High-temperature-resistant clean fracturing fluid and preparation method thereof

Abstract

The invention provides a high-temperature-resistant clean fracturing fluid which comprises the following components in percentage by mass: 0.3%-0.5% of guanidine gum, 0.2%-0.5% of a cross-linking agent, 0.1%-0.2% of a pH regulator, 0.02%-0.05% of a gel breaker, 0.2%-0.5% of a clay stabilizer, 0.1%-0.5% of a cleanup additive and the balance of water. The high-temperature-resistant clean fracturing fluid has the advantages of high temperature resistance and environmental friendliness, and is suitable for oil and gas exploitation.

Description

Technical Field

[0001] This invention relates to the field of oil and gas extraction, and more specifically, to a high-temperature resistant clean fracturing fluid and its preparation method. Background Technology

[0002] Fracturing fluid is a special liquid used in oil and gas well fracturing operations. Its main functions are to transmit pressure, create fractures, and carry proppant into the fracture. Currently, there are many types of fracturing fluids on the market, such as water-based fracturing fluids, oil-based fracturing fluids, and foam fracturing fluids. These fracturing fluids are mostly composed of base fluid, thickeners, surfactants, and crosslinking agents. Crosslinking agents are the core component of fracturing fluids. The active groups (such as metal ions and functional groups) in the crosslinking agent molecules undergo coordination reactions or covalent bonds with the active sites (such as hydroxyl and carboxyl groups) on the thickener molecular chains, connecting the linear polymer chains into a three-dimensional network structure. Through the crosslinking effect of the crosslinking agent, the viscosity of the fracturing fluid can be effectively increased, enhancing its proppant-carrying capacity. Simultaneously, it can effectively transmit pump pressure, forming wider and longer fractures, reducing the damage of fluid shear forces to the molecular chains, and enhancing high-temperature stability. However, the crosslinked network structure of conventional fracturing fluids is easily destroyed by high temperatures, affecting the normal use of the fracturing fluid.

[0003] In order to solve the above problems, people have been seeking an ideal technological solution. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing technologies by providing a high-temperature resistant, clean fracturing fluid and its preparation method.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A high-temperature resistant, clean fracturing fluid, by mass percentage, comprises the following components: guar gum 0.3%-0.5%, crosslinking agent 0.2%-0.5%, pH adjuster 0.1%-0.2%, breaker 0.02%-0.05%, clay stabilizer 0.2%-0.5%, flow aid 0.1%-0.5%, with the balance being water;

[0007] The crosslinking agent is prepared by the following steps: pretreating multi-walled carbon nanotubes and modifying the pretreated multi-walled carbon nanotubes with silane coupling agent KH550 to obtain aminated carbon nanotubes; wherein the mass ratio of silane coupling agent KH550 to multi-walled carbon nanotubes is (10-20):1.

[0008] Aminated carbon nanotubes were mixed with ethanol to prepare an aminated carbon nanotube dispersion. Under nitrogen protection, a mixture of silane coupling agent KH550 and titanium tetrachloride was added to an ethanol solution and mixed evenly. Then, the aminated carbon nanotube dispersion was added and reacted for 3-6 hours. Part of the solvent was removed to increase the solid content to 25%-30%. The mixture was then dispersed at high speed to form a composite sol with a viscosity of 500-800 mPa·s. The molar ratio of titanium tetrachloride to silane coupling agent KH550 was 1:(1.2-1.4), and the amount of aminated carbon nanotubes was 0.5%-1% of the titanium tetrachloride.

[0009] The organic monomer and initiator were dissolved in the reaction solvent, and the composite sol was added and reacted for 2-6 hours. Malic acid and diethanolamine were added in sequence, and the reaction continued. The pH was adjusted to 6-7, and the mixture was aged. The solvent was removed to obtain the crosslinking agent.

[0010] The molar ratio of organic monomer to titanium tetrachloride is (0.8-0.9):1; the amount of initiator is 0.5%-1.5% of the organic monomer, which includes N-isopropylacrylamide and methyl methacrylate in a mass ratio of (2-3):1, and the molar ratio of malic acid and diethanolamine to titanium tetrachloride is (1.3-1.7):1.2:1.

[0011] The solvent is one or a combination of at least two of toluene, N,N'-dimethylformamide, dimethyl sulfoxide, anhydrous ethanol, and deionized water.

[0012] The de-gluing agent is one or a combination of at least two of sodium sulfite, ammonium persulfate, sodium persulfate, and potassium persulfate.

[0013] The clay stabilizer is potassium chloride.

[0014] pH adjusters are one or a combination of at least two of sodium carbonate, sodium bicarbonate, and sodium hydroxide.

