Reticular polymer, preparation method thereof, oil field crack plugging material and oil field crack plugging method

Abstract

The invention relates to the field of oilfield chemistry, and discloses a network polymer and a preparation method thereof, an oilfield crack plugging material and an oilfield crack plugging method. The network polymer comprises a structural unit A and a structural unit B, and the structural unit A is at least one selected from the structural unit B. The network polymer is used as a cross-linking agent, the oil field crack plugging material containing the gel particles and the cross-linking agent is injected into the deep position of an oil field stratum crack, the salinity and the temperature of an oil field are utilized, the cross-linking agent and the gel particles react to form high-strength covalent bridging gel, and the mechanical performance and the high temperature resistance are greatly improved. The oil field crack plugging agent has good application prospects in oil field crack plugging, and has the advantages of convenient raw material synthesis, high bearing pressure, high temperature resistance and stability.

Description

Technical Field

[0001] This invention relates to the field of oilfield chemistry, specifically to a network polymer and its preparation method, an oilfield fracture sealing material, and a method for sealing oilfield fractures. Background Technology

[0002] In the field of oil and gas exploration, excessive water production and drilling fluid loss caused by fractures, cavities and void channels in the formation matrix pose a huge challenge to improving recovery rate, reducing production costs and production time. If not handled properly, it can even lead to well abandonment and major engineering accidents.

[0003] Profile control and water shut-off are common methods for enhancing oil recovery in oilfields. Fracture plugging technology, as the core technology of profile control and water shut-off, has always been a research hotspot in the field of oil and gas exploration. It plays a crucial role in preventing severe water loss and controlling water production to enhance oil recovery. Fracture plugging mainly relies on injecting plugging materials into the pores of the formation to forcefully block the pores, achieving isolation between the inside and outside of the well and thus achieving the sealing effect.

[0004] Pore ​​sealing materials are divided into two types: inorganic and organic. Inorganic plugging materials, represented by materials such as cement and calcium carbonate, have the characteristics of high sealing strength and stable performance after sealing. However, they are difficult to remove after sealing, and most have a permanent sealing effect, causing serious damage to the formation and hindering multiple oil recovery. They are mostly used for the last oil recovery cycle. Organic plugging materials commonly use hydrogels, represented by polyacrylamide systems, which have high water absorption and high strength. On the one hand, the three-dimensional network structure gives hydrogels good mechanical properties, enabling them to withstand high liquid pressure and ensuring a smooth fracturing process. On the other hand, hydrogels have a small volume before absorbing water and swelling, allowing them to easily enter the fracture and expand inside to achieve a strong sealing effect. Hydrogels used for plugging can undergo a chemical gelation reaction within the channel to form a polymer gel in situ. Alternatively, gel particles can be prepared in advance and injected into the channel, where they expand after absorbing water to further form a bulk gel. Polymer gels, due to their low initial viscosity, can be easily injected deep into formation fractures to form a gel through chemical cross-linking. However, due to the complex formation environment, their gelation time and strength are difficult to control. They are often diluted with water before gelation, resulting in reduced gel strength and poorer water-blocking effect. Particulate gels, because they polymerize on the surface, can be artificially controlled, and their stability is significantly improved compared to in-situ gels. By reducing particle size through chemical synthesis, they can also be injected deep into formation fractures. However, after absorbing water and swelling, the interparticle forces are weak, making it difficult to withstand high water pressure.

[0005] Therefore, there is an urgent need for an oilfield fracture sealing material with high strength and good high-temperature resistance. Summary of the Invention

[0006] The purpose of this invention is to overcome the problems of weak interparticle forces, low gel strength, easy secondary leakage, and poor high-temperature resistance of traditional pre-formed granular gels after water absorption and swelling. This invention provides a network polymer and its preparation method, an oilfield fracture sealing material, and a method for sealing oilfield fractures. The oilfield fracture sealing material utilizes the salinity and temperature of the oilfield itself, and the gel particles and crosslinking agent react to form a high-strength covalently bridged gel, which greatly improves mechanical properties and high-temperature resistance. At the same time, the gel can be stable and degraded at high temperatures for a period of time.

[0007] To achieve the above objectives, a first aspect of the present invention provides a network polymer, wherein the network polymer includes structural unit A and structural unit B, wherein structural unit A is... The structural unit B is selected from At least one of them.

[0008] A second aspect of the present invention provides a method for preparing a network polymer, wherein the method comprises: mixing 4-vinylbenzyltetrahydrothiophene tetrafluoroborate with a crosslinking material in the presence of a first initiator and a first solvent to carry out a polymerization reaction; wherein 4-vinylbenzyltetrahydrothiophene tetrafluoroborate is... The compound shown, wherein the crosslinking material is selected from... At least one of the compounds shown.

[0009] A third aspect of the present invention provides a network polymer prepared by the preparation method provided by the present invention.

[0010] A fourth aspect of the present invention provides an oilfield fracture sealing material, wherein the oilfield fracture sealing material comprises gel particles and a crosslinking agent; wherein the crosslinking agent is a network polymer provided by the present invention.

[0011] The fifth aspect of the present invention provides a method for sealing oilfield fractures, wherein the method includes: injecting the oilfield fracture sealing material provided by the present invention into the depth of oilfield formation fractures.

