Temporary plugging agent for fracturing and preparation method thereof

Abstract

The invention relates to the technical field of oil-gas field development, and discloses a temporary plugging agent for fracturing and a preparation method thereof, the temporary plugging agent is composed of 25-30 parts by weight of phenyl polyester, 3-5 parts by weight of modified carbon nanotubes, 0.5-2 parts by weight of a coupling agent, and 0.3-1 part by weight of nano calcium carbonate; the preparation method comprises the following steps: mixing the inorganic filler and the coupling agent at a high speed to obtain the surface modified filler, melting the phenyl polyester, carrying out melt blending on the phenyl polyester and the modified filler, cooling, pelletizing, grading and screening the blended material, and compounding to obtain a finished product. The temporary plugging agent is excellent in temperature resistance, high in plugging efficiency, low in damage rate to strata, good in compatibility with fracturing fluid, simple and controllable in preparation process and suitable for temporary plugging steering operation of hydraulic fracturing of unconventional oil and gas reservoirs.

Description

Technical Field

[0001] This invention relates to the field of oil and gas field development technology, specifically to a temporary plugging agent for fracturing and its preparation method. Background Technology

[0002] Hydraulic fracturing is a core production enhancement technology for the efficient development of unconventional oil and gas reservoirs (shale oil, tight gas, coalbed methane, etc.), while temporary plugging and diversion fracturing is a key technology for achieving artificial fracture diversion, expanding fracture network sweep volume, and improving reservoir utilization. Among these technologies, the temporary plugging agent is the core material that determines the effectiveness of temporary plugging and diversion.

[0003] Currently, commonly used fracturing plugging agents still have many technical defects: First, conventional granular plugging agents mostly adopt a single particle size design, which makes them poorly adaptable to artificial and natural fractures of different widths. They are difficult to form a step-by-step plugging structure of "bridging-filling-sealing," and their pressure-bearing capacity is insufficient in high-temperature and high-pressure deep well environments, easily leading to problems such as plugging failure and fracture diversion failure. Second, fibrous plugging agents have poor dispersibility in fracturing fluids and are prone to agglomeration, which can easily cause pump blockage during pumping. Moreover, their plugging efficiency is low when used alone, and they need to be used in combination with granular materials. Third, some plugging agents leave solid residues after degradation, which cause irreversible damage to the reservoir matrix and fracture conductivity, failing to meet environmental protection development requirements.

[0004] Therefore, developing a temporary plugging agent for fracturing that is temperature and salt resistant, has high pressure resistance, low formation damage, good compatibility with fracturing fluids, and simple preparation process has become an urgent technical problem to be solved in this field. Summary of the Invention

[0005] In order to overcome the shortcomings of the prior art, the present invention aims to provide a temporary plugging agent for fracturing and its preparation method, thereby solving the problems of insufficient pressure bearing capacity, poor temperature resistance, and significant formation damage of existing temporary plugging agents.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a temporary plugging agent for fracturing, comprising the following weight components: 25-30 parts by weight of phenyl polyester, 3-5 parts by weight of organosilicon compatibilizer modified carbon nanotubes, 0.5-2 parts by weight of coupling agent, and 0.3-1 parts by weight of nano-calcium carbonate;

[0007] This polyester incorporates a rigid benzene ring structure, exhibiting excellent temperature resistance, mechanical strength, and biodegradability. Under oil and gas reservoir conditions, it can slowly degrade into small-molecule organic matter without solid residue, reducing formation damage. Modified carbon nanotubes are enhanced with organosilicon compatibilizers and combined with nano-calcium carbonate as an inorganic filler. After surface modification with a coupling agent, the compatibility with the phenyl polyester substrate is significantly improved. The modified carbon nanotubes can form a three-dimensional network reinforcement structure, significantly improving the pressure resistance and erosion resistance of the temporary plugging agent. A four-stage particle size classification design (20-40 mesh, 40-60 mesh, 60-80 mesh, and 80-100 mesh) allows for a step-by-step plugging structure in fractures of varying widths: "large-size bridging - medium-size filling - small-size sealing." This design demonstrates strong adaptability and excellent temporary plugging redirection effect.

[0008] The preparation method of the phenyl polyester is as follows:

[0009] S1: Diolefinic diphenyl ether with carbon-carbon double bonds at both ends is prepared by reflux reaction in tetrahydrofuran solvent using 4,4′-dibromodiphenyl ether, undecenol and copper acetylacetonate as raw materials under alkaline conditions.

[0010] S2: In DMF solvent, diene diphenyl ether and mercaptoacetic acid undergo a thiol-alkene click reaction under UV light to introduce a carboxyl group and obtain a dicarboxyl-modified diphenyl ether.

[0011] S3: Under a nitrogen atmosphere, dicarboxylated diphenyl ether and 1,3-butanediol are first subjected to segmental heating and polycondensation, and then terephthalic acid and 1,4-butanediol are added to react and obtain phenyl polyester.

