Flocculants for fracturing flowback fluid treatment

Abstract

This invention discloses a flocculant for treating fracturing flowback fluid, relating to the field of oilfield wastewater treatment technology. The flocculant comprises modified starch and organic acid. The preparation method of the modified starch includes the following steps: reacting allyl alcohol glycidyl ether with 1,4,7-trimethyldiethylenetriamine; after the reaction, separating and purifying to obtain an intermediate product; taking the intermediate product and dissolving it, adding an alkyl halide to perform a quaternization reaction; after the reaction, separating and purifying to obtain a cationic monomer; taking pregelatinized starch and dispersing it in water, then adding the cationic monomer, acrylamide, and an initiator to perform free radical polymerization; after the reaction, drying to obtain the final product. The flocculant for treating fracturing flowback fluid provided by this invention not only has strong salt resistance, making it suitable for the high-salt environment of fracturing flowback fluid, but also effectively removes oil, turbidity, color, and suspended solids from the fracturing flowback fluid, and has a strong COD removal capacity.

Description

Technical Field

[0001] This invention relates to the field of oilfield wastewater treatment technology, specifically to a flocculant for treating fracturing flowback fluid. Background Technology

[0002] Domestic and international practices have proven that hydraulic fracturing is currently an irreplaceable technology for developing low-permeability oil and gas reservoirs. Hydraulic fracturing, based on the pressure transmitted by fracturing fluid, breaks up low-permeability reservoirs to create a complex network of fractures, facilitating oil and gas development within these reservoirs and playing a crucial role in stabilizing and increasing oil and gas production. Fracturing fluid is the core of the hydraulic fracturing process, typically composed of thickeners, clay stabilizers, and flowback aids, resulting in a complex composition. After hydraulic fracturing, considering factors such as pressure balance and reservoir damage, the fracturing fluid needs to be flowed back. This flowback fluid contains not only organic components such as thickeners but also a large amount of metal ions and suspended particles carried from the reservoir. Therefore, the treatment of fracturing flowback fluid is currently a challenging and critical aspect of oil and gas field development.

[0003] Currently, the most important step in treating fracturing flowback fluid is the flocculation and sedimentation step. In this step, flocculants are added to promote the demulsification and sedimentation of suspended particles and emulsion particles in the fracturing flowback fluid. Polyacrylamide flocculants are currently the most widely used flocculants. They mainly achieve flocculation and sedimentation through particle adsorption and charge neutralization. Their molecular structure can be designed according to the actual situation of pollutants, making them more flexible in practical applications. However, due to their poor degradation properties and salt tolerance, polyacrylamide flocculants have limited effectiveness in high-salt fracturing flowback fluids and also have poor environmental performance. Summary of the Invention

[0004] To address at least one of the aforementioned problems, this invention proposes a flocculant for treating fracturing flowback fluid, which has strong salt resistance and can effectively flocculate fracturing flowback fluid.

[0005] The technical solution of this invention is: a flocculant for treating fracturing flowback fluid, comprising modified starch and organic acid, wherein the preparation method of the modified starch includes the following steps:

[0006] Allyl alcohol glycidyl ether and 1,4,7-trimethyldiethylenetriamine were reacted in a molar ratio of 1:1 to 1.2. After the reaction was completed, the intermediate product was separated and purified to obtain the intermediate product. The intermediate product was taken and dissolved, and an alkyl halide was added to carry out a quaternization reaction. After the reaction was completed, the intermediate product was separated and purified to obtain the cationic monomer. The molar ratio of the intermediate product to the alkyl halide was 1:2.2 to 4.

[0007] Take 10 parts by weight of pregelatinized starch and disperse it in water. Then add 0.5-5 parts of cationic monomer, 2-5 parts of acrylamide and initiator to carry out free radical polymerization. After the reaction is completed, dry it to obtain the product.

[0008] In this invention, considering the high metal ion content of fracturing flowback fluid, modified starch and organic acid are used in combination. The organic acid enables the cationic chains of the modified starch to extend more fully. In this embodiment, polyacrylamide and cationic monomers are also used to modify the modified starch. The resulting modified starch not only has a certain salt resistance, but also has good demulsification and flocculation effects.

