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

Abstract

The invention provides a high-temperature-resistant clean fracturing fluid and a preparation method thereof, and belongs to the technical field of fracturing fluids. The cleaning agent is prepared from the following raw materials in parts by weight: 3-5 parts of a high-temperature-resistant gemini surfactant, 0.5-1 part of a cosurfactant, 5-7 parts of a cleanup additive, 1-2 parts of nano granules and 70-80 parts of water. The high-temperature-resistant clean fracturing fluid prepared by the invention has better high-temperature resistance, salt resistance and shear resistance, good sand-carrying effect and excellent viscoelasticity, avoids the damage of a large number of inorganic ions to the change of original properties of a stratum, is simple in preparation process and wide in raw material source, and has a wide application prospect in oil and gas field exploitation and yield increase.

Description

Technical Field

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

[0002] Compared to traditional water-based plant-based fracturing fluids, clean fracturing fluids offer superior performance in areas such as gel breaking, proppant carrying, and reservoir protection. They address the cumulative formation damage caused by traditional water-based plant-based fracturing fluids, enabling long-term production and representing a key focus of next-generation fracturing fluid development. However, as oilfields gradually shift towards deeper, higher-temperature, and lower-permeability reservoirs, clean fracturing fluids are exhibiting two major problems: ① their temperature resistance cannot meet the requirements of high-temperature reservoirs; ② their synthesis methods are demanding, resulting in high production costs. Therefore, developing clean fracturing fluids that retain the advantages of easy gel breaking and minimal formation damage while significantly improving temperature resistance and reducing production costs is crucial for my country's economic growth and reservoir protection.

[0003] Clean fracturing fluid, also known as viscoelastic surfactant fracturing fluid (VES), is a solution based on viscoelastic surfactants. It has the advantages of rapid and thorough flowback, low damage, good proppant carrying capacity, and good filtration control performance, which solves the defect of incomplete gel breaking in conventional fracturing fluid systems.

[0004] Several studies have been reported on clean fracturing fluids. A literature review ("Fine Chemicals," 2014, Vol. 31, No. 12, pp. 66-70) discloses a clean fracturing fluid and its preparation method. It uses octadecylamine and 1,6-dibromohexane as raw materials to synthesize a cationic gemini surfactant, which is then combined with sodium salicylate and potassium chloride to form a clean fracturing fluid. However, this clean fracturing fluid has low temperature resistance and is only suitable for formations around 110°C, failing to meet the requirements of high-temperature oil and gas fields. Chinese invention patent CN103525391B discloses a high-temperature resistant clean fracturing fluid and its preparation method, using an amphoteric gemini surfactant, a sulfonate or sulfate co-surfactant, and a low-carbon small-molecule alcohol flushing agent to formulate a clean fracturing fluid. Although this clean fracturing fluid has good temperature resistance, its preparation process is cumbersome and costly, making large-scale application in oil fields difficult. Summary of the Invention

[0005] The purpose of this invention is to propose a high-temperature resistant clean fracturing fluid and its preparation method. It has good high-temperature resistance, salt resistance and shear resistance, good sand carrying capacity, excellent viscoelasticity, avoids damage to the original formation properties caused by a large number of inorganic ions, has a simple preparation process, and has a wide range of raw material sources. It has broad application prospects in oil and gas field development and production enhancement.

[0006] The technical solution of this invention is implemented as follows:

[0007] This invention provides a high-temperature resistant clean fracturing fluid, prepared from the following raw materials in parts by weight: 3-5 parts of high-temperature resistant Gemini surfactant, 0.5-1 part of co-surfactant, 5-7 parts of drainage aid, 1-2 parts of nanoparticles, and 70-80 parts of water; the structural formula of the high-temperature resistant Gemini surfactant is shown in Formula I:

[0008]

[0009] Among them, R1, R2, and R3 are C6-C12 alkyl chains;

[0010] The nanoparticle agent is a surfactant-modified silica nanoparticle.

[0011] As a further improvement of the present invention, the preparation method of the high-temperature resistant gemini surfactant is as follows:

[0012] S1. Reaction of long-chain fatty alcohols with epichlorohydrin yields intermediate 1, with the following structure:

[0013] S2. Reaction of ethylenediamine with a haloalkane yields intermediate 2, with the following structure:

[0014] S3. Intermediate 1 and intermediate 2 are reacted to obtain intermediate 3, with the following structure:

[0015]

[0016] S4. Intermediate 3 was reacted with butyryl lactone to obtain intermediate 4, with the following structure:

[0017]

[0018] S5. React intermediate 4 with 4-bromoalkoxybenzene to obtain the product.

