A fiber-based temporary plugging agent for water-based fracturing and preparation method thereof

Abstract

The invention discloses a fiber-based temporary plugging agent for water-based fracturing and a preparation method thereof, which belong to the technical field of fiber-based temporary plugging agents. The invention carries out graft polymerization reaction between hydrophilic cellulose and hydrophobic p-divinylbenzene. The hydrophilic cellulose is flexible and can be inserted into different cracks and plugging materials through high flexibility. The p-divinylbenzene in the hydrophobic segment can form a polymer with a benzene ring structure as the main chain, has certain rigidity, can form good mechanical support in cracks of different sizes, can form rapid plugging of the cracks, and improve the plugging performance.

Description

Technical Field

[0001] The invention belongs to the technical field of fiber-based temporary plugging agents, and specifically refers to a fiber-based temporary plugging agent for water-based fracturing and a preparation method thereof. Background Art

[0002] Fracturing technology injects high-pressure fracturing fluid into the wellbore to press the formation rock open to form cracks. These cracks serve as high-permeability channels for the flow of oil and gas, connecting the reservoir to the wellbore, greatly improving the recovery efficiency of the reservoir. The typical fracturing process includes the following steps: First, injecting fracturing fluid: The fracturing fluid is composed of water, proppant (such as ceramsite or quartz sand) and chemical additives, and can enter the formation under high pressure; Second, crack formation and expansion: The high pressure of the fracturing fluid causes the reservoir rock to break and form cracks. After the proppant enters the crack, it prevents the crack from closing and maintains the high permeability of the crack; Third, crack optimization and pressure control: In order to avoid excessive concentration of fracturing fluid and proppant in specific fracture areas and form a complex fracture network structure, it is necessary to achieve uniform distribution of cracks through pressure and fluid regulation. Fiber-based temporary plugging agent is a special functional material widely used in oil and gas extraction, especially in fracturing and production increase technology. It forms a temporary plugging layer in the formation cracks through the physical and chemical properties of the fiber itself, optimizes the fracturing effect and improves the efficiency of oil and gas extraction. In oil and gas well fracturing and production enhancement technology, fracturing fluid carrying proppants (such as quartz sand or expanded clay) is injected into formation cracks to form high permeability channels. In order to improve the efficiency of fracturing operations and the uniformity of fracture distribution, temporary plugging agents are used to temporarily plug certain fractures or pores, playing the following roles: ① Control fracture expansion: prevent fracturing fluid from being overly concentrated in large fractures, and guide fracturing fluid to expand to areas that are not fully cracked; ② Optimize pressure distribution: temporary plugging agents form plugging points in the formation, increase local pressure, and promote the generation of fractures in other reservoir units; ③ Enhance recovery: in secondary fracturing or repeated fracturing, temporary plugging agents help to redistribute pressure and increase the utilization of production layers; Temporary plugging agents mainly include granular, fibrous and colloidal forms. Traditional temporary plugging agents have the following problems: Granular temporary plugging agents: easy to deposit at the entrance of fractures, difficult to penetrate deep into fractures, lack flexibility, and cannot adapt to complex fracture shapes; Colloidal temporary plugging agents: strong adhesion, but easy to fail or dissolve under high temperature and high pressure, high preparation cost, and environmental pollution risks; Traditional fibrous temporary plugging agents are mostly based on oil-based or non-environmentally friendly materials, and have poor compatibility with water-based fracturing fluids. A single fiber form may result in insufficient plugging effect or insufficient strength. Summary of the invention

[0003] In view of the above situation, in order to overcome the defects of the prior art, the present invention provides a fiber-based temporary plugging agent for water-based fracturing and a preparation method thereof. The present invention carries out a graft polymerization reaction between hydrophilic cellulose and hydrophobic p-divinylbenzene. The hydrophilic cellulose is flexible and can be interspersed in different cracks and plugging materials through high flexibility. The p-divinylbenzene in the hydrophobic segment can form a polymer with a benzene ring structure as the main chain, has a certain rigidity, can form good mechanical support in cracks of different sizes, can form rapid plugging of cracks, and improve plugging performance.