[0012] Furthermore, the method for preparing the phenyl polyester is as follows:

[0013] S1. Add 4,4'-dibromodiphenyl ether, undecenol and copper acetylacetonate to a reactor containing tetrahydrofuran solvent, stir and mix, then add potassium carbonate and 8-hydroxyquinoline, reflux at 80-85℃ for 6-8h, after which distill under reduced pressure, wash and dry to obtain diene diphenyl ether.

[0014] S2. Add diene diphenyl ether and mercaptoacetic acid to N,N-dimethylformamide solvent, stir and mix, and continue to add benzoin dimethyl ether photoinitiator. Irradiate with 365nm ultraviolet light at 20-25℃. After the irradiation is completed, centrifuge, wash and dry to obtain dicarboxylate modified diphenyl ether.

[0015] S3. Dicarboxylated modified diphenyl ether, 1,3-butanediol, and tetrabutyl titanate are placed in a reactor. Under a N2 atmosphere, the temperature is raised to 175-180℃ and reacted until no more water evaporates. The temperature is then raised to 190-200℃ and reacted for 1-1.5 hours. The reaction is then carried out under vacuum at 220-230℃ for 0.5-1 hours. After the reaction is completed, the temperature is lowered to 150-155℃, and terephthalic acid and 1,4-butanediol are added. The temperature is raised to 175-180℃ and reacted until no more water evaporates. The temperature is then raised to 190-200℃ and reacted for 1-1.5 hours. The reaction is then carried out under vacuum at 220-230℃ for 0.5-1 hours to obtain phenyl polyester.

[0016] Further, in S1, the ratio of 4,4'-dibromodiphenyl ether, undecenol, copper acetylacetonate, tetrahydrofuran, potassium carbonate, and 8-hydroxyquinoline is 5-10 mmol: 12-25 mmol: 35-45 mL: 5-6 mmol: 0.1-0.2 mmol.

[0017] Furthermore, the ratio of N,N-dimethylformamide, diene diphenyl ether, mercaptoacetic acid, and benzoin dimethyl ether photoinitiator in S2 is 30-40 mL: 6-10 mmol: 15-25 mmol: 0.04-0.06 mmol.

[0018] Furthermore, in S2, the irradiation time of 365nm ultraviolet light is 2-4 hours.

[0019] Further, in S3, the ratio of dicarboxylated modified diphenyl ether, 1,3-butanediol, tetrabutyl titanate, terephthalic acid, and 1,4-butanediol is 8-10 mmol: 8-12 mmol: 0.05-0.06 mmol: 5-8 mmol: 10-15 mmol.

[0020] Furthermore, the coupling agent is one of KH550 and KH560.

[0021] Furthermore, the preparation method of the fracturing temporary plugging agent is as follows:

[0022] Step 1: Weigh each raw material according to the weight parts, add the organosilicon compatibilizer modified carbon nanotubes, nano calcium carbonate and coupling agent into a high-speed mixer, mix at 80-90℃ and 1500-2000r / min for 10-15min to obtain surface-modified inorganic filler.

[0023] Step 2: Add phenyl polyester to a twin-screw extruder and heat it to a molten state at 210-220℃. Add the surface-modified inorganic filler obtained in Step 1 to the twin-screw extruder and melt-blend at 210-220℃ and a speed of 300-350 r / min for 15-20 min. Extrude to obtain the blend.

[0024] Step 3: Cool the blend to room temperature with circulating water, pelletize it with a pelletizer, and then sieve it through a standard sieve to obtain temporary plugging agent particles with four particle sizes: 20-40 mesh, 40-60 mesh, 60-80 mesh, and 80-100 mesh. Mix these particles in a mass ratio of 1:2:3:2 to obtain the temporary plugging agent for fracturing.

[0025] Compared with the prior art, the present invention has the following beneficial technical effects:

[0026] The phenyl polyester matrix of this invention introduces a rigid benzene ring structure into the molecular chain, endowing the material with excellent high-temperature resistance and structural mechanical strength. It is suitable for the extreme high-temperature and high-pressure formation environments of deep and ultra-deep wells, maintaining stable morphology and mechanical properties even under high-temperature conditions. This fundamentally avoids the problem of temporary plugging failure caused by high-temperature softening and deformation collapse. Simultaneously, this phenyl polyester possesses controllable degradation characteristics, completely degrading into small-molecule organic matter in the formation environment without solid residue. This eliminates the permanent damage to the reservoir matrix and fracture conductivity caused by temporary plugging agents, meeting the industry requirements for green and environmentally friendly development of unconventional oil and gas reservoirs.

