Preparation method and application of oil-based drilling fluid filtrate reducer

Abstract

The invention provides an oil-based drilling fluid filtrate reducer and a preparation method and application thereof, and the preparation method comprises the following steps: preparing acrylate, lignin and water into a pre-emulsion in the presence of an emulsifier; and initiating emulsion polymerization of the pre-emulsion under the conditions of alkalinity, nitrogen and an initiator, and controlling the molecular chain length by using a chain transfer agent to obtain the oil-based drilling fluid filtrate reducer. The lignin grafted polymer oil-based drilling fluid filtrate reducer provided by the invention not only has good filtrate reduction ability, but also can assist in improving demulsification voltage and enhancing the stability of an oil-based drilling fluid system, and has good compatibility with diesel oil-based, white oil-based and synthetic-based drilling fluids. The oil-based drilling fluid filtrate reducer provided by the invention takes natural material lignin and the like as preparation raw materials, the lignin raw material is cheap and easy to obtain, the temperature resistance is strong, the reaction condition is mild, the product production process is simple and convenient, the operation is easy, and the comprehensive use cost is low.

Description

Technical Field

[0001] The present invention belongs to the technical field of drilling fluids, and particularly relates to a preparation method and application of a filtrate reducer for oil-based drilling fluids. Background Art

[0002] Oil-based drilling fluids have advantages such as good lubricity, high temperature resistance, strong inhibition, being beneficial to wellbore stability, strong anti-pollution ability, and being beneficial to protecting oil and gas layers, and are used for drilling in complex formations such as horizontal wells, highly deviated directional wells, and strongly water-sensitive formations. With the exploration and development of unconventional oil and gas such as shale gas and shale oil, oil-based drilling fluids are more and more widely used. As one of the most important treatment agents for oil-based drilling fluids, the filtrate reducer can help form a thin and dense filter cake on the wellbore wall, reduce the filtration loss, reduce the filtrate and solid phase invasion into the formation, and maintain wellbore stability, etc.

[0003] Currently, commonly used filtrate reducers for oil-based drilling fluids mainly include products such as asphalt-based and humic acid amine-based. Among them, asphalt-based filtrate reducers are widely used because of their low cost and easy availability. However, asphalt contains gum, which affects the mechanical drilling rate and is prone to polluting the environment. Its use in oil-based drilling fluids has been restricted in domestic environmentally sensitive areas and most foreign regions. Humic acid amine-based filtrate reducers mainly use humic acid and long-chain organic polyamines for direct high-temperature pyrolysis or add appropriate cross-linking agents to enhance the oil solubility of modified humic acid-based filtrate reduction. The synthesis conditions are harsh, the production energy consumption is large, the cost is high (the price of long-chain organic polyamines is expensive), and there is still a certain gap in filtration loss performance compared with asphalt-based products.

[0004] With the increasing intensity of shale gas and shale oil exploitation and the continuous improvement of safety and environmental protection requirements, it is required that the filtrate reducer for oil-based drilling fluids must have good filtration loss reduction performance and environmental friendliness, and at the same time should also have advantages such as simple and easy-to-operate production process and low price. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a preparation method and application of a filtrate reducer for oil-based drilling fluids. The filtrate reducer prepared by the method provided by the present invention has good filtration loss reduction ability, can assist in increasing the demulsification voltage, enhance the stability of the oil-based drilling fluid system, and has good compatibility with diesel-based, white oil-based, and synthetic-based drilling fluids.

[0006] The present invention provides a preparation method of a filtrate reducer for oil-based drilling fluids, including:

[0007] Emulsifying acrylate, lignin, and water in the presence of an emulsifier to form a pre-emulsion;

[0008] Under the condition of an initiator, carrying out emulsion polymerization on the pre-emulsion to obtain a filtrate reducer for oil-based drilling fluids.

[0009] The fluid loss reducer for oil-based drilling fluid prepared by the method provided by the present invention has strong fluid loss reduction ability, and also has the ability to improve the demulsification voltage and enhance the system stability. Moreover, the reaction conditions of the present invention are mild, the preparation process is simple, and no waste gas or waste residue is generated.

