Multifunctional self-suspending proppant and preparation method thereof

Abstract

The invention relates to the technical field of oil-gas field development, and discloses a multifunctional self-suspending proppant and a preparation method thereof. The proppant comprises a core aggregate; the surface of the inner core aggregate is coated with the magnetic suspension resin compound; and / or a magnetic suspension resin compound filled in holes of the inner core aggregate. The magnetic suspension resin compound comprises thermosetting resin and Fe3O4 PAM composite particles, and can absorb water to swell, so that the proppant achieves a self-suspension effect; holes in the surface of aggregate are filled, so that the strength of the proppant can be enhanced; and a magnetic signal is provided, and monitoring of underground support cracks can be assisted. According to the proppant provided by the invention, the effective supporting length of the crack can be increased, and meanwhile, the problem of real-time monitoring of the crack in the fracturing process is solved, and the problem of relatively low strength of the proppant is solved.

Description

Technical Field

[0001] The invention relates to the technical field of oil and gas field development, in particular to a multifunctional self-suspending proppant and a preparation method thereof. Background Art

[0002] With the deepening development of unconventional oil and gas resources, fracturing technology has gradually evolved towards high intensity, intelligence and low cost. The current mainstream fracturing technologies include horizontal well segmented multi-cluster fracturing (using soluble bridge plugs or sliding sleeves to achieve multi-stage transformation), synchronous fracturing (multi-well linkage to improve the complexity of the fracture network), temporary plugging fracturing (adding temporary plugging agents to force fractures to turn and form new fractures), water-free / low-water fracturing (using non-aqueous media such as supercritical CO2 to replace traditional fracturing fluids), etc. Its core goal is to improve the fracture conductivity through the construction of complex fracture networks and refined transformation.

[0003] Proppants are carried into underground fractures by fracturing fluids and support the fractures, serving as a key material for maintaining conductivity. Density and strength are two key indicators of proppant performance. Low density extends the proppant's migration distance within the fracture, improving fracture conductivity in areas far from the wellbore. High strength resists breakage under high closure pressures at depth, maintaining long-term fracture conductivity. However, conventional proppants have a high density, requiring high-viscosity sand-carrying fluids (such as guar gum fracturing fluids) for long-distance transport within underground fractures. This is costly and leaves residue that can easily clog the fractures, reducing conductivity.

[0004] In order to solve the problem of proppant transportation, self-suspending proppants came into being. As a new type of proppant, self-suspending proppants combine proppant and fracturing fluid into one. They can achieve the purpose of long-term suspension without the help of conventional fracturing fluid system, realize water fracturing, reduce construction costs, and simplify the liquid preparation process. According to the difference in suspension mechanism, self-suspending proppants can be divided into three categories: (1) expansion type: through water-soluble polymer coating (such as polyacrylamide, hydrogel) swelling in water to form a low-density hydration layer; (2) viscosity-increasing type: through the release of polymer chains (such as guar gum, hydroxypropyl cellulose) by the coating to increase the viscosity of the liquid and improve the suspension stability; (3) air suspension type: composed of conventional proppant particles and hydrophobic and air-philic coating, the polymer coating on the surface changes the wettability of the proppant surface. However, these self-suspending proppants have significant drawbacks when used to coat low-cost, low-strength substrates such as quartz sand and solid waste particles. Due to limitations in the coating process, it's difficult to achieve both suspension and strength. For example, CN106832145A discloses an effervescent gas-suspended proppant for slick water fracturing and its preparation method. The proppant aggregate is coated with a hydrophobic, air-philic coating and an effervescent membrane coating. The outer effervescent membrane rapidly reacts in slick water to generate self-generated bubbles, which effectively adsorb to the inner surface of the proppant—the hydrophobic, air-philic membrane—thus increasing the proppant's buoyancy in slick water. However, when using quartz sand as the proppant aggregate, the compressive strength of this suspending proppant remains at only 35 MPa, showing no fundamental improvement.