[0027] This invention employs a composite inorganic filler system formed by combining carbon nanotubes modified with organosilicon compatibilizers and nano-calcium carbonate. After surface modification treatment with a coupling agent, the interfacial compatibility between the inorganic filler and the polyester matrix is ​​significantly improved, effectively avoiding material performance degradation caused by filler agglomeration. Specifically, the modified carbon nanotubes can form a continuous three-dimensional network reinforcement structure in the polyester matrix, which, combined with the dense filling effect of nano-calcium carbonate, significantly enhances the deformation resistance, erosion resistance, and pressure resistance of the temporary plugging agent. Simultaneously, through a multi-particle-size graded compounding structure design, it can form a step-by-step sealing structure of "bridging-filling-dense" for artificial and natural cracks of different openings, solving the industry pain point of conventional temporary plugging agents having poor crack compatibility and difficulty in forming an effective sealing layer. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely. Obviously, the described embodiments are only some embodiments of the present invention, 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.

[0029] The reagents used in the following specific embodiments are of analytical grade. Additionally:

[0030] KH550: γ-aminopropyltriethoxysilane;

[0031] KH560: γ-glycidoxypropyltrimethoxysilane.

[0032] The preparation of carbon nanotubes modified with organosilicon compatibilizers was based on the paper "Preparation and Performance Study of Long-Chain Organosilicon Compatibilizer Modified Carbon Nanotubes / Silicone Rubber Thermally Conductive Composites" published by Lin Jiazhi et al. in the journal "Organosilicon Materials" (Vol. 39, No. 6, 2025). 2.0 g of CNTs were plasma-treated for 15 min and then dispersed in 100 mL of anhydrous ethanol. The dispersion was ultrasonically stirred for 0.5 h under ice-water bath conditions. The CNT dispersion was then transferred to a 250 mL reaction flask, and 50 mL of an ethanol dispersion containing organosilicon compatibilizers was slowly added dropwise under stirring at 60 °C. After the addition was complete, the reaction continued for 24 h. After cooling to room temperature, the carbon nanotubes modified with organosilicon compatibilizers (CNT-PHGE) were obtained by filtration, washing, and drying.

[0033] Example 1

[0034] This embodiment provides a temporary plugging agent for fracturing, which is composed of the following weight components: 30 parts by weight of phenyl polyester, 5 parts by weight of organosilicon compatibilizer modified carbon nanotubes, 2 parts by weight of KH560 coupling agent, and 1 part by weight of nano calcium carbonate.

[0035] Preparation of phenyl polyester

[0036] S1. Weigh 10 mmol of 4,4'-dibromodiphenyl ether, 25 mmol of undecenol, 0.2 mmol of copper acetylacetonate, 45 mL of tetrahydrofuran, 6 mmol of potassium carbonate, and 0.2 mmol of 8-hydroxyquinoline according to the specified ratio, add them to a closed reactor equipped with a reflux condenser, stir and mix evenly, and reflux at 85 °C for 8 h; after the reaction is completed, remove the solvent by vacuum distillation, wash the product three times each with deionized water and anhydrous ethanol, and dry it in a vacuum drying oven at 60 °C for 12 h to obtain diene diphenyl ether.

[0037] S2. Weigh 40 mL of N,N-dimethylformamide, 10 mmol of the prepared diene diphenyl ether, 25 mmol of mercaptoacetic acid, and 0.06 mmol of benzoin dimethyl ether photoinitiator according to the specified ratio, add them to a light-protected reactor, stir and mix evenly, and react for 4 h under 25 °C and 365 nm ultraviolet light irradiation. After the reaction is completed, centrifuge to obtain the solid product, wash it 3 times with anhydrous ethanol, and dry it under vacuum at 60 °C for 10 h to obtain dicarboxylate modified diphenyl ether.

[0038] S3. Weigh 10 mmol of the prepared dicarboxylated modified diphenyl ether, 12 mmol of 1,3-butanediol, and 0.06 mmol of tetrabutyl titanate according to the ratio, place them in a polycondensation reactor under nitrogen protection, stir and mix evenly, raise the temperature to 180°C, and react at a constant temperature until no more water evaporates; continue to raise the temperature to 200°C and react for 1.5 h, then raise the temperature to 230°C and react under vacuum conditions of ≤-0.095 MPa for 1 h; after the reaction is completed, lower the temperature to 155°C, add 8 mmol of terephthalic acid and 15 mmol of 1,4-butanediol, raise the temperature to 180°C and react at a constant temperature until no more water evaporates, then raise the temperature to 200°C and react for 1.5 h, then react under vacuum conditions of 230°C and ≤-0.095 MPa for 1 h, cool down and discharge to obtain phenyl polyester.

[0039] Preparation of temporary plugging agents for fracturing

[0040] Step 1: Weigh each raw material according to the above weight proportions, add the organosilicon compatibilizer-modified carbon nanotubes, nano calcium carbonate and KH560 coupling agent into a high-speed mixer, and mix at 90℃ and 2000r / min for 15min to obtain surface-modified inorganic filler.

