A mud cake hardening and strengthening agent for drilling fluid and its preparation method

Abstract

The present invention relates to the field of drilling technology, and specifically to a mud cake hardening enhancer for drilling fluid and a preparation method thereof: The raw material composition includes the following parts by weight: 60-80 parts of dihydroxyethoxypropyl polydimethylsiloxane, 40-60 parts of hardening agent, 10-20 parts of modified starch, 6-8 parts of film-forming agent, 4-6 parts of additive, 4-6 parts of chelating agent, and 2-4 parts of asbestos. In the present invention, after acid hydrolysis and carbonization of rice husks, a porous active structure is formed, which is tightly bonded by adsorption with the modified starch material in the mud cake hardening enhancer for drilling fluid, improving the bonding strength between the mud cake and the wellbore wall. A slightly cross-linked network is formed in the hardening agent obtained by ultraviolet light treatment, which can endow the mud cake with a skeleton support structure. This cross-linked network enhances the compressive capacity of the mud cake through intermolecular entanglement, reduces the risk of wellbore wall collapse, reduces the brittleness of the mud cake, avoids cracking caused by underground pressure fluctuations, and effectively improves the use efficiency of the drilling fluid.

Description

Technical Field

[0001] The invention relates to the technical field of drilling, in particular to a mud cake hardening enhancer for drilling fluid and a preparation method thereof. Background Art

[0002] Mud cake hardening enhancer for drilling fluid is an additive used in drilling fluid, which can improve the bonding and viscosity properties of drilling fluid, enhance the strength and stability of mud cake, and ensure the smooth progress of drilling operations.

[0003] In the prior art, the conventional mud cake hardening enhancer for drilling fluid is made of a single polymer, which has a single molecular chain structure and is easily degraded in the underground working environment, resulting in a significant decrease in the bonding strength, which affects the performance of the drilling fluid. Based on this, the present invention provides a mud cake hardening enhancer for drilling fluid and a preparation method thereof. Summary of the invention

[0004] The object of the present invention is to provide a mud cake hardening enhancer for drilling fluid and a preparation method thereof. The mud cake hardening enhancer for drilling fluid prepared by the present invention not only has good bonding strength performance, but also has excellent viscosity performance, which effectively improves the use performance of drilling.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] In a first aspect, the present invention provides a mud cake hardening enhancer for drilling fluid, comprising the following raw materials in parts by weight: 60 to 80 parts of bishydroxyethoxypropyl polydimethylsiloxane, 40 to 60 parts of a hardener, 10 to 20 parts of modified starch, 6 to 8 parts of a film-forming agent, 4 to 6 parts of an additive, 4 to 6 parts of a chelating agent and 2 to 4 parts of asbestos.

[0007] Furthermore, the additive is prepared by the following method: acrylic acid and pure water are mixed in a beaker, the mass ratio of acrylic acid to pure water is 1:(0.2-0.3), sodium hydroxide solution is added dropwise after sufficient mixing, the mass of the sodium hydroxide solution is 1.2-1.3 times the mass of acrylic acid, and the mass concentration of the sodium hydroxide solution is 30-40%, and after the addition is completed, the mixture is fully mixed, heated in a water bath to 40-50°C, and kept warm for 6-10 minutes to obtain a first mixture.

[0008] Furthermore, a sodium sulfite solution is added to the first mixture, wherein the mass of the sodium sulfite solution is 0.4-0.8% of the mass of the mixed liquid, and the mass concentration of the sodium sulfite solution is 18-20%. After mixing, the mixture is heated in a water bath to 50-54° C. and kept warm for 10-14 minutes to obtain a second mixture. After mixing, the second mixture is sent to a UV curing machine at a distance of 20-30 cm from the light source and cured for 1-3 hours to obtain an additive.

[0009] Further, the hardener is prepared by the following method: Rice husk is selected as the base material of the hardener. After the rice husk is cleaned and dried, it is ground, and the grinding particle size is 20-30 μm to obtain the first powder material.