[0005] On the other hand, the fracture conductivity is not only related to the suspension performance of the proppant, but also closely related to the real-time control of the distribution law of the fracture after fracturing. Through crack monitoring, the crack size and crack distribution can be understood in a timely manner, which is of great significance to the optimization of fracturing construction parameters and production evaluation. However, existing crack monitoring technologies are difficult to monitor the distribution and laying efficiency of proppant, especially self-suspending proppant. Combining tracers and proppant can effectively monitor the proppant position and crack conditions, and verify the usefulness of self-suspending proppant. CN109423270A and CN109423271A disclose magnetic self-suspending proppant and its preparation method, which is to spray a solution of silane coupling agent onto the surface of magnetic proppant aggregate, onto which a water-based bulking polymer material is grafted. Conventional proppant is quartz sand, ceramsite, which is a relatively cheap and easy-to-obtain material. The proppant aggregate described in this method is Fe3O4, γ-Fe2O3, etc. The aggregate has a large density, low strength and high price, which makes it difficult to support the large-scale sand addition demand during fracturing. Similarly, CN115873589A discloses an intelligent oil-phase-releasing self-suspending tracer proppant and its preparation method. The proppant is organically synthesized from oil-based magnetic nano-Fe3O4, divinylbenzene, styrene, polyvinyl alcohol, etc., and its aggregate is also Fe3O4 particles, which is difficult to support the large-scale sand addition requirements during the fracturing process. Summary of the Invention

[0006] Technical problems solved by the present invention: The present invention provides a multifunctional self-suspending proppant and a preparation method thereof, which are used to solve the problems of rapid sedimentation and difficulty in filling the distal end of cracks of conventional proppants, and simultaneously solve the problem of real-time monitoring of cracks during fracturing and the problem of low strength of existing self-suspending proppants.

[0007] The technical solution adopted in the present invention is: In a first aspect, the present invention provides a multifunctional self-suspending proppant, comprising: core aggregate; A magnetic suspension resin composite coated on the surface of the core aggregate; and / or, A magnetic suspension resin composite that fills the pores of the core aggregate; The magnetic suspension resin composite comprises a thermosetting resin and Fe3O4@PAM composite particles.

[0008] As a preferred embodiment of any of the first aspects of the present invention, the core aggregate comprises at least one of porous ceramsite, quartz sand, solid waste particles, and rock debris particles. In the aforementioned embodiments, the solid waste particles comprise at least one of fly ash, coal gangue, bauxite tailings, and oil sludge residue. In addition to these, those skilled in the art may also select other similar solid waste particles besides those mentioned above.

[0009] As a preferred embodiment of any embodiment of the first aspect of the present invention, the particle size of the core aggregate is preferably 106~425um, and the bulk density is 1.3~1.6g / cm 3 .

[0010] As a preferred embodiment of any one of the first aspects of the present invention, in the magnetic suspension resin composite, the thermosetting resin includes at least one of a phenolic resin, an epoxy resin, and a polyurethane resin.

[0011] As a preferred embodiment of any one of the first aspects of the present invention, in the magnetic suspension resin composite, the mass ratio of the thermosetting resin to the Fe3O4@PAM composite particles is 1:0.1-0.5.

[0012] As a preferred embodiment of any embodiment of the first aspect of the present invention, in the magnetic suspension resin composite, the Fe3O4@PAM composite particles are microspheres with nano-Fe3O4 particles as the core and PAM as the shell.

[0013] As a preferred embodiment of any embodiment of the first aspect of the present invention, in the magnetic suspension resin composite, the Fe3O4@PAM composite particles are prepared by an inverse emulsion polymerization method, specifically by the following steps: 2.0 g acrylamide (AM), 0.12 g sodium dodecyl sulfate (SDS) and 0.43 g Fe3O4 particles were added to 10 mL of deionized water and ultrasonically dispersed for 15 minutes to form an aqueous phase. 2.88 g Span 80 was added to 30 mL of toluene and stirred evenly to form an oil phase. The aqueous phase was slowly added to the oil phase and stirred for 1.5 hours to form a stable inverse emulsion. The temperature was then increased while nitrogen was introduced into the inverse emulsion for 0.5 hours. When the temperature reached 60°C, 0.03 g potassium persulfate was added as an initiator to initiate acrylamide polymerization. After 4 hours of reaction, the product was filtered and rinsed with ethanol to obtain Fe3O4@PAM composite particles.

[0014] As a preferred embodiment of any embodiment of the first aspect of the present invention, in the magnetic suspension resin composite, the nano-Fe3O4 particles have a particle size of 20-50 nm and a saturation magnetization of 50-80 emu / g, which is used for tracing and positioning of the proppant.