[0012] The beneficial effects of the present invention through the above technical solution include at least the following:

[0013] This invention, by preparing negatively charged particulate gels and positively charged crosslinking agents, utilizes the salinity and temperature of the oilfield itself to form a high-strength covalently bridged gel under the influence of brine and heating, resulting in significantly improved mechanical properties and high-temperature resistance. Simultaneously, the gel can remain stable at high temperatures for a period and then degrade. It shows great promise for application in oilfield fracture sealing, offering advantages such as convenient raw material synthesis, high pressure resistance, and high-temperature stability.

[0014] In a preferred embodiment of the present invention, when preparing the crosslinking agent, by selecting appropriate monomer types and weight ratios, as well as appropriate polymerization reaction conditions; when preparing gel particles, by selecting appropriate monomer types and molar ratios, as well as appropriate reaction conditions; and when preparing oilfield fracture sealing materials, by selecting appropriate weight ratios of gel particles and crosslinking agents and average particle size, the mechanical properties and high-temperature resistance of the bulk gel (covalently bridged gel) obtained by the reaction of gel particles and crosslinking agents are further improved. Attached Figure Description

[0015] Figure 1 a is a schematic diagram of the morphology of the particulate gel prepared in Example 1 of the present invention when testing mechanical integrity;

[0016] Figure 1 b is a schematic diagram of the morphology of the bulk gel obtained by reacting the particulate gel prepared in Example 1 of the present invention with the crosslinking agent during the mechanical integrity test.

[0017] Figure 2 This is a comparison diagram of the mechanical properties of the particulate gel prepared in Example 1 of the present invention and the bulk gel obtained by reacting the particulate gel prepared in Example 1 with a crosslinking agent.

[0018] Figure 3 a is a schematic diagram of the morphology of the bulk gel obtained by reacting the particulate gel prepared in Example 1 of the present invention with the crosslinking agent during the test of temperature resistance.

[0019] Figure 3 b is a schematic diagram of the morphology of the bulk gel obtained by reacting the particulate gel prepared in Example 1 of the present invention with the crosslinking agent after maintaining a high temperature of 130°C for four days when testing the temperature resistance performance.

[0020] Figure 4 This is a displacement experiment data graph of the bulk gel obtained by reacting the particulate gel prepared in Example 1 of the present invention with a crosslinking agent. Detailed Implementation

[0021] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0022] A first aspect of the present invention provides a network polymer, wherein the network polymer includes structural unit A and structural unit B, wherein structural unit A is... The structural unit B is selected from At least one of them (the structure of the structural unit B is as follows) As shown, R is selected from phenylene or -CONH-CH2-NHCO-).

[0023] According to the present invention, preferably, the structural unit B is selected from... At least one of them.

[0024] According to the present invention, preferably, the weight ratio of structural unit A to structural unit B in the network polymer is (100-1000):1, more preferably (200-500):1.

[0025] In this invention, conventional methods in the prior art can be used to test the content of each structural unit in the network polymer, such as infrared spectroscopy, nuclear magnetic resonance, and the amount of monomers fed during polymerization. Preferably, the amount of monomers fed is used to determine the content of each structural unit in the polymer. Specifically, the actual feeding ratio of each monomer participating in polymerization is determined by testing the content of unreacted monomers, thereby determining the content of each structural unit in the polymer. Furthermore, in this invention, the content of each unreacted monomer in the polymer is found to be below 0.5% by weight, indicating that almost all monomers participate in the polymerization reaction. Specifically, the content of the residual monomers is determined using liquid chromatography.

[0026] According to the present invention, preferably, the weight-average molecular weight of the network polymer is 10,000-40,000 g / mol.

[0027] A second aspect of the present invention provides a method for preparing a network polymer, wherein the method comprises: mixing 4-vinylbenzyltetrahydrothiophene tetrafluoroborate with a crosslinking material in the presence of a first initiator and a first solvent to carry out a polymerization reaction; wherein 4-vinylbenzyltetrahydrothiophene tetrafluoroborate is... The compound shown; the crosslinking material is selected from... At least one of the compounds shown, preferably selected from At least one of the compounds shown.

[0028] According to the present invention, preferably, 4-vinylbenzyltetrahydrothiophene tetrafluoroborate and crosslinking material are mixed in a weight ratio of (100-1000):1, more preferably in a weight ratio of (200-500):1.

[0029] According to the present invention, 4-vinylbenzyltetrahydrothiophene tetrafluoroborate can be prepared by existing methods, specifically as follows: 4-vinylbenzyl chloride and tetrahydrothiophene are mixed in a molar ratio of 1:(1.5-2.5) and dissolved in methanol (1-2 mL of methanol for 1 g of 4-vinylbenzyl chloride), and stirred for 3-5 days. The product is concentrated using a rotary evaporator, and the crude product is slowly added to ethyl acetate to precipitate (15-20 mL of ethyl acetate for 1 g of 4-vinylbenzyl chloride). The precipitate is filtered and washed three times with 100-300 mL of petroleum ether, and then dried under vacuum for 20-40 hours to obtain 4-vinylbenzyltetrahydrothiophene. Dissolve 4-vinylbenzyltetrahydrothiophene in deionized water (2-5 mL of deionized water for every 1 g of 4-vinylbenzyltetrahydrothiophene). Dissolve sodium tetrafluoroborate in deionized water (weight ratio of sodium tetrafluoroborate to 4-vinylbenzyltetrahydrothiophene: 1:(1-2); 1-3 mL of deionized water for every 1 g of sodium tetrafluoroborate). Stir the 4-vinylbenzyltetrahydrothiophene solution while simultaneously adding sodium tetrafluoroborate solution dropwise. After the addition is complete, stir for 0.5-3 hours. Filter and wash three times with 200-500 mL of ice-cold deionized water. Dissolve the crude product in methanol, then precipitate it in diethyl ether (1.5-3 mL of methanol and 15-30 mL of diethyl ether for every 1 g of sodium tetrafluoroborate). Filter and wash three times with 100-300 mL of diethyl ether. The solvent was removed by rotary evaporation for 2-5 hours to obtain 4-vinylbenzyltetrahydrothiophene tetrafluoroborate.

