Flocculant for oil-based drilling fluid and preparation method and application thereof

Abstract

The application provides a flocculant for oil-based drilling fluid and a preparation method and application thereof. The preparation method of the flocculant for oil-based drilling fluid comprises the following steps: adding an oleophilic monomer A into a solvent, heating to a reaction temperature, adding an initiator a and a chain transfer agent to obtain a mixed solution I; mixing an oleophilic monomer B and a hydrophilic monomer uniformly to obtain a mixed solution II; adding the obtained mixed solution II into the mixed solution I, and then adding an initiator b to perform a reaction to obtain the flocculant for oil-based drilling fluid. The flocculant for oil-based drilling fluid is synthesized by a reversible addition-fragmentation chain transfer polymerization method based on two kinds of oleophilic monomers and one kind of hydrophilic monomer, and is added into oil-based drilling fluid, so that the flocculant can adsorb nanometer and micrometer poor solid phases, and the purpose of efficiently removing the nanometer and micrometer poor solid phases and improving the repeated utilization rate of the oil-based drilling fluid is achieved.

Description

Technical Field

[0001] This invention relates to a flocculant for oil-based drilling fluids, its preparation method and application, belonging to the field of oilfield chemistry in the petroleum industry. Background Technology

[0002] As oil and gas exploration and development moves towards deeper and more complex formations, the depth and complexity of drilling are constantly increasing, leading to more and more problems during the drilling process and placing increasingly higher demands on drilling fluid performance. Oil-based drilling fluids, due to their advantages such as strong temperature resistance, good inhibition of shale hydration, significant lubrication and drag reduction effects, and minimal damage to the reservoir, have been widely used in oil and gas drilling in deep wells, ultra-deep wells, horizontal wells, extended reach wells, and complex formation conditions.

[0003] Oil-based drilling fluids are dispersion systems composed of oil as the continuous phase, water as the dispersed phase, and appropriate amounts of emulsifiers, wetting agents, and weighting materials. Due to the excessive depth of ultra-deep wells, the large inclination variations of horizontal and extended-reach wells, and the limitations of oil-based drilling's cuttings carrying capacity, some drill cuttings cannot be carried out of the wellbore in a timely manner during drilling fluid circulation. The drill cuttings are repeatedly abraded by the drill string within the wellbore, causing a continuous increase in the concentration of nano- and micron-sized inferior solid phases in the drilling fluid, thus affecting its usability. Excessive levels of nano- and micro-sized inferior solids have a severe impact on the performance of oil-based drilling fluids. High levels of these inferior solids reduce drilling speed and affect drilling progress; they also increase viscosity, decrease lubrication, and increase friction, thus exacerbating drill string wear. Furthermore, excessive inferior solids degrade the fluid's filtration performance, leading to increased filtration loss under high temperature and pressure, which affects wellbore stability during drilling. Recycled oil-based drilling fluids are typically reused by removing inferior solids using solids control equipment and diluting the old fluid with new drilling fluid. However, solids control equipment has limited capacity to remove micro- and nano-sized inferior solids. Excessive levels necessitate increasing the amount of new drilling fluid added for reuse, significantly increasing usage and processing costs.

[0004] Therefore, to reduce the content of inferior solid phases in recycled oil-based drilling fluids, decrease the amount of new drilling fluid added, and lower the cost of drilling fluid use and treatment, appropriate flocculants can be added. Studies have found that flocculants have a highly efficient flocculation effect on solid particles in liquids; only a small amount needs to be added to significantly reduce the amount of suspended solids and colloidal contaminants in the liquid, thus purifying it. Flocculants can be broadly classified into inorganic and organic flocculants based on their chemical composition. Inorganic flocculants include inorganic coagulants and inorganic polymeric flocculants; organic flocculants include organic polymeric flocculants, natural organic polymeric flocculants, and microbial flocculants. However, regardless of the type, most flocculants are used for the purification and flocculation of aqueous solutions, while reports on flocculants for oil solutions are relatively few. For example, Chinese patent document CN114605582A discloses an oil-based drilling fluid flocculant, which is formed by compounding an oil-soluble polymer with fatty acids, wherein the oil-soluble polymer is formed by emulsion polymerization of styrene, p-hydroxystyrene, and acrylates. While the polymeric flocculant used in this method can bind with solids in the drilling fluid, the resulting floc strength is low. Furthermore, the flocculant prepared using emulsion polymerization contains emulsifiers and water, which may affect the stability of the drilling fluid during subsequent use. Chinese patent document CN117164752A discloses an oil-based drilling fluid flocculant and its preparation method. The flocculant uses lipophilic monomers such as lauryl methacrylate or styrene, fluorinated monomers such as trifluoroethyl methacrylate, and cationic monomers such as dimethyl diallyl ammonium chloride. The oil-based drilling fluid flocculant prepared by this method has a higher cost due to the presence of fluorinated monomers, and its overall flocculation effect is relatively limited.