[0010] In the embodiments of the present invention, the acrylate can be selected from one or more of ethyl acrylate, methyl 2-methylacrylate, ethyl 2-methylacrylate, butyl acrylate, and octadecyl acrylate. In the embodiments of the present invention, taking acrylate as one of the raw materials, on the one hand, the ester substances have good oil solubility, which can improve the lipophilicity of the fluid loss reducer; on the other hand, the ester substances themselves can be used as emulsifiers to improve the demulsification voltage of the oil-based drilling fluid and enhance the stability of the system, realizing the dual functions of fluid loss reduction and enhanced emulsification.

[0011] In the embodiments of the present invention, lignin contains a benzene ring structure and has good heat resistance and dispersibility. It is often used as a raw material for high-temperature resistant fluid loss reducers in water-based drilling fluids. However, as a water-soluble macromolecular compound, lignin cannot be directly added to the oil-based drilling fluid system and needs to be modified by introducing long-chain amines, long-chain alkanes, etc. to enhance its lipophilicity. Under the condition of maintaining the comprehensive performance of the modified lignin fluid loss reducer for oil-based drilling fluids, exploring different modified synthesis process routes not only helps to reduce the production cost and energy consumption of the modified lignin fluid loss reducer, but also can effectively reduce the use cost of the oil-based drilling system.

[0012] In the embodiments of the present invention, lignin is an amorphous macromolecular natural compound. Its basic aromatic ring has strong heat resistance, and hydrophilic functional groups such as carboxyl and hydroxyl are connected to the ring, having hydrophilicity, as well as strong adsorption and dispersion abilities. It can enhance the adsorption ability with the rock surface and is often selected as the main material for producing high-temperature resistant drilling fluid treatment agents. Using lignin to prepare a fluid loss reducer for oil-based drilling fluids is cheap and easy to obtain, has strong heat resistance, dispersion, and adsorption abilities, and has good prospects when applied to the field of drilling and completion fluids.

[0013] In the embodiments of the present invention, the emulsifier can be selected from the compound of sodium dodecyl sulfate and OP-10; the mass ratio of sodium dodecyl sulfate to OP-10 can be selected from 1:(2-4), such as 1:3.

[0014] In the embodiments of the present invention, emulsification can be carried out under stirring conditions, and emulsification can be carried out under the condition of a protective gas, such as nitrogen; the emulsification time can be selected from 25-35 min, such as 30 min.

[0015] In the embodiments of the present invention, emulsion polymerization can be carried out under alkaline conditions, and an alkaline environment can be achieved by adding sodium bicarbonate.

[0016] In an embodiment of the present invention, the initiator can be selected from potassium persulfate, such as a potassium persulfate solution; the mass fraction of the potassium persulfate solution can be selected from 15% to 25%, such as 20%.

[0017] In an embodiment of the present invention, the emulsion polymerization can be carried out under the condition of a protective gas, such as nitrogen; the potassium persulfate solution can be dropped into the reaction kettle through a constant pressure dropping funnel, and the emulsion polymerization is carried out under the condition of nitrogen protection.

[0018] In an embodiment of the present invention, the temperature of the emulsion polymerization can be selected from 75°C to 85°C, such as 78°C, 89°C, 82°C; the time of the emulsion polymerization can be selected from 3 h to 5 h, such as 3.5 h, 4 h, 4.5 h.

[0019] In an embodiment of the present invention, a chain transfer agent can be used to control the molecular chain length during the emulsion polymerization process, and the chain transfer agent can be selected from dodecyl mercaptan.

[0020] In an embodiment of the present invention, the mass ratio of lignin, acrylate, sodium dodecyl sulfate, OP-10, potassium persulfate, dodecyl mercaptan, sodium bicarbonate and water can be selected from (60 - 70):(70 - 80):(1 - 1.2):(3 - 3.6):(0.6 - 0.8):(0.15 - 0.25):(1.0 - 1.2):(330 - 370), such as (63 - 67):(73 - 78):(1.05 - 1.15):(3.2 - 3.4):(0.75 - 0.85):(0.18 - 0.22):(1.05 - 1.15):(340 - 360), 65:75:1.1:3.3:0.7:0.2:1.1:350.

