High-temperature-resistant composite capsule gel breaker for fracturing and preparation method of high-temperature-resistant composite capsule gel breaker

Abstract

The invention relates to the technical field of gas reservoir exploitation, and discloses a high-temperature-resistant fracturing composite capsule gel breaker and a preparation method thereof.The high-temperature-resistant fracturing composite capsule gel breaker comprises a capsule core and a capsule coating wrapping the surface of the capsule core; the capsule core is prepared from the following raw materials in parts by weight: 20-30 parts of a peroxide chemical gel breaker, 1-3 parts of a dispersing agent, 1-3 parts of an initiator and 58-78 parts of deionized water, and the capsule dressing is at least one of a capsule dressing A, a capsule dressing B or a capsule dressing C; the capsule gel breaker is uniform in particle and good in roundness, and the selected membrane material has delayed degradation and temperature resistance and water repellency; according to the slow-release gel breaker, the gel breaking time is obviously prolonged, the residue amount after gel breaking of the fracturing fluid is relatively small, gel breaking of a guanidine gel fracturing fluid system can be delayed, the method has important significance for effectively reducing damage to a low-permeability oil reservoir, and the method is simple in preparation process, high in operability and suitable for industrial production.

Description

Technical Field

[0001] This invention belongs to the field of gas reservoir development technology, specifically relating to a high-temperature resistant composite capsule breaker for fracturing and its preparation method. Background Technology

[0002] Fracturing is one of the main measures for increasing oil and gas well production. During fracturing operations, a solution containing thickeners and crosslinking agents forms a high-viscosity gel-like fracturing fluid, which is injected into the formation. The higher the viscosity of the fracturing fluid, the stronger its sand-carrying capacity, and the higher the success rate of the operation. However, after the operation, the high-viscosity fracturing fluid must be completely broken down and flowed back as soon as possible. Adding a breaker is necessary to completely break down the polymer and reduce damage to the reservoir. However, adding the breaker too early or at too fast a rate will cause the viscosity of the fracturing fluid to decrease prematurely, leading to sand shedding and sand blockage during the fracturing operation. At this point, the flowback fluid has a complex composition, containing both broken and unbroken gels, high molecular weight polymers, petroleum hydrocarbons, iron ions, etc., resulting in high viscosity. This affects the diffusion of reagents during the flocculation and sedimentation processes of the fracturing flowback fluid, causing long reaction times and poor treatment effects. Therefore, the fracturing flowback fluid must be broken down before further treatment. Meanwhile, poor capsule encapsulation and low effective content can lead to incomplete fracturing fluid breaking. Therefore, the quality of the capsule breaking agent is crucial to the successful completion of fracturing operations.

[0003] Under conventional breaker conditions, it is difficult to effectively degrade high-concentration polymers and filter cake within a specified time, which can cause permanent damage to the formation. Only with a sufficiently large dosage of breaker can high-concentration polymers and filter cake be completely degraded, reducing formation damage and improving oil and gas well productivity. However, increasing the dosage of breaker will cause the viscosity of the frozen fracturing fluid to drop rapidly, weakening its proppant-carrying capacity and increasing filtrate. Using delayed-release capsule breaker can fundamentally solve the contradiction between proppant carrying and breaker breaking in fracturing fluid. By coating ordinary breaker particles with a thin layer of shielding material, the breaker is isolated from the frozen fracturing fluid, allowing it to be used under high-concentration conditions, effectively reducing fracturing fluid viscosity, removing filter cake, and significantly reducing damage to propped fractures.

[0004] Breakers primarily disrupt the molecular chain structure of thickeners, reducing viscosity and hydrating them to achieve breakage. These breakages can occur through thermal, mechanical, chemical, and biological methods. Biological and chemical methods are commonly used. Chemical methods mainly employ oxidants such as potassium persulfate and ammonium persulfate. At high temperatures, the peroxides decompose into highly reactive free radicals, disrupting the polymer backbone structure and achieving breakage. The higher the temperature, the stronger the oxidant's reactivity; however, the breakage effect significantly decreases below 50℃. Bio-enzyme breakers are a green and environmentally friendly type of breaker, significantly improving the reduction of breakage residue, but they suffer from slow breakage speed and incomplete breakage, failing to meet the requirement of rapid breakage.

