Efficient degradable oil field temporary plugging agent and preparation method thereof

Abstract

The invention belongs to the field of oil field chemicals, and discloses an efficient degradable oil field temporary plugging agent and a preparation method thereof.The temporary plugging agent is based on a novel controllable degradable polymer skeleton, ultrasonic degradation groups and magnetic response nanoparticles are introduced into molecules at the same time, and the temporary plugging agent has a double-response degradation triggering mechanism. The prepared temporary plugging agent has the characteristics of high-initial-stage shear thinning, blockage recovery by standing, controllable degradation and magnetic recovery of residual products, and can realize the plugging effect and accurate control of degradation time in a high-temperature and high-salt environment of an oil field. The polymer skeleton is prepared by copolymerizing a controllable degradable monomer and an ultrasonic cleavable disulfide bond structural monomer; the magnetic response nanoparticles and the adsorption groups are encapsulated in the microcapsules, and can be recycled through an external magnetic field or an adsorption medium after being degraded.

Description

Technical Field

[0001] This invention belongs to the field of oilfield chemicals, specifically relating to a highly efficient biodegradable oilfield temporary plugging agent and its preparation method. Background Technology

[0002] With the widespread development of deep and unconventional oil and gas resources, fracturing and water injection operations in oilfields have placed higher demands on efficient temporary plugging agents. Traditional temporary plugging agents are mainly composed of non-degradable polymers or inorganic particles. Although they can rapidly form a plugging layer in the wellbore and fractures, improving fracturing support and water injection coverage, the residues are difficult to remove, often causing prolonged blockage of reservoir pores and reducing the permeability of subsequent wellbore and reservoir. In addition, unblocking operations require additional chemical reagents or mechanical cleaning, which is costly, inefficient, and prone to secondary pollution of the reservoir and surface environment. To address this issue, some researchers have introduced biodegradable polymer frameworks to achieve self-removal of residues through hydrolysis or biodegradation. However, these biodegradable systems often exhibit instability under high temperature and high salinity conditions, with degradation rates that are either too slow or too fast, making it difficult to meet the balance between dynamic plugging and delayed unblocking. A few other schemes use thermal, pH, or microbial triggering degradation, which can improve degradation controllability under certain conditions, but still suffer from drawbacks such as a single triggering mechanism, low degradation efficiency, and difficulty in recovering degradation products. Currently, no temporary plugging agent has been found that can maintain low viscosity during high-shear pumping, quickly restore plugging performance after standing, and precisely initiate degradation through multiple triggering methods such as ultrasound and magnetic fields, while simultaneously achieving efficient recovery of degradation residues by combining magnetic response or adsorption groups. Summary of the Invention

[0003] To address the shortcomings mentioned in the background art, the present invention aims to provide a highly efficient and biodegradable oilfield temporary plugging agent and its preparation method. The temporary plugging agent has a copolymer polymer with a controllable degradable backbone, and introduces disulfide bonds that can be broken by ultrasound and magnetically responsive nanoparticles into the molecular chain to achieve "shear thinning-static recovery" plugging performance and dual ultrasonic and magnetic field triggered degradation.

[0004] The objective of this invention can be achieved through the following technical solutions: A highly efficient biodegradable oilfield plugging agent comprises the following raw materials in parts by weight: 80-120 parts of a controllable biodegradable polymer backbone, 5-15 parts of magnetically responsive nanoparticles, 5-10 parts of microencapsulation additive, 0.5-2 parts of an environmentally friendly crosslinking agent, 0.2-0.8 parts of an antifoaming agent, 0.5-1.5 parts of a stabilizer, 0.5-1.5 parts of a rheology modifier, and 0.2-0.8 parts of a preservative. More preferably, the preparation steps of the controllable degradable polymer backbone are as follows: S101. Dissolve methacrylate, dithiopropylacrylamide, and hydroxyethyl acrylate in a suitable solvent; S102. Add a free radical initiator to the mixed solution and stir to carry out polymerization, and then crosslink an appropriate amount of crosslinking by adding a crosslinking aid; S103. The controllable degradable polymer backbone is obtained through solvent recovery and neutralization treatment.

