A filtration reducer for oil-based drilling fluid and its preparation method

Abstract

The present invention aims to provide a filtrate reducer for oil-based drilling fluids and its preparation method, belonging to the technical field of oil drilling. The filtrate reducer for oil-based drilling fluids, in parts by weight, comprises the following raw materials: natural rubber powder, 20 to 40 parts; asphalt powder, 10 to 20 parts; calcium carbonate, 10 to 20 parts; modified humic acid amide, 5 to 15 parts; oil-soluble resin, 5 to 15 parts; oxidant, 1 to 5 parts; temperature stabilizer, 1 to 5 parts; emulsifier, 1 to 5 parts; wherein, the natural rubber powder, the asphalt powder, the modified humic acid amide, the oil-soluble resin and the oxidant are first heat-treated at 120 to 130 °C, and after cooling, they are mixed with the remaining raw materials. The present invention has the characteristics of wide raw material sources, good compatibility with oil-based drilling fluids, easy industrial production, and controllable environmental pollution problems.

Description

Technical Field

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

[0002] Due to its excellent lubricity, inhibition, and high-temperature resistance, oil-based drilling fluids are widely used in drilling operations in complex formations such as deep wells, ultra-deep wells, and horizontal wells. However, oil-based drilling fluids also have the problem of large filtrate loss, which is prone to causing downhole complex situations such as formation damage and wellbore instability. Therefore, it is of great significance to develop an efficient and environmentally friendly filtrate reducer for oil-based drilling fluids.

[0003] Chinese Invention (Title: "A Preparation Method of a Filtrate Reducer for Drilling Fluids and the Filtrate Reducer", Publication Number: CN114591464B, Publication Date: 20231128) discloses that the filtrate reducer for drilling fluids is obtained by polymerization reaction of 60 - 100 parts of distilled water; 20 - 40 parts of 2-acrylamido-2-methylpropanesulfonic acid; 20 - 40 parts of sodium styrenesulfonate; 20 - 40 parts of liquid paraffin; 2 - 10 parts of a dispersant; 2 - 10 parts of an initiator; and 10 - 20 parts of 2-hydroxyethyl methacrylate. The filtrate reducer prepared by this preparation method has good filtrate reduction performance, dispersibility, and temperature resistance, can withstand high temperatures above 200 °C, has good compatibility with drilling fluids, can effectively improve the safety and drilling speed of drilling, and is non-toxic, harmless, and easily degradable. However, in this preparation method, a polymerization reaction needs to be carried out, the production process is relatively complex, and the preparation cost (including equipment investment) is relatively high.

[0004] Chinese Invention (Title: "A Filtrate Reducer for Asphalt-Based Drilling Fluids and a Preparation Method Thereof", Publication Number: CN117757445B, Publication Date: 20240430) discloses that the filtrate reducer includes raw materials such as modified asphalt, white oil, modified lignin, and polyacrylamide; among them, the modified asphalt is asphalt after hydrophilic modification, and the modified lignin is lignin with a carboxyl sodium group introduced into its structure. The asphalt-based filtrate reducer for drilling fluids in the present invention is used in combination with water-based drilling fluids, can effectively reduce the filtrate loss of water-based drilling fluids, and can prevent bit sticking. However, in this method, modified asphalt is used as the main raw material, and the environmental pollution problem is relatively serious. Summary of the Invention

[0005] The present invention aims to provide a filtrate reducer for oil-based drilling fluids and a preparation method thereof, which have the characteristics of wide raw material sources, good compatibility with oil-based drilling fluids, easy industrial production, and controllable environmental pollution problems.

[0006] The technical solution adopted by the present invention is:

[0007] A filtrate reducer for oil-based drilling fluids, in parts by weight, includes the following raw materials:

[0008] Natural rubber powder, 20 - 40 parts;

[0009] Asphalt powder, 10 - 20 parts;

[0010] Calcium carbonate, 10 - 20 parts;

[0011] Modified humic acid amide, 5 - 15 parts;

[0012] Oil-soluble resin, 5 - 15 parts;

[0013] Temperature stabilizer, 1 - 5 parts;

[0014] Oxidizer, 1 - 5 parts;

[0015] Emulsifier, 1 - 5 parts;

[0016] Among them, after the natural rubber powder, the asphalt powder, the modified humic acid amide, the oil-soluble resin and the oxidizer are mixed, they are first heat-treated at 120 - 130 °C, and after cooling, they are mixed with the remaining raw materials.