[0005] Therefore, in order to address the problem that oil-based drilling fluids have excessively high micro- and nano-sized inferior solid content during recycling and are difficult to remove by solids control equipment, there is an urgent need to develop a flocculant for oil-based drilling fluids that can efficiently remove nano- and micro-sized inferior solids. Summary of the Invention

[0006] To address the shortcomings of existing technologies, particularly the high content of nano- and micro-sized inferior solid phases in existing oil-based drilling fluids during recycling, the difficulty in removing them, the poor reusability of waste oil-based drilling fluids, and the limited removal capacity of existing flocculants, this invention provides a flocculant for oil-based drilling fluids, its preparation method, and its application. The flocculant of this invention is an oil-soluble flocculant synthesized through a reversible addition-fragmentation chain transfer polymerization method using two lipophilic monomers and one hydrophilic monomer. When added to oil-based drilling fluids, it can adsorb nano- and micro-sized inferior solid phases, thereby achieving efficient removal of these phases and improving the reusability of oil-based drilling fluids.

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

[0008] A method for preparing a flocculant for oil-based drilling fluids includes the following steps:

[0009] The lipophilic monomer A is added to a solvent and heated to the reaction temperature. Initiator a and chain transfer agent are added to obtain mixture I. The lipophilic monomer B and the hydrophilic monomer are mixed evenly to obtain mixture II. Mixture II is added to mixture I, and then initiator b is added to react and obtain flocculant for oil-based drilling fluid.

[0010] According to a preferred embodiment of the present invention, the lipophilic monomer A is one or more of lauryl methacrylate, lauryl acrylate, and octadecyl methacrylate.

[0011] According to a preferred embodiment of the present invention, the solvent is one or more of white oil, dimethyl sulfoxide, N,N-dimethylformamide, and toluene, wherein the white oil is No. 3 white oil, No. 5 white oil, No. 7 white oil, or No. 10 white oil; and the mass ratio of the solvent to the lipophilic monomer A is 3-6:1.

[0012] According to a preferred embodiment of the present invention, the reaction temperature is 80-100°C.

[0013] According to a preferred embodiment of the present invention, the initiator a is one or a combination of two or more of ammonium persulfate, potassium persulfate, benzoyl peroxide, and azobisisobutyronitrile; the mass of the initiator a is 0.1-1% of the total mass of the lipophilic monomer A, the lipophilic monomer B, and the hydrophilic monomer.

[0014] According to a preferred embodiment of the present invention, the chain transfer agent is one or more selected from 2-cyano-2-propyldodecyl trithiocarbonate, 4-cyano-4-[(dodecylthioalkylthiocarbonyl)thioalkyl]valeric acid, and 4-cyano-4-(phenylcarbonylthio)valeric acid; the mass of the chain transfer agent is 0.3-0.8% of the total mass of the lipophilic monomer A, the lipophilic monomer B, and the hydrophilic monomer.

[0015] According to a preferred embodiment of the present invention, the lipophilic monomer B is methyl methacrylate and / or vinyltrimethoxysilane; the molar ratio of the lipophilic monomer B to the lipophilic monomer A is 0.8-1.2:1, more preferably 1:1.

[0016] According to a preferred embodiment of the present invention, the hydrophilic monomer is one or more selected from dimethylaminoethyl methacrylate, acrylamide, acrylic acid, and methacrylic acid; the molar ratio of the hydrophilic monomer to the lipophilic monomer A is 0.2-0.4:1, more preferably 1:3.

