Self-degradable blocking agent for water-based drilling fluid as well as preparation method and application of self-degradable blocking agent

Abstract

The invention relates to the technical field of drilling fluid compositions, and provides a self-degradable blocking agent for a water-based drilling fluid as well as a preparation method and application of the self-degradable blocking agent. The self-degradable blocking agent for the water-based drilling fluid, provided by the invention, is prepared from a p-styrenesulfonic acid modified epoxy resin core and polycaprolactone polyhydric alcohol wrapped outside the p-styrenesulfonic acid modified epoxy resin core. By introducing polycaprolactone polyol and p-styrenesulfonic acid modified epoxy resin, compact plugging, leakage prevention and seepage prevention of an oil and gas reservoir in the drilling process are realized, and meanwhile, the reservoir can be effectively protected. The water-based drilling fluid formed by the self-degradation plugging agent for the water-based drilling fluid is suitable for oil and gas reservoirs in the temperature range of 60-150 DEG C and has excellent filtration and rheological properties, compact plugging performance and self-degradation, the initial plugging rate of the reservoirs can reach 98% or above, the permeability recovery value of the reservoirs can reach 97%, and effective protection of the reservoirs is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of drilling fluid compositions, and particularly relates to a self-degradable plugging agent for water-based drilling fluids, a preparation method thereof, and an application thereof. Background Art

[0002] To ensure the stable supply of oil and gas resources, oil and gas exploration and development in China are gradually advancing into complex formations. The exploration and development degree of major oil and gas fields is getting higher and higher, and the trend of inferior quality of oil and gas resources is becoming more and more obvious. Therefore, higher requirements are put forward for the exploration and development technologies of complex formations.

[0003] Strengthening the protection of oil and gas reservoirs and reducing the damage to oil and gas reservoirs are the key means to ensure the efficient exploitation of oil and gas resources. The reservoir protection materials of drilling fluids can be decomposed in a high-temperature formation environment to achieve self-unplugging, without the need for processes such as pickling to remove mud cakes, avoiding secondary damage to the reservoir, and it is a simple, efficient, and non-side-effect self-unplugging reservoir protection technology.

[0004] However, currently in the subsequent treatment of formation plugging in reservoir protection technologies, conventional plugging removal technologies such as chemical methods, physical methods, microbial methods, and composite plugging removal methods still need to be used. These plugging removal processes are complex. If the plugging removal measures are not properly handled, new chemical blockages, mechanical blockages, etc. will be caused, reducing the permeability of the formation. Ming Xu et al. developed a self-degradable temporary plugging agent, which almost completely degraded within 55 hours at a temperature of 90 °C and a hydrochloric acid concentration of 15%. However, the degradation conditions of this self-degradable temporary plugging agent are complex, a relatively high concentration of hydrochloric acid needs to be added, the on-site construction difficulty is large, the self-degradation degree is low, and the reservoir protection effect is limited. Chinese Patent CN115612465A discloses a self-degradable plugging agent for fractured reservoirs, which consists of a high-strength bridging material, a self-degradable filling material, and a self-degradable fiber. However, the high-strength bridging material in this plugging agent contains quartz sand and ceramsite, which are non-degradable and will cause irreversible effects on the permeability of the reservoir, and its self-unplugging effect is poor, and the actual reservoir protection effect is limited.

[0005] Therefore, the current drilling fluid protection materials for oil and gas reservoirs all need to be unplugged under certain conditions, do not have good self-degradation characteristics, and the actual reservoir protection effect is limited. How to balance the sealing, plugging prevention, leakage prevention, and invasion prevention of oil and gas reservoirs during drilling and reservoir protection has become a major problem. Summary of the Invention

[0006] The purpose of the present invention is to provide a self-degradable plugging agent for water-based drilling fluids to solve the problem that it is difficult to balance and cannot be simultaneously satisfied between the sealing, plugging prevention, leakage prevention, and invasion prevention of oil and gas reservoirs and reservoir protection during the drilling process in the prior art.

[0007] The second purpose of the present invention is to provide a preparation method of a self-degradable plugging agent for water-based drilling fluids.

[0008] The third object of the present invention is to provide an application of a self-degrading plugging agent for water-based drilling fluids.

