Clean fracturing fluid

Abstract

The invention discloses a clean fracturing fluid, and relates to the technical field of fracturing fluids. The clean fracturing fluid comprises water and a micromolecular thickening agent, and a preparation method of the micromolecular thickening agent comprises the following steps: taking N, N '-dihydroxyethyl-1, 3-propane diamine and dissolving, dropwise adding a first monomer and reacting under a deoxygenization condition, dropwise adding alkyl primary amine and continuing reacting after the reaction is finished, and separating and purifying after the reaction is finished to obtain the micromolecular thickening agent. The fracturing fluid disclosed by the invention has relatively high temperature resistance, and can be degraded and broken after being subjected to heat preservation for several days to dozens of days under a high-temperature condition, so that the viscosity of the fracturing fluid is quickly reduced, the soaking time of the fracturing fluid is controllable, and the fracturing and soaking requirements in the actual production process can be met.

Description

Technical Field

[0001] The invention relates to the technical field of fracturing fluid, and in particular to a 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 clean fracturing fluid to address the defects of the prior art. The clean fracturing fluid has good temperature resistance and causes less damage to the reservoir.

[0005] The present invention adopts the following technical scheme: a clean fracturing fluid, comprising water and a small molecule thickener, wherein the preparation method of the small molecule thickener comprises the following steps: Take N,N'-dihydroxyethyl-1,3-propylenediamine and dissolve it, add a first monomer dropwise under deoxygenation conditions and react, add an alkyl primary amine dropwise after the reaction is completed and continue the reaction, separate and purify it after the reaction is completed; the first monomer is one of methyl acrylate or methyl methacrylate, the molar ratio of the N,N'-dihydroxyethyl-1,3-propylenediamine, the first monomer and the alkyl primary amine is 1:2-2.2:2-2.2; the carbon chain length of the alkyl primary amine is 8-14.

[0006] In the preparation process of the small molecule thickener, when the first monomer is methyl acrylate, the following reactions mainly occur:

[0007] Wherein, R is an alkyl group with a carbon chain length of 8 to 14.

[0008] The above reaction is essentially a reaction that imitates the preparation process of dendrimers. In the first step, two methyl propionate groups are grafted onto the terminal primary amine of N,N'-dihydroxyethyl-1,3-propylenediamine through Michael addition reaction, and then in the second step, an alkyl group with a longer carbon chain length is grafted through amine ester exchange reaction. For alkyl primary amines, after a large number of experiments, the inventors found that when the carbon chain length is 8 to 14, the obtained product has a better effect. Whether the carbon chain length is longer or shorter, it will have an adverse effect on the final product.

[0009] The small molecule thickener prepared above has good temperature resistance and thickening performance. At the same time, it will self-degrade after being maintained under reservoir conditions for a period of time, so that the fracturing fluid of the present invention is a clean fracturing fluid, which is more in line with the actual working conditions. In actual use, common fracturing fluid components such as bactericides, drainage aids, clay stabilizers, etc. can also be added to the fracturing fluid.

[0010] In one embodiment of the present invention, the carbon chain length of the alkyl primary amine is 10 to 12. Under this condition, the obtained product has better performance and only needs a smaller amount to form worm-like micelles to achieve the purpose of viscosity increase. However, since decylamine is toxic, the alkyl primary amine is more preferably dodecylamine.

[0011] One embodiment of the present invention is that the reaction temperature is 15~40℃, the reaction time when the first monomer is added dropwise is 4~10h, and the reaction time when the alkyl primary amine is added dropwise is 10~24h. In fact, for the present invention, there are many reaction modes, for example, when the first monomer is added dropwise, an ice bath can be used, but its defect is that the reaction time will be greatly extended, which can reach more than 72h; there are also reaction conditions of 50℃ or even higher, and its reaction conditions are relatively rapid, but the controllability is poor; when the alkyl primary amine is added dropwise, an inorganic base can also be added as a catalyst, such as sodium hydroxide, etc., which can greatly shorten the reaction time, but its separation and purification steps are relatively cumbersome, and the yield of the final product is relatively low. Therefore, the reaction conditions provided in this embodiment are only one of the more suitable reaction conditions, and those skilled in the art can select different reaction conditions according to actual conditions.

