Natural polymer shear strength improving agent for temperature-resistant tackifying water-based drilling fluid as well as preparation method and application of natural polymer shear strength improving agent

Abstract

The invention provides a natural polymer shear strength improving agent for temperature-resistant tackifying water-based drilling fluid as well as a preparation method and application of the natural polymer shear strength improving agent. The shear strength improving agent is prepared from the following raw materials in parts by mass: 1 to 7 parts of carboxymethyl starch, 1 to 5 parts of 2-acrylamido-2-methylpropanesulfonic acid, 1 to 5 parts of dimethyl diallyl ammonium chloride, 1 to 5 parts of N-vinyl pyrrolidone, 1 to 5 parts of acrylamide, 0.01 to 0.05 part of an initiator I, 0.01 to 0.05 part of an initiator II, 0.01 to 0.07 part of a cross-linking agent epoxy chloropropane, 50 to 70 parts of water and 150 to 220 parts of absolute ethyl alcohol. According to the shear strength improving agent, natural high polymer materials are used, a polymer net structure is formed through polymerization reaction, the cross-linking agent is used for promoting the net structure to be tighter for tackifying, and the shear strength improving agent has better thermal stability, dynamic shear force, flocculation capacity and suspension stability while the cost and the environmental load are reduced.

Description

Technical Field

[0001] This invention relates to a natural polymeric cutting agent for high-temperature resistant, thickening, and water-based drilling fluids, its preparation method, and its application, belonging to the technical field of drilling fluid treatment agents. Background Technology

[0002] With the increasing urgency of energy demand and the growing difficulty and depth of exploration, low-cost, high-efficiency deep wells and extended-reach horizontal wells are becoming more prevalent and dominant in drilling engineering. This has led to higher requirements and new standards for drilling fluid performance. Drilling fluids need to possess excellent rheological properties, such as low apparent viscosity, plastic viscosity, and high static and dynamic shear strength, posing significant challenges to their practicality and effectiveness.

[0003] Currently, xanthan gum (XG) is widely used as a cutting agent for water-based drilling fluids due to its good cutting performance. Its solution is a typical non-Newtonian fluid with a highly branched structure. Its advantages include significantly improving the rheological properties of drilling fluids with relatively small dosages and good salt resistance. However, its disadvantages are also significant. It has poor temperature resistance; at higher temperatures, the original double-helix structure is destroyed, and its main chain directly contacts acids, alkalis, and free radicals in the drilling fluid, damaging the original rheological properties and drastically reducing the cutting effect. Furthermore, due to the irreplaceable role of xanthan gum in many industries, its price has been rising in recent years, increasing its usage cost during drilling. Therefore, current research on thickening and cutting agents mainly focuses on modified natural polymer thickeners, synthetic polymer thickeners, and nanomaterial thickening and cutting agents.

[0004] Modified natural polymer thickeners can be classified into modified biopolymers and modified polysaccharides based on their raw materials, such as guar gum, xanthan gum, vetiver gum, and polysaccharides. Synthetic polymeric high-temperature resistant thickeners and shearing agents include polyacrylamide and its related derivatives. For example, Chinese patent document CN116478330A provides a thickener and shearing polymer for high-temperature brine-based low-solids drilling-completion fluids, comprising the following raw materials by mass percentage: 15-35% natural polyhydroxy compound, 20-40% cationic monomer, 5-10% alkyl acrylic monomer, 5-15% sulfonic acid monomer, 10-15% nano-silica, 2-5% initiator, and 0-0.6% chain transfer agent; wherein the natural polyhydroxy compound is at least one of starch and its modified products and cellulose and its modified products. However, it usually requires the use of modified silica to form a weak cross-linked network with hydroxyl groups, sulfonic acid groups, etc. on other polymer molecular chains through hydrogen bonding to improve performance. Vapor-phase nano silica (such as Cabot M-5) is expensive, which increases the cost of polymer production. In addition, nano silica is difficult to degrade or recycle, which causes solid waste pollution to a certain extent.