[0009] To achieve the above object, the technical solution of the self-degrading plugging agent for water-based drilling fluids of the present invention is as follows:

[0010] A self-degrading plugging agent for water-based drilling fluids is composed of an epoxy resin core modified with styrene sulfonic acid and a polycaprolactone polyol wrapped outside the epoxy resin core modified with styrene sulfonic acid.

[0011] The self-degrading plugging agent for water-based drilling fluids provided by the present invention improves the adhesiveness of the plugging material by introducing polycaprolactone polyol, and then enables the plugging materials to bond together in the drilling fluid to form a dense filter cake, realizing tight plugging during the drilling process, reducing the invasion risk of the liquid phase and solid particles of the drilling fluid, achieving the purpose of protecting the reservoir, and can be hydrolyzed at high temperature without affecting the degradability of the plugging agent, and delaying the degradation rate in a short time through polycaprolactone polyol, and can effectively plug the reservoir pores during the drilling process; by introducing epoxy resin modified with styrene sulfonic acid, it can be applicable to different temperature ranges, enabling the self-deplugging plugging agent to be applicable to more oil and gas reservoir conditions, and having excellent degradation performance, and can undergo self-degradation under in-situ formation conditions, decomposing into small molecules soluble in formation fluids, ensuring the efficient automatic removal of the filter cake, achieving extremely low damage to the oil and gas reservoir, maximizing the recovery of the permeability of the oil and gas reservoir. In addition, the sulfonic acid generated after the decomposition of the formed sulfonate group by heat is soluble in water and acidic, which can not only automatically unplug and restore the permeability of the oil and gas reservoir, but also react with the oxides in the rock of the oil and gas reservoir to improve the reservoir permeability, significantly improving the reservoir protection effect. The simultaneous introduction of the two can achieve tight plugging, leakage prevention and invasion prevention of the oil and gas reservoir during the drilling process, and can effectively protect the reservoir.

[0012] To more effectively regulate the self-degradation rate, preferably, the mass ratio of the polycaprolactone polyol to the epoxy resin modified with styrene sulfonic acid is 1-3.5:6-16.2.

[0013] To further control the degradation rate of the polycaprolactone polyol in the outer shell at a certain temperature, playing the role of tight plugging in a short time and then self-degrading to protect the reservoir, preferably, the weight-average molecular weight of the polycaprolactone polyol is 200-360, and the softening point is 50-70 °C.

[0014] To further improve the hydrophilicity and degradation rate of the self-degrading plugging agent and be applicable to different temperature ranges, preferably, the polycaprolactone polyol is polycaprolactone diol.

[0015] To better achieve plugging, preferably, the self-degrading plugging agent is solid particles, and the particle size is 0.1-1 mm.

[0016] To obtain polycaprolactone diol simply and efficiently, preferably, the polycaprolactone diol is obtained by ring-opening polymerization of 1,4-butanediol and ε-caprolactone monomers. The ring-opening polymerization reaction includes the following steps: stirring 1,4-butanediol and ε-caprolactone monomers under an inert atmosphere, and then adding a metal anion complex catalyst for ring-opening polymerization reaction.

[0017] The technical solution of the preparation method of the self-degrading plugging agent for water-based drilling fluid of the present invention is as follows:

[0018] A preparation method of a self-degrading plugging agent for water-based drilling fluid includes the following steps: (1) uniformly stirring a p-styrenesulfonic acid-modified epoxy resin, a curing agent, and a curing accelerator, and pulverizing after curing to obtain a pulverized cured product; (2) wrapping the pulverized cured product obtained in step (1) with polycaprolactone polyol.

[0019] The preparation method of the self-degrading plugging agent for water-based drilling fluid provided by the present invention has a simple and efficient process, low cost, and the particle size distribution of the prepared self-deplugging plugging agent is relatively wide, which is beneficial to reasonably select the particle size of the self-deplugging plugging agent according to the pore structure and size characteristics of the oil and gas reservoir, achieve a good match with the oil and gas reservoir, form a dense filter cake, and achieve a strong plugging effect.