[0005] Based on the current research status of capsule breaker agents both domestically and internationally, and considering the actual development situation of deep, low-permeability oil and gas reservoirs in the Changqing Oilfield, we have formulated a research direction focused on reducing production costs, improving the technical performance of capsule breaker agents, and expanding the product's adaptability and application range. Therefore, the developed capsule breaker agent must have a low release rate in water and sufficient compressive strength, with uniform particle size similar to that of the proppant. After construction, under formation closure pressure, it should deform and rupture within the propped fractures, releasing the breaker agent in a concentrated manner. This effectively reduces the viscosity of the fracturing fluid, removes the filter cake, and significantly reduces the damage of the fracturing fluid to the propped fractures. The capsule breaker agent should be finely graded according to actual field application conditions, requiring in-depth and meticulous research on the selection of capsule coating materials and production processes. Summary of the Invention

[0006] The purpose of this invention is to overcome the above-mentioned problems and provide a high-temperature resistant composite capsule breaker for fracturing and its preparation method. This capsule breaker not only has good encapsulation, high viscosity, and strong sand-carrying capacity, but also can adapt to different well temperature reservoirs and various fracturing operation scenarios, thus solving the problem of the limited application range of capsule breaker.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: This invention provides a high-temperature resistant composite capsule breaker for fracturing and its preparation method, comprising a capsule core and a capsule coating on the surface of the capsule core. The capsule core is prepared from the following raw materials in parts by weight: 20-30 parts of peroxide chemical breaker, 1-3 parts of dispersant, 1-3 parts of initiator, and 58-78 parts of deionized water.

[0008] The peroxide chemical degreasing agent is one or a mixture of several of the following: ammonium persulfate, sodium persulfate, potassium persulfate, and solid acid.

[0009] A further improvement of the present invention is that the sac is at least one of sac A, sac B or sac C; The coating A is prepared by first synthesizing diethyl terephthalate by ester exchange of dimethyl terephthalate and ethylene glycol or by esterification of terephthalic acid and ethylene glycol, and then performing a polycondensation reaction to obtain polyethylene terephthalate.

[0010] A further improvement of the present invention is that the capsule B is prepared by polymerizing vinyl chloride dimethylacrylamide to obtain a polyvinyl chloride dimethylacrylamide copolymer.

[0011] A further improvement of the present invention is that the capsule C is a mixture of vinylidene chloride, hydroxypropyl cellulose, glycerol, sorbitol and polyacrylol.

[0012] A further improvement of the present invention is that the capsule C is prepared by an ethanol or cyclohexane solution of 1% vinylidene chloride, 3% hydroxypropyl cellulose, 2% glycerol, 1% sorbitol and 1% polyacrylol at 120°C; or by an ethanol or cyclohexane solution of 1% vinylidene chloride, 5% hydroxypropyl cellulose, 2% glycerol, 1% sorbitol and 1% polyacrylol at 120°C-150°C.

[0013] A further improvement of the present invention is that the mass ratio of the capsule to the core is 100:3-5.

[0014] A further improvement of the present invention is that the initiator is a polyol and deionized water.

[0015] A further improvement of the present invention is that the polyols include triethanolamine and methyldiethanolamine.

[0016] A further improvement of the present invention is that the dispersant is glycerol, sorbitol or a high molecular weight polypeptide polymer.