[0021] In an embodiment of the present invention, after the emulsion polymerization is completed, it may further include:

[0022] The obtained product is dried and pulverized to obtain an oil-based drilling fluid filtrate reducer.

[0023] In an embodiment of the present invention, the drying temperature can be selected from 101°C to 105°C, such as 102°C, 103°C, 104°C.

[0024] In an embodiment of the present invention, the mesh number of the pulverization can be selected from 30 to 300 meshes, such as 50 meshes, 100 meshes, 150 meshes, 200 meshes, 250 meshes.

[0025] The preparation method of the lignin graft polymer oil-based drilling fluid filtrate reducer provided by the embodiment of the present invention has mild reaction conditions, and the product production process is simple and easy to operate.

[0026] The present invention provides a lignin-grafted polymer oil-based drilling fluid filtrate reducer obtained by the preparation method described in the above technical solution, an oil-based drilling fluid prepared with the lignin-grafted polymer oil-based drilling fluid filtrate reducer. After aging at 150 °C for 16 h, for the diesel-based drilling fluid, the high-temperature and high-pressure filtration loss volume is reduced from 26.4 mL (blank) to 3.8 mL, and the demulsification voltage is increased from 560 V to 857 V; for the white oil-based drilling fluid, the high-temperature and high-pressure filtration loss volume is reduced from 24.2 mL (blank) to 4.0 mL, and the demulsification voltage is increased from 572 V to 812 V; for the biomass synthesis-based drilling fluid, the high-temperature and high-pressure filtration loss volume is reduced from 22.6 mL (blank) to 5.4 mL, and the demulsification voltage is increased from 504 V to 723 V.

[0027] The present invention provides a drilling fluid, comprising: the oil-based drilling fluid filtrate reducer prepared by the method described in the above technical solution.

[0028] In an embodiment of the present invention, the density of the drilling fluid can be selected from 1 to 2 g / cm 3 , such as 1.5 g / cm 3 ; the mass content of the oil-based drilling fluid filtrate reducer in the drilling fluid can be selected from 3 to 4%, such as 3.5%.

[0029] The lignin-grafted polymer oil-based drilling fluid filtrate reducer prepared by the present invention has outstanding filtrate reduction ability and also has an emulsifying function, giving full play to the performance advantages of both polyester and lignin. The polyester has a certain viscoelasticity, there is a certain viscous force with the organophilic clay, and it plays a cementing role on the organophilic clay particles, making it difficult for the base slurry to pass through smaller micropores, thereby reducing the filtration loss volume of the oil-based drilling fluid. In addition, the ester group is beneficial to enhancing the emulsion stability of the product. After being added to the drilling fluid, the strength of the emulsion droplet emulsification film increases, making it difficult for the emulsion droplets to be compressed and deformed to pass through the formation micropores and microfractures. This can not only reduce the filtration loss volume of the oil-based drilling fluid, but also increase the demulsification voltage of the oil-based drilling fluid. Lignin is beneficial to enhancing the dispersibility, temperature resistance and adsorption of the product. The hydroxyl groups, carboxyl groups and other adsorption groups in the lignin network structure are preferentially adsorbed on the rock surface, the ester groups extend into the oil phase and are arranged in an oriented manner. In addition, the oxygen atoms in the ester groups are easy to form hydrogen bonds with water molecules, enhancing the stability of the emulsion.

[0030] In the preparation method of the lignin graft polymer oil-based drilling fluid filtrate reducer provided by the present invention, emulsion polymerization reaction is mainly carried out between acrylate and lignin to obtain the lignin graft polymer oil-based drilling fluid filtrate reducer with the functions of filtrate reduction and emulsification. Moreover, the present invention uses water as the reaction solvent (humic acid amine and humic acid amide need to react in an organic solvent), the reaction temperature does not exceed 90 °C (the reaction temperature of humic acid amine and humic acid amide is as high as 200 °C), the reaction conditions are mild, the production process is simple and easy to implement, no waste gas or waste residue is generated during the production process, and the yield is greater than 98%. The raw materials lignin and acrylate are cheap (the polyamine raw materials of lignin amine and lignin amide are expensive), the product has prominent price advantages, high cost performance, and is applicable to diesel-based drilling fluid, white oil-based drilling fluid, and biomass synthetic-based drilling fluid.

