Thickening agent as well as preparation method and application thereof

Abstract

The invention provides a thickening agent as well as a preparation method and application thereof. The thickening agent is prepared from acrylamide, acrylic acid long-chain ester and dichloromethyl (1-methyl ethylene) benzene, the thickening agent can be self-crosslinked under the acidic condition, the use of a cross-linking agent can be avoided, and the thickening agent can be self-crosslinked in the stratum under the acidic condition, so that the thickening effect can be achieved in the stratum, and the thickening effect is good. And the acidizing fracturing fluid can be prevented from being reduced along with the rise of the temperature in the stratum.

Description

Technical Field

[0001] The present invention belongs to the technical field of preparation and application of functional thickeners, and in particular relates to a thickener and a preparation method and application thereof. Background Art

[0002] Carbonate reservoir development plays a crucial role in oil and gas exploration and development. This development relies heavily on acid fracturing technology, which presents new challenges due to the strong heterogeneity and poor connectivity of oil and gas reservoirs. To achieve optimal acid fracturing results, thickeners, as the most important additive in retarded acid fluids, have long been a research hotspot in oil and gas exploration and development.

[0003] Currently, conventional thickeners used in acid fracturing are primarily prepared by polymerizing acrylamide with other monomers. Early acrylamide-based thickeners had poor temperature resistance, resulting in rapid reaction between the acid and carbonate rock, and suboptimal acid fracturing results. To improve the effectiveness of acid fracturing, gelled acids with high mass fraction thickeners and cross-linked acids that increase viscosity through chemical crosslinking are generally used. However, the introduction of cross-linkers results in higher viscosity after mixing. Excessively high viscosity often makes pumping difficult, results in high friction resistance, and makes gel breaking difficult, causing significant damage to the reservoir. Furthermore, as formation temperature rises, viscosity decreases, resulting in poorer acid fracturing results later in the process.

[0004] Therefore, in order to solve the above problems, it is crucial to develop a low-viscosity, high-temperature-resistant thickener that can self-cross-link underground. Summary of the Invention

[0005] In order to solve the problems that existing thickeners for acid fracturing require additional addition of a crosslinking agent during preparation, the viscosity of the prepared liquid is high, and the viscosity decreases with increasing formation temperature, the present invention provides a thickener, a preparation method, and an application thereof.

[0006] The present invention is achieved through the following technical solutions: In a first aspect, the present invention provides a thickener, which is a polymer formed by polymerization of the following three repeating units:

[0007] Wherein, n is an integer from 11 to 17.

[0008] The structural formula of the thickener can be expressed as: .

[0009] Among them, a, b and c are the degrees of polymerization, the value range of a is 500~2500, the value range of b is 50~100, and the value range of c is 50~100.

[0010] The thickening principle of the thickener described in the present invention is mainly as follows: the pH value of the downhole environment in the oil field is generally 2-3. The thickener is used as a thickener for acid fracturing. Under acidic conditions downhole, the halogenated groups in the polymer molecules will generate aldehyde groups. Then, the aldehyde groups react with the amino groups of acrylamide in the polymer molecules to generate imines through nucleophilic reaction. The imines can be added to the amino groups of another polymer molecule to produce crosslinking. Therefore, after the thickener is used to prepare the acid fracturing fluid, because there is no crosslinking agent, it will not cause the viscosity of the acid fracturing fluid to be too high. However, after entering the formation, the thickener will undergo self-crosslinking under acidic conditions, thereby playing a thickening role. The reaction process of the self-crosslinking of the thickener of the present invention is as follows:

[0011] Secondly, the present invention introduces long hydrophobic chains into the polymer molecules through long-chain acrylic acid esters. As hydrophobic groups, these long hydrophobic chains aggregate, causing intermolecular association of the polymer molecules, increasing the fluid dynamics volume, and thus increasing the viscosity of the acid fracturing fluid. In addition, the long hydrophobic chains can also increase the side chains and temperature resistance of the polymer, thereby preventing the acid fracturing fluid from decreasing in the formation as the temperature increases.