[0004] In order to achieve the above object, the technical solution adopted by the present invention is as follows: The present invention proposes a method for preparing a fiber-based temporary plugging agent for water-based fracturing, which specifically comprises the following steps:

[0005] S1. Dissolve cellulose in DMSO, add 2,2-bis(bromomethyl)-1,3-propanediol and mix well, then slowly add sodium hydride, stir at 50-80 rpm for 15-25 min, raise the temperature to 150-170°C, introduce argon, reflux for 20-28 h, add deionized water to quench the reaction, add ethyl acetate and saturated sodium chloride solution for extraction, collect the organic phase, dry it with anhydrous sodium sulfate, purify and concentrate it to obtain modified cellulose;

[0006] Preferably, in step S1, the mass concentration of cellulose in DMSO is 10-20 mg / mL;

[0007] Preferably, in step S1, the mass ratio between the cellulose and 2,2-bis(bromomethyl)-1,3-propanediol is 4-5:1;

[0008] Preferably, in step S1, the mass ratio of cellulose to sodium hydride is 2-3:1;

[0009] S2, dissolving the modified cellulose and p-toluenesulfonyl chloride prepared in step S1 in dichloromethane, mixing evenly, adding pyridine solution dropwise, stirring at 150-180 rpm for 30-50 min, raising the reaction temperature to 40-50° C., stirring and reacting for 10-14 h under argon atmosphere, adding 1 M hydrochloric acid solution to quench the reaction, adding ethyl acetate and saturated sodium chloride solution to extract, collecting the organic phase, drying with anhydrous magnesium sulfate, purifying and concentrating to obtain activated modified cellulose;

[0010] Preferably, in step S2, the mass concentration of the modified cellulose in dichloromethane is 0.02-0.04 g / mL;

[0011] Preferably, in step S2, the mass ratio between the modified cellulose and p-toluenesulfonyl chloride is 0.4-0.5:1;

[0012] Preferably, in step S2, the pyridine solution is a solution of pyridine dissolved in dichloromethane, wherein the mass fraction of pyridine is 0.1-0.15 g / mL, and the added volume of the pyridine solution is 20%-25% of the volume of dichloromethane;

[0013] S3, dissolving the activated modified cellulose prepared in step S2 in DMSO, adding 1,4-dibromo-2,5-divinylbenzene, mixing evenly, adding sodium hydride, reacting at a speed of 100-120 rpm for 10-20 min, raising the temperature to 150-160° C., introducing argon gas, reflux reacting for 28-36 h, adding deionized water to quench the reaction, adding ethyl acetate and a saturated sodium chloride solution to extract, collecting the organic phase, drying with anhydrous sodium sulfate, purifying and concentrating to obtain the grafted modified cellulose;

[0014] Preferably, in step S3, the mass concentration of the activated modified cellulose in DMSO is 10-20 mg / mL;

[0015] Preferably, in step S3, the mass ratio between the activated modified cellulose and 1,4-dibromo-2,5-divinylbenzene is 1.5-2.5:1;

[0016] Preferably, in step S3, the mass ratio of the activated modified cellulose to sodium hydride is 0.5-0.8:1;

[0017] S4, placing the grafted modified cellulose prepared in step S3 in toluene, introducing nitrogen, adding azobisisobutyronitrile (AIBN), raising the reaction temperature to 65-75°C, stirring the reaction at a speed of 150-180 rpm, reacting for 6-10 hours, cooling, extracting with ethyl acetate and saturated sodium chloride aqueous solution, adding deionized water for washing, collecting the organic phase, adding anhydrous magnesium sulfate to dry the organic phase, concentrating and purifying, and obtaining a fiber precursor;

[0018] Preferably, in step S4, the mass concentration of the grafted modified cellulose in toluene is 0.05-0.06 g / mL;

[0019] Preferably, in step S4, the added mass of AIBN is 1%-2% of the mass of the grafted modified cellulose;

[0020] S5, placing the fiber precursor prepared in step S4 in a mixed solution of DMF / DCM, stirring at a speed of 180-220 rpm for 20-30 min, and then electrospinning through a stainless steel needle, setting the injection speed to 1-1.2 mL / h, setting the electrospinning voltage to 10-12 kV, setting the distance between the stainless steel needle and the collector to 10-15 cm, setting the electrospinning temperature to 38-40 ° C, collecting the fibers and drying them, and obtaining a fiber-based temporary plugging agent;

[0021] Preferably, in step S5, the mass concentration of the fiber precursor in the DMF / DCM mixed solution is 0.1-0.15 g / mL;

[0022] Preferably, in step S5, the volume ratio between DMF and DCM in the DMF / DCM mixed solution is 1-3:7-9.