[0005] Therefore, in order to reduce costs and environmental impact while enhancing performance, it is urgent to develop a low-cost, environmentally friendly natural polymer water-based drilling fluid additive with good temperature resistance and thickening ability. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a natural polymer-based shearing agent for high-temperature resistant, thickening, and water-based drilling fluids, along with its preparation method and applications. The shearing agent of this invention uses natural polymer materials, forming a polymer network structure through polymerization. A crosslinking agent further strengthens the network structure, resulting in increased viscosity. This reduces cost and environmental impact while providing better thermal stability, dynamic shear force, flocculation ability, and suspension stability.

[0007] The technical solution of the present invention is as follows:

[0008] A temperature-resistant, viscosity-enhancing water-based drilling fluid natural polymer cutting agent is prepared from the following raw materials in parts by weight:

[0009] Carboxymethyl starch (CMS) 1-7 parts, 2-acrylamido-2-methylpropanesulfonic acid (AMPS) 1-5 parts, dimethyl diallyl ammonium chloride (DMDAAC) 1-5 parts, N-vinylpyrrolidone (NVP) 1-5 parts, acrylamide (AM) 1-5 parts, initiator I 0.01-0.05 parts, initiator II 0.01-0.05 parts, crosslinking agent epichlorohydrin 0.01-0.07 parts, water 50-70 parts, anhydrous ethanol 150-220 parts.

[0010] According to a preferred embodiment of the present invention, the heat-resistant, viscosity-enhancing water-based drilling fluid natural polymer cutting agent is prepared from the following raw materials in parts by weight: 4-5 parts carboxymethyl starch (CMS), 2-3 parts 2-acrylamido-2-methylpropanesulfonic acid (AMPS), 2-3 parts dimethyl diallyl ammonium chloride (DMDAAC), 1-2 parts N-vinylpyrrolidone (NVP), 1-2 parts acrylamide (AM), 0.03-0.05 parts initiator I, 0.01-0.03 parts initiator II, 0.03-0.05 parts epichlorohydrin crosslinking agent, 55-60 parts water, and 195-200 parts anhydrous ethanol.

[0011] According to a preferred embodiment of the present invention, the degree of substitution (DS) of the carboxymethyl starch (CMS) is 0.6-0.8, and the weight-average molecular weight (Mw) is 5 × 10⁻⁶. 4 -1×10 5 Da.

[0012] According to a preferred embodiment of the present invention, the initiator I is azobisisobutyronitrile (AIBN).

[0013] According to a preferred embodiment of the present invention, the initiator II is ascorbic acid (Vc).

[0014] According to the present invention, the preparation method of the above-mentioned temperature-resistant, viscosity-enhancing water-based drilling fluid natural polymer cutting agent includes the following steps:

[0015] (1) Add carboxymethyl starch (CMS), 2-acrylamido-2-methylpropanesulfonic acid (AMPS) and dimethyl diallyl ammonium chloride (DMDAAC) to water and stir until homogeneous to obtain an aqueous phase; add ethanol solution of initiator I dropwise to the aqueous phase to carry out the reaction and obtain reaction solution A;

[0016] (2) After cooling reaction solution A to room temperature, N-vinylpyrrolidone (NVP) and acrylamide (AM) are added and stirred evenly. Then, initiator II aqueous solution is added dropwise to carry out the first reaction. Finally, crosslinking agent epichlorohydrin is added to carry out the second reaction. After the reaction is completed, the solution is cooled and the resulting reaction solution B is added to anhydrous ethanol for precipitation. After filtration, drying and pulverization, a natural polymeric cutting agent for heat-resistant and thickening water-based drilling fluid is obtained.

[0017] According to a preferred embodiment of the present invention, the carboxymethyl starch (CMS), 2-acrylamido-2-methylpropanesulfonic acid (AMPS) and dimethyl diallyl ammonium chloride (DMDAAC) in step (1) are added to water at 35-45°C under a nitrogen atmosphere; before adding the carboxymethyl starch (CMS), 2-acrylamido-2-methylpropanesulfonic acid (AMPS) and dimethyl diallyl ammonium chloride (DMDAAC) to the water, the system is first purged with nitrogen to remove oxygen for 20-40 minutes.

