Preparation method of self-repairing proppant

Abstract

The invention discloses a preparation method of a self-repairing proppant, which comprises the following steps: S1, uniformly mixing a monomer A and formaldehyde, adding an alkaline reagent to adjust the pH value to 8-9, and stirring and reacting for 0.5-1 hour in a constant-temperature water bath at 50-80 DEG C to obtain a prepolymer solution; adding a repairing agent, a diluent and a surfactant into the prepolymer solution, stirring and emulsifying, adding an acidic reagent to adjust the pH value of the solution to 3-5, and stirring and reacting at 40-60 DEG C for 1-3 hours to obtain a microcapsule solution A; s2, uniformly mixing a monomer B, a cross-linking agent, an initiator and an inorganic filler, and adding a curing agent to form a solution B; s3, mixing the solution A with the solution B, heating the mixed solution to 50-60 DEG C, and carrying out constant-temperature reaction for 0.5-1 hour to form particles in the solution; continuously heating to 80-100 DEG C, keeping the constant temperature for 2-3 hours to cure the particles, and finally carrying out suction filtration, washing and drying on the cured particles while the particles are hot to obtain particles, namely the self-repairing proppant. The self-repairing proppant provided by the invention can be effectively prevented from being broken through self-repairing, so that the flow conductivity of cracks is maintained.

Description

Technical Field

[0001] The invention relates to the technical field of fracturing in petroleum production, in particular to a method for preparing a self-repairing proppant. Background Art

[0002] Fracturing plays a key role in oil and gas field development, increasing well production and recovery rates. However, deep reservoirs, due to their deep underground location and complex geological conditions, present significant challenges in fracturing. In particular, traditional proppants struggle to maintain long-term stability and integrity in these complex geological conditions, leading to fracture closure and hindering the smooth flow of oil and gas.

[0003] To address these issues, most researchers are currently focusing on developing a new proppant that can adapt to complex geological conditions and maintain long-term stability and integrity. For example, patent CN115261011A discloses a new fracturing proppant and its preparation method. This new proppant has low bulk and apparent density, is lightweight, resistant to breakage, has high strength, and exhibits excellent acid solubility. It also offers excellent conductivity and ease of pumping, reducing the viscosity requirements for the fracturing fluid and minimizing damage to the pump, effectively lowering both construction difficulty and costs.

[0004] However, these new proppant technologies still face a significant challenge: self-repair. During the fracturing process, the high temperatures and high pressures of the formation often damage the proppant, leading to a decrease in performance. Although some new proppants utilize advanced materials and manufacturing processes to improve their compressive strength and wear resistance, they can still develop tiny cracks or breakage under long-term formation stress.

[0005] Therefore, in further research, it is necessary to deeply solve the problem of easy breakage of proppants. The proppant system developed should have self-repairing ability, high temperature and high pressure resistance, high conductivity and permeability, so as to maintain the stability of cracks, expand channels, reduce resistance, and ensure the efficient outflow of oil and gas. Summary of the Invention

[0006] In view of the problem that current proppants used for fracturing lack self-repairing ability, the present invention provides a proppant with self-repairing ability and a method for preparing the proppant.

[0007] The self-repairing proppant provided by the present invention has the following steps for preparing the same:

[0008] S1: Monomer A and formaldehyde are mixed evenly, an alkaline reagent is added to adjust the pH to 8-9, and the mixture is stirred in a constant temperature water bath at 50-80°C for 0.5-1 hour to obtain a prepolymer solution; a repair agent, a diluent, and a surfactant are added to the prepolymer solution, stirred and emulsified for 30-40 minutes, an acidic reagent is added to adjust the pH of the solution to 3-5, and the mixture is stirred at 40-60°C for 1-3 hours to obtain a microcapsule solution A;

[0009] The monomer A is at least one of melamine, urea, and melamine;

[0010] The repair agent is at least one of bisphenol A epichlorohydrin copolymer, glycidyl methacrylate, glycidyl tetrahydrophthalate, ethylene vinyl acetate, cyanoacrylate, and isocyanate;

[0011] The diluent is at least one of benzyl alcohol, n-butyl glycidyl ether, phenylacetic acid, chlorobenzene, and ethyl phenylacetate;

[0012] S2: uniformly mixing monomer B, a crosslinking agent, an initiator, and an inorganic filler, and adding a curing agent and stirring to dissolve to form a solution B; the monomer B is styrene or methyl methacrylate;

[0013] S3: Mix solution A and solution B, heat the mixed solution to 50-60°C and keep it at this temperature for 0.5-1h to form particles in the solution; continue to heat it to 80-100°C and keep it at this temperature for 2-3h to mature the particles, and finally filter the mature particles while they are hot, wash them, dry them, and after cooling, use a standard test sieve to select particles with a mesh size of 20-40 (425-850μm), which are the self-healing proppant.