[0017] Secondly, the present invention provides a method for preparing a high-temperature resistant composite capsule breaker, comprising the following steps: S1, mix peroxide chemical desiccant, dispersant, initiator and deionized water evenly in proportion to obtain core particles; S2, mix the coating material with the solvent, heat and stir until the material dissolves to form a uniform coating solution; S3, suspend the capsule core particles to be packaged in a fluidized bed, select the capsule coating solution and spray it onto the capsule core particles in a spray manner until a complete coating layer is observed on the surface of the capsule core particles, then stop the operation to obtain the capsule decapsulating agent. S4. The prepared capsule breaker is sieved to remove small particles and powder impurities. The sieved capsule breaker is then placed in an oven to dry.

[0018] Compared with the prior art, the present invention has the following beneficial effects: This invention provides a high-temperature resistant composite capsule breaker for fracturing. The core particles are composed of a mixture of a peroxide chemical breaker, a dispersant, and an initiator. The peroxide chemical breaker is selected from one or more of ammonium persulfate, sodium persulfate, potassium persulfate, and solid acids. Compared to single-component breakers, this mixing method significantly improves the chemical stability and adaptability of the core particles, maintaining stable breaker performance in different fracturing environments. By adjusting the proportions of various breaker components in the core, the most suitable breaker formulation can be prepared according to specific fracturing operation requirements and geological conditions, thereby optimizing fracturing effects and improving oil and gas recovery. Simultaneously, the core is coated with a shell material. By selecting a suitable shell material, the release rate and breaker timing of the breaker can be further adjusted to adapt to different well temperature reservoirs. Due to the diverse selection of core particles, this composite capsule breaker can more flexibly adapt to various fracturing operation scenarios, thereby improving operational efficiency and success rate.

[0019] This invention also provides a method for preparing a high-temperature resistant composite capsule breaker. This method ensures the uniformity and stability of the capsule core particles by precisely controlling the raw material ratio and mixing process. The coating solution is sprayed onto the capsule core particles, optimizing the coating process, significantly improving the coating efficiency, and ensuring the uniform coverage and integrity of the coating layer. This further enhances the high-temperature resistance and chemical stability of the capsule breaker. The preparation process of this invention is simple and can complete the granulation, sizing, coating and drying processes in one step, which is energy-saving and environmentally friendly. Detailed Implementation

[0020] The present invention will be further described below with reference to embodiments, but it should not be construed that the scope of the present invention is limited to the following embodiments. Various substitutions and modifications made based on ordinary technical knowledge and common practices in the art without departing from the above-described technical concept of the present invention should be included within the scope of protection of the present invention.

[0021] This invention provides a high-temperature resistant composite capsule breaker for fracturing, comprising a capsule core and a capsule coating on the surface of the capsule core. The capsule core is prepared from the following raw materials in parts by weight: 20-30 parts of peroxide chemical breaker, 1-3 parts of dispersant, 1-3 parts of initiator, and 58-78 parts of deionized water. Peroxide chemical degreasing agents are one or a mixture of several of the following: ammonium persulfate, sodium persulfate, potassium persulfate, and solid acid; The capsule is either capsule A, capsule B, or capsule C; capsule A is prepared by transesterification of dimethyl terephthalate with ethylene glycol or by esterification of terephthalic acid with ethylene glycol to synthesize dihydroxyethyl terephthalate, followed by polycondensation to obtain polyethylene terephthalate; capsule B is prepared by free radical copolymerization of polyvinyl chloride and dimethacrylamide to obtain polyvinyl chloride and dimethacrylamide copolymer; capsule C is prepared by ethanol or cyclohexane solution of 1% vinylidene chloride, 3% hydroxypropyl cellulose, 2% glycerol, 1% sorbitol and 1% polyacrylamide at 120°C; or by ethanol or cyclohexane solution of 1% vinylidene chloride, 5% hydroxypropyl cellulose, 2% glycerol, 1% sorbitol and 1% polyacrylamide at 120°C-150°C.

[0022] The mass ratio of the sac membrane to the sac core is 100:3-5.

[0023] The initiators are polyols and deionized water, including triethanolamine and methyldiethanolamine.