[0017] Furthermore, the natural rubber powder is a natural rubber powder with a softening point of 80 - 120 °C.

[0018] Furthermore, the asphalt powder is a petroleum asphalt powder with a softening point of 80 - 120 °C.

[0019] Furthermore, the calcium carbonate is composed of 40 - 50 wt% of hard calcium carbonate with a particle size of 200 mesh, 30 - 40 wt% of hard calcium carbonate with a particle size of 400 mesh, and 20 - 25 wt% of hard calcium carbonate with a particle size of 1000 mesh.

[0020] Furthermore, the modified humic acid amide is formed by mixing humic acid amide and nano-silica or nano-aluminum oxide in a weight ratio of 5:1.

[0021] Furthermore, the oxidizer is benzoyl peroxide, dicumyl peroxide, potassium permanganate or sodium hypochlorite.

[0022] Furthermore, the temperature stabilizer is calcium stearate or zinc stearate.

[0023] Furthermore, the oil-soluble resin is a C5 petroleum resin or a C9 petroleum resin with a softening point of 80 - 120 °C.

[0024] Furthermore, the emulsifier is Span-80 or Tween-80.

[0025] Based on the same inventive concept, the present invention also provides a preparation method of a filtrate reducer for oil-based drilling fluids, including the following steps:

[0026] Step S1: Add natural rubber powder, asphalt powder, modified humic acid amide, oil-soluble resin and oxidant into the reaction kettle in proportion respectively;

[0027] Step S2: Start stirring, with the stirring speed of 300 - 400 r / min, and pre-mix evenly;

[0028] Step S3: Dilute the emulsifier with appropriate amount of ethanol and add it into the mixture in Step S2 by spraying method, then continue stirring and mix evenly.

[0029] Step S4: Set the temperature of the reaction kettle at 120 - 130 °C, and heat-treat the mixture in Step S3 at this temperature for 2 - 3 h;

[0030] Step S5: Cool the mixture in Step S4 to room temperature, crush it to 150 - 200 mesh, and then mix and stir it with calcium carbonate and temperature stabilizer for 30 min to obtain the filtration reducer for oil-based drilling fluid.

[0031] The beneficial effects of the present invention are as follows:

[0032] 1. The filtration reducer for oil-based drilling fluid in the present invention uses natural rubber powder, asphalt powder and calcium carbonate as the main raw materials, with wide sources of raw materials and low cost; meanwhile, compared with the filtration reducer mainly based on asphalt, the filtration reducer for oil-based drilling fluid in the present invention uses asphalt powder and reduces the dosage, and the environmental pollution problem is relatively controllable.

[0033] 2. An appropriate amount of oxidant is added to the filtration reducer for oil-based drilling fluid in the present invention, and a heat-treatment process at 120 - 130 °C is introduced. Appropriate C-C bonds and C-H bonds on the surfaces of natural rubber powder and oil-soluble resin are opened to form more oxygen-containing groups such as hydroxyl groups and carbonyl groups. These active groups react with the sulfoxide, carboxyl and anhydride groups in asphalt and humic acid amide (the synthetic raw material components of asphalt and humic acid amide are relatively complex and will contain sulfoxide, carboxyl and anhydride groups), improving the interaction force between the interfaces of natural rubber powder, asphalt powder, humic acid amide and oil-soluble resin, which is beneficial to improving the stability and plugging effect after the filtration reducer is compatible with the oil-based drilling fluid, and the effect of reducing the filtration loss is more obvious.

[0034] 3. The filtration reducer for oil-based drilling fluid in the present invention contains an appropriate amount of humic acid amide, which has hydrophilicity, lipophilicity, complexing ability and strong adsorption and dispersion ability, and is not easily decomposed at high temperature. The humic acid amide modified by adding nano-silica or nano-aluminum oxide has a more stable network structure, improving the rigidity and thermal stability of humic acid amide, and thus effectively improving the high-temperature resistance and salt resistance of the filtration reducer.

[0035] 4. The filtrate reducer for oil-based drilling fluid in the present invention contains an appropriate amount of oil-soluble resin. The oil-soluble resin has good dispersibility in the oil-based drilling fluid, can be well compatible with other components in the drilling fluid, and does not affect the emulsion stability of the drilling fluid. At the same time, the oil-soluble resin can form a dense filter cake in the drilling fluid in combination with natural rubber powder, asphalt powder, and humic acid amide, effectively reducing the filtrate loss of the drilling fluid.

