A water-based fracturing fluid delayed crosslinking microcapsule crosslinking agent, its preparation method and application

Abstract

The present invention discloses a water-based fracturing fluid delayed crosslinking microcapsule crosslinking agent, its preparation method and application, belonging to the technical field of oilfield chemical additives. The microcapsule crosslinking agent comprises a core material and a wall material coating the selected core material. The core material comprises one or several of organic boron crosslinking agents or modified organic boron crosslinking agents. The wall material comprises one or several of ethyl cellulose or polyethylene waxes. The wall material is a double-layer structure, with a porous structure skeleton in the inner layer and a dense outer shell in the outer layer. The present invention can achieve the controllable crosslinking of water-based fracturing fluids, reduce the frictional resistance along the pipe string during the deep well fracturing of water-based fracturing fluids, reduce the fracturing construction pressure, enhance the strength of the microcapsules and serve as a temperature-responsive material. It has the characteristics of high encapsulation rate, stability at normal temperature and not easy to release, convenient storage and transportation. When in use, the outer shell of the microcapsules softens and unseals under specific temperature conditions, and the porous structure controls the slow release of the internal crosslinking agent, so as to achieve the purpose of delayed crosslinking of water-based fracturing fluids.

Description

Technical Field

[0001] The present invention belongs to the technical field of oilfield chemical additives, and relates to a water-based fracturing fluid delayed crosslinking microcapsule crosslinking agent, a preparation method thereof and an application thereof. Background Art

[0002] Fracturing technology is a widely used oil and gas field stimulation and transformation technology, which plays an important role in increasing the production of oil and gas wells. With the development of oilfield exploration towards deeper layers, the fracturing technology for deep low-permeability reservoirs is playing an increasingly important role and has become the preferred stimulation technology for the development of deep oil and gas reservoirs, attracting more and more attention. The friction problem in deep well fracturing leads to too high pressure at the pipe manifold wellhead during surface construction, and there is even a phenomenon that the construction cannot be carried out because it exceeds the bearing capacity of the equipment. In terms of construction energy consumption, during the process of the fracturing fluid flowing in the wellbore, the increase in flow friction greatly increases the construction energy consumption and cost. Achieving delayed crosslinking, reducing construction friction, and reducing construction pump pressure are one of the key technologies for deep well and ultra-deep well fracturing fluids.

[0003] Therefore, how to develop a water-based fracturing fluid delayed crosslinking microcapsule crosslinking agent, a preparation method thereof and an application thereof to solve the problem of large frictional resistance along the pipeline in deep well fracturing is an urgent problem to be solved by those skilled in the art. Summary of the Invention

[0004] In view of this, the present invention provides a water-based fracturing fluid delayed crosslinking microcapsule crosslinking agent, a preparation method thereof and an application thereof.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A water-based fracturing fluid delayed crosslinking microcapsule crosslinking agent, comprising a core material and a wall material coating the selected core material. The core material includes one or more of organic boron crosslinking agents or modified organic boron crosslinking agents. The wall material includes one or more of ethyl cellulose or polyethylene waxes. The above wall material is a double-layer structure, with the inner layer being a porous structure framework and the outer layer being a dense outer shell.

[0007] The advantages of the present invention are:

[0008] (1) The porous structure of the microcapsules is controllable. By adjusting different parameters during the preparation process, the thickness of the outer shell and the size and distribution of the surface holes are regulated to achieve the controllable release of the internal crosslinking agent. Delayed crosslinking is achieved by controlling the formation speed of crosslinking particles, thereby increasing the delayed crosslinking time of the organic boron crosslinking agent. The microcapsules have the characteristics of high encapsulation rate, stability at room temperature and not easy to release, and are convenient for storage and transportation.

[0009] (2) The softening and unsealing temperature of the microcapsule shell is controllable. By adjusting the type, dosage, and compounding ratio of the wall material added during the preparation process, the softening and unsealing temperature of the microcapsule shell can be regulated, thereby improving the high-temperature resistance and the ability to resist external environmental influences of the organic boron crosslinking agent.

