Cationic flocculants, their preparation methods and applications

Abstract

This invention belongs to the field of oilfield chemical technology and relates to a cationic flocculant, its preparation method, and its application. The preparation method of the cationic flocculant provided by this invention includes: (1) dissolving dimethylaminoethyl methacrylate and cationic acrylamide monomer in ethanol and purging with nitrogen to remove oxygen; (2) adding an initiator after heating to a first reaction temperature, and obtaining a prepolymer solution A after the reaction is completed; (3) adding alkyl chloride to the prepolymer solution A, heating to a second reaction temperature to continue the reaction, and obtaining an oil-based drilling fluid flocculant after the reaction is completed. The oil-based drilling fluid flocculant prepared by this invention has the following advantages: (1) it can act as an oil-based flocculant and can flocculate small-diameter inferior solids into large particles, reducing the content of inferior solid phases, and has almost no flocculation effect on barite; (2) it can optimize the rheological properties of drilling fluid, has the effect of reducing viscosity and shear, but does not affect the stability of drilling fluid.

Description

Technical Field

[0001] This invention belongs to the field of oilfield chemical technology, and relates to a cationic flocculant, its preparation method and application, especially to a cationic flocculant, its preparation method and its application in removing low-density inferior solid phases in oil-based drilling fluids. Background Technology

[0002] Oil-based drilling fluids are widely used due to their excellent inhibition, lubrication, and anti-fouling properties. However, after repeated use, the content of low-density, inferior solid phases in oil-based drilling fluids increases. Statistics show that in the Sichuan-Chongqing region, the content of low-density, inferior solid phases (by volume) increases by 4%-6% after each well is drilled. The accumulation of these low-density, inferior solid phases not only increases the viscosity and shear stress of the drilling fluid, deteriorating its rheological properties, but also slows down the rate of penetration (ROP) due to increased internal friction, reducing drilling efficiency and thus increasing drilling costs. Therefore, effectively reducing the content of low-density, inferior solid phases in drilling fluids is of great significance for stabilizing drilling fluid performance.

[0003] Conventional solids control systems are poor at removing low-density, inferior solids smaller than 10 μm. To improve the removal efficiency, it is necessary to flocculate small-diameter inferior solids into larger particles, making them suitable for the processing conditions of solids control equipment for removal. This improves drilling fluid performance and reduces the occurrence of downhole complications. Therefore, it is necessary to develop oil-soluble flocculants to address the problem of removing inferior solids from oil-based drilling fluids.

[0004] Chinese invention patent application CN109652026A discloses a method for preparing a flocculating flow modifier for oil-based drilling fluids. The method includes the following steps: (1) adding nano-activated carbon by weight percentage to a beaker equipped with a stirrer and a thermometer; (2) adding low-viscosity synthetic base oil to the reactor of step (1) at a rate of 1-40% and stirring at 50-90°C for 3-6 hours; (3) adding emulsifier to the reactor of step (1) at a rate of 1-5% and stirring for 3-6 hours; (4) adding wetting agent to the reactor of step (1) at a rate of 1-10% and stirring for 3-5 hours. The resulting suspension is the flocculating flow modifier for oil-based drilling fluids. This method can reduce the content of fine dispersed particles in oil-based drilling fluids, but the flocculation effect is relatively limited. It also has a flocculation effect on useful solid phases such as barite and organic soil in oil-based drilling fluids, which limits its application in high-density oil-based drilling fluids.

[0005] Chinese invention patent application CN113292731A discloses a flocculant for cuttings removal in oil-based drilling fluids, its preparation method, and its application. The method includes the following steps: (1) dissolving a hydrophilic monomer, a cationic monomer, and glycidyl methacrylate in a first solvent to obtain solution a; (2) adding a first initiator to solution a for polymerization to obtain prepolymer A; (3) dissolving a dispersant in a second solvent to obtain solution b; (4) adding an oil-soluble monomer, acrylamide, and 2-mercaptoethylamine hydrochloride to solution b and mixing, then adding a second initiator for polymerization to obtain prepolymer B; (5) dissolving prepolymer A and prepolymer B in a third solvent for graft polymerization to obtain the flocculant. This method can reduce the content of fine dispersed particles in oil-based drilling fluids. However, the preparation process is complex and costly, limiting its application in oil-based drilling fluids.