[0017] According to a preferred embodiment of the present invention, the mixture II is added dropwise to the mixture I over a period of 1-3 hours at a temperature of 80-100°C.

[0018] According to a preferred embodiment of the present invention, the type and amount of initiator b are the same as those of initiator a.

[0019] According to a preferred embodiment of the present invention, the reaction time is 3-5 hours.

[0020] The present invention also provides a flocculant for oil-based drilling fluids, which is prepared by the above-described preparation method.

[0021] According to the present invention, the above-mentioned flocculant for oil-based drilling fluid is used in oil-based drilling fluid to adsorb nano- and micro-sized inferior solid phases.

[0022] The technical features and beneficial effects of this invention are as follows:

[0023] 1. The flocculant of the present invention utilizes the carbonyl group in the molecular structure to provide the interaction force (hydrogen bonding) with the harmful solid phase. At the same time, the long carbon chains can intertwine to play the role of adsorption bridging and netting, which can efficiently adsorb nano- and micron-sized particles in oil-based drilling fluids. When used with solids control equipment, it can effectively reduce the content of inferior solid phases in drilling fluids.

[0024] 2. The flocculant of the present invention has long carbon chains and hydrophilic groups in its molecular structure, which can reduce surface tension, have a certain emulsification effect, improve the emulsion stability of oil-based drilling fluids, and increase the demulsification voltage.

[0025] 3. The flocculant of the present invention can significantly improve the reuse efficiency of oil-based drilling fluid and reduce the cost of use.

[0026] 4. The flocculant prepared by the RAFT polymerization method of this invention has a controllable molecular weight and a narrow molecular weight distribution, resulting in a higher effective component. The flocculant prepared by the RAFT polymerization method has stable chemical properties, a short reaction cycle, high yield, high flocculation efficiency, and high floc strength after flocculation. Detailed Implementation

[0027] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] Methyl methacrylate, liquid, purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0029] Example 1

[0030] A method for preparing a flocculant for oil-based drilling fluids includes the following steps:

[0031] (1) Place 8g of lauryl methacrylate and 37g of dimethyl sulfoxide into a three-necked flask and then place it in a water bath and stir and heat. When the temperature reaches 90℃, add 0.06g of azobisisobutyronitrile and 0.06g of 2-cyano-2-propyldodecyl trithiocarbonate to obtain mixture I.

[0032] (2) Stir 3g of methyl methacrylate and 1.5g of dimethylaminoethyl methacrylate in a beaker for 5 minutes to obtain mixture II; slowly add mixture II to the three-necked flask in step (1) at 90°C using a constant pressure dropping funnel for 2 hours; after the addition is complete, add 0.06g of azobisisobutyronitrile to the three-necked flask again and react at 90°C for 4 hours; after the reaction is complete, cool naturally to room temperature to obtain flocculant for oil-based drilling fluid.

[0033] Example 2

[0034] A method for preparing a flocculant for oil-based drilling fluids includes the following steps:

[0035] (1) Put 10g of octadecyl methacrylate and 41g of No. 3 white oil into a three-necked flask and then put it into a water bath and stir and heat it; when the temperature rises to 90℃, add 0.07g of benzoyl peroxide and 0.07g of 2-cyano-2-propyldodecyl trithiocarbonate to obtain mixture I;

[0036] (2) Add 3g of methyl methacrylate and 0.9g of methacrylic acid to a beaker and stir for 5 minutes to obtain mixture II; slowly add mixture II to the three-necked flask in step (1) at 90°C using a constant pressure dropping funnel for 2 hours; after the addition is complete, add 0.07g of benzoyl peroxide to the three-necked flask again and react at 90°C for 4 hours; after the reaction is complete, cool naturally to room temperature to obtain flocculant for oil-based drilling fluid.

[0037] Example 3

[0038] A method for preparing a flocculant for oil-based drilling fluids includes the following steps:

[0039] (1) Place 8g of lauryl methacrylate and 39g of N,N-dimethylformamide into a three-necked flask and then place it in a water bath and stir and heat. When the temperature reaches 90℃, add 0.07g of ammonium persulfate and 0.07g of 2-cyano-2-propyldodecyl trithiocarbonate to obtain mixture I.