[0010] (3) The microcapsule crosslinking agent has a low density, enabling it to achieve full suspension in the liquid phase and be evenly distributed throughout the liquid phase system. This results in a higher concentration of crosslinking particles and effective particles in the crosslinking system, achieving efficient crosslinking at low concentrations and improving the crosslinking performance and shear resistance of the fracturing fluid system.

[0011] (4) The crosslinking agent is protected inside the microcapsule shell, achieving a true physical isolation effect and blocking the crosslinking process between the boron ions in the organic boron crosslinking agent and the water-based molecules. This delays the crosslinking time longer and has a stronger ability to resist external environmental influences. It improves the temperature resistance and acid resistance of the crosslinking agent. Introducing the microcapsule encapsulation technology into the field of crosslinking agents for fracturing fluid additives is expected to improve the performance of organic boron crosslinking agent water-based fracturing fluids, such as delaying the crosslinking time, temperature resistance, and acid resistance.

[0012] The microcapsule crosslinking agent of the present invention has a double-layer structure. The release of the microcapsule is first controlled by temperature. At specific temperature conditions, the outermost layer of the microcapsule softens, exposing the inner porous structure. The inner porous structure controls the slow release of the internal crosslinking agent, thereby controlling the binding process between the crosslinking agent and the water-based material, and thus achieving delayed crosslinking of the fracturing fluid under specific temperature conditions. The release temperature and release rate of the above microcapsule crosslinking agent can be specifically designed and adjusted according to the actual needs of the fracturing construction.

[0013] The microcapsule crosslinking agent achieves delayed crosslinking of the fracturing fluid under specific temperature conditions, reducing the pipe string friction during the fracturing construction, thereby reducing the construction pressure, and thus reducing the construction cost and construction risk.

[0014] The present invention also provides a preparation method for the above water-based fracturing fluid delayed crosslinking type microcapsule crosslinking agent, including the following steps:

[0015] (1) Formation of the W / O / W dispersion system: Under water bath conditions, add the wall material to organic solvent A and stir to dissolve it, then add the primary emulsion emulsifier and stir and mix as the oil phase; maintain the water bath temperature, and under high-speed mechanical stirring, add the core material aqueous solution to the oil phase and stir for a certain time to form a W / O primary emulsion system; at the same water bath temperature, add the phase stabilizer, osmotic pressure stabilizer, and double emulsion emulsifier to deionized water, stir evenly as the outer water phase, and at a magnetic stirring speed of V 1 drop the W / O primary emulsion system into the outer water phase and stir for a certain time to form a W / O / W double emulsion system;

[0016] (2) Formation and curing of microcapsules: Lower the temperature of the prepared W / O / W double emulsion system; when flocculation appears in the system and there is demulsification, stop cooling, and gradually add organic solvent B dropwise into the system. First, stir at a magnetic stirring speed of V 2 Keep stirring. Wait until the microcapsules are formed, and then reduce the stirring rate to the magnetic stirring speed of V 3 Stir to cure the microcapsules;

[0017] (3) Output of microcapsules: After the microcapsules are cured, after centrifugal separation, let it stand for sedimentation, filter by suction, wash with deionized water, and dry at low temperature to obtain the microcapsule crosslinking agent.

[0018] Preparation principle of the preparation method of the microcapsule crosslinking agent of the present invention: Prepare a W / O / W double emulsion by a two-step method. Low temperature induces ethyl cellulose to precipitate first and wrap the organic boron crosslinking agent in it, forming a porous structure in the inner layer; adding a non-solvent promotes the precipitation of polyethylene wax to form the outer layer of the microcapsule and seal the microcapsule. Specifically, first prepare a W / O / W double emulsion system by a two-step method, lock the particle size of the microcapsules in advance by regulating the diameter and distribution of the emulsion droplets, improve the disadvantages of easy agglomeration and adhesion of the wall material precipitation during the single emulsion phase separation process, improve the size uniformity of the microcapsules, and then make ethyl cellulose with large solubility affected by temperature precipitate first by reducing the temperature, control the formation of a porous structure through the temperature drop gradient, and finally use the method of dropping a non-solvent to make polyethylene wax precipitate to fill the ethyl cellulose skeleton and seal to form microcapsules.

