Semi-interpenetrating network polymer blocking agent for drilling fluid as well as preparation method and application of semi-interpenetrating network polymer blocking agent

Abstract

The invention provides a semi-interpenetrating network polymer plugging agent for drilling fluid and a preparation method and application thereof, and the preparation method comprises the following steps: 1) mixing an oil-soluble monomer A and an oil-soluble polymer B, and completely dissolving the oil-soluble polymer B to obtain an oil phase; 2) mixing an emulsifier A, an emulsifier B, a water-soluble organic monomer C and water to obtain a water phase; 3) mixing 65-70% of the oil phase and the water phase, and emulsifying to obtain an emulsion reaction mixed solution; (4) carrying out heat-preservation polymerization on the emulsion reaction mixed solution and a section of initiator to obtain a polymerized emulsion; and 5) continuously carrying out heat preservation polymerization on the polymerized emulsion, 30-35% of the remaining oil phase, a cross-linking agent and a second-stage initiator to obtain the semi-interpenetrating network polymer plugging agent. The plugging agent has temperature resistance, elastic deformability and cohesiveness, the temperature resistance can reach 180 DEG C, the plugging agent is good in compatibility with oil-based drilling fluid and water-based drilling fluid, the filtration loss reduction and plugging effects are obvious, and the plugging agent can be used for plugging high-temperature strata; and the adhesive wall protection effect is also achieved.

Description

Technical Field

[0001] This invention belongs to the technical field of drilling fluid treatment agents in oil drilling engineering, and particularly relates to a semi-interpenetrating network polymer plugging agent for drilling fluid, its preparation method and application. Background Technology

[0002] In deep and ultra-deep well drilling, problems such as low-pressure leakage, unstable wellbore collapse, and wellbore instability due to stress are frequent. The risks of well leakage and stuck pipe are high, and the handling is difficult. Both water-based and oil-based drilling fluids have experienced these issues. For example, in the Hongxing block, the Wujiaping Formation has well-developed fractures, with both collapse and leakage occurring. In the Zigong and Weiyuan blocks, the Longmaxi Formation mudstone and shale formations, and the Dongyuemiao Formation of Well Xingye 7, the stress release is severe due to fracturing. The Shunbei Santamu Formation limestone and the Maokou Formation in the Southwest work area are also geologically fractured. When drilling encounters formations with well-developed micro- and nano-porous structures, drilling fluid loss and wellbore instability / collapse are likely to occur. Micro- and nano-sealing materials need to be added to form a tight sealing layer, reduce drilling fluid intrusion, and improve the formation's pressure-bearing capacity to prevent "collapse due to leakage." Simultaneously, to further improve the anti-collapse effect, the material needs to have a certain degree of adhesion to act as a bonding and protective layer for the wellbore.

[0003] Commonly used polymer plugging materials cannot simultaneously achieve optimal performance in terms of elastic deformation, bonding, and temperature resistance, thus failing to simultaneously satisfy the requirements for high-temperature plugging, leakage prevention, and wellbore stability. Therefore, it is necessary to develop a micro / nano plugging material with a special structure that combines deformability, bonding, and high-temperature resistance to improve the density, pressure resistance, and wall-protecting properties of the plugging layer, thereby effectively sealing micro / nano pores and enhancing wellbore stability. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a semi-interpenetrating network polymer plugging agent for drilling fluid, its preparation method and application. The plugging agent prepared by this method has a temperature resistance of up to 180°C, good compatibility with both oil-based and water-based drilling fluids, significant filtration loss reduction and plugging effect, and can be used for plugging high-temperature formations; it also has a bonding and wall protection effect.

[0005] This invention provides a method for preparing a semi-interpenetrating network polymer plugging agent for drilling fluids, comprising the following steps:

[0006] 1) Mix oil-soluble monomer A and oil-soluble polymer B. The oil-soluble polymer B is completely dissolved to obtain the oil phase;

[0007] 2) Mix emulsifier A, emulsifier B, water-soluble organic monomer C, and water to obtain an aqueous phase;

[0008] 3) Mix 65%–70% of the oil phase and the water phase, emulsify, and obtain an emulsion reaction mixture;

[0009] 4) The emulsion mixture and a first-stage initiator are subjected to heat treatment and polymerization to obtain the polymerized emulsion;

[0010] 5) The polymerized emulsion, along with 30%–35% of the remaining oil phase, crosslinking agent, and second-stage initiator, are further polymerized at a constant temperature to obtain a semi-interpenetrating network polymer plugging agent.

