Composite blocking remover for oil field and preparation method of composite blocking remover

Abstract

The invention relates to a composite blocking remover for an oil field and a preparation method thereof, and belongs to the technical field of oil exploitation. The composite blocking remover is prepared from the following components: 18 to 22 weight percent of composite acid, 2.7 to 3.5 weight percent of a modified chitosan oligosaccharide synergist, 0.35 to 0.52 weight percent of a surfactant, 0.1 to 0.12 weight percent of a corrosion inhibitor and the balance of water, according to the modified chitosan oligosaccharide synergist, chitosan oligosaccharide is used as a rigid base chain, a supporting effect is provided, double chains are prevented from being intertwined in a water-based environment, a polythioamide chain containing an alkyl quaternary ammonium structure is used as a functional auxiliary chain, redeposition of dissolved matter is relieved through gel breaking-chelation integration, meanwhile, a chain structure forms an adhesive tape effect, and the synergistic effect is achieved. And the blockage removing driving force is increased, so that efficient blockage removing is realized.

Description

Technical Field

[0001] The invention belongs to the technical field of oil extraction, and in particular relates to a composite plugging remover for oil fields and a preparation method thereof. Background Art

[0002] During oilfield production, blockage near the wellbore is a key factor contributing to production decline. Blockages are primarily composed of asphalt colloids, carbonate scale, silicate scale, and microbial metabolites. The current mainstream deblocking technology utilizes a composite acid system (hydrochloric acid / hydrofluoric acid / acetic acid combination) to remove blockages through acid dissolution, supplemented by surfactants to break up organic matter and chelating agents to inhibit metal ion redeposition. However, this system faces three major bottlenecks: Dynamic chelation failure: In an acidic environment, the chelating agent is protonated, the chelation rate of metal ions decreases, and the dissolved metal ions are secondary deposited to form colloidal blockage; Risk of formation damage: High-concentration chelating agents can theoretically improve plugging removal efficiency by carrying dissolved metal ions, but they can easily cause clay mineral lattice expansion and acid erode the rock skeleton, leading to increased sand production. Limited molecular efficiency: Small molecule chelating agents, such as the common ethylenediaminetetraacetic acid and diethylenetriaminepentaacetic acid, can only bind to free metal ions and cannot actively destroy scale crystals. Macromolecular chelating agents, such as polyaspartic acid, tend to clump together in the aqueous phase due to hydrophobic interactions, resulting in insufficient exposure of effective chelating sites. Therefore, the existing surfactant + chelating agent enhancement system faces serious technical bottlenecks, directly restricting the development of efficient plugging removers. Summary of the Invention

[0003] In order to solve the technical problems mentioned in the background technology, the purpose of the present invention is to provide a composite plugging remover for oil fields and a preparation method thereof.

[0004] The purpose of the present invention can be achieved through the following technical solutions: A composite plugging remover for oil fields comprises the following components: 18-22 wt% of a composite acid, 2.7-3.5 wt% of a modified chitosan oligosaccharide synergist, 0.35-0.52 wt% of a surfactant, 0.1-0.12 wt% of a corrosion inhibitor, and the balance being water.

[0005] The modified chitosan oligosaccharide synergist is prepared by the following method: Step A1: Dissolve chitosan oligosaccharide and acetic acid aqueous solution, add epichlorohydrin, and heat to 45-55°C with stirring for 2-2.5 hours. Then, add sodium hydroxide solution to adjust the pH to 12, continue heating to 70-80°C with stirring for 4-5 hours. After the reaction is completed, remove water by vacuum rotary evaporation, and then wash with ethanol and deionized water, and dry to obtain epoxidized chitosan oligosaccharide; In the step A1 reaction, the dosage ratio of chitosan oligosaccharide, epichlorohydrin and acetic acid aqueous solution is 50g:0.15-0.22mol:300-350mL, the mass fraction of acetic acid aqueous solution is 2-3%, epichlorohydrin and chitosan oligosaccharide open the ring, and then close the ring in a strong alkaline environment to introduce epoxy group modification into the chitosan oligosaccharide molecule.