[0031] The lignin graft polymer oil-based drilling fluid filtrate reducer for oil-based drilling fluid in the embodiments of the present invention has good filtrate reduction effect and emulsification function, and has the advantages of simple preparation method, no waste gas or waste residue generation, etc., and is suitable for large-scale popularization and application. Brief Description of the Drawings

[0032] Figure 1 It is the infrared spectrogram of the filtrate reducer prepared in Example 1 of the present invention. Detailed Embodiments

[0033] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0034] Potassium persulfate, OP-10, sodium dodecyl sulfate, dodecanethiol, sodium bicarbonate, methyl acrylate, ethyl acrylate, methyl 2-methylacrylate, ethyl 2-methylacrylate, butyl acrylate, and octadecyl acrylate used in the following embodiments of the present invention are purchased from Aladdin Reagent Co., Ltd. The base oils are No. 0 diesel and No. 3 white oil; the biomass synthetic base fluid comes from the Drilling Engineering Technology Research Institute of Zhongyuan Petroleum Engineering Co., Ltd., Sinopec, and can be obtained according to the method for preparing biomass base oil disclosed in the patent with the application number 201810743989.3; the organic bentonite is purchased from Sichuan Xinchuangneng Petroleum Engineering Technology Co., Ltd.; the emulsifier is provided by the Drilling Engineering Technology Research Institute of Zhongyuan Petroleum Engineering Co., Ltd., Sinopec, and the main component is polyester amide ether; calcium oxide is purchased from Hubei Longhai Chemical Co., Ltd.; oxidized asphalt is purchased from Henan Longxiang Petroleum Auxiliary Co., Ltd.; humic acid amide comes from the Drilling Engineering Technology Research Institute of Zhongyuan Petroleum Engineering Co., Ltd., Sinopec, and barite is purchased from Zhengzhou Xinzheng Meijiu Industry Co., Ltd.

[0035] Example 1

[0036] Under stirring, 350 parts by mass of water, 1.1 parts by mass of sodium dodecyl sulfate, 3.3 parts by mass of OP-10, 1.1 parts by mass of sodium bicarbonate, 0.2 parts by mass of dodecanethiol, 75 parts by mass of butyl acrylate, and 65 parts by mass of lignin were successively added into the reaction kettle. Emulsification was carried out for 30 min under nitrogen protection, and the temperature was raised to 70 °C. 0.7 parts by mass of potassium persulfate solution (mass fraction 20%) was added dropwise through a constant pressure dropping funnel, and the dropping rate was controlled (it could not flow in linearly). After dropping, it was kept at 80 °C for 4 h; the obtained reaction product was dried at 105 °C and pulverized with a pulverizer of 30-300 meshes to obtain a lignin-grafted polymer oil-based drilling fluid filtrate reducer.

[0037] Figure 1 The infrared absorption spectrum of the lignin-grafted polymer oil-based drilling fluid filtrate reducer prepared in Example 1 of the present invention is shown. It can be seen that the broad and medium-strong absorption peak at 3340 cm -1 is the stretching vibration absorption peak of lignin -OH in the copolymer, and the peak at 2960 cm -1 is the anti-symmetric stretching vibration absorption peak of methyl -CH 3 and methylene -CH 2 - in butyl acrylate. The peak at 2880 cm -1 is caused by the symmetric stretching vibration of ester group methyl -CH 3 and methylene -CH 2 -. The vibration absorption peaks of the lignin aromatic ring skeleton are at 1602 cm-1, 1514 cm-1 and 1460 cm-1. The stretching vibration absorption peak of C=O in butyl acrylate is at 1738 cm -1 . The anti-symmetric stretching vibration absorption peak of C-O-C is at 1250 cm -1 , and the symmetric stretching vibration absorption peak of C-O-C is at 1170 cm -1 . And the absorption peak at 1170 cm -1 is greater than the absorption peak at 1250 cm - , indicating that butyl acrylate participated in the graft copolymerization reaction. Through the analysis of the infrared absorption spectrum, it is proved that butyl acrylate all participated in the lignin graft copolymerization reaction.