[0030] The present invention does not impose any particular limitation on the amount of the first initiator, as long as it can successfully initiate the crosslinking polymerization of 4-vinylbenzyltetrahydrothiophene tetrafluoroborate and the crosslinking material. Preferably, based on the amount of 4-vinylbenzyltetrahydrothiophene tetrafluoroborate being 1 mmol, the amount of the first initiator is 0.01-0.04 mmol.

[0031] This invention does not impose any particular limitation on the type of the first initiator, and it can be any type of free radical initiator conventionally used in the art for initiating polymerization reactions, including peroxide initiators, azo initiators, and redox initiators, etc. Peroxide initiators are further divided into organic peroxide initiators and inorganic peroxide initiators. Preferably, the first initiator is selected from azo initiators, and more preferably 2,2'-azobisisobutyronitrile.

[0032] The present invention does not impose any particular limitation on the amount of the first solvent, as long as it can fully dissolve 4-vinylbenzyltetrahydrothiophene tetrafluoroborate and the crosslinking material in the first solvent and allow the crosslinking polymerization reaction to proceed smoothly. Preferably, based on the amount of 4-vinylbenzyltetrahydrothiophene tetrafluoroborate being 1 mmol, the amount of the first solvent is 2-5 mL.

[0033] The present invention does not have any particular limitation on the type of the first solvent, as long as it can fully dissolve 4-vinylbenzyltetrahydrothiophene tetrafluoroborate and the crosslinking material in the first solvent and can carry out the crosslinking polymerization reaction smoothly. Preferably, the first solvent is selected from ethanol and / or acetonitrile, and more preferably a mixture of ethanol and acetonitrile.

[0034] Furthermore, the volume ratio of ethanol to acetonitrile in the first solvent is (3-7):1.

[0035] According to the present invention, preferably, the mixture obtained by mixing further contains an emulsifier. The present invention does not particularly limit the type of emulsifier, and it can be any type of emulsifier conventional in the art; preferably, the emulsifier is polyvinylpyrrolidone.

[0036] According to the present invention, preferably, the amount of emulsifier is 0.05-0.2g, based on 1g of 4-vinylbenzyltetrahydrothiophene tetrafluoroborate.

[0037] According to the present invention, preferably, the reaction temperature is 60-80°C and the time is 10-24h, preferably 12-24h.

[0038] According to the present invention, preferably, the reaction is carried out under anaerobic conditions. The present invention does not particularly limit the method for removing oxygen from the reaction system of 4-vinylbenzyltetrahydrothiophene tetrafluoroborate and the crosslinking material. In a specific embodiment of the present invention, oxygen in the reaction system is removed by introducing a protective gas. The protective gas is selected from nitrogen and / or an inert gas, preferably nitrogen.

[0039] A third aspect of the present invention provides a network polymer prepared by the preparation method provided by the present invention.

[0040] A fourth aspect of the present invention provides an oilfield fracture sealing material, wherein the oilfield fracture sealing material comprises gel particles and a crosslinking agent; wherein the crosslinking agent is a network polymer provided by the present invention.

[0041] According to the present invention, preferably, the gel particles contain structural unit C and structural unit D, wherein structural unit C is derived from at least one of acrylic acid, acrylate and acrylamide, preferably from acrylic acid; and structural unit D is derived from N,N'-methylenebisacrylamide.

[0042] According to the present invention, preferably, the molar ratio of structural unit C to structural unit D in the gel particles is (800-4000):1, more preferably (1000-2000):1.

[0043] In this invention, conventional methods in the prior art can be used to test the content of each structural unit in the gel particles, such as infrared spectroscopy, nuclear magnetic resonance, and the amount of monomers fed during polymerization. Preferably, the amount of monomers fed is used to determine the content of each structural unit in the polymer. Specifically, the actual feeding ratio of each monomer participating in polymerization is determined by testing the content of unreacted monomers, thereby determining the content of each structural unit in the polymer. Furthermore, in this invention, the content of each unreacted monomer in the polymer is found to be below 0.5% by weight, indicating that almost all monomers participate in the polymerization reaction. Specifically, the content of the residual monomers is determined using liquid chromatography.

[0044] This invention does not impose any particular limitation on the weight ratio of gel particles to crosslinking agent in the oilfield fracture sealing material. As long as the oilfield fracture sealing material is injected deep into the oilfield formation fractures, the gel particles and crosslinking agent can utilize the salinity and temperature of the oilfield itself to form an organic covalently crosslinked nanocomposite, thereby sealing the oilfield formation fractures. Preferably, the weight ratio of gel particles to crosslinking agent in the oilfield fracture sealing material is (5-20):1, such as 5, 7, 9, 10, 11, 13, 15, 17, 19, 20 or any value between the above values.

