A CO2-triggered delayed crosslinking agent, its preparation method and application

Abstract

The application discloses a CO2 triggered delayed crosslinking agent, and a structural formula is shown in the description.The application also discloses a CO2 triggered delayed crosslinking system, which is composed of the CO2 triggered delayed crosslinking agent, polyacrylamide and water.The application further discloses a preparation method of the CO2 triggered delayed crosslinking agent, which comprises the following steps: (1) dissolving a certain amount of binary aldehyde and sodium bisulfite in a reactor with water, and performing an addition reaction under the condition of continuously blowing air, so as to obtain a reaction liquid after the reaction is completed; (2) performing vacuum distillation on the reaction liquid obtained in the step (1) to remove water, extracting the residual material in the reactor with an appropriate amount of extraction agent for at least two times, filtering out inorganic salts, taking the extraction liquid, then distilling and removing the extraction agent under normal pressure, and finally vacuum drying the product, so that the CO2 triggered delayed crosslinking agent is obtained after the drying is completed.

Description

Technical Field

[0001] This invention relates to the field of crosslinking agents, specifically to a CO2-triggered delayed crosslinking agent, its preparation method, and its application. Background Technology

[0002] In the process of tertiary oil recovery using CO2 flooding, the reservoir has many natural fractures and the pressure is lower than that of the miscible phase, which leads to severe CO2 gas channeling and reduces the oil displacement efficiency.

[0003] Currently, the feasible approaches to overcome the technical challenges of gas channeling prevention and suppression are mainly as follows: (1) Water-gas alternation technology: Water and gas are alternately injected into the oil layer. Water has a high viscosity, and CO2 gas is easy to disperse in water, making it easy to control the fluid flow rate. (2) Thickening and sealing technology: By adding surfactants and polymers to CO2, CO2 dissolves in the polymer under the action of a cosolvent. After thickening, it can effectively resist the driving force of formation fluids and effectively prevent gas channeling. (3) Gel system: In the later stage of oil displacement, gas channeling is more serious. By adding polymers, a gel is formed in the formation to seal deep fractures and channeling channels in the reservoir. (4) Precipitation treatment: By adding salt solution to react with CO2 to generate precipitation to seal the gaps, there is no pollution to the formation environment.

[0004] Gas channeling is very likely to occur during CO2 oil displacement. Once gas channeling occurs, it will form a channeling channel. From the perspective of avoiding spending extra effort to identify and detect it, among the four anti-channeling and suppression technologies mentioned above, using gel to directly block it is a relatively effective method. However, gel has poor fluidity and its range of action is limited. Summary of the Invention

[0005] Purpose of the invention: In order to improve CO2 displacement efficiency and effectively suppress gas channeling, this invention provides a CO2-triggered delayed crosslinking agent, its preparation method and application.

[0006] CO2-triggered delayed crosslinking agent is injected separately into the oil layer during the later stage of displacement. It has good mobility during flow. The oxidation reaction triggered by CO2 forms aldehyde groups that crosslink with polyacrylamide emulsion. After a delay, it forms a gel in the channeling channel. It has accurate positioning, high sealing efficiency, good injection capacity and stability. This system has the dual functions of thickening and gelling, and can effectively suppress gas channeling.

[0007] Technical solution: A CO2-triggered delayed crosslinking agent, the structural formula of which is as follows:

[0008]

[0009] Where n is 2 to 8.

[0010] A CO2-triggered delayed crosslinking system is composed of the above-mentioned CO2-triggered delayed crosslinking agent, polyacrylamide, and water. By mass percentage, the CO2-triggered delayed crosslinking agent accounts for 0.5-1%, the polyacrylamide accounts for 0.5-1%, and the balance is water.

[0011] A method for preparing a CO2-triggered delayed crosslinking agent includes the following steps:

[0012] (1) A certain amount of dialdehyde and sodium bisulfite were dissolved in water in a reactor and an addition reaction was carried out while air was continuously bubbled in. After the reaction was completed, a reaction solution was obtained.

