Temporary plugging agent, preparation method and application thereof

Abstract

The application belongs to the technical field of acid fracturing, and relates to a temporary plugging agent and a preparation method and application thereof. The temporary plugging agent comprises a continuous phase, an acid response sacrificial phase and a chain extender dispersed in the continuous phase. The material of the continuous phase is a polyester matrix, and the polyester matrix is selected from one or a combination of two or more of polylactic acid, poly-L-lactic acid and poly-beta-hydroxybutyric acid. The acid response sacrificial phase is a first substance and / or a second substance. The first substance is selected from active metal oxide inorganic particles that are soluble in an acid solution. The second substance is selected from a polyester. The application provides a polyester-based temporary plugging agent suitable for an acid fracturing environment. By introducing an acid response sacrificial phase into the polyester continuous phase, time-controllable degradation is achieved by using the difference in degradation rates. The technical problem that existing temporary plugging agents cannot simultaneously meet the technical requirements of 1-3 hours of acid solubility of less than or equal to 15% and 48 hours of complete degradation under acid fracturing process conditions is solved.

Description

Technical Field

[0001] This invention belongs to the field of acid fracturing technology, and relates to a temporary plugging agent, its preparation method and application. Background Technology

[0002] Acid fracturing is a key technology for enhancing oil and gas field production. This technology involves injecting high-pressure acid (such as hydrochloric acid) into the formation, dissolving blockages and creating new fractures to form highly conductive acid-etched channels. In heterogeneous reservoirs, acid fracturing often preferentially enters high-permeability zones or existing fractures, leading to uneven reservoir stimulation and severely impacting production enhancement. Temporary plugging and redirection acid fracturing technology temporarily blocks high-permeability channels by injecting a temporary plugging agent, forcing subsequent acid to redirect to low-permeability areas, achieving uniform stimulation of the entire reservoir. Therefore, the plugging stability of the temporary plugging agent under complex environments of strong acid and high temperature, as well as its controllable degradation after application, directly determines the success or failure of acid fracturing.

[0003] Temporary plugging agents used in acid fracturing need to meet two seemingly contradictory requirements: on the one hand, they should have sufficient acid resistance and pressure resistance during the acid injection stage to ensure that the plugging does not fail prematurely; on the other hand, they should be able to degrade quickly after the operation to avoid prolonged retention in the formation and causing secondary damage.

[0004] Currently, various technical approaches have been developed in this field, but all of them have limitations: (1) Polyester alloy / chain extender copolymerization path: Chinese patent CN105295321A discloses a method for preparing resin alloys by melt-blending two or more of polyhydroxyacetic acid, polycaprolactone, polylactic acid, polybutylene succinate and poly-3-hydroxybutyrate with a chain extender. This technology chemically bonds different polyesters together to form a polyester alloy material, but the degradation behavior of each component is "averaged" and cannot achieve time-differentiated degradation; no degradation performance data are provided under 120℃ and 20% hydrochloric acid conditions, so it cannot be proven that it can meet the requirements of acid fracturing conditions; PBS and other components lose their independent degradation ability and cannot play a role as an active sacrificial phase.

[0005] (2) Inorganic nanoparticle reinforcement pathway: Chinese patent CN112745819A discloses a polyester composite temporary plugging agent with 1%-5% inorganic nanoparticles such as nano-silica and nano-titanium dioxide. The inorganic nanoparticles serve as the dispersed phase and catalyst, and nanoparticles with good reinforcing properties are selected to enhance mechanical properties. The nano-SiO2 / TiO2 added in this technology is an inert filler that does not participate in the degradation process and may remain in the pores after degradation, hindering complete degradation; the degradation performance test is conducted at 100℃, which is significantly different from the real acid fracturing environment of 120℃ and strong acid; the filler addition amount is only 1%-5%, and its main function is to enhance mechanical properties rather than regulate degradation.

[0006] (3) Cyclodextrin inclusion complex slow-release pathway: Chinese patent CN119331588A discloses a liquid rubber plugging agent using a cyclodextrin and benzoyl peroxide inclusion complex as a degradation control agent, which achieves delayed degradation by slowly releasing the breaker in crude oil through the inclusion complex. This technology is a liquid rubber plug system, which is not suitable for acid fracturing scenarios that require high-strength solid particle temporary plugging agents; the degradation triggering mechanism depends on the crude oil medium, which is not compatible with the acid fracturing operation environment; the applicable temperature is only 45-60℃, which cannot meet the high-temperature conditions of 120℃.

