Heat-resistant thickener and preparation method thereof, clean fracturing fluid

Abstract

The invention discloses a heat-resistant thickener and a preparation method thereof, clean fracturing fluid, and relates to the technical field of fracturing fluid. The heat-resistant thickener is prepared by the following method: take N, N-dimethyl-1,3-diaminopropane and dissolve, under the condition of deoxygenation, methyl acrylate is added and reacted, after the reaction is completed, small molecule alcohol amine is added and continued to react, after the reaction is completed, it is separated and purified to obtain an intermediate; take the intermediate and dissolve, add long-chain alkyl halide and acid binding agent and continue to react, after the reaction is completed, it is separated and purified to obtain a thickener. The thickener of the present invention has strong heat resistance, and will degrade and break gel after being kept warm for several days to tens of days under high temperature conditions, so that the viscosity of the fracturing fluid decreases rapidly, and its degradation time is controllable, and a suitable thickener can be selected according to the well soaking time, which can meet the fracturing and well soaking requirements in the actual production process.

Description

Technical Field

[0001] The invention relates to the technical field of fracturing fluids, and in particular to a temperature-resistant thickener and a preparation method thereof, and clean fracturing fluid. Background Art

[0002] With the in-depth development of tight reservoirs and shale reservoirs, fracturing operations have received more and more attention. The main component of fracturing fluid is thickener. At present, conventional thickeners include natural plant gum and synthetic polymer as thickeners. However, whether it is natural plant gum or synthetic polymer, even if a breaker is added to the fracturing fluid, the breaking of the gel is still incomplete, which will cause the tiny cracks in the formation to be blocked and the fracturing effect to be greatly reduced.

[0003] To this end, existing technicians have proposed the use of clean fracturing fluid for fracturing. Clean fracturing fluid mainly refers to fracturing fluid that does not require gel breaking and is basically harmless to the formation. It either uses some self-degradable polymers as thickeners or uses a surfactant system as a thickener. However, although the existing clean fracturing fluid system has a certain viscosity, its temperature resistance is poor. Under high temperature conditions, its viscosity drops rapidly, making it difficult to apply to high temperature oil reservoirs; at the same time, the existing clean fracturing fluid system has a relatively large addition amount and a high cost. Summary of the invention

[0004] In view of the above technical problems, the purpose of the present invention is to provide a temperature-resistant thickener and a preparation method thereof, and a clean fracturing fluid to address the defects of the prior art. The thickener has good temperature resistance and causes less damage to the reservoir.

[0005] The present invention adopts the following technical scheme: a preparation method of a heat-resistant thickener, characterized in that it comprises the following steps: taking N, N-dimethyl-1, 3-diaminopropane and dissolving it, under the condition of deoxygenation, dripping methyl acrylate and reacting, after the reaction is completed, dripping small-molecule alcohol amine to continue the reaction, after the reaction is completed, separating and purifying it to obtain an intermediate; taking the intermediate and dissolving it, adding a long-chain alkyl halide and an acid binding agent at 50-70°C and continuing the reaction for 10-25 hours, after the reaction is completed, separating and purifying it to obtain a thickener; the molar ratio of the N, N-dimethyl-1, 3-diaminopropane, methyl acrylate and small-molecule alcohol amine is 1:2-2.2:2-2.2; the molar ratio of the intermediate and the long-chain alkyl halide is 1:1-1.1, and the carbon chain length of the long-chain alkyl halide is 16-20.

[0006] In the present invention, the following reactions mainly occur:

[0007]

[0008] In the formula, the carbon chain length of R1 is 2~3, and the carbon chain length of R2 is 16~20.

[0009] For the above reaction, two methyl propionate groups are grafted on the terminal primary amine of N,N-dimethyl-1,3-diaminopropane by Michael addition reaction in the first step, and then small molecule alcohol amine is grafted by amine transesterification reaction in the second step, and quaternary ammonium is generated by the reaction of alkyl halide and tertiary amine in the third step. For long-chain alkyl halide, when the carbon chain length is controlled to be 16-20, it has a better effect; in particular, when the long-chain alkyl halide is chlorooctadecane, the effect is better; the acid binding agent is one of organic bases or inorganic bases, such as sodium hydroxide, potassium hydroxide, sodium ethoxide, etc., and the amount of the acid binding agent added is not less than the molar amount of the long-chain alkyl halide.

[0010] One embodiment of the present invention is that the solvent of the N,N-dimethyl-1,3-diaminopropane is one of methanol or ethanol, and the solvent of the intermediate is ethylene glycol. These solvents can dissolve the corresponding raw materials, and those skilled in the art can also select other solvents.