[0018] According to a preferred embodiment of the present invention, in step (1), the mass ratio of initiator I to anhydrous ethanol in the initiator I ethanol solution is 0.01-0.05:5; the initiator I ethanol solution is added dropwise to the aqueous phase at 50-70°C under a nitrogen atmosphere, with a dropping rate of 1-2 drops / second.

[0019] According to a preferred embodiment of the present invention, the temperature of the reaction in step (1) is 50-70°C, the reaction time is 20-40 min, and the reaction is carried out in a nitrogen atmosphere.

[0020] According to a preferred embodiment of the present invention, the N-vinylpyrrolidone (NVP) and acrylamide (AM) mentioned in step (2) are added to reaction solution A under a nitrogen atmosphere.

[0021] According to a preferred embodiment of the present invention, the mass ratio of initiator II to water in the aqueous solution of initiator II in step (2) is 0.01-0.05:5; the aqueous solution of initiator II is added dropwise to the system at 70-80°C under a nitrogen atmosphere, with a dropping rate of 1-2 drops / second.

[0022] According to a preferred embodiment of the present invention, the temperature of the first reaction in step (2) is 70-80°C, and the reaction time is 0.5-1.5 h; the first reaction is carried out in a nitrogen atmosphere.

[0023] According to a preferred embodiment of the present invention, the crosslinking agent epichlorohydrin in step (2) is added to the system at 70-80°C under a nitrogen atmosphere; the temperature of the second reaction is 70-80°C, and the time of the second reaction is 1-3 hours; the second reaction is carried out under a nitrogen atmosphere.

[0024] According to a preferred embodiment of the present invention, in step (2), the reaction solution B is added dropwise to anhydrous ethanol at a dropping rate of 4-6 g / min; the precipitation step is as follows: after the addition is completed, the mixture is stirred for 20-40 min and then allowed to stand for 0.5-1.5 h; the drying is performed by vacuum drying at 60-70 °C to constant weight.

[0025] According to the present invention, the total mass of water is the amount of water used in step (1) plus the amount of water in the aqueous solution of initiator II in step (2); the total mass of ethanol is the amount of anhydrous ethanol in the ethanol solution of initiator I in step (1) plus the amount of anhydrous ethanol used for precipitation in step (2).

[0026] According to the present invention, the above-mentioned heat-resistant and viscosity-enhancing natural polymer shearing agent for water-based drilling fluid is used as a shearing agent in water-based drilling fluid to improve thermal stability, dynamic shear force, drilling fluid flocculation ability, and suspension stability.

[0027] In this invention, room temperature has a commonly known meaning, referring to 25±5℃.

[0028] The technical features and beneficial effects of this invention are as follows:

[0029] 1. The preparation process of this invention is simple, the synthetic monomers are common, inexpensive and readily available, the synthesis temperature and time are easy to control, and the resulting slitting agent is safe and environmentally friendly, has no irritating odor, and is low in cost.

[0030] 2. The carboxymethyl starch (CMS) used in this invention gives the cutting agent higher solubility and is stable in alkaline or weakly acidic solutions, making it less prone to chemical changes and ensuring the long-term effectiveness of the cutting agent during the drilling process. As a hydrosol, it has a significant thickening effect, which can increase the viscosity of the drilling fluid and improve the rock-carrying capacity. On the other hand, the addition of CMS can make the cutting agent have better rheological properties, making the drilling fluid more sensitive to shear rate.

[0031] 3. This invention utilizes acrylamide (AM) to readily form macromolecular thickeners. Simultaneously, after undergoing a polymerization reaction with dimethyl diallyl ammonium chloride (DMDAAC), a polymer network structure is formed. Under the action of a crosslinking agent, the network structure formed by the polymerization product becomes more compact, resulting in a more significant thickening effect.

[0032] 4. The dimethyl diallyl ammonium chloride (DMDAAC) component used in this invention has cationic charges that can interact with clay, preventing swelling and maintaining formation stability. At the same time, its polymer has good hydrolytic stability and temperature and salt resistance, which enables it to maintain stable performance in high-temperature and high-salinity drilling environments.

[0033] 5. The 2-acrylamido-2-methylpropanesulfonic acid (AMPS) used in this invention can improve the polymer's resistance to temperature and salt, especially its resistance to high-valence metal ions. At the same time, when AMPS is used as a thickener, it can also effectively improve the shear force and viscosity of the drilling fluid, thereby enhancing the drilling fluid's sand-carrying capacity and wellbore stability.