[0036] 5. The filtrate reducer for oil-based drilling fluid in the present invention has good compatibility with the oil-based drilling fluid and can be widely used in drilling operations. The filtrate reducer for oil-based drilling fluid contains calcium carbonate with different particle size gradations, which can widely block microcracks. Moreover, the filtrate reducer for oil-based drilling fluid contains film-forming particles that can be softened. By participating in the formation of the mud cake, a high-strength adsorption film is formed on the surface of the mud cake, which can reduce the permeability of the mud cake and improve the quality of the mud cake. Under the dual plugging effects of rigid particles and film-forming particles, the plugging effect is better.

[0037] 6. The preparation process of the filtrate reducer for oil-based drilling fluid in the present invention mainly involves heat treatment. Compared with the polymerization reaction process, the production process is relatively simple, the preparation cost (including equipment investment) is relatively low, and it is easy to industrialize production. Specific Embodiments

[0038] The embodiments of the invention will be described in detail below.

[0039] Example 1

[0040] Add 20 kg of natural rubber powder (softening point 80 - 120 °C), 10 kg of asphalt powder (softening point 80 - 120 °C), 5 kg of modified humic acid amide (humic acid amide and nano-silica are mixed and modified according to a weight ratio of 5:1), 5 kg of C5 petroleum resin (softening point 80 - 120 °C), and 1 kg of benzoyl peroxide into the reaction kettle, start stirring, and pre-mix evenly at a stirring speed of 350 r / min. Atomize and add 1 kg of Span-80 (diluted with 0.5 kg of ethanol, and the ethanol volatilizes when heated during subsequent heat treatment), continue stirring, and mix evenly. Set the temperature of the reaction kettle at 120 °C, and stir and heat-treat at 120 °C for 3 h, then cool to room temperature, crush to 150 mesh, and then mix evenly with 10 kg of calcium carbonate (calcium carbonate is composed of 45 wt% of hard calcium carbonate with a particle size of 200 mesh, 30 wt% of hard calcium carbonate with a particle size of 400 mesh, and 25 wt% of hard calcium carbonate with a particle size of 1000 mesh) and 1 kg of calcium stearate to obtain the filtrate reducer for oil-based drilling fluid.

[0041] Example 2

[0042] Add 30 kg of natural rubber powder (softening point 80 - 120 °C), 15 kg of asphalt powder (softening point 80 - 120 °C), 10 kg of modified humic acid amide (humic acid amide and nano-silica are mixed and modified according to a weight ratio of 5:1), 10 kg of C5 petroleum resin (softening point 80 - 120 °C) and 3 kg of benzoyl peroxide into a reaction kettle, start stirring, and pre-mix evenly at a stirring speed of 350 r / min. Atomize and add 3 kg of Span-80 (diluted with 1.5 kg of ethanol, and the ethanol volatilizes when heated during subsequent heat treatment), continue stirring and mix evenly. Set the temperature of the reaction kettle at 125 °C, and stir and heat-treat at 125 °C for 2.5 h, then cool to room temperature, crush to 150 mesh, and then mix evenly with 15 kg of calcium carbonate (calcium carbonate is composed of 45 wt% of hard calcium carbonate with a particle size of 200 mesh, 30 wt% of hard calcium carbonate with a particle size of 400 mesh, and 25 wt% of hard calcium carbonate with a particle size of 1000 mesh) and 3 kg of calcium stearate to obtain a fluid loss reducer for oil-based drilling fluid.

[0043] Example 3

[0044] Add 40 kg of natural rubber powder (softening point 80 - 120 °C), 20 kg of asphalt powder (softening point 80 - 120 °C), 15 kg of modified humic acid amide (humic acid amide and nano-silica are mixed and modified according to a weight ratio of 5:1), 15 kg of C5 petroleum resin (softening point 80 - 120 °C) and 5 kg of benzoyl peroxide into a reaction kettle, start stirring, and pre-mix evenly at a stirring speed of 350 r / min. Atomize and add 5 kg of Span-80 (diluted with 2.5 kg of ethanol, and the ethanol volatilizes when heated during subsequent heat treatment), continue stirring and mix evenly. Set the temperature of the reaction kettle at 130 °C, and stir and heat-treat at 130 °C for 2 h, then cool to room temperature, crush to 150 mesh, and then mix evenly with 20 kg of calcium carbonate (calcium carbonate is composed of 45 wt% of hard calcium carbonate with a particle size of 200 mesh, 30 wt% of hard calcium carbonate with a particle size of 400 mesh, and 25 wt% of hard calcium carbonate with a particle size of 1000 mesh) and 5 kg of calcium stearate to obtain a fluid loss reducer for oil-based drilling fluid.