[0040] (2) Add 4.5g of vinyltrimethoxysilane and 0.7g of acrylamide to a beaker and stir for 5 minutes to obtain mixture II; slowly add mixture II to the three-necked flask of step (1) at 90°C using a constant pressure dropping funnel for 2 hours; after the addition is complete, add 0.07g of ammonium persulfate to the three-necked flask again and react at 90°C for 4 hours; after the reaction is complete, cool naturally to room temperature to obtain flocculant for oil-based drilling fluid.

[0041] Example 4

[0042] A method for preparing a flocculant for oil-based drilling fluids includes the following steps:

[0043] (1) Place 7g lauryl acrylate and 32g toluene into a three-necked flask and then place it in a water bath and stir and heat. When the temperature reaches 90℃, add 0.05g potassium persulfate and 0.05g 2-cyano-2-propyldodecyl trithiocarbonate to obtain mixture I.

[0044] (2) Add 3g of methyl methacrylate and 0.7g of acrylic acid to a beaker and stir for 5 minutes to obtain mixture II; slowly add mixture II to the three-necked flask in step (1) at 90°C using a constant pressure dropping funnel for 2 hours; after the addition is complete, add 0.05g of potassium persulfate to the three-necked flask again and react at 90°C for 4 hours; after the reaction is complete, cool naturally to room temperature to obtain flocculant for oil-based drilling fluid.

[0045] Comparative Example 1

[0046] A method for preparing a flocculant for oil-based drilling fluid is described in Example 1, except that in step (2), lauryl methacrylate is used instead of methyl methacrylate in an equal molar amount, and other conditions are the same as in Example 1.

[0047] Comparative Example 2

[0048] A method for preparing a flocculant for oil-based drilling fluid is described in Example 2, except that in step (2), octadecyl methacrylate is used instead of methyl methacrylate in an equal molar amount, and other conditions are the same as in Example 2.

[0049] Comparative Example 3

[0050] A method for preparing a flocculant for oil-based drilling fluid is described in Example 1, except that in step (1), methyl methacrylate is used instead of lauryl methacrylate in equal molar amounts, and other conditions are the same as in Example 1.

[0051] Comparative Example 4

[0052] A method for preparing a flocculant for oil-based drilling fluid is described in Example 2, except that: in step (1), methyl methacrylate is used instead of octadecyl methacrylate in equal molar amounts, and other conditions are the same as in Example 2.

[0053] Comparative Example 5

[0054] A method for preparing a flocculant for oil-based drilling fluid is described in Example 1, except that 0.02 g of 2-cyano-2-propyldodecyl trithiocarbonate is added in step (1), and other conditions are the same as in Example 1.

[0055] Comparative Example 6

[0056] A method for preparing a flocculant for oil-based drilling fluid is described in Example 1, except that 0.2g of 2-cyano-2-propyldodecyl trithiocarbonate is added in step (1), and other conditions are the same as in Example 1.

[0057] Comparative Example 7

[0058] A method for preparing a flocculant for oil-based drilling fluid is described in Example 1, except that in step (1), benzyl dithiobenzoate is used instead of 2-cyano-2-propyldodecyl trithiocarbonate, and other conditions are the same as in Example 1.

[0059] Comparative Example 8

[0060] A method for preparing a flocculant for oil-based drilling fluid is described in Example 1, except that in step (1), 2-cyano-2-propyldodecyl trithiocarbonate is replaced with an equal mass of tetraethylthiuram disulfide, and other conditions are the same as in Example 1.

[0061] Comparative Example 9

[0062] A method for preparing a flocculant for oil-based drilling fluid is described in Example 1, except that in step (1), 2-(thiobenzoylthio)propionic acid of equal mass is used instead of 2-cyano-2-propyldodecyl trithiocarbonate, and other conditions are the same as in Example 1.