[0011] This invention involves mixing an oil-soluble monomer A and an oil-soluble polymer B, wherein the oil-soluble polymer B is completely dissolved to obtain an oil phase. The oil-soluble monomer A in this invention is selected from one or more of butyl methacrylate, methyl acrylate, vinyl acetate, butyl acrylate, and isooctyl acrylate. Preferably, the oil-soluble monomer A is washed three times with a 20% NaOH aqueous solution before use. The oil-soluble polymer B in this invention is selected from one or more of polystyrene, styrene-acrylate copolymers, polymethyl methacrylate, acrylate homopolymers, acrylate copolymers, and styrene-butadiene rubber.

[0012] In this invention, the cleaned oil-soluble monomer A is added to a three-necked flask containing a stirring rod, and the oil-soluble polymer B is added. The mixture is stirred until fully dissolved to obtain an oil phase.

[0013] This invention involves mixing emulsifier A, emulsifier B, water-soluble organic monomer C, and water to obtain an aqueous phase. Preferably, emulsifier A and emulsifier B are added sequentially to water, stirred until homogeneous, and then water-soluble monomer C is added. The emulsifier and water-soluble monomer are completely mixed and dissolved to obtain the aqueous phase. The pH value of the aqueous phase in this invention is 7.5–8.5.

[0014] 65-70% of the oil phase and the aqueous phase are mixed and emulsified to obtain an emulsified reaction mixture. In this invention, emulsification is performed under stirring at a speed of 580-620 rpm. The emulsification time is 28-33 min, preferably 29-31 min; in a specific embodiment, the emulsification time is 30 min.

[0015] This invention involves mixing an initiator with water to obtain an initiator solution. Preferably, the initiator solution is divided into two portions: a primary initiator solution and a secondary initiator solution, for later use. The concentration of the initiator solution is 4%–10%.

[0016] This invention involves thermopolymerizing the emulsion reaction mixture and a primary initiator solution at a controlled temperature to obtain a polymerized emulsion. In this invention, the primary initiator solution comprises 60%–80% of the total mass of the initiator solution. The thermopolymerization is carried out under stirring conditions at a speed of 430–480 rpm. The primary initiator solution is added dropwise to the emulsion reaction mixture.

[0017] After obtaining the polymerized emulsion, the present invention further polymerizes the polymerized emulsion with 20% to 40% of the remaining oil phase, crosslinking agent, and second-stage initiator solution at a constant temperature to obtain a semi-interpenetrating network polymer plugging agent.

[0018] The crosslinking agent used in this invention is selected from one or more of N,N'-methylenebisacrylamide, polyvinyl alcohol diacrylate, 1,3-butadiene, and 1,4-divinylbenzene. Preferably, 20%–40% of the remaining oil phase, crosslinking agent, and second-stage initiator solution are added dropwise to the post-polymerization emulsion over a period of 3–6.5 hours.

[0019] In this invention, the temperature for both the heat-preserving polymerization and the continued heat-preserving polymerization is 70–80°C. The heat-preserving polymerization time is 50–70 min; the continued heat-preserving polymerization time is 110–130 min.

[0020] The present invention is based on the total amount of oil-soluble monomer A, oil-soluble polymer B and water-soluble monomer C as 100%, wherein the water-soluble monomer C accounts for 10% to 20%, the oil-soluble monomer A accounts for 60% to 80%, and the oil-soluble polymer B accounts for 10% to 30%.

[0021] Based on the total mass of oil-soluble monomer A, oil-soluble polymer B, and water-soluble monomer C, the present invention specifies that the amount of emulsifier A added is 2% to 3%; the amount of emulsifier B added is 2% to 3%; the amount of crosslinking agent added is 0.1% to 0.5%; and the amount of initiator added is 0.5% to 2.0%.

