Leaking stoppage material, preparation method and application

Abstract

The invention relates to the technical field of oil and gas drilling and completion, in particular to a leaking stoppage material and a preparation method and application thereof, and the leaking stoppage material comprises 1-3 wt% of calcium carbonate, 1-2 wt% of white asphalt and 1-2 wt% of modified polylactic acid. Through the synergistic effect of white asphalt and calcium carbonate, the structural stability of the plugging layer is enhanced; under the action of modified polylactic acid, polymer micelles can be pressed and attached to the surface of well wall rock and are associated to form a plugging layer, so that the permeability of the plugging layer is effectively reduced, and the damage to a reservoir is reduced; under the combined action of calcium carbonate, white asphalt and modified polylactic acid, the plugging material is endowed with better plugging strength, has better degradability, does not need a complicated plugging removal procedure, and does not generate new chemical or mechanical plugging, so that secondary damage to a reservoir is avoided. The problems that in the prior art, a leakage-proof and leakage-stopping material is poor in leakage-proof and leakage-stopping capacity, the later-period plug removal process is complex, and a reservoir is prone to being damaged are solved.

Description

Technical Field

[0001] This invention relates to the field of oil and gas drilling and completion technology, specifically to a plugging material, its preparation method, and its application, particularly a low-damage, easily removable plugging material, its preparation method, and its application suitable for drilling and completion of fractured reservoirs. Background Technology

[0002] Well leakage refers to the phenomenon where various working fluids leak into the formation under pressure differential during downhole operations such as drilling, cementing, and testing in oil and gas exploration and development. Well leakage causes a drop in fluid column pressure within the wellbore, increasing the risk of well collapse and stuck pipe. It not only prolongs the drilling cycle and results in significant mud loss, but also triggers numerous complex downhole situations, even leading to wellbor abandonment, causing substantial economic losses and safety hazards. For fractured reservoirs, the naturally developed fracture network serves as the main seepage channel, which is beneficial for the efficient development of fractured oil and gas reservoirs. However, the presence of the fracture network also leads to working fluid loss, resulting in well leakage, which in turn induces severe reservoir damage, delays the development of oil and gas resources, and reduces economic benefits. Working fluid loss is very common during the exploration and development of fractured oil and gas reservoirs, and can occur at multiple stages of exploration and development, including drilling, completion, well testing, and workover. Typical fractured oil and gas reservoirs mainly include carbonate rock, tight sandstone, and shale oil and gas reservoirs. Therefore, reservoir protection is a key technology and an important research area throughout the entire process of exploration and development of fractured oil and gas reservoirs, and effectively controlling the loss of working fluid is the core issue of reservoir protection in fractured oil and gas reservoirs.

[0003] Current reservoir protection methods and unblocking technologies mainly involve scientifically and rationally selecting early-stage shielding and temporary plugging, or later-stage acidizing and unblocking technologies, such as bio-enzyme unblocking, based on different blockage and reservoir conditions. Chinese invention patent CN105154046A discloses a method for plugging lost drilling fluid during oil and gas reservoir drilling, specifically involving a plugging slurry for fractured reservoirs and methods for temporary plugging and unblocking of fractured reservoirs. This method includes a scaling agent, a scale inhibitor that prevents chemical reaction of the scaling agent under normal temperature conditions and is susceptible to formation temperature degradation, and a stabilizer. The plugging slurry is pumped into the lost reservoir using a mud pump. The scale inhibitor in the slurry, affected by formation temperature, undergoes a chemical reaction to generate calcium carbonate particles, which seal the fractured layer. After drilling is completed, an acid washing solution is pumped from the wellhead to release the calcium carbonate particles from the fractured layer. This plugging method effectively reduces damage to reservoir fractures and achieves temporary sealing. However, this method of sealing involves complex unblocking processes. If the acid unblocking is not handled properly, it can cause new chemical or mechanical blockages, resulting in secondary damage to the reservoir and reduced formation permeability.

[0004] Chinese invention patent CN117343699A discloses a drilling-while-drilling plugging gel composite fiber, comprising 30-50 parts by weight of ultrafine plant fiber, 0.5-4 parts by weight of composite wetting agent, 0.5-4 parts by weight of flow modifier, 1-5 parts by weight of liquid sand-fixing agent, 20-40 parts by weight of calcium carbonate, and 10-30 parts by weight of composite special gel. The fineness of the raw materials of the gel composite fiber of this invention meets the requirement of passing through a 120-mesh sieve, thus meeting the purpose of long-term leakage prevention and plugging. The gel composite fiber can improve the sealing performance of drilling fluid, and the filtration loss of 40-60 mesh sand beds is reduced by 20% compared with conventional drilling-while-drilling leakage prevention and plugging agents. It can improve the compressive strength of sand beds. Under a pressure of 3.5 MPa, the depth of sand bed sealing and solidification is 1 cm, and the sand bed maintains its aggregated state without loosening. Under extreme dosage conditions, a sealing mud cake is formed, and the solidified compressive strength is ≥1 MPa. This increases the formation pressure bearing capacity of the drilling well by 2 MPa / 1000m. However, the main components of the drilling plugging gel composite fiber material include a composite special gel (white silicate cement, diatomaceous earth, and mineral fiber powder in a weight percentage of 9:5:6) and composite plant fibers. When the silicate cement and diatomaceous earth solid particles invade the fractures near the wellbore under the extreme dosage conditions, they will form a plugging mud cake. The solidified compressive strength of this mud cake is ≥1MPa, which seriously affects the recovery of fracture productivity in the later stage and causes reservoir pollution and damage. In addition, the composite plant fibers are difficult to be dissolved by acid in the later acid unblocking process, causing pollution.

[0005] Therefore, it is urgent to select suitable low-damage leak prevention and plugging materials and form a reasonable particle size distribution to ensure the leak prevention and plugging capabilities of drilling fluid while enhancing the reservoir protection performance of the plugging layer and reducing reservoir damage. Summary of the Invention

[0006] To address the problems of poor leak prevention and plugging capabilities, complex post-plugging processes, and potential damage to reservoirs in existing leak prevention and plugging materials, this invention provides a plugging material, its preparation method, and its application.

[0007] To achieve the above objectives, the present invention employs the following technical solution: The present invention provides a leak-sealing material comprising 1 wt% to 3 wt% calcium carbonate, 1 wt% to 2 wt% white asphalt and 1 wt% to 2 wt% modified polylactic acid.