[0063] Comparative Example 10

[0064] A method for preparing a flocculant for oil-based drilling fluid is described in Example 1, except that in step (2), an equimolar amount of N-[2-(dimethylamino)ethyl]acrylamide is used instead of dimethylaminoethyl methacrylate, and other conditions are the same as in Example 1.

[0065] Comparative Example 11

[0066] A method for preparing a flocculant for oil-based drilling fluid is described in Example 1, except that 2.5g of lauryl methacrylate is added in step (1), and other conditions are the same as in Example 1.

[0067] Comparative Example 12

[0068] A method for preparing a flocculant for oil-based drilling fluid is described in Example 1, except that 15g of lauryl methacrylate is added in step (1), and other conditions are the same as in Example 1.

[0069] Comparative Example 13

[0070] A method for preparing a flocculant for oil-based drilling fluid is described in Example 2, except that 3.4g of octadecyl methacrylate is added in step (1), and other conditions are the same as in Example 2.

[0071] Comparative Example 14

[0072] A method for preparing a flocculant for oil-based drilling fluid is described in Example 2, except that 20g of octadecyl methacrylate is added in step (1), and other conditions are the same as in Example 2.

[0073] Experimental Example 1

[0074] The following performance evaluations were conducted on the flocculants for oil-based drilling fluids prepared in the examples and comparative examples: flocculation sedimentation evaluation, turbidity evaluation, and impact on drilling fluid performance.

[0075] 1. Evaluation of flocculation and sedimentation

[0076] Flocculation and sedimentation is one of the most intuitive and important ways to evaluate the flocculation effect. In order to intuitively evaluate the flocculation effect of flocculants, a flocculation and sedimentation experiment was used to study the time taken for the flocculant to reach a sedimentation height of 80 mm under different dosages.

[0077] Add 520 mL of white oil to the slurry cup, then add 2.6 g of primary emulsifier, 2.6 g of secondary emulsifier, and 78 g of organic soil. Stir at 11000 rpm for 20 minutes to ensure thorough mixing. This mixture will be used as the base slurry for flocculation and sedimentation evaluation. Add 250 mL of the base slurry to a stoppered measuring vessel, then add 2.5 g of flocculant. Slowly pour the mixture 30 times at a frequency of once every 2 seconds (one forward and one backward movement counts as two). Then let it stand while simultaneously starting a stopwatch and recording the time taken for the sedimentation height to reach 80 mm. The results are shown in Table 1.

[0078] The white oil is No. 5 white oil from Changde Hengtong Petrochemical Additives Co., Ltd.

[0079] The main emulsifier is MO-12, a high-temperature resistant emulsifier for drilling fluids, produced by Quanzhou Lanhai Boda Technology Development Co., Ltd. in Fujian Province.

[0080] The co-emulsifier is CO-12, a high-temperature resistant emulsifier for drilling fluids, produced by Tianjin Xiongguan Technology Development Co., Ltd.

[0081] The organic clay is BP-182, an organic bentonite thickening rheology modifier produced by Zhejiang Huamao New Materials Co., Ltd.

[0082] Table 1. Time taken for the settlement height to reach 80mm

[0083] none 969 Example 1 49 Example 2 55 Example 3 62 Example 4 52 Comparative Example 1 95 Comparative Example 2 94 Comparative Example 3 103 Comparative Example 4 102 Comparative Example 5 156 Comparative Example 6 226 Comparative Example 7 323 Comparative Example 8 217 Comparative Example 9 221 Comparative Example 10 163 Comparative Example 11 103 Comparative Example 12 97 Comparative Example 13 102 Comparative Example 14 96

[0084] Table 1 shows that the flocculant has a positive effect on flocculation and settling properties. For the base slurry without flocculant, the settling height only reached 80 mm after 969 seconds. After adding the flocculant, the flocculation and settling phenomenon was significantly improved, and the settling height reached 80 mm within 70 seconds. In particular, with the flocculant obtained in the example, the time required to reach a settling height of 80 mm was greatly reduced, indicating that the flocculant of the present invention can reduce flocculation time.