[0009] In this invention, the reaction equation for the preparation of the cationic monomer is shown below. The first step of this reaction involves preparing a compound containing two tertiary amines, one ether bond, one hydroxyl group, and one double bond. The double bond provides a site for subsequent polymerization, while the ether bond and hydroxyl group increase the water solubility of the cationic monomer and enhance the flocculation effect of the final modified starch. For allyl alcohol glycidyl ether, although there are compounds with similar structures, such as methyl allyl glycidyl ester, methyl allyl glycidyl ester is prone to hydrolysis during the preparation of the cationic monomer, resulting in relatively poor flocculation performance of the final product. The second step is a quaternization reaction. Theoretically, a fully bis-quaternary ammonium salt product can be obtained due to the large amount of alkyl halide added. However, in actual production, considering the complexity of the reaction process, a mixture of mono- and bis-quaternary ammonium salts is usually obtained.

[0010]

[0011] Of course, the two products in the above reaction are only two relatively ideal products. In fact, there are also some products with terminal amino groups that are secondary amines or even quaternary ammonium.

[0012] As can be seen from the above reaction formula, the final quaternary ammonium salts obtained by the reaction are mono-quaternary ammonium salts and bis-quaternary ammonium salts. According to the inventors' experience, the longer the reaction time and the higher the reaction temperature, the higher the content of the bis-quaternary ammonium salt. Therefore, in this invention, the prepared cationic monomer has a high density of positive charge, and its cation distribution is hierarchical, which can better achieve its flocculation function. In this invention, "the molar ratio of the intermediate product to the alkyl halide" refers to calculating the molar amount of the intermediate product based on the molecular weight of the target intermediate product and comparing this molar amount with the molar amount of the alkyl halide.

[0013] For pregelatinized starch, commonly available pregelatinized starches can be used, such as pregelatinized corn starch, pregelatinized tapioca starch, and pregelatinized sweet potato starch. When these pregelatinized starches are used as the matrix of flocculants, they not only have good flocculation effects but also good biodegradability and strong environmental friendliness. Alternatively, commercially available pregelatinized starch products can be purchased, or they can be made at home using existing methods.

[0014] For modified starch, acrylamide and cationic monomers are grafted onto it. Since the cationic monomers are prepared in advance, the density of positive charge can be precisely controlled. Due to the special properties of the cationic monomers, not only is the positive charge density in the modified starch higher, but its positive charge distribution is also more hierarchical. Furthermore, the polymer chains formed by acrylamide and cationic monomers make the flocculation effect of the modified starch stronger.

[0015] Meanwhile, the modified starch obtained is usually only dried. However, in some cases, in order to improve its purity, the following operation can be performed: add at least twice the volume of acetone to the reaction liquid, stir, take the precipitate, wash it several times with acetone and dry it. The modified starch obtained in this way has higher purity. However, since acrylamide polymer itself also has a certain flocculation effect, not purifying it has little impact on the product performance.

[0016] In one embodiment of the present invention, the mass ratio of the modified starch to the organic acid is 10:0.1~3.

[0017] Furthermore, the organic acid is one of citric acid and salicylic acid, which are common organic acids in the art.

[0018] In one embodiment of the present invention, isopropanol is used as the solvent in the preparation of the intermediate product, and acetone is used as the solvent in the preparation of the cationic monomer. These are common solvents; of course, those skilled in the art can choose other solvents according to the actual situation.

[0019] In one embodiment of the present invention, the alkyl halide is one of iodomethane and bromoethane. These are common alkyl halides, and other alkyl halides such as chloromethane and iodomethane are also commonly used. Theoretically, all of these can be applied to the present invention, but in practical use, iodomethane and bromoethane are cheaper, easier to obtain, and easier to control in reaction.