[0008] Optionally, the calcium carbonate includes 20-30 mesh calcium carbonate, 35-45 mesh calcium carbonate and 50-60 mesh calcium carbonate, and the mass ratio of the 20-30 mesh calcium carbonate, 35-45 mesh calcium carbonate and 50-60 mesh calcium carbonate is (45-55):(30-40):(10-25).

[0009] Optionally, the pH value of the white asphalt is 7-10, and the high-temperature and high-pressure filtration loss is ≤25ml under the following conditions: 120℃, pressure difference of 3.5Mpa, and test time of 30min, and the fluorescence level is ≤5.

[0010] Optionally, the modified polylactic acid comprises the following raw material components by mass: 15-20 parts of polyacrylamide, 7.5-10 parts of polylactic acid, 2-4 parts of sodium bicarbonate, 0.2-4 parts of potassium hydroxide, and 5-10 parts of triethylamine.

[0011] Optionally, the modified polylactic acid is prepared by: Polyacrylamide was heated, and polylactic acid, sodium bicarbonate, potassium hydroxide and triethylamine were added in sequence to obtain modified polylactic acid.

[0012] Optionally, the method of heating polyacrylamide and sequentially adding polylactic acid, sodium bicarbonate, potassium hydroxide, and triethylamine to obtain modified polylactic acid is as follows: Polyacrylamide particles were placed in a high-temperature reactor and heated to 260℃~280℃ using an oil bath. Polylactic acid, sodium bicarbonate, and potassium hydroxide were added sequentially under stirring at 100~200r / min. The mixture was stirred continuously for 60~90min. After adding triethylamine, heating and stirring were stopped. The reactants were allowed to cool naturally to obtain a grayish-white solid product. The obtained grayish-white solid product was pulverized and passed through a standard 65~85 mesh solid particle filter to modify polylactic acid.

[0013] The preparation method of the above-mentioned sealing material includes: Mix white asphalt with water until homogeneous to obtain white asphalt adhesive; After mixing calcium carbonate and modified polylactic acid evenly, add them to white asphalt adhesive and mix evenly to obtain a sealing material.

[0014] Optionally, the method for uniformly mixing white asphalt with water to obtain white asphalt adhesive is as follows: mix white asphalt with water, stir at room temperature at a speed of 3500-4500 r / min for 25-35 min, and let stand for 18-24 h to obtain white asphalt adhesive.

[0015] Optionally, calcium carbonate and modified polylactic acid are mixed evenly and then added to white asphalt adhesive, and mixed evenly to obtain the sealing material. Calcium carbonate and modified polylactic acid are mixed evenly and dried at 70℃~75℃ for 5~7h to obtain a mixed powder. The mixed powder is added to the white asphalt adhesive and stirred for more than 2 hours at room temperature to obtain the sealing material.

[0016] Such as the application of plugging materials in drilling and completion of fractured reservoirs.

[0017] Compared with the prior art, the present invention has the following beneficial effects: This invention discloses a plugging material comprising 1 wt%–3 wt% calcium carbonate, 1 wt%–2 wt% white bitumen, and 1 wt%–2 wt% modified polylactic acid. The calcium carbonate exhibits significant acid solubility (up to 99.9%) and high compressive strength, enabling it to form the framework of the plugging layer. The white bitumen particles are non-toxic and readily degradable, causing no impact on geological logging. Furthermore, under formation temperature of 90°C and pressure, they undergo elastic deformation, filling the pores between the calcium carbonate particles, thereby improving the internal structure of the plugging layer and significantly enhancing its structural stability. Finally, the introduced modified polylactic acid is a self-degradable polymer, and when it reaches a critical concentration, it can form polymer micelles in water. Under the action of pressure difference, the polymer micelles can be pressed onto the surface of the wellbore rock and associate to form a plugging layer. When the pressure increases, the micelles are further compressed, effectively reducing the permeability of the plugging layer and reducing damage to the reservoir. By combining the effects of calcium carbonate, white asphalt and modified polylactic acid, the plugging material is given better plugging strength and better degradability. It does not require a complicated unplugging procedure and will not generate new chemical or mechanical blockages, thus avoiding secondary damage to the reservoir. The calcium carbonate includes 20-30 mesh (850-600μm) calcium carbonate, 35-45 mesh (500-300μm) calcium carbonate, and 50-60 mesh (300-250μm) calcium carbonate. The mass ratio of 20-30 mesh, 35-45 mesh, and 50-60 mesh calcium carbonate is (45-55):(30-40):(10-25). This allows for the formation of a drilling-while-drilling sealing layer framework for fractures of 0.8 mm and below. Specifically, 20-30 mesh calcium carbonate can form a bridging structure within the fracture width range of 0.8*2 / 3 mm to 0.8 mm, 35-45 mesh (500-300μm) calcium carbonate can form a bridging structure within the fracture width range of 0.8*1 / 3 mm to 0.8*2 / 3 mm, and 50-60 mesh calcium carbonate can form a bridging structure within the fracture width range below 0.8*1 / 3 mm.

[0018] The white asphalt has a pH value of 7-10, a high-temperature and high-pressure filtration loss of ≤25ml / (120℃×3.5MPa×30min), and a fluorescence level of ≤5. Low fluorescence (fluorescence level ≤5) minimizes interference with formation parameter information acquisition during logging, meeting petroleum geology requirements while protecting the environment. Under high-temperature and high-pressure conditions, the white asphalt can transform into tough particles of a certain size, filling the pores and micro-fractures between calcium carbonate bridging particles and participating in filter cake formation. Controlling the high-temperature and high-pressure filtration loss of the white asphalt to ≤25ml / (120℃×3.5MPa×30min) effectively prevents drilling fluid loss, improves mud cake quality, enhances the internal structure of the sealing layer, and significantly strengthens the structural stability of the sealing layer.

[0019] Polylactic acid (PLA) possesses excellent mechanical properties and good biodegradability. Under natural conditions, it can be completely degraded into CO2 and H2O, although the degradation cycle still takes several years. The purpose of modification is to enhance its self-degradability. Compared to existing PLA, the self-made PLA (70-75 mesh) is itself a self-degradable polymer. When added to the plugging material formulation, the degradation rate of the mud cake formed in the drilling fluid system significantly increases, effectively improving the efficiency of unblocking in the later stages. Furthermore, when a critical concentration is reached, it can form polymer micelles in water, easily suspending and stabilizing in the plugging fluid. It can be used as a filler material to densely fill micropores and fissures in the formation, improving the drilling fluid's leak-proof and plugging capabilities.