[0015] In a second aspect, the present invention provides a method for preparing the aforementioned multifunctional self-suspending proppant, comprising the following steps: S1 core aggregate is washed with water to remove impurities and adhesion on the surface; S2 thermosetting resin and Fe3O4@PAM composite particles are ball-milled to obtain magnetic suspension resin slurry; The S3 core aggregate is vacuum degassed, and then magnetic suspension resin slurry is added and impregnated to obtain the filling aggregate; S4 solidifies and disperses the filling aggregate to obtain a multifunctional self-suspending proppant.

[0016] As a preferred embodiment of any embodiment of the second aspect of the present invention, during ball milling, the dispersion medium is ethanol, the ball milling time is 4-6 hours, the ball milling speed is 100-300 r / min, and the amount of the dispersion medium added is 1-3 times that of the magnetic suspension resin slurry.

[0017] As a preferred embodiment of any embodiment of the second aspect of the present invention, the mass ratio of the core aggregate to the magnetic suspension resin slurry is 1:0.01~0.1.

[0018] As a preferred embodiment of any embodiment of the second aspect of the present invention, vacuum degassing: degassing at -0.08 to -0.1 MPa for 0.5 to 1.5 hours, the purpose is to allow the magnetic suspension resin slurry to penetrate the surface pores more easily.

[0019] As a preferred embodiment of any embodiment of the second aspect of the present invention, the soaking is carried out by stirring at 400-800 r / min for 1-4 hours.

[0020] As a preferred embodiment of any embodiment of the second aspect of the present invention, curing: the temperature is raised to 110-140°C and a curing agent is added, with the amount of the curing agent added being 10-15% by weight of the thermosetting resin. When the thermosetting resin is a phenolic resin or a polyurethane resin, the curing agent is hexamethylenetetramine; when the thermosetting resin is an epoxy resin, the curing agent is an aliphatic amine curing agent, specifically at least one of ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, hexamethylenediamine, and polyethylenepolyamine.

[0021] As a preferred embodiment of any embodiment of the second aspect of the present invention, after solidification, the temperature is naturally lowered to 70-90° C. before dispersion treatment is performed.

[0022] As a preferred embodiment of any embodiment of the second aspect of the present invention, a dispersion treatment is performed on the solidified filler aggregate to prevent excessive adhesion between the proppants. Specifically, calcium stearate is added for dispersion, and the amount of calcium stearate added is 0.1-1 wt% of the proppant mass. After dispersion, the multifunctional self-suspending proppant is obtained by stirring, cooling, and sieving.

[0023] The technical mechanism and beneficial effects adopted by the present invention are: (1) The self-suspending proppant provided by the present invention combines the proppant and the fracturing fluid into one, reducing the amount of conventional fracturing fluid thickeners such as guar gum and polyacrylamide, thereby reducing construction costs and simplifying the fluid preparation process. At the same time, it can reduce reservoir damage, increase the effective support length of the fracture, and increase the conductivity of underground oil and gas.

[0024] (2) The self-suspending proppant provided by the present invention is obtained by introducing a magnetic suspension resin composite into the core aggregate. The Fe3O4@PAM composite particles in the magnetic suspension resin composite can enhance the magnetic signal intensity while maintaining the self-suspension of the proppant. The self-suspension characteristics are combined to extend the conveying distance, and the distribution of the proppant is monitored in real time through magnetic positioning, thereby achieving the purpose of determining the proppant conveying distance.

[0025] (3) The self-suspending proppant provided by the present invention is based on the selection of traditional core aggregates. In order to overcome the problem of low strength caused by the traditional core aggregates, the core aggregates are coated and / or filled with magnetic suspension resin composites, and Fe3O4 is used to support the pores of the proppant. At the same time, the PAM polymer coated on the surface of Fe3O4 increases viscosity when it comes into contact with water. While achieving the self-suspension of the proppant, the pores / cracks on the surface of the proppant can be self-repaired, so that the strength of the proppant can reach up to 86MPa. At the same time, it has the characteristics of self-suspension, traceability, high strength and low density. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a physical picture of the proppant settlement; Figure 2This is a physical picture of the proppant after burning ( Figure 2 1-4 represent Example 1, Example 2, Comparative Example 1, and Comparative Example 2, respectively). DETAILED DESCRIPTION

[0027] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, all are conventional products that can be purchased commercially.