[0022] The semi-interpenetrating polymer blocker prepared by the method provided in this invention has a micro-nano particle size, ranging from 0.05 to 50 μm, and a D... 50 ≤15μm.

[0023] The oil-soluble monomer A and the oil-soluble polymer B used in this invention have different glass transition temperatures. Uncrosslinked oil-soluble monomer A and oil-soluble polymer B exhibit adhesiveness at different temperatures, adapting to a wide range of lost circulation temperatures. The crosslinked oil-soluble polymer from oil-soluble monomer A provides viscoelasticity and has a deformable filling effect. Through interpenetration between the two polymers, the adhesiveness and elastic deformation of the polymers can be further controlled. Through the combined action of oil-soluble monomer A and water-soluble monomer C, the plugging agent exhibits good compatibility with both oil-based and water-based drilling fluids. Through the elastic deformation and adhesiveness of the plugging agent, a strong and dense adhesive plugging layer is formed, effectively preventing lost circulation and achieving the purpose of sealing and protecting the wellbore wall.

[0024] This invention provides a semi-interpenetrating network polymer plugging agent for drilling fluids, which is prepared by the preparation method described in the above technical solution.

[0025] This invention provides an application of a semi-interpenetrating network polymer plugging agent for drilling fluid prepared by the above-described method in oil-based drilling fluids, water-based drilling fluids, or high-temperature formations above 180°C.

[0026] This invention provides a method for preparing a semi-interpenetrating polymer network plugging agent for drilling fluids, comprising the following steps: 1) mixing oil-soluble monomer A and oil-soluble polymer B, wherein the oil-soluble polymer B is completely dissolved to obtain an oil phase; 2) mixing emulsifier A, emulsifier B, water-soluble organic monomer C, and water to obtain an aqueous phase; 3) mixing 65-70% of the oil phase and the aqueous phase, and emulsifying to obtain an emulsion reaction mixture; 4) polymerizing the emulsion reaction mixture with a first-stage initiator at a controlled temperature to obtain a polymerized emulsion; 5) further polymerizing the polymerized emulsion with 30-35% of the remaining oil phase, a crosslinking agent, and a second-stage initiator at a controlled temperature to obtain a semi-interpenetrating polymer network plugging agent. The plugging agent prepared by this method has a temperature resistance of up to 180℃, good compatibility with both oil-based and water-based drilling fluids, significant filtration loss reduction and plugging effects, and can be used for plugging high-temperature formations; it also has a bonding and wall-protecting effect. Attached Figure Description

[0027] Figure 1 This is a particle size distribution diagram of the semi-interpenetrating network polymer plugging agent for drilling fluid prepared in Example 1 of the present invention;

[0028] Figure 2 This is a schematic diagram of the structure of the semi-interpenetrating network polymer plugging agent for drilling fluid prepared in Example 1 of the present invention;

[0029] Figure 3 The infrared spectrum of the semi-interpenetrating network polymer plugging agent for drilling fluid in Example 1 of this invention;

[0030] Figure 4 This is a morphology diagram of the API medium-pressure filter cake of the plugging agent prepared in Example 1 of the present invention;

[0031] Figure 5 This is a graph showing the API medium-pressure filter cake wettability test of the sealing agent prepared in Example 1 of the present invention. Detailed Implementation

[0032] To further illustrate the present invention, the following detailed description, in conjunction with embodiments, provides a semi-interpenetrating network polymer plugging agent for drilling fluids, its preparation method, and its application. However, these descriptions should not be construed as limiting the scope of protection of the present invention.

[0033] Example 1

[0034] The preparation method of the semi-interpenetrating network polymer plugging agent for drilling fluid of the present invention includes the following steps:

[0035] Add 20g of butyl methacrylate to a beaker, wash it three times with 20% NaOH aqueous solution, transfer it to a four-necked flask, add 5g of polystyrene, dissolve it completely, and obtain the oil phase;

[0036] Dissolve 0.24g of initiator (ammonium persulfate) in 6g of deionized water to make two initiator solutions (2 / 3 and 1 / 3 respectively) for later use.