[0020] One embodiment of the present invention involves adding the allyl alcohol glycidyl ether solution dropwise to a 1,4,7-trimethyldiethylenetriamine solution during the preparation of the intermediate product, at a reaction temperature of 30-70°C for 1-5 hours; and adding the alkyl halide dropwise to the intermediate product solution during the preparation of the cationic monomer, at a reaction temperature of 30-50°C for 10-25 hours. In the preparation of the intermediate product, the reaction is a conventional ring-opening reaction between an epoxy group and an amino group. However, considering that 1,4,7-trimethyldiethylenetriamine contains two secondary amines, to minimize the formation of disubstituted products of 1,4,7-trimethyldiethylenetriamine, the allyl alcohol glycidyl ether solution is typically added dropwise to the 1,4,7-trimethyldiethylenetriamine solution for the reaction. During the preparation of the cationic monomer, when the reaction temperature is 30-50°C and the reaction time is 10-25 hours, the prepared product has fewer byproducts, and the final product exhibits better performance.

[0021] One embodiment of the present invention includes the following steps for separating and purifying the intermediate product: taking the product and removing low-boiling substances by vacuum distillation; and the following steps for separating and purifying the cationic monomer: taking the product, adding at least three times the volume of the reaction liquid to diethyl ether, stirring rapidly, allowing it to stand, taking the solid phase, and washing it several times with diethyl ether. For the intermediate product, since the ring-opening reaction of the amino and epoxy groups is relatively fast and the reaction is relatively easy to carry out, a relatively large amount of 1,4,7-trimethyldiethylenetriamine and solvent water remain in the product. Therefore, vacuum distillation can be performed for its separation and purification. Considering the boiling point of the material, vacuum distillation can be carried out at 2 kPa and 90°C. For the separation and purification of the cationic monomer, since the product is a quaternary ammonium salt, and quaternary ammonium salts are insoluble in diethyl ether, its solubility is utilized by adding diethyl ether for separation and purification, resulting in a relatively high purity of the final product.

[0022] In one embodiment of the present invention, during the preparation of the cationic monomer, the molar ratio of the intermediate product to the alkyl halide is 1:3 to 3.5; and during the preparation of the modified starch, the weight ratio of pregelatinized starch, cationic monomer, and acrylamide is 10:3 to 4:3 to 4. Under these conditions, the modified starch obtained has better performance.

[0023] In one embodiment of the present invention, the initiator is cerium ammonium nitrate, and the amount of the initiator added is 0.5-2% of the total mass of the pregelatinized starch, cationic monomer, and acrylamide. This is a common initiator, and the reaction temperature is usually 40-65°C.

[0024] The beneficial effects of this invention are as follows:

[0025] The flocculant for treating fracturing flowback fluid provided by this invention not only has strong salt resistance and can be used in the high-salt environment of fracturing flowback fluid, but also effectively removes oil, turbidity, color and suspended solids from fracturing flowback fluid, and has a strong ability to remove COD. Detailed Implementation

[0026] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0027] In the following embodiments, unless otherwise specified, all raw materials can be purchased through conventional channels;

[0028] Unless otherwise specified, the operations described in the following embodiments are all conventional operations in the art.

[0029] Example 1: In this example, the flocculant is composed of modified starch and salicylic acid in a mass ratio of 10:1. The preparation method of the modified starch is as follows:

[0030] 11.4 g of allyl alcohol glycidyl ether and 15.8 g of 1,4,7-trimethyldiethylenetriamine were prepared into solutions with isopropanol. Under continuous stirring at 60 °C, the allyl alcohol glycidyl ether solution was added dropwise to the 1,4,7-trimethyldiethylenetriamine solution. After the addition was complete, the reaction was allowed to proceed for 1.5 h, followed by vacuum distillation to obtain the intermediate product. 13.0 g of the intermediate product was dissolved in acetone. Under continuous stirring at 40 °C, 16.4 g of bromoethane was added dropwise to the intermediate product solution and the reaction was allowed to proceed for 20 h. After the reaction was completed, three times the volume of diethyl ether was added to the reaction solution. After stirring evenly, the mixture was allowed to stand for a period of time. The solid phase was collected, washed several times with diethyl ether, and dried to obtain the cationic monomer.

[0031] Take 10g of pregelatinized corn starch and add water to disperse it evenly under ultrasonic conditions. Under a nitrogen atmosphere, add 3.5g of cationic monomer and 3.5g of acrylamide and dissolve them. After heating to 50℃, add an aqueous solution of 0.15g of cerium ammonium nitrate and continue to react for 2h. After the reaction is completed, add 2.5 times the volume of acetone to the reaction liquid, stir evenly and let it settle naturally. Then take the solid phase, wash it several times with acetone and dry it to obtain the product.