[0019] As a further improvement of the present invention, in step S1, the molar ratio of the long-chain fatty alcohol and epichlorohydrin is 1:1.2-1.5, and the long-chain fatty alcohol is selected from at least one of acetalol, heptol, octanol, nonanol, decol, and dodecylol. A base is also added, which is NaOH or KOH. The reaction temperature is 30-50℃ and the time is 5-7h. In step S2, the molar ratio of ethylenediamine and haloalkanes is 1.1-1.2:2, and the haloalkanes are selected from at least one of 1-chlorohexane, 1-bromohexane, 1-chloroheptane, 1-bromoheptane, 1-chlorooctane, 1-bromooctane, 1-chlorononane, 1-bromononane, 1-chlorodecane, 1-bromodecane, 1-chlorododecane, and 1-bromododecane. The reaction temperature is 40-50℃ and the time is 3-5h.

[0020] As a further improvement of the present invention, in step S3, the molar ratio of intermediate 1 to intermediate 2 is 1:1-1.1, the reaction temperature is 30-40℃, and the time is 8-12h; in step S4, the molar ratio of intermediate 3 to butyrylolactone is 1:2-2.2, the reaction temperature is 30-40℃, and the time is 10-12h; in step S5, the molar ratio of intermediate 4 to 4-bromoalkoxybenzene is 1:1-1.2, the reaction temperature is 50-60℃, and the time is 5-7h. A base is also added, the base being selected from at least one of triethylamine, NaOH, and KOH, and the 4-bromoalkoxybenzene being selected from at least one of 4-bromohexyloxybenzene, 4-bromoheptyloxybenzene, 4-bromononoxybenzene, 4-bromooctyloxybenzene, 4-bromodiphenyloxybenzene, 4-bromoundecyloxybenzene, and 4-bromododecyloxybenzene.

[0021] As a further improvement of the present invention, the preparation method of the nanoparticle agent is as follows:

[0022] T1. Preparation of silica nanospheres: Ethanol, ammonia and water were mixed evenly, tetraethyl orthosilicate was added, the mixture was heated to hydrolyze, centrifuged, washed and dried to obtain silica nanospheres;

[0023] T2. Aminosilane modification: The silica nanospheres obtained in step T1 were added to ethanol, and an amino-containing silane coupling agent was added. The mixture was heated and stirred to react, centrifuged, washed, and dried to obtain aminosilane-modified silica nanospheres.

[0024] T3. Surface modification: The aminosilane-modified silica nanospheres obtained in step T2 were added to acetonitrile, along with triethylamine and haloalkanes. The mixture was heated and stirred to react, then centrifuged, washed, and dried to obtain nanoparticles.

[0025] As a further improvement of the present invention, in step T1, the mass ratio of ethanol, ammonia, water, and tetraethyl orthosilicate is 160-170:3-4:15-20:9-12, and the heating hydrolysis reaction time is 10-12 h at a temperature of 30-35 °C; in step T2, the amino-containing silane coupling agent is selected from at least one of KH550, KH602, and KH792, and the mass ratio of silica nanospheres to the amino-containing silane coupling agent is 100:7-10. The temperature of the hot stirring reaction is 40-45℃, and the time is 2-4h; in step T3, the mass ratio of the aminosilane-modified silica nanospheres, triethylamine, and haloalkanes is 100:12-15:15-20, and the haloalkanes are selected from at least one of 1-chlorododecane, 1-chlorotetradecane, 1-chlorohexadecane, 1-chlorooctadecane, 1-bromododecane, 1-bromotetradecane, 1-bromohexadecane, and 1-bromooctadecane; the temperature of the hot stirring reaction is 50-60℃, and the time is 3-5h.

[0026] Preferably, the amino-containing silane coupling agent is a mixture of KH550 and KH602 in a mass ratio of 3-5:2.