[0045] Comparative Example 1

[0046] Add 20 kg of natural rubber powder (softening point 80 - 120 °C) and 10 kg of asphalt powder (softening point 80 - 120 °C) into the reaction kettle, start stirring, and pre-mix evenly at a stirring speed of 350 r / min. Atomize and add 1 kg of Span-80 (diluted with 0.5 kg of ethanol, and the ethanol volatilizes when heated during subsequent heat treatment), continue stirring and mix evenly. Set the temperature of the reaction kettle at 120 °C, and stir and heat-treat at 120 °C for 3 h, then cool to room temperature, crush to 150 mesh, and then mix evenly with 10 kg of calcium carbonate (calcium carbonate consists of 45 wt% of hard calcium carbonate with a particle size of 200 mesh, 30 wt% of hard calcium carbonate with a particle size of 400 mesh, and 25 wt% of hard calcium carbonate with a particle size of 1000 mesh) and 1 kg of calcium stearate to obtain the fluid loss reducer for oil-based drilling fluid.

[0047] Comparative Example 2

[0048] Add 20 kg of natural rubber powder (softening point 80 - 120 °C), 10 kg of asphalt powder (softening point 80 - 120 °C), 5 kg of modified humic acid amide (humic acid amide and nano-silica are mixed and modified according to a weight ratio of 5:1), and 5 kg of C5 petroleum resin (softening point 80 - 120 °C) into the reaction kettle, start stirring, and pre-mix evenly at a stirring speed of 350 r / min. Atomize and add 1 kg of Span-80 (diluted with 0.5 kg of ethanol, and the ethanol volatilizes when heated during subsequent heat treatment), continue stirring and mix evenly. Set the temperature of the reaction kettle at 120 °C, and stir and heat-treat at 120 °C for 3 h, then cool to room temperature, crush to 150 mesh, and then mix evenly with 10 kg of calcium carbonate (calcium carbonate consists of 45 wt% of hard calcium carbonate with a particle size of 200 mesh, 30 wt% of hard calcium carbonate with a particle size of 400 mesh, and 25 wt% of hard calcium carbonate with a particle size of 1000 mesh) and 1 kg of calcium stearate to obtain the fluid loss reducer for oil-based drilling fluid.

[0049] Comparative Example 3

[0050] Add 20 kg of natural rubber powder (softening point 80 - 120 °C), 10 kg of asphalt powder (softening point 80 - 120 °C), 5 kg of modified humic acid amide (humic acid amide and nano-silica are mixed and modified according to a weight ratio of 5:1), 5 kg of C5 petroleum resin (softening point 80 - 120 °C) and 1 kg of benzoyl peroxide into a reaction kettle, start stirring, and pre-mix evenly at a stirring speed of 350 r / min. Atomize and add 1 kg of Span-80 (diluted with 0.5 kg of ethanol, and the ethanol volatilizes naturally during subsequent mixing treatment), continue stirring and mix evenly, then mix evenly with 10 kg of calcium carbonate (calcium carbonate is composed of 45 wt% of hard calcium carbonate with a particle size of 200 mesh, 30 wt% of hard calcium carbonate with a particle size of 400 mesh and 25 wt% of hard calcium carbonate with a particle size of 1000 mesh) and 1 kg of calcium stearate to obtain a filtrate reducer for oil-based drilling fluid.

[0051] Comparative Example 4

[0052] Add 20 kg of natural rubber powder (softening point 80 - 120 °C), 10 kg of asphalt powder (softening point 80 - 120 °C) and 1 kg of benzoyl peroxide into a reaction kettle, start stirring, and pre-mix evenly at a stirring speed of 350 r / min. Atomize and add 1 kg of Span-80 (diluted with 0.5 kg of ethanol, and the ethanol volatilizes when heated during subsequent heat treatment), continue stirring and mix evenly. Set the temperature of the reaction kettle at 120 °C, and stir and heat-treat at 120 °C for 3 h, then cool to room temperature, pulverize to 150 mesh, and then mix evenly with 10 kg of calcium carbonate (calcium carbonate is composed of 45 wt% of hard calcium carbonate with a particle size of 200 mesh, 30 wt% of hard calcium carbonate with a particle size of 400 mesh and 25 wt% of hard calcium carbonate with a particle size of 1000 mesh) and 1 kg of calcium stearate to obtain a filtrate reducer for oil-based drilling fluid.