[0020] To further meet the requirements of reservoir plugging and self-degrading use environments in different temperature ranges of the reservoir protection drilling fluid, preferably, based on 100% by mass fraction, it consists of 4.2 - 14.3% of p-styrenesulfonic acid-modified epoxy resin and the following components by mass fraction: 25 - 68% of polycaprolactone polyol, 5.42 - 18.6% of curing agent, and 4 - 10.7% of curing accelerator.

[0021] To further improve the number of sulfonate functional groups in the styrene sulfonate epoxy resin and regulate the self-degrading rate, preferably, the curing agent in step (1) is an acid anhydride curing agent, the acid anhydride curing agent is 4-methylhexahydrophthalic anhydride or methyltetrahydrophthalic anhydride, and the curing accelerator is 2-ethyl-4-methylimidazole or m-phenylenediamine.

[0022] To further improve the curing effect, preferably, the curing in step (1) includes three times of curing. The first curing temperature is 90 - 140 °C, the curing time is 1 - 2 h, the second curing temperature is 160 - 170 °C, the curing time is 3 - 4 h, and the third curing temperature is 180 - 190 °C, the curing time is 1 - 2 h.

[0023] To improve the wrapping performance and stability, preferably, the wrapping temperature during wrapping in step (2) is 50 - 70 °C.

[0024] The technical solution for the application of the self-degrading plugging agent for water-based drilling fluid of the present invention is as follows:

[0025] An application of a self-degrading plugging agent for water-based drilling fluid, adding the self-degrading plugging agent for water-based drilling fluid with a mass fraction of 3-12.5% into the water-based drilling fluid, and applying it to reservoirs with a temperature above 60°C.

[0026] The application of the self-degrading plugging agent for water-based drilling fluid provided by the present invention, through the water-based drilling fluid formed by directly adding the self-degrading plugging agent for water-based drilling fluid, can be applicable to oil and gas reservoirs in the temperature range of 60-150°C, and has excellent filtration loss and rheological properties, sealing and plugging performance and self-degradation. The initial plugging rate of the reservoir can reach more than 98%. With the self-degradation of the plugging agent, the reservoir permeability recovery value can reach 97% after 15 days, realizing the effective protection of the reservoir. Brief Description of the Drawings

[0027] Figure 1 It is a graph showing the change of the self-degradation rate of the self-degrading plugging agent provided by the present invention with time under the conditions of 60°C and 0.1 MPa;

[0028] Figure 2 It is a graph showing the change of the self-degradation rate of the self-degrading plugging agent provided by the present invention with time under the conditions of 100°C and 0.1 MPa;

[0029] Figure 3 It is a graph showing the change of the self-degradation rate of the self-degrading plugging agent provided by the present invention with time under the conditions of 150°C and 2.0 MPa. Detailed Embodiments

[0030] A self-degrading plugging agent for water-based drilling fluid is composed of an epoxy resin core modified with p-styrenesulfonic acid and a polycaprolactone polyol wrapped outside the epoxy resin core modified with p-styrenesulfonic acid.

[0031] In the detailed embodiments, when the polycaprolactone polyol is polycaprolactone diol, the polycaprolactone diol is obtained by the ring-opening polymerization reaction of 1,4-butanediol and ε-caprolactone monomers, and the metal anion complex catalyst used in the ring-opening polymerization reaction is tetrabutyl titanate or tetraphenyltin.

[0032] Taking 100% as the total mass fraction of the 1,4-butanediol, ε-caprolactone monomers and the metal anion complex catalyst, their mass fractions are respectively 2.8-4.3%, 95-97%, and 0.006-0.013%.

[0033] The inert gas introduced into the ring-opening reaction is nitrogen.

[0034] The open-loop polymerization reaction temperature is 110-130 °C, the reaction time is 3-5 h, and after the reaction, the product is cooled to 50-60 °C and stored in a product dryer for standby.