[0015] The discharge aid is one or a combination of at least two of the following: sodium dodecyl sulfate anionic surfactant, alkylphenol polyoxyethylene ether nonionic surfactant, and perfluorooctylcarboxylic acid polyoxyethylene ether.

[0016] A method for preparing a high-temperature resistant, clean fracturing fluid, comprising the following steps:

[0017] At 20-30℃ and with high-speed stirring, guar gum and clay stabilizer are added to water and dispersed evenly; with continuous stirring, breaker, drainage aid, pH adjuster and crosslinking agent are added in sequence and mixed evenly to obtain high-temperature resistant clean fracturing fluid.

[0018] During the mixing of guar gum and water, the stirring speed is 1000-3000 r / min and the stirring time is 15-45 min, so that the solution viscosity is ≥30 mPa·s; the subsequent stirring speed is 200-400 r / min, the breaker is added and stirred for 1-3 min, the flow aid is added and stirred for 1-2 min, the pH adjuster is added and the pH is adjusted to 6.5-7, the crosslinking agent is added, and the mixture is mixed evenly to obtain a high-temperature resistant clean fracturing fluid.

[0019] This invention possesses significant substantive features and substantial advancements compared to existing technologies. Specifically, it provides a high-temperature resistant and clean fracturing fluid. This fluid utilizes a titanium-based crosslinking agent, combined with silane coupling agent KH550, carbon nanotubes, N-isopropylacrylamide, and methyl methacrylate polymerized and modified. The resulting high-temperature resistant crosslinking agent, in conjunction with guar gum, forms a high-temperature resistant and clean fracturing fluid. The fracturing fluid is formulated in a weakly acidic environment to prevent rapid crosslinking. During use, the fracturing fluid is delivered downhole, gradually creating a weakly alkaline environment with a gradually increasing temperature, facilitating the crosslinking reaction. Detailed Implementation

[0020] The technical solution of the present invention will be further described in detail below through specific embodiments. It should be noted that, in the embodiments, the de-gelling agent can be a commercially available microencapsulated de-gelling agent.

[0021] Example 1

[0022] This embodiment provides a method for preparing a high-temperature crosslinking agent for fracturing fluid, which includes the following steps:

[0023] The water bath temperature is ≤20℃. A mixed solution of concentrated sulfuric acid and concentrated nitric acid with a volume ratio of 3:1 is added to the multi-walled carbon nanotubes. The mixture is ultrasonically reacted for 2 hours. The nanotubes are washed with deionized water until the pH reaches 6-7, filtered, and dried to complete the pretreatment of the multi-walled carbon nanotubes. The pretreated multi-walled carbon nanotubes are carboxylated carbon nanotubes. The diameter of the multi-walled carbon nanotubes is 10-20 nm, and the aspect ratio is 300-800.

[0024] Pretreated multi-walled carbon nanotubes were dispersed in ethanol, and silane coupling agent KH550 was added. The mixture was reacted at 50°C for 3 hours, filtered, and dried to obtain aminated carbon nanotubes. The mass ratio of silane coupling agent KH550 to multi-walled carbon nanotubes was 15:1, and the mass of ethanol was 10 times the sum of the mass of silane coupling agent KH550 and multi-walled carbon nanotubes.

[0025] Aminated carbon nanotubes were mixed with ethanol to prepare an aminated carbon nanotube dispersion, with the ethanol content being 100 times the mass of the aminated carbon nanotubes. Under nitrogen protection and at a temperature of 20-30℃, a mixed solution of silane coupling agent KH550 and titanium tetrachloride was slowly added to an ethanol solution, with a volume ratio of ethanol to water of 2:1. The mixture was stirred at 200-400 r / min until homogeneous, and then the aminated carbon nanotube dispersion was added. The reaction was carried out at 50-60℃ for 4 h to obtain a mixed solution with a particle size of 50-80 nm. Part of the solvent was removed by vacuum distillation to increase the solid content to 28.5%. The mixture was then dispersed at 3000 r / min for 1 min to form a composite sol with a viscosity of 600 mPa·s. The molar ratio of titanium tetrachloride to silane coupling agent KH550 was 1:1.2, and the amount of aminated carbon nanotubes was 0.1% of the mass of titanium tetrachloride.

[0026] Organic monomers and azobisisobutyronitrile were dissolved in a reaction solvent, and a composite sol was added. The mixture was reacted at 60-80℃ and 200-400 r / min for 3 h. Then, malic acid was added and reacted for 0.5 h. Diethanolamine was then added in three equal portions and reacted for 0.5 h each time. The pH was adjusted to 6-7, and the mixture was aged for 2 h to obtain a crude product. Anhydrous ethanol was added, and the mixture was cooled to 5℃. The supernatant was removed, and the mixture was centrifuged. The product was washed with a 1:1 mixture of ethanol and diethyl ether and dried to obtain a crosslinking agent.