[0041] Step 2: Add the phenyl polyester prepared above into a twin-screw extruder and heat it to 220°C until it is completely melted. Add the surface-modified inorganic filler obtained in Step 1 into the twin-screw extruder and melt-blend at 220°C and 350 r / min for 20 min. Extrude the blend uniformly to obtain the blend.

[0042] Step 3: Cool the blend to room temperature with circulating water, feed it into a pelletizer to pelletize, and then sieve it through a standard inspection sieve to obtain temporary plugging agent particles of four particle sizes: 40 mesh, 60 mesh, 80 mesh, and 100 mesh. Mix these particles evenly in a mass ratio of 1:2:3:2 to obtain the temporary plugging agent for fracturing in this embodiment.

[0043] Example 2

[0044] This embodiment provides a temporary plugging agent for fracturing, which is composed of the following weight components: 27.5 parts by weight of phenyl polyester, 4 parts by weight of organosilicon compatibilizer modified carbon nanotubes, 1.25 parts by weight of coupling agent (KH550:KH560 mass ratio = 1:1), and 0.65 parts by weight of nano calcium carbonate.

[0045] Preparation of phenyl polyester

[0046] S1. Weigh 7.5 mmol of 4,4'-dibromodiphenyl ether, 18.5 mmol of undecenol, 0.15 mmol of copper acetylacetonate, 40 mL of tetrahydrofuran, 5.5 mmol of potassium carbonate, and 0.15 mmol of 8-hydroxyquinoline according to the specified ratio, add them to a closed reactor equipped with a reflux condenser, stir and mix evenly, and reflux at 82 °C for 7 h; after the reaction is completed, remove the solvent by vacuum distillation, wash the product three times each with deionized water and anhydrous ethanol, and dry it in a vacuum drying oven at 60 °C for 12 h to obtain diene diphenyl ether.

[0047] S2. Weigh 35 mL of N,N-dimethylformamide, 8 mmol of the prepared diene diphenyl ether, 20 mmol of mercaptoacetic acid, and 0.05 mmol of benzoin dimethyl ether photoinitiator according to the specified ratio, add them to a light-protected reactor, stir and mix evenly, and react for 3 h under 22 °C and 365 nm ultraviolet light irradiation; after the reaction is completed, centrifuge to obtain solid product, wash 3 times with anhydrous ethanol, and vacuum dry at 60 °C for 10 h to obtain dicarboxylate modified diphenyl ether.

[0048] S3. Weigh out 9 mmol of the prepared dicarboxylated modified diphenyl ether, 10 mmol of 1,3-butanediol, and 0.055 mmol of tetrabutyl titanate according to the ratio, place them in a polycondensation reactor under nitrogen protection, stir and mix evenly, raise the temperature to 178°C, and react at a constant temperature until no more water evaporates; continue to raise the temperature to 195°C and react for 1.2 h, then raise the temperature to 225°C and react under vacuum of ≤-0.095 MPa for 0.75 h; after the reaction is completed, lower the temperature to 152°C, add 6.5 mmol of terephthalic acid and 12.5 mmol of 1,4-butanediol, raise the temperature to 178°C and react at a constant temperature until no more water evaporates, then raise the temperature to 195°C and react for 1.2 h, then react under vacuum of 225°C and ≤-0.095 MPa for 0.75 h, cool down and discharge to obtain phenyl polyester.

[0049] Preparation of temporary plugging agents for fracturing

[0050] Step 1: Weigh each raw material according to the above weight proportions, add the organosilicon compatibilizer-modified carbon nanotubes, nano calcium carbonate and mixed coupling agent into a high-speed mixer, and mix at 85℃ and 1750 r / min for 12 min to obtain surface-modified inorganic filler.

[0051] Step 2: Add the phenyl polyester prepared above into a twin-screw extruder and heat it to 215°C until it is completely melted. Add the surface-modified inorganic filler obtained in Step 1 into the twin-screw extruder and melt-blend it at 215°C and 325 r / min for 17 min. Extrude it uniformly to obtain the blend.

[0052] Step 3: The blend is cooled to room temperature by circulating water, then fed into a pelletizer for pelletizing, and then sieved through a standard inspection sieve to obtain temporary plugging agent particles of four particle sizes: 30 mesh, 50 mesh, 70 mesh, and 90 mesh. These particles are then uniformly compounded at a mass ratio of 1:2:3:2 to obtain the temporary plugging agent for fracturing in this embodiment.

[0053] Example 3

[0054] This embodiment provides a temporary plugging agent for fracturing, which is composed of the following weight components: 25 parts by weight of phenyl polyester, 3 parts by weight of organosilicon compatibilizer modified carbon nanotubes, 0.5 parts by weight of KH550 coupling agent, and 0.3 parts by weight of nano calcium carbonate.