[0020] This invention also provides a method for preparing the above-mentioned plugging material. This method involves uniformly mixing white asphalt with water to obtain a white asphalt binder; uniformly mixing calcium carbonate and modified polylactic acid and then adding the mixture to the white asphalt binder, mixing thoroughly to obtain the plugging material. The preparation method is simple, the reaction conditions are mild, the equipment requirements are low, and it is suitable for industrialization. Furthermore, the plugging material produced has a high-temperature and high-pressure (HTHP) filtration loss of only 7.2 mL after aging at 120°C, effectively reducing the intrusion of drilling fluid filtrate. Simultaneously, after plugging with the plugging material of this invention, the particle size value (D) corresponding to a cumulative volume fraction of drilling fluid reaching 90% on the cumulative particle size distribution curve is... 90 The value increased from 200μm to 756μm, which is conducive to the formation of a dense plugging layer. It can plug fractures with a width of ≤0.8mm during drilling. Under a pressure of 5MPa, the leakage of a 0.8mm fracture plate is only 185mL. The permeability recovery value of the core is as high as 90% or more. Moreover, the degradation rate of the mud cake formed by the drilling fluid system after 8 days increased from 2.56% to 40.48%.

[0021] The aforementioned plugging material is used in the drilling and completion of fractured reservoirs. Applying this plugging material to fractured reservoir drilling and completion can effectively fill the fractures in the reservoir, preventing leakage of drilling fluid or other fluids, improving the safety and efficiency of drilling operations. Furthermore, due to its good biodegradability, the plugging material can degrade itself after completion, eliminating the need for additional unplugging operations. This reduces the damage to the reservoir caused by cumbersome unplugging procedures, minimizes the environmental impact of drilling operations and the subsequent production recovery, and enhances the productivity and stability of drilling operations. This is of great significance for the sustainable development of the oil and gas exploration and development industry. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of a method for preparing a leak-sealing material according to the present invention.

[0023] Figure 2 This is a particle size distribution test diagram of the composite salt drilling fluid in the field.

[0024] Figure 3 This is a particle size distribution test diagram of the plugging material formulation plus the on-site composite salt drilling fluid in Example 1 of the present invention.

[0025] Figure 4 This is a graph showing the degradation performance evaluation of the composite salt drilling fluid after aging for different times.

[0026] Figure 5 The degradation performance evaluation diagram is shown for the plugging material prepared according to the embodiments of the present invention after aging for different times with the on-site composite salt drilling fluid. Detailed Implementation

[0027] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0028] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0029] The present invention will be further described in detail below with reference to specific embodiments. These descriptions are for explanation purposes only and are not intended to limit the scope of the invention.

[0030] This invention discloses a plugging material comprising 1 wt% to 3 wt% calcium carbonate, 1 wt% to 2 wt% white asphalt, and 1 wt% to 2 wt% modified polylactic acid, with the balance being water or on-site drilling fluid; preferably, it comprises 2 wt% to 3 wt% calcium carbonate, 1.5 wt% to 2 wt% white asphalt, and 1 wt% to 2 wt% modified polylactic acid; more preferably, it comprises 2 wt% to 3 wt% calcium carbonate, 1.5 wt% to 2 wt% white asphalt, and 1 wt% to 2 wt% modified polylactic acid; The calcium carbonate is composed of calcium carbonate of different particle sizes. Preferably, the calcium carbonate includes 20-30 mesh (850-600 μm) calcium carbonate, 35-45 mesh (500-300 μm) calcium carbonate, and 50-60 mesh (300-250 μm) calcium carbonate, with a mass ratio of (45-55):(30-40):(10-25). More preferably, the mass ratio of 20-30 mesh, 35-45 mesh, and 50-60 mesh calcium carbonate is (45-50):(30-35):(15-20). More preferably, the mass ratio of 20-30 mesh, 35-45 mesh, and 50-60 mesh calcium carbonate is 50:35:15. Preferably, the white asphalt has a pH value of 7-10, a high-temperature and high-pressure filtration loss of ≤25ml / (120℃×3.5MPa×30min), and a fluorescence level of ≤5; The modified polylactic acid comprises the following raw material components by mass: 15-20 parts of polyacrylamide, 7.5-10 parts of polylactic acid, 2-4 parts of sodium bicarbonate, 0.2-4 parts of potassium hydroxide, and 5-10 parts of triethylamine. Preferably, it comprises 15-18 parts of polyacrylamide, 9-10 parts of polylactic acid, 2-3 parts of sodium bicarbonate, 0.2-3 parts of potassium hydroxide, and 5-8 parts of triethylamine. More preferably, it comprises 15-17 parts of polyacrylamide, 9-9.5 parts of polylactic acid, 2-2.5 parts of sodium bicarbonate, 0.2-2 parts of potassium hydroxide, and 7-8 parts of triethylamine. More preferably, 16 parts of polyacrylamide are heated to 260°C, and 9 parts of polylactic acid, 3 parts of sodium bicarbonate, 2 parts of potassium hydroxide, and 7 parts of triethylamine are added sequentially. The modified polylactic acid is prepared by: Polyacrylamide was heated to 250℃~280℃, and polylactic acid, sodium bicarbonate, potassium hydroxide, and triethylamine were added sequentially to react and obtain modified polylactic acid. The specific operation was as follows: polyacrylamide particles were placed in a high-temperature reactor, and the temperature was gradually raised to 260℃~280℃ using an oil bath heating device. Polylactic acid, sodium bicarbonate, and potassium hydroxide were added sequentially under stirring at 100~200r / min, and stirring was continued for 60~90min. After adding triethylamine, heating and stirring were stopped, and the reactants were allowed to cool naturally to obtain a grayish-white solid product. The obtained solid product was pulverized into solid particles that passed through a standard 65~85 mesh sieve, preferably 70~75 mesh, to obtain modified polylactic acid.