[0005] More preferably, the magnetically responsive nanoparticles are synthesized by the following method: FeCl3·6H2O and FeCl2·4H2O are dissolved in water at a molar ratio of 2:1, ammonia is added to precipitate, the mixture is reacted at 80 °C for 1 h, and then coated with 1% chitosan acetate solution and dried.

[0006] More preferably, the microcapsule adjuvant is prepared by: ultrasonically emulsifying polylactic acid and chitosan in an oil / water double emulsion system at a mass ratio of 3:1 for 30-60 min, and then solidifying and shaping.

[0007] More preferably, the dithiopropylacrylamide monomer in step S101 can be broken down within 1 to 2 hours under ultrasonic treatment at 20 kHz and 200 W.

[0008] More preferably, the magnetically responsive nanoparticles can achieve a residual product recovery efficiency of not less than 90% under a magnetic field of 0.3 T.

[0009] More preferably, the controllable degradable polymer skeleton exhibits shear thinning and resting recovery properties under reservoir simulation conditions, with a viscosity decrease of ≥60% under high shear stress and a viscosity recovery of ≥85% after resting.

[0010] A method for preparing a highly efficient and biodegradable oilfield temporary plugging agent includes the following steps: S1. Prepare a controllable degradable polymer backbone according to the steps of claim 2, and dry and grind the obtained polymer into a uniform powder; S2. Disperse the polymer backbone powder in tetrahydrofuran or other organic solvent, stir to dissolve it completely, and form a homogeneous polymer solution; add magnetically responsive nanoparticles and microcapsule additives to the solution in sequence, and mix and react under low-speed shear conditions; S3. Add the biodegradable crosslinking agent dropwise to the mixed solution, keep stirring slowly, and continue the crosslinking reaction at room temperature for a period of time. After the crosslinking is completed, recover the solvent by vacuum distillation or rotary evaporation, and wash the solution multiple times with a neutral buffer solution until the pH of the system is stable at neutral. S4. Add pre-dispersed auxiliary ingredients (including defoamer, stabilizer, rheology modifier and preservative) to the treated product, and homogenize and stir in a high-speed emulsifier until a stable suspension emulsion is formed, to obtain a highly efficient biodegradable oilfield temporary plugging agent with good rheological properties and reservoir adaptability.

[0011] More preferably, the magnetically responsive nanoparticles have a particle size of 20–50 nm.

[0012] The beneficial effects of this invention are: This invention is based on a novel controllable degradable polymer backbone, embedding ultrasonically breakable disulfide bonds into the molecular chain and introducing magnetically responsive nanoparticles. Combined with microencapsulation additives and environmentally friendly crosslinking agents, it achieves a seamless integration of plugging performance and degradation recovery. The polymer backbone exhibits thinning flow under high shear stress and rapidly recovers high viscosity and elasticity after settling, effectively sealing fractures. Ultrasonic or magnetic field-triggered degradation reactions initiate within a predetermined time window, with molecular chain breaking and nanoparticle recovery proceeding synergistically. The degradation product recovery efficiency exceeds 90%, significantly reducing the risk of secondary plugging and minimizing chemical reagent consumption. The microencapsulation structure maintains plugging stability under high temperature and high salinity conditions. The crosslinking agent enhances network strength and also possesses degradability. The system yields high-purity products through solvent recovery and neutralization washing, resulting in a final suspension emulsion with excellent rheological regulation properties and reservoir compatibility. The rational formulation of the additive system ensures sustained defoaming, stabilizing, and anti-corrosion functions. The product demonstrates high efficiency, precision, and environmental friendliness in on-site construction, reservoir protection, and degradation recovery, meeting the comprehensive needs of unconventional reservoir production enhancement and green development. Attached Figure Description

[0013] The invention will now be further described with reference to the accompanying drawings.

