Preparation method of acid slick water based on betaine surfactant

Abstract

The invention belongs to the technical field of oil field reservoir exploitation, and discloses a preparation method of acid slick water based on a betaine surfactant. The preparation method comprises the following steps: adding N, N-di-n-alkylamine, 2-chloroethanol and a sodium hydroxide solution into a flask, reacting at 80-90 DEG C, and removing redundant 2-chloroethanol in a product to obtain an intermediate I; and adding the intermediate I into the flask, heating, slowly adding maleic anhydride into the flask, reacting at 80-85 DEG C, and drying the product to obtain the betaine surfactant drag reducer. And adding the drag reducer into water, stirring, adding the clay stabilizer and the cleanup additive, and uniformly dissolving to obtain the acid slick water based on the betaine surfactant. According to the acid slick water, acid fracturing is carried out without additional acid liquid, the acid betaine surfactant firstly forms wormlike micelles, the wormlike micelles reach a target reservoir, gel breaking is carried out, then the wormlike micelles are hydrolyzed to generate maleic acid, gradient release of the acid liquid can be achieved, far-end fracture steering is better facilitated, and the acid fracturing effect is enhanced.

Description

Technical Field

[0001] The invention relates to the technical field of oilfield reservoir exploitation, and in particular to a method for preparing acidic slick water based on betaine surfactant. Background Art

[0002] At present, my country's unconventional oil and gas reservoirs account for a large proportion of resource reserves and have rich resource potential. However, due to the difficulty of mining, a large amount of resources cannot be used. The domestic demand for oil resources continues to expand, and the exploration and development of unconventional oil and gas layers is imminent. Shale gas reservoirs have the characteristics of poor physical properties, small throat radius, small porosity, and low permeability. Therefore, in the process of shale gas reservoir exploration and development, it is often necessary to adopt hydraulic fracturing and other production-increasing measures to increase the output of shale gas wells. When fracturing shale reservoirs, the fracturing fluid needs to enter the natural fractures of the formation. On the basis of forming a certain number of main fractures, more natural fractures are connected through its own filtration effect, thereby forming 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. It can form a more complex formation fracture network and become the main construction method for unconventional reservoirs.

[0003] Slickwater fracturing fluid system has been widely used in major oil fields at home and abroad. At present, the research on slickwater fracturing fluid mainly focuses on the optimization of drag reducers. In the case of large-volume injection, drag reducers are added to slickwater to achieve large-volume pumping, which can make up for the problems of low water viscosity and poor sand carrying capacity. However, the existing drag reducers generally have the problems of 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. Acid fracturing technology relies on the dissolution of acid to corrode the wall of the crack into an uneven surface, improve its pore structure, and improve the conductivity of the supporting crack, thereby improving the production increase effect of fracturing. The general acidic slickwater fracturing fluid is a "acid + slickwater" combined fracturing mode, which is not conducive to the diversion of the distal crack and affects the fracturing effect. Summary of the invention

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

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

[0006] The first aspect of the present invention provides a method for preparing acidic slippery water based on betaine surfactant, comprising the following steps:

[0007] S1: Add a certain amount of N,N-di-n-alkylamine, 2-chloroethanol and alkali solution into a flask and stir evenly. The molar ratio of 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;

[0008] S2: Add intermediate I into a flask and heat it at 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;

[0009] 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.

[0010] 2-Chloroethanol undergoes a nucleophilic substitution reaction with N,N-di-n-alkylamine in the reaction. The chloride ion (Cl-) in 2-chloroethanol is a leaving group. In the presence of a base, the hydroxyethyl part of 2-chloroethanol will be connected to N,N-di-n-alkylamine, thereby obtaining an amine intermediate containing a hydroxyethyl group. The base acts as a catalyst in this reaction. It can promote the departure of the chloride ion in 2-chloroethanol and generate a nucleophilic alkoxy anion, which is beneficial to the reaction.

[0011] Furthermore, in S1, the alkyl carbon chain length of the N,N-di-n-alkylamine is 12-22.

[0012] Preferably, the N,N-di-n-alkylamine is N,N-di-n-dodecylamine, N,N-di-n-octadecylamine, or N,N-di-n-docosylamine.

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

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

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

[0016] The second aspect of the present invention provides the use of the acidic slick water based on betaine surfactant in oil field fracturing.

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

[0018] 1. The acidic slick water of the present invention is used for acid fracturing without adding an acid liquid. The acidic betaine surfactant provided in the preparation process first forms worm-like micelles, which are then hydrolyzed to generate maleic acid after reaching the target reservoir and breaking the micelles. This can realize the step-by-step release of the acid liquid, is more conducive to the diversion of the distal fractures, and enhances the effect of acid fracturing.

[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, good viscosity increasing and drag reducing capabilities, and can significantly improve the sand carrying capacity and drag reducing performance of the slippery water system.