[0006] Chinese invention patent application CN112029033A discloses a nano- and micron-sized inferior solid phase polymer flocculant for oil-based drilling fluids and its preparation method. This method uses two monomers—cationic diallyl ammonium chloride and methacrylate—to prepare the flocculant via free radical copolymerization. This flocculant can selectively flocculate inferior solid phases with negatively charged surfaces, while hardly flocculating useful solid phases such as barite with uncharged surfaces. However, the presence of some uncharged particles in the inferior solid phase limits the flocculation effect of this flocculant. Summary of the Invention

[0007] The purpose of this invention is to provide a cationic flocculant and its preparation method for removing low-density inferior solid phases in oil-based drilling fluids, in order to solve the problems that field solids control equipment has insufficient ability to remove small-particle-size low-density inferior solid phases in oil-based drilling fluids, and that existing flocculants also have a flocculating effect on useful solid phases in drilling fluids during the flocculation of inferior solid phases.

[0008] The technical solution adopted is:

[0009] A method for preparing a cationic flocculant, comprising:

[0010] (1) Dissolve dimethylaminoethyl methacrylate and cationic acrylamide monomer in ethanol and purge with nitrogen to remove oxygen;

[0011] (2) After heating to the first reaction temperature, an initiator is added, and after the reaction is completed, prepolymer solution A is obtained;

[0012] (3) Add alkyl chloride to the prepolymer solution A, raise the temperature to the second reaction temperature and continue the reaction. After the reaction is completed, an oil-based drilling fluid flocculant is obtained.

[0013] In the above-mentioned method for preparing cationic flocculants, the cationic acrylamide monomer includes one or two of methacryloyloxyethyl ammonium chloride and acryloyloxyethyl trimethyl ammonium chloride.

[0014] In the above-mentioned method for preparing cationic flocculants, the first reaction temperature is 45-80℃ and the reaction time is 8-24h.

[0015] In the above-mentioned method for preparing cationic flocculants, the first reaction temperature is 55-70℃ and the reaction time is 8-16h.

[0016] In the above-mentioned method for preparing cationic flocculants, the initiator is one or more of azobisisobutyronitrile, dimethyl azobisisobutyrate, benzoyl peroxide, and tert-butyl peroxide.

[0017] In the above-described method for preparing cationic flocculants, the general structural formula of the alkyl chloride is as follows:

[0018]

[0019] Where n is an integer between 10 and 22.

[0020] In the above-mentioned method for preparing cationic flocculants, the second reaction temperature is 30-60℃ and the reaction time is 2-10h.

[0021] In the above-mentioned method for preparing cationic flocculants, the second reaction temperature is 45-55℃ and the reaction time is 3-6h.

[0022] The above-mentioned method for preparing cationic flocculants uses 100 parts by weight of ethanol as a base, wherein the dimethylaminoethyl methacrylate is 60-95 parts by weight; the cationic acrylamide monomer is 5-30 parts by weight; the alkyl chloride is 20-60 parts by weight; and the initiator is 0.001-3 parts by weight.

[0023] The above-mentioned method for preparing cationic flocculants uses 100 parts by weight of ethanol as a base, wherein the dimethylaminoethyl methacrylate is 75-80 parts by weight; the cationic acrylamide monomer is 10-20 parts by weight; the alkyl chloride is 35-45 parts by weight; and the initiator is 0.1-1 parts by weight.

[0024] On the other hand, the present invention provides a cationic flocculant prepared by the above-described preparation method.

[0025] In another aspect, the present invention also provides the application of the above-mentioned cationic flocculant in removing low-density, inferior solid phases from oil-based drilling fluids.

[0026] The oil-based drilling fluid flocculant prepared by the method of the present invention has the following advantages:

[0027] (1) It can act on oil-based flocculants and can flocculate small-diameter inferior solids into large particles, reduce the content of inferior solid phase, and has almost no flocculation effect on barite.

[0028] (2) It can optimize the rheological properties of drilling fluid and has the effect of reducing viscosity and shear, but does not affect the stability of drilling fluid. Detailed Implementation

[0029] To fully understand the purpose, features, and effects of this invention, the following detailed embodiments are provided. Except as described below, the process methods of this invention employ conventional methods or apparatus in the art. Unless otherwise specified, the terms and expressions used below have the meanings commonly understood by those skilled in the art.