[0007] (4) PGA-based accelerator blending pathway: Chinese patent CN119955493A discloses a polyglycolic acid (PGA) temporary plugging agent, which achieves degradation rate regulation by adding amine compounds, inorganic carbonates, metal hydroxides, etc. as degradation accelerators, or adding chain extenders as degradation retarders. The degradation accelerators (amines, carbonates) in this technology will react violently and instantaneously in a strong acid environment, leading to premature material failure; the degradation performance test is carried out at 90℃, and does not involve an acidification environment of 120℃; the matrix is ​​PGA, which itself degrades too quickly and has poor stability in acid.

[0008] (5) Ternary copolymer molecular design path: Chinese patent CN109575248B discloses a ternary copolymer temporary plugging agent composed of any three monomers selected from caprolactone, lactide, glycolide, and polypropylene carbonate diol, which controls the degradation rate by adjusting the monomer ratio. This technology can only achieve linear adjustment of the degradation rate, and the time required for complete degradation is too long; the synthesis process is complex and costly; and no degradation performance data under 120℃ and 20% hydrochloric acid conditions are provided.

[0009] (6) PLA / PBAT / PBS blending enhancement pathway: Chinese patent CN112745819A also discloses a blending system of polylactic acid ester, polyglycolic acid, and polybutylene succinate, with the addition of inorganic nanoparticles for reinforcement. PBS, as one of the matrix components, did not play the role of an active sacrificial phase. The degradation performance test was conducted at 100℃ and normal pressure, and the performance under acidification environment at 120℃ was not verified.

[0010] In summary, the existing technologies generally have the following defects: (1) They cannot simultaneously meet the dual performance requirements of early stability and rapid and complete degradation in a high-temperature and acidic environment of 120℃; (2) Inorganic fillers are mostly inert reinforcing agents and do not have acidic environment responsiveness; (3) The test conditions are mostly normal pressure and medium and low temperature, which are significantly different from the actual acid fracturing conditions. Summary of the Invention

[0011] The main objective of this invention is to overcome the deficiencies in the prior art and provide a temporary plugging agent, its preparation method and application, which can adapt to acid fracturing process conditions and achieve early-stage stability and rapid and complete degradation in the later stage.

[0012] To achieve the above objectives, the specific technical solution is as follows: The present invention provides a temporary plugging agent, comprising a continuous phase and an acid-responsive sacrificial phase and a chain extender dispersed in the continuous phase. The continuous phase is made of a polyester matrix, which is selected from one or more of polylactic acid (PLA), poly-L-lactic acid (PLLA), and poly-β-hydroxybutyrate (PHB). The acid-responsive sacrificial phase is a first substance and / or a second substance. The first substance is selected from inorganic particles of active metal oxides that are soluble in acidic solutions; The second substance is selected from polyester; under acidic conditions, the hydrolysis rate of the second substance is higher than the hydrolysis rate of the continuous phase material.

[0013] The polyester matrix used in this invention has good mechanical strength and processability, making it a potential matrix material for temporary plugging agents. However, while pure polyester matrix can maintain a certain level of stability within a short operating time, its subsequent complete degradation rate is still relatively slow. Directly adding degradation accelerators can improve the later degradation rate, but they often react prematurely in a strongly acidic environment, causing early instability. On the other hand, adjusting the degradation rate by changing the copolymer structure has problems such as complex processes, high customization costs, and difficulty in achieving significant stage-differentiated degradation.

[0014] This invention provides a polyester-based temporary plugging agent suitable for acid fracturing environments. By introducing an acid-responsive sacrificial phase into the continuous phase of the polyester matrix, time-controlled degradation is achieved by utilizing the difference in degradation rates. The structure remains intact in the early stages of acid treatment, while in the later stages, the acid-responsive sacrificial phase forms microstructural units within the material. This triggerable structural evolution significantly improves the degradation rate.