[0010] Further, the first powder material is mixed with sulfuric acid in a beaker. The mass of the sulfuric acid is 8-12 times that of the first powder material, and the concentration of the sulfuric acid is 5-7%. After mixing evenly, it is heated in a water bath to 50-60 °C, and a magnetic stirrer is used to set the stirring speed at 160-200 r / min, and the heat preservation stirring treatment is carried out for 10-20 min. Then, filtration treatment is carried out to obtain a solution. The above steps 2-4 are repeated for the obtained solution. The obtained product is dried to obtain a slag material. The slag material is ground, and the grinding particle size is 6-10 μm. The ground slag material is sent into a carbonization furnace. The carbonization furnace is set with a heating rate of 10-12 °C / min, heated to 450-550 °C, and kept warm for 20-30 min. Nitrogen is introduced during the heating process to obtain the hardener.

[0011] Further, the modified starch is prepared by the following method: Chickpea is selected as the base material of the modified starch. The chickpea is cleaned, dried, and ground, and the grinding particle size is 10-20 μm to obtain the second powder material.

[0012] Further, the second powder material is mixed with deionized water and added into a reaction kettle. The mass ratio of the second powder material to deionized water is 1:(4-6). The reaction kettle is set to stir at 200-300 r / min for 10-20 min. Sodium bicarbonate is added to the obtained product to adjust the pH value to 7-8. Octenyl succinic anhydride is added into the reaction kettle. The mass of the octenyl succinic anhydride is 2-4% of the mass of the second powder material. The reaction kettle is set to heat up to 40-50 °C, and the rotation speed is 80-100 r / min. The heat preservation stirring treatment is carried out for 4-6 min. The product obtained by the heat preservation stirring treatment is added into a centrifuge for centrifugation treatment. The centrifuge is set to treat at 4000-5000 r / min for 6-10 min, and the supernatant is discarded to obtain a precipitate. The obtained precipitate is sent into an oven. The oven is set to dry at 42-44 °C for 50-60 min, and then grinding treatment is carried out, and the grinding particle size is 6-10 μm to obtain the modified starch.

[0013] Further, the film-forming agent is selected as polymethyl methacrylate.

[0014] Further, the chelating agent is selected as ethylenediaminetriacetic acid, and the asbestos has a fiber length of 20-40 μm and a diameter of 0.4-1 μm.

[0015] In the second aspect, the present invention also provides a preparation method of a mud cake hardening and strengthening agent for drilling fluid, comprising the following steps:

[0016] S1: Weigh dihydroxyethoxypropyl polydimethylsiloxane, film-forming agent, chelating agent and asbestos as required and add them to a mixer. The mixer is set to stir at 800 - 1000 r / min for 1 - 3 h to obtain a preliminary mixture.

[0017] S2: Add a hardening agent, additives and modified starch to the preliminary mixture. The mixer is set to stir at 200 - 400 r / min for 6 - 8 min to obtain a mud cake hardening and strengthening agent for drilling fluid.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0019] 1. In the present invention, during the preparation of the mud cake hardening and strengthening agent for drilling fluid, by adding a hardening agent, the hardening agent is based on rice husk and is processed. After the rice husk is acid-hydrolyzed and carbonized, a porous active structure is formed, which is tightly bonded to the modified starch material in the mud cake hardening and strengthening agent for drilling fluid through adsorption, improving the bonding strength between the mud cake and the wellbore wall. The hardening agent obtained by ultraviolet treatment forms a lightly cross-linked network, which can endow the mud cake with a skeleton support structure. This cross-linked network enhances the compressive capacity of the mud cake through intermolecular entanglement, reduces the risk of wellbore collapse, reduces the brittleness of the mud cake, avoids cracking caused by underground pressure fluctuations, and effectively improves the use efficiency of the drilling fluid.

[0020] 2. In the present invention, during the preparation of the mud cake hardening and strengthening agent for drilling fluid, by adding modified starch, the modified starch made from chickpea as the base material has rich hydrophilic groups. The hydrophilic groups can form hydrogen bond interactions with water molecules, making the modified starch have good hydrophilicity. After being added to the drilling fluid, the modified starch forms a viscous network after absorbing water. Combined with the addition of asbestos, it effectively improves the interfacial bonding force between the mud cake and the wellbore wall, thereby increasing the internal friction of the drilling fluid and improving the viscosity performance of the drilling fluid. Detailed implementation mode

[0021] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in combination with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all 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 belong to the scope of protection of the present invention.