[0030] When a range of values ​​is disclosed herein, the range is considered continuous and includes the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0031] Specifically, the preparation method of the cationic flocculant provided by the present invention includes:

[0032] (1) Dissolve dimethylaminoethyl methacrylate and cationic acrylamide monomer in ethanol and purge with nitrogen to remove oxygen;

[0033] (2) After heating to the first reaction temperature, an initiator is added, and after the reaction is completed, prepolymer solution A is obtained;

[0034] (3) Add alkyl chloride to the prepolymer solution A, raise the temperature to the second reaction temperature and continue the reaction. After the reaction is completed, an oil-based drilling fluid flocculant is obtained.

[0035] In this process, the cationic acrylamide monomer provides adsorption groups in the flocculant to enhance the adhesion of flocculant molecules to the harmful solid phase. In some preferred embodiments, the cationic acrylamide monomer includes one or both of methacryloyloxyethyl ammonium chloride and acryloyloxyethyl trimethyl ammonium chloride.

[0036] In step (2), a prepolymer solution A is obtained by adding an initiator to induce redox free radical polymerization of dimethylaminoethyl methacrylate and cationic acrylamide monomer.

[0037] In some preferred embodiments, the first reaction temperature is 45-80°C and the reaction time is 8-24h; more preferably, the first reaction temperature is 55-70°C and the reaction time is 8-16h.

[0038] In some preferred embodiments, the initiator is one or more of azobisisobutyronitrile, dimethyl azobisisobutyrate, benzoyl peroxide, and tert-butyl peroxide.

[0039] In step (3), the halogen in the alkyl chloride undergoes an atomic substitution reaction with prepolymer A.

[0040] In some preferred embodiments, the general structural formula of the alkyl chloride is as follows:

[0041]

[0042] Where n is an integer between 10 and 22.

[0043] Alkyl chlorides, as functional monomers in flocculants, can improve the dispersion of flocculants in drilling fluids and act as adsorption groups to enhance the flocculation effect of flocculants on harmful solid phases. The 'n' value in alkyl chlorides has a significant impact on the polymer dispersion; too small or too large a value can lead to poor dispersibility of the flocculant in drilling fluids.

[0044] In some preferred embodiments, the second reaction temperature is 30-60°C and the reaction time is 2-10 hours; more preferably, the second reaction temperature is 45-55°C and the reaction time is 3-6 hours.

[0045] In some preferred embodiments, based on 100 parts by weight of ethanol, the dimethylaminoethyl methacrylate is 60-95 parts by weight; the cationic acrylamide monomer is 5-30 parts by weight; the alkyl chloride is 20-60 parts by weight; and the initiator is 0.001-3 parts by weight.

[0046] In practice, excessive or insufficient amounts of dimethylaminoethyl methacrylate, cationic acrylamide monomer, and alkyl chloride can lead to poor flocculation performance of the flocculant. Excessive initiator can cause overly rapid initiation, resulting in decreased flocculant performance.

[0047] More preferably, based on 100 parts by weight of ethanol, the dimethylaminoethyl methacrylate is 75-80 parts by weight; the cationic acrylamide monomer is 10-20 parts by weight; the alkyl chloride is 35-45 parts by weight; and the initiator is 0.1-1 parts by weight.

[0048] On the other hand, the present invention also provides a cationic flocculant, which is prepared by the above-described preparation method.

[0049] The cationic flocculant of the present invention is a transparent amber-colored viscous liquid that can selectively flocculate inferior solid phases with negatively charged surfaces to form large and dense flocs, making them easy to remove by solids control equipment. At the same time, it hardly flocculates useful solid phases such as barite with uncharged surfaces. Moreover, it can reduce the viscosity and shear stress of oil-based drilling fluids and improve the utilization rate of oil-based drilling fluids.

[0050] In another aspect, the present invention also provides the application of the above-mentioned cationic flocculant in removing low-density, inferior solid phases from oil-based drilling fluids.

[0051] The cationic flocculant of this invention exhibits excellent solubility in oil-based drilling fluids. Furthermore, it selectively flocculates inferior solid phases in oil-based drilling fluids, while showing weaker flocculation effects on useful solid phases such as barite and organic clays. This significantly improves the removal efficiency of cuttings from oil-based drilling fluids. (Example)

[0052] The present invention is further illustrated below by way of embodiments, but the invention is not limited to the scope of the embodiments described herein. Experimental methods in the following embodiments, unless otherwise specified, were performed according to conventional methods and conditions. The raw materials used in the following embodiments were all commercially available.

[0053] Example 1:

[0054] A cationic oil-based drilling fluid flocculant was prepared by solution polymerization.

