particle intrusion, and prevent drilling fluid loss.

[0101] According to some preferred embodiments of the present invention, the weighting agent is one or more combinations of barite and micro-manganese ore, which can increase the density of the drilling fluid to 1.2 g / cm³. 3 -1.8g / cm 3 This balances formation pressure and maintains bottom hole pressure balance, making the drilling process smoother.

[0102] It should be understood that the above-mentioned additive A can be a common commercially available product or a product prepared by conventional methods in this field, which will not be elaborated here.

[0103] According to some preferred embodiments of the present invention, the drilling fluid is an oil-based drilling fluid, which further contains base oil, a brine phase, and additive B, wherein additive B is selected from at least one of emulsifiers, wetting agents, lipophilic colloids, and weighting agents.

[0104] Adding the modified styrene-butadiene latex to an oil-based drilling fluid system results in an oil-based drilling fluid that maintains good shear strength and high-temperature performance, and to some extent replaces difficult-to-degrade additives such as asphalt and lignite. The amount of modified styrene-butadiene latex added to the oil-based drilling fluid system is not particularly limited; it can be added at the same amount as commonly used oil-based drilling fluid plugging agents or filtration reducers, and can be adjusted appropriately according to different needs. Preferably, based on the total mass of the oil-based drilling fluid, the amount of modified styrene-butadiene latex added is 1wt%-4wt%, more preferably 1wt%-3wt%. Oil-based drilling fluids within this preferred range exhibit better plugging performance and lower filtration loss.

[0105] According to the present invention, there is no particular limitation on the above-mentioned oil-based drilling fluid system, and conventional oil-based drilling fluid systems in the art can be used.

[0106] According to some preferred embodiments of the present invention, in the oil-based drilling fluid, based on the total mass of the oil-based drilling fluid, the content of the emulsifier is 3wt%-10wt%, the content of the wetting agent is 0.5wt%-3wt%, the content of the oleophilic colloid is 1wt%-2wt%, and the content of the weighting agent is such that the density of the oil-based drilling fluid is 1.0 g / cm³. 3 -2.0g / cm 3 The remainder consists of the base oil and the brine phase, and the volume ratio of the base oil to the brine phase is (1-9):1.

[0107] According to some preferred embodiments of the present invention, the base oil is at least one of crude oil, diesel oil, No. 3 white oil, and No. 5 white oil, preferably No. 3 white oil or No. 5 white oil, and the base oil is used to control the overall rheological properties and stability of the oil-based drilling fluid.

[0108] According to some preferred embodiments of the present invention, the brine phase is an aqueous solution containing CaCl2 or NaCl, preferably a CaCl2 aqueous solution with a concentration of 10wt%-60wt%, more preferably a CaCl2 aqueous solution with a concentration of 20-40wt%. The brine phase is used to control the activity of the aqueous phase and prevent or reduce the hydration swelling of the mudstone and shale formations.

[0109] It should be noted that the volume ratio of base oil to brine phase is simply referred to as the oil-water ratio. In this invention, the oil-water ratio is (1-9):1, more preferably (2-4):1. This preferred condition enables the oil-based drilling fluid to maintain excellent performance while reducing the cost of the oil-based drilling fluid.

[0110] According to some preferred embodiments of the present invention, the emulsifier refers to an emulsifier that forms an adsorption film with a certain strength at the oil-water interface, reduces interfacial tension, and increases the viscosity of the external phase. The emulsifier of the present invention is one or more of fatty acids, alkyl sulfonates, Span-80, and stearamide, preferably a combination of organic fatty acids and fatty acid amides. The content of the organic fatty acids is 2wt%-6wt% and the content of the fatty acid amides is 1wt%-4wt%, based on the total mass of the water-based drilling fluid.

[0111] According to some preferred embodiments of the present invention, the wetting agent is one or more combinations of quaternary ammonium salts, lecithin, and petroleum sulfonates. Preferably, the content of the wetting agent is 1wt%-2wt% based on the total mass of the oil-based drilling fluid. In this preferred embodiment, the wetting agent can rapidly transform the hydrophilic surface of barite or drill cuttings into an oil-wetted wall surface, ensuring its stable suspension in the continuous phase, and significantly improving the demulsification voltage of the oil-based drilling fluid system.