[0014] Figure 1 A bar chart comparing the shear thinning and viscosity recovery of temporary plugging agents in oil fields; Figure 2 This is a graph showing the mass change of oilfield temporary plugging agent under ultrasonic degradation. Figure 3 This is a graph showing the change in the retention rate of the temporary plugging agent in the oilfield from 0 to 72 hours. Detailed Implementation

[0015] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. 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.

[0016] Example 1 I. Preparation of Controlled Degradable Polymer Backbone Add 200 mL of tetrahydrofuran to the reaction flask and place it in an 80 ℃ oil bath. Preheat the mixture for 15 min under nitrogen protection by stirring at 200 rpm. Weigh out 45.0 g of methyl methacrylate, 10.0 g of dithiopropylacrylamide, and 15.0 g of hydroxyethyl acrylate, and add them to the reaction flask sequentially. Continue stirring for 10 min to completely dissolve the monomers. Dissolve 0.5 g of ammonium persulfate in 10 mL of deionized water and slowly add it dropwise to the reaction solution. At the same time, add 0.1 mL of N,N,N′,N′-tetramethylethylenediamine. Adjust the stirring speed to 300 rpm and maintain the reaction at 80 ℃ under nitrogen protection for 5 h. Observe the system as it changes from transparent to milky white.

[0017] When the polymerization reaction was in progress for 4 hours, 0.5 g of polyethylene glycol diisocyanate was added and the mixture was stirred and crosslinked for another hour to enhance the network strength. After the reaction was completed, the mixture was cooled to room temperature and transferred to a rotary evaporator. Most of the tetrahydrofuran was recovered under reduced pressure at 50 °C. The concentrated product was poured into 500 mL of ice-cold methanol and stirred for 30 min to precipitate the polymer. The precipitate was washed three times with deionized water until the pH was approximately 7.

[0018] The precipitate was dispersed in 100 mL of 1% chitosan acetate solution and stirred for 1 h to form a thin film on the surface, which enhances the subsequent binding performance with magnetic particles. The precipitate was filtered and rinsed with deionized water. The coated polymer was collected and the wet precipitate was placed in a vacuum drying oven and dried to constant weight. Then, it was ground with a ball mill to obtain a white controllable degradable polymer backbone powder with a particle size of <200 μm.

[0019] II. Preparation of Magnetic-Responsive Nanoparticles The reaction was carried out under nitrogen protection. 10.8 g of ferric chloride hexahydrate and 4.0 g of ferric chloride tetrahydrate were dissolved in 100 mL of deionized water. After stirring at room temperature for 10 min, the mixture was transferred to an oil bath, heated to 80 °C, and stirred at 400 rpm. While maintaining the temperature at 80 °C, 30 mL of 28% ammonia was rapidly injected to initiate the formation of Fe3O4 precipitate. The reaction was continued for 60 min to ensure sufficient nucleation and growth of the particles. After the reaction was complete, the system was allowed to cool naturally to room temperature. The black precipitate was separated by centrifugation at 8000 rpm for 10 min, and the supernatant was discarded to remove unreacted iron salts and byproducts.

[0020] The obtained Fe3O4 precipitate was dispersed in 100 mL of 1% (w / v) chitosan acetate solution and stirred at room temperature for 60 min to allow chitosan molecules to form a stable coating layer on the surface of the nanoparticles. After coating, the nanoparticles were separated again by centrifugation at 8000 rpm for 10 min, the supernatant was discarded, and the precipitate was washed three times with deionized water to remove residual acetate. Finally, the moistened chitosan-coated Fe3O4 particles were placed in a vacuum drying oven and dried at 60 ℃ and 5 mbar for 12 h to obtain uniformly sized, positively charged brown-black magnetically responsive nanoparticles.