[0038] Example 2

[0039] Under stirring conditions, 370 parts by mass of water, 1 part by mass of sodium dodecyl sulfate, 3 parts by mass of OP-10, 1 part by mass of sodium bicarbonate, 0.15 part by mass of dodecanethiol, 70 parts by mass of octadecyl acrylate, and 60 parts by mass of lignin were successively added to the reaction kettle. Emulsification was carried out for 30 min under nitrogen protection, then the temperature was raised to 70 °C, and 0.6 part by mass of potassium persulfate solution (mass fraction 20%) was added dropwise through a constant-pressure dropping funnel, controlling the dropping rate (it cannot flow in a line). After dropping, it was kept at 80 °C for 4 h. The obtained reaction product was dried at 105 °C and pulverized with a pulverizer of 30 - 300 meshes to obtain a lignin-grafted polymer oil-based drilling fluid filtrate reducer.

[0040] Example 3

[0041] Under stirring conditions, 330 parts by mass of water, 1.2 parts by mass of sodium dodecyl sulfate, 3.6 parts by mass of OP-10, 1.2 parts by mass of sodium bicarbonate, 0.25 part by mass of dodecanethiol, 80 parts by mass of methyl methacrylate, and 70 parts by mass of lignin were successively added to the reaction kettle. Emulsification was carried out for 30 min under nitrogen protection, then the temperature was raised to 70 °C, and 0.8 part by mass of potassium persulfate solution (mass fraction 20%) was added dropwise through a constant-pressure dropping funnel, controlling the dropping rate (it cannot flow in a line). After dropping, it was kept at 80 °C for 4 h. The obtained reaction product was dried at 105 °C and pulverized with a pulverizer of 30 - 300 meshes to obtain a lignin-grafted polymer oil-based drilling fluid filtrate reducer.

[0042] Example 4

[0043] Under stirring conditions, 350 parts by mass of water, 1.1 parts by mass of sodium dodecyl sulfate, 3.3 parts by mass of OP-10, 1.1 parts by mass of sodium bicarbonate, 0.2 part by mass of dodecanethiol, 30 parts by mass of ethyl acrylate, 45 parts by mass of butyl acrylate, and 65 parts by mass of lignin were successively added to the reaction kettle. Emulsification was carried out for 30 min under nitrogen protection, then the temperature was raised to 70 °C, and 0.7 part by mass of potassium persulfate solution (mass fraction 20%) was added dropwise through a constant-pressure dropping funnel, controlling the dropping rate (it cannot flow in a line). After dropping, it was kept at 80 °C for 4 h. The obtained reaction product was dried at 105 °C and pulverized with a pulverizer of 30 - 300 meshes to obtain a lignin-grafted polymer oil-based drilling fluid filtrate reducer.

[0044] Example 5

[0045] No. 0 diesel: 255 mL (volume fraction 85%), calcium chloride aqueous solution with a mass fraction of 20% 45 mL (volume fraction 15%);

[0046] Based on the total volume of diesel and calcium chloride aqueous solution: successively add 3% (mass / volume ratio, mass content) of organobentonite, 6% (mass / volume ratio, mass content) of emulsifier, and 4% (mass / volume ratio, mass content) of the lignin polymer oil-based drilling fluid filtrate reducer prepared in Example 1 to diesel, stir at high speed (10,000 r / min, the same below) for 12 minutes, then add the calcium chloride aqueous solution and stir at high speed for 8 minutes, then add 4% (mass / volume ratio, mass content) of calcium oxide and stir at high speed for 8 minutes, and then add barite to adjust the density of the drilling fluid to 1.5 g / cm 3 , stir at high speed for 20 min to obtain the drilling fluid.

[0047] Example 6

[0048] Prepare the drilling fluid according to the method of Example 5. The difference from Example 5 is that the lignin grafted polymer oil-based drilling fluid filtrate reducer prepared in Example 2 is used to replace the lignin grafted polymer oil-based drilling fluid filtrate reducer prepared in Example 1.