[0013] (2) The reaction solution obtained in step (1) is subjected to vacuum distillation to remove water. The residue after distillation in the reactor is extracted at least twice with an appropriate amount of extractant. Inorganic salts are filtered out, and the extract is collected. The extract is then distilled under normal pressure to remove the extractant. Finally, the product is dried under vacuum. After drying, the CO2-triggered delayed crosslinking agent is obtained, wherein:

[0014] The structure of the dialdehyde is as follows:

[0015] Where: n is 2 to 8;

[0016] The structural formula of the CO2-triggered delayed crosslinking agent is as follows:

[0017]

[0018] Where n is 2 to 8.

[0019] Further, in step (1), the molar ratio of the dialdehyde and the sodium bisulfite is 1:(2-2.3).

[0020] Furthermore, by mass, the amount of water used in step (1) is 3 to 8 times the sum of the masses of the dialdehyde and the sodium bisulfite.

[0021] Furthermore, the reaction temperature of the addition reaction in step (1) is 20-30°C, and the reaction time is 1-3 hours.

[0022] Further, the extractant in step (2) is one of acetone, methanol, and isopropanol, preferably acetone.

[0023] Furthermore, by mass, the amount of extractant used in step (2) is 3 to 5 times the amount of the dialdehyde used.

[0024] The above-mentioned CO2-triggered delayed crosslinking agent is used in CO2 flooding or CO2 single-well huff and puff in oil fields.

[0025] The aforementioned CO2-triggered delayed crosslinking system is applied in CO2 flooding or CO2 single-well huff and puff in oilfields. In use, the CO2-triggered delayed crosslinking system is prepared at the surface according to the specified ratio and then directly injected into the formation. As CO2 is injected, the CO2-triggered oxidation reaction forms aldehyde groups that crosslink with the polyacrylamide emulsion. After a delay, a gel forms in the gas channel, resulting in accurate targeting, high sealing efficiency, and good injection capacity and stability. This system possesses both thickening and gelling functions, effectively suppressing gas channeling.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] A CO2-triggered delayed crosslinking agent is prepared by an addition reaction using dialdehyde and sodium bisulfite as raw materials. Under the action of CO2 in the oil well, the synthesized delayed crosslinking agent crosslinks with polyacrylamide emulsion to form a complex three-dimensional network structure, increasing the viscosity of the hydrogel system and sealing fractures. This system can significantly improve the CO2 displacement ratio and effectively inhibit CO2 gas channeling, providing convenience for oilfield construction. Attached Figure Description

[0028] Figure 1 The image shows the 1H NMR spectrum of the CO2-triggered delayed crosslinking agent obtained in Example 5. Detailed implementation method:

[0029] The specific embodiments of the present invention are described in detail below.

[0030] 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.

[0031] To enable those skilled in the art to understand the features and effects of the present invention, the terms and expressions used in the specification and claims are explained and defined in general below. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.

[0032] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0033] In this document, all features defined by numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0034] In this article, unless otherwise specified, “contains,” “includes,” “containing,” “has,” or similar terms cover the meanings of “composed of” and “mainly composed of,” for example, “A contains a” covers the meanings of “A contains a and others” and “A contains only a.”

[0035] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0036] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0037] The following examples use instruments and equipment conventional in the art. Experimental methods in the following examples, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. All raw materials used in the following examples are conventional commercially available products with specifications conventional in the art. In this specification and the following examples, unless otherwise specified, "%" refers to weight percentage, "parts" refers to parts by weight, and "ratio" refers to weight proportion.

[0038] A CO2-triggered delayed crosslinking agent, the structural formula of which is as follows:

[0039]

[0040] Where n is 2 to 8.

[0041] In one embodiment, a CO2-triggered delayed crosslinking agent has the following structural formula:

[0042]

[0043] Where n is 2.

[0044] In another embodiment, a CO2-triggered delayed crosslinking agent has the following structural formula:

[0045]

[0046] Where n is 8.

[0047] In yet another embodiment, a CO2-triggered delayed crosslinking agent has the following structural formula:

[0048]

[0049] Where n is 4.

[0050] A CO2-triggered delayed crosslinking system is composed of the above-mentioned CO2-triggered delayed crosslinking agent, polyacrylamide, and water. By mass percentage, the CO2-triggered delayed crosslinking agent accounts for 0.5-1%, the polyacrylamide accounts for 0.5-1%, and the balance is water.