[0006] Step A2: Diethylenetriamine, diethyl thiodiacetate, and dioxane were mixed, and dry nitrogen was introduced. p-Toluenesulfonic acid and tetrabutylammonium hydroxide were added and mixed. The mixture was heated to 80-100°C and stirred for 12-15 hours. After the reaction, the dioxane was removed by rotary evaporation. The substrate was washed with deionized water and dried to obtain a modified matrix. In the reaction of step A2, the usage ratio of diethyl thiodiacetate, diethylenetriamine, toluenesulfonic acid, tetrabutylammonium hydroxide, and dioxane is 0.1 mol: 0.11-0.12 mol: 0.3-0.5 g: 0.15-0.2 g: 220-300 mL, and diethyl thiodiacetate and diethylenetriamine undergo amine transesterification to form a low molecular weight polythioamide compound.

[0007] Step A3: Mix the epoxidized chitosan oligosaccharide, the modified substrate, triethylamine and dimethyl sulfoxide, heat to 60-70°C and stir to react for 1.5-2 hours, then add n-decane bromide and continue heating to 100-110°C and reflux for 3.5-4 hours. After the reaction is completed, remove the dimethyl sulfoxide by vacuum rotary evaporation, dissolve the substrate with deionized water, and dry the aqueous phase to obtain a modified chitosan oligosaccharide synergist; In the step A3 reaction, the amount ratio of epoxidized chitosan oligosaccharide, modified substrate, bromodecane, triethylamine and dimethyl sulfoxide is 50g:8.5-11g:0.12-0.16mol:15-20mL:280-360mL, the secondary amine in the molecular chain segment of the modified substrate is ring-opened and grafted with the epoxidized chitosan oligosaccharide, and then bromodecane and the ring-opened tertiary amine are quaternized to form an alkyl-containing quaternary ammonium structure modification.

[0008] Preferably, the composite acid is a mixture of hydrochloric acid, hydrofluoric acid and acetic acid, which work synergistically with each other and have a good dissolving and unblocking effect on common blockages such as carbonates, silicates, sulfates, etc., and is suitable for most oilfield production conditions.

[0009] Preferably, the surfactant is a non-ionic alkylphenol polyoxyethylene ether preparation, which has good compatibility with the quaternary ammonium structure of the modified chitosan oligosaccharide synergist and has a stable gel-breaking and viscosity-reducing effect in most oil fields.

[0010] Preferably, the corrosion inhibitor is hydroxyethylidene diphosphonic acid, which has good water solubility, is compatible with a water-based plugging removal system, and has a stable and efficient corrosion inhibition effect on the tubing string.

[0011] A preparation method of a composite plugging remover for oil fields comprises the following steps: dissolving a modified chitosan oligosaccharide synergist, a corrosion inhibitor, a surfactant and water, and then adding a composite acid and mixing the mixture to obtain the composite plugging remover.