[0049] Example 7

[0050] Prepare the drilling fluid according to the method of Example 5. The difference from Example 5 is that the lignin grafted polymer oil-based drilling fluid filtrate reducer prepared in Example 3 is used to replace the lignin grafted polymer oil-based drilling fluid filtrate reducer prepared in Example 1.

[0051] Example 8

[0052] Prepare the drilling fluid according to the method of Example 5. The difference from Example 5 is that the lignin grafted polymer oil-based drilling fluid filtrate reducer prepared in Example 4 is used to replace the lignin grafted polymer oil-based drilling fluid filtrate reducer prepared in Example 1.

[0053] Example 9

[0054] Prepare the drilling fluid according to the method of Example 5. The difference from Example 5 is that barite is added to make the density of the drilling fluid 2.2 g / cm 3 .

[0055] Example 10

[0056] Prepare the drilling fluid according to the method of Example 5. The difference from Example 5 is that No. 3 white oil is used to replace No. 0 diesel.

[0057] Example 11

[0058] Prepare the drilling fluid according to the method of Example 5. The difference from Example 5 is that a biomass synthetic base fluid is used to replace No. 0 diesel.

[0059] Example 12

[0060] The drilling fluid was prepared according to the method of Example 5, which was different from Example 5 in that the lignin-grafted polymer oil-based drilling fluid filtrate reducer with a mass volume ratio (mass content) of 3% was used to replace 4% of the mass volume ratio (mass content).

[0061] Example 13

[0062] The drilling fluid was prepared according to the method of Example 5, which was different from Example 5 in that the lignin-grafted polymer oil-based drilling fluid filtrate reducer with a mass volume ratio of 5% was used to replace 4% of the mass volume ratio.

[0063] Example 14

[0064] The drilling fluid was prepared according to the method of Example 5, which was different from Example 5 in that the lignin-grafted polymer oil-based drilling fluid filtrate reducer with a mass volume ratio of 6% was used to replace 4% of the mass volume ratio.

[0065] Comparative Example 1

[0066] The drilling fluid was prepared according to the method of Example 5, which was different from Example 5 in that the lignin-grafted polymer oil-based drilling fluid filtrate reducer was not added.

[0067] Comparative Example 2

[0068] The drilling fluid was prepared according to the method of Example 10, which was different from Example 10 in that the lignin-grafted polymer oil-based drilling fluid filtrate reducer was not added.

[0069] Comparative Example 3

[0070] The drilling fluid was prepared according to the method of Example 11, which was different from Example 11 in that the lignin-grafted polymer oil-based drilling fluid filtrate reducer was not added.

[0071] Comparative Example 4

[0072] The drilling fluid was prepared according to the preparation method of Example 5, which was different from Example 5 in that the lignin-grafted polymer oil-based drilling fluid filtrate reducer was replaced with oxidized asphalt with a mass volume ratio (mass content) of 4%.

[0073] Comparative Example 5

[0074] The drilling fluid was prepared according to the preparation method of Example 5, which was different from Example 5 in that the lignin-grafted polymer oil-based drilling fluid filtrate reducer was replaced with humic acid amide with a mass volume ratio (mass content) of 4%.

[0075] Comparative Example 6

[0076] The drilling fluid was obtained according to the preparation method of Example 11, which was different from Example 11 in that the lignin-grafted polymer oil-based drilling fluid filtrate reducer was replaced with oxidized asphalt at a mass volume ratio (mass content) of 4%.

[0077] Comparative Example 7

[0078] The drilling fluid was obtained according to the preparation method of Example 11, which was different from Example 11 in that the lignin-grafted polymer oil-based drilling fluid filtrate reducer was replaced with humic acid amide at a mass volume ratio (mass content) of 4%.

[0079] Performance detection

[0080] The lignin-grafted polymer oil-based drilling fluid filtrate reducer prepared in the following examples of the present invention was tested for rheological properties at 60 °C, demulsification voltage at 50 °C, and high-temperature and high-pressure filtration loss at 150 °C in accordance with the national standard GB / T 16783.2-2012 "Petroleum and natural gas industry - Drilling fluid field testing - Part 2: Oil-based drilling fluid". The test results are shown in the following table.