[0051] In one embodiment, a CO2-triggered delayed crosslinking system comprises a CO2-triggered delayed crosslinking agent, polyacrylamide, and water, wherein, by mass percentage, the CO2-triggered delayed crosslinking agent accounts for 0.5%, the polyacrylamide accounts for 0.5%, and the balance is water, wherein:

[0052] The CO2-triggered delayed crosslinking agent has the following structural formula:

[0053]

[0054] Where n is 2.

[0055] In another embodiment, a CO2-triggered delayed crosslinking system is composed of the aforementioned CO2-triggered delayed crosslinking agent, polyacrylamide, and water, wherein, by mass percentage, the CO2-triggered delayed crosslinking agent accounts for 1%, the polyacrylamide accounts for 1%, and the balance is water, wherein:

[0056] The CO2-triggered delayed crosslinking agent has the following structural formula:

[0057]

[0058] Where n is 8.

[0059] In another embodiment, a CO2-triggered delayed crosslinking system is composed of the aforementioned CO2-triggered delayed crosslinking agent, polyacrylamide, and water. By mass percentage, the CO2-triggered delayed crosslinking agent accounts for 0.8%, the polyacrylamide accounts for 0.8%, and the balance is water.

[0060] The CO2-triggered delayed crosslinking agent has the following structural formula:

[0061]

[0062] Where n is 4.

[0063] A method for preparing a CO2-triggered delayed crosslinking agent includes the following steps:

[0064] (1) A certain amount of dialdehyde and sodium bisulfite were dissolved in water in a reactor and an addition reaction was carried out while air was continuously bubbled in. After the reaction was completed, a reaction solution was obtained.

[0065] (2) The reaction solution obtained in step (1) is subjected to vacuum distillation to remove water. At the same time, a large amount of inorganic salt (sodium sulfate) is precipitated in the reaction solution of the reactor. The residue after distillation in the reactor is extracted at least twice with an appropriate amount of extractant. The inorganic salt is filtered out, and the extract is taken. Then the extract is distilled under normal pressure to remove the extractant. Finally, the product is placed in a vacuum oven to dry. After drying, the CO2-triggered delayed crosslinking agent is obtained, wherein:

[0066] The structure of the dialdehyde is as follows:

[0067] Where: n is 2 to 8;

[0068] The structural formula of the CO2-triggered delayed crosslinking agent is as follows:

[0069]

[0070] Where n is 2 to 8.

[0071] The specific preparation process is achieved through the following reaction:

[0072]

[0073] Further, in step (1), the molar ratio of the dialdehyde and the sodium bisulfite is 1:(2-2.3).

[0074] Furthermore, by mass, the amount of water used in step (1) is 3 to 8 times the sum of the masses of the dialdehyde and the sodium bisulfite.

[0075] Furthermore, the reaction temperature of the addition reaction in step (1) is 20-30°C, and the reaction time is 1-3 hours.

[0076] Further, the extractant in step (2) is one of acetone, methanol, and isopropanol, preferably acetone.

[0077] Furthermore, by mass, the amount of extractant used in step (2) is 3 to 5 times the amount of the dialdehyde used.

[0078] The above-mentioned CO2-triggered delayed crosslinking agent is used in CO2 flooding or CO2 single-well huff and puff in oil fields.

[0079] The above-mentioned CO2-triggered delayed crosslinking system is applied in CO2 flooding or CO2 single-well huff and puff in oil fields.

[0080] The working principle of this invention is as follows:

[0081] CO2-triggered delayed crosslinking agents crosslink with polyacrylamide emulsions via CO2 triggering. This CO2-triggered delayed crosslinking system seals fractures, significantly improves the CO2 displacement ratio, effectively inhibits CO2 channeling, and facilitates oilfield operations. Its action is achieved through the following reaction equation:

[0082]

[0083] In one embodiment: a method for preparing a CO2-triggered delayed crosslinking agent includes the following steps:

[0084] (1) A certain amount of dialdehyde and sodium bisulfite were dissolved in water in a reactor and an addition reaction was carried out while air was continuously bubbled in. After the reaction was completed, a reaction solution was obtained.