[0055] 75g of dimethylaminoethyl methacrylate and 10g of methacryloyloxyethyl ammonium chloride were dissolved in 100g of ethanol. The mixture was purged with nitrogen for 20min to remove oxygen. After heating to 60℃, 0.5g of azobisisobutyronitrile was added. After reacting for 12h, prepolymer solution A was obtained.

[0056] Add 35g of alkyl chloride 18 (18 carbons) to prepolymer solution A, heat to 50℃ and continue the reaction for 4h. After the reaction is completed, a transparent amber viscous liquid is obtained, which is oil-based drilling fluid flocculant S1.

[0057] Example 2:

[0058] A cationic oil-based drilling fluid flocculant was prepared by solution polymerization.

[0059] 75g of dimethylaminoethyl methacrylate and 10g of acryloyloxyethyltrimethylammonium chloride were dissolved in 100g of ethanol. The mixture was purged with nitrogen for 20min to remove oxygen. After heating to 60℃, 0.5g of azobisisobutyronitrile was added. After reacting for 12h, prepolymer solution A was obtained.

[0060] Add 35g of alkyl chloride 18 (18 carbons) to prepolymer solution A, heat to 50℃ and continue the reaction for 4h. After the reaction is completed, a transparent amber viscous liquid is obtained, which is oil-based drilling fluid flocculant S2.

[0061] Example 3:

[0062] A cationic oil-based drilling fluid flocculant was prepared by solution polymerization.

[0063] 75g of dimethylaminoethyl methacrylate and 10g of methacryloyloxyethyl ammonium chloride were dissolved in 100g of ethanol. The mixture was purged with nitrogen for 20min to remove oxygen. After heating to 60℃, 0.1g of azobisisobutyronitrile was added. After reacting for 12h, prepolymer solution A was obtained.

[0064] Add 35g of alkyl chloride 12 (12 carbon atoms) to prepolymer solution A, heat to 50℃ and continue the reaction for 4h. After the reaction is completed, a transparent amber viscous liquid is obtained, which is oil-based drilling fluid flocculant S3.

[0065] Example 4:

[0066] A cationic oil-based drilling fluid flocculant was prepared by solution polymerization.

[0067] 75g of dimethylaminoethyl methacrylate and 10g of methacryloyloxyethyl ammonium chloride were dissolved in 100g of ethanol. The mixture was purged with nitrogen for 20min to remove oxygen. After heating to 60℃, 0.1g of benzoyl peroxide was added. After reacting for 12h, prepolymer solution A was obtained.

[0068] Add 35g of alkyl chloride 18 (18 carbons) to prepolymer solution A, heat to 50℃ and continue the reaction for 4h. After the reaction is completed, a transparent amber viscous liquid is obtained, which is oil-based drilling fluid flocculant S4.

[0069] Example 5:

[0070] A cationic oil-based drilling fluid flocculant was prepared by solution polymerization.

[0071] 65g of dimethylaminoethyl methacrylate and 30g of methacryloyloxyethyl ammonium chloride were dissolved in 100g of ethanol. The mixture was purged with nitrogen for 20min to remove oxygen. After heating to 70℃, 1.5g of azobisisobutyronitrile was added. After reacting for 12h, prepolymer solution A was obtained.

[0072] Add 20g of alkyl chloride 12 (12 carbon atoms) to prepolymer solution A, heat to 50℃ and continue the reaction for 8h. After the reaction is completed, a transparent amber viscous liquid is obtained, which is oil-based drilling fluid flocculant S5.

[0073] Comparative Example 1:

[0074] The method of Example 1 was followed, except that methacryloyloxyethyl ammonium chloride was not used in step (1). Other conditions were the same as in Example 1, and flocculant D1 was obtained.

[0075] Comparative Example 2:

[0076] The method of Example 1 was followed, except that no alkyl chloride was added in step (2). Other conditions were the same as in Example 1, and flocculant D2 was obtained.

[0077] The performance of the flocculant for cuttings removal from oil-based drilling fluids provided by this invention was evaluated by treating oil-based drilling fluids with the flocculants prepared in Examples 1-5 and Comparative Examples 1-2. In the following test examples,

[0078] The median solid particle size of the drilling fluid was measured using a focused beam reflectometer (Mettler-Toledo, ParticleTrack G600B).

[0079] The plastic viscosity (mPa·s), dynamic shear force (Pa), and initial and final shear force (Pa) of the drilling fluid were determined using a six-speed viscometer according to the method specified in GB / T 16783.2-2012.