[0011] One embodiment of the present invention is that the small molecule alcohol amine is one of ethanolamine and isopropanolamine. These are common small molecule alcohol amines in the art; other small molecule alcohol amines, such as 2-amino-n-butanol, isobutanolamine, etc., although they can also be applied to the present invention, their effects are relatively poor.

[0012] One embodiment of the present invention is that during the preparation of the intermediate, the reaction temperature is 15-40°C, the reaction time when methyl acrylate is added dropwise is 4-10 hours, and the reaction time when a small molecule alcohol amine is added dropwise is 6-15 hours. During the preparation of the intermediate, the Michael addition reaction of the primary amine and methyl acrylate occurs first, and then the amine transesterification reaction occurs. During the Michael addition reaction, due to its small molecular weight and the fact that N,N-dimethyl-1,3-diaminopropane itself has a certain alkalinity, it can react at room temperature without a catalyst. Although the reaction can increase the temperature, it is known to those skilled in the art that too high a temperature will lead to too fast and incomplete reaction, and the yield is low; at the same time, it can also be achieved by ice bathing, but the reaction time is longer, which can reach more than 72 hours. During the reaction of amine transesterification, it also belongs to a more conventional reaction mode. Compared with Michael addition, its reaction speed is slower, so the reaction time will be appropriately extended.

[0013] One embodiment of the present invention is that the separation and purification operation of the intermediate is to dry under reduced pressure at room temperature to remove low boiling points. As described above, the separation and purification method is relatively simple by adopting the reaction conditions in this embodiment, and only requires drying under reduced pressure at room temperature to obtain the intermediate.

[0014] In one embodiment of the present invention, the thickener is separated and purified by filtering out the liquid phase, then washing the solid phase several times with a detergent and drying the solid phase, wherein the detergent is one of ethanol and ethylene glycol. This is to separate and purify the final product by utilizing its solubility characteristics, and those skilled in the art can select other detergents according to actual conditions.

[0015] In one embodiment of the present invention, the long-chain alkyl halide is octadecane chloride, the acid-binding agent is an organic base or an inorganic base, and the amount of the acid-binding agent added is not less than the molar amount of the long-chain alkyl halide.

[0016] Another object of the present invention is to disclose a temperature-resistant thickener, which is prepared by any of the above methods.

[0017] Another object of the present invention is to disclose a clean fracturing fluid, which comprises water, the above-mentioned temperature-resistant thickener and a counter-ion compound, wherein the addition amount of the temperature-resistant thickener is 1.5-3wt%, and the addition amount of the counter-ion compound is 0.25-1.0wt%.

[0018] An embodiment of the present invention is that the counter ion compound is one of salicylic acid and its salt, and potassium chloride.

[0019] The beneficial effects of the present invention are:

[0020] The thickener of the present invention has strong temperature resistance. At the same time, it will degrade and break after being kept warm for several days to dozens of days under high temperature conditions, so that the viscosity of the fracturing fluid decreases rapidly. The degradation time is controllable, and a suitable thickener can be selected according to the soaking time, which can meet the fracturing and soaking requirements in the actual production process. DETAILED DESCRIPTION

[0021] In order to have a clearer understanding of the technical features, purposes and beneficial effects of the present invention, the technical scheme of the present invention is described in detail below in conjunction with embodiments, but it should not be construed as limiting the applicable scope of the present invention.

[0022] In the following embodiments, unless otherwise specified, the operations described are routine operations in the art.

[0023] In the following examples, unless otherwise specified, all raw materials used are conventional commercial products in the art.

[0024] Example 1: Preparation of a heat-resistant thickener: 10.2 g of N,N-dimethyl-1,3-diaminopropane was dissolved in 100 ml of ethanol, and nitrogen was introduced for deoxygenation for 30 min at 30° C. with continuous stirring. Then, 18 g of methyl acrylate was added dropwise. After the addition was completed, the reaction was continued for 6 h. After the reaction was completed, 13 g of ethanolamine was added dropwise. After the addition was completed, the reaction was continued for 8 h. After the reaction was completed, it was dried under reduced pressure at room temperature to obtain an intermediate;

[0025] Take 16.6 g of the intermediate prepared above and add ethylene glycol to dissolve it, and add 2.1 g of sodium hydroxide. At 55°C and under continuous stirring, add 14.5 g of chlorooctadecane dropwise, followed by reaction for 12 hours. After the reaction is completed, filter out the liquid phase, wash the solid phase with ethanol several times and then dry it.