[0085] (2) The reaction solution obtained in step (1) is subjected to vacuum distillation to remove water. At the same time, a large amount of inorganic salt (sodium sulfate) is precipitated in the reaction solution of the reactor. The residue after distillation in the reactor is extracted twice with an appropriate amount of extractant. The inorganic salt is filtered out, and the extract is taken. Then, the extract is distilled under normal pressure to remove the extractant. Finally, the product is placed in a vacuum oven to dry. After drying, the CO2-triggered delayed crosslinking agent is obtained, wherein:

[0086] The structure of the dialdehyde is as follows:

[0087] Where: n is 2;

[0088] The structural formula of the CO2-triggered delayed crosslinking agent is as follows:

[0089]

[0090] Where n is 2.

[0091] Further, in step (1), the molar ratio of the dialdehyde and the sodium bisulfite is 1:2.

[0092] Furthermore, by mass, the amount of water used in step (1) is three times the sum of the masses of the dialdehyde and the sodium bisulfite.

[0093] Furthermore, the reaction temperature of the addition reaction in step (1) is 20°C and the reaction time is 3 hours.

[0094] Furthermore, the extractant in step (2) is acetone.

[0095] Furthermore, by mass, the amount of extractant used in step (2) is three times the amount of the dialdehyde used.

[0096] The above-mentioned CO2-triggered delayed crosslinking agent is used in CO2 flooding or CO2 single-well huff and puff in oil fields.

[0097] The above-mentioned CO2-triggered delayed crosslinking system is applied in CO2 flooding or CO2 single-well huff and puff in oil fields.

[0098] In another embodiment, a method for preparing a CO2-triggered delayed crosslinking agent includes the following steps:

[0099] (1) A certain amount of dialdehyde and sodium bisulfite were dissolved in water in a reactor and an addition reaction was carried out while air was continuously bubbled in. After the reaction was completed, a reaction solution was obtained.

[0100] (2) The reaction solution obtained in step (1) is subjected to vacuum distillation to remove water. At the same time, a large amount of inorganic salt (sodium sulfate) is precipitated in the reaction solution of the reactor. The residue after distillation in the reactor is extracted at least twice with an appropriate amount of extractant. The inorganic salt is filtered out, and the extract is taken. Then the extract is distilled under normal pressure to remove the extractant. Finally, the product is placed in a vacuum oven to dry. After drying, the CO2-triggered delayed crosslinking agent is obtained, wherein:

[0101] The structure of the dialdehyde is as follows:

[0102] Where: n is 8;

[0103] The structural formula of the CO2-triggered delayed crosslinking agent is as follows:

[0104]

[0105] Where n is 8.

[0106] Further, in step (1), the molar ratio of the dialdehyde and the sodium bisulfite is 1:2.3.

[0107] Furthermore, by mass, the amount of water used in step (1) is 8 times the sum of the masses of the dialdehyde and the sodium bisulfite.

[0108] Furthermore, the reaction temperature of the addition reaction in step (1) is 30°C and the reaction time is 1 hour.

[0109] Furthermore, the extractant in step (2) is methanol.

[0110] Furthermore, by mass, the amount of extractant used in step (2) is 5 times the amount of the dialdehyde used.

[0111] The above-mentioned CO2-triggered delayed crosslinking agent is used in CO2 flooding or CO2 single-well huff and puff in oil fields.

[0112] The above-mentioned CO2-triggered delayed crosslinking system is applied in CO2 flooding or CO2 single-well huff and puff in oil fields.

[0113] In yet another embodiment, a method for preparing a CO2-triggered delayed crosslinking agent includes the following steps:

[0114] (1) A certain amount of dialdehyde and sodium bisulfite were dissolved in water in a reactor and an addition reaction was carried out while air was continuously bubbled in. After the reaction was completed, a reaction solution was obtained.

