Preparation method of acidic slickwater based on betaine surfactant

Abstract

The present invention belongs to the technical field of oilfield reservoir exploitation, and discloses a preparation method of acidic slickwater based on betaine surfactant. Add N,N-dialkylamine, 2-chloroethanol and sodium hydroxide solution into a flask, react at 80-90 °C, and remove the excess 2-chloroethanol in the product to obtain intermediate I; heat intermediate I in the flask, slowly add maleic anhydride into the flask, react at 80-85 °C, and dry the product to obtain a betaine surfactant drag reducer; add the drag reducer into water and stir, then add a clay stabilizer and a flowback aid, and dissolve evenly to obtain acidic slickwater based on betaine surfactant. The acidic slickwater of the present invention does not use externally added acid solution for acid fracturing. The acidic betaine surfactant first forms worm-like micelles, and then hydrolyzes to generate maleic acid after breaking the gel at the target reservoir, which can realize the cascade release of acid solution, is more conducive to the diversion of distal fractures, and enhances the acid fracturing effect.

Description

Technical Field

[0001] The present invention relates to the technical field of oilfield reservoir exploitation, and particularly relates to a preparation method of acidic slickwater based on betaine surfactant. Background Art

[0002] At present, the reserves of unconventional oil and gas reservoir resources in China account for a relatively large proportion, with rich resource potential. However, due to the difficult exploitation, a large amount of resources cannot be utilized. With the continuous expansion of domestic oil resource demand, the exploration and development of unconventional oil and gas reservoirs are imminent. Shale gas reservoirs have characteristics such as poor physical properties, small throat radius, small porosity, and low permeability. Therefore, during the exploration and development of shale gas reservoirs, stimulation measures such as hydraulic fracturing are often required to increase the production of shale gas wells. When fracturing shale reservoirs, fracturing fluid needs to enter the natural fractures in the formation. On the basis of forming a certain number of main fractures, more natural fractures are connected through its own filtration effect, so as to form a large number of fracture networks to improve the reservoir seepage area. The slickwater fracturing fluid system has the characteristics of large displacement, low sand ratio, and high pump pressure, and can form a more complex formation fracture network, becoming the main construction method for unconventional reservoirs.

[0003] The slickwater fracturing fluid system has been widely used in major oilfields at home and abroad. At present, the research on slickwater fracturing fluid mainly focuses on the optimization of drag reducers. Under the condition of large displacement injection, drag reducers are added to the slickwater to achieve large displacement pumping, which can make up for problems such as low water viscosity and poor sand-carrying capacity. However, the existing drag reducers generally have problems such as low sand-carrying capacity and poor drag reduction performance. In addition, with the continuous development of shale gas resources, more requirements are put forward for the performance of slickwater fracturing fluid. The acid fracturing technology relies on the dissolution of acid fluid to corrode the wall surface of the fracture into an uneven surface, improve its pore structure, and enhance the conductivity of the propped fracture, thereby improving the stimulation effect of fracturing. Generally, the general acidic slickwater fracturing fluid is a combined fracturing mode of "acid fluid + slickwater", which is not conducive to the diversion of distal fractures and affects the fracturing effect. Summary of the Invention

[0004] In order to overcome the above-mentioned disadvantages of the prior art, the purpose of the present invention is to provide a preparation method of acidic slickwater based on betaine surfactant, which overcomes the problems of low sand-carrying capacity and poor drag reduction performance of traditional slickwater fracturing fluid, and effectively combines the acid fracturing technology to provide a more feasible solution for productivity improvement.