[0045] According to the present invention, when the network polymer provided by the present invention is used as a crosslinking agent in oilfield fracture sealing materials, the crosslinking polymerization reaction product needs to be subjected to solid-liquid separation to separate the solvent and unreacted raw materials and collect the solid product. Then, the solid product is dried and pulverized to obtain granular network polymer, which serves as the crosslinking agent in the oilfield fracture sealing material. Solid-liquid separation can be performed using a centrifuge, drying can be performed in a vacuum drying oven for 2-4 hours, and pulverization can be performed mechanically. Preferably, the pulverization conditions result in an average particle size of 50-300 nm for the obtained crosslinking agent.

[0046] According to the present invention, preferably, the method for preparing the gel particles includes: reacting a monomer and N,N'-methylenebisacrylamide in the presence of a second initiator and a second solvent; wherein the monomer is selected from at least one of acrylic acid, acrylate and acrylamide.

[0047] According to the present invention, preferably, the monomer and N,N'-methylenebisacrylamide are mixed in a molar ratio of (800-4000):1, and more preferably in a molar ratio of (1000-1800):1.

[0048] The present invention does not impose any particular limitation on the amount of the second initiator, as long as it can successfully initiate the reaction between the monomer and N,N'-methylenebisacrylamide. Preferably, based on the amount of the monomer being 1 mol, the amount of the second initiator is 0.1-0.3 mmol.

[0049] This invention does not impose any particular limitation on the type of the second initiator. It can be any type of free radical initiator conventionally used in the art for initiating polymerization reactions, including peroxide initiators, azo initiators, and redox initiators. Peroxide initiators are further divided into organic peroxide initiators and inorganic peroxide initiators. Preferably, the second initiator is selected from peroxide initiators, more preferably inorganic peroxide initiators, and even more preferably ammonium persulfate.

[0050] The present invention does not impose any particular limitation on the amount of the second solvent, as long as the monomer and N,N'-methylenebisacrylamide are fully dissolved in the second solvent and the reaction can proceed smoothly. Preferably, based on the amount of the monomer being 1 mol, the amount of the second solvent is 200-400 mL.

[0051] The present invention does not have any particular restrictions on the type of the second solvent, as long as the monomer and N,N'-methylenebisacrylamide can be fully dissolved in the second solvent and the reaction can proceed smoothly. Preferably, the second solvent is water.

[0052] According to the present invention, preferably, the reaction temperature is 50-70°C and the time is 2-6 hours.

[0053] According to the present invention, preferably, the reaction is carried out under conditions with a pH of 7-8. The pH of the reaction system can be adjusted by adding a pH adjuster to the reaction system. The pH adjuster can be various alkaline substances, preferably sodium hydroxide.

[0054] According to the present invention, preferably, the reaction is carried out under anaerobic conditions. The present invention does not particularly limit the method for removing oxygen from the reaction system of monomer and N,N'-methylenebisacrylamide; in a specific embodiment of the present invention, oxygen in the reaction system is removed by introducing a protective gas. The protective gas is selected from nitrogen and / or an inert gas, preferably nitrogen.

[0055] In preparing gel particles, the reaction product obtained from the reaction of monomer and N,N'-methylenebisacrylamide is a gel-like product. This gel-like product needs to be dried and pulverized into granules to obtain gel particles. Therefore, the preparation method of the gel particles further includes drying and pulverizing the reaction product obtained from the reaction. In a preferred embodiment of the present invention, the drying method includes first naturally drying at room temperature for 3-5 days, and then drying in an oven at 35-50°C for 1-3 days; pulverization is performed by mechanical pulverization, and the pulverization conditions result in an average particle size of 0.3-0.6 mm for the pulverized gel particles.

[0056] The fifth aspect of the present invention provides a method for sealing oilfield fractures, wherein the method includes: injecting the oilfield fracture sealing material provided by the present invention into the depth of oilfield formation fractures.

[0057] When the oilfield fracture sealing material provided by this invention is injected deep into oilfield formation fractures, the negatively charged gel particles and positively charged crosslinking agent in the material can utilize the salinity and temperature of the oilfield itself. In brine, the crosslinking agent and gel particles first form weak crosslinks through electrostatic interaction. Under heating, the electrostatic interaction transforms into covalent crosslinking, increasing the interaction force between gel particles and forming a high-strength covalently bridged gel, which seals the oilfield formation fractures. Simultaneously, the high-temperature resistance of the gel is also improved. The covalently bridged gel can remain stable at high temperatures for a period of time and then degrade. It has excellent application prospects in oilfield fracture sealing, possessing advantages such as convenient raw material synthesis, high pressure resistance, and high-temperature stability.

[0058] According to the present invention, preferably, the temperature at the depth of the oilfield formation fracture is 60-110°C. When the temperature at the depth of the oilfield formation fracture is 60-110°C, in a preferred case, after heating for 12-168 hours, the crosslinking agent and gel particles form a high-strength covalently bridged gel.

[0059] Furthermore, the temperature deep within the oilfield formation fractures is 60-90℃. When the temperature deep within the oilfield formation fractures is 60-90℃, under preferred conditions, after heating for 24-168 hours, the crosslinking agent and gel particles form a high-strength covalently bridged gel.

[0060] According to the present invention, preferably, the salt concentration of the brine deep in the oilfield formation fractures is 1-12 wt%. The salt in the brine may be calcium chloride and / or sodium chloride.

[0061] The present invention will be described in detail below through examples and comparative examples. Unless otherwise specified, the methods used in the following examples are conventional; the reagents and materials used are commercially available unless otherwise specified.