[0055] Preparation of phenyl polyester

[0056] S1. Weigh out 5 mmol of 4,4'-dibromodiphenyl ether, 12 mmol of undecenol, 0.1 mmol of copper acetylacetonate, 35 mL of tetrahydrofuran, 5 mmol of potassium carbonate, and 0.1 mmol of 8-hydroxyquinoline according to the specified ratio, add them to a closed reactor equipped with a reflux condenser, stir and mix evenly, and reflux at 80 °C for 6 h. After the reaction is completed, remove the solvent by vacuum distillation, wash the product three times each with deionized water and anhydrous ethanol, and dry it in a vacuum drying oven at 60 °C for 12 h to obtain diene diphenyl ether.

[0057] S2. Weigh 30 mL of N,N-dimethylformamide, 6 mmol of the prepared diene diphenyl ether, 15 mmol of mercaptoacetic acid, and 0.04 mmol of benzoin dimethyl ether photoinitiator according to the specified ratio, add them to a light-protected reactor, stir and mix evenly, and react for 2 h under 20 °C and 365 nm ultraviolet light irradiation; after the reaction is completed, centrifuge to obtain solid product, wash 3 times with anhydrous ethanol, and vacuum dry at 60 °C for 10 h to obtain dicarboxylate modified diphenyl ether.

[0058] S3. Weigh out 8 mmol of the prepared dicarboxylated modified diphenyl ether, 8 mmol of 1,3-butanediol, and 0.05 mmol of tetrabutyl titanate according to the ratio, place them in a polycondensation reactor under nitrogen protection, stir and mix evenly, raise the temperature to 175°C, and react at a constant temperature until no more water evaporates; continue to raise the temperature to 190°C and react for 1 hour, then raise the temperature to 220°C and react under vacuum of ≤-0.095 MPa for 0.5 hours; after the reaction is completed, lower the temperature to 150°C, add 5 mmol of terephthalic acid and 10 mmol of 1,4-butanediol, raise the temperature to 175°C and react at a constant temperature until no more water evaporates, then raise the temperature to 190°C and react for 1 hour, then react under vacuum of 220°C and ≤-0.095 MPa for 0.5 hours, cool down and discharge to obtain phenyl polyester.

[0059] Preparation of temporary plugging agents for fracturing

[0060] Step 1: Weigh each raw material according to the above weight proportions, add the organosilicon compatibilizer-modified carbon nanotubes, nano calcium carbonate and KH550 coupling agent into a high-speed mixer, and mix at 80℃ and 1500r / min for 10min to obtain surface-modified inorganic filler.

[0061] Step 2: Add the phenyl polyester prepared above into a twin-screw extruder and heat it to 210°C until it is completely melted. Add the surface-modified inorganic filler obtained in Step 1 into the twin-screw extruder and melt-blend at 210°C and 300 r / min for 15 min. Extrude the blend uniformly to obtain the blend.

[0062] Step 3: Cool the blend to room temperature with circulating water, feed it into a pelletizer to pelletize, and then sieve it through a standard inspection sieve to obtain temporary plugging agent particles of four particle sizes: 20 mesh, 40 mesh, 60 mesh, and 80 mesh. Mix these particles evenly in a mass ratio of 1:2:3:2 to obtain the temporary plugging agent for fracturing in this embodiment.

[0063] Comparative Example 1

[0064] The main difference between this comparative example and Example 3 is that no organosilicon compatibilizer is added to modify the carbon nanotubes, while the other raw material ratios, preparation processes, and particle size compounding methods are completely consistent with Example 3.

[0065] Comparative Example 2

[0066] The main difference between this comparative example and Example 3 is that commercially available polylactic acid (the model of polylactic acid is Anhui Fengyuan PLA FY201) is used instead of the self-made phenyl polyester in Example 3. The other raw material ratios, preparation processes, and particle size compounding methods are completely consistent with Example 3.

[0067] Comparative Example 3

[0068] The main difference between this comparative example and Example 3 is that the temporary plugging agent particles use a single 60-mesh particle size, without the four-level particle size compounding of 20-mesh, 40-mesh, 60-mesh, and 80-mesh. The other raw material ratios and preparation processes are completely consistent with Example 3.

[0069] To verify the comprehensive performance of the temporary plugging agent for fracturing according to the present invention, the temporary plugging agents prepared in Examples 1-3 and Comparative Examples 1-3 were subjected to tests on fracturing fluid compatibility, pressure-bearing plugging performance, temperature resistance, degradation performance, and formation damage evaluation. Unless otherwise specified, all tests were performed in triplicate, and the average value of the test results was taken.

[0070] 1. Fracturing fluid compatibility test

[0071] Test medium: 2% KCl slickwater fracturing fluid system.

[0072] Test method: Weigh 5.0g of the temporary plugging agent samples prepared in Examples 1-3 and Comparative Examples 1-3 respectively, add them to 100mL of fracturing fluid system, stir at 500r / min for 30min at 25℃, and then let stand for 2h. Observe the dispersion state of the particles in the system and whether there is obvious agglomeration, sedimentation or stratification.