[0014] Preferably, based on the total mass of all raw materials being 100%, the mass proportions of the respective raw materials are as follows:

[0015] Monomer A 3%-5%, formaldehyde 3%-5%, repair agent 5%-8%, diluent 0%-2%, surfactant 3%-6%, monomer B 40%-55%, cross-linking agent 15%-30%, initiator 0.5%-5%, inorganic filler 0.5%-5%, curing agent 5%-8%.

[0016] The alkaline reagent is one of triethanolamine, sodium hydroxide and sodium carbonate.

[0017] The acidic reagent is one of dilute sulfuric acid, acetic acid and citric acid.

[0018] The cross-linking agent is divinylbenzene.

[0019] The inorganic filler is at least one of carbon black, graphite, nano-silicon dioxide, carbon nanotubes, silica fume, graphene, pine bark, and fly ash.

[0020] The surfactant is sodium dodecylbenzenesulfonate or octylphenol polyoxyethylene ether.

[0021] The curing agent is at least one of diethylenetriamine, imidazole curing agent, a complex of copper bromide and 2-methylimidazole, triethanolamine, boron trifluoride ether complex, and ethylenediamine.

[0022] The initiator is one of KPS, APS, AIBN, ABVN and BPO.

[0023] Compared with the prior art, the present invention is beneficial in that:

[0024] The present invention incorporates microcapsules containing a repair agent into ultra-low-density proppants. When excessive pressure causes the proppant to break, cracks in the proppant, generated by the pressure, proppantically extend to the microcapsules. Stress concentration at the crack tip causes the capsule wall to rupture, and the liquid repair agent diffuses into the crack. Once the repair agent reaches the cracked area, it comes into contact with the curing agent in the proppant, triggering a polymerization reaction that bonds and repairs the crack. This significantly reduces the breakage rate of the proppant, extends its service life, and maintains the conductivity of the crack for a long time. This effectively solves the problem of traditional proppants easily breaking during use, which leads to a decrease in fracture conductivity.

[0025] Other advantages, objectives and features of the present invention will be reflected in part from the following description and will be understood by those skilled in the art through study and practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is the infrared spectrum test chart of the proppant A2 prepared in Example 1.

[0027] Figure 2 This is an infrared spectrum test chart of the self-repairing proppant A1 prepared in Example 1 after the pressure crushing test.

[0028] Figure 3 This is the fracture conductivity effect of the self-healing proppant of Example 3 and the proppant without a repairing agent under the same conditions. DETAILED DESCRIPTION

[0029] The preferred embodiments of the present invention are described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0030] Example 1

[0031] A self-repairing proppant, wherein the total mass of all raw materials is taken as 100%, and the percentage content of each raw material is the percentage of its mass to the total mass of all raw materials, is prepared as follows:

[0032] S1. Mix 3% melamine and 3% formaldehyde in a beaker and stir uniformly with a glass rod or a magnetic stirrer. Add a certain amount of sodium hydroxide solution to adjust the pH to 8-9. Then, react in a 70°C constant temperature water bath at 400-450 rpm for 1 hour, and cool to room temperature to obtain a prepolymer solution. Add 5% epoxy resin E-51, 1% n-butyl glycidyl ether, and 4% sodium dodecylbenzenesulfonate to the prepolymer solution. Stir and emulsify for 30-40 minutes, then add a certain amount of acetic acid solution to adjust the pH to 3-5. React at 40-60°C at a certain rotational speed for 1-3 hours to obtain microcapsule solution A. The shell material of the microcapsules contained in this solution is formed by the reaction of melamine and formaldehyde. The shell material encapsulates the repair agent epoxy resin E-51 to form microcapsules.

[0033] S2: 45% methyl methacrylate, 27.5% divinylbenzene, 1% benzoyl peroxide, 4.5% carbon black, and 6% imidazole epoxy resin curing agent MC120D were mixed and dissolved with stirring at 45°C to form solution B;

[0034] S3: Solution A and solution B were mixed, and the mixture was heated to 50°C and stored for 0.5 h, then stored at 80°C for 2 h, then heated to 85°C and stored for 2 h, and finally boiled at 90°C for 2 h for maturation. The matured particles were filtered while hot, washed three times with hot water and once with methanol, and the obtained particles were placed in an air flow drying oven for drying. After cooling, the particles of 20-40 mesh (425-850 μm) were screened out with a standard test sieve, namely the self-healing proppant A1.

[0035] Based on the above preparation method, the imidazole epoxy resin curing agent MC120D is not added in step S2, and the other steps remain unchanged to obtain the proppant A2.

[0036] The proppant A2 was tested by infrared spectroscopy. The test results are shown in Figure 1 The self-repairing proppant A1 was subjected to a crushing test under a pressure of 35 MPa, and the proppant after the crushing test was subjected to an infrared spectrum test. The test results are shown in Figure 2 .