[0021] III. Preparation of Highly Efficient Biodegradable Oilfield Temporary Plugging Agent The preparation of the high-efficiency biodegradable oilfield temporary plugging agent includes the following raw materials in parts by weight: 80 parts of controllable biodegradable polymer skeleton, 5 parts of magnetically responsive nanoparticles, 5 parts of microcapsule additive, 0.5 parts of environmentally friendly crosslinking agent, 0.2 parts of defoamer, 0.5 parts of stabilizer, 0.5 parts of rheology modifier, and 0.2 parts of preservative; The preparation steps are as follows: 80 g of controllable degradable polymer backbone is dissolved in 200 mL of tetrahydrofuran and stirred for 10 min to ensure complete dissolution. 5 g of chitosan-coated magnetically responsive nanoparticles and 5 g of microcapsule additive are added to the solution, and stirring is continued at low speed (200 rpm) for 1 h to ensure uniform dispersion. 0.5 g of polyethylene glycol diisocyanate crosslinking agent is added, and stirring continues for 2 h to form a crosslinked three-dimensional structure. The solvent is recovered to 1 / 3 of its original volume using a rotary evaporator to remove excess tetrahydrofuran. 0.2 g of defoamer, 0.5 g of stabilizer, 0.5 g of rheology modifier, and 0.2 g of preservative are added to the recovered product and stirred until homogeneous. The mixture is then transferred to a high-speed emulsifier, set to 8000 rpm, and homogenized for 2 min to obtain a stable, highly efficient, and biodegradable oilfield temporary plugging agent.

[0022] Example 2 The preparation methods for the controllable degradable polymer framework and magnetically responsive nanoparticles are the same as in Example 1.

[0023] The preparation of the high-efficiency biodegradable oilfield temporary plugging agent includes the following raw materials in parts by weight: 120 parts of controllable biodegradable polymer skeleton, 15 parts of magnetically responsive nanoparticles, 10 parts of microcapsule additive, 2 parts of environmentally friendly crosslinking agent, 0.8 parts of defoamer, 1.5 parts of stabilizer, 1.5 parts of rheology modifier, and 0.8 parts of preservative; The preparation steps are as follows: 120 g of controllable degradable polymer backbone is dissolved in 220 mL of tetrahydrofuran and stirred for 10 min until completely dissolved. 15 g of chitosan-coated Fe3O4 nanoparticles and 10 g of microcapsule additive are added to the above solution. The mixture is stirred continuously at low speed (200 rpm) for 1.5 h. 2 g of polyethylene glycol diisocyanate crosslinking agent is added, and stirring is continued for 3 h to carry out the crosslinking reaction. The solvent is recovered to 1 / 3 of its original volume using a rotary evaporator to remove excess tetrahydrofuran. 0.8 g of defoamer, 1.5 g of stabilizer, 1.5 g of rheology modifier, and 0.8 g of preservative are added to the reaction solution and stirred until homogeneous. The mixture is then transferred to a high-speed emulsifier, set to 8000 rpm, and homogenized for 2 min to obtain a stable, highly efficient, and biodegradable oilfield temporary plugging agent.

[0024] Example 3 The preparation methods for the controllable degradable polymer framework and magnetically responsive nanoparticles are the same as in Example 1.

[0025] The preparation of the high-efficiency biodegradable oilfield temporary plugging agent includes the following raw materials in parts by weight: 100 parts of controllable biodegradable polymer skeleton, 10 parts of magnetically responsive nanoparticles, 8 parts of microcapsule additive, 1 part of environmentally friendly crosslinking agent, 0.5 parts of defoamer, 1 part of stabilizer, 1 part of rheology modifier, and 0.5 parts of preservative. The preparation steps are as follows: 100 g of controllable degradable polymer backbone is dissolved in 200 mL of tetrahydrofuran and stirred for 10 min until completely dissolved. 10 g of chitosan-coated Fe3O4 nanoparticles and 8 g of microcapsule additive are added to the solution, and stirring is continued at low speed (200 rpm) for 2 h. 1 g of polyethylene glycol diisocyanate crosslinking agent is added, and stirring continues for 2 h to carry out the crosslinking reaction. The solvent is recovered to 1 / 3 of its original volume using a rotary evaporator to remove excess tetrahydrofuran. 0.5 g of defoamer, 1.0 g of stabilizer, 1.0 g of rheology modifier, and 0.5 g of preservative are added to the reaction solution and stirred until homogeneous. The mixture is then transferred to a high-speed emulsifier, set to 8000 rpm, and homogenized for 2 min to obtain a stable, highly efficient, and degradable oilfield temporary plugging agent.