[0023] The present invention also provides a fiber-based temporary plugging agent for water-based fracturing prepared according to the above preparation method.

[0024] The beneficial effects achieved by the present invention are as follows:

[0025] The invention provides a fiber-based temporary plugging agent for water-based fracturing and a preparation method thereof. The invention carries out graft polymerization reaction on hydrophilic cellulose and hydrophobic p-divinylbenzene. The hydrophilic cellulose is flexible and can be inserted into different cracks and plugging materials through high flexibility. The p-divinylbenzene in the hydrophobic segment can form a polymer with a benzene ring structure as the main chain, has certain rigidity, can form good mechanical support in cracks of different sizes, can form rapid plugging of cracks, and improves plugging performance. The invention forms a cellulose polymer with a neopentyl glycol structure as the center by reacting bromine of 2,2-bis(bromomethyl)-1,3-propanediol with hydroxyl groups on cellulose. After being activated with p-toluenesulfonyl chloride, the hydroxyl groups on the neopentyl glycol structure are activated. -The bromine on dibromo-2,5-divinylbenzene undergoes a substitution reaction, and the divinylbenzene structure is grafted onto cellulose. Through the polymerization reaction of divinylbenzene, a rigid polymer segment is formed. The temporary plugging agent prepared by the present invention has a flexible cellulose polymer block and a rigid polydivinylbenzene block in its structure. Fibers are formed by electrospinning technology, and after being cut into suitable lengths, a fiber-based temporary plugging agent is obtained. In the fiber temporary plugging agent, cellulose is used as a hydrophilic soft segment fiber, and a polymer fiber with a benzene ring as the main chain is a hydrophobic hard segment fiber. In the process of following the fracturing fluid to be transported to the crack, the hydrophobic hard segment polymer can improve the supporting performance of the fiber-based temporary plugging agent and withstand the high pressure in the crack. At the same time, the soft fiber block can improve the affinity between the crack walls, reduce the leakage of the crack, and improve the plugging performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is an infrared spectrum image of the fiber precursor prepared in Example 1 of the present invention;

[0027] Figure 2 This is a SEM image of the fiber-based temporary plugging agent prepared in Example 1 of the present invention;

[0028] Figure 3 The graph is a result of the adsorption performance of the fiber-based temporary plugging agent prepared in Examples 1-3 of the present invention and Comparative Examples 1-2 on bentonite;

[0029] Figure 4 This is a graph showing the filtration loss reduction performance of the fiber-based temporary plugging agent prepared in the present invention.

[0030] The accompanying drawings are used to provide further understanding of the present invention and constitute a part of the specification. They are used to explain the present invention together with the embodiments of the present invention and do not constitute a limitation of the present invention. DETAILED DESCRIPTION

[0031] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments; based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0032] Unless otherwise defined, all professional and scientific terms used herein have the same meanings as those familiar to those skilled in the art. In addition, any methods and materials similar or equivalent to those described herein may be applied to the present invention. The preferred implementation methods and materials described herein are for demonstration purposes only and are not intended to limit the content of this application.

[0033] The experimental methods in the following examples are conventional methods unless otherwise specified; the experimental materials and test strains used in the following examples are purchased from commercial channels unless otherwise specified.

[0034] The materials used in the present invention are as follows:

[0035] The cellulose used is cellulose powder (α-Cellulose, CasNo: 9004-34-6), the brand is McLean, and the product number is C804602.

[0036] Example 1

[0037] This embodiment provides a method for preparing a fiber-based temporary plugging agent for water-based fracturing, which specifically includes the following steps:

[0038] S1. Accurately weigh 5 g of cellulose and dissolve it in 250 mL of DMSO solvent. Stir until the cellulose is completely dissolved. Add 1 g of 2,2-bis(bromomethyl)-1,3-propanediol and mix well. Slowly add 2 g of sodium hydride to the reaction system and stir at 80 rpm. After reacting for 15 min, introduce flowing argon gas and raise the temperature to 150°C. Under the protection of argon atmosphere, reflux reaction is carried out for 20 h. After the reaction is completed, cool the reaction to room temperature, add deionized water to quench the reaction, remove excess sodium hydride, add ethyl acetate and saturated sodium chloride solution to extract, wash with deionized water, collect the organic phase, add anhydrous sodium sulfate to dry the organic phase, concentrate the organic phase by rotary evaporation, and purify to obtain modified cellulose.