[0019] Advantages of the present invention:

[0020] (1) The raw materials of the method of the present invention are relatively easy to obtain, and the experimental operation process is simple, green and safe, with mild reaction conditions and easy control of the reaction process, etc.

[0021] (2) The method of the present invention combines the W / O / W double emulsion method and the oil phase phase separation method, avoiding the disadvantages of easy agglomeration and adhesion during the formation of microcapsules by the traditional single emulsion phase separation method, and improving the size uniformity of the microcapsule products.

[0022] (3) The method of the present invention can prepare microcapsules with a double-layer structure of a porous structure and a dense outer shell on the outer shell. The outermost layer material has a temperature-responsive function, and the response temperature is adjusted by selecting different molecular weights and dosages of the wall material. The inner layer material is a porous structure, and the release rate of the internal core material is adjusted by adjusting the pore size and the pore distribution. By combining the two release mechanisms, the controllable delay of the crosslinking time of the crosslinking agent at different temperature regulations is achieved, so as to meet the deep well fracturing construction at different depths.

[0023] (4) The microcapsules prepared by the present invention have a relatively low density, so that the microcapsule crosslinking agent can be evenly dispersed in the water-based liquid phase system, so that there are more crosslinking particles and a higher effective particle concentration in the crosslinking system, thereby achieving efficient crosslinking at a low concentration, improving the crosslinking performance and shear resistance of the fracturing fluid system, and reducing the amount of crosslinking agent used.

[0024] Furthermore, the weight parts of each raw material are: 20-30 parts of core material aqueous solution, 3-5 parts of wall material, 50-70 parts of organic solvent A, 1.75-4.9 parts of colostrum emulsifier, 150-250 parts of deionized water, 2.5-5 parts of phase stabilizer, 1.25-5 parts of osmotic pressure stabilizer, 2.5-5 parts of double emulsion emulsifier, 100-200 parts of organic solvent B, and the concentration of the core material aqueous solution is 30-50wt%.

[0025] Furthermore, the organic solvent A is any one of toluene, xylene, cyclohexane or ethylene dichloride;

[0026] The colostrum emulsifier is one or more of Span 40, Span 60 or Span 80;

[0027] The phase stabilizer is polyvinyl alcohol or polyisobutylene;

[0028] The above-mentioned osmotic pressure stabilizer is chloride salt;

[0029] The above-mentioned multiple emulsion emulsifier is one or more of Tween 20, Tween 40, Tween 60 or Tween 80;

[0030] The organic solvent B is any one of dichloromethane, acetone, cyclohexane or n-hexane.

[0031] Beneficial effects of the above further technical solution: By optimizing the types and ratios of organic solvent A and colostrum emulsifier, a stable W / O colostrum system is obtained. By optimizing the phase stabilizer, osmotic pressure stabilizer and double emulsion emulsifier, a W / O / W double emulsion system with suitable particle size and strong stability can be obtained.

[0032] Furthermore, the above-mentioned chloride salt is sodium chloride.

[0033] Furthermore, the organic boron crosslinking agent is one of BSA-601, SRJL-YL4 or BY-X, and the polyethylene wax is a low-density polyethylene wax with a molecular weight of 1500 to 3500.

[0034] The beneficial effect of adopting the above further technical solution is that the softening and unsealing temperature of the shell can be adjusted by optimizing polyethylene waxes with different molecular weights.

[0035] Furthermore, the wall material includes ethyl cellulose and polyethylene wax.

[0036] Beneficial effects of adopting the above further technical solution: Ethyl cellulose and polyethylene wax are used in combination as wall materials, with ethyl cellulose as the main component, to form a porous structure framework of microcapsules. Polyethylene wax enhances the strength of the microcapsules and serves as a temperature-responsive material. The porous structure of ethyl cellulose in the framework part realizes the controlled release of the internal core material. The externally filled polyethylene wax seals the internal liquid core material inside the microcapsules, facilitating storage and transportation under normal temperature conditions, and softening and unsealing at specific temperature conditions to expose the porous structure of the inner layer.

[0037] Further, in step (1), the stirring speed of the above mechanical high-speed stirring is 4000 r / min to 6000 r / min, and the magnetic stirring speed V 1 is 800 r / min to 1200 r / min.