[0035] In the specific embodiment, the preparation method of the styrene sulfonic acid-modified epoxy resin is obtained by reacting 8-17 parts by mass of sodium styrene sulfonate and 35-45 parts of bisphenol A epoxy resin. The specific method includes the following steps: Dissolve 8-17 parts by mass of sodium styrene sulfonate in 100 parts of water, then add 12-15 parts of N,N-dimethylformamide and 5-8 parts of butyl acetate, and stir and react at 50-60 °C for 20-40 min; Add a hydrochloric acid solution with a mass fraction of 5% to adjust the pH of the solution to 3-5; Add 35-45 parts of bisphenol A epoxy resin, raise the temperature to 100-113 °C, and stir and react for 2-3.5 h to obtain the styrene sulfonic acid-modified epoxy resin, which is a light yellow liquid, and the effective content of the modified resin is 33-37%. The bisphenol A epoxy resin is provided by Baling Petrochemical Co., Ltd. of Sinopec Group, and the model is CYD-011E-20.

[0036] A preparation method of a self-degrading plugging agent for water-based drilling fluid includes the following steps: (1) Stir the styrene sulfonic acid-modified epoxy resin, curing agent and curing accelerator evenly, and pulverize after curing to obtain a pulverized cured product; (2) Wrap the pulverized cured product obtained in step (1) with polycaprolactone polyol.

[0037] In the specific embodiment, the pulverization in step (1) is to pulverize the cured product to a particle size of 0.01-1 mm.

[0038] An application of a self-degrading plugging agent for water-based drilling fluid is to add 3-12.5% by mass of the self-degrading plugging agent for water-based drilling fluid to the water-based drilling fluid and apply it to reservoirs with a temperature above 60 °C.

[0039] In the specific embodiment, the water-based drilling fluid includes fresh water and 0.32-0.75% by mass of a viscosifier, 0.82-3.5% of an anti-mud-pack lubricant, 1.3-5.8% of a filtration reducer, and 3-5% of KCl.

[0040] In the specific embodiment, the water-based drilling fluid is prepared according to the standard GB / T 16783.1-2014 "Drilling Fluid Field Test Part 1 Water-Based Drilling Fluid".

[0041] The following further illustrates the implementation manners of the present invention in combination with specific embodiments. The raw materials used in the following embodiments are all conventional commercially available products and are well-known products in this technical field. The tackifier, filtration reducer, and anti-caking lubricant involved in the specific embodiments are all provided by Sinopec North China Oil and Gas Branch Company.

[0042] I. Specific embodiments of the preparation method of the self-degradable plugging agent for water-based drilling fluid of the present invention

[0043] Example 1

[0044] The preparation method of the self-degradable plugging agent for water-based drilling fluid in this example includes the following steps:

[0045] 1. Preparation of styrene sulfonic acid-modified epoxy resin

[0046] Dissolve 10 parts by mass of sodium styrene sulfonate in 100 parts of water, then add 13 parts of N,N-dimethylformamide and 6 parts of butyl acetate, and stir and react at 55°C for 30 min; add a hydrochloric acid solution with a mass fraction of 5% to adjust the pH of the solution to 4; add 40 parts of bisphenol A epoxy resin (CYD-011E-20), raise the temperature to 110°C, and stir and react for 3 h to obtain styrene sulfonic acid-modified epoxy resin, which is a light yellow liquid, and the effective content of the modified resin is 35%.

[0047] 2. Preparation of self-degradable plugging agent for water-based drilling fluid

[0048] (1) Place 5.6 parts by weight of the above-prepared styrene sulfonic acid-modified epoxy resin, 1.46 parts of curing agent 4-methylhexahydrophthalic anhydride, and 1.1 parts of curing accelerator 2-ethyl-4-methylimidazole in a reactor, stir evenly to remove bubbles, heat to 90°C for 2 hours, 160°C for 4 hours, and 180°C for 2 hours to obtain a cured product for pulverization;

[0049] (2) Add 0.056 parts by weight of 1,4-butanediol and 1.9 parts of ε-caprolactone monomer to the reactor, start stirring, pass nitrogen, the reaction temperature is 120°C, add 0.00026 parts of catalyst, after 4 hours of reaction time, cool to 60°C, and store the obtained product polycaprolactone diol in a dryer for standby. Then, fully wrap the pulverized product in step (1) with polycaprolactone diol at 60°C and cool to obtain self-degradable plugging agent particle material with a particle size of 0.01 - 1 mm, denoted as F1.

[0050] The self-degradable plugging agent particle material obtained through the preparation method of this example is the self-degradable plugging agent for water-based drilling fluid provided by the present invention. The same applies to the subsequent examples and will not be repeated.