[0039] S2. Accurately weigh 2.4 g of the modified cellulose prepared in step S1 and add it to 120 mL of dichloromethane. After mixing evenly, add 6 g of p-toluenesulfonyl chloride, prepare a 0.1 g / mL pyridine / dichloromethane solution, take 30 mL and add it to the reaction system. After stirring at 180 rpm for 30 min, raise the reaction temperature to 50° C., continue stirring for 12 h under an argon atmosphere, add 1 M hydrochloric acid solution to quench the reaction, add ethyl acetate and saturated sodium chloride solution to perform extraction reaction, collect the organic phase, add anhydrous sodium sulfate to the organic phase for drying, concentrate the organic phase by rotary evaporation, and purify it to obtain activated modified cellulose;

[0040] S3, accurately weighing 2 g of the activated modified cellulose prepared in step S2 and dissolving it in 100 mL of DMSO, adding 0.8 g of 1,4-dibromo-2,5-divinylbenzene to mix, stirring and mixing at a speed of 100 rpm, slowly adding 4 g of sodium hydride, stirring and reacting for 20 min, introducing flowing argon gas, raising the temperature to 150° C., and performing reflux reaction for 36 h, cooling the reaction to room temperature, adding deionized water to quench the reaction, adding ethyl acetate and saturated sodium chloride solution to extract, collecting the organic phase, drying the organic phase with anhydrous sodium sulfate, concentrating the organic phase by rotary evaporation, and purifying to obtain grafted modified cellulose;

[0041] S4. Accurately weigh 1 g of the grafted modified cellulose prepared in step S3 and place it in 20 mL of anhydrous toluene. After flowing nitrogen, add 20 mg of AIBN under a nitrogen atmosphere. After the reaction system is mixed evenly, raise the temperature to 70° C. and stir the reaction at a speed of 150 rpm. After reacting for 8 hours, after the reaction system is cooled to room temperature, add ethyl acetate and a saturated sodium chloride aqueous solution for extraction, add deionized water for washing, collect the organic phase, add anhydrous magnesium sulfate to dry the organic phase, use a rotary evaporator to perform rotary evaporation concentration, and obtain a fiber precursor after purification;

[0042] The fiber precursor prepared in Example 1 was analyzed using a Nicolet is10 Fourier transform infrared spectrometer and tested using a potassium bromide tablet method with a scanning beam range of 4000-500 cm -1 ; Figure 1 This is the infrared spectrum image of the fiber precursor prepared in Example 1. As shown in the figure, due to the large number of hydroxyl groups on cellulose, the stretching vibration peak of CH on the benzene ring is not obvious, but at 750-710cm -1 The bending vibration peak of CH on the benzene ring appeared at 1600-1450cm -1 The appearance of the characteristic absorption peak of the benzene ring indicates that the fiber precursor of the present invention is successfully synthesized.

[0043] S5. Accurately weigh 1 g of the fiber precursor prepared in step S4 and place it in a flask. Add 10 mL of DMF and DCM in a volume ratio of 1:9 into the flask. Stir at 180 rpm for 30 min, dissolve the fiber precursor in the DMF / DCM mixed solution, install a 21G stainless steel needle on a syringe pump, adjust the distance between the receiving device and the needle to 10 cm, set the electrospinning voltage to 10 kV, and set the electrospinning temperature to 40 ° C. After the electrospinning is completed, collect the fibers and dry them to obtain a fiber-based temporary plugging agent.

[0044] The fiber-based temporary plugging agent prepared in Example 1 was dispersed in deionized water at 5 wt %, and after freeze-drying, the microstructure was observed at room temperature (25° C.) using a Quanta 450 scanning electron microscope; Figure 2 This is a SEM image of the fiber-based temporary plugging agent prepared in Example 1 of the present invention.