[0034] 6. The initiators added in this invention are azobisisobutyronitrile (AIBN) and ascorbic acid (Vc). AIBN has a high initiation rate and can effectively promote monomer polymerization in the polymerization reaction, improving the yield and quality of the polymer product. Simultaneously, the reaction is relatively stable, with virtually no induced decomposition. This makes its kinetic behavior in the polymerization reaction more predictable, which is beneficial for controlling the structure and properties of the polymer product. Ascorbic acid (Vc) is a naturally occurring vitamin, harmless to the human body, and readily biodegradable. It has strong reducing properties and can be used as a reducing agent in the polymerization reaction to help initiate the polymerization reaction and stabilize the polymer product.

[0035] 7. The cutting agent of this invention is synthesized using derivatives of natural polymer compounds, exhibiting good biodegradability and avoiding long-term environmental pollution. Furthermore, it is widely available and relatively inexpensive. This provides a cost advantage during synthesis, reducing the production cost of drilling fluid cutting agents. The cutting agent of this invention possesses excellent rheological properties, enabling the drilling fluid to form a more stable liquid film between the drill string and the wellbore, reducing friction between the drill string and the wellbore, and lowering torque and resistance. It also helps form a dense filter cake, reducing drilling fluid loss and thus protecting the wellbore and preventing wellbore collapse. The cutting agent of this invention can adapt to various geological conditions, including complex environments such as high temperature, high pressure, and high salinity, demonstrating strong applicability. By adjusting the proportions and formulation of each component, the rheological properties and cutting effect of the drilling fluid can be precisely controlled to meet the needs of different drilling operations. Detailed Implementation

[0036] The present invention will be further described below through specific embodiments, but is not limited thereto.

[0037] Unless otherwise specified, the experimental methods described in the examples are conventional methods; the reagents and materials used are commercially available unless otherwise specified.

[0038] The degree of substitution (DS) of the carboxymethyl starch used in the examples was 0.7, and the weight-average molecular weight (Mw) was 8 × 10⁻⁶. 4 Da.

[0039] Example 1

[0040] A method for preparing a natural polymeric cutting agent for temperature-resistant, viscosity-enhancing water-based drilling fluid includes the following steps:

[0041] (1) Take a round-bottom flask, add 55g of deionized water, purge with nitrogen to remove oxygen for 30 minutes, heat to 40℃, add 4.7g of carboxymethyl starch (CMS), 2.115g of 2-acrylamido-2-methylpropanesulfonic acid (AMPS) and 2.115g of dimethyl diallyl ammonium chloride (DMDAAC) to the above round-bottom flask at 40℃ under nitrogen purging, stir evenly to obtain an aqueous phase for later use;

[0042] (2) Dissolve 0.04g of initiator I azobisisobutyronitrile (AIBN) in 5g of anhydrous ethanol. Under the conditions of stirring at 60°C and nitrogen atmosphere, add the resulting AIBN ethanol solution dropwise to the aqueous phase obtained in step (1) at a dropping rate of 2 drops / second. After the addition is completed, react at 60°C and nitrogen atmosphere for 30min to obtain reaction solution A.

[0043] (3) The reaction solution A obtained in step (2) was naturally cooled to room temperature under a nitrogen atmosphere. Under stirring, 1.175g of N-vinylpyrrolidone (NVP) and 1.175g of acrylamide (AM) were added to the above reaction solution A in sequence to obtain a mixed solution.

[0044] (4) Dissolve 0.02g of initiator II ascorbic acid (Vc) in 5g of deionized water to obtain Vc aqueous solution. Under the conditions of stirring at 75℃ and nitrogen atmosphere, add it dropwise to the mixed solution obtained in step (3) at a dropping rate of 2 drops / second. After the addition is completed, react at a constant temperature of 75℃ and nitrogen atmosphere for 1h.

[0045] (5) Add 0.04 g of epichlorohydrin to the mixed solution obtained in step (4) at 75°C under nitrogen atmosphere and stirring, and react at 75°C under nitrogen atmosphere for 2 h; after the reaction is completed, cool the resulting reaction solution B naturally to room temperature.