[0012] In a second aspect, the present invention provides a method for preparing the thickener, comprising the following steps: (1) acrylamide, long-chain acrylic acid ester, emulsifier and first initiator are mixed and reacted under a protective atmosphere to obtain modified polyacrylamide; (2) Adding modified polyacrylamide, dichloromethyl (1-methylvinyl) benzene and a second initiator to a solvent, reacting under a protective atmosphere, and removing the solvent after the reaction is completed. The obtained polymer is the thickener.

[0013] The preparation method of the thickener of the present invention has the following reaction equation:

[0014] Preferably, in the preparation method of the thickener of the present invention, in step (1), the long-chain acrylic acid ester is one of lauryl acrylate, tetradecyl acrylate, hexadecyl acrylate and octadecyl acrylate.

[0015] Preferably, in the preparation method of the thickener of the present invention, in step (1), the mass ratio of acrylamide to long-chain acrylic acid ester is 1:(1-1.5), more preferably 1:(1.2-1.5).

[0016] Preferably, in the preparation method of the thickener of the present invention, in step (1), the reaction temperature is 40-70° C., and the reaction time is 2-5 h.

[0017] Preferably, in the preparation method of the thickener of the present invention, in step (1), the emulsifier is one of sodium lauryl sulfate, sodium lauryl sulfonate and sodium dodecylbenzene sulfonate, and the amount of the emulsifier is 10% to 20% of the mass of acrylamide.

[0018] Preferably, in the preparation method of the thickener of the present invention, in step (1), the first initiator is ammonium persulfate, potassium persulfate, hydrogen peroxide, or a combination of ammonium persulfate and sodium bisulfite, and the amount of the first initiator is 1% to 3% of the mass of acrylamide.

[0019] Preferably, in the preparation method of the thickener of the present invention, in step (2), the second initiator is ammonium persulfate, potassium persulfate, hydrogen peroxide, or a combination of ammonium persulfate and sodium bisulfite, and the amount of the second initiator is 0.5% to 1% of the mass of the modified polyacrylamide.

[0020] In the preparation method of the thickener of the present invention, the first initiator and the second initiator in step (1) and step (2) may be the same or different, and there is no particular limitation on this.

[0021] Preferably, in the preparation method of the thickener of the present invention, in step (2), the mass ratio of the modified polyacrylamide to dichloromethyl (1-methylvinyl) benzene is 1: (2-3).

[0022] Preferably, in the preparation method of the thickener of the present invention, in step (2), the reaction temperature is 50-70° C., and the reaction time is 3-4 h.

[0023] Preferably, in the preparation method of the thickener of the present invention, in step (2), the solvent can be N,N-dimethylformamide (DMF).

[0024] Preferably, in the method for preparing the thickener of the present invention, the protective atmosphere in step (1) and step (2) can be nitrogen (N2) or argon, preferably nitrogen.

[0025] In a third aspect, the present invention provides use of the thickener as a thickener in an oilfield acid fracturing process, wherein the pH value of the oilfield downhole environment is 2-3.

[0026] Compared with the prior art, the present invention has the following beneficial effects: First, the thickener of the present invention is highly sensitive to acidic conditions. When used in acidic fracturing fluids, the halogenated groups in the polymer molecules generate aldehyde groups under the acidic conditions of the formation. These aldehyde groups then undergo a nucleophilic reaction with the amino groups of acrylamide in the polymer molecules to form imines. The imines can then be added to the amino groups of other polymer molecules to produce crosslinks. This crosslinking process occurs gradually, avoiding the problem of excessive viscosity early in the process. Therefore, the thickener of the present invention can self-crosslink under acidic conditions, eliminating the need for a crosslinker. Without a crosslinker, the problem of excessive viscosity after the acidic fracturing fluid is eliminated. Furthermore, because the thickener can self-crosslink under acidic conditions in the formation, it can thicken the fluid in the formation. Secondly, the polymer molecules of the present invention contain long hydrophobic chains. When used in acid fracturing fluid, the polymer molecules aggregate under the action of hydrophobicity, causing intermolecular association of the polymer molecules, increasing the fluid dynamics volume, and thus increasing the viscosity of the acid fracturing fluid. The long hydrophobic chains can increase the side chains and temperature resistance of the polymer, thereby preventing the acid fracturing fluid from decreasing in the formation as the temperature increases.