[0115] (2) The reaction solution obtained in step (1) is subjected to vacuum distillation to remove water. At the same time, a large amount of inorganic salt (sodium sulfate) is precipitated in the reaction solution of the reactor. The residue after distillation in the reactor is extracted at least twice with an appropriate amount of extractant. The inorganic salt is filtered out, and the extract is taken. Then the extract is distilled under normal pressure to remove the extractant. Finally, the product is placed in a vacuum oven to dry. After drying, the CO2-triggered delayed crosslinking agent is obtained, wherein:

[0116] The structure of the dialdehyde is as follows:

[0117] Where: n is 5;

[0118] The structural formula of the CO2-triggered delayed crosslinking agent is as follows:

[0119]

[0120] Where n is 5.

[0121] Further, in step (1), the molar ratio of the dialdehyde and the sodium bisulfite is 1:2.1.

[0122] Furthermore, by mass, the amount of water used in step (1) is 5 times the sum of the masses of the dialdehyde and the sodium bisulfite.

[0123] Furthermore, the reaction temperature of the addition reaction in step (1) is 25°C and the reaction time is 2.5 hours.

[0124] Furthermore, the extractant in step (2) is isopropanol.

[0125] Furthermore, by mass, the amount of extractant used in step (2) is 4 times the amount of the dialdehyde used.

[0126] The above-mentioned CO2-triggered delayed crosslinking agent is used in CO2 flooding or CO2 single-well huff and puff in oil fields.

[0127] The above-mentioned CO2-triggered delayed crosslinking system is applied in CO2 flooding or CO2 single-well huff and puff in oil fields.

[0128] The present invention will be further described below with reference to specific embodiments and accompanying drawings:

[0129] Example 1

[0130] A method for preparing a CO2-triggered delayed crosslinking agent includes the following steps:

[0131] (1) Dissolve 3.6g glutaraldehyde and 7.8g sodium bisulfite in 60g distilled water in a reactor. With air continuously bubbling in, carry out the addition reaction at 30°C for 1.5h. After the reaction is completed, the reaction solution is obtained.

[0132] (2) The reaction solution obtained in step (1) is subjected to vacuum distillation to remove water. At the same time, a large amount of inorganic salt (sodium sulfate) is precipitated in the reaction solution of the reactor. The residue after distillation in the reactor is extracted twice with 14g of extractant. The inorganic salt is filtered off, and the extract is collected. Then, the extract is distilled under normal pressure to remove the extractant. Finally, the product is placed in a vacuum oven to dry. After drying, the CO2-triggered delayed crosslinking agent is obtained, wherein:

[0133] The structure of glutaraldehyde is as follows:

[0134] Where: n is 3;

[0135] The structural formula of the CO2-triggered delayed crosslinking agent is as follows:

[0136]

[0137] Where n is 3.

[0138] The above-mentioned CO2-triggered delayed crosslinking agent is used in CO2 flooding or CO2 single-well huff and puff in oil fields.

[0139] The above-mentioned CO2-triggered delayed crosslinking system is applied in CO2 flooding or CO2 single-well huff and puff in oil fields.

[0140] Example 2

[0141] A method for preparing a CO2-triggered delayed crosslinking agent includes the following steps:

[0142] (1) Dissolve 10g of succinaldehyde and 25g of sodium bisulfite in 140g of water in a reactor and carry out an addition reaction while continuously bubbling in air. After the reaction is completed, the reaction solution is obtained.

[0143] (2) The reaction solution obtained in step (1) is subjected to vacuum distillation to remove water. At the same time, a large amount of inorganic salt (sodium sulfate) is precipitated in the reaction solution of the reactor. The residue after distillation in the reactor is extracted three times with 35g of extractant. The inorganic salt is filtered off, and the extract is collected. Then, the extract is distilled under normal pressure to remove the extractant. Finally, the product is placed in a vacuum oven to dry. After drying, the CO2-triggered delayed crosslinking agent is obtained, wherein:

[0144] The structure of succinyl aldehyde is as follows:

[0145] Where: n is 2;

[0146] The structural formula of the CO2-triggered delayed crosslinking agent is as follows:

[0147]

[0148] Where n is 2.

[0149] Furthermore, the reaction temperature of the addition reaction in step (1) is 20°C and the reaction time is 2 hours.

[0150] Furthermore, the extractant in step (2) is methanol.

[0151] The above-mentioned CO2-triggered delayed crosslinking agent is used in CO2 flooding or CO2 single-well huff and puff in oil fields.