[0037] Figure 1 Medium, 3398cm -1 It is the NH stretching vibration, corresponding to the characteristic peak of melamine resin; 2939cm -1 is the CH stretching vibration, corresponding to the characteristic peak of PMMA; 1547cm -1 It is the NH angle vibration and CN stretching vibration, corresponding to the characteristic peak of melamine resin; 1459cm -1 is the CH bending vibration, corresponding to the characteristic peak of PMMA; 902cm -1It is the asymmetric stretching vibration of the epoxy group, corresponding to the characteristic peak of epoxy resin; it shows that the proppant contains a self-healing agent (epoxy resin).

[0038] Figure 2 Medium, 3363cm -1 It is the NH stretching vibration, corresponding to the characteristic peak of melamine resin; 2945cm -1 is the CH stretching vibration, corresponding to the characteristic peak of PMMA; 1538cm -1 It is the NH angle vibration and CN stretching vibration, corresponding to the characteristic peak of melamine resin; 905cm -1 A weak peak is shown. This is because the microcapsules of the self-repairing proppant A1 are broken and the epoxy resin reacts with the curing agent, so the peak at 905 cm -1 The cracks weakened, indicating that the epoxy resin repaired the cracked proppant.

[0039] Example 2

[0040] A self-repairing proppant, wherein the total mass of all raw materials is taken as 100%, and the percentage content of each raw material is the percentage of its mass to the total mass of all raw materials, is prepared as follows:

[0041] S1. Mix 4% melamine and 3% formaldehyde in a beaker and stir uniformly with a glass rod or a magnetic stirrer. Add a certain amount of sodium hydroxide solution to adjust the pH to 8-9. Then, react in a constant-temperature water bath at 400-450 rpm for 1 hour, then cool to room temperature to obtain a prepolymer solution. Add 5% glycidyl tetrahydrophthalate and 4% sodium dodecylbenzenesulfonate to the prepolymer solution. Stir and emulsify for 30-40 minutes, then add a certain amount of acetic acid solution to adjust the pH to 3-5. React at 40-60°C at a constant speed for 1-3 hours to obtain microcapsule solution A. Due to the low viscosity of glycidyl tetrahydrophthalate, no diluent is required.

[0042] S2: 45% methyl methacrylate, 28% divinylbenzene, 1% benzoyl peroxide, 6% carbon black, and 6% pentaerythritol mercaptopropionate were mixed and dissolved with stirring at 45°C to form solution B;

[0043] S3: Solution A and solution B were mixed, and the mixture was heated to 50°C and stored for 0.5 h, then stored at 80°C for 2 h, then heated to 85°C and stored for 2 h, and finally boiled at 90°C for 2 h for maturation. The matured particles were filtered while hot, washed three times with hot water and once with methanol, and the obtained particles were placed in an air flow drying oven for drying. After cooling, the particles of 20-40 mesh (425-850 μm) were screened out with a standard test sieve, namely the self-healing proppant B1.

[0044] Based on the above preparation method, in step S1, glycidyl tetrahydrophthalate is replaced with an equal amount of deionized water to finally obtain proppant B2.

[0045] The resulting self-healing proppant B1 and proppant B2 were tested for breakage rate under a certain pressure. The test results are shown in Table 1. The results show that self-healing proppant B1 is more effective in reducing proppant breakage than proppant B2. This is because proppant B2 does not contain a repair agent and therefore lacks self-healing properties.

[0046] Table 1 Test results of the crushing rate of self-repairing proppant B1 and proppant B2 at different pressures

[0047] 35MPa 52MPa Breakage rate of proppant B1 4.8％ 6.5％ Breakage rate of proppant B2 7.3％ 9％

[0048] Example 3

[0049] A self-repairing proppant, wherein the total mass of all raw materials is taken as 100%, and the percentage content of each raw material is the percentage of its mass to the total mass of all raw materials, is prepared as follows:

[0050] S1. Mix 3% urea and 3% formaldehyde in a beaker and stir thoroughly with a glass rod or magnetic stirrer. Add a certain amount of triethanolamine to adjust the pH to 8-9. Then, react in a constant temperature water bath at 70°C at 400-450 rpm for 1 hour, and then cool to room temperature to obtain a prepolymer solution. Add 7% epoxy resin E-51, 1% n-butyl glycidyl ether, and 4% sodium dodecylbenzenesulfonate to the prepolymer solution. Stir and emulsify for 30-40 minutes, then add a certain amount of dilute sulfuric acid solution to adjust the pH to 3-5. React at 40-60°C at a certain speed for 1-3 hours to obtain microcapsule solution A.