[0026] Comparative Example 1 The preparation method of the controllable degradable polymer backbone is the same as in Example 1.

[0027] The preparation of the high-efficiency biodegradable oilfield temporary plugging agent includes the following raw materials in parts by weight: 100 parts of controllable biodegradable polymer backbone, 8 parts of microcapsule additive, 1 part of environmentally friendly crosslinking agent, 0.5 parts of defoamer, 1 part of stabilizer, 1 part of rheology modifier, and 0.5 parts of preservative; The preparation steps are as follows: 100 g of the controllable degradable polymer backbone is dissolved in 200 mL of tetrahydrofuran and stirred for 10 min until completely dissolved. 8 g of microencapsulation agent is added to the solution, and the mixture is stirred at low speed for 2 h. 1 g of polyethylene glycol diisocyanate crosslinking agent is added, and stirring continues for 2 h to carry out the crosslinking reaction. The solvent is recovered to 1 / 3 of its original volume using a rotary evaporator to remove excess tetrahydrofuran. 0.5 g of defoamer, 1.0 g of stabilizer, 1.0 g of rheology modifier, and 0.5 g of preservative are added to the reaction solution and stirred until homogeneous. The mixture is then transferred to a high-speed emulsifier, set to 8000 rpm, and homogenized for 2 min to obtain a stable, highly efficient, and biodegradable oilfield temporary plugging agent.

[0028] Comparative Example 2 The preparation methods for the controllable degradable polymer framework and magnetically responsive nanoparticles are the same as in Example 1.

[0029] The preparation of the high-efficiency biodegradable oilfield temporary plugging agent includes the following raw materials in parts by weight: 100 parts of controllable biodegradable polymer backbone, 10 parts of magnetically responsive nanoparticles, 1 part of environmentally friendly crosslinking agent, 0.5 parts of defoamer, 1 part of stabilizer, 1 part of rheology modifier, and 0.5 parts of preservative; The preparation steps are as follows: 100 g of controllable degradable polymer backbone is dissolved in 200 mL of tetrahydrofuran and stirred for 10 min until completely dissolved. 10 g of chitosan-coated Fe3O4 nanoparticles are added to the above solution, and the mixture is stirred at low speed for 2 h. 1 g of polyethylene glycol diisocyanate crosslinking agent is added, and stirring continues for 2 h to carry out the crosslinking reaction. The solvent is recovered to 1 / 3 of its original volume using a rotary evaporator to remove excess tetrahydrofuran. 0.5 g of defoamer, 1.0 g of stabilizer, 1.0 g of rheology modifier, and 0.5 g of preservative are added to the reaction solution and stirred until homogeneous. The mixture is then transferred to a high-speed emulsifier, set to 8000 rpm, and homogenized for 2 min to obtain a stable, highly efficient, and biodegradable oilfield temporary plugging agent.

[0030] Performance testing 1. Shear thinning and viscosity recovery performance test Take temporary plugging agent samples from Examples 1-3 and Comparative Examples 1-2, ensuring they are thoroughly mixed at the standard temperature (25°C). Place the samples in a rotational viscometer, set an appropriate shear rate range, and record the viscosity changes at different shear rates to simulate oilfield operating conditions. Apply high shear stress by adjusting the shear rate for 2 minutes. Record the viscosity decrease of the samples under these conditions and calculate their shear thinning performance. After removing the shear stress, keep the samples stationary and measure the viscosity recovery after stationary time. Record the percentage of viscosity recovered to the stationary state. The results are shown in Table 1 below.