[0062] 4-Vinylbenzyltetrahydrothiophene tetrafluoroborate was prepared according to the method described in Lizhu Wang, Jingping Liu, Yifu Long (2018) Delayed gelation kinetics of hydrogel formation by ionic nano-gel cross-linkers. J Mater Sci 53:14789-14800. Specifically, 54.72 g of 4-vinylbenzyl chloride and 48 g of tetrahydrothiophene were mixed and dissolved in 60 mL of methanol, and stirred for 4 days. The product was concentrated using a rotary evaporator, and the crude product was slowly added to 1 L of ethyl acetate to precipitate. The precipitate was filtered and washed three times with 200 mL of petroleum ether, then dried under vacuum for 24 hours to obtain 4-vinylbenzyltetrahydrothiophene. 66 g of 4-vinylbenzyltetrahydrothiophene was dissolved in 250 mL of deionized water, and 60 g of sodium tetrafluoroborate was dissolved in 100 mL of deionized water. The 4-vinylbenzyltetrahydrothiophene solution was stirred while the sodium tetrafluoroborate solution was added dropwise. After the addition was complete, the mixture was stirred for 1 hour, filtered, and washed three times with 300 mL of ice-cold deionized water. The crude product was dissolved in 120 mL of methanol, then precipitated in 1.2 L of diethyl ether. The precipitate was filtered and washed three times with 200 mL of diethyl ether. The solvent was removed by rotary evaporation for 3 hours to obtain 4-vinylbenzyltetrahydrothiophene tetrafluoroborate.

[0063] The following examples illustrate the preparation methods of particulate gels and crosslinking agents.

[0064] Example 1

[0065] Preparation of particulate gel:

[0066] s1. Preparation stage: Add 200 mL of deionized water and 0.8 mol of acrylic acid monomer to a flask. While stirring, add sodium hydroxide and test the pH value of the mixture to observe whether it is neutral (if it is acidic, add sodium bicarbonate to neutralize the mixture to pH 7). After the mixture cools to room temperature, add 0.8 mmol of N,N'-methylenebisacrylamide and 0.16 mmol of ammonium persulfate, and purge with nitrogen gas for 30 minutes to remove oxygen from the system.

[0067] s2, Free radical polymerization stage: Place the flask in a magnetically stirred oil bath at a pre-set temperature of 60℃, with a rotation speed of 300r / min. After reacting for 3 hours, stop heating and allow it to cool naturally to room temperature to obtain a gel.

[0068] s3. Post-processing stage: The gel obtained in the previous stage was naturally dried indoors for three days, then placed in a 40℃ oven for 2 days, and finally crushed into granular gel by mechanical pulverization. The average particle size of the granular gel obtained by sieving through a sieve was 0.4 mm.

[0069] Preparation of crosslinking agent:

[0070] S1. Preparation stage: Add 0.5g of polyvinylpyrrolidone, 42.5mL of anhydrous ethanol and 8.5mL of acetonitrile to a flask, stir for 15 minutes, then add 5g of 4-vinylbenzyltetrahydrothiophene tetrafluoroborate, 58mg of 2,2'-azobisisobutyronitrile and 25mg of 1,2-divinylbenzene, and purge with nitrogen for 30 minutes to remove oxygen from the system.

[0071] S2, Free radical polymerization stage: Place the flask in a magnetically stirred oil bath at a pre-set temperature of 70℃, with a rotation speed of 170r / min. After reacting for 12 hours, stop heating and allow it to cool naturally to room temperature to obtain a mixture of crosslinking agent and solution.

[0072] S3. Post-processing stage: The mixture obtained in the previous step is centrifuged for 10 minutes using a centrifuge with the speed set at 6000 r / min. The lower precipitate is collected, vacuum dried for 3 hours, and mechanically pulverized to obtain particulate crosslinking agent with an average particle size of 100 nm. The weight average molecular weight of the crosslinking agent is 21352 g / mol, as determined by gel permeation chromatography (GPC).

[0073] Example 2

[0074] The particulate gel and crosslinking agent were prepared according to the method of Example 1, except that in the preparation of the crosslinking agent, "1,2-divinylbenzene 50 mg" was replaced with "1,2-divinylbenzene 25 mg" in step S1. Particulate gel and particulate crosslinking agent were obtained. The weight-average molecular weight of the crosslinking agent was 10755 g / mol.

[0075] Example 3

[0076] The particulate gel and crosslinking agent were prepared according to the method of Example 1, except that in the preparation of the crosslinking agent, "1,2-divinylbenzene 5 mg" was replaced with "1,2-divinylbenzene 25 mg" in step S1. Particulate gel and particulate crosslinking agent were obtained. The weight-average molecular weight of the crosslinking agent was 39532 g / mol.

[0077] Example 4

[0078] The particulate gel and crosslinking agent were prepared according to the method of Example 1, except that in the preparation of the particulate gel, "N,N'-methylenebisacrylamide 0.4 mmol" was used instead of "N,N'-methylenebisacrylamide 0.8 mmol" in s1. Particulate gel and particulate crosslinking agent were obtained.

[0079] Example 5

[0080] The particulate gel and crosslinking agent were prepared according to the method of Example 1, except that in the preparation of the crosslinking agent, N,N'-methylenebisacrylamide was used instead of an equal weight of 1,2-divinylbenzene in step S1. Particulate gel and particulate crosslinking agent were obtained. The weight-average molecular weight of the crosslinking agent was 14563 g / mol.