[0027] As a further improvement of the present invention, the co-surfactant is selected from at least one of sodium dodecylbenzenesulfonate, sodium dodecyl sulfonate, sodium dodecyl sulfate, sodium tetradecyl sulfonate, sodium tetradecylbenzenesulfonate, sodium tetradecyl sulfate, sodium hexadecyl sulfate, sodium hexadecyl sulfonate, and sodium hexadecylbenzenesulfonate.

[0028] As a further improvement of the present invention, the exhaust aid is selected from at least one of methanol, ethanol, isopropanol, and cyclohexanol.

[0029] This invention further protects a method for preparing the above-mentioned high-temperature resistant clean fracturing fluid, comprising the following steps:

[0030] (1) Dissolve the high-temperature resistant Gemini surfactant and co-surfactant in water, stir and mix evenly, add nanoparticles, emulsify, and obtain a mixture.

[0031] (2) Add drainage aid to the mixture in step (1), stir and mix evenly to obtain high temperature resistant clean fracturing fluid.

[0032] This invention further protects the application of the above-mentioned high-temperature resistant clean fracturing fluid in oil and gas field development and production enhancement.

[0033] The present invention has the following beneficial effects:

[0034] This invention prepares a high-temperature resistant gemini surfactant. On one hand, the introduction of a benzene ring into the molecular chain increases molecular rigidity, significantly improving the surfactant's thermal stability and shear resistance. Simultaneously, the introduction of amino groups increases molecular weight, acid solubility, and temperature resistance. The introduced sulfonic acid groups enhance temperature and salt resistance. Furthermore, the hydrophobic long-chain alkyl chain exhibits a salt-thickening effect, further improving the molecule's temperature and salt resistance. Therefore, the high-temperature resistant gemini surfactant prepared by this invention, through its special structural design, results in fracturing fluids with excellent temperature, salt, and shear resistance. Simultaneously, the strong interaction between the viscoelastic surfactant and counterions gives the system excellent viscoelastic properties and proppant carrying capacity. It can achieve spontaneous gel breaking, and the small-molecule surfactant in the breaking fluid causes low reservoir damage. Due to the synergistic effect with the co-surfactant, the breaking fluid typically exhibits high interfacial activity, contributing to further improving post-fracturing crude oil displacement capacity. Moreover, the preparation method is simple, the raw materials are widely available, and the preparation cost is low.

[0035] This invention further incorporates nanoparticles. By controlling the reaction conditions, small-diameter silica nanospheres were prepared. These nanospheres were then modified using an amino-containing silane coupling agent, resulting in amino groups on the surface of the nanospheres. Through nucleophilic reactions, these nanospheres react with haloalkanes under alkaline conditions to form long-chain alkyl groups and quaternary ammonium salt structures. The long-chain alkyl groups on the surface of the prepared nanoparticles can interact with the long-chain alkyl groups of surfactants, stabilizing the micelles formed by the surfactants and exhibiting synergistic effects. The interfacial adsorption energy is much higher than that of the surfactants, which enhances the strength of the foam film and improves the high-temperature and salt resistance of the fracturing fluid. The small particle size of the nanoparticles makes them less likely to clog porous media, thus exhibiting lower toxicity.

[0036] The high-temperature resistant clean fracturing fluid prepared by this invention has good high-temperature resistance, salt resistance and shear resistance, good sand carrying capacity, and excellent viscoelasticity. It avoids damage to the original formation properties caused by a large number of inorganic ions. The preparation process is simple and the raw materials are widely available. It has broad application prospects in oil and gas field development and production enhancement. Detailed Implementation

[0037] The technical solutions in the embodiments of the present invention will be clearly and completely described below. 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 skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] Preparation Example 1: Preparation of High-Temperature Resistant Gemini Surfactants

[0039] The synthesis route is as follows:

[0040]

[0041] The method is as follows:

[0042] S1. Add 0.1 mol hexanol, 0.15 mol NaOH (prepared as a 50 wt% aqueous solution), and 0.01 mol tetrabutylammonium bromide to 200 mL n-hexane, add 0.12 mol epichlorohydrin, stir at 30 °C for 5 h, separate the organic phase, remove the solvent under reduced pressure, wash, and dry to obtain intermediate 1.