[0022] It should be noted that the raw materials used in the following embodiments are all commercially available raw materials.

[0023] Embodiment 1:

[0024] It includes the following raw materials in parts by weight: 60 parts of dihydroxyethoxypropyl polydimethylsiloxane, 40 parts of hardening agent, 10 parts of modified starch, 6 parts of film-forming agent, 4 parts of additives, 4 parts of chelating agent and 2 parts of asbestos.

[0025] The additive is prepared by the following method: Acrylic acid is mixed with pure water in a beaker, and the mass ratio of acrylic acid to pure water is 1:(0.2). After thorough mixing, sodium hydroxide solution is added dropwise. The mass of the sodium hydroxide solution is 1.2 times the mass of acrylic acid, and the mass concentration of the sodium hydroxide solution is 30%. After the addition is completed, it is thoroughly mixed, heated in a water bath to 40 °C, and kept warm for 6 min to obtain the first mixture.

[0026] Sodium sulfite solution is added to the first mixture. The mass of the sodium sulfite solution is 0.4% of the mass of the mixed solution, and the mass concentration of the sodium sulfite solution is 18%. After mixing evenly, it is heated in a water bath to 50 °C and kept warm for 10 min to obtain the second mixture. After the second mixture is mixed evenly, it is sent into an ultraviolet curing machine, 20 cm away from the light source, and cured for 1 h to obtain the additive.

[0027] The hardener is prepared by the following method: Rice husk is selected as the base material for the hardener. After the rice husk is cleaned and dried, it is ground, and the grinding particle size is 20 μm to obtain the first powder.

[0028] The first powder is mixed with sulfuric acid in a beaker. The mass of sulfuric acid is 8 times the mass of the first powder, and the concentration of sulfuric acid is 5%. After mixing evenly, it is heated in a water bath to 50 °C, and stirred at 160 r / min with a magnetic stirrer, and kept warm and stirred for 10 min. Then, filtration is carried out to obtain a solution. The above steps are repeated 2 times for the obtained solution. The obtained product is dried to obtain a residue. The residue is ground, and the grinding particle size is 6 μm. The ground residue is sent into a carbonization furnace. The carbonization furnace is set with a heating rate of 10 °C / min, heated to 450 °C, and kept warm for 20 min. Nitrogen is introduced during the heating process to obtain the hardener.

[0029] The modified starch is prepared by the following method: Chickpea is selected as the base material for the modified starch. The chickpea is cleaned, dried, and ground, and the grinding particle size is 10 μm to obtain the second powder.

[0030] The second powder is mixed with deionized water and added to a reaction kettle. The mass ratio of the second powder to deionized water is 1:(4). The reaction kettle is set to stir at 200 r / min for 10 min. Sodium bicarbonate is added to the obtained product to adjust the pH value to 7. Octenyl succinic anhydride is added to the reaction kettle. The mass of octenyl succinic anhydride is 2% of the mass of the second powder. The reaction kettle is set to heat up to 40 °C and rotate at 80 r / min, and kept warm and stirred for 4 min. The product obtained by the heat preservation and stirring treatment is centrifuged by a centrifuge. The centrifuge is set to process at 4000 r / min for 6 min, and the supernatant is discarded to obtain a precipitate. The obtained precipitate is sent into an oven. The oven is set to dry at 42 °C for 50 min, and then ground, and the grinding particle size is 6 μm to obtain the modified starch.

[0031] The film-forming agent is polymethyl methacrylate.

[0032] The chelating agent is ethylethylenediaminetriacetic acid, and the asbestos is selected with a fiber length of 20 μm and a diameter of 0.4 μm.

[0033] A method for preparing a mud cake hardening enhancer for drilling fluid comprises the following steps:

[0034] S1: Weigh bishydroxyethoxypropyl polydimethylsiloxane, film-forming agent, chelating agent and asbestos as needed and add them into a mixer. Set the mixer to 800 r / min and stir for 1 hour to obtain a primary mixture;

[0035] S2: Add hardener, additives and modified starch to the primary mixture, set the mixer at 200 r / min and stir for 6 minutes to obtain a mud cake hardening enhancer for drilling fluid.