[0005] In order to achieve the above purpose, the present invention adopts the following technical solutions to implement:

[0006] The first aspect of the present invention provides a preparation method of acidic slickwater based on betaine surfactant, including the following steps:

[0007] S1: Add a certain amount of N,N-dialkylamine, 2-chloroethanol and an alkali solution into a flask and stir evenly. The molar ratio of N,N-dialkylamine, 2-chloroethanol and the alkali is 1:(100 - 120):(1 - 1.1). React at 80 - 90 °C for 36 - 40 h, and then remove the excess 2-chloroethanol in the product by rotary evaporation to obtain intermediate Ⅰ;

[0008] S2: Heat intermediate Ⅰ in a flask to 75 - 80 °C, and then slowly add a certain amount of maleic anhydride into the flask. The molar ratio of intermediate Ⅰ and maleic anhydride is 1:(2.2 - 2.5). React at 80 - 85 °C for 2 - 3 h, and finally vacuum dry the product to obtain a betaine surfactant drag reducer;

[0009] S3: Add the drag reducer into an appropriate amount of water and stir, then gradually add a clay stabilizer and a drainage aid, and stir well until dissolved evenly to obtain an acidic slickwater based on betaine surfactant. By mass percentage, the drag reducer accounts for 0.2 - 2.0 wt%, the clay stabilizer accounts for 0.3 - 1.0 wt%, the drainage aid accounts for 0.4 - 0.8 wt%, and the rest is water.

[0010] In the reaction, 2-chloroethanol undergoes a nucleophilic substitution reaction with N,N-dialkylamine. The chloride ion (Cl-) in 2-chloroethanol is the leaving group. In the presence of an alkali, the hydroxyethyl part of 2-chloroethanol will be attached to N,N-dialkylamine, thus obtaining an amine intermediate containing a hydroxyethyl group. The alkali acts as a catalyst in this reaction. It can promote the departure of the chloride ion in 2-chloroethanol and simultaneously generate a nucleophilic alkoxide anion, which is beneficial to the progress of the reaction.

[0011] Further, in S1, the alkyl carbon chain length of the N,N-dialkylamine is 12 - 22.

[0012] Preferably, the N,N-dialkylamine is N,N-didodecylamine, N,N-dioctadecylamine, N,N-didocosylamine.

[0013] Further, the alkali is sodium hydroxide or potassium hydroxide, and the concentration of its solution is 0.3 - 0.33 mol / L

[0014] Further, the clay stabilizer is one or more of polyepichlorohydrin-diethanolamine, ammonium chloride, potassium chloride.

[0015] Further, the drainage aid is one or more of nonylphenol polyoxyethylene ether, dodecanol polyoxyethylene ether, ethanol, butanol.

[0016] The second aspect of the present invention is to provide the application of the acidic slickwater based on betaine surfactant in oilfield fracturing.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] 1. The acidic slickwater of the present invention performs acid fracturing without adding external acid solution. During the preparation process, the acidic betaine surfactant forms worm-like micelles first, and after breaking the gel at the target reservoir, it hydrolyzes to generate maleic acid, which can realize the cascade release of acid solution, is more conducive to the diversion of distal fractures, and enhances the acid fracturing effect.

[0019] 2. The betaine surfactant prepared by the present invention is a viscoelastic surfactant, which easily forms worm-like micelles in water, making its aqueous solution have excellent viscoelasticity, and has good thickening and drag reduction capabilities, and can significantly improve the sand-carrying capacity and drag reduction performance of the slickwater system.

[0020] 3. The present invention prepares an acidic viscoelastic betaine surfactant as a drag reducer, and prepares an acidic slickwater with a certain proportion of clay stabilizer and drainage aid, effectively enhancing the performance of the slickwater fracturing fluid.

[0021] 4. The acidic slickwater prepared by the present invention has strong acidity, can use the acid solution to corrode and create fractures, and the present invention has important significance for the production increase of oil and gas reservoirs. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a schematic diagram of the preparation mechanism of the drag reducer described in the present invention;

[0023] Figure 2 is a schematic diagram of the acid release mechanism in the acidic slickwater described in the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0024] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0025] Example 1

[0026] (1) Add 0.001 mol of N,N-didodecylamine, 1.1 mol of 2-chloroethanol and 3.3 ml of sodium hydroxide solution with a concentration of 0.3 mol / L into a flask, stir evenly, react at 85 °C for 38 h, and then remove the excess 2-chloroethanol in the product by rotary evaporation to obtain an intermediate.