[0015] During the use of the temporary plugging agent, the acid-responsive sacrificial phase preferentially degrades, leaving micropores inside the temporary plugging agent material. These micropores can improve the later medium penetration efficiency and contact area with the continuous phase of the polyester matrix without significantly weakening the initial plugging strength, and promote the degradation of the polyester matrix, thus balancing initial stability and later rapid degradation.

[0016] This invention solves the technical problem that existing temporary plugging agents cannot simultaneously meet the requirements of acid solubility ≤15% within 1-3 hours and complete degradation within 48 hours under acid fracturing process conditions.

[0017] Furthermore, the active metal oxide inorganic particles are selected from one or more of magnesium oxide, zinc oxide, and calcium oxide; the sacrificial phase polyester is selected from one or more of polybutylene succinate (PBS), polybutylene terephthalate (PBAT), polybutylene adipate succinate (PBSA), and polyglycolic acid (PGA).

[0018] This invention utilizes the difference in degradation rate between the aforementioned easily acid-degradable active metal oxide inorganic particles and polyester to control the degradation rate of polyester-based plugging agents in an acidic environment, achieving nonlinear degradation with initial stability in acid and subsequent rapid and complete degradation. This overcomes the technical defects of existing technologies in degrading plugging agents during acid fracturing processes.

[0019] Among them, acid-soluble oxides such as magnesium oxide and zinc oxide are introduced into the temporary plugging agent system as active acid-responsive sacrificial phases. Taking advantage of their solubility in acidic environments and their slower dissolution rate compared to existing carbonate nanoparticles, the system can precisely control the two-stage degradation characteristics. Moreover, after dissolution, soluble ions are generated without solid residue. Polybutylene succinate (PBS), polybutylene terephthalate (PBAT), polybutylene succinate-adipate (PBSA), and polyglycolic acid (PGA) have lower melting points than polyester matrix and significantly higher degradation rates under acidic conditions than polyester matrix, and can be completely degraded within 1 hour.

[0020] Furthermore, the temporary plugging agent is prepared from raw materials comprising the following components in parts by weight: 92.5 to 96.5 parts of polyester matrix, 3 to 7 parts of acid-responsive sacrificial phase, and 0.5 to 3.5 parts of chain extender.

[0021] The acid-responsive sacrificial phase used in this invention, when its content is too low, the micropores formed in the later stage are insufficient to significantly accelerate degradation; when its content is too high, the integrity and pressure resistance of the material in the early stage of acid hydrolysis are easily reduced.

[0022] Furthermore, the number-average molecular weight of the polyester matrix is ​​80,000 to 200,000, preferably 100,000 to 180,000; the melting point of the polyester matrix is ​​150 to 170°C, preferably 160 to 170°C.

[0023] When the number-average molecular weight of the polyester matrix is ​​between 80,000 and 200,000 and the melting point is between 150 and 170°C, it can provide good mechanical properties, processing properties and degradation characteristics for the temporary plugging agent. By controlling the number-average molecular weight and melting point of PLA within this range, the processability, mechanical strength and degradation performance of the temporary plugging agent can be balanced, so that it can better meet the comprehensive requirements of the temporary plugging agent in the acid fracturing process.

[0024] Furthermore, the particle size of the magnesium oxide, zinc oxide, and calcium oxide is 0.1 μm to 10 μm, preferably 0.2 μm to 4 μm.

[0025] Within this particle size range, magnesium oxide and zinc oxide can be well dispersed in the polylactic acid matrix, avoiding stress concentration problems caused by excessively large particle sizes, thus ensuring the uniformity of the overall structure and the stability of the mechanical properties of the temporary plugging agent material. Simultaneously, this particle size range is beneficial during the use of the temporary plugging agent. When external acidic conditions trigger the action of the acid-responsive sacrificial phase, the magnesium oxide and zinc oxide particles can form micropores to promote degradation without affecting the initial pressure-bearing sealing effect of the temporary plugging agent. Furthermore, the suitable particle size also facilitates better mixing with other components during material preparation, improving the feasibility of the processing technology and the consistency of product quality.

[0026] Furthermore, the number-average molecular weight of the sacrificial polyester is 20,000 to 120,000, preferably 40,000 to 100,000; the melting point of the polyester is 110-140°C, preferably 110-130°C.