[0012] Furthermore, the separation and purification operation is drying under reduced pressure at room temperature to remove low-boiling point materials or solvents. As described above, using the reaction conditions in this embodiment, the separation and purification method is relatively simple, and only requires drying under reduced pressure at room temperature.

[0013] One embodiment of the present invention is that the solvent for dissolving the N,N'-dihydroxyethyl-1,3-propylenediamine is one of methanol and ethanol. These are common solvents in the art and have good solubility for all the raw materials in the present invention.

[0014] One embodiment of the present invention is that the alkyl primary amine is prepared into a solution before dropwise addition, and the solvent of the solution is methanol or ethanol. For primary amines with a slightly longer carbon chain length, such as tetradecylamine, it is solid at room temperature, so it can be dissolved before dropwise addition.

[0015] One embodiment of the present invention is that the addition amount of the small molecule thickener is 2-4wt%. When the addition amount is within this range, it has a higher viscosity and can also be quickly degraded within a certain period of time.

[0016] One embodiment of the present invention is that the pH of the clean fracturing fluid is 8 to 14. This can be achieved by adding a pH adjuster, such as sodium carbonate or sodium hydroxide.

[0017] The beneficial effects of the present invention are as follows: the fracturing fluid of the present invention has strong temperature resistance, and will degrade and break after being kept warm for several to dozens of days under high temperature conditions, so that the viscosity of the fracturing fluid decreases rapidly, and its self-degradation time is controllable, which can meet the fracturing and well soaking requirements in the actual production process. DETAILED DESCRIPTION

[0018] 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.

[0019] In the following embodiments, unless otherwise specified, the operations described are routine operations in the art.

[0020] In the following examples, unless otherwise specified, all raw materials used are conventional commercial products in the art.

[0021] Example 1: Take 16.2 g of N,N'-dihydroxyethyl-1,3-propylenediamine and dissolve it in 150 mL of ethanol. At 30°C and under continuous stirring, introduce nitrogen to deoxygenate for 30 minutes, then add 17.6 g of methyl acrylate dropwise. After the addition is complete, continue to react for 6 hours. After the reaction is completed, continue to add 38.8 g of dodecylamine dropwise. After the addition is complete, continue to react for 15 hours. After the reaction is completed, dry it under reduced pressure at room temperature to obtain the small molecule thickener GWC-1.

[0022] Add 1000g of water into the liquid preparation tank, add a certain amount of small molecule thickener and dissolve it under continuous stirring, and then add sodium carbonate to adjust the pH to 10.

[0023] Example 2: Take 16.2 g of N,N'-dihydroxyethyl-1,3-propylenediamine and dissolve it in 150 mL of ethanol. At 20°C and under continuous stirring, introduce nitrogen to deoxygenate for 30 minutes, then add 17.6 g of methyl acrylate dropwise. After the addition is complete, continue to react for 8 hours. After the reaction is completed, continue to add 32.0 g of n-decylamine dropwise. After the addition is complete, continue to react for 18 hours. After the reaction is completed, dry it under reduced pressure at room temperature to obtain the small molecule thickener GWC-2.

[0024] Add 1000g of water into the liquid preparation tank, add a certain amount of small molecule thickener and dissolve it under continuous stirring, and then add sodium carbonate to adjust the pH to 10.

[0025] Example 3: Take 16.2 g of N,N'-dihydroxyethyl-1,3-propylenediamine and dissolve it in 150 mL of ethanol. At 20°C and under continuous stirring, introduce nitrogen to deoxygenate for 30 minutes, then add 18.5 g of methyl acrylate dropwise. After the addition is complete, continue to react for 8 hours. After the reaction is completed, continue to add 27.2 g of n-octylamine dropwise. After the addition is complete, continue to react for 22 hours. After the reaction is completed, dry it under reduced pressure at room temperature to obtain the small molecule thickener GWC-3.