[0027] (2) Add 0.001 mol of the intermediate into a flask and heat it to 75 °C. Then slowly add 0.0023 mol of maleic anhydride into the flask and react at 85 °C for 2.5 h. Finally, vacuum dry the product to obtain the drag reducer.

[0028] (3) Add 0.2 wt% of the drag reducer into an appropriate amount of water and stir. Then gradually add 0.5 wt% of polyepichlorohydrin - diethanolamine and 0.5 wt% of nonylphenol polyoxyethylene ether, and stir well until dissolved uniformly to obtain an acidic slickwater based on betaine surfactant.

[0029] Example 2

[0030] The difference from Example 1 is that the dosage of the drag reducer in step (3) is 2 wt%.

[0031] Example 3

[0032] (1) Add 0.001 mol of N,N - didodecylamine, 1 mol of 2 - chloroethanol and 3.3 ml of potassium hydroxide solution with a concentration of 0.3 mol / L into a flask, stir evenly, react at 80 °C for 36 h, and then remove the excess 2 - chloroethanol in the product by rotary evaporation to obtain the intermediate.

[0033] (2) Add 0.001 mol of the intermediate into a flask and heat it to 80 °C. Then slowly add 0.0022 mol of maleic anhydride into the flask and react at 80 °C for 2 h. Finally, vacuum dry the product to obtain the drag reducer.

[0034] (3) Add 0.2 wt% of the drag reducer into an appropriate amount of water and stir. Then gradually add 0.3 wt% of polyepichlorohydrin - diethanolamine and 0.4 wt% of nonylphenol polyoxyethylene ether, and stir well until dissolved uniformly to obtain an acidic slickwater based on betaine surfactant.

[0035] Example 4

[0036] (1) Add 0.001 mol of N,N - didodecylamine, 1.2 mol of 2 - chloroethanol and 3.3 ml of sodium hydroxide solution with a concentration of 0.33 mol / L into a flask, stir evenly, react at 90 °C for 40 h, and then remove the excess 2 - chloroethanol in the product by rotary evaporation to obtain the intermediate.

[0037] (2) Add 0.001 mol of the intermediate into a flask and heat it to 80 °C. Then slowly add 0.0025 mol of maleic anhydride into the flask and react at 85 °C for 3 h. Finally, vacuum dry the product to obtain the drag reducer.

[0038] (3) Add 2 wt% of the drag reducer to an appropriate amount of water and stir. Then gradually add 1 wt% of polyepichlorohydrin - diethanolamine and 0.8 wt% of nonylphenol polyoxyethylene ether, and stir well until dissolved uniformly to obtain an acidic slippery water based on betaine surfactant.

[0039] Example 5

[0040] (1) Add 0.001 mol of N,N - didodecylamine, 1.1 mol of 2 - chloroethanol, and 3.3 ml of sodium hydroxide solution with a concentration of 0.32 mol / L to a flask and stir evenly. React at 85 °C for 40 h, and then remove the excess 2 - chloroethanol in the product by rotary evaporation to obtain an intermediate.

[0041] (2) Add 0.001 mol of the intermediate to a flask and heat to 80 °C. Then slowly add 0.0023 mol of maleic anhydride to the flask, react at 85 °C for 3 h, and finally dry the product under vacuum to obtain the drag reducer.

[0042] (3) Add 1.0 wt% of the drag reducer to an appropriate amount of water and stir. Then gradually add 0.5 wt% of potassium chloride and 0.6 wt% of dodecyl alcohol polyoxyethylene ether, and stir well until dissolved uniformly to obtain an acidic slippery water based on betaine surfactant.

[0043] Example 6

[0044] (1) Add 0.001 mol of N,N - didocosylamine, 1.1 mol of 2 - chloroethanol, and 3.3 ml of sodium hydroxide solution with a concentration of 0.3 mol / L to a flask and stir evenly. React at 85 °C for 40 h, and then remove the excess 2 - chloroethanol in the product by rotary evaporation to obtain an intermediate.

[0045] (2) Add 0.001 mol of the intermediate to a flask and heat to 80 °C. Then slowly add 0.0024 mol of maleic anhydride to the flask, react at 85 °C for 3 h, and finally dry the product under vacuum to obtain the drag reducer.