[0031] The calcium carbonate itself has significant acid solubility, reaching 99.9%, and possesses high compressive strength, enabling it to form the sealing layer skeleton. The white asphalt particles are non-toxic and easily degradable, having no impact on geological logging. Furthermore, they undergo elastic deformation under formation temperature of 120℃ and pressure, with the deformed white asphalt filling the pores between the calcium carbonate particles, thereby improving the internal structure of the sealing layer and significantly enhancing its structural stability. Finally, the introduced modified polylactic acid is a self-degradable polymer. When a critical concentration is reached, it can form polymer micelles in water. Under pressure differential, these micelles can adhere to the wellbore rock surface and associate to form the sealing layer. As pressure increases, the micelles further compress, effectively reducing the permeability of the sealing layer and minimizing damage to the reservoir. Through the combined action of calcium carbonate, white asphalt, and modified polylactic acid, the plugging material is endowed with better sealing strength and better degradability, eliminating the need for complex unblocking procedures and preventing new chemical or mechanical blockages, thus avoiding secondary damage to the reservoir.

[0032] See Figure 1 The present invention also provides a method for preparing the above-described sealing material, comprising: S1: Mix white asphalt and water evenly to obtain white asphalt adhesive. The specific operation is as follows: Mix white asphalt with water or on-site drilling fluid, stir at 3500-4500 r / min for 25-35 min at room temperature, and let stand for 18-24 h to obtain white asphalt adhesive; S2: After thoroughly mixing calcium carbonate and modified polylactic acid, add them to the white asphalt adhesive and mix well to obtain the sealing material. The specific operation is as follows: Calcium carbonate and modified polylactic acid are mixed evenly and dried at 70℃~75℃ for 5~7h to obtain a mixed powder. The mixed powder is added to the white asphalt adhesive and stirred for more than 2 hours at room temperature to obtain the sealing material.

[0033] This method is simple, has mild reaction conditions, low equipment requirements, and is suitable for industrialization. The produced plugging material has better plugging performance and is biodegradable, which can ensure production capacity and stability while reducing the risk of damage to reservoirs and the environment.

[0034] Example 1 This invention provides a method for preparing a sealing material, the sealing material comprising 2 wt% calcium carbonate, 1 wt% white asphalt and 1 wt% modified polylactic acid, wherein the calcium carbonate is a composite of 20-30 mesh calcium carbonate, 35-45 mesh calcium carbonate and 50-60 mesh calcium carbonate, in a mass ratio of 50:35:15. The modified polylactic acid is prepared as follows: 18 parts of polyacrylamide are heated to 260°C, and 8 parts of polylactic acid, 4 parts of sodium bicarbonate, 3 parts of potassium hydroxide, and 8 parts of triethylamine are added sequentially to obtain modified polylactic acid. Specifically, polyacrylamide particles are placed in a high-temperature reactor, and the temperature is gradually increased to 260°C using an oil bath heating device. Polylactic acid, sodium bicarbonate, and potassium hydroxide are added sequentially under stirring at 150 r / min, and stirring is continued for 75 min. After adding triethylamine, heating and stirring are stopped, and the reactants are allowed to cool naturally to obtain a grayish-white solid product. The obtained solid product is pulverized to pass through a standard 75 mesh to obtain modified polylactic acid.

[0035] White asphalt was mixed with on-site drilling fluid and stirred at 4000 r / min for 30 min at room temperature. After standing for 24 h, white asphalt adhesive was obtained. Calcium carbonate and modified polylactic acid were mixed evenly and dried at 75°C for 6 hours to obtain a mixed powder. The mixed powder is added to the white asphalt adhesive and stirred for more than 2 hours at room temperature to obtain the sealing material.

[0036] Example 2 This invention provides a method for preparing a sealing material, the sealing material comprising 1.5 wt% calcium carbonate, 2 wt% white asphalt and 1 wt% modified polylactic acid, wherein the calcium carbonate composition is: 20-30 mesh calcium carbonate, 35-45 mesh calcium carbonate and 50-60 mesh calcium carbonate in a mass ratio of 50:35:15; The modified polylactic acid is prepared as follows: 20 parts of polyacrylamide are heated to 260°C, and 10 parts of polylactic acid, 4 parts of sodium bicarbonate, 3 parts of potassium hydroxide, and 8 parts of triethylamine are added sequentially to obtain modified polylactic acid. Specifically, polyacrylamide particles are placed in a high-temperature reactor, and the temperature is gradually increased to 260°C using an oil bath heating device. Polylactic acid, sodium bicarbonate, and potassium hydroxide are added sequentially under stirring at 150 r / min, and stirring is continued for 75 min. After adding triethylamine, heating and stirring are stopped, and the reactants are allowed to cool naturally to obtain a grayish-white solid product. The obtained solid product is pulverized to pass through a standard 75 mesh to obtain modified polylactic acid.

[0037] White asphalt was mixed with on-site drilling fluid and stirred at 4000 r / min for 30 min at room temperature. After standing for 24 h, white asphalt adhesive was obtained. Calcium carbonate and modified polylactic acid were mixed evenly and dried at 75°C for 6 hours to obtain a mixed powder. The mixed powder is added to the white asphalt adhesive and stirred for more than 2 hours at room temperature to obtain the sealing material.

[0038] Example 3 This invention provides a method for preparing a sealing material, the sealing material comprising 2.0 wt% calcium carbonate, 1.5 wt% white asphalt and 1.5 wt% modified polylactic acid, wherein the calcium carbonate is a composite of 20-30 mesh calcium carbonate, 35-45 mesh calcium carbonate and 50-60 mesh calcium carbonate, in a mass ratio of 50:35:15. The modified polylactic acid is prepared as follows: 15 parts of polyacrylamide are heated to 260°C, and 7.5 parts of polylactic acid, 2 parts of sodium bicarbonate, 0.5 parts of potassium hydroxide, and 5 parts of triethylamine are added sequentially to obtain modified polylactic acid. Specifically, polyacrylamide particles are placed in a high-temperature reactor, and the temperature is gradually increased to 260°C using an oil bath heating device. Polylactic acid, sodium bicarbonate, and potassium hydroxide are added sequentially under stirring at 150 r / min, and stirring is continued for 75 min. After adding triethylamine, heating and stirring are stopped, and the reactants are allowed to cool naturally to obtain a grayish-white solid product. The obtained solid product is pulverized to pass through a standard 75 mesh to obtain modified polylactic acid.

[0039] White asphalt was mixed with on-site drilling fluid and stirred at 4000 r / min for 30 min at room temperature. After standing for 24 h, white asphalt adhesive was obtained. Calcium carbonate and modified polylactic acid were mixed evenly and dried at 75°C for 6 hours to obtain a mixed powder. The mixed powder is added to the white asphalt adhesive and stirred for more than 2 hours at room temperature to obtain the sealing material.