[0024] The dispersant is glycerol, sorbitol, or a high molecular weight polypeptide polymer.

[0025] This invention also provides a method for preparing a high-temperature resistant composite capsule breaker, comprising the following steps: S1, mix peroxide chemical desiccant, dispersant, initiator and deionized water evenly in proportion to obtain core particles; S2, mix the coating material with the solvent, heat and stir until the material dissolves to form a uniform coating solution; S3, suspend the capsule core particles to be packaged in a fluidized bed, select the capsule coating solution and spray it onto the capsule core particles in a spray manner until a complete coating layer is observed on the surface of the capsule core particles, then stop the operation to obtain the capsule decapsulating agent. S4. The prepared capsule breaker is sieved to remove small particles and powder impurities. The sieved capsule breaker is then placed in an oven to dry.

[0026] Example 1 This embodiment provides a method for preparing a composite capsule breaker for high-temperature fracturing, the main preparation steps of which are as follows: By weight, 1 part ammonium persulfate, 1 part sodium persulfate, 1 part potassium persulfate, and 1 part solid acid are mixed to form the core material. The coating A is produced by transesterification of dimethyl terephthalate and ethylene glycol terephthalate under the conditions of zinc, cobalt, and manganese acetic acid (0.01%-0.05%) salt to generate ethylene glycol terephthalate. Polycondensation reaction is then carried out at a reaction temperature of 260℃ to obtain polyethylene terephthalate (PET) as the coating. The capsule is formed by suspending the core particles to be coated on a fluidized bed and spraying the coating material onto the particles in a spray manner, thus completing the granulation, granulation, coating, and drying process in one step to form the capsule breaker JNPJJ-1.

[0027] Example 2 This embodiment provides a high-temperature resistant composite capsule detonator for fracturing and its preparation method. The main preparation steps are as follows: By weight, 2 parts ammonium persulfate, 1 part sodium persulfate, and 1 part potassium persulfate are weighed and mixed to form the core material. The coating A is produced by transesterification of dimethyl terephthalate and ethylene glycol terephthalate under the conditions of zinc, cobalt, and manganese in acetic acid (0.01%-0.05%) salt, which produces ethylene glycol terephthalate. The condensation reaction is then carried out at a reaction temperature of 260℃ to obtain polyethylene terephthalate (PET) as the coating. The capsule is made by suspending the core particles to be coated in a fluidized bed and spraying the coating material onto the particles in a spray manner, thus completing the granulation, granulation, coating, and drying process in one step to form the capsule breaker JNPJJ-2.

[0028] Example 3 This embodiment provides a high-temperature resistant composite capsule detonator for fracturing and its preparation method. The main preparation steps are as follows: By weight, 2 parts ammonium persulfate and 2 parts potassium persulfate are mixed to form the core material. The coating A is produced by transesterification of dimethyl terephthalate and ethylene glycol terephthalate under the conditions of zinc, cobalt and manganese acetic acid (0.01%-0.05%) salt, which produces ethylene glycol terephthalate. The condensation reaction is then carried out at a reaction temperature of 280℃ to obtain polyethylene terephthalate (PET) as the coating. The capsule is made by suspending the core particles to be coated on a fluidized bed and spraying the coating material onto the particles in a spray manner, thus completing the granulation, granulation, coating and drying process in one step to form the capsule breaker JNPJJ-3.

[0029] Example 4 This embodiment provides a high-temperature resistant composite capsule detonator for fracturing and its preparation method. The main preparation steps are as follows: By weight, 1 part ammonium persulfate, 1 part sodium persulfate, 1 part potassium persulfate, and 1 part solid acid are mixed to form the core material. The coating B is prepared by polymerization of polyvinyl chloride dimethacrylamide at a reaction temperature of 270°C with the addition of azobisisobutyramidine hydrochloride as a promoter, resulting in a polyvinyl chloride dimethacrylamide copolymer as the coating. The capsule is formed by suspending the core particles to be coated on a fluidized bed and spraying the coating material onto the particles in a spray manner, thus completing the granulation, sizing, coating, and drying processes in one step, forming the capsule breaker JNPJJ-4.