[0026] Example 2: 10.2 g of N, N-dimethyl-1, 3-diaminopropane was dissolved in 100 ml of ethanol, and nitrogen was introduced for deoxygenation for 30 min at 30 ° C with continuous stirring, and then 18 g of methyl acrylate was added dropwise. After the addition was completed, the reaction was continued for 6 h. After the reaction was completed, 15.5 g of isopropanolamine was continued to be added dropwise. After the addition was completed, the reaction was continued for 12 h. After the reaction was completed, it was dried under reduced pressure at room temperature to obtain an intermediate;

[0027] Take 17.3 g of the intermediate prepared above and add ethylene glycol to dissolve it, and add 2.1 g of sodium hydroxide. At 65°C and under continuous stirring, add 15.0 g of octadecane bromide dropwise, followed by reaction for 20 hours. After the reaction is completed, filter out the liquid phase, wash the solid phase with ethylene glycol several times, and then dry it.

[0028] Example 3: 10.2 g of N,N-dimethyl-1,3-diaminopropane was dissolved in 100 ml of ethylene glycol, and nitrogen was introduced for deoxygenation for 30 min at 30° C. with continuous stirring. Then, 18 g of methyl acrylate was added dropwise. After the addition was completed, the reaction was continued for 6 h. After the reaction was completed, 18.5 g of 2-amino-n-butanol was added dropwise. After the addition was completed, the reaction was continued for 14 h. After the reaction was completed, it was dried under reduced pressure at room temperature to obtain an intermediate;

[0029] Take 18.0 g of the intermediate prepared above and add ethanol to dissolve it, and add 2.1 g of sodium hydroxide. At 60°C and under continuous stirring, add 15.0 g of chlorooctadecane dropwise, followed by reaction for 15 hours. After the reaction is completed, filter out the liquid phase, wash the solid phase with ethanol several times and then dry it.

[0030] Comparative Example 1

[0031] Take 10.2 g of N, N-dimethyl-1, 3-diaminopropane and dissolve it in 100 ml of ethanol. At 30°C and under continuous stirring, introduce nitrogen to deoxygenate for 30 min. Then, add 18 g of methyl acrylate dropwise. After the addition is complete, continue to react for 6 h. After the reaction is completed, continue to add 13 g of ethanolamine dropwise. After the addition is complete, continue to react for 8 h. After the reaction is completed, dry it under reduced pressure at room temperature to obtain an intermediate.

[0032] Take 13.7 g of the intermediate prepared above and add ethylene glycol to dissolve it, and add 2.1 g of sodium hydroxide. At 55°C and under continuous stirring, add 14.5 g of chlorooctadecane dropwise, followed by reaction for 12 hours. After the reaction is completed, filter out the liquid phase, wash the solid phase with ethanol several times and then dry it.

[0033] Comparative Example 2

[0034] Take 10.2 g of N, N-dimethyl-1, 3-diaminopropane and dissolve it in 100 ml of ethanol. At 30°C and under continuous stirring, introduce nitrogen to deoxygenate for 30 min. Then, add 18 g of methyl acrylate dropwise. After the addition is complete, continue to react for 6 h. After the reaction is completed, continue to add 13 g of ethanolamine dropwise. After the addition is complete, continue to react for 8 h. After the reaction is completed, dry it under reduced pressure at room temperature to obtain an intermediate.

[0035] Take 16.6 g of the intermediate prepared above and add ethylene glycol to dissolve it, and add 2.1 g of sodium hydroxide. At 55°C and under continuous stirring, add 13.0 g of dodecane bromide dropwise, followed by reaction for 12 hours. After the reaction is completed, filter out the liquid phase, wash the solid phase with ethanol several times and then dry it.

[0036] Example 4: 1000 g of water was added to a liquid preparation tank, and the thickener prepared in the above examples and comparative examples and 0.8 wt % of sodium salicylate were added and dissolved under continuous stirring, wherein the amount of the thickener added was 1.5-3 wt %.

[0037] Example 5: 1000 g of water was added to a liquid preparation tank, and the thickeners prepared in the above examples and comparative examples and 0.4 wt % of potassium chloride were added and dissolved under continuous stirring, wherein the amount of the thickener added was 1.5-3 wt %.

[0038] In order to further illustrate the performance of the thickener prepared by the present invention, specific tests are used to illustrate it below.

[0039] 1. Viscosity test

[0040] The thickeners of Examples 1 to 3 and Comparative Examples 1 to 2 were prepared into fracturing fluids according to the method of Example 4 or Example 5. The fracturing fluids were stirred at a temperature of 100° C. and a shear rate of 170 s. -1The apparent viscosity was recorded under the conditions of shearing for different times. The final results are shown in Table 1.

[0041] Table 1 Viscosity test table

[0042]

[0043] In Table 1, “——” indicates that the viscosity is lower than 50 mPa·s.