[0038] Furthermore, in step (1), after adding the aqueous core material solution to the oil phase, stir for 3 min to form a W / O primary emulsion system; after dropping the W / O primary emulsion system into the external aqueous phase under the above magnetic stirring speed V 1 and stir for 30 min to form a W / O / W double emulsion system.

[0039] Beneficial effects of adopting the above further technical solution: The core material is evenly dispersed, and the particle size of the microcapsules is locked in advance by regulating the diameter and distribution of the emulsion droplets.

[0040] Further, in step (1), the water bath heating temperature is 50°C to 70°C.

[0041] Beneficial effects of adopting the above further technical solution: Utilizing the characteristic that the solubility of ethyl cellulose varies greatly at different temperatures, the temperature of the system needs to be controlled within the temperature range where the solubility of ethyl cellulose is relatively high, but not too high, as too high a temperature will cause the organic solvent A to volatilize. This temperature range not only satisfies the relatively high solubility of ethyl cellulose but also does not cause the organic solvent to volatilize.

[0042] Further, in step (2), the magnetic stirring speed V 2 is 500 r / min, and the magnetic stirring speed V 3 is 200 r / min.

[0043] Beneficial effects of adopting the above further technical solution: During the precipitation and forming process of the wall material, first use a higher stirring speed to evenly disperse each microcapsule matrix, avoiding adhesion or agglomeration during the forming of the microcapsules and facilitating the formation of microcapsule products with high sphericity; after the microcapsules are basically formed, reduce the stirring speed, which is beneficial to the sealing and curing of the microcapsule shell.

[0044] Furthermore, in step (2), the temperature reduction gradient for reducing the system temperature is 10°C / min.

[0045] Beneficial effects of adopting the above further technical solution: The cooling gradient affects the precipitation rate of ethyl cellulose, and further affects the formation of the porous structure in the inner layer of the microcapsule shell. By regulating the cooling gradient, the inner layer structure of the microcapsule is controlled.

[0046] Further, in step (2), first, at a magnetic stirring speed V 2 The continuous stirring time is 2 min to 5 min. The above-mentioned reduces the stirring speed to the magnetic stirring speed V 3 The stirring time is 20 min.

[0047] Beneficial effects of adopting the above further technical solution: For different material ratios, the forming time of the microcapsules is different. The accurate time is when the microcapsules are formed until they are visible to the naked eye. By adjusting the dosage, type, and compounding ratio of the materials, and the selection of process parameters in the preparation process, the structure adjustment of the microcapsules is achieved. Microcapsule crosslinking agents with different shell structures and corresponding temperatures can be prepared according to the actual needs of on-site construction.

[0048] The present invention also provides an application of the above water-based fracturing fluid delayed crosslinking type microcapsule crosslinking agent or the water-based fracturing fluid delayed crosslinking type microcapsule crosslinking agent prepared by the above method in the deep well fracturing technology field of petroleum and natural gas or the stimulation technology field with prominent friction problems. Description of the Drawings

[0049] Figure 1 Scanning electron microscope image of the water-based fracturing fluid delayed crosslinking type microcapsule crosslinking agent prepared in Example 1;

[0050] Figure 2 Laser particle size analysis chart of the water-based fracturing fluid delayed crosslinking type microcapsule crosslinking agent prepared in Example 1;

[0051] Figure 3 High-temperature rheology curve graph of the fracturing fluid prepared with the water-based fracturing fluid delayed crosslinking type microcapsule crosslinking agent prepared in Example 1;

[0052] Figure 4 Friction curve graph of the fracturing fluid prepared with the water-based fracturing fluid delayed crosslinking type microcapsule crosslinking agent prepared in Example 1. Detailed Embodiments

[0053] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0054] Example 1

[0055] A water-based fracturing fluid delayed crosslinking type microcapsule crosslinking agent, comprising a core material and a wall material coating the selected core material. The core material includes an organic boron crosslinking agent, and the wall material includes ethyl cellulose and polyethylene wax. The wall material has a double-layer structure, with the inner layer being a porous structure framework and the outer layer being a dense outer shell.