[0027] The thickener preparation method of the present invention involves hydrophobically modifying acrylamide with a long-chain acrylic acid ester, followed by polymerization of the modified polyacrylamide with dichloromethyl (1-methylvinyl) benzene to obtain a polymer thickener. The thickener is obtained using conventional polymerization methods, has simple synthesis steps, and is suitable for large-scale production.

[0028] The thickener of the present invention can be used in acid fracturing fluid without the need for introducing a cross-linking agent. Therefore, the viscosity of the prepared fluid will not be too high. Under acidic conditions in the formation, the thickener undergoes self-cross-linking to achieve a thickening effect. In addition, the thickener has good temperature resistance and can still maintain a high viscosity after the formation temperature rises. The application effect is good and the agent is suitable for industrial applications in acid fracturing. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0030] Figure 1 This is the infrared spectrum of the thickener prepared in Example 6. DETAILED DESCRIPTION

[0031] To help those skilled in the art understand the features and effects of the present invention, the following provides a general description and definition of the terms and expressions used in this specification. Unless otherwise indicated, all technical and scientific terms used herein have the ordinary meanings understood by those skilled in the art regarding the present invention. In the event of conflict, the definitions in this specification shall prevail.

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

[0033] All features, such as values, amounts, contents, and concentrations, described herein as numerical ranges or percentage ranges are provided for simplicity and convenience only. Accordingly, the description of numerical ranges or percentage ranges should be considered to include and specifically disclose all possible subranges and individual values ​​within the range (including integers and fractions).

[0034] In this document, for the sake of brevity, not all possible combinations of the various technical features in each embodiment or example are described. Therefore, as long as there are no contradictions in the combination of these technical features, the various technical features in each embodiment or example can be combined in any way, and all possible combinations should be considered to be within the scope of this specification.

[0035] Below in conjunction with specific embodiment, further set forth the present invention.Should be understood that these embodiments are only used to illustrate the present invention and are not used in limiting the scope of the present invention.In addition, should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall equally within the scope limited by the appended claims of the application.

[0036] The following examples were prepared using conventional instruments and equipment in the art. Experimental methods in the following examples, where specific conditions are not specified, were generally performed under conventional conditions or according to the conditions recommended by the manufacturer. The various raw materials used in the following examples, unless otherwise specified, were conventional commercially available products, with specifications conventional in the art. In the present specification and the following examples, unless otherwise specified, "%" indicates mass percentage, and "ratio" indicates mass ratio.

[0037] Example 1 (1) Weigh 50g acrylamide and 50g lauryl acrylate, add them into a three-necked flask, pass nitrogen protection, raise the temperature to 40℃, add 5g sodium lauryl sulfate and 0.5g potassium persulfate, react for 2h, stop the reaction, and obtain modified polyacrylamide.

[0038] (2) Weigh 30 g of modified polyacrylamide and 60 g of dichloromethyl (1-methylvinyl) benzene, put them into a three-necked flask, add 100 mL of solvent DMF, pass N2 protection, add 0.15 g of potassium persulfate, react at 50 ° C for 3 h, and rotary evaporate to obtain a thickener.

[0039] Example 2 (1) Weigh 50g acrylamide and 75g tetradecyl acrylate, add them into a three-necked flask, pass nitrogen protection, heat to the reaction temperature of 70℃, add 10g sodium dodecylsulfonate and 1.5g ammonium persulfate, react for 5h, stop the reaction, and obtain modified polyacrylamide.