[0027] The polyesters used in this invention, such as polybutylene succinate (PBS), polybutylene terephthalate (PBAT), polybutylene succinate-adipate (PBSA), or polyglycolic acid (PGA), exhibit good compatibility with the polyester matrix within this number-average molecular weight range. They can be uniformly dispersed within the polyester matrix, thus ensuring the uniformity of the temporary plugging agent's structure and the stability of its performance. Furthermore, a suitable molecular weight also helps to regulate the degradation rate of the temporary plugging agent, allowing it to gradually degrade at the expected rate after temporary plugging, ultimately forming harmless products and avoiding secondary damage to the reservoir. This meets the requirements of acid fracturing processes for the degradation performance of the temporary plugging agent.

[0028] Furthermore, the chain extender is selected from polymeric epoxy chain extenders, such as type 9013; or isocyanate chain extenders, such as MDI and HMDI; or other chain extenders commonly used in the industry.

[0029] This invention features selective chain extension enhancement. The chain extender is used only to increase the molecular weight of the polyester matrix to enhance its high-temperature stability, without bonding the acid-responsive sacrificial phase, such as PBS, to the PLA molecular chain, thus ensuring that the acid-responsive sacrificial phase maintains its independent degradation capability.

[0030] Furthermore, the temporary plugging agent also includes processing aids.

[0031] Furthermore, the processing aid is selected from one or more of acetylated tributyl citrate (ATBC), tributyl citrate (TBC), dioctyl phthalate (DOP), and dioctyl adipate (DOA).

[0032] The present invention also provides a method for preparing the above-mentioned temporary plugging agent: after melt blending the continuous phase material, the acid-responsive sacrificial phase and the chain extender, the mixture is extruded and granulated by a twin-screw extruder.

[0033] The acid-responsive sacrificial phase of the present invention is distributed in the polyester matrix through a melt blending process so as to form a connected microporous network after the acid-responsive sacrificial phase is removed; the preparation process is simple, cost is controllable, and it is suitable for industrial production.

[0034] In a specific embodiment of the present invention, the preparation method of the temporary plugging agent is as follows: (1) Add the continuous phase polyester matrix and the sacrificial phase polyester particles to the processing aid and mix for 2-5 minutes to make the processing aid evenly adhere to the particle surface; add the active metal oxide inorganic particles and mix for 2-5 minutes to ensure that the powder is evenly adhered to the wet particle surface; add the chain extender and mix for 2-5 minutes to make the premix evenly dispersed. (2) The premixed material is melted, extruded and granulated by a twin-screw extruder.

[0035] Furthermore, the material of the continuous phase and the polyester are dried at 55-65°C for 7-9 hours before use.

[0036] Furthermore, the melting temperature is 70–180°C.

[0037] Specifically, the temperature settings of the twin-screw extruder are as follows: Zone 1: 75-85℃, Zone 2: 115-125℃, Zone 3: 145-155℃, Zone 4: 175-185℃, Zone 5: 175-185℃, Zone 6: 165-175℃, Zone 7: 165-175℃, Zone 8: 165-175℃, Zone 9: 170℃, Zone 10: 175-185℃, Zone 11: 175-185℃, and Die Head: 175-185℃.

[0038] Furthermore, the screw speed of the twin-screw extruder is 100-200 RPM, and the feeding speed is 3-8 Hz.

[0039] Furthermore, the particle size of the temporary plugging agent is 9-32 mesh.

[0040] The present invention further provides the application of the above-mentioned temporary plugging agent in acid fracturing processes with a temperature of 100-130°C and a hydrochloric acid concentration of 15%-25%.

[0041] In acidic temperature environments, acidity greatly accelerates the degradation of polyester. Conventional neutral environment temporary plugging agents degrade too quickly and cannot guarantee the initial plugging performance.

[0042] Compared with the prior art, the present invention has the following significant advantages: This invention does not simply rely on external degradation promoters to directly accelerate the overall reaction. Instead, it achieves the regulation of the degradation rate of the temporary plugging agent by first preserving the main structure of the polyester matrix and then sacrificing local phases to form a medium that penetrates into the micropores. This method is suitable for acid fracturing, which requires both stable plugging in the early stage and complete degradation in the later stage of the temporary plugging agent. Furthermore, the acid solubility characteristics of the temporary plugging agent system of this invention in the early and late stages under acid fracturing process conditions have been verified through systematic experiments.