[0012] Beneficial effects of the present invention: The invention is based on a composite acid deblocking system and is compounded with a modified chitosan oligosaccharide synergist. The chitosan oligosaccharide is ring-opened by epichlorohydrin and then closed under strong alkalinity, and epoxy groups are introduced into the chitosan oligosaccharide molecules for modification to obtain epoxidized chitosan oligosaccharide. Diethylenetriamine and diethyl thiodiacetate are subjected to amine ester exchange to prepare a small molecular weight polythioamide compound, i.e., a modified matrix. The epoxidized chitosan oligosaccharide and the secondary amine in the modified matrix are then ring-opened, and the molecular chain of the modified matrix is ​​grafted onto the epoxidized chitosan oligosaccharide to form a double-chain structure. Finally, n-decyl bromide and the ring-opened tertiary amine are subjected to a quaternization reaction to form an alkyl-containing quaternary ammonium structure modification to obtain the modified chitosan oligosaccharide synergist. Compared with the prior art, the present invention has the following advantages: the modified chitosan oligosaccharide synergist has a double-chain structure, and its polythioamide chain containing an alkyl quaternary ammonium structure is a functional auxiliary chain. The alkyl quaternary ammonium structure in the chain has a good gel-breaking ability for asphalt colloids in petroleum and colloids produced by microorganisms, fully exposing carbonates and silicates in blockages. After being dissolved by acid, the formed metal salt ions can be captured by the chelation formed by the sulfur and nitrogen elements on the main chain of the auxiliary chain, realizing gel-breaking-chelation integration and avoiding the redeposition of dissolved matter; its chitosan oligosaccharide is the base chain, and in the water-based plugging liquid system, the chitosan oligosaccharide base chain itself has good The water-affinity dispersibility of the chain and the β-1,4 glycosidic bonds form a rigid helical structure, which provides rigid support for the functional auxiliary chain and avoids the double chain from tangling in a water-based environment, so that the auxiliary chain can fully adhere and chelate, thereby improving the unblocking efficiency. In addition, the fully unfolded double-chain structure is subject to greater flow resistance of the unblocking liquid, thereby increasing the peeling property of the auxiliary chain after chelation, making the modified chitosan oligosaccharide enhancer like a "tape", chelating and binding with the blockage and tearing it off, thereby increasing the driving force for unblocking. In addition, the chitosan oligosaccharide chain, as a carrier chain, has its own natural degradation characteristics and has far-reaching application value in green and environmentally friendly unblocking agents. DETAILED DESCRIPTION

[0013] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0014] Example 1: Preparation of a composite plugging remover for oil fields. The specific implementation process is as follows: (1) Preparation of modified chitosan oligosaccharide synergist Step A1: Prepare a 3% mass fraction acetic acid aqueous solution, take chitosan oligosaccharide (3000Da) and the acetic acid aqueous solution and mix them, add epichlorohydrin and mix, heat to 55°C and stir to react for 2 hours, then add sodium hydroxide solution (mass fraction 20%) to adjust the pH value to 12, continue to heat to 80°C and stir to react for 4 hours, wherein the amount ratio of chitosan oligosaccharide, epichlorohydrin and acetic acid aqueous solution is 50g:0.22mol:350mL. After the reaction is completed, remove water by vacuum rotary evaporation, then wash with ethanol and deionized water, and dry to obtain epoxidized chitosan oligosaccharide.

[0015] Step A2: Diethylenetriamine, diethyl thiodiacetate and dioxane were mixed, dry nitrogen was introduced for protection, p-toluenesulfonic acid and tetrabutylammonium hydroxide were added, and the mixture was heated to 100°C and stirred for 12 hours. The amount ratio of diethyl thiodiacetate, diethylenetriamine, toluenesulfonic acid, tetrabutylammonium hydroxide and dioxane was 0.1 mol: 0.12 mol: 0.5 g: 0.2 g: 300 mL. After the reaction was completed, the dioxane was removed by rotary evaporation, and the substrate was washed with deionized water and dried to obtain a modified matrix.

[0016] Step A3: Mix epoxidized chitosan oligosaccharide, modified matrix, triethylamine and dimethyl sulfoxide, heat to 70°C and stir to react for 1.5h, then add bromodecane and continue to heat to 110°C and reflux for 3.5h, wherein the amount ratio of epoxidized chitosan oligosaccharide, modified matrix, bromodecane, triethylamine and dimethyl sulfoxide is 50g:11g:0.16mol:20mL:360mL. After the reaction is completed, dimethyl sulfoxide is removed by vacuum rotary evaporation, the substrate is dissolved with deionized water, and the aqueous phase is dried to obtain a modified chitosan oligosaccharide synergist.