[0031] Table 1. Results of Shear Thinning and Viscosity Recovery Performance As shown in Table 1, the samples in Examples 1-3 exhibited significantly greater viscosity reductions after the application of high shear stress, especially Example 3, where the viscosity decreased from 1000 cP to 300 cP, demonstrating a shear thinning performance of up to 70%. In contrast, Comparative Example 1 showed a shear thinning performance of only 50%. This indicates that the magnetically responsive nanoparticles and microencapsulation additives used in this invention can significantly improve the flowability of the temporary plugging agent under high shear stress, facilitating pumping and ensuring its smooth passage through pipelines.

[0032] After shear stress removal, Example 3 exhibited a 90% viscosity recovery, indicating that the temporary plugging agent could rapidly restore the sealing effect. Comparative Example 1 showed a poor viscosity recovery of only 70%, demonstrating its inadequacy in restoring the sealing effect. Example 2 also demonstrated a high viscosity recovery capability, further validating the innovation and advantages of the material design in this invention.

[0033] 2. Degradation and recycling efficiency test Different samples were placed in 100 mL of deionized water and added to an ultrasonic cleaner. The ultrasonic degradation treatment was carried out at a frequency of 20 kHz and a power of 200 W for 2 hours. During the treatment, samples were taken periodically to measure the mass change of the samples and calculate the degradation rate.

[0034] After degradation, a magnetic field with a strength of 0.3 T was used to recover the sample, and the recovery efficiency was recorded, i.e., the proportion of degradation products that could be recovered by the magnetic field. The recovery rate was calculated to evaluate the recovery efficiency of the residue, ensuring that the degraded products could be efficiently recovered. The recovered sample was then analyzed using UV-Vis spectroscopy and Fourier transform infrared spectroscopy to determine whether the degradation products were harmless. The results are shown in Table 2 below.

[0035] Table 2 Degradation and recovery efficiency results As shown in Table 2, the degradation rates in Examples 1-3 were significantly higher than those in Comparative Examples 1 and 2, especially in Example 3, which reached 92%. This accelerated degradation effect stems from the controllable degradable polymer framework of this invention, which allows for the design and control of the degradation rate, enabling the temporary plugging agent to degrade rapidly during oilfield operations and precisely adjusting the degradation timing as needed. The introduction of magnetically responsive nanoparticles also influences the polymer structure through an external magnetic field, accelerating the degradation process.

[0036] The magnetic field recovery efficiency of Example 3 was 95%, significantly higher than that of Comparative Example 1 (60%) and Comparative Example 2 (65%). The introduction of magnetically responsive nanoparticles endowed the temporary plugging agent with the ability to be recovered after degradation. Through the action of an external magnetic field, the residue can be efficiently recovered, avoiding environmental pollution and enabling resource recycling. The degradation products of Examples 1-3 were harmless and met environmental protection standards, while Comparative Example 1 and Comparative Example 2 contained incompletely degraded harmful substances, indicating that the degradation mechanism in this invention can ensure that the degradation products are non-toxic and harmless.

[0037] 3. Sealing strength and durability test Under simulated oilfield operating conditions, pressure ranges were set between 5-30 MPa and temperature ranges between 40-120°C, and the plugging strength of the samples was recorded. At the given pressure and temperature, the flow rate was gradually increased to test the plugging effect, and the pressure and flow rate required for the oil to pass through the sample were recorded to evaluate the plugging strength. The test duration was 72 hours, and the plugging stability of the samples under high temperature and high pressure conditions was recorded. During the test, the plugging effect was measured every 24 hours to evaluate the persistence of the temporary plugging agent and the maintenance of the plugging effect. The results are shown in Table 3 below.

[0038] Table 3. Results of sealing strength and durability tests As shown in Table 3, the initial plugging strength of Examples 1-3 is relatively high, especially Example 3, which reaches a plugging strength of 30 MPa, significantly higher than Comparative Examples 1 and 2. This improvement in plugging strength is attributed to the introduction of magnetically responsive nanoparticles. These particles can enhance the cross-linking and structural stability of the polymer through an external magnetic field during oilfield operations, thereby maintaining a stronger plugging effect under high pressure conditions.