[0045] This embodiment provides a fiber-based temporary plugging agent for water-based fracturing prepared according to the above method.

[0046] Example 2

[0047] This embodiment provides a method for preparing a fiber-based temporary plugging agent for water-based fracturing, which specifically includes the following steps:

[0048] S1. Accurately weigh 5 g of cellulose and dissolve it in 500 mL of DMSO solvent. Stir until the cellulose is completely dissolved. Add 1.25 g of 2,2-bis(bromomethyl)-1,3-propanediol and mix well. Slowly add 2.5 g of sodium hydride to the reaction system and stir at 50 rpm. After reacting for 25 min, introduce flowing argon gas and raise the temperature to 170°C. Under the protection of argon atmosphere, reflux reaction is carried out for 24 h. After the reaction is completed, cool the reaction to room temperature, add deionized water to quench the reaction, remove excess sodium hydride, add ethyl acetate and saturated sodium chloride solution to extract, wash with deionized water, collect the organic phase, add anhydrous sodium sulfate to dry the organic phase, concentrate the organic phase by rotary evaporation, and purify to obtain modified cellulose.

[0049] S2. Accurately weigh 3 g of the modified cellulose prepared in step S1 and add it to 100 mL of dichloromethane. After mixing evenly, add 6 g of p-toluenesulfonyl chloride, prepare a 0.15 g / mL pyridine / dichloromethane solution, take 20 mL and add it to the reaction system. After stirring at 170 rpm for 50 min, increase the reaction temperature to 40°C, continue stirring for 10 h under an argon atmosphere, add 1 M hydrochloric acid solution to quench the reaction, add ethyl acetate and saturated sodium chloride solution to perform extraction reaction, collect the organic phase, add anhydrous sodium sulfate to the organic phase for drying, concentrate the organic phase by rotary evaporation, and purify it to obtain activated modified cellulose;

[0050] S3, accurately weighing 3 g of the activated modified cellulose prepared in step S2 and dissolving it in 100 mL of DMSO, adding 2 g of 1,4-dibromo-2,5-divinylbenzene to mix, stirring and mixing at a speed of 120 rpm, slowly adding 5 g of sodium hydride, stirring and reacting for 15 min, introducing flowing argon gas, raising the temperature to 160° C., and performing reflux reaction for 28 h, cooling the reaction to room temperature, adding deionized water to quench the reaction, adding ethyl acetate and saturated sodium chloride solution to extract, collecting the organic phase, drying the organic phase with anhydrous sodium sulfate, concentrating the organic phase by rotary evaporation, and purifying to obtain grafted modified cellulose;

[0051] S4. Accurately weigh 1.2 g of the grafted modified cellulose prepared in step S3 and place it in 20 mL of anhydrous toluene. After flowing nitrogen, add 18 mg of AIBN under a nitrogen atmosphere. After the reaction system is mixed evenly, raise the temperature to 65° C. and stir the reaction at a speed of 160 rpm. After reacting for 6 hours, after the reaction system is cooled to room temperature, add ethyl acetate and a saturated sodium chloride aqueous solution for extraction, add deionized water for washing, collect the organic phase, add anhydrous magnesium sulfate to dry the organic phase, use a rotary evaporator to perform rotary evaporation concentration, and obtain a fiber precursor after purification;

[0052] S5. Accurately weigh 1.5 g of the fiber precursor prepared in step S4 and place it in a flask. Add 10 mL of DMF and DCM in a volume ratio of 2:8 into the flask. Stir at 150 rpm for 20 min, dissolve the fiber precursor in the DMF / DCM mixed solution, use a 21G stainless steel needle, install it on the injection pump, adjust the distance between the receiving device and the needle to 15 cm, set the electrospinning voltage to 12 kV, set the electrospinning temperature to 38 ° C. After the electrospinning is completed, collect the fibers and dry them to obtain a fiber-based temporary plugging agent.

[0053] This embodiment provides a fiber-based temporary plugging agent for water-based fracturing prepared according to the above method.