[0056] A preparation method of the water-based fracturing fluid delayed crosslinking type microcapsule crosslinking agent, comprising the following steps:

[0057] (1) Weigh 30 g of an aqueous solution of organic boron crosslinking agent BSA-601 with a concentration of 40 wt%, 70 g of toluene, 2.8 g of ethyl cellulose, 2.1 g of polyethylene wax, 3.15 g of span 80, 250 g of deionized water, 5 g of polyisobutene, 2.5 g of sodium chloride, 2.5 g of tween 60, and 200 g of cyclohexane;

[0058] (2) Formation of the W / O / W dispersion system: Under the condition of a 70°C water bath, add ethyl cellulose and polyethylene wax to toluene and stir to dissolve, then add span 80 and stir and mix as the oil phase; maintain the water bath temperature, and under mechanical high-speed stirring at 5000 r / min, add the aqueous solution of the organic boron crosslinking agent to the oil phase and continue stirring for 3 min to form a W / O primary emulsion system; at the same water bath temperature, add polyisobutene, sodium chloride, and tween 60 to deionized water and stir evenly as the outer aqueous phase; then, under magnetic stirring at 1000 r / min, dropwise add the W / O primary emulsion system and keep stirring for 30 min to form a W / O / W double emulsion system;

[0059] (3) Formation and curing of the microcapsules: Gradually reduce the temperature of the W / O / W double emulsion system at a gradient of 10°C / min. When the system shows flocculation and demulsification phenomena, stop cooling; under the condition of a magnetic stirring speed of 500 r / min, gradually add cyclohexane to the system, stir for 4 min until the microcapsules are formed, then reduce the stirring speed to 200 r / min and stir for 20 min to cure the microcapsules;

[0060] (4) Output of the microcapsules: After the microcapsules are cured, after centrifugal separation, let it stand for sedimentation, filter by suction, wash with deionized water, and dry at a low temperature of 25°C for 3 h to obtain microspherical white powder, and obtain the microcapsule crosslinking agent.

[0061] Example 2

[0062] A preparation method of the water-based fracturing fluid delayed crosslinking type microcapsule crosslinking agent, comprising the following steps:

[0063] (1) Weigh 20 g of an aqueous solution of organic boron crosslinking agent SRJL-YL with a concentration of 30 wt%, 50 g of toluene, 1.75 g of ethyl cellulose, 1.75 g of polyethylene wax, 2 g of span 80, 175 g of deionized water, 3.5 g of polyisobutene, 1.75 g of sodium chloride, 3.5 g of tween 60, and 150 g of n-hexane;

[0064] (2) Formation of W / O / W dispersion system: Under the condition of a 60 °C water bath, ethyl cellulose and polyethylene wax were added to toluene and stirred until dissolved, and then Span 80 was added and stirred and mixed for use as the oil phase; maintaining the water bath temperature, under mechanical high-speed stirring at 4000 r / min, the aqueous solution of organic boron crosslinking agent was added to the oil phase and stirred continuously for 3 min to form a W / O primary emulsion; at the same water bath temperature, polyisobutylene, sodium chloride, and Tween 60 were added to deionized water and stirred evenly as the external water phase; then, the W / O primary emulsion system was added dropwise under magnetic stirring at 800 r / min and stirred for 30 min to form a W / O / W double emulsion system;

[0065] (3) Formation and curing of microcapsules: The temperature of the W / O / W double emulsion system was decreased at a gradient of 10 °C / min. When flocculation appeared in the system and there was a demulsification phenomenon, the temperature reduction was stopped; under the condition of a magnetic stirring speed of 500 r / min, n-hexane was added dropwise to the system; after stirring for 3 min for the microcapsules to take shape, the stirring speed was reduced to 200 r / min and stirred for 20 min to cure the microcapsules;

[0066] (4) Output of microcapsules: After the microcapsules were cured, they were centrifuged, allowed to stand and settle, filtered by suction, rinsed with deionized water, and dried at a low temperature of 25 °C for 3 h to obtain a microspherical white powder, and the microcapsule crosslinking agent was obtained.