[0043] The present invention has a simple process and controllable cost. It adopts conventional melt blending and pulverization processes, and the raw materials are all industrial-grade products, which is suitable for large-scale industrial production. Attached Figure Description

[0044] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0045] Figure 1 These are the original morphology and the morphology after acid hydrolysis for 1 h and 3 h of the temporary plugging agents in Examples 1 and 2 of the present invention; (a) Original morphology of the temporary plugging agent in Example 1; (a') After acid hydrolysis for 1 hour; (a'') After acid hydrolysis for 3 hours; (b) Original morphology of the temporary plugging agent in Example 2; (b') After acid hydrolysis for 1 hour; (b'') After acid hydrolysis for 3 hours; Figure 2 These are the original and 1-hour and 3-hour degradation XRD spectra of Examples (a) 1 and (b) 2 of the present invention; (a) XRD patterns of the temporary plugging agent in Example 1 at its original state, 1 h after degradation, and 3 h after degradation; (b) XRD patterns of the temporary plugging agent in Example 2 at its original state, 1 h after degradation, and 3 h after degradation; Figure 3 These are the infrared spectra of the original and degraded samples after 1 hour and 3 hours, respectively, in Examples (a) 1 and (b) 2 of the present invention. (a) Infrared spectra of the temporary plugging agent in Example 1 at its original state, 1 hour, and 3 hours of degradation; (b) Infrared spectra of the temporary plugging agent in Example 2 at the original stage, 1 hour and 3 hours after degradation. Detailed Implementation

[0046] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0047] Unless otherwise specified in the embodiments of the present invention, the techniques or conditions described in the literature in this field or the product instructions shall be followed; if the manufacturers of the reagents or instruments used are not specified, they are all conventional products that can be purchased through legitimate channels.

[0048] Polylactic acid (PLA): Number average molecular weight of 100,000 to 180,000, melting point of 160-170℃, Xinjiang Lanshan Tunhe Technology Co., Ltd. Zinc oxide: Particle size 0.2μm~4μm; Magnesium oxide: Particle size 0.2μm~4μm; Polybutylene succinate (PBS): Number average molecular weight 40,000-100,000, melting point 110-120℃, Xinjiang Lanshan Tunhe Technology Co., Ltd. Polybutylene terephthalate (PBAT): number average molecular weight 40,000 to 100,000, melting point 110-130℃, Xinjiang Lanshan Tunhe Technology Co., Ltd.

[0049] The above substances are used in the embodiments or comparative examples of this invention.

[0050] Example 1 This embodiment provides a temporary plugging agent and its preparation method, as detailed below: The temporary plugging agent, by weight, is prepared from 96.5 parts by weight of PLA, 3 parts by weight of PBS, and 0.5 parts by weight of MDI chain extender; the specific preparation method is as follows: PLA and acid-responsive sacrificial phase were dried at 60°C for 8 hours, then ATBC oil was added and mixed for 3 minutes to ensure uniform oil adhesion to the particle surface. A chain extender was added and mixed for 2 minutes to obtain a premix. The premix was then melt-blended in a twin-screw extruder. The extrudate was water-cooled, pelletized, dried, and sieved to obtain temporary blockage agent particles, designated as sample S1, with a particle size of 10-16 mesh. The twin-screw extruder has the following temperature settings: Zone 1: 80℃, Zone 2: 120℃, Zone 3: 150℃, Zone 4: 180℃, Zone 5: 180℃, Zone 6: 170℃, Zone 7: 170℃, Zone 8: 170℃, Zone 9: 170℃, Zone 10: 180℃, Zone 11: 180℃, and Die Head: 180℃; the screw speed of the twin-screw extruder is 150 RPM; and the feeding speed is 5 Hz.

[0051] Example 2 This embodiment provides a temporary plugging agent and its preparation method, as detailed below: The temporary plugging agent, by weight, is prepared from 94.5 parts by weight of PLA, 5 parts by weight of PBS, and 0.5 parts by weight of 9013 type chain extender; the specific preparation method is the same as in Example 1, and will not be repeated here. It is referred to as sample S2, with a particle size of 10-16 mesh.