[0054] Example 3

[0055] This embodiment provides a method for preparing a fiber-based temporary plugging agent for water-based fracturing, which specifically includes the following steps:

[0056] S1. Accurately weigh 6 g of cellulose and dissolve it in 400 mL of DMSO solvent. Stir until the cellulose is completely dissolved. Add 1.25 g of 2,2-bis(bromomethyl)-1,3-propanediol and mix well. Slowly add 2 g of sodium hydride to the reaction system and stir at 60 rpm. After reacting for 20 min, introduce flowing argon gas and raise the temperature to 160° C. Under the protection of argon atmosphere, reflux reaction is carried out for 28 h. After the reaction is completed, cool the reaction to room temperature, add deionized water to quench the reaction, remove excess sodium hydride, add ethyl acetate and saturated sodium chloride solution to extract, wash with deionized water, collect the organic phase, add anhydrous sodium sulfate to dry the organic phase, concentrate the organic phase by rotary evaporation, and purify to obtain modified cellulose.

[0057] S2. Accurately weigh 4 g of the modified cellulose prepared in step S1 and add it to 100 mL of dichloromethane. After mixing evenly, add 10 g of p-toluenesulfonyl chloride, prepare a 0.12 g / mL pyridine / dichloromethane solution, take 25 mL and add it to the reaction system. After stirring at 180 rpm for 40 min, raise the reaction temperature to 45° C., continue stirring for 14 h under an argon atmosphere, add 1 M hydrochloric acid solution to quench the reaction, add ethyl acetate and saturated sodium chloride solution to perform extraction reaction, collect the organic phase, add anhydrous sodium sulfate to the organic phase for drying, concentrate the organic phase by rotary evaporation, and purify it to obtain activated modified cellulose;

[0058] S3, accurately weighing 2 g of the activated modified cellulose prepared in step S2 and dissolving it in 100 mL of DMSO, adding 1 g of 1,4-dibromo-2,5-divinylbenzene to mix, stirring and mixing at a speed of 100 rpm, slowly adding 2.5 g of sodium hydride, stirring and reacting for 10 min, introducing flowing argon gas, raising the temperature to 155° C., and reflux reacting for 30 h, cooling the reaction to room temperature, adding deionized water to quench the reaction, adding ethyl acetate and saturated sodium chloride solution to extract, collecting the organic phase, drying the organic phase with anhydrous sodium sulfate, concentrating the organic phase by rotary evaporation, and purifying to obtain grafted modified cellulose;

[0059] S4. Accurately weigh 1 g of the grafted modified cellulose prepared in step S3 and place it in 20 mL of anhydrous toluene. After flowing nitrogen, add 10 mg of AIBN under a nitrogen atmosphere. After the reaction system is mixed evenly, raise the temperature to 75° C. and stir the reaction at a speed of 180 rpm. After reacting for 10 hours, after the reaction system is cooled to room temperature, add ethyl acetate and a saturated sodium chloride aqueous solution for extraction, add deionized water for washing, collect the organic phase, add anhydrous magnesium sulfate to dry the organic phase, use a rotary evaporator to perform rotary evaporation concentration, and obtain a fiber precursor after purification;

[0060] S5. Accurately weigh 1.2 g of the fiber precursor prepared in step S4 and place it in a flask. Add 10 mL of DMF and DCM in a volume ratio of 3:7 into the flask. Stir at 160 rpm for 30 min, dissolve the fiber precursor in the DMF / DCM mixed solution, use a 21G stainless steel needle, install it on the injection pump, adjust the distance between the receiving device and the needle to 12 cm, set the electrospinning voltage to 10 kV, set the electrospinning temperature to 40 ° C. After the electrospinning is completed, collect the fibers and dry them to obtain a fiber-based temporary plugging agent.

[0061] This embodiment provides a fiber-based temporary plugging agent for water-based fracturing prepared according to the above method.

[0062] Comparative Example 1

[0063] This comparative example provides a fiber-based temporary plugging agent and a preparation method thereof, which is different from Example 1 only in that the fiber-based temporary plugging agent is obtained by mixing cellulose and poly(p-divinylbenzene) and then subjecting the mixture to electrostatic spinning.

[0064] Comparative Example 2

[0065] This comparative example provides a fiber-based temporary plugging agent and a preparation method thereof, which is different from Example 1 only in that the fiber-based temporary plugging agent is prepared from cellulose and polypropylene fibers in a mass ratio of 2:1, and the length of the polypropylene fibers is 12 mm.