[0032] Example 2: In this example, the flocculant is composed of modified starch and citric acid in a mass ratio of 10:1.2. The preparation method of the modified starch is as follows:

[0033] 11.4 g of allyl alcohol glycidyl ether and 15.8 g of 1,4,7-trimethyldiethylenetriamine were prepared into solutions with isopropanol. Under continuous stirring at 65 °C, the allyl alcohol glycidyl ether solution was added dropwise to the 1,4,7-trimethyldiethylenetriamine solution. After the addition was complete, the reaction was allowed to proceed for 1 h, followed by vacuum distillation to obtain the intermediate product. 13.0 g of the intermediate product was dissolved in acetone. Under continuous stirring at 35 °C, 23.4 g of iodomethane was added dropwise to the intermediate product solution and the reaction was allowed to proceed for 12 h. After the reaction was completed, three times the volume of diethyl ether was added to the reaction solution. After stirring evenly, the mixture was allowed to stand for a period of time. The solid phase was collected, washed several times with diethyl ether, and dried to obtain the cationic monomer.

[0034] Take 10g of pregelatinized corn starch and add water to disperse it evenly under ultrasonic conditions. Under a nitrogen atmosphere, add 3g of cationic monomer and 4g of acrylamide and dissolve them. After heating to 60℃, add 0.15g of aqueous solution of cerium ammonium nitrate and continue to react for 1.5h. After the reaction is completed, add 2.5 times the volume of acetone to the reaction liquid, stir evenly and let it settle naturally. Then take the solid phase, wash it several times with acetone and dry it to obtain the product.

[0035] Example 3: In this example, the flocculant is composed of modified starch and salicylic acid in a mass ratio of 10:0.8. The difference between the preparation method of the modified starch and that in Example 1 is that cerium ammonium nitrate is added and dried after the reaction is completed.

[0036] Example 4: In this example, the flocculant is composed of modified starch and salicylic acid in a mass ratio of 10:1.5. The preparation method of the modified starch is as follows:

[0037] 11.4 g of allyl alcohol glycidyl ether and 15.8 g of 1,4,7-trimethyldiethylenetriamine were prepared into solutions by adding isopropanol to each solution. Under continuous stirring at 40 °C, the allyl alcohol glycidyl ether solution was added dropwise to the 1,4,7-trimethyldiethylenetriamine solution. After the addition was complete, the reaction was allowed to proceed for 4 h, followed by vacuum distillation to obtain the intermediate product. 13.0 g of the intermediate product was dissolved in acetone. Under continuous stirring at 40 °C, 16.4 g of bromoethane was added dropwise to the intermediate product solution and the reaction was allowed to proceed for 20 h. After the reaction was completed, three times the volume of diethyl ether was added to the reaction solution. After stirring evenly, the mixture was allowed to stand for a period of time. The solid phase was collected, washed several times with diethyl ether, and dried to obtain the cationic monomer.

[0038] Take 10g of pregelatinized corn starch and add water to disperse it evenly under ultrasonic conditions. Under a nitrogen atmosphere, add 1.5g of cationic monomer and 4.5g of acrylamide and dissolve them. After heating to 50℃, add 0.15g of aqueous solution of cerium ammonium nitrate and continue to react for 2h. After the reaction is completed, add 2.5 times the volume of acetone of the reaction liquid, stir evenly and let it settle naturally. Then take the solid phase, wash it several times with acetone and dry it to obtain the product.

[0039] Comparative Example 1 differs from Example 1 in that the cationic monomer is methacryloyloxyethyltrimethylammonium chloride, while all other aspects are the same.

[0040] Comparative Example 2 differs from Example 1 in that 11.4 g of allyl alcohol glycidyl ether is replaced with 14.2 g of glycidyl methacrylate, while all other aspects remain the same.

[0041] Comparative Example 3 differs from Example 1 in that the amount of bromoethane added during the preparation of the cationic monomer is 9.8 g, while the rest are the same.

[0042] Comparative Example 4 differs from Example 1 in that the raw materials used in the preparation of the modified starch are pregelatinized corn starch, intermediate products, and acrylamide; all other aspects are the same.