[0051] S2: 53% styrene, 20% divinylbenzene, 1.5% benzoyl peroxide, 2.5% graphite, and 5% imidazole curing agent MC120D were mixed and dissolved with stirring at 45°C to form solution B;

[0052] S3: Solution A and Solution B were mixed and heated to 50°C for 0.5 h, 80°C for 2 h, 85°C for 2 h, and then boiled at 90°C for 2 h. The matured particles were then filtered while hot, washed three times with hot water, and once with methanol. The resulting particles were then dried in an airflow drying oven. After cooling, the particles were sieved using a standard test sieve to obtain particles with a mesh size of 20-40 (425-850 μm), which constituted the self-healing proppant D1.

[0053] Based on the above preparation method, in step S1, the epoxy resin is replaced with an equal amount of deionized water to finally obtain proppant D2. The self-repairing proppant D1 and proppant D2 were tested for their conductivity, and the test results were as follows: Figure 3 As shown, the results show that the self-healing proppant D1 can more effectively maintain the conductivity of the crack than the proppant D2. This is because the self-healing proppant D1 contains a healing agent capsule, and the proppant has a self-healing function, while the proppant D2 does not contain a healing agent and has no healing function. The self-healing proppant D1 has lower proppant breakage than the proppant D2, which extends the service life of the proppant and maintains the conductivity of the crack for a long time.

[0054] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as a preferred embodiment as above, it is not intended to limit the present invention. Any technician familiar with this profession can make some changes or modifications to equivalent embodiments of the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for preparing a self-repairing proppant, characterized in that: The following steps are involved: S1: Monomer A and formaldehyde are mixed evenly, an alkaline reagent is added to adjust the pH to 8-9, and the mixture is stirred in a constant temperature water bath at 50-80°C for 0.5-1 hour to obtain a prepolymer solution; a repair agent, a diluent, and a surfactant are added to the prepolymer solution, stirred and emulsified for 30-40 minutes, an acidic reagent is added to adjust the pH of the solution to 3-5, and the mixture is stirred at 40-60°C for 1-3 hours to obtain a microcapsule solution A; The monomer A is at least one of melamine, urea, and melamine; The repair agent is at least one of bisphenol A epichlorohydrin copolymer, glycidyl methacrylate, glycidyl tetrahydrophthalate, ethylene vinyl acetate, cyanoacrylate, and isocyanate; The diluent is at least one of benzyl alcohol, n-butyl glycidyl ether, phenylacetic acid, chlorobenzene, and ethyl phenylacetate; S2: uniformly mixing monomer B, a crosslinking agent, an initiator, and an inorganic filler, and adding a curing agent and stirring to dissolve to form a solution B; the monomer B is styrene or methyl methacrylate; S3: Mix solution A and solution B, heat the mixed solution to 50-60°C and keep it at this temperature for 0.5-1h to form particles in the solution; continue to heat it to 80-100°C and keep it at this temperature for 2-3h to mature the particles, and finally filter the mature particles while they are hot, wash them, and dry them to obtain the particles that are the self-healing proppant.

2. The method for preparing the self-repairing proppant according to claim 1, wherein: The alkaline reagent is one of triethanolamine, sodium hydroxide and sodium carbonate.

3. The method for preparing the self-repairing proppant according to claim 1, wherein: The acidic reagent is one of dilute sulfuric acid, acetic acid and citric acid.

4. The method for preparing the self-repairing proppant according to claim 1, wherein: The cross-linking agent is divinylbenzene.

5. The method for preparing the self-repairing proppant according to claim 1, wherein: The inorganic filler is at least one of carbon black, graphite, nano-silicon dioxide, carbon nanotubes, silica fume, graphene, pine bark, and fly ash.

6. The method for preparing the self-repairing proppant according to claim 1, wherein: The surfactant is sodium dodecylbenzenesulfonate or octylphenol polyoxyethylene ether.

7. The method for preparing the self-repairing proppant according to claim 1, wherein: The curing agent is at least one of diethylenetriamine, imidazole curing agent, a complex of copper bromide and 2-methylimidazole, triethanolamine, boron trifluoride ether complex, and ethylenediamine.

8. The method for preparing the self-repairing proppant according to claim 1, wherein: The initiator is one of KPS, APS, AIBN, ABVN and BPO.

9. The method for preparing the self-repairing proppant according to claim 1, wherein: Taking the total mass of all raw materials as 100%, the mass proportion of each raw material is as follows: Monomer A 3%-5%, formaldehyde 3%-5%, repair agent 5%-8%, diluent 0%-2%, surfactant 3%-6%, monomer B 40%-55%, cross-linking agent 15%-30%, initiator 0.5%-5%, inorganic filler 0.5%-5%, curing agent 5%-8%.

10. A self-repairing proppant, characterized in that: Prepared by the preparation method according to any one of claims 1 to 9.

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