[0040] Example 4 This invention provides a method for preparing a sealing material, the sealing material comprising 2 wt% calcium carbonate, 2 wt% white asphalt and 2 wt% modified polylactic acid, wherein the calcium carbonate is a composite of 20-30 mesh calcium carbonate, 35-45 mesh calcium carbonate and 50-60 mesh calcium carbonate, in a mass ratio of 50:35:15. The modified polylactic acid is prepared as follows: 17 parts of polyacrylamide are heated to 260°C, and 8 parts of polylactic acid, 2.5 parts of sodium bicarbonate, 0.8 parts of potassium hydroxide, and 8 parts of triethylamine are added sequentially to obtain modified polylactic acid. Specifically, polyacrylamide particles are placed in a high-temperature reactor, and the temperature is gradually raised to 260°C using an oil bath heating device. Polylactic acid, sodium bicarbonate, and potassium hydroxide are added sequentially under stirring at 150 r / min, and stirring is continued for 75 min. After adding triethylamine, heating and stirring are stopped, and the reactants are allowed to cool naturally to obtain a grayish-white solid product. The obtained solid product is pulverized to pass through a standard 75 mesh to obtain modified polylactic acid.

[0041] White asphalt was mixed with on-site drilling fluid and stirred at 4000 r / min for 30 min at room temperature. After standing for 24 h, white asphalt adhesive was obtained. Calcium carbonate and modified polylactic acid were mixed evenly and dried at 75°C for 6 hours to obtain a mixed powder. The mixed powder is added to the white asphalt adhesive and stirred for more than 2 hours at room temperature to obtain the sealing material.

[0042] Example 5 This invention provides a method for preparing a sealing material, the sealing material comprising 2 wt% calcium carbonate, 2.0 wt% white asphalt and 1.5 wt% modified polylactic acid, wherein the calcium carbonate is a composite of 20-30 mesh calcium carbonate, 35-45 mesh calcium carbonate and 50-60 mesh calcium carbonate, in a mass ratio of 50:35:15. The modified polylactic acid is prepared as follows: 18 parts of polyacrylamide are heated to 260°C, and 10 parts of polylactic acid, 3.5 parts of sodium bicarbonate, 3 parts of potassium hydroxide, and 8 parts of triethylamine are added sequentially to obtain modified polylactic acid. Specifically, polyacrylamide particles are placed in a high-temperature reactor, and the temperature is gradually increased to 260°C using an oil bath heating device. Polylactic acid, sodium bicarbonate, and potassium hydroxide are added sequentially under stirring at 150 r / min, and stirring is continued for 75 min. After adding triethylamine, heating and stirring are stopped, and the reactants are allowed to cool naturally to obtain a grayish-white solid product. The obtained solid product is pulverized to pass through a standard 75 mesh to obtain modified polylactic acid.

[0043] White asphalt was mixed with water and stirred at 4000 r / min for 30 min at room temperature. After standing for 24 h, white asphalt adhesive was obtained. Calcium carbonate and modified polylactic acid were mixed evenly and dried at 75°C for 6 hours to obtain a mixed powder. The mixed powder is added to the white asphalt adhesive and stirred for more than 2 hours at room temperature to obtain the sealing material.

[0044] Example 6 This invention provides a method for preparing a sealing material, the sealing material comprising 1.5 wt% calcium carbonate, 1.5 wt% white asphalt and 1.5 wt% modified polylactic acid, wherein the calcium carbonate is a composite of 20-30 mesh calcium carbonate, 35-45 mesh calcium carbonate and 50-60 mesh calcium carbonate, in a mass ratio of 50:35:15. The modified polylactic acid is prepared as follows: 18 parts of polyacrylamide are heated to 260°C, and 8 parts of polylactic acid, 3.5 parts of sodium bicarbonate, 3 parts of potassium hydroxide, and 7 parts of triethylamine are added sequentially to obtain modified polylactic acid. Specifically, polyacrylamide particles are placed in a high-temperature reactor, and the temperature is gradually increased to 260°C using an oil bath heating device. Polylactic acid, sodium bicarbonate, and potassium hydroxide are added sequentially under stirring at 150 r / min, and stirring is continued for 75 min. After adding triethylamine, heating and stirring are stopped, and the reactants are allowed to cool naturally to obtain a grayish-white solid product. The obtained solid product is pulverized to pass through a standard 75 mesh to obtain modified polylactic acid.

[0045] White asphalt was mixed with water and stirred at 4000 r / min for 30 min at room temperature. After standing for 24 h, white asphalt adhesive was obtained. Calcium carbonate and modified polylactic acid were mixed evenly and dried at 75°C for 6 hours to obtain a mixed powder. The mixed powder is added to the white asphalt adhesive and stirred for more than 2 hours at room temperature to obtain the sealing material.

[0046] Example 7 This invention provides a method for preparing a sealing material, the sealing material comprising 1.0 wt% calcium carbonate, 1.0 wt% white asphalt and 1.0 wt% modified polylactic acid, wherein the calcium carbonate is a composite of 20-30 mesh calcium carbonate, 35-45 mesh calcium carbonate and 50-60 mesh calcium carbonate, in a mass ratio of 50:35:15. The modified polylactic acid is prepared as follows: 19 parts of polyacrylamide are heated to 260°C, and 9 parts of polylactic acid, 4 parts of sodium bicarbonate, 3 parts of potassium hydroxide, and 8 parts of triethylamine are added sequentially to obtain modified polylactic acid. Specifically, polyacrylamide particles are placed in a high-temperature reactor, and the temperature is gradually increased to 260°C using an oil bath heating device. Polylactic acid, sodium bicarbonate, and potassium hydroxide are added sequentially under stirring at 150 r / min, and stirring is continued for 75 min. After adding triethylamine, heating and stirring are stopped, and the reactants are allowed to cool naturally to obtain a grayish-white solid product. The obtained solid product is pulverized to pass through a standard 75 mesh to obtain modified polylactic acid.

[0047] White asphalt was mixed with water and stirred at 4000 r / min for 30 min at room temperature. After standing for 24 h, white asphalt adhesive was obtained. Calcium carbonate and modified polylactic acid were mixed evenly and dried at 75°C for 6 hours to obtain a mixed powder. The mixed powder is added to the white asphalt adhesive and stirred for more than 2 hours at room temperature to obtain the sealing material.