[0046] (6) The reaction solution B obtained in step (5) is added dropwise to 195g of anhydrous ethanol at room temperature and under stirring conditions. The addition rate is 5g / min. After the addition is completed, stirring is continued for 30min. White flocculent material is precipitated. After standing for 1h, it is filtered. The white flocculent material is vacuum dried at 60℃ to constant weight, crushed, and sieved to obtain a heat-resistant, thickening water-based drilling fluid natural polymer cutting agent.

[0047] Example 2

[0048] A method for preparing a natural polymeric cutting agent for a temperature-resistant, thickening water-based drilling fluid is described in Example 1, except that the amount of carboxymethyl starch (CMS) used in step (1) is 1.56 g; the other steps and conditions are the same as in Example 1.

[0049] Example 3

[0050] A method for preparing a natural polymeric cutting agent for a temperature-resistant, thickening water-based drilling fluid is described in Example 1, except that the amount of carboxymethyl starch (CMS) used in step (1) is 6.3g; the other steps and conditions are the same as in Example 1.

[0051] Example 4

[0052] A method for preparing a natural polymeric cutting agent for a temperature-resistant, viscosity-enhancing water-based drilling fluid is described in Example 1, except that the amount of azobisisobutyronitrile (AIBN) used in step (2) is 0.02 g; the other steps and conditions are the same as in Example 1.

[0053] Example 5

[0054] A method for preparing a natural polymeric cutting agent for a temperature-resistant, viscosity-enhancing water-based drilling fluid is described in Example 1, except that the amount of ascorbic acid (Vc) used in step (4) is 0.04g; the other steps and conditions are the same as in Example 1.

[0055] Example 6

[0056] A method for preparing a natural polymeric cutting agent for a temperature-resistant, viscosity-enhancing water-based drilling fluid is described in Example 1, except that the amount of 2-acrylamido-2-methylpropanesulfonic acid (AMPS) used in step (1) is 4.23 g; the other steps and conditions are the same as in Example 1.

[0057] Example 7

[0058] A method for preparing a natural polymeric cutting agent for a temperature-resistant, thickening water-based drilling fluid is described in Example 1, except that the amount of epichlorohydrin, the crosslinking agent, in step (5) is 0.02 g; the other steps and conditions are the same as in Example 1.

[0059] Example 8

[0060] A method for preparing a natural polymeric cutting agent for a temperature-resistant, thickening water-based drilling fluid is described in Example 1, except that the amount of N-vinylpyrrolidone (NVP) used in step (3) is 2.35 g; the other steps and conditions are the same as in Example 1.

[0061] Comparative Example 1

[0062] A method for preparing a cutting agent is as described in Example 1, except that carboxymethyl starch (CMS) is not added in step (1); the other steps and conditions are the same as in Example 1.

[0063] Comparative Example 2

[0064] A method for preparing a cutting agent is described in Example 1, except that carboxymethyl starch (CMS) in step (1) is replaced with carboxymethyl cellulose (CMC); the other steps and conditions are the same as in Example 1.

[0065] Comparative Example 3

[0066] A method for preparing a cutting agent is described in Example 1, except that 2-acrylamido-2-methylpropanesulfonic acid (AMPS) is not added in step (1).

[0067] Comparative Example 4

[0068] A method for preparing a cutting agent is described in Example 1, except that 2-acrylamido-2-methylpropanesulfonic acid (AMPS) in step (1) is replaced with sodium styrene sulfonate (SSS); the other steps and conditions are the same as in Example 1.

[0069] Comparative Example 5

[0070] A method for preparing a cutting agent is described in Example 1, except that dimethyl diallyl ammonium chloride (DMDAAC) is not added in step (1).

[0071] Comparative Example 6

[0072] A method for preparing a cutting agent is described in Example 1, except that: dimethyl diallyl ammonium chloride (DMDAAC) in step (1) is replaced with N,N-dimethylacrylamide (DMAA); other steps and conditions are the same as in Example 1.

[0073] Comparative Example 7

[0074] A method for preparing a cutting agent is as described in Example 1, except that N-vinylpyrrolidone (NVP) is not added in step (3); the other steps and conditions are the same as in Example 1.