[0073] Evaluation criteria: Those that are uniformly dispersed and have no obvious agglomeration or stratification are considered to have "good compatibility"; those that show obvious agglomeration, sedimentation or stratification are considered to have "poor compatibility".

[0074] 2. Test on the pressure-bearing sealing performance of artificial cracks

[0075] Testing device: Artificial crack simulation evaluation device.

[0076] Crack conditions: crack width 2mm, crack length 300mm.

[0077] Test fluid: 2% KCl slickwater fracturing fluid system.

[0078] Test temperature: 120℃.

[0079] Test method: Add 3.0 wt% of temporary plugging agent to fracturing fluid, stir evenly, and then pump it into the artificial fracture device. The discharge rate is controlled at 50 mL / min. Record the time required for the temporary plugging agent to establish effective sealing from the start of injection, and continue to increase the pressure to the maximum pressure before the temporary plugging zone becomes unstable. Record this as the maximum pressure bearing value.

[0080] Evaluation indicators: The shorter the effective sealing time and the higher the maximum pressure value, the better the sealing performance of the temporary plugging agent.

[0081] 3. Temperature resistance test

[0082] Testing equipment: high-temperature aging reactor, electronic balance.

[0083] Test conditions: Aging at 140℃ for 6 hours.

[0084] Test method: Accurately weigh 10.0g of temporary plugging agent sample, place it in simulated formation water, age it at 140℃ for 6 hours, cool it, remove it, filter it, dry it and weigh it, and record the mass of the intact particles after aging. The initial mass is denoted as Calculate the particle integrity rate using the following formula:

[0085]

[0086] A higher particle integrity rate indicates better temperature resistance and stability of the material.

[0087] 4. Degradation performance test

[0088] Test medium: simulated formation water.

[0089] Test conditions: Immersion at a constant temperature of 120℃ for 72 hours.

[0090] Test method: Accurately weigh 5.0g of temporary plugging agent sample, place it in a sealed reaction vessel, add 100mL of simulated formation water, and soak at 120℃ for 72h; after the test, filter, wash, dry, and weigh the sample, recording the remaining mass as _____. Calculate the mass loss rate using the following formula:

[0091]

[0092] A higher mass loss rate indicates a better ability of the sample to degrade in the later stages.

[0093] 5. Formation damage assessment test

[0094] Testing apparatus: Core displacement evaluation apparatus.

[0095] Test sample: Artificial fracture core.

[0096] Test method: First, determine the initial permeability of the core. Subsequently, fracturing fluid containing 3.0 wt% temporary plugging agent was injected into the core fractures for temporary plugging. After plugging was completed, the core was left to stand at 120°C for 72 hours to simulate the formation degradation process. Then, water was used for flowback, and the permeability after flowback was measured. Calculate the damage rate using the following formula:

[0097]

[0098] The lower the formation damage rate, the less damage the temporary plugging agent causes to the reservoir after degradation and flowback.

[0099] Table 1: Performance Tests

[0100] project Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Fracturing fluid compatibility Evenly dispersed, without clumping or stratification Evenly dispersed, without clumping or stratification Evenly dispersed, without clumping or stratification Slight aggregation, with a small amount of sedimentation at the bottom. Significant subsidence, with localized clumping. Generally dispersed, with localized settlement. Establish effective blocking time / min 6.9 6.8 6.5 10.6 11.4 12.2 Maximum bearing pressure (MPa) 23.8 22.5 20.9 15.7 14.2 12.8 Particle integrity rate (140℃, 6h) / % 93.6 92.1 89.8 76.5 70.1 82.3 Mass loss rate (120℃, 72h) / % 81.5 79.6 78.8 68.6 60.7 71.4 Formation damage rate / % 10.8 11.5 12.3 18.7 22.4 19.6

[0101] As shown in Table 1, Comparative Example 1, which removes the silicone compatibilizer-modified carbon nanotubes, is a key reinforcing component of this invention. After silicone modification, the modified carbon nanotubes can form excellent interfacial bonding with the phenyl polyester matrix. Simultaneously, the one-dimensional nanostructure can construct a continuous three-dimensional network reinforcement framework within the matrix, and can also form a synergistic effect of "framework support + pore filling" with nano-calcium carbonate. Removing this component results in: decreased pressure resistance and reduced sealing efficiency: Without the three-dimensional reinforcement framework, the mechanical strength, deformation resistance, and erosion resistance of the phenyl polyester matrix significantly decrease. Under high temperature and pressure of 120℃, it easily softens and collapses, failing to form a stable bridging sealing structure in the crack. The sealing layer is easily washed away by fracturing fluid, directly leading to a prolonged effective sealing time and a decrease in the maximum pressure resistance. Significantly deteriorated temperature stability: Carbon nanotubes themselves possess excellent thermal conductivity and structural rigidity, effectively dispersing the internal stress generated by heat and improving thermal stability. Deformation temperature: After removal, the matrix is ​​easily damaged by heat at 140℃, and the particle integrity rate decreases by 1%. The compatibility and controllability of degradation deteriorate, and formation damage increases: Without the steric hindrance dispersion effect of modified carbon nanotubes, nano-calcium carbonate is prone to secondary agglomeration, resulting in slight agglomeration and sedimentation in the fracturing fluid. At the same time, insufficient matrix structural strength causes non-uniform melting and damage of the material, and the degradation process becomes out of control. Incompletely degraded solid fragments and agglomerated nano-calcium carbonate remain and block the core pores, ultimately resulting in a decrease in degradation rate and an increase in formation damage rate.