[0081] Table 1 Performance test results of the drilling fluid prepared in the examples of the present invention

[0082]

[0083] In Table 1, AV is the apparent viscosity, PV is the plastic viscosity, YP is the yield point, Gel is the initial and final shear force, ES is the demulsification voltage, HTHP is the high-temperature and high-pressure filtration loss, and YP / PV is the yield point / plastic viscosity ratio.

[0084] As can be seen from Table 1, for the diesel-based drilling fluid (Examples 5 to 9) prepared with the lignin-grafted polymer oil-based drilling fluid filtrate reducer prepared by the present invention, at a dosage of 4% (mass content), aged at 150 °C for 16 h, the high-temperature and high-pressure filtration loss is 3.8 - 5.2 mL, the demulsification voltage is greater than 800 V, and the yield point / plastic viscosity ratio is 0.28 - 0.32. Compared with Comparative Example 1, Examples 5 to 9 show better rheological stability, significantly reduced high-temperature and high-pressure filtration loss, and significantly increased demulsification voltage. In particular, Example 1 has the best effect, with the high-temperature and high-pressure filtration loss reduced from 26.4 mL to 3.8 mL and the demulsification voltage increased from 560 V to 857 V. Compared with Example 1, Example 9 has slightly increased viscosity and shear force, increased demulsification voltage, and reduced filtration loss, which conforms to the change law of high-density drilling fluid. This filtrate reducer can be used in high-density drilling fluid, indicating that this filtrate reducer not only has good filtration loss reduction ability but also has the function of increasing the demulsification voltage.

[0085] In order to reflect the dosage of the lignin-grafted polymer oil-based drilling fluid filtrate reducer prepared by the present invention, the effects of different dosages on the performance of the drilling fluid were investigated, and the specific results are shown in Table 2.

[0086] Table 2 Influence of the dosage increase in the embodiments of the present invention on the performance of drilling fluid

[0087]

[0088] As can be seen from Table 2, in Examples 12, 5, and 13-14, as the dosage of the filtrate reducer increases, the high-temperature and high-pressure filtrate loss decreases, and the demulsification voltage increases. When the dosage is 3%-4%, the viscosity effect has little impact. When the dosage is 5%-6%, the viscosity effect increases. The optimal dosage is controlled at 3%-4%.

[0089] In order to reflect the applicability and compatibility of the lignin-grafted polymer oil-based drilling fluid filtrate reducer prepared by the present invention in various oil-based drilling fluid systems, its performance in diesel-based, white oil-based, and biomass synthetic-based drilling fluid systems was investigated. The specific results are shown in Table 3.

[0090] Table 3 Comparison of the drilling fluid performance of the filtrate reducer in Example 1 in different systems

[0091]

[0092] As can be seen from Table 3, for the diesel-based drilling fluid, when comparing Comparative Example 1 with Example 5, the high-temperature and high-pressure filtrate loss decreased significantly (from 26.4 mL to 3.8 mL), and the demulsification voltage increased significantly (from 560 V to 857 V). For the white oil-based drilling fluid, when comparing Comparative Example 2 with Example 10, the high-temperature and high-pressure filtrate loss decreased significantly (from 24.2 mL to 4.0 mL), and the demulsification voltage increased significantly (from 572 V to 823 V). For the biomass synthetic-based drilling fluid, when comparing Comparative Example 3 with Example 11, the high-temperature and high-pressure filtrate loss decreased significantly (from 22.6 mL to 5.4 mL), and the demulsification voltage increased significantly (from 504 V to 723 V). The above comparisons further illustrate that the lignin-grafted polymer oil-based drilling fluid filtrate reducer prepared by the present invention has good compatibility and is applicable to drilling fluid systems such as diesel-based, white oil-based, and biomass synthetic-based.

[0093] In order to reflect the effect of the lignin-grafted polymer oil-based drilling fluid filtrate reducer prepared by the present invention, the conventional oil-based drilling fluid filtrate reducer oxidized asphalt and humic acid amide were selected for comparison. The performance of the three filtrate reducers in diesel-based and biomass synthetic-based drilling fluid systems was investigated. The specific results are shown in Table 4.