[0048] Example 8 This invention provides a method for preparing a sealing material, the sealing material comprising 2.0 wt% calcium carbonate, 1.5 wt% white asphalt and 2.0 wt% modified polylactic acid, wherein the calcium carbonate is a composite of 20-30 mesh calcium carbonate, 35-45 mesh calcium carbonate and 50-60 mesh calcium carbonate, in a mass ratio of 50:35:15. The modified polylactic acid is prepared as follows: 20 parts of polyacrylamide are heated to 260°C, and 10 parts of polylactic acid, 4 parts of sodium bicarbonate, 3.5 parts of potassium hydroxide, and 8 parts of triethylamine are added sequentially to obtain modified polylactic acid. Specifically, polyacrylamide particles are placed in a high-temperature reactor, and the temperature is gradually increased to 280°C using an oil bath heating device. Polylactic acid, sodium bicarbonate, and potassium hydroxide are added sequentially under stirring at 200 r / min, and stirring is continued for 60 min. After adding triethylamine, heating and stirring are stopped, and the reactants are allowed to cool naturally to obtain a grayish-white solid product. The obtained solid product is pulverized to pass through a standard 70 mesh to obtain modified polylactic acid.

[0049] White asphalt was mixed with water and stirred at 4000 r / min for 30 min at room temperature. After standing for 24 h, white asphalt adhesive was obtained. Calcium carbonate and modified polylactic acid were mixed evenly and dried at 70°C for 7 hours to obtain a mixed powder. The mixed powder is added to the white asphalt adhesive and stirred for more than 2 hours at room temperature to obtain the sealing material.

[0050] Comparative Example 1 4 wt% calcium carbonate was mixed with water and stirred at 4000 r / min for more than 2 hours at room temperature to obtain a sealing material, designated as No. 1. The calcium carbonate was a composite of 20-30 mesh calcium carbonate, 35-45 mesh calcium carbonate, and 50-60 mesh calcium carbonate in a mass ratio of 50:35:15. Comparative Example 2 4 wt% white asphalt was mixed with the on-site drilling fluid and stirred at 4000 r / min for 30 min at room temperature. After standing for 24 h, the plugging material was obtained.

[0051] Comparative Example 3 4 wt% of modified polylactic acid was mixed with the on-site drilling fluid and stirred at 4000 r / min for more than 2 hours at room temperature to obtain the plugging material.

[0052] Comparative Example 4 4 wt% of polymer-modified bitumen waterproof coating (PB-1) was mixed with the on-site drilling fluid, stirred at 4000 r / min for 30 min at room temperature, and allowed to stand for 24 h to obtain the plugging material.

[0053] Comparative Example 5 4 wt% of high-performance polytetrafluoroethylene composite material (SFT-1) was mixed with the on-site drilling fluid, stirred at 4000 r / min for 30 min at room temperature, and allowed to stand for 24 h to obtain the plugging material.

[0054] Comparative Example 6 4 wt% of bridge plug plugging agent (DQ-1) was mixed with the on-site drilling fluid, stirred at 4000 r / min for 30 min at room temperature, and then allowed to stand for 24 h to obtain the plugging material.

[0055] Comparative Example 7 Mix 4 wt% of bridge plug plugging agent (DQ-2) with the on-site drilling fluid, stir at 4000 r / min for 30 min at room temperature, and let stand for 24 h to obtain the plugging material.

[0056] To further illustrate the beneficial effects of the present invention, the performance of the sealing materials prepared in the examples is now evaluated: Leak-stopping performance evaluation: Take 13L of on-site composite salt drilling fluid and add it evenly into 13 high-speed stirring cups (1L / cup). Turn on the stirrer and adjust the speed to 6000-8000r / min for 30min to obtain 13 samples to be tested.

[0057] Take the drilling plugging material combination according to the composition ratio in the table below, add it to the mixer, dry mix for 30 minutes at 50℃ and 40r / min, add the mixture to the No.1 to No.13 high stirring cups in step 1, adjust the speed to 8000r / min and stir for 30 minutes to suspend it in the base slurry, and finally obtain the sample to be tested.

[0058] Using pure in-situ composite salt drilling fluid as sample #14, the sealing performance of the developed drilling plugging formulation was evaluated using a QD-1 plugging tester. The specific steps are as follows: ① Hot-roll samples #1 through #14 (120℃ × 16h) respectively, then pour the slurry into the QD-1 plugging instrument and install the gas supply manifold; ② Increase the pressure to 5MPa at a rate of 0.069MPa per second, or until the plugging is broken and the drilling fluid in the instrument container runs out. Record the volume of outflowing drilling fluid and the maximum pressure reached. If the plugging is successful, maintain this pressure for 10 minutes and record the final drilling fluid volume; ③ Gradually increase the gap plate number (0.2mm, 0.5mm, 0.8mm, 1.0mm), repeat the experiment, until no permanent plugging occurs under 5MPa pressure. The plugging material formulation and test results are shown in the table below:

[0059] The results showed that, compared with other field-applied plugging materials, composite calcium carbonate exhibited the best plugging ability for cracks of 0.5–0.8 mm, white asphalt for 0.2–0.5 mm, and modified polylactic acid and SFT-1 high-performance polytetrafluoroethylene composite material for cracks smaller than 0.2 mm. Considering the plugging ability of these two materials combined with composite calcium carbonate for cracks smaller than 0.5–0.8 mm, composite calcium carbonate, white asphalt, and modified polylactic acid were selected as the preferred raw materials for the plugging formulation. The resulting field-applied plugging formulation #11 was optimally matched to plug a wide range of crack widths. For a 0.8 mm crack plate under a pressure of 5 MPa, the water loss was only 185 mL, indicating that it can plug cracks with a width of 0–0.8 mm during drilling. The pressure resistance of the plugging layer can reach 5 MPa, the temperature resistance of the plugging material is >120℃, and the overall performance is good, ensuring safe and efficient drilling in formations prone to leakage.

[0060] Rheological performance testing: Step 1: Take 800 mL of the on-site compound salt drilling fluid and add it evenly to the high-speed stirring cup. Turn on the stirrer and adjust the speed to 4000-6000 r / min. After stirring for 30 min, two samples to be tested are obtained.