[0036] Embodiment 2:

[0037] The invention comprises the following raw materials in parts by weight: 70 parts of bishydroxyethoxypropyl polydimethylsiloxane, 50 parts of hardener, 15 parts of modified starch, 7 parts of film former, 5 parts of additive, 5 parts of chelating agent and 3 parts of asbestos.

[0038] The additive is prepared by the following method: acrylic acid and pure water are mixed in a beaker, the mass ratio of acrylic acid to pure water is 1: (0.25), sodium hydroxide solution is added dropwise after thorough mixing, the mass of the sodium hydroxide solution is 1.25 times the mass of acrylic acid, and the mass concentration of the sodium hydroxide solution is 35%, after the addition is completed, the mixture is thoroughly mixed, heated to 45° C. in a water bath, and kept warm for 8 minutes to obtain a first mixture.

[0039] Sodium sulfite solution was added to the first mixture, the mass of the sodium sulfite solution was 0.6% of the mass of the mixed liquid, and the mass concentration of the sodium sulfite solution was 19%. After mixing, it was heated to 52° C. in a water bath and kept warm for 12 minutes to obtain a second mixture. After mixing, the second mixture was sent to a UV curing machine at a distance of 25 cm from the light source and cured for 2 hours to obtain an additive.

[0040] The hardener is prepared by the following method: the hardener selects rice husk as the base material, the rice husk is cleaned and dried, and then ground into powder with a particle size of 25 μm to obtain the first powder.

[0041] The first powder is mixed with sulfuric acid in a beaker. The mass of sulfuric acid is 10 times that of the first powder, and the concentration of sulfuric acid is 6%. After mixing evenly, it is heated in a water bath to 55°C, and a magnetic stirrer is used to set the stirring speed at 180 r / min. It is kept warm and stirred for 15 min, and then filtered to obtain a solution. The obtained solution is repeated the above steps 3 times. The obtained product is dried to obtain a slag material. The slag material is ground, and the grinding particle size is 8 μm. The ground slag material is sent into a carbonization furnace. The carbonization furnace is set with a heating rate of 11°C / min and heated to 500°C, and kept warm for 25 min. Nitrogen is introduced during the heating process to obtain a hardener.

[0042] The modified starch is prepared by the following method: Chickpeas are selected as the base material for the modified starch. The chickpeas are washed, dried, and ground, and the grinding particle size is 15 μm to obtain the second powder.

[0043] The second powder is mixed with deionized water and added to a reaction kettle. The mass ratio of the second powder to deionized water is 1:(5). The reaction kettle is set to stir at 250 r / min for 15 min. Sodium bicarbonate is added to the obtained product to adjust the pH value to 7.5. Octenyl succinic anhydride is added to the reaction kettle. The mass of octenyl succinic anhydride is 3% of the mass of the second powder. The reaction kettle is set to heat up to 45°C and the rotation speed is 90 r / min. It is kept warm and stirred for 5 min. The product obtained by the heat-preservation stirring treatment is centrifuged in a centrifuge. The centrifuge is set to process at 4500 r / min for 8 min, and the supernatant is discarded to obtain a precipitate. The obtained precipitate is sent into an oven. The oven is set to dry at 43°C for 55 min, and then ground. The grinding particle size is 8 μm to obtain the modified starch.

[0044] The film-forming agent is selected as polymethyl methacrylate.

[0045] The chelating agent is selected as ethylenediaminetriacetic acid, and the asbestos has a fiber length of 30 μm and a diameter of 0.7 μm.

[0046] A preparation method of a mud cake hardening enhancer for drilling fluid includes the following steps:

[0047] S1: Weigh dihydroxyethoxypropyl polydimethylsiloxane, film-forming agent, chelating agent, and asbestos as required and add them to a mixer. The mixer is set to stir at 900 r / min for 2 h to obtain a preliminary mixture.