[0081] Example 6

[0082] The particulate gel and crosslinking agent were prepared according to the method of Example 1, except that in the preparation of the crosslinking agent, anhydrous ethanol was used instead of an equal volume of acetonitrile in step S1. Particulate gel and particulate crosslinking agent were obtained. The weight-average molecular weight of the crosslinking agent was 17594 g / mol.

[0083] Example 7

[0084] The particulate gel and crosslinking agent were prepared according to the method of Example 1, except that in the preparation of the crosslinking agent, "3g of polyvinylpyrrolidone" was used instead of "0.5g of polyvinylpyrrolidone" in step S1. Particulate gel and particulate crosslinking agent were obtained. The weight-average molecular weight of the crosslinking agent was 7135 g / mol.

[0085] Example 8

[0086] The particulate gel and crosslinking agent were prepared according to the method of Example 1, except that the reaction temperature for preparing the crosslinking agent was different. Specifically, in S2, a 90°C magnetically stirred oil bath was used instead of a 70°C magnetically stirred oil bath. Particulate gel and particulate crosslinking agent were obtained. The weight-average molecular weight of the crosslinking agent was 13582 g / mol.

[0087] Example 9

[0088] The particulate gel and crosslinking agent were prepared according to the method of Example 1, except that in the preparation of the particulate gel, "0.4 mol of acrylic monomer and 0.4 mol of acrylamide monomer" were used instead of "0.8 mol of acrylic monomer" in step 1. Particulate gel and particulate crosslinking agent were obtained.

[0089] Example 10

[0090] The particulate gel and crosslinking agent were prepared according to the method of Example 1, except that in the preparation of the particulate gel, "N,N'-methylenebisacrylamide 2 mmol" was used instead of "N,N'-methylenebisacrylamide 0.8 mmol" in step 3. Particulate gel and particulate crosslinking agent were obtained.

[0091] Example 11

[0092] The particulate gel and crosslinking agent were prepared according to the method of Example 1, except that in the preparation of the particulate gel, in step s3, "the average particle size of the particulate gel is 1 mm" was replaced with "the average particle size of the particulate gel is 0.4 mm". Particulate gel and particulate crosslinking agent were obtained.

[0093] Comparative Example 1

[0094] The particulate gel and crosslinking agent were prepared according to the method of Example 1, except that in the preparation of the crosslinking agent, 4-vinylbenzyltetrahydrothiophene tetrafluoroborate was used instead of an equal weight of 1,2-divinylbenzene in step S1. Particulate gel and particulate crosslinking agent were obtained. The weight-average molecular weight of the crosslinking agent was 8129 g / mol.

[0095] Comparative Example 2

[0096] The particulate gel and crosslinking agent were prepared according to the method of Example 1, except that in the preparation of the crosslinking agent, triethylene glycol diacrylate was used instead of an equal weight of 1,2-divinylbenzene in step S1. Particulate gel and particulate crosslinking agent were obtained. The weight-average molecular weight of the crosslinking agent was 12583 g / mol.

[0097] Test Example 1

[0098] Take 1g of the particulate gel and 0.1g of the crosslinking agent prepared in each example and comparative example, add them to 10mL of sodium chloride aqueous solution (sodium chloride concentration 6wt%), and react at 90℃ for 24h to obtain an organic covalently crosslinked nanocomposite, denoted as the bulk gel. The mechanical properties and temperature resistance of the bulk gel obtained from the reaction of the particulate gel and the crosslinking agent in each example and comparative example were measured. The results are shown in Table 1. The mechanical property testing method of the gel was as follows: the bulk gel was cut into cylindrical samples with a diameter of 25mm and a thickness of 3mm using a cutter as subsequent test samples. The testing instrument was a rotational rheometer with a fixed frequency of 1Hz, a fixed amplitude of 1%, and a test time of 5 minutes.

[0099] A schematic diagram of the morphology of the particulate gel prepared in Example 1 during mechanical integrity testing is shown below. Figure 1 As shown in Figure a, a schematic diagram of the morphology of the bulk gel obtained by reacting the particulate gel prepared in Example 1 with the crosslinking agent is shown in Figure a. Figure 1 As shown in b. From Figure 1 a and Figure 1 As can be seen from b, the particulate gel remains loose after absorbing water and swelling, but it acquires mechanical integrity after reacting with the crosslinking agent.

[0100] When testing mechanical properties, a comparison of the mechanical properties of the particulate gel prepared in Example 1 and the bulk gel obtained by reacting the particulate gel prepared in Example 1 with a crosslinking agent is shown in the figure below. Figure 2 As shown, by Figure 2It can be seen that the mechanical properties of the cross-linked bulk gel are greatly improved compared with the particulate gel.

[0101] A schematic diagram of the morphology of the bulk gel obtained by reacting the particulate gel prepared in Example 1 with the crosslinking agent during the temperature resistance test is shown below. Figure 3 As shown in Figure a, the morphology of the bulk gel after being maintained at 130°C for four days is illustrated in Figure a. Figure 3 As shown in b, by Figure 3 a and Figure 3 As can be seen from b, the cross-linked bulk gel remained stable for four days at a high temperature of 130℃ before finally degrading into a solution state.