[0061] Step 2: According to the formulation ratio in Example 1, add calcium carbonate, white asphalt, and modified polylactic acid to the mixer and dry mix for 30 minutes under specific conditions (50℃, 40r / min). Add the mixture to the mixture in Step 1.# In a high-speed stirring cup, the stirring speed was adjusted to 8000-10000 r / min and stirred for 30 minutes to suspend it in the base slurry. This resulted in a low-damage, plugging drilling fluid suitable for drilling fractured reservoirs. The test results are shown in the table below:

[0062] 1 # Drilling fluid density: 1.24 g / cm³ 3 ,2 # Drilling fluid density: 1.25 g / cm³ 3 Aging conditions: 120℃×16h; High temperature and high pressure filtration loss test: 120℃×3.5MPa, 30min.

[0063] The results showed that, referring to the national standard GB / T16783.1-2014 "Field Testing of Drilling Fluids for Petroleum and Natural Gas Industry - Part 1: Water-based Drilling Fluids", the plugging formulation of this invention can improve the rheological properties of the field composite salt drilling fluid system, slightly increase the apparent viscosity AV and dynamic plasticity ratio, and significantly reduce the filtration loss. After high-temperature aging at 120℃, the HTHP filtration loss of the drilling fluid is only 7.2 mL, which can effectively reduce the damage to the reservoir caused by the intrusion of drilling fluid filtrate.

[0064] Particle size distribution test: Step 1: Take 400mL of on-site compound salt drilling fluid and add it evenly to a high-speed stirring cup. Turn on the stirrer and adjust the speed to 4000-6000r / min. Stir for 30min to obtain the sample to be tested.

[0065] Step 2: According to the formulation ratio in Example 1, add calcium carbonate, white asphalt and modified polylactic acid to the mixer and dry mix for 30 minutes under specific conditions (55℃, 40 r / min). Add the mixture to the high-speed stirring cup in Step 1 and adjust the speed to 8000~10000 r / min and stir for 30 minutes to suspend it in the base slurry. Finally, a low-damage drilling fluid suitable for drilling fractured reservoirs is obtained.

[0066] Referring to section 3.3.2 of the petroleum industry standard "Indoor Test Method for Bridging and Pouring Materials for Drilling Fluids SY / T5840-2007" for particle size distribution determination, the particle size distribution of the plugging formulation constructed in this embodiment was determined. The experimental results are shown in [Figure 1]. Figure 2 and Figure 3 As shown, Figure 2The particle size distribution of the composite salt drilling fluid in the field shows that the particle size distribution range is 0.3 to 1000 μm, but the D90 value is only 200 μm. Due to the influence of formation heterogeneity, when the reservoir section encounters fractured formations (fracture width ≥ 0.2 mm), the drilling fluid's ability to prevent leakage and plug leakage is obviously insufficient, which can easily lead to the intrusion of drilling fluid filtrate and solid particles into the reservoir, resulting in serious reservoir damage. Figure 3 After adding the plugging material formulation from the examples, the drilling fluid particle size distribution ranged from 3 to 1000 μm, but D 90 With the D90 value increasing to 756 μm, the drilling fluid's ability to prevent and plug leaks is significantly enhanced when encountering fractured formations (0.2 mm ≤ fracture width ≤ 0.8 mm) in the reservoir section. It can effectively form a sealing skeleton structure within the fractures, and, in conjunction with other materials in the drilling plugging formulation, prevent drilling fluid filtrate and fine solid particles from invading the reservoir, reducing the degree of reservoir damage. It is evident that after adding the drilling plugging formulation, the D90 value of the drilling fluid increases from 200 μm to 756 μm, which is beneficial for forming a tight plugging layer and sealing fractures with a width ≤ 0.8 mm during drilling.

[0067] Lubrication performance test: Step 1: Take 800 mL of the on-site compound salt drilling fluid and add it evenly to a high-speed stirring cup. Turn on the stirrer and adjust the speed to 4000-6000 r / min. After stirring for 30 min, two test samples are obtained (1... # ,2 # ).

[0068] Step 2: According to the formulation ratio in Example 3, add calcium carbonate, white asphalt, and modified polylactic acid to the mixer and dry mix for 30 minutes under specific conditions (50°C, 40 r / min). Add the mixture to the mixture in Step 1. # In a high-speed stirring cup, the stirring speed was adjusted to 8000-10000 r / min and stirred for 30 minutes to suspend it in the base slurry. This resulted in a low-damage, plugging drilling fluid suitable for drilling fractured reservoirs. Lubrication tests were conducted, and the results are shown in the table below.

[0069] The results showed that, referring to the "SY / T 6094—94 Evaluation Procedure for Lubricants for Drilling Fluids", the lubrication performance was evaluated using an extreme pressure lubrication tester and a mud cake viscosity coefficient measuring instrument. The plugging material formulation provided by this invention has little effect on the extreme pressure lubrication coefficient and mud cake viscosity coefficient of the composite salt drilling fluid in the field.

[0070] Degradation performance evaluation: Step 1: Take 4.0L of on-site compound salt drilling fluid and add it evenly to the high-speed stirring cup (1 # ,2 # 3 # 4 # 5# 6 # 7 # 8 # 9 # 10 # In the test sample, turn on the stirrer, adjust the speed to 4000-6000 r / min, and stir for 30 minutes to obtain the sample to be tested.

[0071] Step 2: According to the formulation ratio in Example 4, add calcium carbonate, white asphalt, and modified polylactic acid to the mixer and dry mix for 30 minutes under specific conditions (25℃, 40r / min). Then, add the mixture to the high-speed stirring cup (5) from Step 1. # 6 # 7 # 8 # 9 # 10 # In the mixture, adjust the rotation speed to 8000-10000 r / min and stir for 30 minutes to suspend it in the base slurry.

[0072] Step 3: Place the test samples (0#, 1#, 2#, 3#, 4#, 5#, 6#, 7#, 8#, 9#, 10#) in the aging tank of the roller heating furnace, adjust the aging temperature to 120℃, and after hot rolling for a certain period of time, remove the aging tank. Refer to the national standard GB / T16783.1-2014 "Field Testing of Drilling Fluids for Petroleum and Natural Gas Industry - Part 1: Water-based Drilling Fluids" to determine the thickness of the mud cake, and evaluate the degradation performance of the drilling plugging formulation constructed in this invention. Experimental results are shown below. Figure 4 and Figure 5 As shown, Figure 4 In the study, after 8 days of aging, the self-degradation rate of the mud cake formed by the on-site composite drilling fluid was only 2.56%, indicating that the mud cake formed by the on-site composite drilling fluid was relatively dense, but its self-unblocking and reservoir protection effect was poor, and the reservoir unblocking efficiency was low in the later stage, affecting the oil and gas production capacity of a single well. Figure 5 After adding the plugging material formulation from Example 4, the degradation rate of the mud cake formed in the drilling fluid system after 8 days of aging increased from 2.56% to 40.48%, indicating that the plugging material prepared by this invention has good self-degradable reservoir protection performance and can effectively improve the unblocking efficiency in the later unblocking process.