[0026] Add 1000g of water into the liquid preparation tank, add a certain amount of small molecule thickener and dissolve it under continuous stirring, and then add sodium carbonate to adjust the pH to 10.

[0027] Example 4: Take 16.2 g of N,N'-dihydroxyethyl-1,3-propylenediamine and dissolve it in 150 mL of ethanol. At 50°C and under continuous stirring, introduce nitrogen to deoxygenate for 30 minutes. Then, add 18.5 g of methyl acrylate dropwise. After the addition is complete, continue to react for 30 minutes. After the reaction is completed, continue to add 38.8 g of dodecylamine dropwise. After the addition is complete, continue to react for 60 minutes. After the reaction is completed, dry it under reduced pressure at room temperature to obtain thickener GWC-4.

[0028] Add 1000g of water into the liquid preparation tank, add a certain amount of small molecule thickener and dissolve it under continuous stirring, and then add sodium carbonate to adjust the pH to 10.

[0029] Comparative Example 1 Take 16.2 g of N,N'-dihydroxyethyl-1,3-propylenediamine and dissolve it in 150 mL of ethanol. At 30°C and under continuous stirring, introduce nitrogen to deoxygenate for 30 minutes. Then, add 17.6 g of methyl acrylate dropwise. After the addition is complete, continue to react for 6 hours. After the reaction is completed, continue to add 21.0 g of n-phenylamine dropwise. After the addition is complete, continue to react for 15 hours. After the reaction is completed, dry it under reduced pressure at room temperature to obtain the small molecule thickener DB-1.

[0030] Add 1000g of water into the liquid preparation tank, add a certain amount of small molecule thickener and dissolve it under continuous stirring, and then add sodium carbonate to adjust the pH to 10.

[0031] Comparative Example 2 Take 16.2 g of N,N'-dihydroxyethyl-1,3-propylenediamine and dissolve it in 150 mL of ethanol. At 30°C and under continuous stirring, introduce nitrogen to deoxygenate for 30 minutes. Then, add 17.6 g of methyl acrylate dropwise. After the addition is complete, continue to react for 6 hours. After the reaction is completed, continue to add 49.2 g of hexadecylamine dropwise. After the addition is complete, continue to react for 24 hours. After the reaction is completed, dry it under reduced pressure at room temperature to obtain thickener DB-2.

[0032] Add 1000g of water into the liquid preparation tank, add a certain amount of small molecule thickener and dissolve it under continuous stirring, and then add sodium carbonate to adjust the pH to 10.

[0033] Comparative Example 3 Take 16.2 g of N,N'-dihydroxyethyl-1,3-propylenediamine and dissolve it in 150 mL of ethanol. At 30°C and under continuous stirring, introduce nitrogen to deoxygenate for 30 minutes. Then, add 8.8 g of methyl acrylate dropwise. After the addition is complete, continue to react for 6 hours. After the reaction is completed, continue to add 16.5 g of dodecylamine dropwise. After the addition is complete, continue to react for 15 hours. After the reaction is completed, dry it under reduced pressure at room temperature to obtain the small molecule thickener DB-3.

[0034] Add 1000g of water into the liquid preparation tank, add a certain amount of small molecule thickener and dissolve it under continuous stirring, and then add sodium carbonate to adjust the pH to 10.

[0035] In order to further illustrate the performance of the fracturing fluid prepared by the present invention, specific tests are used to illustrate it below.

[0036] 1. Viscosity test Take the fracturing fluids of Examples 1 to 4 and Comparative Examples 1 to 3, and heat them at a temperature of 120°C and a shear rate of 170S -1 The apparent viscosity was recorded under the conditions of shearing for different times, and the final results are shown in Table 1. The time taken to heat to 120°C was 15 min.

[0037] Table 1 Viscosity test table

[0038] In Table 1, “——” indicates that the viscosity is lower than 50 mPa·s.