[0043] S2. Add 0.11 mol ethylenediamine, 0.3 mol NaOH, and 0.2 mol 1-chloroheptane to 200 mL of dichloromethane, heat to 40 °C, stir and react for 3 h, filter, remove solvent under reduced pressure, wash, and dry to obtain intermediate 2;

[0044] S3. Add 0.1 mol of intermediate 1 and 0.11 mol of intermediate 2 to 200 mL of methanol, stir at 30 °C for 8 h, remove solvent under reduced pressure, wash, dry, and obtain intermediate 3;

[0045] S4. Add 0.1 mol of intermediate 3 and 0.2 mol of butyryl lactone to 200 mL of acetone, heat to 30 °C, stir and react for 10 h, filter, wash and dry to obtain intermediate 4;

[0046] S5. 0.1 mol intermediate 4, 0.1 mol 4-bromononoxybenzene, and 0.3 mol triethylamine were added to 200 mL of dichloromethane, and the mixture was heated under reflux for 5 h. The mixture was then filtered, washed, and dried to obtain the product, with an overall yield of 55.2%.

[0047] Infrared spectral analysis: at 3415 cm⁻¹ -1 The peak at 2867-2880 cm⁻¹ represents the stretching vibration peak of NH₄⁺ on quaternary ammonium salts. -1 The peak at 917-1115 cm⁻¹ is a symmetrical absorption peak for the hydrophobic carbon chain -CH₂-. -1 The peak at 954 cm⁻¹ represents the stretching vibration of CoC. -1 621cm -1 And 522cm -1 The peak at 812 cm⁻¹ represents the stretching vibration of the sulfonate group. -1 The characteristic absorption peak of the benzene ring is at 712 cm⁻¹. -1 The absorption peak is the in-plane rocking vibration of -(CH2)n-.

[0048] Preparation Example 2: Preparation of High-Temperature Resistant Gemini Surfactants

[0049] The method is as follows:

[0050] S1. Add 0.1 mol dodecanol, 0.15 mol NaOH (prepared as a 50 wt% aqueous solution), and 0.01 mol tetrabutylammonium bromide to 200 mL of n-hexane, add 0.15 mol epichlorohydrin, stir the reaction at 50 °C for 7 h, separate the organic phase, remove the solvent under reduced pressure, wash, and dry to obtain intermediate 1.

[0051] S2. Add 0.12 mol ethylenediamine, 0.3 mol NaOH, and 0.2 mol 1-chlorohexane to 200 mL dichloromethane, heat to 50 °C, stir and react for 5 h, filter, remove solvent under reduced pressure, wash, and dry to obtain intermediate 2;

[0052] S3. Add 0.1 mol of intermediate 1 and 0.12 mol of intermediate 2 to 200 mL of methanol, stir at 40 °C for 12 h, remove solvent under reduced pressure, wash, dry, and obtain intermediate 3.

[0053] S4. Add 0.1 mol of intermediate 3 and 0.22 mol of butyryl lactone to 200 mL of acetone, heat to 40 °C, stir and react for 12 h, filter, wash and dry to obtain intermediate 4.

[0054] S5. 0.1 mol of intermediate 4, 0.12 mol of 4-bromododecyloxybenzene, and 0.3 mol of triethylamine were added to 200 mL of dichloromethane, and the mixture was heated under reflux for 7 h. The mixture was then filtered, washed, and dried to obtain the product, with an overall yield of 57.1%.

[0055] Preparation Example 3: Preparation of High-Temperature Resistant Gemini Surfactants

[0056] The method is as follows:

[0057] S1. Add 0.1 mol octanol, 0.15 mol NaOH (prepared as a 50 wt% aqueous solution), and 0.01 mol tetrabutylammonium bromide to 200 mL n-hexane, add 0.135 mol epichlorohydrin, stir the reaction at 40 °C for 6 h, separate the organic phase, remove the solvent under reduced pressure, wash, and dry to obtain intermediate 1.

[0058] S2. Add 0.115 mol ethylenediamine, 0.3 mol NaOH, and 0.2 mol 1-chlorododecane to 200 mL of dichloromethane, heat to 45 °C, stir and react for 4 h, filter, remove solvent under reduced pressure, wash, and dry to obtain intermediate 2;

[0059] S3. Add 0.1 mol of intermediate 1 and 0.115 mol of intermediate 2 to 200 mL of methanol, stir and react at 35 °C for 10 h, remove the solvent under reduced pressure, wash and dry to obtain intermediate 3;

[0060] S4. Add 0.1 mol of intermediate 3 and 0.21 mol of butyryl lactone to 200 mL of acetone, heat to 35 °C, stir and react for 11 h, filter, wash and dry to obtain intermediate 4.