[0094] Table 4 Comparison of the drilling fluid performance of different oil-based drilling fluid filtrate reducers

[0095]

[0096] Compared with Comparative Example 4 and Comparative Example 5, in diesel-based drilling fluids, the filtration loss reducer of lignin grafted polymer oil-based drilling fluid has comparable filtration loss reduction ability to oxidized asphalt and humic acid amide, but has a stronger ability to increase the demulsification voltage. Compared with Comparative Example 6 and Comparative Example 7, in biomass synthesis-based drilling fluids, using oxidized asphalt and humic acid amide alone to control the filtration loss at high temperature and high pressure has unsatisfactory effects. While using the filtration loss reducer of lignin grafted polymer oil-based drilling fluid alone, the filtration loss at high temperature and high pressure is 5.4 mL and the demulsification voltage is 723 V, which is significantly better than oxidized asphalt and humic acid amide.

[0097] In summary, it can be seen that the drilling fluid prepared with the filtration loss reducer of lignin grafted polymer oil-based drilling fluid prepared by the present invention has good filtration loss control ability and emulsification function, has good compatibility with the drilling fluid, and is applicable to diesel, white oil, and biomass synthesis-based drilling fluids.

[0098] As can be seen from the above examples, the filtration loss reducer of lignin grafted polymer oil-based drilling fluid prepared by the method provided by the present invention under the optimal conditions not only has good filtration loss control ability and emulsification function, but also has comparable or even better filtration loss reduction ability to traditional oxidized asphalt-based and humic acid amide-based filtration loss reducers. Moreover, it has mild reaction conditions, low comprehensive cost, strong environmental protection performance, and good compatibility with the drilling fluid, and is applicable to diesel-based, white oil-based, biomass synthesis-based and other drilling fluids.

[0099] Although the present invention has been described and illustrated with reference to specific embodiments thereof, such description and illustration do not limit the present invention. Those skilled in the art can clearly understand that various changes can be made without departing from the true spirit and scope of the present invention as defined by the appended claims, so as to adapt a particular situation, material, composition of matter, substance, method, or process to the objectives, spirit, and scope of the present application. All such modifications are intended to be within the scope of the appended claims. Although the methods disclosed herein have been described with reference to specific operations performed in a specific order, it should be understood that these operations can be combined, subdivided, or reordered without departing from the teachings of the present invention to form equivalent methods. Therefore, unless specifically indicated herein, the order and grouping of operations are not limitations of the present application.

Claims

1. A preparation method of an oil-based drilling fluid filtrate reducer, comprising: Emulsifying acrylate, lignin, and water in the presence of an emulsifier to form a pre-emulsion; Under the condition of an initiator, subjecting the pre-emulsion to emulsion polymerization to obtain an oil-based drilling fluid filtrate reducer.

2. The preparation method according to claim 1, wherein, The emulsifier is selected from sodium dodecyl sulfate and OP-10.

3. The preparation method according to claim 1, wherein, The emulsion polymerization is carried out under alkaline conditions.

4. The preparation method according to claim 1, wherein, During the emulsion polymerization process, a chain transfer agent is used to control the molecular chain length; The chain transfer agent is selected from dodecyl mercaptan.

5. The preparation method according to claim 1, wherein, The initiator is selected from potassium persulfate.

6. The preparation method according to claim 1, wherein, The acrylate is selected from one or more of ethyl acrylate, methyl 2-methylacrylate, ethyl 2-methylacrylate, butyl acrylate, and octadecyl acrylate.

7. The preparation method according to claim 1, wherein, The temperature of the emulsion polymerization is selected from 75 - 85 °C, and the time of the emulsion polymerization is selected from 3 - 5 h.

8. The preparation method according to claim 1, wherein, The emulsification time is selected from 25 - 35 min.

9. The preparation method according to claim 1, wherein, After the emulsion polymerization is completed, it further includes: Drying and pulverizing the obtained polymerization product to obtain an oil-based drilling fluid filtrate reducer.

10. A drilling fluid, comprising: The oil-based drilling fluid filtrate reducer prepared by the method according to claim 1.

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