[0039] Examples 1-3 all maintained high plugging effectiveness within 72 hours, with Example 3 achieving a plugging effectiveness retention rate of 95%, significantly higher than Comparative Examples 1 and 2. This durability indicates that the polymer framework in these examples can operate stably under high temperature and high pressure environments, and its long-term plugging performance is further optimized through the synergistic effect of controllable degradation and magnetically responsive nanoparticles.

[0040] 4. Thermal stability and environmental adaptability test Take 10 mg of each of the different samples and place them in a thermogravimetric analyzer (TGA). Set the temperature range to 30°C to 500°C and the heating rate to 10°C / min. Test their thermogravimetric properties, record the mass change of the samples at different temperatures, and evaluate their thermal stability. The samples were heated to 200°C, and their specific heat capacity changes at that temperature were tested to evaluate their thermal response characteristics at high temperatures. The samples were placed in a solution containing 5% NaCl and soaked at 120°C for 72 hours. Their mass change and sealing effect were measured periodically to evaluate their stability and adaptability in oilfield operations. The results are shown in Table 4 below.

[0041] Table 4 Thermal stability and environmental adaptability tests As shown in Table 4, the thermal weight loss of Examples 1-3 was significantly lower than that of Comparative Examples 1 and 2. In particular, Example 3 showed a thermal weight loss of only 2%, indicating that the addition of the controllable degradable polymer backbone and the environmentally friendly crosslinking agent effectively enhanced the thermal stability of the polymer, enabling it to withstand the challenges of high temperatures in oilfield operations. In contrast, Comparative Example 1 showed a thermal weight loss as high as 10%, indicating poor thermal stability and an inability to withstand high temperatures for extended periods.

[0042] The specific heat capacity change in Example 3 was 0.18 J / g·°C, significantly higher than that in Comparative Examples 1 and 2. This indicates that the temporary plugging agent of the present invention can better adapt to high-temperature environments and maintain stable thermal response capabilities. The magnetically responsive nanoparticles, through the modulation of an external magnetic field, can further optimize the thermal response characteristics of the polymer. The lower specific heat capacity change in Comparative Example 1 indicates its weaker thermal response capability at high temperatures, leading to unstable plugging effects and failing to meet the high-temperature requirements of oilfield operations.

[0043] After soaking in a high-temperature, high-salt solution for 72 hours, Example 3 showed only a 1% mass change and a 95% retention rate of the sealing effect. In contrast, Comparative Example 1 showed an 8% mass change and a sealing effect retention rate of only 70%, indicating poor degradation and performance retention in high-salt solutions.

[0044] 5. Long-term stability and storage performance testing The temporary plugging agent samples from Examples 1-3 and Comparative Examples 1-2 were placed in sealed containers to ensure they were not contaminated during storage. The samples were then placed at different storage temperatures (room temperature: 25°C, 40°C, 60°C) for 1 month, 3 months, and 6 months, respectively. After the storage period, samples were taken for shear thinning and viscosity recovery tests and plugging effect retention tests. Viscosity changes and plugging effect retention rates were recorded at different storage times and temperatures, and comparative analysis was performed. The results are shown in Table 5 below.

[0045] Table 5. Results of Long-Term Stability and Storage Performance Tests As shown in Table 5, the viscosity recovery and plugging effect retention rates of Examples 1-3 remained stable under different storage temperatures. Example 3, in particular, maintained 85% viscosity recovery and 91% plugging effect retention after 6 months of storage at 60°C. In contrast, Comparative Example 1 showed only 60% viscosity recovery and 60% plugging effect retention after 6 months of storage at 60°C. This indicates that the present invention effectively improves the stability and durability of the temporary plugging agent during long-term storage through the synergistic effect of the controllable degradable polymer backbone and the microencapsulation additive, avoiding the performance degradation seen in traditional temporary plugging agents.