[0028] Example 1 This embodiment provides a method for preparing a multifunctional self-suspending proppant, comprising the following steps: (1) Preparation of Fe3O4@PAM composite particles: 2.0 g acrylamide (AM), 0.12 g sodium dodecyl sulfate (SDS) and 0.4 g Fe3O4 particles were added to 10 mL of deionized water and ultrasonically dispersed for 15 minutes to form an aqueous phase. 2.88 g Span 80 was added to 30 mL of toluene and stirred evenly to form an oil phase. The aqueous phase was slowly added to the oil phase and stirred for 1.5 hours to form a stable inverse emulsion. The temperature was then increased while nitrogen was introduced into the inverse emulsion for 0.5 hours. When the temperature reached 70°C, 0.03 g potassium persulfate was added as an initiator to initiate acrylamide polymerization. After 4 hours of reaction, the product was filtered and rinsed with ethanol to obtain Fe3O4@PAM composite particles.

[0029] (2) Preparation of magnetic suspension resin slurry: Prepare 20g of phenolic resin and 4g of Fe3O4 / PAM composite particles, add 20g of ethanol as a dispersion medium, and ball mill and disperse at 300r / min for 2 hours to obtain a magnetic suspension resin slurry after dispersion.

[0030] (3) Preparation of multifunctional self-suspending proppant: ① Prepare 500g of core aggregate (quartz sand, 70 / 140 mesh [0.106~0.212μm], strength 35MPa, density 1.5g / cm 3 ), rinse with water 2 to 3 times to remove surface impurities, and dry at 45℃ to remove surface moisture.

[0031] ② Place the core aggregate in a -0.08~-0.1MPa environment for degassing for 1 hour, then add the magnetic suspension resin slurry and stir for 2 hours at a stirring speed of 600r / min. After stirring, the surface-filled modified aggregate is obtained.

[0032] ③ Place the modified aggregate in a heating furnace and heat it to 120°C, then add 6g of urotropol solution (2g of urotropol dissolved in 4g of water) to solidify; ④ Stop heating, wait for the proppant to cool to 90℃, add 2g of calcium stearate, continue stirring, cooling, and sieving to obtain a multifunctional self-suspending proppant.

[0033] Example 2 The difference between this embodiment and embodiment 1 is that in (2), the amount of Fe3O4@PAM composite particles added is 8 g.

[0034] Comparative Example 1 The difference between this comparative example and Example 1 is that in (2), the Fe3O4@PAM composite particles are replaced by nano-Fe3O4 particles.

[0035] Comparative Example 2 The difference between this comparative example and Example 1 is that the proppant is the core aggregate and no modification operation is performed.

[0036] Test example The proppant samples obtained in Examples 1-2 and Comparative Examples 1-2 were used to perform performance tests.

[0037] Test Example 1: Suspension Performance Test Take 400mL of tap water, add 90g of proppant (sand ratio about 15%) at a speed of 600r / min, stir for 3 minutes, start timing, and observe the sedimentation of the proppant within 15 minutes. The results are as follows: Figure 1 shown.

[0038] like Figure 1 The following table shows the observed settling of four proppants at the 15th minute. In Example 1, the proppant was mostly suspended within 15 minutes. In Example 2, more Fe3O4@PAM composite particles were added, achieving full suspension within 15 minutes. In Comparative Example 1, the Fe3O4@PAM composite particles were replaced with nano-Fe3O4 particles. The proppant was not suspended, but some particles, due to the coating, had a density lower than that of clear water and floated in the water. In Comparative Example 2, no modification was performed, resulting in rapid settling of the proppant.

[0039] Test Example 2: Determination of breakage rate Refer to SY / T 5108-2014 "Test Method for Proppant Performance for Hydraulic Fracturing and Gravel Packing Operations" and Q / SHCG0153-2021 "Technical Requirements for Coated Quartz Sand for Fracturing" to test the crushing rate of the proppant. First, crush the sample at the corresponding pressure level, then calcine at 927℃ for 2h. Figure 2 The sample after burning is shown. The burned sample is then sieved and the crushing rate after burning is calculated.