[0067] Example 3

[0068] A preparation method of a water-based fracturing fluid delayed crosslinking type microcapsule crosslinking agent, comprising the following steps:

[0069] (1) Weigh 25 g of an aqueous solution of organic boron crosslinking agent BY-X with a concentration of 50 wt%, 60 g of toluene, 2.7 g of ethyl cellulose, 1.5 g of polyethylene wax, 2.4 g of Span 80, 200 g of deionized water, 4 g of polyisobutylene, 2 g of sodium chloride, 4 g of Tween 60, and 160 g of dichloromethane;

[0070] (2) Formation of W / O / W dispersion system: Under the condition of a 50 °C water bath, ethyl cellulose and polyethylene wax were added to toluene and stirred until dissolved, and then Span 80 was added and stirred and mixed for use as the oil phase; maintaining the water bath temperature, under mechanical high-speed stirring at 6000 r / min, the aqueous solution of organic boron crosslinking agent was added to the oil phase and stirred continuously for 3 min to form a W / O primary emulsion; at the same water bath temperature, polyisobutylene, sodium chloride, and Tween 60 were added to deionized water and stirred evenly as the external water phase; then, the W / O primary emulsion system was added dropwise under magnetic stirring at 1200 r / min and stirred for 30 min to form a W / O / W double emulsion system;

[0071] (3) Formation and curing of microcapsules: The temperature of the W / O / W double emulsion system was decreased at a gradient of 10 °C / min. When flocculation appeared in the system and demulsification occurred, the temperature reduction was stopped. Under the condition of a magnetic stirring speed of 500 r / min, dichloromethane was added dropwise into the system. After stirring for 2 min for microcapsule formation, the stirring speed was reduced to 200 r / min and stirred for 20 min to cure the microcapsules.

[0072] (4) Output of microcapsules: After the microcapsules were cured, they were separated by centrifugation, allowed to settle by standing, filtered by suction, rinsed with deionized water, and dried at a low temperature of 25 °C for 3 h to obtain a microspherical white powder, and the microcapsule crosslinking agent was obtained.

[0073] Example 4

[0074] The surface morphology and structure of the microcapsule crosslinking agent prepared in Example 1 were observed by a scanning electron microscope. The results are shown in Figure 1 . The dried microcapsule powder was evenly coated on the conductive adhesive, and it was dispersed as much as possible to achieve a single-layer microcapsule structure. The conductive adhesive was adhered to the sample stage and placed in a vacuum tube to evacuate. The microscopic morphology was analyzed. The results showed that the prepared microcapsules were spheres with a porous structure on the surface of the shell.

[0075] Example 5

[0076] The microcapsule crosslinking agent prepared in Example 1 was analyzed by a laser particle size analyzer. The particle size distribution of the microcapsules was analyzed by D(0.5). The results are shown in Figure 2 . The results showed that the prepared microcapsules were of uniform size, and D(0.5) = 112 μm.

[0077] Example 6

[0078] The high-temperature rheological properties of the delayed crosslinking microcapsule crosslinking agent fracturing fluid system in Example 1 were tested. The evaluation method referred to SY / T 5107-2016 "Evaluation Method for Water-Based Fracturing Fluid Performance". Using an RS6000 rheometer, after heating to 180 °C and keeping it constant, the rheological properties of the microcapsule crosslinking agent fracturing fluid system were tested under the condition of a shear rate of 170 s -1 . The results are shown in Figure 3 . The results showed that the initial viscosity of the system was low. When the temperature reached 110 °C, the viscosity gradually increased, and the viscosity was still above 50 mPa·s after continuous shearing for 100 min, indicating that the system had good temperature resistance and shear resistance.

[0079] Example 7

[0080] Test the drag reduction performance of the delayed crosslinking microcapsule crosslinking agent fracturing fluid system in Test Example 1. The evaluation method refers to the standard SY / T 6376-2008 "General Technical Conditions for Fracturing Fluids". Use the SY-MZ pipeline friction tester to measure the friction generated when clear water and the microcapsule crosslinking agent fracturing fluid system flow through a pipeline of a certain length and diameter under the shear rate of 12,000 s -1 conditions respectively, and calculate the drag reduction performance of the fracturing fluid from this. The results are shown in Figure 4 . The results show that when the shear rate is 12,000 s -1 conditions, the drag reduction performance of this microcapsule crosslinking agent fracturing fluid system is good, higher than the standard requirement of not less than 50.00%.