[0102] Table 1

[0103]

[0104] As shown in Table 1, the bulk gels obtained from the reaction of the particulate gels and crosslinking agents in Examples 1-11 exhibit good mechanical properties and temperature resistance. In Comparative Example 1, 4-vinylbenzyltetrahydrothiophene tetrafluoroborate was used instead of an equal weight of 1,2-divinylbenzene in the preparation of the crosslinking agent. In Comparative Example 2, triethylene glycol diacrylate was used instead of an equal weight of 1,2-divinylbenzene in the preparation of the crosslinking agent. Compared with the bulk gels obtained from the reaction of the particulate gels and crosslinking agents in Examples 1-11, the mechanical properties and temperature resistance of the bulk gels obtained from the reaction of the particulate gels and crosslinking agents in Comparative Examples 1 and 2 were significantly reduced.

[0105] Furthermore, in Examples 2 and 3, the amount of crosslinking material was changed when preparing the crosslinking agent; in Examples 4 and 10, the amount of N,N'-methylenebisacrylamide was changed when preparing the particulate gel; in Example 5, the type of crosslinking material was changed when preparing the crosslinking agent; in Example 6, the solvent combination was changed when preparing the crosslinking agent; in Example 7, the amount of emulsifier was changed when preparing the crosslinking agent; in Example 8, the reaction temperature was changed when preparing the crosslinking agent; in Example 9, the type of monomer was changed when preparing the particulate gel; and in Example 11, the average particle size of the particulate gel was changed. Compared with the bulk gel obtained by reacting the particulate gel and the crosslinking agent in Example 1, the mechanical properties and temperature resistance of the bulk gel obtained by reacting the particulate gel and the crosslinking agent in Examples 2-11 were all reduced. This indicates that when the type and amount of crosslinking material, the solvent combination, the amount of emulsifier and the reaction temperature are optimized when preparing the crosslinking agent, and the amount of N,N'-methylenebisacrylamide, the type of monomer and the average particle size of the particulate gel are optimized when preparing the particulate gel, the mechanical properties and temperature resistance of the obtained bulk gel can be further improved.

[0106] Test Example 2

[0107] Core displacement experiment

[0108] The artificial rock core was 3.8 cm in diameter and 20 cm in length. The simulated natural crack had a hole 10 cm long and 5 mm in diameter. The experiment was conducted according to the following steps:

[0109] (1) The core was vacuum dried at 60℃ for 24 hours and then weighed;

[0110] (2) First, soak the core in a 6% sodium chloride solution for 24 hours, weigh it again, and calculate the pore volume and porosity of the core.

[0111] (3) Install the core into the bracket of the displacement device, control the confining pressure to be 10 MPa higher than the injection pressure, and inject brine at gradient rates of 1 mL / min, 2 mL / min, 3 mL / min and 4 mL / min respectively until the pressure difference stabilizes. Calculate the core permeability according to Darcy's law.

[0112] (4) 3g of the granular gel and 0.3g of the crosslinking agent prepared in each example and comparative example were absorbed into salt water (sodium chloride salt water with a mass fraction of 6%) until they were fully expanded. The mixture of the expanded granular gel and crosslinking agent after absorbing the salt water was placed into the artificial hole, and the constant temperature heating jacket was heated to 90°C and kept for 24 hours to accelerate the reaction of the granular gel and crosslinking agent.

[0113] (5) Inject saline again at a rate of 4 mL / min and record the breakthrough pressure.

[0114] Pressure changes were continuously recorded throughout the core displacement experiment. The displacement breakthrough pressures of the bulk gels obtained by reacting the particulate gels and crosslinking agents prepared in each example and comparative example are shown in Table 2.

[0115] Figure 4 The graph shows the displacement test data of the bulk gel obtained by reacting the particulate gel prepared in Example 1 with the crosslinking agent. The breakthrough pressure is close to 4.48 MPa, which shows that the crosslinked bulk gel has excellent plugging performance.

[0116] Table 2

[0117] serial number Breakthrough pressure, MPa Example 1 4.48 Example 2 4.27 Example 3 4.09 Example 4 3.74 Example 5 3.79 Example 6 3.92 Example 7 3.9 Example 8 3.55 Example 9 3.7 Example 10 3.49 Example 11 3.38 Comparative Example 1 2.92 Comparative Example 2 3.23

[0118] As shown in Table 2, the bulk gels obtained from the reaction of the particulate gels and crosslinking agents in Examples 1-11 exhibit high displacement breakthrough pressure, indicating good plugging performance. In Comparative Example 1, 4-vinylbenzyltetrahydrothiophene tetrafluoroborate was used instead of an equal weight of 1,2-divinylbenzene in the preparation of the crosslinking agent. In Comparative Example 2, triethylene glycol diacrylate was used instead of an equal weight of 1,2-divinylbenzene in the preparation of the crosslinking agent. Compared to the bulk gels obtained from the reaction of the particulate gels and crosslinking agents in Examples 1-11, the plugging performance of the bulk gels obtained from the reaction of the particulate gels and crosslinking agents in Comparative Examples 1 and 2 was significantly reduced.