[0040] (2) Weigh 30 g of modified polyacrylamide and 90 g of dichloromethyl (1-methylvinyl) benzene, add them into a three-necked flask, add 100 mL of solvent DMF, pass N2 protection, add 0.3 g of ammonium persulfate, react at 70 ° C for 4 h, and rotary evaporate to obtain a thickener.

[0041] Example 3 (1) Weigh 50g acrylamide and 65g hexadecyl acrylate, add them into a three-necked flask, pass nitrogen protection, heat to the reaction temperature of 50℃, add 7.5g sodium dodecylbenzenesulfonate and 1g hydrogen peroxide, react for 4h, stop the reaction, and obtain modified polyacrylamide.

[0042] (2) Weigh 30 g of modified polyacrylamide and 75 g of dichloromethyl (1-methylvinyl) benzene, add them into a three-necked flask, add 100 mL of solvent DMF, pass N2 protection, add 0.24 g of hydrogen peroxide, react at 60 ° C for 3.5 h, and rotary evaporate to obtain a thickener.

[0043] Example 4 (1) Weigh 50 g of acrylamide and 70 g of octadecyl acrylate, add them into a three-necked flask, pass nitrogen protection, heat to the reaction temperature of 60 ° C, add 6.5 g of sodium dodecyl sulfate and 0.75 g of a combination of ammonium persulfate and sodium bisulfite (the mass ratio of ammonium persulfate to sodium bisulfite is 1:1), react for 5 h, stop the reaction, and obtain modified polyacrylamide.

[0044] (2) Weigh 30 g of modified polyacrylamide and 66 g of dichloromethyl (1-methylvinyl) benzene, add them into a three-necked flask, add 100 mL of solvent DMF, pass N2 protection, add 0.18 g of a combination of ammonium persulfate and sodium bisulfite (the mass ratio of ammonium persulfate to sodium bisulfite is 1:1), react at 55 ° C for 4 h, and rotary evaporate to obtain a thickener.

[0045] Example 5 (1) Weigh 50 g of acrylamide and 60 g of octadecyl acrylate, add them into a three-necked flask, pass nitrogen protection, heat to the reaction temperature of 55 ° C, add 9 g of sodium dodecylsulfonate and 1.25 g of a combination of ammonium persulfate and sodium bisulfite (the mass ratio of ammonium persulfate to sodium bisulfite is 1:1), react for 3 h, stop the reaction, and obtain modified polyacrylamide.

[0046] (2) Weigh 30 g of modified polyacrylamide and 84 g of dichloromethyl (1-methylvinyl) benzene, add them into a three-necked flask, add 100 mL of solvent DMF, pass N2 protection, add 0.27 g of potassium persulfate, react at 65 ° C for 3 h, and rotary evaporate to obtain a thickener.

[0047] Example 6 (1) Weigh 50g acrylamide and 75g hexadecyl acrylate, add them into a three-necked flask, pass nitrogen protection, raise the temperature to 50℃, add 7.5g sodium lauryl sulfate and 1.5g ammonium persulfate, react for 5h, stop the reaction, and obtain modified polyacrylamide.

[0048] (2) Weigh 30 g of modified polyacrylamide and 90 g of dichloromethyl (1-methylvinyl) benzene, add them into a three-necked flask, add 100 mL of solvent DMF, pass N2 protection, add 0.18 g of ammonium persulfate, react at 50 ° C for 3.5 h, and rotary evaporate to obtain a thickener.