[0017] (2) Preparation of composite plugging remover The raw materials are calculated according to the following components: 18wt% composite acid, which is compounded with 36% industrial hydrochloric acid, 48% industrial hydrofluoric acid and 80% industrial acetic acid, with specific ratios of 10wt%, 5wt% and 3wt% respectively; 2.7wt% modified chitosan oligosaccharide synergist, which is homemade in this embodiment; 0.52wt% surfactant, which is a non-ionic alkylphenol polyoxyethylene ether, specifically OP-7; 0.1wt% corrosion inhibitor, which is industrial-grade hydroxyethylidene diphosphonic acid; and the balance is water.

[0018] The modified chitosan oligosaccharide synergist, corrosion inhibitor, surfactant and water are stirred and dissolved, and then the composite acid is added and stirred to obtain the composite blocking remover.

[0019] Example 2, preparation of a composite plugging remover for oil fields, the specific implementation process is as follows: (1) Preparation of modified chitosan oligosaccharide synergist Step A1: Prepare a 2% mass fraction acetic acid aqueous solution, take chitosan oligosaccharide (3000Da) and the acetic acid aqueous solution and mix them, add epichlorohydrin and mix, heat to 45°C and stir to react for 2.5 hours, then add sodium hydroxide solution (mass fraction 20%) to adjust the pH value to 12, continue to heat to 70°C and stir to react for 5 hours, wherein the amount ratio of chitosan oligosaccharide, epichlorohydrin and acetic acid aqueous solution is 50g:0.15mol:300mL. After the reaction is completed, remove water by vacuum rotary evaporation, then wash with ethanol and deionized water, and dry to obtain epoxidized chitosan oligosaccharide.

[0020] Step A2: Diethylenetriamine, diethyl thiodiacetate and dioxane were mixed, dry nitrogen was introduced for protection, p-toluenesulfonic acid and tetrabutylammonium hydroxide were added, and the mixture was heated to 80°C and stirred for 15 hours. The amount ratio of diethyl thiodiacetate, diethylenetriamine, toluenesulfonic acid, tetrabutylammonium hydroxide and dioxane was 0.1 mol: 0.11 mol: 0.3 g: 0.15 g: 220 mL. After the reaction was completed, the dioxane was removed by rotary evaporation, and the substrate was washed with deionized water and dried to obtain a modified matrix.

[0021] Step A3: Mix epoxidized chitosan oligosaccharide, modified matrix, triethylamine and dimethyl sulfoxide, heat to 60°C and stir to react for 2h, then add bromodecane and continue to heat to 100°C and reflux for 4h, wherein the amount ratio of epoxidized chitosan oligosaccharide, modified matrix, bromodecane, triethylamine and dimethyl sulfoxide is 50g:8.5g:0.12mol:15mL:280mL. After the reaction is completed, dimethyl sulfoxide is removed by vacuum rotary evaporation, the substrate is dissolved with deionized water, and the aqueous phase is dried to obtain a modified chitosan oligosaccharide synergist.

[0022] (2) Preparation of composite plugging remover The raw materials are calculated according to the following components: 22wt% composite acid, which is compounded with 36% industrial hydrochloric acid, 48% industrial hydrofluoric acid and 80% industrial acetic acid, with specific ratios of 11wt%, 7wt% and 4wt% respectively; 3.5wt% modified chitosan oligosaccharide synergist, which is homemade in this embodiment; 0.35wt% surfactant, which is a non-ionic alkylphenol polyoxyethylene ether, specifically OP-7; 0.12wt% corrosion inhibitor, which is industrial-grade hydroxyethylidene diphosphonic acid; and the balance is water.

[0023] The modified chitosan oligosaccharide synergist, corrosion inhibitor, surfactant and water are stirred and dissolved, and then the composite acid is added and stirred to obtain the composite blocking remover.