[0112] According to some preferred embodiments of the present invention, the oleophilic colloid is one or more combinations of organic clay, oxidized bitumen, and lignite. Preferably, the oleophilic colloid is 1wt%-4wt% based on the total mass of the oil-based drilling fluid. In this preferred case, the oleophilic colloid can increase the shear strength and viscosity of the oil-based drilling fluid, thereby improving the plugging ability of the oil-based drilling fluid and reducing filtration loss.

[0113] According to some preferred embodiments of the present invention, the weighting agent is one or more combinations of barite and micro-manganese ore. The weighting agent can increase the drilling fluid density, raising it to 1.0 g / cm³. 3 -2.0g / cm 3 This balances formation pressure and maintains bottom hole pressure balance, making the drilling process smoother.

[0114] It should be understood that the above-mentioned additive B can be a common commercially available product or a product prepared by conventional methods in this field, which will not be elaborated here.

[0115] The fourth aspect of the present invention provides the application of the drilling fluid provided in the third aspect of the present invention in the field of oil and gas drilling.

[0116] The water-based and oil-based drilling fluids provided by this invention include the modified styrene-butadiene latex provided by this invention. The modified styrene-butadiene latex has nano- to micron-sized particles, which can further optimize the proportion of solid particles in the drilling fluid system, forming a tight sealing layer to evenly seal the nano- to micron-sized pores in the formation and reduce filtration loss. Secondly, the modified styrene-butadiene latex has an amphiphilic structure, which can act as a surfactant to enhance the film strength at the oil-water interface, ensuring the stability and temperature resistance of the oil-water emulsion. Compared with asphalt and lignite, it improves the environmental friendliness of the drilling fluid system and reduces the recycling and treatment costs, and has great potential for widespread application.

[0117] The present invention will be described in detail below through examples. Unless otherwise specified, the experimental methods used in the following examples are conventional methods; unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0118] Bentonite, purchased from Huai'an County Tengfei Bentonite Development Co., Ltd., brand name Na-Bent;

[0119] Xanthan gum, purchased from Beijing Huawirui Chemical Co., Ltd., brand name XC;

[0120] Polyanionic cellulose, purchased from Beijing Huawirui Chemical Co., Ltd., brand name LV-PAC;

[0121] The environmentally friendly asphalt, purchased from Beijing Peikang Jiaye Technology Development Co., Ltd., is grade NFA-25.

[0122] Barite, purchased from Sichuan Zhengrong Industrial Co., Ltd., grade BARITE4.3;

[0123] No. 5 white oil, purchased from Hangzhou Fuda Fine Oil Products Co., Ltd., brand name No. 5 white oil;

[0124] Organic fatty acids, purchased from Beijing Shida Bocheng Technology Co., Ltd., brand name HT-MUL;

[0125] Fatty acid amide, purchased from Beijing Shida Bocheng Technology Co., Ltd., brand name HT-COAT;

[0126] Quaternary ammonium salt, purchased from Beijing Shida Bocheng Technology Co., Ltd., brand name HT-WET;

[0127] Organic soil, purchased from Zhejiang Fenghong New Materials Co., Ltd., brand name OMMT.

[0128] Example 1

[0129] (1) Mixing monomer A' and monomer B' yields solution I; and

[0130] In 70g of distilled water, monomers C' and D' were mixed to obtain a mixture, and the pH of the mixture was adjusted to 7 using sodium hydroxide to obtain solution II;

[0131] Specifically, the monomer A' has the structure shown in formula (Ⅰ), and R therein... 1 For H, the monomer B' has the structure shown in formula (II), and R therein 2 and R 3 Each is independently H, the monomer C' has the structure shown in formula (ⅠII), and R therein 4 For H, R 5 The monomer D' is -CH3, and has the structure shown in formula (IV), where R... 6 and R 7 Each is independently represented by H;

[0132] (2) Mix and emulsify the solution I and a portion of the solution II for 10 minutes until the mixed solution is milky white. Purge nitrogen gas into the container containing the mixed solution and heat to the target temperature I to obtain the first intermediate system; the target temperature I is 50°C.