[0049] In order to characterize the structure of the synthesized thickener, the thickener prepared in Example 6 was subjected to infrared testing. The results are as follows: Figure 1 As shown. Figure 1 It can be seen that at 3353 cm -1 The stretching vibration absorption peak of the NH bond appears at 2939 cm -1 The stretching vibration absorption peak of the saturated CH bond appears at 1724 cm -1 The stretching vibration absorption peak of C=O bond appears at 1650 cm -1 and 1562 cm -1 The stretching vibration absorption peak of the benzene ring carbon skeleton appears at 1396 cm -1 The bending vibration absorption peak of the C-H bond appears at 1188 cm -1 The stretching vibration absorption peak of the C-Cl bond appears at the position, indicating that the thickener molecule of the present invention is successfully synthesized.

[0050] To characterize the performance of the synthesized thickener, the viscosity of the thickener prepared in Example 6 was tested at different pH values ​​and temperatures. The results are shown in Tables 1 and 2 below. As can be seen from the data in Table 1, the viscosity of the synthesized thickener first increases slowly and then sharply with decreasing pH. This is because, under the influence of acidic conditions, the halogenated groups in the structure become aldehyde groups, which further self-crosslink, increasing the viscosity of the system. When the pH value continues to decrease to around 2-3, the viscosity change remains stable, indicating that the emulsion-type thickener for acid fracturing is highly sensitive to acidic conditions and can be used in environments with a pH of around 2-3. As can be seen from Table 2, the viscosity of the thickener does not change much with increasing temperature, indicating that the thickener has good temperature resistance.

[0051] Table 1 Viscosity data of the thickener prepared in Example 6 at different pH values

[0052] Table 2 Viscosity data of the thickener prepared in Example 6 at different temperatures

[0053] The above content is only for explaining the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A thickener, characterized in that: The thickener is a polymer formed by polymerization of the following three repeating units: Wherein, n is an integer from 11 to 17.

2. The method for preparing the thickener according to claim 1, characterized in that: The following steps are involved: (1) acrylamide, a long-chain acrylic acid ester, an emulsifier and a first initiator are mixed and reacted under a protective atmosphere to obtain a modified polyacrylamide; the long-chain acrylic acid ester is ; (2) Adding modified polyacrylamide, dichloromethyl (1-methylvinyl) benzene and a second initiator to a solvent, reacting under a protective atmosphere, and removing the solvent after the reaction is completed to obtain a thickener.

3. The method for preparing a thickener according to claim 2, wherein: In step (1), the long-chain acrylic acid ester is one of lauryl acrylate, tetradecyl acrylate, hexadecyl acrylate and octadecyl acrylate.

4. The method for preparing a thickener according to claim 2, wherein: In step (1), the mass ratio of acrylamide to long-chain acrylic acid ester is 1:(1-1.5).

5. The method for preparing a thickener according to claim 2, wherein: In step (1), the reaction temperature is 40-70°C and the reaction time is 2-5 hours.

6. The method for preparing a thickener according to claim 2, wherein: In step (1), the emulsifier is one of sodium dodecyl sulfate, sodium dodecyl sulfonate and sodium dodecylbenzene sulfonate, and the amount of the emulsifier is 10% to 20% of the mass of acrylamide.

7. The method for preparing a thickener according to claim 2, wherein: In step (1), the first initiator is ammonium persulfate, potassium persulfate, hydrogen peroxide, or a combination of ammonium persulfate and sodium bisulfite, and the amount of the first initiator is 1% to 3% of the mass of the acrylamide; in step (2), the second initiator is ammonium persulfate, potassium persulfate, hydrogen peroxide, or a combination of ammonium persulfate and sodium bisulfite, and the amount of the second initiator is 0.5% to 1% of the mass of the modified polyacrylamide.

8. The method for preparing a thickener according to claim 2, wherein: In step (2), the mass ratio of the modified polyacrylamide to dichloromethyl (1-methylvinyl) benzene is 1: (2-3).

9. The method for preparing a thickener according to claim 2, wherein: In step (2), the reaction temperature is 50-70°C and the reaction time is 3-4 hours.

10. Use of the thickener according to claim 1 as a thickener in an oil field acid fracturing process.

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