[0044] It can be seen from Table 1 that the thickener prepared in the embodiment of the present invention can cooperate with the counterions to form viscoelastic micelles under relatively low concentration conditions, so that the fracturing fluid has a relatively high viscosity; it can also be seen from Table 1 that after 2 hours of shearing, at an addition amount of 1.5-3wt%, the fracturing fluid prepared with the thickener prepared in the embodiment of the present invention has a viscosity greater than 50mPa·s, indicating that the thickener in the embodiment of the present invention has certain stability and shear resistance under high temperature conditions.

[0045] As shown in Comparative Example 1, the raw material ethanolamine has a great influence on the performance of the thickener. When no ethanolamine is added, the viscosity is low. This may be because when the ethanolamine is not used to modify it, its hydrophilicity is poor, resulting in a low viscosity of the final product.

[0046] As shown in Comparative Example 2, the carbon chain length of the long-chain alkyl halide has a great influence on its performance.

[0047] 2. Stability test

[0048] The thickeners of Examples 1 to 3 and Comparative Examples 1 to 2 were prepared into fracturing fluids according to the method of Example 4 or Example 5, and aged for a period of time under different temperature conditions. The apparent viscosity was measured every 1 d, and the change of the apparent viscosity was recorded. The final results are shown in Tables 2 and 3.

[0049] Table 2 Stability test results at 80℃

[0050]

[0051] Table 3 100℃ stability test results

[0052]

[0053] It can be seen from Table 2 and Table 3 that the thickeners of the embodiments of the present invention will degrade after aging for a period of time under high temperature conditions, and thickeners with different degradation times can be prepared according to actual conditions.

[0054] Referring to Comparative Example 1, it can be seen that its viscosity decreases rapidly under reservoir conditions. In fact, the inventors have found through repeated tests that the thickener of Comparative Example 1 drops to below 50 mPa·s in just 28 hours at 80°C, and drops to below 20 mPa·s in just 34 hours; at 100°C, it drops to below 50 mPa·s in just 6 hours, and drops to below 20 mPa·s in just 12 hours.

[0055] As can be seen from Comparative Example 2, its temperature resistance is relatively poor.

[0056] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the embodiments of the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for preparing a temperature-resistant thickener, characterized in that: The following steps are involved: Take N,N-dimethyl-1,3-diaminopropane and dissolve it, add methyl acrylate dropwise under deoxygenation conditions and react, add small molecule alcohol amine dropwise to continue the reaction after the reaction is completed, separate and purify it to obtain an intermediate; take the intermediate and dissolve it, add long-chain alkyl halide and acid binding agent at 50-70° C. and continue the reaction for 10-25 hours, separate and purify it to obtain a thickener after the reaction is completed; the molar ratio of the N,N-dimethyl-1,3-diaminopropane, methyl acrylate and small molecule alcohol amine is 1:2-2.2:2-2.2; the molar ratio of the intermediate and the long-chain alkyl halide is 1:1-1.1, and the carbon chain length of the long-chain alkyl halide is 16-20; the small molecule alcohol amine is one of ethanolamine and isopropanolamine.

2. The method according to claim 1, characterized in that The solvent of the N,N-dimethyl-1,3-diaminopropane is one of methanol and ethanol, and the solvent of the intermediate is ethylene glycol.

3. The method according to claim 1, characterized in that During the preparation of the intermediate, the reaction temperature is 15-40° C., the reaction time when methyl acrylate is added dropwise is 4-10 hours, and the reaction time when a small molecule alcohol amine is added dropwise is 6-15 hours.

4. The method according to claim 1, characterized in that: The separation and purification operation of the intermediate is to dry it at room temperature under reduced pressure to remove low boiling substances.

5. The method according to claim 1, characterized in that The separation and purification operation of the thickener is: filtering out the liquid phase, then washing the solid phase with a detergent for several times and drying the solid phase, wherein the detergent is one of ethanol or ethylene glycol.

6. The method according to claim 1, characterized in that The long-chain alkyl halide is octadecane chloride, the acid-binding agent is an organic base or an inorganic base, and the amount of the acid-binding agent added is not less than the molar amount of the long-chain alkyl halide.

7. A temperature-resistant thickener, characterized in that: The method is prepared by any one of claims 1 to 6.

8. A clean fracturing fluid, characterized in that: It comprises water, the heat-resistant thickener as claimed in claim 7 and a counter-ion compound, wherein the addition amount of the heat-resistant thickener is 1.5-3wt%, and the addition amount of the counter-ion compound is 0.2-1.0wt%; and the counter-ion compound is one of salicylic acid and its salt, and potassium chloride.

Images