[0133] (3) Mix 0.0007 mol of initiator I with the first intermediate system and heat to the target temperature II to obtain the second intermediate system; the initiator I is potassium persulfate and the target temperature II is 70°C;

[0134] (4) The remaining solution II and 0.0007 mol of initiator II are mixed with the second intermediate system and subjected to constant temperature treatment to obtain the modified styrene-butadiene latex; the initiator II is potassium persulfate, the constant temperature treatment temperature is 75°C, and the constant temperature treatment is 5h.

[0135] (5) The modified styrene-butadiene latex was dried in an oven at 80°C for 48 hours and then pulverized to obtain a solid modified styrene-butadiene latex, denoted as X1.

[0136] The molar ratio of monomers A', B', C' and D' is 1:0.963:0.050:0.117, and the specific amounts are shown in Table 1.

[0137] The weight ratio of a portion of solution II in step (2) to the remaining portion of solution II in step (4) is 1:1.

[0138] like Figure 1 The image shown is a transmission electron microscope (TEM) image of the modified styrene-butadiene latex provided in Example 1 of the present invention.

[0139] like Figure 2 The image shown is a thermogravimetric analysis spectrum of the modified styrene-butadiene latex provided in Example 1 of the present invention.

[0140] like Figure 3 The image shown is the 1H NMR spectrum of the modified styrene-butadiene latex provided in Example 1 of this invention.

[0141] Example 2

[0142] This embodiment uses a method similar to that of Example 1, except that R1 in monomer A' is -CH3, and the molar ratio of monomer A', monomer B', monomer C' and monomer D' is 1:1.093:0.057:0.133, as shown in Table 1. The remaining steps and parameters are the same as in Example 1, and a solid modified styrene-butadiene latex is obtained, denoted as X2.

[0143] Example 3

[0144] This embodiment uses a method similar to that of Embodiment 1, except that R in monomer B' is... 2 For H, R 3 The monomer is -CH3, and the molar ratio of monomer A', monomer B', monomer C' and monomer D' is 1:0.634:0.050:0.117, as shown in Table 1. The remaining steps and parameters are the same as in Example 1, and a solid modified styrene-butadiene latex is obtained, denoted as X3.

[0145] Example 4

[0146] This embodiment uses a method similar to that of Embodiment 1, except that R in the monomer D' is... 7 and R 8 Each monomer is independently -CH3, and the molar ratio of monomer A', monomer B', monomer C' and monomer D' is 1:0.963:0.052:0.084, as shown in Table 1. The remaining steps and parameters are the same as in Example 1, and a solid modified styrene-butadiene latex is obtained, denoted as X4.

[0147] Example 5

[0148] This embodiment uses a method similar to that of Embodiment 1, except that R in the monomer D' is... 7 It is isopropyl, R 8 The molar ratio of monomers A', B', C' and D' is 1:0.963:0.050:0.074, and the specific amounts are shown in Table 1. The remaining steps and parameters are the same as in Example 1. A solid modified styrene-butadiene latex is obtained and denoted as X5.

[0149] Comparative Example 1

[0150] This comparative example was prepared using a method similar to that of Example 1. The difference is that monomers C' and D' were not added in this comparative example. The remaining steps and parameters were the same as in Example 1, and a solid modified styrene-butadiene latex was obtained, denoted as DX1.

[0151] Comparative Example 2

[0152] This comparative example was prepared using a method similar to that of Example 1, except that monomer D' was not added. The remaining steps and parameters were the same as in Example 1, and a solid modified styrene-butadiene latex was obtained, denoted as DX2.

[0153] Comparative Example 3

[0154] This comparative example was prepared using a method similar to that of Example 1, except that monomer C' was not added. The remaining steps and parameters were the same as in Example 1, and a solid modified styrene-butadiene latex was obtained, denoted as DX3.