[0053] Add the filtrate reducers for oil-based drilling fluid prepared in Examples 1 - 3 and Comparative Examples 1 - 4 into the oil-based drilling fluid, and test their performance indicators.

[0054] Experimental method [1]: Take 320 mL of diesel oil in a 1000 mL enamel stirring cup. While stirring with a high-speed stirrer at a speed of 10000 r / min, add 16.0 g of organic bentonite, 20.0 g of Span-80, and 4.0 g of Tween-80. After stirring for 10 min, slowly add 80 mL of 20% calcium chloride aqueous solution. After high-speed stirring for 20 min, slowly add 16 g of a fluid loss reducer for oil-based drilling fluid, and then stir at high speed for 5 min. Pour the prepared oil-based drilling fluid into a high-temperature aging kettle, place it in a high-temperature roller heating furnace, age it at 150 °C for 16 h, then take it out, cool it to room temperature, and stir at high speed for 20 min. According to the method specified in GB / T 16783.2, measure the apparent viscosity and high-temperature high-pressure fluid loss volume (150 °C, 3.5 MPa) of the oil-based drilling fluid at 65 °C. The test results are shown in Table 1.

[0055] Table 1 Performance test results of fluid loss reducers for oil-based drilling fluid

[0056]

[0057] As can be seen from Table 1, for the fluid loss reducers for oil-based drilling fluid prepared in Examples 1-3 of the present invention, the high-temperature high-pressure fluid loss volumes are significantly lower than those of Comparative Examples 1-4, indicating that the fluid loss reducers provided by the present invention have excellent fluid loss reduction performance. At the same time, for the fluid loss reducers for oil-based drilling fluid prepared in Examples 1-3 of the present invention, the apparent viscosities are higher than those of Comparative Examples 1-4, indicating that the fluid loss reducers provided by the present invention can effectively improve the rheological properties of oil-based drilling fluid.

[0058] Experimental method [2]: Prepare an oil-based drilling fluid using the materials of the oil-based drilling fluid system produced by Chengdu West Oil Huawei Technology Co., Ltd. Add 3.20 g of the main emulsifier HW Pmul-1 for oil-based drilling fluid, 8.80 g of the auxiliary emulsifier HW Smul-1 for oil-based drilling fluid, 3.20 g of the wetting agent HW Wet-1 for oil-based drilling fluid, and 320 mL of 0# diesel oil into a high-speed stirring cup. While stirring at a speed of 1000 r / min, add 12.00 g of organic bentonite, then stir at a high speed of 11000 r / min for 20 min, add 12.00 g of calcium oxide, stir at high speed for 10 min, then add 80 mL of 25% calcium chloride aqueous solution and stir at high speed for 20 min, then add 20.00 g of the fluid loss reducer for oil-based drilling fluid and stir at high speed for 10 min. Finally, while stirring, add barite powder of the first grade to increase the density to 1.80 g / cm 3, then stir at high speed for another 30 min. Load the prepared weighted mud into a high-temperature aging kettle and age and roll at 150 °C for 16 h. Take it out, cool it to room temperature, then stir at high speed for 10 min, and test the medium-pressure filtration loss and high-temperature and high-pressure filtration loss (150 °C, 3.5 MPa) according to the method specified in GB / T 16783.2. The test results are shown in Table 2.

[0059] Table 2 Performance test results of the filtration loss reducer for oil-based drilling fluids

[0060]

[0061] As can be seen from Table 2, the filtration loss reducers for oil-based drilling fluids prepared in Examples 1-3 of the present invention have good compatibility with the oil-based drilling fluid system, and the medium-pressure filtration loss and high-temperature and high-pressure filtration loss are significantly lower than those of Comparative Examples 1-4, indicating that the filtration loss reducer provided by the present invention has excellent filtration loss reduction performance and compatibility.

[0062] Experimental method [3]: Prepare two portions of oil-based emulsions according to the formula of 240 mL of 0# diesel + 12 g of integrated emulsifier HW Pmul-3 + 6 g of organic bentonite + 9 g of quicklime + 60 mL of 25% calcium chloride brine. Add 4.5% of the filtration loss reducer for oil-based drilling fluid prepared in Example 3 to one of them. After stirring at high speed for 20 min at 10000 r / min, test the rheological parameters, medium-pressure filtration loss, and high-temperature and high-pressure filtration loss (150 °C, 3.5 MPa) at 50 °C. The test results are shown in Table 3.