[0046] (3) Add 0.5 wt% of the drag reducer to an appropriate amount of water and stir. Then gradually add 0.4 wt% of ammonium chloride and 0.7 wt% of ethanol, and stir well until dissolved uniformly to obtain an acidic slippery water based on betaine surfactant.

[0047] Performance test

[0048] In order to characterize the performance of an acidic slippery water based on betaine surfactant of the present invention, its apparent viscosity, drag reduction rate, and pH value after gel breaking at 80 °C were evaluated. The performance test results are shown in Table 1.

[0049] Table 1

[0050]

[0051]

[0052] As can be seen from Table 1, an acidic slickwater based on betaine surfactant prepared by the present invention all has good drag reduction performance and viscosity increasing performance, and can achieve good effects when using a relatively low concentration of betaine surfactant. By comparing Example 1 and Example 2, it can be seen that viscoelastic betaine surfactant can significantly increase the system viscosity and drag reduction performance. When the dosage is as low as 0.2 wt%, the slickwater system can still maintain good drag reduction performance and viscosity increasing performance. Increasing the dosage can significantly increase its viscosity and enhance its sand-carrying performance. In addition, an acidic slickwater based on betaine surfactant prepared by the present invention all has strong acidity and has the ability of acid fracturing, which can further improve the production capacity of oil and gas fields and is of great significance for increasing the production of oil and gas reservoirs.

[0053] The above content is only to illustrate the technical idea of the present invention and cannot be used to limit the protection scope of the present invention. Any modification made on the basis of the technical solution according to the technical idea proposed by the present invention falls within the protection scope of the claims of the present invention.

Claims

1. A preparation method of an acidic slippery water based on betaine surfactant, characterized in that, The following steps are involved: S1: Add a certain amount of N,N-di-n-alkylamine, 2-chloroethanol and alkali solution into a flask and stir evenly, wherein the molar ratio of the N,N-di-n-alkylamine, 2-chloroethanol and alkali is 1:100-120:1-1.1, react at 80-90°C for 36-40h, and then remove excess 2-chloroethanol in the product by rotary evaporation to obtain intermediate I, wherein the alkyl carbon chain length of the N,N-di-n-alkylamine is 12-22; S2: Add intermediate I into a flask and heat to 75-80°C, then slowly add a certain amount of maleic anhydride into the flask, the molar ratio of intermediate I to maleic anhydride is 1:2.2-2.5, react at 80-85°C for 2-3h, and finally vacuum dry the product to obtain a betaine surfactant drag reducer; S3: Add the drag reducer into a proper amount of water and stir, then gradually add the clay stabilizer and drainage aid, stir and dissolve evenly to obtain an acidic slippery water based on betaine surfactant, in which, by mass percentage, the drag reducer accounts for 0.2-2.0wt%, the clay stabilizer accounts for 0.3-1.0wt%, the drainage aid accounts for 0.4-0.8wt%, and the rest is water.

2. The preparation method of the acidic slickwater based on betaine surfactant according to claim 1, characterized in that, The N,N-di-n-alkylamine is N,N-di-n-dodecylamine, N,N-di-n-octadecylamine, and N,N-di-n-behenylamine.

3. The preparation method of the acidic slippery water based on betaine surfactant according to claim 1, characterized in that, The alkali is sodium hydroxide or potassium hydroxide, and the concentration of the solution is 0.3-0.33 mol / L.

4. The preparation method of the acidic slickwater based on betaine surfactant according to claim 1, wherein, The clay stabilizer is one or more of polyepichlorohydrin-diethanolamine, ammonium chloride and potassium chloride.

5. The preparation method of the acidic slippery water based on betaine surfactant according to claim 1, wherein, The drainage aid is one or more than two of nonylphenol polyoxyethylene ether, dodecanol polyoxyethylene ether, ethanol and butanol.

6. Use of the acidic slick water based on betaine surfactant according to any one of claims 1 to 5 in oil field fracturing.

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