[0102] Comparative Example 2 uses commercially available polylactic acid (PLA) to replace the self-made phenyl polyester. The phenyl polyester of this invention is the core matrix of the temporary plugging agent. Through molecular structure design, diphenyl ether and rigid benzene ring groups are introduced into the main chain, combined with aliphatic polyester segments, achieving a balance between "high-temperature mechanical stability, interfacial compatibility, and controllable degradation." Commercially available PLA, however, is a pure aliphatic polyester without a rigid aromatic ring structure, resulting in extremely poor compatibility with the system of this invention. After replacement:

[0103] Decreased temperature resistance and pressure resistance: Polylactic acid has a low glass transition temperature and no rigid structural support for its molecular chains. It softens and melts rapidly at 140°C, completely losing the integrity of its particle structure and mechanical support. Even if the modified carbon nanotube reinforcement system is retained, it cannot form a stable sealing layer, which ultimately leads to a decrease in particle integrity, a longer time to establish an effective sealing layer, and a decrease in the maximum pressure resistance.

[0104] The compatibility of fracturing fluid is severely deteriorated: the molecular polarity of polylactic acid is completely incompatible with that of silane-modified inorganic fillers (modified carbon nanotubes, nano-calcium carbonate), resulting in extremely poor interfacial compatibility. The inorganic fillers agglomerate severely in the matrix, which not only causes uneven material properties but also results in significant sedimentation and localized agglomeration in the fracturing fluid, posing a risk of pump blockage.

[0105] Complete loss of controllable degradation and a significant increase in formation damage: The hydrolysis of polylactic acid is a random chain-breaking degradation, which is prone to non-uniform bulk degradation at high temperatures, producing a large amount of incompletely soluble oligomer solid residues. At the same time, the aggregated inorganic fillers cannot be returned with the degradation products, permanently blocking reservoir pores and fracture conduction channels, ultimately resulting in a decrease in degradation rate and an increase in formation damage rate.

[0106] Comparative Example 3: Single particle size replaces four-stage particle size blend.

[0107] This invention features a 1:2:3:2 compound design with four particle sizes: 20-40 mesh, 40-60 mesh, 60-80 mesh, and 80-100 mesh. The core of this design is a step-by-step sealing mechanism for cracks of different widths: "large-size bridging - medium-size filling - small-size sealing." This is the core structural design for achieving rapid, efficient sealing and high pressure resistance. (After replacing with a single 60-mesh particle size:)

[0108] The sealing efficiency and pressure bearing capacity declined: a single 60-mesh particle size cannot form an effective initial bridging structure in an artificial fracture with a width of 2mm. The particles are easily lost with the fracturing fluid and cannot be quickly accumulated to form a stable sealing layer. At the same time, the sealing layer formed by the accumulation of a single particle size has extremely high porosity. Without the filling of small and medium-sized particles to ensure sealing, high-pressure fluid can easily flow through the pores and scour and destroy the sealing layer, ultimately leading to a longer time to establish an effective sealing layer and a decrease in the maximum pressure bearing value.

[0109] Deterioration in temperature resistance, erosion resistance, and degradation uniformity: Under continuous erosion by high-temperature and high-pressure fluid, particles in the high-porosity sealing layer are easily carried away one by one, causing the overall sealing layer to become unstable and the particle breakage rate to increase; at the same time, the uneven porosity of the sealing layer and the large difference in the contact area between the fluid and the particles lead to uneven degradation, and incompletely degraded particles remain and block cracks, resulting in a simultaneous decrease in particle integrity and degradation rate.

[0110] Poor dispersibility and significantly increased formation damage: Single-size particles lack the spatial steric hindrance effect between different particle sizes, making them prone to particle aggregation and sedimentation, resulting in deteriorated dispersibility; at the same time, the high porosity plugging layer allows more solid particles to penetrate into the deep core matrix, which cannot be completely flushed back, ultimately leading to an increase in formation damage rate.