[0061] S5. Add 0.1 mol of intermediate 4, 0.11 mol of 4-bromohexyloxybenzene, and 0.3 mol of triethylamine to 200 mL of dichloromethane, heat under reflux for 6 h, filter, wash, and dry to obtain the product with an overall yield of 56.5%.

[0062] Test Example 1

[0063] The performance of the high-temperature resistant gemini surfactants prepared in Examples 1-3 was determined by performance testing.

[0064] Surface tension was measured using a fully automated surface tension meter at a test temperature of (25±0.5)℃. The critical micelle concentration (cmc) and the surface tension (γ) at that concentration were determined according to the national standard GB / T22237-2008. cmc .

[0065] According to the national standard GB / T7462-1994, foam was measured using a Roche foam analyzer with the solution falling method. The initial foam volume was recorded, and the time it took for the foam to collapse to half its initial height was also recorded, i.e., the foam half-life. The solution concentration was 0.1 wt%.

[0066] The results are shown in Table 1.

[0067] Table 1

[0068]

[0069] As can be seen from the table above, the high-temperature resistant Gemini surfactants prepared in Examples 1-3 of this invention have low critical micelle concentration and low surface tension, good foaming performance, and good foam stability.

[0070] The preparation method of the nanoparticles in Example 4 is as follows:

[0071] T1. Preparation of silica nanospheres: 160 parts by weight of ethanol, 3 parts by weight of ammonia and 15 parts by weight of water were stirred and mixed for 30 min, 9 parts by weight of tetraethyl orthosilicate were added, heated to 30 °C, and stirred for 10 h for hydrolysis reaction. After centrifugation, washing and drying, silica nanospheres were obtained.

[0072] T2. Aminosilane modification: 100 parts by weight of the silica nanospheres obtained in step T1 were added to 200 parts by weight of ethanol, and 7 parts by weight of amino-containing silane coupling agent were added. The mixture was heated to 40°C, stirred for 2 hours, centrifuged, washed, and dried to obtain aminosilane-modified silica nanospheres.

[0073] The amino-containing silane coupling agent is a mixture of KH550 and KH602 in a mass ratio of 3:2;

[0074] T3. Surface modification: 100 parts by weight of the aminosilane-modified silica nanospheres obtained in step T2 were added to 200 parts by weight of acetonitrile, 12 parts by weight of triethylamine and 15 parts by weight of 1-chlorododecane were added, the mixture was heated to 50°C, stirred for 3 hours, centrifuged, washed and dried to obtain nanoparticles.

[0075] The preparation method of the nanoparticles in Example 5 is as follows:

[0076] T1. Preparation of silica nanospheres: 170 parts by weight of ethanol, 4 parts by weight of ammonia and 20 parts by weight of water were stirred and mixed for 30 min. 12 parts by weight of tetraethyl orthosilicate were added, heated to 35°C, and stirred for 12 h for hydrolysis reaction. After centrifugation, washing and drying, silica nanospheres were obtained.

[0077] T2. Aminosilane modification: 100 parts by weight of the silica nanospheres obtained in step T1 were added to 200 parts by weight of ethanol, and 10 parts by weight of amino-containing silane coupling agent were added. The mixture was heated to 45°C, stirred for 4 hours, centrifuged, washed, and dried to obtain aminosilane-modified silica nanospheres.

[0078] The amino-containing silane coupling agent is a mixture of KH550 and KH602 in a mass ratio of 5:2;

[0079] T3. Surface modification: 100 parts by weight of the aminosilane-modified silica nanospheres obtained in step T2 were added to 200 parts by weight of acetonitrile, along with 15 parts by weight of triethylamine and 20 parts by weight of 1-bromohexadecane. The mixture was heated to 60°C, stirred for 5 hours, centrifuged, washed, and dried to obtain nanoparticles.

[0080] The preparation method of the nanoparticles in Example 6 is as follows:

[0081] T1. Preparation of silica nanospheres: 165 parts by weight of ethanol, 3.5 parts by weight of ammonia and 17 parts by weight of water were stirred and mixed for 30 min. 9-12 parts by weight of tetraethyl orthosilicate were added, heated to 32℃, and stirred for hydrolysis reaction 11. After centrifugation, washing and drying, silica nanospheres were obtained.