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

[0021] 4. The acidic slick water prepared by the present invention has strong acidity and can be used to create cracks by acid corrosion. The present invention is of great significance for increasing the production of oil and gas reservoirs. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of the preparation mechanism of the drag reducing agent of the present invention;

[0023] Figure 2 Schematic diagram of the acid release mechanism in the acidic slippery water of the present invention. DETAILED DESCRIPTION

[0024] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0025] Example 1

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

[0027] (2) 0.001 mol of the intermediate was added to a flask and heated to 75° C., and then 0.0023 mol of maleic anhydride was slowly added to the flask, and the reaction was carried out at 85° C. for 2.5 h. Finally, the product was vacuum dried to obtain a drag reducer.

[0028] (3) 0.2 wt% of the drag reducer is added into a proper amount of water and stirred, and then 0.5 wt% of polyepichlorohydrin-diethanolamine and 0.5 wt% of nonylphenol polyoxyethylene ether are gradually added, and the mixture is stirred and dissolved to obtain an acidic slippery water based on a betaine surfactant.

[0029] Example 2

[0030] The difference from Example 1 is that the amount of drag reducing agent used in step (3) is 2 wt%.

[0031] Example 3

[0032] (1) Add 0.001 mol N,N-di-n-dodecylamine, 1 mol 2-chloroethanol and 3.3 ml 0.3 mol / L potassium hydroxide solution into a flask and stir evenly. React at 80°C for 36 hours, and then remove excess 2-chloroethanol in the product by rotary evaporation to obtain an intermediate.

[0033] (2) 0.001 mol of the intermediate was added to a flask and heated to 80° C., and then 0.0022 mol of maleic anhydride was slowly added to the flask, and the reaction was carried out at 80° C. for 2 h. Finally, the product was vacuum dried to obtain a drag reducer.

[0034] (3) 0.2 wt % of drag reducer is added into a proper amount of water and stirred, and then 0.3 wt % of polyepichlorohydrin-diethanolamine and 0.4 wt % of nonylphenol polyoxyethylene ether are gradually added, and the mixture is stirred and dissolved to obtain an acidic slippery water based on betaine surfactant.

[0035] Example 4

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

[0037] (2) 0.001 mol of the intermediate was added to a flask and heated to 80° C., and then 0.0025 mol of maleic anhydride was slowly added to the flask, and the reaction was carried out at 85° C. for 3 h. Finally, the product was vacuum dried to obtain a drag reducer.

[0038] (3) 2 wt % of the drag reducer is added into a proper amount of water and stirred, and then 1 wt % of polyepichlorohydrin-diethanolamine and 0.8 wt % of nonylphenol polyoxyethylene ether are gradually added, and the mixture is stirred and dissolved to obtain an acidic slippery water based on a betaine surfactant.

[0039] Example 5

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

[0041] (2) 0.001 mol of the intermediate was added to a flask and heated to 80° C., and then 0.0023 mol of maleic anhydride was slowly added to the flask, and the reaction was carried out at 85° C. for 3 h. Finally, the product was vacuum dried to obtain a drag reducer.

[0042] (3) 1.0 wt% of the drag reducer is added into a proper amount of water and stirred, and then 0.5 wt% of potassium chloride and 0.6 wt% of dodecyl alcohol polyoxyethylene ether are gradually added, and the mixture is stirred and dissolved to obtain an acidic slippery water based on a betaine surfactant.

[0043] Example 6

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

[0045] (2) 0.001 mol of the intermediate was added to a flask and heated to 80° C., and then 0.0024 mol of maleic anhydride was slowly added to the flask, and the reaction was carried out at 85° C. for 3 h. Finally, the product was vacuum dried to obtain a drag reducer.

[0046] (3) 0.5 wt % of the drag reducer is added into a proper amount of water and stirred, and then 0.4 wt % of ammonium chloride and 0.7 wt % of ethanol are gradually added, and the mixture is stirred and dissolved to obtain an acidic slippery water based on a betaine surfactant.

[0047] Performance Testing

[0048] In order to characterize the performance of the acidic slick 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, the acidic slick water based on betaine surfactant prepared by the present invention has good drag reduction performance and viscosity increasing performance, and can achieve good results when using a lower concentration of betaine surfactant. Comparing Example 1 and Example 2, it can be seen that the viscoelastic betaine surfactant can significantly increase the viscosity and drag reduction performance of the system. When the dosage is as low as 0.2wt%, the slick water 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, the acidic slick water based on betaine surfactant prepared by the present invention has strong acidity and the ability of acid fracturing, which can further improve the production capacity of oil and gas fields and is of great significance to the increase in production of oil and gas reservoirs.

[0053] The above contents are 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 method for preparing 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 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; 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 method for preparing acidic slippery water based on betaine surfactant according to claim 1, characterized in that: In S1, the alkyl carbon chain length of the N,N-di-n-alkylamine is 12-22.

3. The method for preparing acidic slippery water 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.

4. The method for preparing 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.

5. The method for preparing acidic slippery water based on betaine surfactant according to claim 1, characterized in that: The clay stabilizer is one or more of polyepichlorohydrin-diethanolamine, ammonium chloride and potassium chloride.

6. The method for preparing acidic slippery water based on betaine surfactant according to claim 1, characterized in that: The drainage aid is one or more than two of nonylphenol polyoxyethylene ether, dodecanol polyoxyethylene ether, ethanol and butanol.

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

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