[0085] 2. Turbidity evaluation

[0086] A No. 5 white oil solution containing 0.2 wt% soybean lecithin was prepared, and 10 wt% standard soil was added. After being dispersed evenly, flocculants with concentrations of 0.1 wt%, 0.5 wt%, 1.0 wt%, and 1.5 wt% were added sequentially. After shaking evenly and allowing to settle for 15 minutes, the top 10 mL of liquid in each mixture was collected, shaken evenly, and the permeability of the supernatant was tested using a turbidimeter. The results are shown in Table 2.

[0087] Table 2. Permeability of Supernatant with Different Concentrations of Flocculant

[0088]

[0089] The higher the permeability of the supernatant, the better the flocculation effect. Tables 2, 3, 4, and 5 show that the permeability of the supernatant in organic soil without flocculant was 11%. When the flocculant dosage was 0.1%, 0.5%, and 1.0%, the permeability increased, indicating a significant flocculation effect. However, as the flocculant dosage increased, the flocculation effect decreased, and the turbidity test permeability also decreased. This indicates that the flocculant has a significant flocculation effect on organic soil, and the optimal dosage for the prepared organic soil test solution was 1%.

[0090] 3. Evaluation in drilling fluid systems

[0091] The performance of oil-based drilling fluids is determined according to the latest national standard GB / T 16783.2-2012 Field Testing of Drilling Fluids for Petroleum and Natural Gas Industry - Part 2: Oil-based Drilling Fluids.

[0092] The oil-based drilling fluid formula is: 300mL of No. 5 white oil + 3g flocculant + 3g co-emulsifier + 3g organic clay + 6g filtration loss reducer + 60g water + 15g calcium chloride + 14g calcium oxide. Then, barite is added to adjust the drilling fluid density to 1.5g / cm³. 3 .

[0093] The white oil is No. 5 white oil from Changde Hengtong Petrochemical Additives Co., Ltd.

[0094] The co-emulsifier is CO-12, a high-temperature resistant emulsifier for drilling fluids, produced by Tianjin Xiongguan Technology Development Co., Ltd.

[0095] The organic clay is BP-182, an organic bentonite thickening rheology modifier produced by Zhejiang Huamao New Materials Co., Ltd.

[0096] The filtration loss reducer is oil-based drilling fluid filtration loss reducer D2532 produced by Jiujiang Lanzhuo New Material Technology Co., Ltd.

[0097] The calcium chloride was chemically pure and produced by Beijing Chemical Reagent Company.

[0098] The barite is barite powder produced by Dongxiang Mining Company in Hanbin District, Ankang City.

[0099] Table 3. Effects of flocculants on the properties of oil-based drilling fluids

[0100]

[0101] As shown in Table 3, compared with the oil-based drilling fluid without flocculant, the oil-based drilling fluid with 1% flocculant has a higher demulsification voltage, indicating that its emulsion stability is better than that of the oil-based drilling fluid without flocculant; the oil-based drilling fluid with 1% flocculant has higher dynamic shear force and dynamic plasticity ratio, indicating that its rock-carrying capacity is better than that of the oil-based drilling fluid without flocculant.

[0102] 4. Evaluation after centrifugation

[0103] First, the centrifugation speed was set at 2000 rpm and the centrifugation time at 5 min. The densities of the old slurry after centrifugation were compared between those with and without flocculant, under the same speed and time conditions. The initial density of the old slurry was 1.41 g / cm³. 3 The results are shown in Table 4. Old drilling fluid: oil-based drilling fluid that has been circulated for a period of time on an offshore drilling platform in the Shenzhen sea area.

[0104] Table 4 Densities after centrifugation

[0105] none 1.21 Example 1 1.08 Example 2 1.09 Example 3 1.08 Example 4 1.10 Comparative Example 1 1.12 Comparative Example 2 1.11 Comparative Example 3 1.12 Comparative Example 4 1.12 Comparative Example 5 1.19 Comparative Example 6 1.20 Comparative Example 7 1.20 Comparative Example 8 1.20 Comparative Example 9 1.20 Comparative Example 10 1.19 Comparative Example 11 1.14 Comparative Example 12 1.15 Comparative Example 13 1.16 Comparative Example 14 1.17

[0106] Table 4 shows that the density of the old pulp reached 1.21 g / cm³ after centrifugation. 3After adding 1% flocculant and centrifuging at the same speed and time, the drilling fluid density reached a minimum of 1.08 g / cm³. 3 This indicates that the addition of flocculant has a flocculation and sedimentation effect on the inferior solid phase in the old oil-based drilling fluid, and it can be separated from the old fluid through centrifugation.