[0066] Experimental Example 1

[0067] In this experimental example, the adsorption characteristics of the fiber-based temporary plugging agent prepared in Examples 1-3 and Comparative Examples 1-2 were measured. Bentonite was used as the test soil. The bentonite was treated with hydrogen peroxide to remove organic matter in the bentonite. 1 g of the bentonite after removing organic matter was placed in 100 mL of distilled water. After mixing, 0.3 g of the fiber-based temporary plugging agent prepared in Examples 1-3 and Comparative Examples 1-2 was added. After mixing, a suspension was formed. The suspension was placed in an oscillator and oscillated at 25° C. and 200 rpm. The suspension was centrifuged at 12000 rpm for 30 min using a high-speed centrifuge. The supernatant was taken and the transmittance of the supernatant was measured to evaluate the adsorption performance of the fiber-based temporary plugging agent prepared in the Examples and Comparative Examples on bentonite.

[0068] Figure 3 The adsorption performance result diagram of the fiber-based temporary plugging agent prepared in Examples 1-3 of the present invention and Comparative Examples 1-2 on bentonite is shown in the figure. As shown in the figure, the fiber-based temporary plugging agent prepared in Examples 1-3 can reach adsorption equilibrium within 8-12 hours, and the maximum adsorption amount reaches 68.5-71.7 mg / g. The maximum adsorption amount of the cellulose temporary plugging agent in Comparative Example 1 on bentonite reaches 52.9 mg / g, and the maximum adsorption amount of the cellulose temporary plugging agent in Comparative Example 2 on bentonite reaches 38.3 mg / g. According to the data, in the fiber-based temporary plugging agent prepared in Comparative Example 1, cellulose and poly(p-divinylbenzene) are combined by electrospinning technology, which is essentially a physical mixture. The binding performance between cellulose and poly(p-divinylbenzene) is poor, resulting in poor stability of cellulose. In Comparative Example 2, polypropylene fiber is used to mix cellulose, and the lack of electrospinning treatment has worse stability, resulting in simultaneous adsorption and desorption of cellulose on bentonite, and poor fixation on bentonite. During the mixing process of the fiber temporary plugging agent prepared in the embodiment of the present invention with the bentonite-based slurry, the various active groups on the cellulose of the hydrophilic soft segment form an adsorption effect with the bentonite particles. At the same time, the hydrophobic hard segment provides a higher support formation, so that the structure of the fiber-based temporary plugging agent is stable, thereby providing the ability to adsorb bentonite particles and seal cracks.

[0069] Experimental Example 2

[0070] In this experimental example, the filtration loss reduction performance of the fiber-based temporary plugging agent prepared in Examples 1-3 and Comparative Examples 1-2 was measured. The fiber-based temporary plugging agent prepared in Examples 1-3 and Comparative Examples 1-2 was added to a water-based drilling fluid at a water content of 2% by mass, and the APL filtration loss was measured under hot rolling conditions of 120°C / 16h. The drilling fluid formula is as follows:

[0071] Freshwater drilling fluid was prepared according to the following weight percentages: 1% bentonite, 0.1% NaOH, 4% NaCl;

[0072] The brine-type drilling fluid was prepared according to the following weight percentages: 1% bentonite, 0.1% NaOH, and 25% NaCl;

[0073] Figure 4 The figure is a result diagram of the filtration loss reduction performance of the fiber-based temporary plugging agent prepared by the present invention; as shown in the figure, the fiber-based temporary plugging agent prepared by Examples 1-3 of the present invention has a low filtration loss in the freshwater drilling fluid system and the salt water drilling fluid system, and can still maintain good filtration loss performance after hot rolling at 120°C / 16h.

[0074] While the embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that many changes, modifications, substitutions and variations can be made to the embodiments without departing from the principles and spirit of the invention.

[0075] The present invention and its implementation methods are described above, which is not restrictive. The drawings are only one of the implementation methods of the present invention, and the actual application is not limited thereto. In short, if ordinary technicians in the field are inspired by it and design methods and embodiments similar to the technical solution without creativity without departing from the purpose of the invention, they should all fall within the protection scope of the present invention.