[0037] In a 250 mL four-necked flask equipped with a condenser, stirrer, and N2 gas channel, 65 g of water, 0.7 g of sodium alkylbenzene sulfonate, 0.7 g of polyoxyethylene phenol ether, and 4 g of acrylamide were added and dissolved. Two-thirds of the oil phase was added, and the mixture was stirred at 600 rpm for 30 min under N2 atmosphere. The temperature was then raised from room temperature to 70 °C, and the stirring speed was reduced to 450 rpm. A first-stage initiator solution was slowly added dropwise, and the mixture was kept at this temperature for 1 h to polymerize. The remaining one-third of the oil phase, 0.04 g of 1,4-divinylbenzene, and the second-stage initiator solution were then slowly added dropwise over a period of 5.5 h. The mixture was kept at this temperature and stirred for another 2 h, then heating was stopped, and the mixture was cooled to obtain a semi-interpenetrating network polymer plugging agent for drilling fluid.

[0038] Figure 1 The particle size distribution diagram is shown for the semi-interpenetrating network polymer plugging agent for drilling fluid prepared in Example 1, with a D50 of 8.520 μm.

[0039] Figure 2 Polymer A is formed by the polymerization of oil-soluble monomer A, polymer B is formed by the polymerization of oil-soluble polymer B, and polymer C is formed by the polymerization of water-soluble monomer C; the structural formula of polymer A is as follows:

[0040]

[0041] The structural formula of polymer B is as follows:

[0042]

[0043] The structural formula of polymer C is as follows:

[0044]

[0045] Example 2:

[0046] The preparation method of the semi-interpenetrating network polymer plugging agent for drilling fluid of the present invention includes the following steps:

[0047] Add 20g of butyl acrylate to a beaker, wash it three times with 20% NaOH aqueous solution, transfer it to a four-necked flask, add 5g of polystyrene, dissolve it completely to obtain the oil phase;

[0048] Dissolve 0.24g of initiator (ammonium persulfate) in 6g of deionized water to make two initiator solutions (2 / 3 and 1 / 3 respectively) for later use.

[0049] In a 250 mL four-necked flask equipped with a condenser, stirrer, and N2 gas channel, 64 g of water, 0.8 g of sodium alkylbenzene sulfonate, 0.8 g of polyoxyethylene phenol ether, and 5 g of acrylic acid were added and dissolved. The pH was adjusted to 7.5 with 20% NaOH aqueous solution, and 2 / 3 of the oil phase was added. The mixture was stirred at 600 rpm for 30 min under N2 atmosphere, then the temperature was raised from room temperature to 70°C, and the stirring speed was reduced to 450 rpm. A first-stage initiator solution was slowly added dropwise, and polymerization was maintained at this temperature for 1 h. The remaining 1 / 3 of the oil phase, 0.04 g of 1,4-divinylbenzene, and the second-stage initiator solution were slowly added dropwise over a period of 6 h. After stirring at this temperature for another 2 h, heating was stopped, and the mixture was cooled to obtain a semi-interpenetrating network polymer plugging agent for drilling fluid.

[0050] Example 3:

[0051] The preparation method of the semi-interpenetrating network polymer plugging agent for drilling fluid of the present invention includes the following steps:

[0052] Add 20g of butyl methacrylate to a beaker, wash it three times with 20% NaOH aqueous solution, transfer it to a four-necked flask, add 5g of polystyrene, dissolve it completely, and obtain the oil phase;

[0053] Dissolve 0.24g of initiator (ammonium persulfate) in 6g of deionized water to make two initiator solutions (2 / 3 and 1 / 3 respectively) for later use.

[0054] In a 250 mL four-necked flask equipped with a condenser, stirrer, and N2 gas channel, 65 g of water, 0.8 g of sodium alkylbenzene sulfonate, 0.8 g of polyoxyethylene phenol ether, and 4 g of AMPS were added and dissolved. The pH was adjusted to 7.5 with 20% NaOH aqueous solution, and 2 / 3 of the oil phase was added. The mixture was stirred at 600 rpm for 30 min under N2 atmosphere, then the temperature was raised from room temperature to 70 °C, and the stirring speed was reduced to 450 rpm. A first-stage initiator solution was slowly added dropwise, and polymerization was maintained at this temperature for 1 h. The remaining 1 / 3 of the oil phase, 0.04 g of 1,4-divinylbenzene, and the second-stage initiator solution were slowly added dropwise over a period of 6 h. After stirring at this temperature for another 2 h, heating was stopped, and the mixture was cooled to obtain a semi-interpenetrating network polymer plugging agent for drilling fluid.