[0082] T2. Aminosilane modification: 100 parts by weight of the silica nanospheres obtained in step T1 were added to 200 parts by weight of ethanol, and 8.4 parts by weight of amino-containing silane coupling agent were added. The mixture was heated to 42°C, stirred and reacted for 3 hours, centrifuged, washed and dried to obtain aminosilane-modified silica nanospheres.

[0083] The amino-containing silane coupling agent is a mixture of KH550 and KH602 in a mass ratio of 4:2;

[0084] T3. Surface modification: 100 parts by weight of the aminosilane-modified silica nanospheres obtained in step T2 were added to 200 parts by weight of acetonitrile, along with 13 parts by weight of triethylamine and 17 parts by weight of 1-bromooctadecane. The mixture was heated to 55°C, stirred for 4 hours, centrifuged, washed, and dried to obtain nanoparticles.

[0085] Comparative Preparation Example 1

[0086] The difference compared to Preparation Example 6 is that step T3 was not performed.

[0087] Comparative Preparation Example 2

[0088] The difference compared to Preparation Example 6 is that steps T2 and T3 were not performed.

[0089] Test Example 2

[0090] The nanoparticles prepared in Examples 4-6 of this invention were tested.

[0091] The specific surface area was determined using a Quantachrome nitrogen adsorption surface area analyzer.

[0092] The average particle size was determined using an Omega particle size analyzer.

[0093] The results are shown in Table 2.

[0094] Table 2

[0095] Group <![CDATA[Specific surface area (m 2 / g)]]> Average particle size (nm) Preparation Example 4 227 220 Preparation Example 5 231 215 Preparation Example 6 239 207

[0096] As can be seen from the table above, the nanoparticles prepared in Examples 4-6 of this invention have a large specific surface area and a small average particle size.

[0097] Example 1

[0098] This embodiment provides a method for preparing a high-temperature resistant clean fracturing fluid, including the following steps:

[0099] (1) Dissolve 3 parts by weight of the high-temperature resistant Gemini surfactant prepared in Preparation Example 1 and 0.5 parts by weight of sodium cetylbenzenesulfonate in 70 parts by weight of water, stir and mix for 30 min, add 1 part by weight of the nanoparticle agent prepared in Preparation Example 4, emulsify at 5000 r / min for 15 min, and obtain a mixture.

[0100] (2) Add 5 parts by weight of cyclohexanol to the mixture in step (1) and stir for 30 minutes to obtain a high-temperature resistant and clean fracturing fluid.

[0101] Example 2

[0102] This embodiment provides a method for preparing a high-temperature resistant clean fracturing fluid, including the following steps:

[0103] (1) Dissolve 5 parts by weight of the high-temperature resistant Gemini surfactant prepared in Preparation Example 2 and 1 part by weight of sodium tetradecyl sulfate in 80 parts by weight of water, stir and mix for 30 min, add 2 parts by weight of the nanoparticle agent prepared in Preparation Example 5, emulsify at 5000 r / min for 15 min, and obtain a mixture.

[0104] (2) Add 7 parts by weight of ethanol to the mixture in step (1) and stir for 30 minutes to obtain a high-temperature resistant and clean fracturing fluid.

[0105] Example 3

[0106] This embodiment provides a method for preparing a high-temperature resistant clean fracturing fluid, including the following steps:

[0107] (1) Dissolve 4 parts by weight of the high-temperature resistant Gemini surfactant prepared in Preparation Example 3 and 0.7 parts by weight of sodium dodecylbenzenesulfonate in 75 parts by weight of water, stir and mix for 30 min, add 1.5 parts by weight of the nanoparticle agent prepared in Preparation Example 6, emulsify at 5000 r / min for 15 min, and obtain a mixture.

[0108] (2) Add 6 parts by weight of isopropanol to the mixture in step (1) and stir for 30 minutes to obtain a high-temperature resistant and clean fracturing fluid.

[0109] Comparative Examples 1-2

[0110] The difference from Example 3 is that the nanoparticles were prepared from Comparative Preparation Examples 1-2.

[0111] Comparative Example 3

[0112] The difference compared to Example 3 is that no nanoparticles were added.