[0039] It can be seen from Table 1 that the thickener prepared in the embodiment of the present invention can form viscoelastic micelles under relatively low concentration conditions so that the fracturing fluid has a relatively high viscosity; at the same time, it can also be seen from Table 1 that after 2 hours of shearing, at an addition amount of 2-4 wt%, the fracturing fluid configured with the thickener prepared in the embodiment of the present invention has a viscosity greater than 50 mPa·s. This indicates that the thickener in the embodiment of the present invention has certain stability and shear resistance under high temperature conditions. At the same time, it can be seen from Table 1 that the viscosity of the thickener prepared in the embodiment of the present invention will recover after the shearing stops.

[0040] As can be seen from Comparative Examples 1 and 2, the carbon chain length of the alkyl primary amine has a great influence on its viscosity. At the same time, during the shearing process, the inventors found that after heating to 120°C, the viscosity of Comparative Example 1 could maintain the same viscosity for a short time (about 8 minutes), but then the viscosity dropped rapidly to about 1 mPa·s, and the temperature resistance was relatively poor; the viscosity of Comparative Example 3 was lower than 50 mPa·s throughout the test period.

[0041] 2. Stability test The fracturing fluids of Examples 1 to 4 and Comparative Example 1 were aged for a period of time under different temperature conditions, and their apparent viscosities were measured every 1 day, and the time points of changes in their apparent viscosities were recorded. The total test time was 50 days, and the final results are shown in Table 2. The amount of each thickener added was the mass concentration with a relatively higher viscosity in Test Example 1.

[0042] Table 2 Stability test results at 100°C

[0043] Table 3 120℃ stability test results

[0044] It can be seen from Table 2 and Table 3 that the thickener of the embodiment of the present invention will degrade after aging for a period of time under high temperature conditions, so that the viscosity of the fracturing fluid is reduced to less than 10mPa·s, and the viscosity after complete degradation is reduced to less than 5mPa·s, and thickeners with different degradation times can be prepared according to actual conditions, and the degradation time is controllable. After degradation, the viscosity drops rapidly. Referring to the thickener DB-2, it can be seen that it is difficult to hydrolyze under reservoir conditions, resulting in its viscosity being maintained at a high level during the entire test period, and it is difficult to break the gel, resulting in the difficulty of fracturing fluid backflow after the well is soaked.

[0045] 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 clean fracturing fluid, characterized in that: The invention comprises water and a small molecule thickener, and the preparation method of the small molecule thickener comprises the following steps: Take N,N'-dihydroxyethyl-1,3-propylenediamine and dissolve it, add a first monomer dropwise under deoxygenation conditions and react, add an alkyl primary amine dropwise after the reaction is completed and continue the reaction, separate and purify it after the reaction is completed; the first monomer is one of methyl acrylate or methyl methacrylate, the molar ratio of the N,N'-dihydroxyethyl-1,3-propylenediamine, the first monomer and the alkyl primary amine is 1:2-2.2:2-2.2; the carbon chain length of the alkyl primary amine is 8-14.

2. The clean fracturing fluid according to claim 1, characterized in that: The carbon chain length of the alkyl primary amine is 10-12.

3. The clean fracturing fluid according to claim 1, characterized in that: The reaction temperature is 15-40° C., the reaction time when the first monomer is added dropwise is 4-10 hours, and the reaction time when the alkyl primary amine is added dropwise is 10-24 hours.

4. The clean fracturing fluid according to claim 3, characterized in that: The separation and purification operation is drying under reduced pressure at room temperature to remove low boiling substances.

5. The clean fracturing fluid according to claim 1, characterized in that: The solvent for dissolving the N,N'-dihydroxyethyl-1,3-propylenediamine is one of methanol and ethanol.

6. The clean fracturing fluid according to claim 1, characterized in that: The alkyl primary amine is prepared into a solution before dropwise addition, and the solvent of the solution is methanol or ethanol.

7. The clean fracturing fluid according to claim 1, characterized in that: It is characterized in that The addition amount of the small molecule thickener is 2-4 wt %.

8. The clean fracturing fluid according to claim 1, characterized in that: The pH of the clean fracturing fluid is 8-14.

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