[0027] The molar ratio of organic monomer to titanium tetrachloride is 0.8:1; the amount of azobisisobutyronitrile is 0.8% of the organic monomer, which includes N-isopropylacrylamide and methyl methacrylate in a mass ratio of 3:1; the molar ratio of malic acid and diethanolamine to titanium tetrachloride is 1.5:1.2:1; and the reaction solvent is a mixture of anhydrous ethanol and toluene in a volume ratio of 3:1.

[0028] Example 2

[0029] This embodiment provides a high-temperature resistant, clean fracturing fluid, comprising the following components by mass percentage: 0.5% guar gum, 0.3% crosslinking agent, 0.2% pH adjuster, 0.03% breaker, 0.3% clay stabilizer, 0.2% flow aid, and the balance being water; the breaker is encapsulated ammonium persulfate. The clay stabilizer is potassium chloride. The pH adjuster is sodium hydroxide and microencapsulated sodium hydroxide in a mass ratio of 1:3. The flow aid is sodium dodecyl sulfate anionic surfactant and alkylphenol polyoxyethylene ether nonionic surfactant in a mass ratio of 1:2.

[0030] A method for preparing a high-temperature resistant, clean fracturing fluid, comprising the following steps:

[0031] At 20-30℃ and under high-speed stirring, guar gum and clay stabilizer are added to water and dispersed evenly. With continuous stirring, breaker, flow aid, pH adjuster, and crosslinking agent are added sequentially and mixed evenly to obtain a high-temperature resistant clean fracturing fluid. During the mixing of guar gum and water, the stirring speed is 2000 r / min, the stirring time is 30 min, and the solution viscosity is 40 mPa·s. Subsequently, the stirring speed is 200-400 r / min, breaker is added and stirred for 1 min, flow aid is added and stirred for 1 min, sodium hydroxide is added to adjust the pH to 6.5-7, and encapsulated sodium hydroxide and crosslinking agent are added and mixed evenly to obtain a high-temperature resistant clean fracturing fluid.

[0032] After heating, the fracturing fluid had a pH of 8.5, a temperature of 220℃, a complete cross-linking time of 420s, a peak viscosity of 440mPa·s, a residue content of 0.021%, and a surface tension of 24mN / m after breaking the gel.

[0033] Example 3

[0034] This embodiment provides a high-temperature resistant, clean fracturing fluid, comprising the following components by mass percentage: 0.5% guar gum, 0.45% crosslinking agent, 0.2% pH adjuster, 0.04% breaker, 0.2% clay stabilizer, 0.2% flow aid, and the balance being water. The breaker is one or a combination of at least two of sodium sulfite, ammonium persulfate, sodium persulfate, and potassium persulfate. The clay stabilizer is potassium chloride. The pH adjuster is sodium bicarbonate and sodium hydroxide in a 1:1 mass ratio. The flow aid is perfluorooctyl carboxylic acid polyoxyethylene ether.

[0035] A method for preparing a high-temperature resistant, clean fracturing fluid, comprising the following steps:

[0036] At 20-30℃ and under high-speed stirring, guar gum and clay stabilizer are added to water and dispersed evenly. With continuous stirring, breaker, flow aid, pH adjuster, and crosslinking agent are added sequentially and mixed evenly to obtain a high-temperature resistant clean fracturing fluid. During the mixing of guar gum and water, the stirring speed is 3000 r / min, the stirring time is 20 min, and the solution viscosity is 35 mPa·s. Subsequently, the stirring speed is 200-400 r / min, breaker is added and stirred for 1 min, flow aid is added and stirred for 1 min, pH adjuster is added to adjust the pH to 6.5-7, crosslinking agent is added, and the mixture is mixed evenly to obtain a high-temperature resistant clean fracturing fluid.

[0037] Example 4

[0038] This embodiment provides a high-temperature resistant, clean fracturing fluid, comprising the following components by mass percentage: 0.5% guar gum, 0.5% crosslinking agent, 0.15% pH adjuster, 0.04% breaker, 0.2% clay stabilizer, 0.3% flow aid, and the balance being water; the breaker is potassium persulfate. The clay stabilizer is potassium chloride. The pH adjuster is one or a combination of at least two of sodium hydroxide. The flow aid is perfluorooctylcarboxylic acid polyoxyethylene ether.