[0075] Comparative Example 8

[0076] A method for preparing a cutting agent is as described in Example 1, except that N-vinylpyrrolidone (NVP) in step (3) is replaced with N-vinylformamide (NVF); the other steps and conditions are the same as in Example 1.

[0077] Comparative Example 9

[0078] A method for preparing a cutting agent is as described in Example 1, except that acrylamide (AM) in step (3) is replaced with acryloyloxyethyltrimethylammonium chloride (DAC); the other steps and conditions are the same as in Example 1.

[0079] Comparative Example 10

[0080] A method for preparing a cutting agent is as described in Example 1, except that acrylamide (AM) in step (3) is replaced with isopropylacrylamide (NIPAM); the other steps and conditions are the same as in Example 1.

[0081] Experimental Example 1

[0082] The rheological properties of the slitting agents prepared in the examples and comparative examples were tested.

[0083] (1) Sample preparation:

[0084] Preparation of drilling fluid-based slurry: Add 500g tap water, 20g sodium bentonite, and 1g Na2CO3 to a high-speed stirring cup. Stir at 2000r / min for 60min on a high-speed mixer, then transfer to a sealed container and cure at 25℃ for 24h. This yields one part of drilling fluid-based slurry. A total of 19 parts were prepared. (Refer to GB / T 16783.1 2014 "Field Testing of Drilling Fluids in the Petroleum and Natural Gas Industry - Part 1: Water-based Drilling Fluids")

[0085] Sample preparation: 1.5g of the cutting agent from the examples or comparative examples was added to 1 part of drilling fluid-based slurry and stirred at 2000r / min for 30min on a high-speed mixer to obtain the sample. The samples were aged at 140℃ and 180℃ for 16h respectively, then cooled, and the rheological properties of the samples before and after aging were tested at room temperature.

[0086] (2) Test method:

[0087] A certain amount of the prepared sample was poured into the test slurry cup. The plastic viscosity (PV), dynamic shear force (YP), and dynamic plastic ratio (YP / PV) before and after aging were recorded using a ZNN-D12 digital rotational viscometer to evaluate the rheological properties. The test results are shown in Table 1-2.

[0088] Table 1 Performance test parameters of drilling fluid cutting agent before aging

[0089]

[0090] Table 2 Performance test parameters of drilling fluid cutting agent after aging

[0091]

[0092] As can be seen from the data in Table 1-2, the water-based drilling fluid shearing agent prepared by this invention not only has better thermal stability and temperature resistance, but also effectively improves dynamic shear force. At the same time, it can also form a polymer network structure through polymerization reaction to thicken the drilling fluid, improve the flocculation ability and suspension stability, and has a lower cost.

[0093] In summary, the natural polymeric cutting agent for water-based drilling fluid with temperature resistance and viscosity enhancement of the present invention can meet the requirements of temperature resistance and viscosity enhancement of water-based drilling fluid.

[0094] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0095] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0096] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A natural polymeric cutting agent for temperature-resistant, viscosity-enhancing water-based drilling fluid, characterized in that, It is prepared from the following parts by mass of raw materials: Carboxymethyl starch 1-7 parts, 2-acrylamido-2-methylpropanesulfonic acid 1-5 parts, dimethyl diallyl ammonium chloride 1-5 parts, N-vinylpyrrolidone 1-5 parts, acrylamide 1-5 parts, initiator I 0.01-0.05 parts, initiator II 0.01-0.05 parts, crosslinking agent epichlorohydrin 0.01-0.07 parts, water 50-70 parts, anhydrous ethanol 150-220 parts.

2. The natural polymeric cutting agent for heat-resistant, thickening, water-based drilling fluid according to claim 1, characterized in that, The raw materials are prepared in the following proportions by weight: 4-5 parts carboxymethyl starch, 2-3 parts 2-acrylamido-2-methylpropanesulfonic acid, 2-3 parts dimethyl diallyl ammonium chloride, 1-2 parts N-vinylpyrrolidone, 1-2 parts acrylamide, 0.03-0.05 parts initiator I, 0.01-0.03 parts initiator II, 0.03-0.05 parts epichlorohydrin crosslinking agent, 55-60 parts water, and 195-200 parts anhydrous ethanol.