[0055] Comparative Example 1:

[0056] Add 25g of butyl methacrylate to a beaker, wash three times with 20% NaOH aqueous solution, and transfer to a four-necked flask to obtain the oil phase.

[0057] Dissolve 0.24g of initiator (ammonium persulfate) in 6g of deionized water to make two initiator solutions (2 / 3 and 1 / 3 respectively) for later use.

[0058] In a 250 mL four-necked flask equipped with a condenser, stirrer, and N2 gas channel, 64 g of water, 1 g of sodium alkylbenzene sulfonate, 1 g of polyoxyethylene alkyl ether, and 5 g of acrylic acid were added and dissolved. The pH was adjusted to 7.5 with 20% NaOH aqueous solution, and 2 / 3 of the oil phase was added. The mixture was stirred at 600 rpm for 30 min under N2 atmosphere, then the temperature was raised from room temperature to 70 °C, and the stirring speed was reduced to 450 rpm. A first-stage initiator solution was slowly added dropwise, and the mixture was kept at this temperature for 1 h. The remaining 1 / 3 of the oil phase and the second-stage initiator solution were then slowly added dropwise over a period of 6 h. The mixture was kept at this temperature and stirred for another 2 h, then heating was stopped, and the mixture was cooled to obtain the product, which was Comparative Example 1.

[0059] Comparative Example 2:

[0060] Add 5g of styrene and 20g of butyl acrylate to a beaker, wash three times with 20% NaOH aqueous solution, and transfer to a four-necked flask to obtain the oil phase.

[0061] Dissolve 0.24g of initiator (ammonium persulfate) in 6g of deionized water to make two initiator solutions (2 / 3 and 1 / 3 respectively) for later use.

[0062] In a 250 mL four-necked flask equipped with a condenser, stirrer, and N2 gas channel, 1 g of sodium alkylbenzene sulfonate, 1 g of polyoxyethylene alkyl ether, and 5 g of acrylic acid were added and dissolved. The pH was adjusted to 7.5 with 20% NaOH aqueous solution, and 2 / 3 of the oil phase was added. The mixture was stirred at 600 rpm for 30 min under N2 atmosphere, then the temperature was raised from room temperature to 70°C, and the stirring speed was reduced to 450 rpm. A first-stage initiator solution was slowly added dropwise, and polymerization was maintained at this temperature for 1 h. The remaining 1 / 3 of the oil phase and the second-stage initiator solution were slowly added dropwise over a period of 6 h. The mixture was then stirred at this temperature for another 2 h, and then heating was stopped. The mixture was cooled to obtain the product, which is Comparative Example 2.

[0063] The products prepared according to the embodiments of the present invention were evaluated, and the results are as follows:

[0064] (1) Particle size analysis

[0065] The semi-interpenetrating network polymer plugging agent obtained in the examples was measured using a laser particle size analyzer, and the results are shown in Table 1. Table 1 shows that the semi-interpenetrating network polymer plugging agent for drilling fluid obtained in this invention has a particle size in the micro-nano range, making it suitable for use in drilling plugging and for sealing microfractures and pores.

[0066] Table 1. Particle size D50 of the products from the examples

[0067] Serial Number <![CDATA[Particle size D 50 , μm]]> Example 1 8.52 Example 2 8.46 Example 3 7.23 Comparative Example 1 3.15 Comparative Example 2 3.73

[0068] (2) Blocking performance evaluation

[0069] ① Oil-based drilling fluid

[0070] The drilling fluid obtained from the reaction in the example was added to an oil-based drilling fluid using a semi-interpenetrating polymer network plugging agent. After aging at 180°C for 16 hours, the rheological properties of the drilling fluid were measured using a six-speed rotational viscometer at 65°C. The high-temperature, high-pressure filtration loss of the drilling fluid was also measured, and the results are shown in Table 2. Table 2 shows that adding the product of this invention to the oil-based drilling fluid did not significantly change the rheological properties of the drilling fluid system; however, the high-temperature, high-pressure filtration loss decreased. This indicates that the semi-interpenetrating polymer network plugging agent has good compatibility with oil-based drilling fluids and exhibits good filtration loss reduction and plugging performance.