[0030] Example 5 This embodiment provides a high-temperature resistant composite capsule detonator for fracturing and its preparation method. The main preparation steps are as follows: By weight, 2 parts ammonium persulfate, 1 part sodium persulfate, and 1 part potassium persulfate are weighed and mixed to form the core material. The coating B is prepared by polymerization of polyvinyl chloride dimethacrylamide at a reaction temperature of 260°C with the addition of azobisisobutyramidine hydrochloride as a promoter, resulting in a polyvinyl chloride dimethacrylamide copolymer as the coating. The capsule is formed by suspending the core particles to be coated in a fluidized bed and spraying the coating material onto the particles in a spray manner, thus completing the granulation, sizing, coating, and drying processes in one step, forming the capsule breaker JNPJJ-5.

[0031] Example 6 This embodiment provides a high-temperature resistant composite capsule detonator for fracturing and its preparation method. The main preparation steps are as follows: By weight, 2 parts ammonium persulfate, 1 part sodium persulfate and 1 part potassium persulfate are weighed and mixed to form the core material. The coating C is made of vinylidene chloride, hydroxypropyl cellulose, glycerol, sorbitol and polyacrylol. The capsule is formed by suspending the core particles to be coated in a fluidized bed and spraying the coating material onto the particles in a spray manner, thus completing the granulation, granulation, coating and drying process in one step to form the capsule breaker JNPJJ-5.

[0032] To further determine the performance of the composite capsule breaker, the performance of the capsule breaker prepared in Examples 1-6 was measured at different reservoir temperatures. The composite capsule breaker prepared in Examples 1-6 was then combined with a Changqing guar gum fracturing fluid system (0.4% CJ2-6), and viscosity tests were performed. The test results are shown in Table 1. Table 1 shows the viscosity test results for the compound capsule breaker.

[0033] Since the on-site fracturing operation requires that the gel breaking be completed within one hour to meet the conditions, the first 30 minutes are the time for the fracturing fluid to enter the ground, and the viscosity requirement is high so that it can carry sand. In the next 30 minutes, the gel breaking can be completed to below 5 mPa.s to meet the flowback requirements.

[0034] Table 1 shows that the composite capsule breaker prepared in Examples 1-6 has stable performance and its breaker performance at different reservoir temperatures can meet the field requirements, that is, the index meets the standard requirements (≤5mPa.s).

[0035] The release rate of the compound capsule breaker under low and high temperature conditions was further determined, and the test results are shown in Table 2: Table 2 shows the effect of temperature on the release rate of the decompressing agent in fracturing capsules.

[0036] Table 2 shows that the composite capsule breaker prepared in Examples 1-6 exhibits different release rates under low and high temperature conditions. When the temperature is below a certain value (e.g., 30°C), the release rate of the capsule breaker is less affected by time, which means that the release rate of the breaker is relatively stable under low temperature conditions and is not easily affected by small temperature fluctuations. As the temperature increases, the release rate of the capsule breaker increases because high temperature accelerates the dissolution or softening process of the capsule shell material, making it easier for the breaker to be released from the capsule. Especially after the temperature exceeds a certain threshold (e.g., 90°C), the increasing trend of the release rate may be more obvious. In addition, the composite capsule breaker prepared in Examples 1-6 can meet the requirement of a release rate greater than 70% under both low and high temperature conditions, which means that the composite capsule breaker can effectively function under various environmental conditions without performance degradation due to temperature changes, ensuring the stability and reliability of fracturing operations.