[0073] Reservoir protection performance evaluation: Step 1: Take 800mL of on-site compound salt drilling fluid and add it evenly to 1 # 2 # In a high-speed mixing cup, turn on the stirrer and adjust the speed to 4000-6000 r / min, and stir for 30 minutes.

[0074] Step 2: According to the formulation ratio in Example 1, add calcium carbonate, white asphalt, and modified polylactic acid to the mixer and dry mix for 30 minutes under specific conditions (50°C, 40 r / min). Add the mixture to the mixture in Step 1. # In a high-speed stirring cup, adjust the speed to 8000-10000 r / min and stir for 30 minutes to suspend it in the base slurry.

[0075] Referring to the testing procedures in the petroleum industry's "Indoor Evaluation Method for Damage to Oil Reservoirs by Drilling Fluid and Completion Fluid," the damage assessment of the drilling plugging formulation constructed in this embodiment was performed, and the experimental results are shown in the table below:

[0076] As can be seen, after adding the leak-sealing material formulation from Example 1, 2 # The permeability recovery value of the core sample can reach 92.3%, indicating that the plugging material provided by this invention has a good reservoir protection effect and can effectively reduce the damage of drilling fluid to the reservoir.

[0077] The aforementioned plugging material is used in the drilling and completion of fractured reservoirs. Applying this plugging material to fractured reservoirs effectively fills the fractures, preventing leakage of drilling fluid or other fluids, thus improving the safety and efficiency of drilling operations. Furthermore, due to its excellent biodegradability, the material degrades automatically after completion, eliminating the need for additional unplugging operations and reducing the damage to the reservoir caused by cumbersome unplugging procedures.

[0078] In summary, this invention provides a plugging material, a preparation method, and an application. Through the combined action of calcium carbonate, white asphalt, and modified polylactic acid, the plugging material is endowed with better sealing strength and better degradability. It does not require a complex unblocking procedure and will not generate new chemical or mechanical blockages, thereby avoiding secondary damage to the reservoir and improving the productivity and stability of drilling operations. This is of great significance for the sustainable development of the oil and gas exploration and development industry.

[0079] The above description is merely a preferred embodiment of the present invention and is not intended to limit the technical solution of the present invention in any way. Those skilled in the art should understand that, without departing from the spirit and principles of the present invention, the technical solution can be modified and replaced in several simple ways, and these modifications and replacements are all within the scope of protection covered by the claims.

Claims

1. A leak-sealing material, characterized in that, It includes 1wt% to 3wt% calcium carbonate, 1wt% to 2wt% white pitch and 1wt% to 2wt% modified polylactic acid.

2. The sealing material according to claim 1, characterized in that, The calcium carbonate includes 20-30 mesh calcium carbonate, 35-45 mesh calcium carbonate and 50-60 mesh calcium carbonate, and the mass ratio of the 20-30 mesh calcium carbonate, 35-45 mesh calcium carbonate and 50-60 mesh calcium carbonate is (45-55):(30-40):(10-25).

3. The sealing material according to claim 1, characterized in that, The white asphalt has a pH value of 7-10, and under the high-temperature and high-pressure filtration conditions of 120℃, a pressure difference of 3.5 MPa, and a test time of 30 min, the high-temperature and high-pressure filtration loss is ≤25 ml, and the fluorescence level is ≤5.

4. The sealing material according to claim 1, characterized in that, The modified polylactic acid comprises the following raw material components by mass: 15-20 parts of polyacrylamide, 7.5-10 parts of polylactic acid, 2-4 parts of sodium bicarbonate, 0.2-4 parts of potassium hydroxide, and 5-10 parts of triethylamine.

5. The sealing material according to claim 4, characterized in that, The modified polylactic acid is prepared by: Polyacrylamide was heated, and polylactic acid, sodium bicarbonate, potassium hydroxide and triethylamine were added in sequence to obtain modified polylactic acid.

6. The sealing material according to claim 5, characterized in that, The method for obtaining modified polylactic acid by heating polyacrylamide and sequentially adding polylactic acid, sodium bicarbonate, potassium hydroxide, and triethylamine is as follows: Polyacrylamide particles were placed in a high-temperature reactor and heated to 260℃~280℃ using an oil bath. Polylactic acid, sodium bicarbonate, and potassium hydroxide were added sequentially under stirring at 100~200r / min. The mixture was stirred continuously for 60~90min. After adding triethylamine, heating and stirring were stopped. The reactants were allowed to cool naturally to obtain a grayish-white solid product. The obtained grayish-white solid product was pulverized and passed through a standard 65~85 mesh solid particle filter to modify polylactic acid.

7. The method for preparing the sealing material according to any one of claims 1-6, characterized in that, include: Mix white asphalt with water until homogeneous to obtain white asphalt adhesive; After mixing calcium carbonate and modified polylactic acid evenly, add them to white asphalt adhesive and mix evenly to obtain a sealing material.

8. The method for preparing the sealing material according to claim 7, characterized in that, The method for obtaining white asphalt adhesive by mixing white asphalt and water evenly is as follows: mix white asphalt and water, stir at room temperature at a speed of 3500-4500 r / min for 25-35 min, and let stand for 18-24 h to obtain white asphalt adhesive.

9. The method for preparing the sealing material according to claim 7, characterized in that, The method for obtaining the sealing material by uniformly mixing calcium carbonate and modified polylactic acid and then adding the mixture to white asphalt adhesive and mixing thoroughly is as follows: Calcium carbonate and modified polylactic acid are mixed evenly and dried at 70℃~75℃ for 5~7h to obtain a mixed powder. The mixed powder is added to the white asphalt adhesive and stirred for more than 2 hours at room temperature to obtain the sealing material.

10. The application of the plugging material as described in any one of claims 1-6 in drilling and completion of fractured reservoirs.

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