[0048] S2: The hardener, additive, and modified starch are added to the preliminary mixture. The mixer is set to stir at 300 r / min for 7 min to obtain a mud cake hardening enhancer for drilling fluid.

[0049] Example 3:

[0050] The invention comprises the following raw materials in parts by weight: 80 parts of bishydroxyethoxypropyl polydimethylsiloxane, 60 parts of hardener, 20 parts of modified starch, 8 parts of film former, 6 parts of additive, 6 parts of chelating agent and 4 parts of asbestos.

[0051] The additive is prepared by the following method: acrylic acid and pure water are mixed in a beaker, the mass ratio of acrylic acid to pure water is 1: (0.3), sodium hydroxide solution is added dropwise after thorough mixing, the mass of the sodium hydroxide solution is 1.3 times the mass of acrylic acid, and the mass concentration of the sodium hydroxide solution is 40%, after the addition is completed, the mixture is thoroughly mixed, heated to 50° C. in a water bath, and kept warm for 10 minutes to obtain a first mixture.

[0052] Sodium sulfite solution was added to the first mixture, the mass of the sodium sulfite solution was 0.8% of the mass of the mixed liquid, and the mass concentration of the sodium sulfite solution was 20%. After mixing, it was heated to 54°C in a water bath and kept warm for 14 minutes to obtain a second mixture. After mixing, the second mixture was sent to a UV curing machine at a distance of 30 cm from the light source and cured for 3 hours to obtain an additive.

[0053] The hardener is prepared by the following method: the hardener selects rice husk as the base material, washes and dries the rice husk, and then grinds it into powder with a particle size of 30 μm to prepare the first powder.

[0054] The first powder and sulfuric acid are mixed in a beaker, the mass of the sulfuric acid is 12 times the mass of the first powder, and the concentration of the sulfuric acid is 7%. After mixing, the mixture is heated to 60°C in a water bath, and stirred at 200r / min using a magnetic stirrer. The mixture is kept warm and stirred for 20 minutes, and then filtered to obtain a solution. The solution is repeated with the above steps 4 times, and the obtained product is dried to obtain a slag. The slag is ground to a powder particle size of 10μm. The ground slag is fed into a carbonization furnace, and the carbonization furnace is set to a heating rate of 12°C / min, and the temperature is raised to 550°C, and the temperature is kept warm for 30 minutes. Nitrogen is introduced during the heating process to obtain a hardener.

[0055] The modified starch is prepared by the following method: chickpeas are selected as the base material of the modified starch, the chickpeas are washed, dried, and ground into powder with a particle size of 20 μm to prepare the second powder.

[0056] The second powder is mixed with deionized water and added into a reaction kettle. The mass ratio of the second powder to deionized water is 1:(6). The reaction kettle is set to stir at 300 r / min for 20 min. Sodium bicarbonate is added to the obtained product to adjust the pH value to 8. Octenyl succinic anhydride is added into the reaction kettle, and the mass of octenyl succinic anhydride is 4% of the mass of the second powder. The reaction kettle is set to heat up to 50 °C and the rotation speed is 100 r / min, and keep warm and stir for 6 min. The product obtained by the heat preservation stirring treatment is added into a centrifuge for centrifugation. The centrifuge is set to treat at 5000 r / min for 10 min, and the supernatant is discarded to obtain a precipitate. The obtained precipitate is sent into an oven, and the oven is set to dry at 44 °C for 60 min, and then subjected to powder grinding treatment. The powder grinding particle size is 10 μm to obtain modified starch.

[0057] The film-forming agent is selected as polymethyl methacrylate.

[0058] The chelating agent is selected as ethylenediaminetriacetic acid, and the asbestos has a fiber length of 40 μm and a diameter of 1 μm.

[0059] A preparation method of a mud cake hardening enhancer for drilling fluid includes the following steps:

[0060] S1: Weigh dihydroxyethoxypropyl polydimethylsiloxane, film-forming agent, chelating agent and asbestos as required and add them into a mixer. The mixer is set to stir at 1000 r / min for 3 h to obtain a preliminary mixture.

[0061] S2: A hardening agent, an additive and modified starch are added into the preliminary mixture. The mixer is set to stir at 400 r / min for 8 min to obtain a mud cake hardening enhancer for drilling fluid.