[0051] Example 2

[0052] The preparation method of the self-degrading plugging agent for water-based drilling fluid in this example includes the following steps:

[0053] (1) Put 10.2 parts by weight of the p-styrenesulfonic acid-modified epoxy resin prepared in Example 1, 2.91 parts of the curing agent methyltetrahydrophthalic anhydride, and 1.43 parts of the curing accelerator m-phenylenediamine into a reactor. After stirring evenly to remove bubbles, heat to 120 °C for curing for 1.5 hours, 170 °C for curing for 3 hours, and 190 °C for curing for 2 hours to obtain a cured product, which is then pulverized;

[0054] (2) Add 0.123 parts by weight of 1,4-butanediol and 2.78 parts of ε-caprolactone monomer to the reactor. After starting stirring, pass nitrogen, with the reaction temperature at 120 °C. Add 0.00031 parts of the catalyst. After a reaction time of 4 h, cool to 60 °C. The obtained product polycaprolactone diol is stored in a dryer for standby. Then, the pulverized product from step (1) and polycaprolactone diol are fully wrapped at 60 °C and then cooled to obtain self-degrading plugging agent particulate material with a particle size of 0.01 - 1 mm, denoted as F2.

[0055] Example 3

[0056] The preparation method of the self-degrading plugging agent for water-based drilling fluid in this example includes the following steps:

[0057] (1) Put 17 parts by weight of the p-styrenesulfonic acid-modified epoxy resin prepared in Example 1, 4.56 parts of the curing agent 4-methylhexahydrophthalic anhydride, and 2.7 parts of the curing accelerator m-phenylenediamine into a reactor. After stirring evenly to remove bubbles, heat to 140 °C for curing for 1 hour, 160 °C for curing for 4 hours, and 190 °C for curing for 2 hours to obtain a cured product, which is then pulverized;

[0058] (2) Add 0.1176 parts by weight of 1,4-butanediol and 4.074 parts of ε-caprolactone monomer to the reactor. After starting stirring, pass nitrogen, with the reaction temperature at 120 °C. Add 0.00042 parts of the catalyst. After a reaction time of 4 h, cool to 60 °C. The obtained product polycaprolactone diol is stored in a dryer for standby. Then, the pulverized product from step (1) and polycaprolactone diol are fully wrapped at 60 °C and then cooled to obtain self-degrading plugging agent particulate material with a particle size of 0.01 - 1 mm, denoted as F3.

[0059] II. Specific examples of the application of the self-degrading plugging agent for water-based drilling fluid of the present invention

[0060] Example 4

[0061] The application of the self-degrading plugging agent for water-based drilling fluid in this example is to add the self-degrading plugging agent particulate material obtained in Example 1 with a mass fraction of 3% into the water-based drilling fluid. The water-based drilling fluid includes fresh water, a thickening agent with a mass fraction of 0.32%, an anti-caking lubricant with a mass fraction of 3.5%, a filtration reducer with a mass fraction of 5.8%, and 4% KCl.

[0062] Example 5

[0063] The application of the self-degrading plugging agent for water-based drilling fluid in this example is to add the self-degrading plugging agent particulate material obtained in Example 2 with a mass fraction of 8.5% into the water-based drilling fluid. The water-based drilling fluid includes fresh water, a thickening agent with a mass fraction of 0.5%, an anti-caking lubricant with a mass fraction of 1.5%, a filtration reducer with a mass fraction of 3.8%, and 4% KCl.

[0064] Example 6

[0065] The application of the self-degrading plugging agent for water-based drilling fluid in this example is to add the self-degrading plugging agent particulate material obtained in Example 3 with a mass fraction of 12.5% into the water-based drilling fluid. The water-based drilling fluid includes fresh water, a thickening agent with a mass fraction of 0.75%, an anti-caking lubricant with a mass fraction of 0.82%, a filtration reducer with a mass fraction of 1.3%, and 4% KCl.