[0155] Comparative Example 4

[0156] This comparative example was conducted using a method similar to that of Example 1. The difference is that the molar ratio of monomers A', B', C', and D' in this comparative example is 1:0.963:0.1:0.25. The specific dosage ratio is shown in Table 1. The resulting solid modified styrene-butadiene latex is denoted as DX4.

[0157] Table 1

[0158]

[0159] Test Example 1

[0160] This test example was conducted according to the standard test method in GB / T 16783.2-2014 "Field testing of drilling fluids for the petroleum and natural gas industry - Part 1: Water-based drilling fluids".

[0161] The basic formula for water-based drilling fluid WBDF is: 4wt% bentonite + 0.2wt% xanthan gum + 0.8wt% polyanionic cellulose + 3wt% environmentally friendly asphalt + 7wt% potassium chloride + 5wt% calcium carbonate + barite (the amount of barite added makes the density of the oil-based drilling fluid 1.5 g / cm³). 3 The remainder is water.

[0162] The above-mentioned water-based drilling fluid WBDF was added to the modified styrene-butadiene latex prepared in the embodiments and comparative examples of the present invention to obtain water-based drilling fluids S1, S2, S3, S4, S5, DS1, DS2, DS3, and DS4.

[0163] Based on the total mass of the water-based drilling fluid, the amount of modified styrene-butadiene latex added is 3 wt%.

[0164] This test case includes the following performance tests for water-based drilling fluid systems: apparent viscosity (AV, mPa·s), plastic viscosity (PV, mPa·s), dynamic shear force (YP, Pa), and high-temperature, high-pressure filtration loss (FL) at 150℃ and 3.5MPa. HTHP (mL). The test results are shown in Table 2:

[0165] Table 2

[0166] Modified styrene-butadiene latex AV / mPa·s PV / mPa·s YP / Pa <![CDATA[FL HTHP / mL]]> WBDF / 32.5 27 5.5 17.6 S1 X1 41 32.5 8.5 4 S2 X2 42 32 10 5.2 S3 X3 37 26 11 6.8 S4 X4 39 30.5 8.5 6 S5 X5 35 26 9 7.2 DS1 DX1 38 32 6 16.4 DS2 DX2 29 25.5 3.5 22 DS3 DX3 31 27 4 19 DS4 DX4 48 34 14 17.6

[0167] As shown in Table 2, the water-based drilling fluid with modified styrene-butadiene latex prepared in the examples exhibits higher rheological parameters (AV, PV, YP) ​​than both the water-based drilling fluid without modified styrene-butadiene latex and the water-based drilling fluid with modified styrene-butadiene latex prepared in the comparative example, and significantly reduces the filtration loss of the drilling fluid under high temperature and high pressure conditions. Analysis shows that the addition of the modified styrene-butadiene latex prepared in the examples of this invention can effectively seal previously unblockable nano-micro pores, forming a dense sealing layer that prevents further intrusion of water molecules. The further polymerization of latex particles into a film at high temperatures alters the wetting properties of the drilling cake, greatly improving the basic performance of the water-based drilling fluid system.

[0168] Test Example 2

[0169] This test example was conducted according to the standard test method in GB / T 16783.2-2012 "Field Testing of Drilling Fluids for Petroleum and Gas Industry - Part 2: Oil-based Drilling Fluids".

[0170] The basic formulation of OBDF oil-based drilling fluid is: 3 wt% organic fatty acids + 3 wt% fatty acid amides + 1.5 wt% quaternary ammonium salt + 2 wt% organic clay + barite (the amount of barite added makes the density of the oil-based drilling fluid 1.5 g / cm³). 3 The remainder consists of No. 5 white oil and brine phase, wherein the volume ratio of No. 5 white oil to brine phase is 4:1, and the brine phase is a 30wt% CaCl2 aqueous solution.

[0171] The modified styrene-butadiene latex prepared in the embodiments and comparative examples of the present invention were added to the above-mentioned oil-based drilling fluid OBDF to obtain oil-based drilling fluids Y1, Y2, Y3, Y4, Y5, DY1, DY2, DY3, and DY4.