[0071] Table 2 Evaluation of Product Dosage and Drilling Fluid Compatibility in Examples

[0072] Semi-interpenetrating network polymer plugging agent / % PV / mPa·s YP / Pa <![CDATA[FL HTHP / mL]]> Oil-based drilling fluid 50 8 16.8 Oil-based drilling fluid + 1% of the product from Example 1 51 9 13.2 Oil-based drilling fluid + 2% of the product from Example 1 53 11 11.0 Oil-based drilling fluid + 3% of the product from Example 1 55 12 9.4 Oil-based drilling fluid + 2% of the product from Example 2 52 10 11.4 Oil-based drilling fluid + 2% of the product from Example 3 51 10 11.8 Oil-based drilling fluid + 2% of Comparative Example 1 product 51 8 15.8 Oil-based drilling fluid + 2% of Comparative Example 2 product 53 7 15.2

[0073] Note: The oil-based drilling fluid formulation is diesel oil + 20% calcium chloride aqueous solution (0 # Diesel fuel: 20% calcium chloride aqueous solution (80:20) + 4% emulsifier + 2% calcium oxide + 2% organic clay + 2% filtration reducer (density 2.0 g / cm³) 3 The emulsifier is a polyamide integrated emulsifier (LEMUL emulsifier for oil-based drilling fluids), Zhongyuan Petroleum Engineering Co., Ltd., patent number ZL.201711027059.X; organic soil, Zhejiang Fenghong New Material Co., Ltd. (BS-1C); filtration loss reducer is an oxidized asphalt filtration loss reducer, Shandong Deshunyuan Petroleum Technology Co., Ltd. (OFC).

[0074] ② Water-based drilling fluid

[0075] The drilling fluid obtained from the reaction in the example was added to a 4% bentonite-based slurry (prepared by adding 0.8g Na2CO3 and 16g bentonite to 400mL of clean water, stirring thoroughly, and curing at room temperature for 24h) with a semi-interpenetrating network polymer plugging agent. The slurry was aged at 180℃ for 16h. Rheological properties were measured at room temperature using a six-speed rotational viscometer, and API filtration loss was measured using an API medium-pressure fluid loss meter. High-temperature, high-pressure filtration loss was measured at 150℃. The results are shown in Table 3. Table 3 shows that the product of this invention can effectively reduce drilling fluid filtration loss in water-based drilling fluids.

[0076] Table 3 Evaluation of Product Dosage and Drilling Fluid Compatibility in Examples

[0077]

[0078]

[0079] The experimental results show that the characteristics of this product include: temperature resistance up to 180℃, good compatibility with both oil-based and water-based drilling fluids, significant reduction in filtration loss and plugging effect, and suitability for plugging high-temperature formations.

[0080] (2) Adhesion and wall protection

[0081] The drilling fluid obtained from the reaction in Example 1 (5%) was added to clean water with a semi-interpenetrating network polymer plugging agent. The pressure filtration loss in the API was measured at room temperature. After the filter cake was dried at room temperature, its state was observed under an electron scanning microscope (see...). Figure 4 Add water to the filter cake and observe its wettability (see...). Figure 5 The medium-pressure filter cake surface has a dense film and some polymer microparticles, indicating that the material has the functions of particle blocking and wall bonding; the evaluation of water wettability shows that the hydrophilicity of the film is reduced, which can delay the water wetting of the filter cake.

[0082] As can be seen from the above embodiments, the present invention provides a method for preparing a semi-interpenetrating network polymer plugging agent for drilling fluids, comprising the following steps: 1) mixing oil-soluble monomer A and oil-soluble polymer B, wherein the oil-soluble polymer B is completely dissolved to obtain an oil phase; 2) mixing emulsifier A, emulsifier B, water-soluble organic monomer C, and water to obtain an aqueous phase; 3) mixing 65-70% of the oil phase and the aqueous phase, emulsifying to obtain an emulsion reaction mixture; 4) polymerizing the emulsion reaction mixture with a first-stage initiator under heat preservation to obtain a polymerized emulsion; 5) polymerizing the polymerized emulsion with 30-35% of the remaining oil phase, crosslinking agent, and a second-stage initiator under heat preservation to obtain a semi-interpenetrating network polymer plugging agent. The plugging agent prepared by this method has a temperature resistance of up to 180℃, good compatibility with both oil-based and water-based drilling fluids, significant filtration loss reduction and plugging effects, and can be used for plugging high-temperature formations; it also has a bonding and wall-protecting effect.