[0043] Comparative Example 5 differs from Example 1 in that salicylic acid was not added; all other aspects are the same.

[0044] To further illustrate the advantages of the flocculant prepared according to the embodiments of the present invention, it is tested below.

[0045] 1. Flocculation effect test

[0046] Fracturing flowback fluid from a well site in Karamay was first subjected to natural sedimentation to remove large particulate impurities. Then, 0.5 wt% flocculant was added, and the fluid was shaken upside down 10 times. After standing for 20 minutes, its oil content, turbidity, color, and salinity were measured. The oil content was measured using the method in SL93.2-1994, the color using the method in GB11903-89, the turbidity using the method in GB13200-91, and the COD using the method in HJ 828-2017. The salinity of the fracturing flowback fluid was 18725 mg / L, and the total calcium and magnesium ion content was 1814 mg / L. The changes in the indicators of the fracturing flowback fluid before and after flocculation treatment are shown in Table 1.

[0047] Table 1. Changes in parameters before and after fracturing flowback fluid treatment

[0048]

[0049] As shown in Table 1, the flocculant prepared in the embodiments of the present invention can effectively remove oil, turbidity, color and suspended matter from fracturing flowback fluid under high salinity conditions, and also has a strong removal ability for COD.

[0050] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A flocculant for fracturing flowback fluid treatment, characterized by, The preparation method of the modified starch comprises the following steps: The molar ratio of the allyl glycidyl ether and 1,4,7-trimethyl diethylene triamine is 1:1-1.2, and after the reaction, the intermediate product is separated and purified; the intermediate product is taken and dissolved, and the quaternary ammonium reaction is carried out by adding alkyl halide, and after the reaction, the intermediate product is separated and purified to obtain the cationic monomer; the molar ratio of the intermediate product to the alkyl halide is 1:2.2-4. 10 parts of pregelatinized starch is taken and dispersed with water, and then 0.5-5 parts of cationic monomer, 2-5 parts of acrylamide and an initiator are added for free radical polymerization, and after the reaction, the product is dried to obtain the modified starch.

2. The flocculant for fracturing flowback fluid treatment according to claim 1, characterized in that, The mass ratio of the modified starch to the organic acid is 10:0.1-3.

3. The flocculant for fracturing flowback fluid treatment according to claim 1 or 2, characterized by, The organic acid is one of citric acid and salicylic acid.

4. The fracturing fluid according to claim 1, wherein In the preparation process of the intermediate product, the solvent of the allyl glycidyl ether and 1,4,7-trimethyl diethylene triamine is isopropyl alcohol; and in the preparation process of the cationic monomer, the solvent of the intermediate product is acetone.

5. The fracturing fluid according to claim 1, wherein The alkyl halide is one of methyl iodide and ethyl bromide.

6. The fracturing fluid flocculant according to claim 1, characterized in that, In the preparation of the intermediate product, the allyl glycidyl ether solution is added dropwise into the 1,4,7-trimethyl diethylene triamine solution, the reaction temperature is 30-70 DEG C, and the reaction time is 1-5 h; and in the preparation of the cationic monomer, the alkyl halide is added dropwise into the intermediate product solution, the reaction temperature is 30-50 DEG C, and the reaction time is 10-25 h.

7. The fracturing fluid flocculant according to claim 1, characterized in that, The separation and purification method of the intermediate product comprises the following steps: taking the product, and removing low-boiling substances by vacuum distillation to obtain the product; and the separation and purification method of the cationic monomer comprises the following steps: taking the product, adding ethyl ether with a volume of at least 3 times of the reaction liquid, stirring quickly, standing, taking the solid phase, and washing with ethyl ether for several times to obtain the product.

8. The fracturing fluid according to claim 1, wherein In the preparation process of the cationic monomer, the molar ratio of the intermediate product to the alkyl halide is 1:3-3.5; and in the preparation process of the modified starch, the weight ratio of the pregelatinized starch, the cationic monomer and the acrylamide is 10:3-4:3-4.

9. The fracturing fluid flocculant according to claim 1, characterized in that, The initiator is cerium ammonium nitrate, and the amount of the initiator is 0.5-2% of the mass sum of the pregelatinized starch, the cationic monomer and the acrylamide.

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