[0172] This test case includes the following performance tests for oil-based drilling fluid systems: demulsification voltage (ES, V), apparent viscosity (AV, mPa·s), plastic viscosity (PV, mPa·s), dynamic shear force (YP, Pa), and high-temperature, high-pressure filtration loss (FL) at 150℃ and 3.5 MPa. HTHP (mL). The test results are shown in Table 3:

[0173] Table 3

[0174] Modified styrene-butadiene latex ES / V AV / mPa·s PV / mPa·s YP / Pa <![CDATA[FL HTHP / mL]]> OBDF / 745 33.5 30.5 3 7.2 Y1 X1 892 39.5 29 10.5 1.5 Y2 X2 891 40 31 9 3.2 Y3 X3 852 42.5 30 12.5 1.5 Y4 X4 897 41 35 6 3.5 Y5 X5 866 44 33 11 2 DY1 DX1 702 28.5 27 1.5 6 DY2 DX2 684 34 32.5 1.5 7.6 DY3 DX3 657 30 29 1 7.8 DY4 DX4 712 31 30 1 8.2

[0175] As shown in Table 3, the water-based drilling fluid with modified styrene-butadiene latex prepared in the examples exhibits higher rheological parameters (AV, PV, YP) ​​than both the water-based drilling fluid without modified styrene-butadiene latex and the water-based drilling fluid with modified styrene-butadiene latex prepared in the comparative examples. Furthermore, it significantly increases the demulsification voltage, viscosity, and dynamic shear force of the drilling fluid system, while reducing filtration loss under high temperature and high pressure conditions by 30%-70% to varying degrees. Analysis reveals that the modified styrene-butadiene latex prepared in the examples possesses both hydrophobic and hydrophilic structural units, which enhance the strength of the emulsion film. In addition, as nano-sized particles, it can adsorb at the oil-water interface to maintain emulsion stability. The combined effect of multiple structural units and nano-size properties improves the emulsion stability, high-temperature stability, and many other fundamental properties of the oil-based drilling fluid system.

[0176] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing modified styrene-butadiene latex, characterized in that, Includes the following steps: (1) Mix monomer A' and monomer B' to obtain solution I; as well as In an aqueous solvent, monomers C' and D' are mixed and the pH is adjusted to 7-9 to obtain solution II; The molar ratio of monomer A', monomer B', monomer C', and monomer D' is 1:(0.5-1.20):(0.04-0.08):(0.05-0.20). (2) Mix solution I and a portion of solution II and heat to target temperature I to obtain a first intermediate system; the target temperature I is 25℃-60℃. (3) Initiator I is mixed with the first intermediate system and heated to the target temperature II to obtain the second intermediate system; the target temperature II is 60℃-82℃ and the target temperature II is higher than the target temperature I; (4) The remaining solution II and initiator II are mixed with the second intermediate system and subjected to constant temperature treatment to obtain the modified styrene-butadiene latex; Wherein, monomer A' is selected from at least one of the monomers shown in formula (I), monomer B' is selected from at least one of the monomers shown in formula (II), monomer C' is selected from at least one of the monomers shown in formula (III), and monomer D' is selected from at least one of the monomers shown in formula (IV). The amounts of monomer A', monomer B', monomer C', and monomer D' are such that the weight-average molecular weight of the obtained modified styrene-butadiene latex is 20,000 to 25,000. The monomers A', B', C', and D' respectively make the modified styrene-butadiene latex contain structural units A, B, C, and D, respectively. Structural unit A is at least one of the structural units shown in formula (1), structural unit B is at least one of the structural units shown in formula (2), structural unit C is at least one of the structural units shown in formula (3), and structural unit D is at least one of the structural units shown in formula (4). Formula (I), Equation (II), Formula (III) Formula (IV); Equation (1), Equation (2), Equation (3), Equation (4); wherein R 1 , R 2 , R 3 , R 6 are each independently selected from one of H or C1-C4 alkyl; R 4 , R 5 , R 7 , R 8 each independently is selected from one of H or C1-C6 alkyl; M is selected from H or an alkali metal element.

2. The preparation method according to claim 1, characterized in that, The R 4 The R 5 The R 7 The R 8 Each is independently selected from one of methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, and n-hexyl; M is selected from one of H, Na, and K.