[0024] Example 3, preparation of a composite plugging remover for oil fields, the specific implementation process is as follows: (1) Preparation of modified chitosan oligosaccharide synergist Step A1: Prepare a 3% mass fraction acetic acid aqueous solution, take chitosan oligosaccharide (3000Da) and the acetic acid aqueous solution and mix them, add epichlorohydrin and mix, heat to 50°C and stir to react for 2.2 hours, then add sodium hydroxide solution (mass fraction 20%) to adjust the pH value to 12, continue to heat to 75°C and stir to react for 4.5 hours, wherein the amount ratio of chitosan oligosaccharide, epichlorohydrin and acetic acid aqueous solution is 50g:0.18mol:320mL. After the reaction is completed, remove water by vacuum rotary evaporation, then wash with ethanol and deionized water, and dry to obtain epoxidized chitosan oligosaccharide.

[0025] Step A2: Diethylenetriamine, diethyl thiodiacetate and dioxane were mixed, dry nitrogen was introduced for protection, p-toluenesulfonic acid and tetrabutylammonium hydroxide were added, and the mixture was heated to 90°C with stirring for 13 hours. The amount ratio of diethyl thiodiacetate, diethylenetriamine, toluenesulfonic acid, tetrabutylammonium hydroxide and dioxane was 0.1 mol: 0.12 mol: 0.4 g: 0.18 g: 260 mL. After the reaction was completed, the dioxane was removed by rotary evaporation, and the substrate was washed with deionized water and dried to obtain a modified matrix.

[0026] Step A3: Take epoxidized chitosan oligosaccharide, modified matrix, triethylamine and dimethyl sulfoxide, mix them, heat to 65°C and stir to react for 1.7h, then add bromodecane and continue to heat to 100°C and reflux for 4h, wherein the amount ratio of epoxidized chitosan oligosaccharide, modified matrix, bromodecane, triethylamine and dimethyl sulfoxide is 50g:10g:0.14mol:18mL:320mL. After the reaction is completed, dimethyl sulfoxide is removed by vacuum rotary evaporation, the substrate is dissolved with deionized water, and the aqueous phase is dried to obtain a modified chitosan oligosaccharide synergist.

[0027] (2) Preparation of composite plugging remover The raw materials are calculated according to the following components: 20wt% composite acid, which is compounded with 36% industrial hydrochloric acid, 48% industrial hydrofluoric acid and 80% industrial acetic acid, with specific ratios of 10wt%, 8wt% and 2wt% respectively; 3wt% modified chitosan oligosaccharide synergist, which is homemade in this embodiment; 0.47wt% surfactant, which is a non-ionic alkylphenol polyoxyethylene ether, specifically OP-7; 0.11wt% corrosion inhibitor, which is industrial-grade hydroxyethylidene diphosphonic acid; and the balance is water.

[0028] The modified chitosan oligosaccharide synergist, corrosion inhibitor, surfactant and water are stirred and dissolved, and then the composite acid is added and stirred to obtain the composite blocking remover.

[0029] Example 4, preparing a composite plugging remover for oil fields, the specific implementation process is as follows: (1) Preparation of modified chitosan oligosaccharide synergist Step A1: Prepare a 2% mass fraction acetic acid aqueous solution, take chitosan oligosaccharide (3000Da) and the acetic acid aqueous solution and mix them, add epichlorohydrin and mix, heat to 50°C and stir to react for 2.5 hours, then add sodium hydroxide solution (mass fraction 20%) to adjust the pH value to 12, continue to heat to 75°C and stir to react for 4.2 hours, wherein the amount ratio of chitosan oligosaccharide, epichlorohydrin and acetic acid aqueous solution is 50g:0.2mol:330mL. After the reaction is completed, remove water by vacuum rotary evaporation, then wash with ethanol and deionized water, and dry to obtain epoxidized chitosan oligosaccharide.