[0052] Example 3 This embodiment provides a temporary plugging agent and its preparation method, as detailed below: The temporary plugging agent is prepared by weight of 96.5 parts PLA, 3 parts PBS, and 0.5 parts 9013 chain extender; the specific preparation method is the same as in Example 1, and will not be repeated here. It is referred to as sample S3, with a particle size of 10-16 mesh.

[0053] Example 4 This embodiment provides a temporary plugging agent and its preparation method, as detailed below: The temporary plugging agent, by weight, is prepared from 95 parts PLA, 5 parts magnesium oxide particles, and 0.5 parts MDI chain extender. The PLA and magnesium oxide particles are dried at 60°C for 8 hours. The PLA is then added to ATBC oil and mixed for 3 minutes to ensure the oil evenly adheres to the particle surface. The magnesium oxide particles are then added and mixed for another 3 minutes to ensure the powder evenly adheres to the moist particle surface. The remaining preparation methods are the same as in Example 1 and will not be repeated here. This sample is designated S4, with a particle size of 10-16 mesh.

[0054] Comparative Example 1 This embodiment provides a temporary plugging agent and its preparation method, as detailed below: The temporary plugging agent is prepared by weight of 99.5 parts PLA and 0.5 parts chain extender; the specific preparation method is the same as in Example 1, and will not be repeated here. It is referred to as Comparative Sample 1.

[0055] Comparative Example 2 This embodiment provides a temporary plugging agent and its preparation method, as detailed below: The temporary plugging agent is prepared by weight of 92.5 parts PLA, 7 parts PBS, 4 parts zinc oxide particles, and 0.5 parts chain extender; the specific preparation method is the same as in Example 1, and will not be repeated here. It is referred to as Comparative Sample 2.

[0056] This invention primarily evaluates the short-term acid resistance and long-term degradation ability of the temporary plugging agent through acid degradation experiments. The specific test methods are as follows: Degradation rate in 1 hour: a) Set the temperature of the constant temperature drying oven to 105℃, dry the experimental filter paper to constant weight, and record it as m1 (accurate to 0.0001g); b) Weigh 2g (accurate to 0.0001g) of temporary plugging agent using an analytical balance, record it as m2, add it to an aging tank containing 200mL of 20% hydrochloric acid, the aging tank should be equipped with a polytetrafluoroethylene inner cylinder, and stir evenly. Place the aging tank in an oven, set the oven temperature to the selected 120℃, and stop heating after 1 hour; c) Cool the aging tank to about 30℃ within half an hour, open the aging tank and pour out all the samples, filter the samples with filter paper, and then place the filter paper and samples in an oven at 105℃ to dry to constant weight, record it as m3; d) Calculate the degradation rate φ of the temporary plugging agent at 120℃ and 1 hour according to formula (3): Where: φ - acid solubility at 120℃ for 1 hour, % m1 - Filter paper mass, g; m2 - Mass of temporary plugging agent, in grams; m3 - Mass of the dissolved temporary plugging agent and filter paper, in grams.

[0057] 3-hour degradation rate: The heating time in the aging tank was changed to 3 hours, and the other testing methods were the same as above.

[0058] Degradation rates at 24h and 48h: The heating time of the aging tank was changed to 24h and 48h, the hydrochloric acid concentration was changed to 2%, and the other test methods were the same as above.

[0059] The degradation performance of the temporary plugging agent products S1-S4 from Examples 1-4 was tested, and the results are shown in Table 1.

[0060] Table 1. Degradation performance test results of the temporary plugging agents in Examples 1-4

[0061] As can be seen from the test results in Table 1, the samples of the preferred embodiments of the present invention maintained a low degradation rate in the initial stage (1h), ensuring the plugging efficiency of the temporary plugging agent. In the middle stage of acid hydrolysis (3h), the degradation rate of the temporary plugging agent varied with the content and type of acid-responsive sacrificial phase in the PLA matrix, which could achieve the purpose of controlling the degradation rate. In the medium and long-term degradation experiments, all temporary plugging agent samples could achieve complete degradation without causing secondary pollution to oil and gas wells. As shown in Comparative Example 1, the sample without sacrificial phase had good stability in the early stage, but could not be completely degraded after 48h, which may cause secondary pollution to oil and gas wells. As shown in Comparative Example 2, although the sample with too much sacrificial phase (7 parts by weight) could be completely degraded, the degradation was too fast in the early stage, which could not guarantee the plugging performance during acid fracturing operations.