[0152] The above-mentioned CO2-triggered delayed crosslinking system is applied in CO2 flooding or CO2 single-well huff and puff in oil fields.

[0153] Example 3

[0154] A method for preparing a CO2-triggered delayed crosslinking agent includes the following steps:

[0155] (1) Dissolve 5g of octanedialdehyde and 8g of sodium bisulfite in 50g of distilled water in a reactor and carry out an addition reaction while continuously bubbling in air. After the reaction is completed, the reaction solution is obtained.

[0156] (2) The reaction solution obtained in step (1) is subjected to vacuum distillation to remove water. At the same time, a large amount of inorganic salt (sodium sulfate) is precipitated in the reaction solution of the reactor. The residue after distillation in the reactor is extracted twice with 17g of extractant. The inorganic salt is filtered off, and the extract is collected. Then, the extract is distilled under normal pressure to remove the extractant. Finally, the product is placed in a vacuum oven to dry. After drying, the CO2-triggered delayed crosslinking agent is obtained, wherein:

[0157] The structure of octanedialdehyde is as follows:

[0158] Where: n is 6;

[0159] The structural formula of the CO2-triggered delayed crosslinking agent is as follows:

[0160]

[0161] Where n is 6.

[0162] Furthermore, the reaction temperature of the addition reaction in step (1) is 30°C and the reaction time is 1 hour.

[0163] Further, the extractant in step (2) is propyl isopropanol.

[0164] The above-mentioned CO2-triggered delayed crosslinking agent is used in CO2 flooding or CO2 single-well huff and puff in oil fields.

[0165] The above-mentioned CO2-triggered delayed crosslinking system is applied in CO2 flooding or CO2 single-well huff and puff in oil fields.

[0166] Example 4

[0167] A method for preparing a CO2-triggered delayed crosslinking agent includes the following steps:

[0168] (1) Dissolve 7.2g hexamethylenedialdehyde and 14g sodium bisulfite in 100g distilled water in a reactor and carry out an addition reaction while continuously bubbling in air. After the reaction is completed, the reaction solution is obtained.

[0169] (2) The reaction solution obtained in step (1) is subjected to vacuum distillation to remove water. At the same time, a large amount of inorganic salt (sodium sulfate) is precipitated in the reaction solution of the reactor. The residue after distillation in the reactor is extracted at least twice with 28g of extractant. The inorganic salt is filtered out, and the extract is taken. Then the extract is distilled under normal pressure to remove the extractant. Finally, the product is placed in a vacuum oven to dry. After drying, the CO2-triggered delayed crosslinking agent is obtained, wherein:

[0170] The structure of adipaldehyde is as follows:

[0171] Where: n is 4;

[0172] The structural formula of the CO2-triggered delayed crosslinking agent is as follows:

[0173]

[0174] Where n is 4.

[0175] Furthermore, the reaction temperature of the addition reaction in step (1) is 20°C and the reaction time is 2 hours.

[0176] Furthermore, the extractant in step (2) is acetone.

[0177] The above-mentioned CO2-triggered delayed crosslinking agent is used in CO2 flooding or CO2 single-well huff and puff in oil fields.

[0178] The above-mentioned CO2-triggered delayed crosslinking system is applied in CO2 flooding or CO2 single-well huff and puff in oil fields.

[0179] Example 5

[0180] A method for preparing a CO2-triggered delayed crosslinking agent includes the following steps:

[0181] (1) Dissolve 6.4g glutaraldehyde and 14g sodium bisulfite in 100g distilled water in a reactor and carry out an addition reaction while continuously bubbling in air. After the reaction is completed, the reaction solution is obtained.

[0182] (2) The reaction solution obtained in step (1) is subjected to vacuum distillation to remove water. At the same time, a large amount of inorganic salt (sodium sulfate) is precipitated in the reaction solution of the reactor. The residue after distillation in the reactor is extracted twice with 20g of extractant. The inorganic salt is filtered off, and the extract is collected. Then, the extract is distilled under normal pressure to remove the extractant. Finally, the product is placed in a vacuum oven to dry. After drying, the CO2-triggered delayed crosslinking agent is obtained, wherein:

[0183] The structure of glutaraldehyde is as follows:

[0184] Where: n is 3;

[0185] The structural formula of the CO2-triggered delayed crosslinking agent is as follows:

[0186]

[0187] Where n is 3.