[0062] Comparative Example 1. The difference between this comparative example and Example 1 is that: in this comparative example, an equal amount of corn starch is selected to replace the hardening agent.

[0063] Comparative Example 2. The difference between this comparative example and Example 1 is that: in this comparative example, an equal amount of corn starch is selected to replace the modified starch.

[0064] Comparative Example 3. The difference between this comparative example and Example 1 is that: in this comparative example, the modified starch is not added.

[0065] Comparative Example 4. The difference between this comparative example and Example 1 is that: in this comparative example, the hardening agent is not added.

[0066] Performance test: Perform performance tests on the mud cake hardening enhancers for drilling fluid prepared in Example 1, Example 2, Example 3, Comparative Example 1, Comparative Example 2, Comparative Example 3 and Comparative Example 4, and record the obtained test data in the following table:

[0067]

[0068] In the performance test, at 130 °C, the mud cake hardening and strengthening agents prepared in Example 1, Example 2, Example 3, Comparative Example 1, Comparative Example 2, Comparative Example 3 and Comparative Example 4 were added to the drilling fluid at an addition amount of 3%, and various properties of the drilling fluid were tested.

[0069] It can be seen that the cementation strength performance and viscosity performance of the mud cake hardening and strengthening agents prepared in Comparative Example 1, 2, 3 and 4 are lower than those in Example 1, 2 and 3. This shows that: by adding a hardening agent in the preparation process of the mud cake hardening and strengthening agent for drilling fluid, the hardening agent is based on rice husk and is processed. After the rice husk is acid-hydrolyzed and carbonized, a porous active structure is formed, which is tightly bonded to the modified starch material in the mud cake hardening and strengthening agent for drilling fluid through adsorption, improving the cementation strength between the mud cake and the wellbore. In the hardening agent obtained by ultraviolet light treatment, a lightly cross-linked network is formed, which can endow the mud cake with a skeleton support structure. This cross-linked network enhances the compressive capacity of the mud cake through intermolecular entanglement, reduces the risk of wellbore collapse, reduces the brittleness of the mud cake, avoids cracking caused by downhole pressure fluctuations, and effectively improves the use efficiency of the drilling fluid. By adding modified starch in the preparation process of the mud cake hardening and strengthening agent for drilling fluid, the modified starch made from chickpea as the base material has abundant hydrophilic groups. The hydrophilic groups can form hydrogen bond interactions with water molecules, making the modified starch have good hydrophilicity. After being added to the drilling fluid, the modified starch forms a viscous network after absorbing water. Combined with the addition of asbestos, it effectively improves the interfacial bonding force between the mud cake and the wellbore, thereby increasing the internal friction of the drilling fluid and improving the viscosity performance of the drilling fluid.

[0070] By comparing and analyzing the relevant data in the table, it can be known that the mud cake hardening and strengthening agent prepared by the present invention not only has good cementation strength performance, but also has excellent viscosity performance. This shows that the mud cake hardening and strengthening agent provided by the present invention has a broader market prospect and is more suitable for popularization.

[0071] In the description of this specification, the description referring to terms such as "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in a suitable manner in any one or more embodiments or examples.

[0072] The preferred embodiments of the present invention disclosed above are only used to help illustrate the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to the specific embodiments described. Obviously, many modifications and variations can be made according to the content of this specification. These embodiments are selected and specifically described in this specification to better explain the principles and practical applications of the present invention, so that those skilled in the art can well understand and utilize the present invention. The present invention is only limited by the claims and their full scope and equivalents.