3. The preparation method according to claim 1 or 2, characterized in that, The average particle size of the modified styrene-butadiene latex is 80 nm to 310 nm. And / or, the modified styrene-butadiene latex is in the form of an emulsion or a solid.

4. The preparation method according to claim 1, characterized in that, Based on the total mass of monomer A', monomer B', monomer C', monomer D', and the aqueous solvent, the amount of the aqueous solvent used is 40wt%-70wt%; And / or, the weight ratio of the amount of solution II used in step (2) to the amount of solution II used in step (4) is 1:(0.5-2).

5. The preparation method according to claim 1 or 2, characterized in that, The target temperature I is 50℃-55℃, and the target temperature II is 70℃-75℃; And / or, in step (2), the heating rate to the target temperature I is 0.5℃ / min-2℃ / min; In step (3), the heating rate to the target temperature II is 0.5℃ / min-2℃ / min; And / or, in step (4), the temperature of the isothermal treatment is 70℃-80℃, and the treatment time is 3h-8h; And / or, the initiator I and the initiator II may be the same or different, and each may be independently selected from at least one of potassium persulfate, ammonium persulfate, and sodium persulfate.

6. A drilling fluid, characterized in that, The drilling fluid contains modified styrene-butadiene latex, and the content of the modified styrene-butadiene latex is 1wt%-4wt% based on the total mass of the drilling fluid. The modified styrene-butadiene latex is a modified styrene-butadiene latex obtained by the preparation method described in any one of claims 1-5.

7. The drilling fluid according to claim 6, characterized in that, The drilling fluid is a water-based drilling fluid, which also contains bentonite and additive A. Additive A is selected from at least one of sodium carbonate, filtration loss reducer, inhibitor, plugging agent, and weighting agent.

8. The drilling fluid according to claim 7, characterized in that, Based on the total mass of the water-based drilling fluid, the bentonite content is 1wt%-5wt%, the sodium carbonate content is 0.2wt%-0.5wt%, the filtration loss reducer content is 0.7wt%-1.7wt%, the inhibitor content is 1wt%-10wt%, the plugging agent content is 3wt%-10wt%, and the weighting agent content results in a density of 1.2 g / cm³ for the water-based drilling fluid. 3 -1.8g / cm 3 The remainder is water.

9. The drilling fluid according to claim 7, characterized in that, The filtration loss reducer is a combination of xanthan gum and polyanionic cellulose, wherein, based on the total mass of the water-based drilling fluid, the content of xanthan gum is 0.1wt%-0.5wt% and the content of polyanionic cellulose is 0.6wt%-1.2wt%.

10. The drilling fluid according to claim 7, characterized in that, The plugging agent is a combination of asphalt and calcium carbonate, wherein, based on the total mass of the water-based drilling fluid, the asphalt content is 1wt%-4wt% and the calcium carbonate content is 2wt%-6wt%.

11. The drilling fluid according to claim 6, characterized in that, The drilling fluid is an oil-based drilling fluid, which also contains base oil, a brine phase, and additive B. Additive B is selected from at least one of emulsifiers, wetting agents, lipophilic colloids, and weighting agents.

12. The drilling fluid according to claim 11, characterized in that, In the oil-based drilling fluid, based on the total mass of the oil-based drilling fluid, the content of the emulsifier is 3wt%-10wt%, the content of the wetting agent is 0.5wt%-3wt%, the content of the oleophilic colloid is 1wt%-2wt%, and the content of the weighting agent makes the density of the oil-based drilling fluid 1.0 g / cm³. 3 -2.0g / cm 3 The remainder consists of the base oil and the brine phase, and the volume ratio of the base oil to the brine phase is (1-9):

1.

13. The drilling fluid according to claim 11, characterized in that, The emulsifier is a combination of organic fatty acids and fatty acid amides, wherein, based on the total mass of the oil-based drilling fluid, the content of the organic fatty acids is 2wt%-6wt% and the content of the fatty acid amides is 1wt%-4wt%.

14. The application of the drilling fluid according to any one of claims 6-13 in the field of oil and gas drilling.

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