[0066] III. Comparative Examples

[0067] Comparative Example 1

[0068] The preparation method of the self-degrading plugging agent for drilling fluid in this comparative example is different from that of Example 3 in that: polycaprolactone polyol is not introduced, and it includes the following steps:

[0069] Put 17 parts by weight of p-styrenesulfonic acid-modified epoxy resin, 4.56 parts of curing agent 4-methylhexahydrophthalic anhydride, and 2.7 parts of curing accelerator m-phenylenediamine into a reactor, stir evenly to remove bubbles, heat to 140 °C for 1 hour of curing, 160 °C for 4 hours of curing, and 190 °C for 2 hours of curing. The cured product is pulverized to obtain self-degrading plugging agent particulate material with a particle size of 0.01 - 1 mm, denoted as DF1.

[0070] Comparative Example 2

[0071] The application of the self-degrading plugging agent for drilling fluid in this comparative example is different from that of Example 6 in that: the added self-degrading plugging agent is the self-degrading plugging agent particulate material of Comparative Example 1.

[0072] Comparative Example 3

[0073] The application of the self-degrading plugging agent for drilling fluid in this comparative example is different from that of Example 6 in that: no self-degrading plugging agent is added.

[0074] IV. Experimental Examples

[0075] Experimental Example 1

[0076] In this experimental example, 100 parts of clear water were respectively added with the self-degrading plugging agent particle materials with a particle size of 100 mesh obtained in Examples 1-3 and Comparative Example 1 with a mass fraction of 6%, and the degradation performance tests were carried out under the conditions of 60 °C, 0.1 MPa; 100 °C, 0.1 MPa; 150 °C, 2.0 MPa. The experimental results are as Figures 1-3 shown.

[0077] According to Figure 1 the experimental results, the self-degrading plugging agent provided by the present invention can effectively carry out self-degradation under the condition of 60 °C. In the first 2 days, the degradation rate of the self-degrading plugging agent is very slow, and the degradation rate is only 6.1%. At this time, part of the polycaprolactone diol wrapped outside degrades, and the reservoir pores can be plugged during this period to reduce the invasion of solid particles in the drilling fluid into the formation. As time goes by, the epoxy resin modified with p-styrenesulfonic acid begins to thermally degrade, and the degradation rate can reach 86.1% at 60 °C in 20 days. The self-degrading plugging agent of the comparative example is not wrapped by polycaprolactone diol, and its degradation speed is relatively fast, and the reservoir protection effect is limited.

[0078] Similarly, according to Figure 2 the experimental results, the self-degrading plugging agent provided by the present invention can also effectively carry out self-degradation under the condition of 100 °C. In the first 2 days, the degradation rate of the self-degrading plugging agent is relatively slow, and the degradation rate is 12.1%. As time goes by, the degradation rate is as high as 95.38% at 100 °C in 20 days.

[0079] According to Figure 3 the experimental results, the self-degrading plugging agent provided by the present invention can also effectively carry out self-degradation under the condition of 150 °C. In the first 2 days, the degradation rate of the self-degrading plugging agent is relatively slow, and the degradation rate is 18%. As time goes by, the degradation rate is as high as 100% at 150 °C in 20 days.

[0080] In summary, from the perspective of the degradation effect, the self-degrading plugging agent of the present invention can plug and protect the reservoir within a certain time range and has a strong self-degrading ability under the conditions of 60 °C, 0.1 MPa; 100 °C, 0.1 MPa; 150 °C, 2.0 MPa.

[0081] Experimental Example 2

[0082] In this experimental example, the reservoir protection performance of the water-based drilling fluid prepared with the self-degrading plugging agent provided by the present invention was tested. The specific test method was as follows: The on-site reservoir cores of Sinopec North China Oil and Gas Company were used. According to the national petroleum and natural gas industry standard SY / T 6540-2021 "Laboratory Evaluation Method for Damage of Drilling Fluid and Completion Fluid to Oil Reservoirs" of the People's Republic of China, the degree of formation pollution damage of the water-based drilling fluid prepared in this application was tested through a dynamic pollution experiment. Among them, the test temperatures of Examples 4 to 6 were 60 °C, 100 °C, and 150 °C respectively, and the test temperatures of Comparative Examples 2 to 3 were both 150 °C. The test results are shown in Table 1.