[0119] Furthermore, in Examples 2 and 3, the amount of crosslinking material was changed when preparing the crosslinking agent; in Examples 4 and 10, the amount of N,N'-methylenebisacrylamide was changed when preparing the particulate gel; in Example 5, the type of crosslinking material was changed when preparing the crosslinking agent; in Example 6, the solvent combination was changed when preparing the crosslinking agent; in Example 7, the amount of emulsifier was changed when preparing the crosslinking agent; in Example 8, the reaction temperature was changed when preparing the crosslinking agent; in Example 9, the type of monomer was changed when preparing the particulate gel; and in Example 11, the average particle size of the particulate gel was changed. Compared with the bulk gel obtained by reacting the particulate gel and the crosslinking agent in Example 1, the leak-stopping performance of the bulk gel obtained by reacting the particulate gel and the crosslinking agent in Examples 2-11 was reduced. This indicates that when the type and amount of crosslinking material, the solvent combination, the amount of emulsifier and the reaction temperature are optimized when preparing the crosslinking agent, and the amount of N,N'-methylenebisacrylamide, the type of monomer and the average particle size of the particulate gel are optimized when preparing the particulate gel, the leak-stopping performance of the obtained bulk gel can be further improved.

[0120] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A network polymer, characterized by, The network polymer comprises structural units A and structural units B, the structural units A being The structural units B are selected from at least one of the group consisting of 4-vinylbenzyl tetrahydrothiophene tetrafluoroborate, 4-vinylbenzyl tetrahydrothiophene tetrafluoroborate and cross-linking material.

2. The network polymer of claim 1, wherein The structural unit B is selected from at least one of Preferably, the weight ratio of structural unit A and structural unit B in the reticular polymer is (100-1000):1, preferably (200-500):

1. Preferably, the weight ratio of structural unit A and structural unit B in the reticular polymer is (100-1000):1, preferably (200-500):

1.

3. A method for preparing a network polymer, characterized by, The preparation method comprises: mixing 4-vinylbenzyl tetrahydrothiophene tetrafluoroborate with a cross-linking material in the presence of a first initiator and a first solvent to react; wherein the 4-vinylbenzyl tetrahydrothiophene tetrafluoroborate is at least one compound selected from at least one compound selected from at least one compound selected from Preferably, the weight ratio of 4-vinylbenzyl tetrahydrothiophene tetrafluoroborate and cross-linking material is (100-1000):1, preferably (200-500):

1. Preferably, the amount of the first initiator is 0.01-0.04 mmol, based on 1 mmol of 4-vinylbenzyl tetrahydrothiophene tetrafluoroborate. Preferably, the first initiator is selected from azo initiators, preferably 2,2'-azobis isobutyronitrile. Preferably, the amount of the first solvent is 2-5 mL, based on 1 mmol of 4-vinylbenzyl tetrahydrothiophene tetrafluoroborate. Preferably, the first solvent is selected from ethanol and / or acetonitrile, preferably a mixture of ethanol and acetonitrile. Preferably, the volume ratio of ethanol and acetonitrile in the first solvent is (3-7):

1. Preferably, the mixture obtained further contains an emulsifier, preferably polyvinylpyrrolidone. Preferably, the amount of the emulsifier is 0.05-0.2 g, based on 1 g of 4-vinylbenzyl tetrahydrothiophene tetrafluoroborate.

4. The production method according to claim 3, characterized by, The reaction is carried out at a temperature of 60-80°C for a time of 10-24h, preferably 12-24h. Preferably, the reaction is carried out in an oxygen-free condition.

5. A reticular polymer prepared by the preparation method of claim 3 or 4.

6. An oil field fracture plugging material, characterized by, The oilfield fracture sealing material comprises gel particles and a cross-linking agent; wherein the cross-linking agent is the reticular polymer of any one of claims 1, 2 and 5. Preferably, the gel particles contain structural unit C and structural unit D, the structural unit C is from at least one of acrylic acid, acrylic acid salt and acrylamide, preferably from acrylic acid; and the structural unit D is from N,N'-methylene bisacrylamide. Preferably, the molar ratio of structural unit C and structural unit D in the gel particles is (800-4000):1, preferably (1000-2000):

1.

7. The oil field fracture plugging material of claim 6, wherein, The weight ratio of the gel particles and the cross-linking agent in the oilfield fracture sealing material is (5-20):

1. Preferably, the average particle size of the gel particles is 0.3-0.6 mm, and / or the average particle size of the cross-linking agent is 50-300 nm.

8. The oil field fracture plugging material of claim 6 or 7, wherein, The preparation method of the gel particles comprises mixing and reacting monomers and N,N'-methylene bisacrylamide in the presence of a second initiator and a second solvent; wherein the monomers are selected from at least one of acrylic acid, acrylic acid salt and acrylamide. Preferably, the monomers and N,N'-methylene bisacrylamide are mixed at a molar ratio of (800-4000):1, preferably (1000-1800):

1. Preferably, the amount of the second initiator is 0.1-0.3 mmol, based on 1 mol of the monomers. Preferably, the second initiator is selected from peroxide initiators, preferably ammonium persulfate; Preferably, the amount of the second solvent is 200-400 mL, based on 1 mol of the monomer; Preferably, the second solvent is water.

9. The oil field fracture plugging material of any one of claims 6-8, wherein, The temperature of the reaction is 50-70°C, and the time is 2-6 h; Preferably, the reaction is carried out at a pH value of 7-8; Preferably, the reaction is carried out in an oxygen-free condition.

10. A method of plugging an oil field fracture, characterized by, The method comprises injecting the oilfield fracture sealing material of any one of claims 6-9 into the deep part of the oilfield formation fracture; Preferably, the temperature of the deep part of the oilfield formation fracture is 60-110°C, preferably 60-90°C; Preferably, the salt concentration of the brine in the deep part of the oilfield formation fracture is 1-12 wt%.

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