[0040] Table 1 shows the breakage rate test results for four proppants at different pressure levels. As can be seen from Table 1, the breakage rate of the modified proppants decreased uniformly, with the proppant incorporating Fe₃O₄@PAM composite particles experiencing a greater reduction. With a breakage rate of 9% as the acceptable limit, the multifunctional self-suspending proppant achieved a maximum strength of 86 MPa.

[0041] Table 1 Proppant breakage rate test results

[0042] Test Example 3: Density Test With reference to SY / T 5108-2014 “Test Method for Proppant Performance for Hydraulic Fracturing and Gravel Packing Operations”, the proppant bulk density was measured using a proppant density meter.

[0043] The bulk density test results of the four proppants are shown in Table 2. As can be seen from Table 2, the density of the modified proppants is lower than that of the core aggregate.

[0044] Table 2 Proppant density test results

[0045] Test Example 4: Magnetic Response Distance Test Reference "Ma Yuben, Luo Mingliang, Si Xiaodong, Zhan Yongping, Lei Ming, Zhang Mian. Preparation and properties of magnetic proppants for crack monitoring [J]. Applied Chemical Industry, 2020, 49(S02):1-6", slowly move the magnetic proppant sample close to the electromagnet, and record the distance at which it responds magnetically, which is the magnetic response distance.

[0046] Table 3 shows the magnetic response distance test results for the four proppants. As can be seen from Table 3, the proppants in Examples 1 and 2 exhibited magnetic responses, as did the proppants in Comparative Example 1, which added nano-Fe₃O₄ particles. However, the unmodified quartz sand in Comparative Example 2 lacked magnetic properties and, therefore, had no fracture monitoring capability.

[0047] Table 3 Magnetic response distance test results

[0048] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A multifunctional self-suspending proppant, characterized in that: include: core aggregate; A magnetic suspension resin composite coated on the surface of the core aggregate; and / or, A magnetic suspension resin composite that fills the pores of the core aggregate; The magnetic suspension resin composite comprises a thermosetting resin and Fe3O4@PAM composite particles.

2. The multifunctional self-suspending proppant according to claim 1, characterized in that: The core aggregate includes at least one of porous ceramsite, quartz sand, solid waste particles, and rock debris particles.

3. The multifunctional self-suspending proppant according to claim 1, characterized in that: The thermosetting resin includes at least one of phenolic resin, epoxy resin, and polyurethane resin.

4. The multifunctional self-suspending proppant according to any one of claims 1 to 3, characterized in that: Fe3O4@PAM composite particles are microspheres with nano-Fe3O4 particles as the core and PAM as the shell, which are prepared by inverse emulsion polymerization.

5. A method for preparing the multifunctional self-suspending proppant according to any one of claims 1 to 4, characterized in that: The steps include: S1 core aggregate is washed; S2 thermosetting resin and Fe3O4@PAM composite particles are ball-milled to obtain magnetic suspension resin slurry; The S3 core aggregate is vacuum degassed, and then magnetic suspension resin slurry is added and impregnated to obtain the filling aggregate; S4 solidifies and disperses the filling aggregate to obtain a multifunctional self-suspending proppant.

6. The method for preparing a multifunctional self-suspending proppant according to claim 5, characterized in that: In S2, Ball milling: Use ethanol as the dispersion medium, the amount of ethanol added is 1 to 3 times that of the magnetic suspension resin slurry, the ball milling time is 4 to 6 hours, and the ball milling speed is 100 to 300 r / min; The mass ratio of thermosetting resin to Fe3O4@PAM composite particles is 1:0.1~0.

5.

7. The method for preparing a multifunctional self-suspending proppant according to claim 5, characterized in that: In S3, Vacuum degassing: degas at -0.08~-0.1MPa for 0.5~1.5h; The mass ratio of core aggregate to magnetic suspension resin slurry is 1:0.01~0.1; Soaking: Stir at 400-800 r / min for 1-4 hours.

8. The method for preparing a multifunctional self-suspending proppant according to claim 5, characterized in that: In S4, Curing: Heat to 110-140℃ and add curing agent. The amount of curing agent added is 10-15wt% of the mass of thermosetting resin. After solidification, the temperature is naturally lowered to 70-90°C, and calcium stearate is added for dispersion. The amount of calcium stearate added accounts for 0.1-1wt% of the proppant mass. After dispersion, the multifunctional self-suspending proppant is obtained by stirring, cooling and screening.

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