[0111] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0112] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A temporary plugging agent for fracturing, characterized in that, It includes the following components by weight: 25-30 parts by weight of phenyl polyester, 3-5 parts by weight of organosilicon compatibilizer modified carbon nanotubes, 0.5-2 parts by weight of coupling agent, and 0.3-1 parts by weight of nano calcium carbonate; The preparation method of the phenyl polyester is as follows: S1: Diolefinic diphenyl ether with carbon-carbon double bonds at both ends is prepared by reflux reaction in tetrahydrofuran solvent using 4,4′-dibromodiphenyl ether, undecenol and copper acetylacetonate as raw materials under alkaline conditions. S2: In DMF solvent, diene diphenyl ether and mercaptoacetic acid undergo a thiol-alkene click reaction under UV light to introduce a carboxyl group and obtain a dicarboxyl-modified diphenyl ether. S3: Under a nitrogen atmosphere, dicarboxylated diphenyl ether and 1,3-butanediol are first subjected to segmental heating and polycondensation, and then terephthalic acid and 1,4-butanediol are added to react and obtain phenyl polyester.

2. The temporary plugging agent for fracturing according to claim 1, characterized in that, The preparation method of the phenyl polyester is as follows: S1. Add 4,4'-dibromodiphenyl ether, undecenol and copper acetylacetonate to a reactor containing tetrahydrofuran solvent, stir and mix, then add potassium carbonate and 8-hydroxyquinoline, reflux at 80-85℃ for 6-8h, after which distill under reduced pressure, wash and dry to obtain diene diphenyl ether. S2. Add diene diphenyl ether and mercaptoacetic acid to N,N-dimethylformamide solvent, stir and mix, and continue to add benzoin dimethyl ether photoinitiator. Irradiate with 365nm ultraviolet light at 20-25℃. After the irradiation is completed, centrifuge, wash and dry to obtain dicarboxylate modified diphenyl ether. S3. Dicarboxylated modified diphenyl ether, 1,3-butanediol, and tetrabutyl titanate are placed in a reactor. Under a N2 atmosphere, the temperature is raised to 175-180℃ and reacted until no more water evaporates. The temperature is then raised to 190-200℃ and reacted for 1-1.5 hours. The reaction is then carried out under vacuum at 220-230℃ for 0.5-1 hours. After the reaction is completed, the temperature is lowered to 150-155℃, and terephthalic acid and 1,4-butanediol are added. The temperature is raised to 175-180℃ and reacted until no more water evaporates. The temperature is then raised to 190-200℃ and reacted for 1-1.5 hours. The reaction is then carried out under vacuum at 220-230℃ for 0.5-1 hours to obtain phenyl polyester.

3. The temporary plugging agent for fracturing according to claim 2, characterized in that, In S1, the ratio of 4,4'-dibromodiphenyl ether, undecenol, copper acetylacetonate, tetrahydrofuran, potassium carbonate, and 8-hydroxyquinoline is 5-10 mmol: 12-25 mmol: 35-45 mL: 5-6 mmol: 0.1-0.2 mmol.

4. The temporary plugging agent for fracturing according to claim 2, characterized in that, The ratio of N,N-dimethylformamide, diene diphenyl ether, mercaptoacetic acid, and benzoin dimethyl ether photoinitiator in S2 is 30-40 mL: 6-10 mmol: 15-25 mmol: 0.04-0.06 mmol.

5. The temporary plugging agent for fracturing according to claim 2, characterized in that, In S2, the irradiation time of 365nm ultraviolet light is 2-4 hours.

6. The temporary plugging agent for fracturing according to claim 2, characterized in that, In S3, the ratio of dicarboxylated modified diphenyl ether, 1,3-butanediol, tetrabutyl titanate, terephthalic acid, and 1,4-butanediol is 8-10 mmol: 8-12 mmol: 0.05-0.06 mmol: 5-8 mmol: 10-15 mmol.

7. The temporary plugging agent for fracturing according to claim 1, characterized in that, The coupling agent is one of KH550 and KH560.

8. A method for preparing a temporary plugging agent for fracturing as described in any one of claims 1-7, characterized in that, The preparation method of the temporary plugging agent for fracturing is as follows: Step 1: Weigh each raw material according to the weight parts, add the organosilicon compatibilizer modified carbon nanotubes, nano calcium carbonate and coupling agent into a high-speed mixer, mix at 80-90℃ and 1500-2000r / min for 10-15min to obtain surface-modified inorganic filler. Step 2: Add phenyl polyester to a twin-screw extruder and heat it to a molten state at 210-220℃. Add the surface-modified inorganic filler obtained in Step 1 to the twin-screw extruder and melt-blend at 210-220℃ and a speed of 300-350 r / min for 15-20 min. Extrude to obtain the blend. Step 3: Cool the blend to room temperature with circulating water, pelletize it with a pelletizer, and then sieve it through a standard sieve to obtain temporary plugging agent particles with four particle sizes: 20-40 mesh, 40-60 mesh, 60-80 mesh, and 80-100 mesh. Mix these particles in a mass ratio of 1:2:3:2 to obtain the temporary plugging agent for fracturing.

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