[0080] The drilling fluid density, low-density solids content, and barite solids content are determined according to the methods specified in GB / T16783.2-2012. Unless otherwise specified, the low-density solids content and barite solids content refer to volume content.

[0081] The manufacturer of the six-speed viscometer is Qingdao Tongchun Petroleum Instrument Co., Ltd., and the model number is ZNN-D6B.

[0082] The manufacturer of the low-speed mixer is Qingdao Tongchun Petroleum Instrument Co., Ltd., model D90;

[0083] The centrifuge is manufactured by Hunan Xiangyi Laboratory Instrument Development Co., Ltd., and its model is TG16-WS.

[0084] Oil-based drilling fluid sample S0:

[0085] The oil-based drilling fluid in this test case is the drilling fluid returned to shore from the offshore platform. It is an oil-based drilling fluid sample obtained after being processed by solids control equipment such as vibrating screen, desilter, desander, and centrifuge. The following tests were performed on the sample.

[0086] 1. Solid particle size test of drilling fluid samples after adding flocculant

[0087] 0.1 g of the flocculants prepared in Examples 1-5 and Comparative Examples 1-2 of this invention were added to 100 mL of oil-based drilling fluid samples, respectively. The mixture was stirred at 500 r / min for 5 min using a low-speed mixer to obtain flocculated drilling fluid. The median solid particle size of the drilling fluid was measured using a focused beam reflectance meter. S0 served as a blank control group, without the addition of flocculant; other test conditions were identical to those of the other test groups. The test results are shown in Table 1.

[0088] Table 1. Effect of flocculants on the particle size of inferior solid phase in oil-based drilling fluids

[0089]

[0090] As shown in Table 1, the median solid particle size of the drilling fluid significantly increased after adding the flocculant provided by this invention to the oil-based drilling fluid samples, from 11 μm to over 65 μm. Examples 1-3 showed the best results, with the median solid particle size of the drilling fluid increasing to over 100 μm after flocculation treatment. This indicates that the flocculant provided by this invention has a significant flocculation effect on finely dispersed particles in the oil-based drilling fluid samples.

[0091] 2. Testing of flocculated solid phase composition after adding flocculant to drilling fluid

[0092] 0.1g of the flocculants prepared in Examples 1-5 and Comparative Examples 1-2 of this invention were added to 100mL of oil-based drilling fluid samples, respectively. The mixture was stirred at 500r / min for 5min using a low-speed mixer to obtain flocculated drilling fluid. The drilling fluid was then sieved (using a 200-mesh standard sieve), and the flocculated material retained on the sieve surface was washed with n-hexane, dried at 50℃, and the flocculated solid phase was weighed as the sieve residue. Elemental analysis was performed on the flocculated solid phase to determine the mass percentage of oxides (SiO2, CaO, BaO, Al2O3, Fe2O3, etc.), and the mass percentages of barite (BaSO4), calcium oxide (CaO), and inferior solid phase in the flocculated solid phase were further calculated based on molecular weight (wherein, the mass percentage of inferior solid phase = 100% - mass percentage of barite - mass percentage of calcium oxide). S0 served as a blank control group, without flocculant, and all other test conditions were identical to the other test groups. The test results are shown in Table 2.

[0093] Table 2. Screen Residue Mass and Flocculent Solid Phase Composition

[0094]

[0095] As shown in Table 2, after adding the flocculant provided by this invention to the oil-based drilling fluid samples, the median solid particle size of the drilling fluid increased significantly, and the mass of the residue after passing through a 200-mesh standard sieve increased significantly, from 0.31g to over 5.5g. Examples 1-3 showed the best results, with a residue mass of over 9.5g after flocculation treatment. Furthermore, the composition of the residue showed that with the addition of the flocculant, the amount of inferior solid phase significantly increased, while the amount of barite significantly decreased. This indicates that the flocculant provided by this invention has a selective flocculation effect, with strong flocculation ability for inferior solid phases and weak flocculation ability for barite.

[0096] 3. Rheological property testing of drilling fluid samples after adding flocculant

[0097] 0.1g of the flocculants prepared in Examples 1-5 and Comparative Examples 1-2 of this invention were added to 100mL of oil-based drilling fluid samples, respectively. The mixture was stirred at 500r / min for 5min using a low-speed mixer to obtain flocculated drilling fluid. The supernatant was then centrifuged at 3000rpm for 5min, and its rheological parameters were tested. S0 served as a blank control group, without flocculant, and all other test conditions were identical to the other test groups. The test results are shown in Table 3.