[0083] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a semi-interpenetrating network polymer plugging agent for drilling fluids, comprising the following steps: 1) Mix oil-soluble monomer A and oil-soluble polymer B. The oil-soluble polymer B is completely dissolved to obtain the oil phase; 2) Mix emulsifier A, emulsifier B, water-soluble organic monomer C, and water to obtain an aqueous phase; 3) Mix 65%–70% of the oil phase and the water phase, emulsify, and obtain an emulsion reaction mixture; 4) The emulsion mixture and a first-stage initiator are subjected to heat treatment and polymerization to obtain the polymerized emulsion; 5) The polymerized emulsion and 30%–35% of the remaining oil phase, crosslinking agent, and second-stage initiator solution are further polymerized at a constant temperature to obtain a semi-interpenetrating network polymer plugging agent.

2. The preparation method according to claim 1, characterized in that, The oil-soluble monomer A mentioned in step 1) is selected from one or more of butyl methacrylate, methyl acrylate, vinyl acetate, butyl acrylate, and isooctyl acrylate; The oil-soluble polymer B is selected from one or more of polystyrene, styrene-acrylate copolymers, polymethyl methacrylate, acrylate homopolymers, acrylate copolymers, and styrene-butadiene rubber.

3. The preparation method according to claim 1, characterized in that, In step 2), the emulsifier A is selected from one or more of sodium alkyl sulfate, sodium alkylbenzene sulfonate, sodium dialkyl-2-sulfosuccinate, and sodium alkylallyloxy polyoxyethylene phosphate. The emulsifier B is selected from one or more of polyoxyethylene alkyl ether, polyoxyethylene phenolic ether, polyoxyethylene sorbitan ether stearate, and polyoxyethylene sorbitan monooleate. The water-soluble organic monomer C is selected from one or more of methacrylic acid, acrylamide, acrylic acid, and AMPS.

4. The preparation method according to claim 1, characterized in that, The crosslinking agent is selected from one or more of N,N'-methylenebisacrylamide, polyvinyl alcohol diacrylate, 1,3-butadiene, and 1,4-divinylbenzene.

5. The preparation method according to claim 1, characterized in that, The first-stage initiator and the second-stage initiator are independently selected from one or more of sodium persulfate, potassium persulfate, and ammonium persulfate.

6. The preparation method according to claim 1, characterized in that, With the total amount of oil-soluble monomer A, oil-soluble polymer B and water-soluble monomer C being 100%, the water-soluble monomer C accounts for 10% to 20%, the oil-soluble monomer A accounts for 60% to 80%, and the oil-soluble polymer B accounts for 10% to 30%. Based on the total mass of oil-soluble monomer A, oil-soluble polymer B, and water-soluble monomer C, the amount of emulsifier A added is 2% to 3%; the amount of emulsifier B added is 2% to 3%; the amount of crosslinking agent added is 0.1% to 0.5%; and the amount of initiator added is 0.5% to 2.0%.

7. The preparation method according to claim 1, characterized in that, The temperature for heat preservation polymerization is 70–80℃; The pH of the aqueous phase was adjusted to 7.5–8.5 using a 20% NaOH aqueous solution.

8. The preparation method according to claim 1, characterized in that, The particle size of the semi-interpenetrating network polymer plugging agent is 0.05–50 μm, D 50 ≤15μm.

9. A semi-interpenetrating network polymer plugging agent for drilling fluid, prepared by the preparation method according to any one of claims 1 to 8.

10. The application of a semi-interpenetrating network polymer plugging agent for drilling fluid prepared by the preparation method according to any one of claims 1 to 8 in oil-based drilling fluids, water-based drilling fluids, or high-temperature formations above 180°C.

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