3. The natural polymeric cutting agent for heat-resistant, thickening, water-based drilling fluid according to claim 1, characterized in that, The degree of substitution (DS) of the carboxymethyl starch is 0.6-0.8, and the weight-average molecular weight (Mw) is 5 × 10⁻⁶. 4 ~1×10 5 Da.

4. The natural polymeric cutting agent for heat-resistant, thickening, water-based drilling fluid according to claim 1, characterized in that, Initiator I is azobisisobutyronitrile; initiator II is ascorbic acid.

5. A method for preparing the natural polymeric cutting agent for temperature-resistant, viscosity-enhancing water-based drilling fluid according to any one of claims 1-4, comprising the following steps: (1) Add carboxymethyl starch, 2-acrylamido-2-methylpropanesulfonic acid and dimethyldiallylammonium chloride to water and stir until homogeneous to obtain an aqueous phase; add ethanol solution of initiator I dropwise to the aqueous phase to carry out the reaction and obtain reaction solution A; (2) After cooling the reaction solution A to room temperature, add N-vinylpyrrolidone and acrylamide to it and stir evenly. Then add initiator II aqueous solution dropwise to carry out the first reaction. Finally, add crosslinking agent epichlorohydrin to carry out the second reaction. After the reaction is completed, cool it and add the resulting reaction solution B to anhydrous ethanol for precipitation. After filtration, drying and crushing, a natural polymeric cutting agent for heat-resistant thickening water-based drilling fluid is obtained.

6. The preparation method of the natural polymeric cutting agent for temperature-resistant, viscosity-enhancing water-based drilling fluid according to claim 5, characterized in that, In step (1), the carboxymethyl starch, 2-acrylamido-2-methylpropanesulfonic acid and dimethyl diallyl ammonium chloride are added to water at 35-45°C under a nitrogen atmosphere; before adding the carboxymethyl starch, 2-acrylamido-2-methylpropanesulfonic acid and dimethyl diallyl ammonium chloride to water, the system is first purged with nitrogen to remove oxygen for 20-40 minutes. The mass ratio of initiator I to anhydrous ethanol in the initiator I ethanol solution is 0.01-0.05:5; the initiator I ethanol solution is added dropwise to the aqueous phase at 50-70℃ under a nitrogen atmosphere at a dropping rate of 1-2 drops / second. The reaction is carried out at a temperature of 50-70°C for 20-40 minutes, and in a nitrogen atmosphere.

7. The preparation method of the natural polymeric cutting agent for temperature-resistant, viscosity-enhancing water-based drilling fluid according to claim 5, characterized in that, The N-vinylpyrrolidone and acrylamide mentioned in step (2) are added to reaction solution A under a nitrogen atmosphere; The mass ratio of initiator II to water in the aqueous solution of initiator II is 0.01-0.05:5; the aqueous solution of initiator II is added dropwise to the system at 70-80℃ under a nitrogen atmosphere, with a dropping rate of 1-2 drops / second.

8. The preparation method of the natural polymeric cutting agent for temperature-resistant, viscosity-enhancing water-based drilling fluid according to claim 5, characterized in that, In step (2), the temperature of the first reaction is 70-80℃, and the reaction time is 0.5-1.5h; the first reaction is carried out in a nitrogen atmosphere. The crosslinking agent epichlorohydrin is added to the system at 70-80°C under a nitrogen atmosphere; the temperature of the second reaction is 70-80°C, and the time of the second reaction is 1-3 hours; the second reaction is carried out under a nitrogen atmosphere.

9. The preparation method of the natural polymeric cutting agent for temperature-resistant, viscosity-enhancing water-based drilling fluid according to claim 5, characterized in that, In step (2), reaction solution B is added dropwise to anhydrous ethanol at a dropping rate of 4-6 g / min; the precipitation step is as follows: after addition, stir for 20-40 min, then let stand for 0.5-1.5 h; the drying is performed by vacuum drying at 60-70℃ to constant weight.

10. The application of the natural polymeric cutting agent for heat-resistant, thickening water-based drilling fluid as described in any one of claims 1-4 in water-based drilling fluids.

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