[0046] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0047] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. A highly efficient biodegradable oilfield temporary plugging agent, characterized in that, It contains the following raw materials in parts by weight: 80-120 parts of controllable degradable polymer backbone, 5-15 parts of magnetically responsive nanoparticles, 5-10 parts of microencapsulation additive, 0.5-2 parts of environmentally friendly crosslinking agent, 0.2-0.8 parts of defoamer, 0.5-1.5 parts of stabilizer, 0.5-1.5 parts of rheology modifier, and 0.2-0.8 parts of preservative.

2. The highly efficient biodegradable oilfield plugging agent according to claim 1, characterized in that, The preparation steps of the controllable degradable polymer backbone are as follows: S101. Dissolve methacrylate, dithiopropylacrylamide and hydroxyethyl acrylate in a suitable solvent; S102. Add a free radical initiator to the mixed solution and stir to carry out polymerization, and then crosslink an appropriate amount of crosslinking by adding a crosslinking aid; S103. The controllable degradable polymer backbone is obtained through solvent recovery and neutralization treatment.

3. The high-efficiency biodegradable oilfield temporary plugging agent according to claim 1, characterized in that, The magnetically responsive nanoparticles were synthesized by the following method: FeCl3·6H2O and FeCl2·4H2O were dissolved in water at a molar ratio of 2:1, ammonia was added to precipitate the nanoparticles, and the mixture was reacted at 80°C for 1 h. The nanoparticles were then coated with a 1% chitosan acetate solution and dried.

4. The highly efficient biodegradable oilfield plugging agent according to claim 1, characterized in that, The microcapsule adjuvant is prepared by ultrasonically emulsifying polylactic acid and chitosan in an oil / water double emulsion system at a mass ratio of 3:1 for 30-60 minutes, followed by solidification.

5. The highly efficient biodegradable oilfield plugging agent according to claim 2, characterized in that, The dithiopropylacrylamide monomer in step S101 can be broken within 1 to 2 hours under ultrasonic treatment at 20 kHz and 200 W.

6. The high-efficiency biodegradable oilfield plugging agent according to claim 1, characterized in that, The magnetically responsive nanoparticles can achieve a residual product recovery efficiency of no less than 90% under a 0.3 T magnetic field.

7. The highly efficient biodegradable oilfield plugging agent according to claim 1, characterized in that, The controllable degradable polymer backbone exhibits shear thinning and resting recovery properties under reservoir simulation conditions, with viscosity decreasing by ≥60% under high shear stress and recovering by ≥85% after resting.

8. A method for preparing a highly efficient and biodegradable oilfield temporary plugging agent, wherein the highly efficient and biodegradable oilfield temporary plugging agent is as described in any one of claims 1-7, characterized in that, Includes the following steps: S1. Prepare a controllable degradable polymer backbone according to the steps of claim 2, and dry and grind the obtained polymer into a uniform powder; S2. Disperse the polymer backbone powder in tetrahydrofuran or other organic solvent, stir to dissolve it completely, and form a homogeneous polymer solution; add magnetically responsive nanoparticles and microcapsule additives to the solution in sequence, and mix and react under low-speed shear conditions; S3. Add the biodegradable crosslinking agent dropwise to the mixed solution, keep stirring slowly, and continue the crosslinking reaction at room temperature for a period of time. After the crosslinking is completed, recover the solvent by vacuum distillation or rotary evaporation, and wash the solution multiple times with a neutral buffer solution until the pH of the system is stable at neutral. S4. Add pre-dispersed auxiliary ingredients (including defoamer, stabilizer, rheology modifier and preservative) to the treated product, and homogenize and stir in a high-speed emulsifier until a stable suspension emulsion is formed, to obtain a highly efficient biodegradable oilfield temporary plugging agent with good rheological properties and reservoir adaptability.

9. The preparation method of the high-efficiency biodegradable oilfield temporary plugging agent according to claim 7, characterized in that, The magnetically responsive nanoparticles have a particle size of 20–50 nm.

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