Claims

1. A method for preparing a fiber-based temporary plugging agent for water-based fracturing, characterized in that: The specific steps include: S1. Dissolve cellulose in DMSO, add 2,2-bis(bromomethyl)-1,3-propanediol and mix well, then slowly add sodium hydride, stir at 50-80 rpm for 15-25 min, raise the temperature to 150-170°C, introduce argon, reflux for 20-28 h, add deionized water to quench the reaction, add ethyl acetate and saturated sodium chloride solution for extraction, collect the organic phase, dry it with anhydrous sodium sulfate, purify and concentrate it to obtain modified cellulose; The mass ratio of the cellulose to 2,2-bis(bromomethyl)-1,3-propanediol is 4-5:1; the mass ratio of the cellulose to sodium hydride is 2-3:1; the mass concentration of the cellulose in DMSO is 10-20 mg / mL; S2, dissolving the modified cellulose and p-toluenesulfonyl chloride prepared in step S1 in dichloromethane, mixing evenly, adding pyridine solution dropwise, stirring at 150-180 rpm for 30-50 min, raising the reaction temperature to 40-50° C., stirring and reacting for 10-14 h under argon atmosphere, adding 1 M hydrochloric acid solution to quench the reaction, adding ethyl acetate and saturated sodium chloride solution to extract, collecting the organic phase, drying with anhydrous magnesium sulfate, purifying and concentrating to obtain activated modified cellulose; The mass concentration of the modified cellulose in dichloromethane is 0.02-0.04 g / mL; the mass ratio of the modified cellulose to p-toluenesulfonyl chloride is 0.4-0.5:1; S3, dissolving the activated modified cellulose prepared in step S2 in DMSO, adding 1,4-dibromo-2,5-divinylbenzene, mixing evenly, adding sodium hydride, reacting at a speed of 100-120 rpm for 10-20 min, raising the temperature to 150-160° C., introducing argon gas, reflux reacting for 28-36 h, adding deionized water to quench the reaction, adding ethyl acetate and a saturated sodium chloride solution to extract, collecting the organic phase, drying with anhydrous sodium sulfate, purifying and concentrating to obtain the grafted modified cellulose; The mass ratio of the activated modified cellulose to 1,4-dibromo-2,5-divinylbenzene is 1.5-2.5:1; the mass ratio of the activated modified cellulose to sodium hydride is 0.5-0.8:1; S4, placing the grafted modified cellulose prepared in step S3 in toluene, introducing nitrogen, adding AIBN, raising the reaction temperature to 65-75°C, stirring the reaction at a speed of 150-180 rpm, reacting for 6-10 hours, cooling, extracting with ethyl acetate and saturated sodium chloride aqueous solution, adding deionized water for washing, collecting the organic phase, adding anhydrous magnesium sulfate to dry the organic phase, concentrating and purifying, and obtaining a fiber precursor; The added mass of AIBN is 1%-2% of the mass of the grafted modified cellulose; S5, placing the fiber precursor prepared in step S4 in a mixed solution of DMF / DCM, stirring at a speed of 180-220 rpm for 20-30 min, and then electrospinning through a stainless steel needle, setting the injection speed to 1-1.2 mL / h, setting the electrospinning voltage to 10-12 kV, setting the distance between the stainless steel needle and the collector to 10-15 cm, setting the electrospinning temperature to 38-40 ° C, collecting the fibers and drying them, and obtaining a fiber-based temporary plugging agent; The mass concentration of the fiber precursor in the DMF / DCM mixed solution is 0.1-0.15 g / mL.

2. The method for preparing a fiber-based temporary plugging agent for water-based fracturing according to claim 1, characterized in that: In step S2, the pyridine solution is a solution of pyridine dissolved in dichloromethane, wherein the mass fraction of pyridine is 0.1-0.15 g / mL, and the added volume of the pyridine solution is 20%-25% of the volume of dichloromethane.

3. The method for preparing a fiber-based temporary plugging agent for water-based fracturing according to claim 2, characterized in that: In step S3, the mass concentration of the activated modified cellulose in DMSO is 10-20 mg / mL.

4. The method for preparing a fiber-based temporary plugging agent for water-based fracturing according to claim 3, characterized in that: In step S4, the mass concentration of the grafted modified cellulose in toluene is 0.05-0.06 g / mL.

5. A fiber-based temporary plugging agent for water-based fracturing, characterized in that: Prepared according to the preparation method according to any one of claims 1 to 4.

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