Claims

1. A mud cake hardening and strengthening agent for drilling fluid, characterized in that: The invention comprises the following raw materials in parts by weight: 60 to 80 parts of bishydroxyethoxypropyl polydimethylsiloxane, 40 to 60 parts of hardener, 10 to 20 parts of modified starch, 6 to 8 parts of film former, 4 to 6 parts of additive, 4 to 6 parts of chelating agent and 2 to 4 parts of asbestos; The additive is prepared by the following method: acrylic acid and pure water are mixed in a beaker, the mass ratio of acrylic acid to pure water is 1: (0.2-0.3), sodium hydroxide solution is added dropwise after fully mixing, the mass of the sodium hydroxide solution is 1.2-1.3 times the mass of acrylic acid, and the mass concentration of the sodium hydroxide solution is 30-40%, fully mixed after the dropwise addition is completed, heated in a water bath to 40-50° C., and kept warm for 6-10 minutes to prepare a first mixed material, sodium sulfite solution is added to the first mixed material, the mass of the sodium sulfite solution is 0.4-0.8% of the mass of the mixed solution, and the mass concentration of the sodium sulfite solution is 18-20%, and after mixing, the second mixed material is heated in a water bath to 50-54° C., and kept warm for 10-14 minutes to prepare a second mixed material, and the second mixed material is mixed and sent to an ultraviolet curing machine, 20-30 cm away from the light source, and cured for 1-3 hours to prepare the additive; The modified starch is prepared by the following method: the modified starch uses chickpea as a base material, the chickpea is washed, dried, and ground, the particle size of the ground powder is 10-20 μm, and a second powder is prepared, the second powder is mixed with deionized water and added to a reactor, the mass ratio of the second powder to the deionized water is 1: (4-6), the reactor is set at 200-300 r / min and stirred for 10-20 minutes, sodium bicarbonate is added to the obtained product to adjust the pH value to 7-8, octenyl succinic anhydride is added to the reactor, and the octenyl succinic anhydride The mass of the second powder is 2-4% of the mass of the second powder. The reactor is set to heat up to 40-50°C, the speed is 80-100r / min, and the mixture is kept warm and stirred for 4-6min. The product obtained by the kept warm and stirred treatment is added to a centrifuge for centrifugal treatment. The centrifuge is set at 4000-5000r / min for 6-10min, the supernatant is discarded, and a precipitate is obtained. The precipitate is sent to an oven, and the oven is set at 42-44°C for drying for 50-60min, followed by grinding. The powder particle size is 6-10μm to obtain modified starch.

2. The mud cake hardening and strengthening agent for drilling fluid according to claim 1, characterized in that, The hardener is prepared by the following method: Rice husk is selected as the base material for the hardener. After the rice husk is washed and dried, it is ground. The grinding particle size is 20 - 30 μm to obtain the first powder. The first powder is mixed with sulfuric acid in a beaker. The mass of the sulfuric acid is 8 - 12 times the mass of the first powder, and the concentration of the sulfuric acid is 5 - 7%. After mixing evenly, it is heated in a water bath to 50 - 60 °C, and a magnetic stirrer is used to set the stirring speed at 160 - 200 r / min for heat preservation and stirring for 10 - 20 min. Then, filtration is carried out to obtain a solution. The above steps 2 - 4 are repeated for the obtained solution. The obtained product is dried to obtain a residue. The residue is ground. The grinding particle size is 6 - 10 μm. The ground residue is fed into a carbonization furnace. The carbonization furnace is set with a heating rate of 10 - 12 °C / min and heated to 450 - 550 °C, and kept warm for 20 - 30 min. Nitrogen is introduced during the heating process to obtain the hardener.

3. The mud cake hardening and strengthening agent for drilling fluid according to claim 1, wherein, The film-forming agent is selected as polymethyl methacrylate.

4. The mud cake hardening and strengthening agent for drilling fluid according to claim 1, characterized in that The chelating agent is selected as ethylenediaminetriacetic acid, and the asbestos has a fiber length of 20 - 40 μm and a diameter of 0.4 - 1 μm.

5. A preparation method of the mud cake hardening and strengthening agent for drilling fluid according to any one of claims 1 to 4, characterized in that, It includes the following steps: S1: Weigh dihydroxyethoxypropyl polydimethylsiloxane, film-forming agent, chelating agent and asbestos as required and add them into a mixer. The mixer is set to stir at 800 - 1000 r / min for 1 - 3 h to obtain a preliminary mixture. S2: The hardener, additive and modified starch are added to the preliminary mixture. The mixer is set to stir at 200 - 400 r / min for 6 - 8 min to obtain the mud cake hardening and strengthening agent for drilling fluid.

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