[0062] In addition, by Figure 1 It can be seen that the original surfaces of the temporary plugging agents S1 and S2 are dense; after 1 hour of acid hydrolysis, no significant changes were observed on the surface of the temporary plugging agent, indicating excellent structural stability in the early stage of acid hydrolysis, ensuring that the initial plugging performance is not affected; after 3 hours of acid hydrolysis, microcracks appeared in the temporary plugging agent, and their size and density were different, indicating that at this time, microchannels were formed in the temporary plugging agent through the preferential degradation of the acid-responsive sacrificial phase, thereby controlling the degradation rate of the temporary plugging agent.

[0063] Depend on Figure 2 It can be seen that the original temporary plugging agent samples S1 and S2 had low crystallinity, and their X-ray diffraction patterns showed lumpy peaks. In contrast, the samples degraded for 1 h and 3 h showed high crystallinity, and their X-ray diffraction patterns showed strong sharp peaks, primarily characteristic of PLA. This indicates that during the degradation of the temporary plugging agent at 1 h and 3 h, the acid-responsive sacrificial phase and the amorphous phase of PBS preferentially degraded, and the degradation rate was controlled by the microchannels formed during degradation. Figure 3 It can be seen that the original temporary plugging agent and the samples after 1 hour and 3 hours of degradation all maintain the basic chemical structure of polyester, and have little impact on the plugging performance of the temporary plugging agent.

[0064] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A temporary plugging agent, characterized in that, The mixture includes a continuous phase, an acid-responsive sacrificial phase dispersed in the continuous phase, and a chain extender. The continuous phase is made of a polyester matrix, which is selected from one or more of polylactic acid, poly-L-lactic acid, and poly-β-hydroxybutyrate. The acid-responsive sacrificial phase is a first substance and / or a second substance. The first substance is selected from inorganic particles of active metal oxides that are soluble in acidic solutions; The second substance is selected from polyester; under acidic conditions, the hydrolysis rate of the second substance is higher than the hydrolysis rate of the continuous phase material.

2. The temporary plugging agent according to claim 1, characterized in that, The active metal oxide inorganic particles are selected from one or more of magnesium oxide, zinc oxide, and calcium oxide; the polyester is selected from one or more of polybutylene succinate, polybutylene terephthalate, polybutylene adipate, and polyglycolic acid.

3. The temporary plugging agent according to claim 1 or 2, characterized in that, The temporary plugging agent is prepared from raw materials comprising the following components in parts by weight: 92.5 to 96.5 parts polyester matrix, 3 to 7 parts acid-responsive sacrificial phase, and 0.5 parts chain extender.

4. The temporary plugging agent according to claim 1 or 2, characterized in that, The number-average molecular weight of the polyester matrix is ​​80,000 to 200,000, preferably 100,000 to 180,000; the melting point of the polyester matrix is ​​150-170°C, preferably 160-170°C.

5. The temporary plugging agent according to claim 1 or 2, characterized in that, The particle size of the magnesium oxide, zinc oxide, and calcium oxide is 0.1 μm to 10 μm, preferably 0.2 μm to 4 μm; And / or, the number-average molecular weight of the sacrificial phase polyester is 20,000 to 120,000, preferably 40,000 to 100,000; the melting point of the sacrificial phase polyester is 110-140°C, preferably 110-130°C.

6. The temporary plugging agent according to claim 3, characterized in that, The chain extender is selected from one or more of polymeric epoxy chain extenders or isocyanate chain extenders.

7. The temporary plugging agent according to claim 1 or 2, characterized in that, The temporary plugging agent also includes processing aids.

8. The temporary plugging agent according to claim 7, characterized in that, The processing aid is selected from one or more of acetylated tributyl citrate, tributyl citrate, dioctyl phthalate, and dioctyl adipate.

9. A method for preparing a temporary plugging agent as described in any one of claims 1 to 8, characterized in that, The continuous phase material, acid-responsive sacrificial phase and chain extender are melt-blended and then extruded and granulated using a twin-screw extruder.

10. The application of the temporary plugging agent as described in any one of claims 1 to 8 in an acid fracturing process at a temperature of 100 to 130°C and a hydrochloric acid concentration of 15% to 25%.

Images