[0030] Step A2: Diethylenetriamine, diethyl thiodiacetate and dioxane were mixed, dry nitrogen was introduced for protection, p-toluenesulfonic acid and tetrabutylammonium hydroxide were added, and the mixture was heated to 95°C with stirring for 14 hours. The amount ratio of diethyl thiodiacetate, diethylenetriamine, toluenesulfonic acid, tetrabutylammonium hydroxide and dioxane was 0.1 mol: 0.11 mol: 0.35 g: 0.18: 250 mL. After the reaction was completed, the dioxane was removed by rotary evaporation, and the substrate was washed with deionized water and dried to obtain a modified matrix.

[0031] Step A3: Mix epoxidized chitosan oligosaccharide, modified matrix, triethylamine and dimethyl sulfoxide, heat to 65°C and stir to react for 1.8h, then add bromodecane and continue to heat to 110°C and reflux for 3.5h, wherein the amount ratio of epoxidized chitosan oligosaccharide, modified matrix, bromodecane, triethylamine and dimethyl sulfoxide is 50g:9.5g:0.15mol:20mL:340mL. After the reaction is completed, dimethyl sulfoxide is removed by vacuum rotary evaporation, the substrate is dissolved with deionized water, and the aqueous phase is dried to obtain a modified chitosan oligosaccharide synergist.

[0032] (2) Preparation of composite plugging remover The raw materials are calculated according to the following components: 21wt% composite acid, which is compounded with 36% industrial hydrochloric acid, 48% industrial hydrofluoric acid and 80% industrial acetic acid, with specific ratios of 11wt%, 6wt% and 4wt% respectively; 3.2wt% modified chitosan oligosaccharide synergist, which is homemade in this embodiment; 0.44wt% surfactant, which is a non-ionic alkylphenol polyoxyethylene ether, specifically OP-7; 0.11wt% corrosion inhibitor, which is industrial-grade hydroxyethylidene diphosphonic acid; and the balance is water.

[0033] The modified chitosan oligosaccharide synergist, corrosion inhibitor, surfactant and water are stirred and dissolved, and then the composite acid is added and stirred to obtain the composite blocking remover.

[0034] Comparative Example 1, referring to the prior art, a quaternary ammonium salt and chelating agent compound system was used to prepare a blocking agent, and the specific component formula was adjusted to: 21 wt% of composite acid (same as Example 4); 2.4 wt% of chitosan quaternary ammonium salt, using FT-11 type commercially available raw material; 0.8 wt% of chelating agent, using industrial-grade ethylenediaminetetramethylenephosphonic acid and diethylenetriaminepentaacetic acid pentasodium in a weight ratio of 2:1; 0.75 wt% of surfactant and 0.12 wt% of corrosion inhibitor, with the balance being water.

[0035] The specific preparation process is the same as that in Example 4.

[0036] In comparative example 2, commercially available HM-307 composite acidic plugging remover, sourced from Gansu Dark Horse Petrochemical Engineering Co., Ltd., was selected.

[0037] Take a sample from the composite plugging remover prepared as above and dilute it with water to make a 10% plugging remover for later use; A plugging agent was prepared by mixing 30wt% crude oil, 30wt% calcium carbonate, 10wt% calcium silicate, 10wt% calcium sulfate, 10wt% paraffin, 5wt% HPAM gel, and 5wt% asphalt to simulate the plugging components in the actual oil production process; a 50mD low-permeability artificial rock core was used as the plugging matrix.

[0038] Viscosity reduction test: Mix the plugging agent and the unblocking liquid in a weight ratio of 1:1.5, place them in a constant temperature water bath at 50°C for 2 hours, and use a rotational viscometer to measure the viscosity before and after adding the unblocking liquid to calculate the viscosity reduction rate η; ; Among them, μ0 is the original viscosity of the plugging agent, and μ1 is the viscosity after adding the plugging remover.

[0039] Unblocking test: A sand-filled tube method was used to conduct an unblocking simulation test. An artificial rock core was filled with a plugging agent containing 5 wt% of the artificial core. The core was then covered with 5 cm thick machine-made sand. The permeability was tested and recorded as the plugging permeability K1. Unblocking fluid was injected at 0.2 PV and kept at 50°C for 12 hours. The permeability was then tested again and recorded as the unblocking permeability K2. The unblocking rate δ was then calculated. ; Where K0 is the initial permeability (50mD).