[0063] Table 3 Test data of the filtration loss reducer for oil-based drilling fluids in oil-based emulsions

[0064]

[0065] As can be seen from the test results in Table 3, after adding the filtration loss reducer for oil-based drilling fluid of the present invention to the oil-based emulsion, the filtration loss reduction property of the oil-based drilling fluid is significantly improved, the filter cake quality is improved, and there is no obvious influence on the performance of the oil-based drilling fluid, and the compatibility is good.

[0066] Experimental method [4]: Take the oil-based drilling fluid well slurry of a certain well on site for experiments. Add 2% of the filtration loss reducer for oil-based drilling fluid prepared in Example 3 to the well slurry. After stirring at high speed for 20 min at 10000 r / min, test the rheological parameters and high-temperature and high-pressure filtration loss (150 °C, 3.5 MPa) at 50 °C. The test results are shown in Table 4.

[0067] Table 4 Test results of the filtration loss reducer for oil-based drilling fluids in the well slurry of a certain well on site

[0068]

[0069] Table 4 shows that after adding the filtrate reducer for oil-based drilling fluid of the present invention to the well slurry, the filtrate reduction effect is obvious, and the reduction rate can reach 50%; the mud cake becomes thinner, and the quality of the mud cake is significantly improved; it does not affect the rheological properties and electrical stability of the well slurry.

Claims

1. A fluid loss reducer for oil-based drilling fluid, characterized in that: In parts by weight, the following raw materials are included: Natural rubber powder, 20-40 parts; Asphalt powder, 10-20 parts; Calcium carbonate, 10-20 parts; Modified humic acid amide, 5-15 parts; Oil-soluble resin, 5-15 parts; Oxidant, 1-5 parts; Temperature stabilizer, 1~5 parts; Emulsifier, 1-5 parts; The natural rubber powder, the asphalt powder, the modified humic acid amide, the oil-soluble resin and the oxidant are mixed and heat-treated at 120-130° C., and then mixed with the remaining raw materials after cooling; The natural rubber powder is a natural rubber powder with a softening point of 80-120°C; The asphalt powder is petroleum asphalt powder with a softening point of 80-120°C; The modified humic acid amide is prepared by mixing humic acid amide with nano silicon dioxide or nano aluminum oxide in a weight ratio of 5:1; The oil-soluble resin is a C5 petroleum resin or a C9 petroleum resin having a softening point of 80-120°C.

2. The fluid loss reducer for oil-based drilling fluid according to claim 1, characterized in that: The calcium carbonate is composed of 40-50wt% of hard calcium carbonate with a particle size of 200 meshes, 30-40wt% of hard calcium carbonate with a particle size of 400 meshes and 20-25wt% of hard calcium carbonate with a particle size of 1000 meshes.

3. The fluid loss reducer for oil-based drilling fluid according to claim 1, characterized in that: The oxidant is benzoyl peroxide, dicumyl peroxide, potassium permanganate or sodium hypochlorite.

4. The fluid loss reducer for oil-based drilling fluid according to claim 1, characterized in that: The temperature stabilizer is calcium stearate or zinc stearate.

5. The fluid loss reducer for oil-based drilling fluid according to claim 1, characterized in that: The emulsifier is Span-80 or Tween-80.

6. A method for preparing a fluid loss reducer for oil-based drilling fluid, to obtain the fluid loss reducer for oil-based drilling fluid as claimed in any one of claims 1 to 5, characterized in that: The following steps are involved: Step S1: adding natural rubber powder, asphalt powder, modified humic acid amide, oil-soluble resin and oxidant into a reaction kettle in proportion; Step S2: Start stirring at a speed of 300-400 r / min to mix evenly in advance; Step S3: dilute the emulsifier with an appropriate amount of ethanol and add it to the mixture in step S2 by spraying, and continue stirring to mix evenly; Step S4: setting the temperature of the reactor to 120-130° C., and heat treating the mixture in step S3 at this temperature for 2-3 hours; Step S5: The mixture in step S4 is cooled to room temperature, crushed to 150-200 mesh, and then mixed with calcium carbonate and a temperature stabilizer and stirred for 30 minutes to obtain a fluid loss reducer for oil-based drilling fluid.

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