[0188] Furthermore, the reaction temperature of the addition reaction in step (1) is 25°C and the reaction time is 2 hours.

[0189] Furthermore, the extractant in step (2) is acetone.

[0190] The above-mentioned CO2-triggered delayed crosslinking agent is used in CO2 flooding or CO2 single-well huff and puff in oil fields.

[0191] The above-mentioned CO2-triggered delayed crosslinking system is applied in CO2 flooding or CO2 single-well huff and puff in oil fields.

[0192] To characterize the structural features of the CO2-triggered delayed crosslinking agent prepared in Example 3, the CO2-triggered delayed crosslinking agent synthesized in Example 5 was subjected to 1H NMR spectroscopy. The results are as follows: Figure 1 As shown. From Figure 1It can be seen that the product prepared in Example 5 is Where n = 3.

[0193] To characterize the synthesized CO2-triggered delayed crosslinking agent, a CO2-triggered delayed crosslinking system was prepared by combining the CO2-triggered delayed crosslinking agent synthesized in Example 5 with polyacrylamide and an appropriate amount of water. Viscosities at different concentrations before and after CO2 contact were tested, and the results are shown in Table 1. As can be seen from Table 1, with increasing mass concentration, the viscosity of the system before CO2 response did not change significantly across the entire concentration range, while the viscosity of the CO2-triggered delayed crosslinking system increased substantially after the response.

[0194] Table 1. Viscosity changes of crosslinked products before and after CO2 contact.

[0195]

[0196] The embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments, and various changes can be made within the scope of knowledge possessed by those skilled in the art without departing from the spirit of the present invention.

Claims

1. A CO2-triggered delayed crosslinking system, characterized in that, Composed of a CO2-triggered delayed crosslinking agent, polyacrylamide, and water, wherein, by mass percentage, the CO2-triggered delayed crosslinking agent accounts for 0.5-1%, the polyacrylamide accounts for 0.5-1%, and the balance is water, wherein: The structural formula of the CO2-triggered delayed crosslinking agent is as follows: Where n is 2 to 8.

2. The application of a CO2-triggered delayed crosslinking agent in CO2 flooding or CO2 single-well huff and puff in oilfields, characterized in that, The structural formula of the CO2-triggered delayed crosslinking agent is as follows: Where n is 2 to 8; The preparation method of the CO2-triggered delayed crosslinking agent includes the following steps: (1) A certain amount of dialdehyde and sodium bisulfite were dissolved in water in a reactor and an addition reaction was carried out while air was continuously bubbled in. After the reaction was completed, a reaction solution was obtained. (2) The reaction solution obtained in step (1) is subjected to vacuum distillation to remove water. The residue after distillation in the reactor is extracted at least twice with an appropriate amount of extractant. Inorganic salts are filtered out, and the extract is collected. The extract is then distilled under normal pressure to remove the extractant. Finally, the product is dried under vacuum. After drying, the CO2-triggered delayed crosslinking agent is obtained, wherein: The structure of the dialdehyde is as follows: Where n is 2 to 8.

3. The application as described in claim 2, characterized in that, The molar ratio of the dialdehyde and the sodium bisulfite is 1:(2-2.3).

4. The application as described in claim 2, characterized in that, The amount of water used in step (1) is 3 to 8 times the sum of the masses of the dialdehyde and the sodium bisulfite, by mass.

5. The application as described in claim 2, characterized in that, The reaction temperature of the addition reaction in step (1) is 20-30°C and the reaction time is 1-3 hours.

6. The application as described in claim 2, characterized in that, The extractant mentioned in step (2) is one of acetone, methanol, and isopropanol.

7. The application as described in claim 6, characterized in that, The extractant in step (2) is acetone.

8. The application as described in claim 2, characterized in that, By mass, the amount of extractant used in step (2) is 3 to 5 times the amount of the dialdehyde.

9. The application of the CO2-triggered delayed crosslinking system as described in claim 1 in CO2 flooding or CO2 single-well huff and puff in oil fields.

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