[0107] Flocculants can adsorb micro- and nano-sized inferior solid phases to improve the performance of oil-based drilling fluids because flocculant molecules, after dissolving in the drilling fluid, adsorb onto the surface of particles and, through continuous collisions, become entangled to form larger flocs. Once these flocs reach a certain size, they settle and are then separated from the drilling fluid using solids control equipment. The flocculation mechanism of flocculants mainly includes electrostatic neutralization, adsorption bridging, and netting / sweeping. In actual flocculant flocculation, these mechanisms usually work synergistically to complete the flocculation process.

[0108] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing a flocculant for oil-based drilling fluids, characterized in that, The steps include the following: The lipophilic monomer A is added to the solvent and heated to the reaction temperature. Initiator a and chain transfer agent are added to obtain mixture I. The lipophilic monomer B and the hydrophilic monomer are mixed evenly to obtain mixture II. The obtained mixture II is added to mixture I, and then initiator b is added to carry out the reaction to obtain a flocculant for oil-based drilling fluid. The lipophilic monomer A is one or more of lauryl methacrylate, lauryl acrylate, and octadecyl methacrylate; the chain transfer agent is one or more of 2-cyano-2-propyldodecyl trithiocarbonate and 4-cyano-4-[(dodecylthioalkylthiocarbonyl)thioalkyl]valerate; the lipophilic monomer B is methyl methacrylate and / or vinyltrimethoxysilane, and the molar ratio of the lipophilic monomer B to the lipophilic monomer A is 0.8-1.2:1; the hydrophilic monomer is one or more of dimethylaminoethyl methacrylate, acrylamide, acrylic acid, and methacrylic acid, and the molar ratio of the hydrophilic monomer to the lipophilic monomer A is 0.2-0.4:

1.

2. The method for preparing the flocculant for oil-based drilling fluid according to claim 1, characterized in that, The solvent is one or more of white oil, dimethyl sulfoxide, N,N-dimethylformamide, and toluene, wherein the white oil is No. 3 white oil, No. 5 white oil, No. 7 white oil, or No. 10 white oil; the mass ratio of the solvent to the lipophilic monomer A is 3-6:

1.

3. The method for preparing the flocculant for oil-based drilling fluid according to claim 1, characterized in that, The initiator a is one or a combination of two or more of ammonium persulfate, potassium persulfate, benzoyl peroxide, and azobisisobutyronitrile; the mass of the initiator a is 0.1-1% of the total mass of the lipophilic monomer A, lipophilic monomer B, and hydrophilic monomer.

4. The method for preparing the flocculant for oil-based drilling fluid according to claim 1, characterized in that, The mass of the chain transfer agent is 0.3-8% of the total mass of the lipophilic monomer A, lipophilic monomer B, and hydrophilic monomer.

5. The method for preparing the flocculant for oil-based drilling fluid according to claim 1, characterized in that, The molar ratio of the lipophilic monomer B to the lipophilic monomer A is 1:

1.

6. The method for preparing the flocculant for oil-based drilling fluid according to claim 1, characterized in that, The molar ratio of the hydrophilic monomer to the lipophilic monomer A is 1:

3.

7. The method for preparing the flocculant for oil-based drilling fluid according to claim 1, characterized in that, The mixture II is added dropwise to the mixture I over a period of 1-3 hours at a temperature of 80-100°C. The type and amount of the initiator b are the same as those of the initiator a.

8. The method for preparing the flocculant for oil-based drilling fluid according to claim 1, characterized in that, The reaction temperature is 80-100℃; the reaction time is 3-5 hours.

9. A flocculant for oil-based drilling fluids, characterized in that, It is prepared by the preparation method described in any one of claims 1-8.

10. The application of the flocculant for oil-based drilling fluid according to claim 9 in oil-based drilling fluid, characterized in that, Used for adsorbing nano- and micro-sized inferior solid phases.

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