[0040] The specific test results are shown in Table 1: Table 1

[0041] It can be seen from the test results in Table 1 that the plugging remover prepared in the example effectively reduces the viscosity of oilfield blockages, and the plugging removal efficiency is significantly higher than that of existing acidic plugging removers.

[0042] Throughout the specification, references to terms such as "one embodiment," "example," or "specific example" indicate that the specific features, structures, materials, or characteristics described in conjunction with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, schematic representations of these terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0043] The above contents are merely examples and explanations of the present invention. Those skilled in the art may make various modifications or additions to the described specific embodiments or replace them in similar ways. As long as they do not deviate from the invention or exceed the scope defined by the claims, they should all fall within the scope of protection of the present invention.

Claims

1. A composite plugging remover for oil fields, characterized in that: The specific components are: composite acid 18-22wt%, modified chitosan oligosaccharide synergist 2.7-3.5wt%, surfactant 0.35-0.52wt% and corrosion inhibitor 0.1-0.12wt%, and the balance is water; The modified chitosan oligosaccharide synergist is prepared by the following method: Step A1: Dissolve chitosan oligosaccharide and acetic acid aqueous solution, add epichlorohydrin, mix, heat to 45-55°C, stir and react for 2-2.5 hours, then add sodium hydroxide solution to adjust the pH to 12, continue to heat to 70-80°C, stir and react for 4-5 hours to prepare epoxidized chitosan oligosaccharide; Step A2: Diethylenetriamine, diethyl thiodiacetate, and dioxane were mixed, and dry nitrogen was introduced into the mixture. p-Toluenesulfonic acid and tetrabutylammonium hydroxide were added and mixed. The mixture was heated to 80-100° C. and stirred for 12-15 hours to prepare a modified matrix. Step A3: Mix the epoxidized chitosan oligosaccharide, the modified matrix, triethylamine and dimethyl sulfoxide, heat to 60-70° C. and stir to react for 1.5-2 hours, then add bromodecane and continue heating to 100-110° C. and reflux for 3.5-4 hours to prepare a modified chitosan oligosaccharide synergist.

2. The composite plugging remover for oil fields according to claim 1, characterized in that: The dosage ratio of chitosan oligosaccharide, epichlorohydrin and acetic acid aqueous solution is 50g:0.15-0.22mol:300-350mL.

3. The composite plugging remover for oil fields according to claim 2, characterized in that: The usage ratio of diethyl thiodiacetate, diethylenetriamine, toluenesulfonic acid, tetrabutylammonium hydroxide and dioxane is 0.1 mol: 0.11-0.12 mol: 0.3-0.5 g: 0.15-0.2 g: 220-300 mL.

4. The composite plugging remover for oil fields according to claim 3, characterized in that: The usage ratio of the epoxidized chitosan oligosaccharide, the modified matrix, brominated n-decane, triethylamine and dimethyl sulfoxide is 50g:8.5-11g:0.12-0.16mol:15-20mL:280-360mL.

5. The composite plugging remover for oil fields according to claim 1, characterized in that: The compound acid is prepared by mixing hydrochloric acid, hydrofluoric acid and acetic acid.

6. The composite plugging remover for oil fields according to claim 1, characterized in that: The surfactant is a nonionic alkylphenol polyoxyethylene ether preparation.

7. The composite plugging remover for oil fields according to claim 1, characterized in that: The corrosion inhibitor is hydroxyethylidene diphosphonic acid.

8. A method for preparing a composite plugging remover for oil fields according to any one of claims 1 to 7, characterized in that: Specifically, the modified chitosan oligosaccharide synergist, corrosion inhibitor, surfactant and water are mixed, and then composite acid is added and mixed to obtain the composite blocking remover.

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