[0098] Table 3. Rheological properties of centrifuged liquid after flocculation.

[0099]

[0100] As shown in Table 3, after adding the flocculant provided by this invention to the oil-based drilling fluid sample and centrifuging, the plastic viscosity, dynamic shear force, and initial / final shear rate of the drilling fluid were significantly reduced. This is because the removal of inferior solid phases reduces the solid phase in the drilling fluid, thereby reducing the friction between drilling fluid particles and resulting in a decrease in viscosity.

[0101] 3. Testing of density and low-quality solid content in centrifuged drilling fluid samples after adding flocculant.

[0102] 0.1g of the flocculants prepared in Examples 1-5 and Comparative Examples 1-2 of this invention were added to 100mL of oil-based drilling fluid samples, respectively. The mixture was stirred at 500r / min for 5min using a low-speed mixer to obtain flocculated drilling fluid. The supernatant was then centrifuged at 3000rpm for 5min, and its density and content of inferior solids were tested. S0 served as a blank control group, without flocculant, and all other test conditions were identical to the other test groups. The test results are shown in Table 4.

[0103] Table 4. Tests on density and low-quality solid content of centrifuged liquid after flocculation.

[0104]

[0105] As shown in Table 3, after adding the flocculant provided by this invention to the oil-based drilling fluid sample and centrifuging, the density and low-quality solid phase of the drilling fluid were significantly reduced. The density of the centrifuged fluid decreased from 1.51 g / cm³. 3 Reduced to 1.22 g / cm³ 3 The content of inferior solid phase decreased from 15.5% to 5.6%, indicating that the flocculant provided by the present invention has a significant flocculation and removal effect on inferior solid phase in oil-based drilling fluid samples.

[0106] The foregoing description includes examples of one or more embodiments. Of course, those skilled in the art will recognize that the various embodiments can be further combined and arranged. Therefore, the embodiments described herein are intended to cover all such changes, modifications, and variations that fall within the scope of the appended claims. Furthermore, the term "comprising" as used in the specification or claims is interpreted in a manner similar to the term "including," just as "comprising" is interpreted as a conjunction in the claims. Additionally, the use of any term "or" in the specification of the claims is intended to mean "non-exclusive or."

[0107] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from the concept and scope of the invention. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for preparing a cationic flocculant, characterized in that, include: (1) Dissolve 60-95 parts by weight of dimethylaminoethyl methacrylate and 5-30 parts by weight of cationic acrylamide monomer in 100 parts by weight of ethanol, and remove oxygen by passing nitrogen gas. The cationic acrylamide monomer includes one or two of methacryloyloxyethyl ammonium chloride and acryloyloxyethyl trimethyl ammonium chloride; (2) After heating to the first reaction temperature, add 0.001-3 parts by weight of initiator. After the reaction is completed, prepolymer solution A is obtained. (3) Add 20-60 parts by weight of alkyl chloride to the prepolymer solution A, heat to the second reaction temperature and continue the reaction. After the reaction is completed, an oil-based drilling fluid flocculant is obtained. Wherein, the alkyl chloride is alkyl chloride 12 or alkyl chloride 18.

2. The method for preparing the cationic flocculant according to claim 1, characterized in that, The first reaction temperature is 45-80℃, and the reaction time is 8-24h.

3. The method for preparing the cationic flocculant according to claim 1, characterized in that, The first reaction temperature is 55-70℃, and the reaction time is 8-16h.

4. The method for preparing the cationic flocculant according to claim 1, characterized in that, The initiator is one or more of azobisisobutyronitrile, dimethyl azobisisobutyrate, benzoyl peroxide, and tert-butyl peroxide.

5. The method for preparing the cationic flocculant according to claim 1, characterized in that, The second reaction temperature is 30-60℃, and the reaction time is 2-10h.

6. The method for preparing the cationic flocculant according to claim 1, characterized in that, The second reaction temperature is 45-55℃, and the reaction time is 3-6h.

7. The method for preparing the cationic flocculant according to claim 1, characterized in that, Based on 100 parts by weight of ethanol, the dimethylaminoethyl methacrylate is 75-80 parts by weight; the cationic acrylamide monomer is 10-20 parts by weight; the alkyl chloride is 35-45 parts by weight; and the initiator is 0.1-1 parts by weight.

8. A cationic flocculant, characterized in that, It is prepared by the preparation method according to any one of claims 1-7.

9. The application of the cationic flocculant according to claim 8 in removing low-density, inferior solid phases from oil-based drilling fluids.

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