[0039] A method for preparing a high-temperature resistant, clean fracturing fluid, comprising the following steps:

[0040] At 20-30℃ and under high-speed stirring, guar gum and clay stabilizer are added to water and dispersed evenly. With continuous stirring, breaker, flow aid, pH adjuster, and crosslinking agent are added sequentially and mixed evenly to obtain a high-temperature resistant clean fracturing fluid. During the mixing of guar gum and water, the stirring speed is 3000 r / min, the stirring time is 30 min, and the solution viscosity is 40 mPa·s. Subsequently, the stirring speed is 200-400 r / min, breaker is added and stirred for 1 min, flow aid is added and stirred for 1 min, pH adjuster is added to adjust the pH to 6.5-7, crosslinking agent is added, and the mixture is mixed evenly to obtain a high-temperature resistant clean fracturing fluid.

[0041] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them; although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications can still be made to the specific implementation of the present invention or equivalent substitutions can be made to some technical features without departing from the spirit of the technical solutions of the present invention, and all such modifications and substitutions should be covered within the scope of the technical solutions claimed in the present invention.

Claims

1. A high-temperature resistant clean fracturing fluid, comprising, by mass percentage: 0.3%-0.5% guar gum, 0.2%-0.5% crosslinking agent, 0.1%-0.2% pH adjuster, 0.02%-0.05% breaker, 0.2%-0.5% clay stabilizer, 0.1%-0.5% flow aid, with the balance being water; in, The crosslinking agent is prepared by the following steps: pretreating multi-walled carbon nanotubes, and modifying the pretreated multi-walled carbon nanotubes with silane coupling agent KH550 to obtain aminated carbon nanotubes; wherein, the mass ratio of silane coupling agent KH550 to multi-walled carbon nanotubes is (10-20):

1. Aminated carbon nanotubes were mixed with ethanol to prepare an aminated carbon nanotube dispersion. Under nitrogen protection, a mixture of silane coupling agent KH550 and titanium tetrachloride was added to an ethanol solution and mixed thoroughly. Then, the aminated carbon nanotube dispersion was added, and the reaction was carried out for 3-6 hours. Some of the solvent was removed to increase the solid content to 25%-30%. The mixture was then dispersed at high speed to form a composite sol with a viscosity of 500-800 mPa·s. The molar ratio of titanium tetrachloride to silane coupling agent KH550 was 1:(1.2-1.4), and the amount of aminated carbon nanotubes was 0.5%-1% of the titanium tetrachloride. The organic monomer and initiator were dissolved in the reaction solvent, and the composite sol was added and reacted for 2-6 hours. Malic acid and diethanolamine were added in sequence, and the reaction continued. The pH was adjusted to 6-7, and the mixture was aged. The solvent was removed to obtain the crosslinking agent. The molar ratio of organic monomer to titanium tetrachloride is (0.8-0.9):1; the amount of initiator is 0.5%-1.5% of the organic monomer, which includes N-isopropylacrylamide and methyl methacrylate in a mass ratio of (2-3):1, and the molar ratio of malic acid and diethanolamine to titanium tetrachloride is (1.3-1.7):1.2:

1.

2. The high-temperature resistant clean fracturing fluid according to claim 1, characterized in that: The solvent is one or a combination of at least two of toluene, N,N'-dimethylformamide, dimethyl sulfoxide, anhydrous ethanol, and deionized water.

3. The high-temperature resistant clean fracturing fluid according to claim 1, characterized in that: The de-gluing agent is one or a combination of at least two of sodium sulfite, ammonium persulfate, sodium persulfate, and potassium persulfate.

4. The high-temperature resistant clean fracturing fluid according to claim 1, characterized in that: The clay stabilizer is potassium chloride.

5. The high-temperature resistant clean fracturing fluid according to claim 1, characterized in that: pH adjusters are one or a combination of at least two of sodium carbonate, sodium bicarbonate, and sodium hydroxide.

6. The high-temperature resistant clean fracturing fluid according to claim 1, characterized in that: The discharge aid is one or a combination of at least two of the following: sodium dodecyl sulfate anionic surfactant, alkylphenol polyoxyethylene ether nonionic surfactant, and perfluorooctylcarboxylic acid polyoxyethylene ether.

7. A method for preparing the high-temperature resistant clean fracturing fluid according to any one of claims 1-6, comprising the following steps: At 20-30℃ and with high-speed stirring, guar gum and clay stabilizer are added to water and dispersed evenly; with continuous stirring, breaker, drainage aid, pH adjuster and crosslinking agent are added in sequence and mixed evenly to obtain high-temperature resistant clean fracturing fluid.

8. The preparation method according to claim 7, characterized in that: During the mixing of guar gum and water, the stirring speed is 1000-3000 r / min and the stirring time is 15-45 min, so that the solution viscosity is ≥30 mPa·s; the subsequent stirring speed is 200-400 r / min, the breaker is added and stirred for 1-3 min, the flow aid is added and stirred for 1-2 min, the pH adjuster is added and the pH is adjusted to 6.5-7, the crosslinking agent is added, and the mixture is mixed evenly to obtain a high-temperature resistant clean fracturing fluid.