[0081] The description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A water-based fracturing fluid delayed crosslinking type microcapsule crosslinking agent, characterized in that, it includes a core material and a wall material coating the selected core material. The core material includes an organic boron crosslinking agent, and the wall material includes ethyl cellulose and polyethylene wax; The preparation method of the water-based fracturing fluid delayed crosslinking type microcapsule crosslinking agent includes the following steps: (1)Formation of W / O / W dispersion system: Under water bath conditions, the wall material is added to organic solvent A and stirred to dissolve, and then the primary emulsion emulsifier is added and stirred and mixed as the oil phase; maintaining the water bath temperature, under high-speed mechanical stirring, the core material aqueous solution is added to the oil phase, and stirred for a certain time to form a W / O primary emulsion system; at the same water bath temperature, a phase stabilizer, an osmotic pressure stabilizer and a double emulsion emulsifier are added to deionized water, stirred evenly as the outer aqueous phase, and the W / O primary emulsion system is added dropwise to the outer aqueous phase at the magnetic stirring speed V 1 After that, the W / O / W double emulsion system is formed by stirring for a certain time. (2) Formation and curing of microcapsules: Lower the temperature of the prepared W / O / W double emulsion system. The temperature reduction gradient for lowering the system temperature is 10 °C / min. When flocculation appears in the system and there is demulsification, stop cooling, and add organic solvent B dropwise into the system. First, stir at a magnetic stirring speed V 2 Continue stirring until the microcapsules are formed, and then reduce the stirring rate to the magnetic stirring speed V 3 Stir to cure the microcapsules; (3) Output of microcapsules: After the microcapsules are cured, they are centrifuged, then allowed to stand and settle, filtered by suction, rinsed with deionized water, and dried at low temperature to obtain the microcapsule crosslinking agent; The organic solvent A is any one of toluene, xylene, cyclohexane or dichloroethane; The organic solvent B is any one of dichloromethane, acetone, cyclohexane or n-hexane.

2. The water-based fracturing fluid delayed crosslinking type microcapsule crosslinking agent according to claim 1, characterized in that, The weight parts of each raw material are: 20-30 parts of core material aqueous solution, 3-5 parts of wall material, 50-70 parts of organic solvent A, 1.75-4.9 parts of primary emulsion emulsifier, 150-250 parts of deionized water, 2.5-5 parts of phase stabilizer, 1.25-5 parts of osmotic pressure stabilizer, 2.5-5 parts of double emulsion emulsifier, 100-200 parts of organic solvent B, and the concentration of the core material aqueous solution is 30-50wt%.

3. The water-based fracturing fluid delayed crosslinking type microcapsule crosslinking agent according to claim 1, characterized in that, The primary emulsion emulsifier is one or several of Span 40, Span 60 or Span 80; The phase stabilizer is polyvinyl alcohol or polyisobutylene; The osmotic pressure stabilizer is a chloride salt; The double emulsion emulsifier is one or several of Tween 20, Tween 40, Tween 60 or Tween 80.

4. The water-based fracturing fluid delayed crosslinking type microcapsule crosslinking agent according to claim 1, characterized in that, In step (1), the stirring speed of the mechanical high-speed stirring is 4000 r / min to 6000 r / min, and the magnetic stirring speed V 1 is 800 r / min to 1200 r / min.

5. The water-based fracturing fluid delayed crosslinking type microcapsule crosslinking agent according to claim 1, characterized in that, In step (1), the water bath heating temperature is 50°C to 70°C.

6. The water-based fracturing fluid delayed crosslinking type microcapsule crosslinking agent according to claim 1, characterized in that, In step (2), the magnetic stirring speed V 2 is 500 r / min, and the magnetic stirring speed V 3 is 200 r / min.

7. Application of the water-based fracturing fluid delayed crosslinking type microcapsule crosslinking agent according to claim 1 in the deep well fracturing technology field of petroleum and natural gas or the stimulation technology field with prominent friction problems.

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