[0037] Many embodiments and applications beyond the examples provided will be apparent to those skilled in the art upon reading the foregoing description. Therefore, the scope of this teaching should not be determined by reference to the foregoing description, but rather by reference to the foregoing claims and the full scope of their equivalents. For purposes of completeness, all articles and references, including patent applications and publications, are incorporated herein by reference. The omission of any aspect of the subject matter disclosed herein in the foregoing claims is not intended as a waiver of that subject matter, nor should it be construed as an indication that the applicant has not considered that subject matter as part of the disclosed inventive subject matter.

[0038] The above content provides a further detailed description of the present invention. It should not be construed that the specific embodiments of the present invention are limited to this. For those skilled in the art, several simple deductions or substitutions can be made without departing from the concept of the present invention, and all such deductions or substitutions should be considered to fall within the scope of protection of the present invention as defined by the submitted claims.

Claims

1. A high-temperature resistant composite capsule detonator for fracturing, characterized in that, The product includes a core and a coating covering the surface of the core. The core is prepared from the following raw materials in parts by weight: 20-30 parts peroxide chemical degumming agent, 1-3 parts dispersant, 1-3 parts initiator, and 58-78 parts deionized water. The peroxide chemical degreasing agent is one or a mixture of several of the following: ammonium persulfate, sodium persulfate, potassium persulfate, and solid acid.

2. The high-temperature resistant composite capsule de-gelling agent for fracturing according to claim 1, characterized in that, The sac is at least one of sac A, sac B, or sac C; The coating A is prepared by first synthesizing diethyl terephthalate by ester exchange of dimethyl terephthalate and ethylene glycol or by esterification of terephthalic acid and ethylene glycol, and then performing a polycondensation reaction to obtain polyethylene terephthalate.

3. The preparation method of the high-temperature resistant composite capsule breaker for fracturing according to claim 1, characterized in that, The pod B is prepared by polymerizing vinyl chloride dimethylacrylamide to obtain a polyvinyl chloride dimethylacrylamide copolymer.

4. The high-temperature resistant composite capsule de-gelling agent for fracturing according to claim 1, characterized in that, The capsule C is a mixture of vinylidene chloride, hydroxypropyl cellulose, glycerol, sorbitol and polyacrylol.

5. The preparation method of the high-temperature resistant composite capsule breaker for fracturing according to claim 4, characterized in that, The capsule C is prepared by using an ethanol or cyclohexane solution of 1% vinylidene chloride, 3% hydroxypropyl cellulose, 2% glycerol, 1% sorbitol and 1% polyacrylol at 120°C; or by using an ethanol or cyclohexane solution of 1% vinylidene chloride, 5% hydroxypropyl cellulose, 2% glycerol, 1% sorbitol and 1% polyacrylol at 120°C-150°C.

6. The high-temperature resistant composite capsule de-gelling agent for fracturing according to claim 1, characterized in that, The mass ratio of the sac to the core is 100:3-5.

7. The high-temperature resistant composite capsule de-gelling agent for fracturing according to claim 1, characterized in that, The initiator is a polyol and deionized water.

8. The high-temperature resistant composite capsule de-gelling agent for fracturing according to claim 7, characterized in that, The polyols include triethanolamine and methyldiethanolamine.

9. The preparation method of the high-temperature resistant composite capsule breaker for fracturing according to claim 1, characterized in that, The dispersant is glycerol, sorbitol, or a high molecular weight polypeptide polymer.

10. A method for preparing a high-temperature resistant composite capsule breaker as described in claim 1, characterized in that, Includes the following steps: S1, mix peroxide chemical desiccant, dispersant, initiator and deionized water evenly in proportion to obtain core particles; S2, mix the coating material with the solvent, heat and stir until the material dissolves to form a uniform coating solution; S3, suspend the capsule core particles to be packaged in a fluidized bed, select the capsule coating solution and spray it onto the capsule core particles in a spray manner until a complete coating layer is observed on the surface of the capsule core particles, then stop the operation to obtain the capsule decapsulating agent. S4. The prepared capsule breaker is sieved to remove small particles and powder impurities. The sieved capsule breaker is then placed in an oven to dry.

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