[0083] Table 1 Changes in core permeability after displacement of reservoir protection water-based drilling fluid

[0084]

[0085] As can be seen from Table 1, for the on-site sandstone reservoir, the reservoir protection water-based drilling fluid formed by the self-degrading plugging agent of the present invention can effectively plug the core under the reservoir conditions of 60-150 °C. The plugging rate can reach 99.57%. The recovery value of the plugging permeability after backflow displacement is as high as 99.43% after 15 days. Compared with the degradable plugging agent not wrapped by polycaprolactone diol in Comparative Example 2, its plugging effect in the drilling fluid is poor and the permeability recovery is too fast, indicating that polycaprolactone polyol can delay the thermal degradation rate of the epoxy resin modified with styrene sulfonic acid, enabling it to have enough time to ensure the reservoir protection effect. In Comparative Example 3, the drilling fluid without the addition of the self-degrading plugging agent has a very poor plugging effect on the reservoir and cannot completely prevent the invasion of solid particles in the drilling fluid into the formation.

[0086] Therefore, the water-based drilling fluid formed by the self-degrading plugging agent of the present invention can automatically achieve backflow plug removal through self-degrading reaction after the drilling is completed, maximize the release of oil and gas production capacity, without the need for additional operations such as acid washing to remove the filter cake, avoiding secondary damage to the oil and gas reservoir, saving operation procedures and time, effectively shortening the completion cycle, and the formed organic acid during degradation helps to remove partial particulate matter blockage in the formation, can effectively improve the connectivity between reservoirs, increase the permeability of the oil and gas reservoir, and improve the fluidity of oil and gas in the reservoir. It is a simple, efficient, economical, and non-side-effect reservoir protection new technology.

[0087] The above embodiments are only the preferred embodiments of the present invention. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A self-degradable plugging agent for water-based drilling fluid, characterized in that: The invention consists of an epoxy resin core modified with p-styrene sulfonic acid and a polycaprolactone polyol wrapped outside the epoxy resin core modified with p-styrene sulfonic acid.

2. The self-degradable plugging agent for water-based drilling fluid according to claim 1, characterized in that: The mass ratio of the polycaprolactone polyol to the epoxy resin modified by styrene sulfonic acid is 1-3.5:6-16.

2.

3. The self-degradable plugging agent for water-based drilling fluid according to claim 1, characterized in that: The weight average molecular weight of the polycaprolactone polyol is 200-360, and the softening point is 50-70°C.

4. The self-degradable plugging agent for water-based drilling fluid according to any one of claims 1 to 3, characterized in that: The polycaprolactone polyol is polycaprolactone diol.

5. The self-degradable plugging agent for water-based drilling fluid according to claim 1, characterized in that: The self-degradable plugging agent is solid particles with a particle size of 0.1 to 1 mm.

6. A method for preparing a self-degradable plugging agent for water-based drilling fluid according to claim 1, characterized in that: The method comprises the following steps: (1) uniformly stirring a styrene sulfonic acid-modified epoxy resin, a curing agent and a curing accelerator, and crushing the mixture after curing to obtain a crushed cured product; and (2) wrapping the crushed cured product of step (1) with polycaprolactone polyol.

7. The method for preparing a self-degradable plugging agent for water-based drilling fluid according to claim 6, characterized in that: Based on 100% by mass, the epoxy resin modified with 4.2-14.3% p-styrene sulfonic acid and the following components by mass fraction: Composition: 25-68% of polycaprolactone polyol, 5.42-18.6% of curing agent and 4-10.7% of curing accelerator.

8. The method for preparing a self-degradable plugging agent for water-based drilling fluid according to claim 6, characterized in that: The curing agent in step (1) is an acid anhydride curing agent, the acid anhydride curing agent is 4-methylhexahydrophthalic anhydride or methyltetrahydrophthalic anhydride, and the curing accelerator is 2-ethyl-4-methylimidazole or m-phenylenediamine.

9. The method for preparing a self-degradable plugging agent for water-based drilling fluid according to claim 6, characterized in that: The wrapping temperature during wrapping in the step (2) is 50-70°C.

10. An application of the self-degradable plugging agent for water-based drilling fluid according to claim 1, characterized in that: The water-based drilling fluid self-degradable plugging agent with a mass fraction of 3 to 12.5% ​​is added to the water-based drilling fluid and applied to a reservoir with a temperature above 60°C.

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