[0113] Specifically as follows:

[0114] (1) Dissolve 4 parts by weight of the high-temperature resistant Gemini surfactant prepared in Example 3 and 0.7 parts by weight of sodium dodecylbenzenesulfonate in 75 parts by weight of water, stir and mix for 30 min, emulsify at 5000 r / min for 15 min to obtain a mixture;

[0115] (2) Add 6 parts by weight of isopropanol to the mixture in step (1) and stir for 30 minutes to obtain a high-temperature resistant and clean fracturing fluid.

[0116] Comparative Example 4

[0117] The difference compared to Example 3 is that sodium dodecylbenzenesulfonate was not added.

[0118] Specifically as follows:

[0119] (1) Dissolve 4.7 parts by weight of the high-temperature resistant Gemini surfactant prepared in Preparation Example 3 in 75 parts by weight of water, stir and mix for 30 min, add 1.5 parts by weight of the nanoparticle agent prepared in Preparation Example 6, emulsify at 5000 r / min for 15 min, and obtain a mixture.

[0120] (2) Add 6 parts by weight of isopropanol to the mixture in step (1) and stir for 30 minutes to obtain a high-temperature resistant and clean fracturing fluid.

[0121] Comparative Example 5

[0122] The difference compared to Example 3 is that no high-temperature resistant Gemini surfactant was added.

[0123] Specifically as follows:

[0124] (1) Dissolve 4.7 parts by weight of sodium dodecylbenzenesulfonate in 75 parts by weight of water, stir and mix for 30 min, add 1.5 parts by weight of the nanoparticles prepared in Preparation Example 6, emulsify at 5000 r / min for 15 min, and obtain a mixture;

[0125] (2) Add 6 parts by weight of isopropanol to the mixture in step (1) and stir for 30 minutes to obtain a high-temperature resistant and clean fracturing fluid.

[0126] Test Example 3

[0127] Static suspension tests were used to determine the settling velocity of sand particles in the high-temperature clean fracturing fluids prepared in Examples 1-3 and Comparative Examples 1-5. The high-temperature clean fracturing fluid was poured into a 100ml graduated cylinder, and the liquid level height h was measured with a ruler. Propped sand particles were gently placed onto the liquid surface, and the time t for the first particle to reach the bottom of the graduated cylinder was recorded at different temperatures. The sand ratio was 20%.

[0128] The method for calculating the settling velocity is: settling velocity v = liquid level height h / settling time t.

[0129] The results are shown in Table 3.

[0130] Table 3

[0131]

[0132] As can be seen from the table above, the high-temperature resistant clean fracturing fluids prepared in Examples 1-3 of this invention have good sand-carrying capacity and temperature resistance.

[0133] Test Example 4

[0134] The viscosity of the high-temperature resistant clean fracturing fluids prepared in Examples 1-3 and Comparative Examples 1-5 of this invention was tested using the rheometer described above. The shear rate was set at 170 s. -1 .

[0135] 1. Temperature resistance

[0136] The viscosity was tested at room temperature and 220°C.

[0137] 2. Shear resistance

[0138] Test at 170s -1 Viscosity after 2 hours of shearing.

[0139] 3. Salt resistance

[0140] Potassium chloride was added to the high-temperature resistant cleaning fracturing fluid to achieve a final KCl concentration of 5%, and its viscosity was tested.

[0141] The results are shown in Table 4.

[0142] Table 4

[0143]

[0144] As can be seen from the table above, the high-temperature resistant clean fracturing fluids prepared in Examples 1-3 of this invention have good viscoelasticity and excellent temperature resistance, salt resistance, and shear resistance.

[0145] Test Example 5

[0146] The damage to the core samples caused by the high-temperature resistant clean fracturing fluids prepared in Examples 1-3 and Comparative Examples 1-5 of this invention was determined.

[0147] The results are shown in Table 5.

[0148] Table 5

[0149]

[0150] As shown in the table above, the high-temperature resistant clean fracturing fluid prepared in Examples 1-3 of this invention has a core permeability damage rate of <2% and a core permeability retention rate of >98%. After the fracturing fluid breaks down, it causes less damage to the reservoir, thus meeting the low damage requirement.

[0151] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A high-temperature resistant, clean fracturing fluid, characterized in that, It is prepared from the following raw materials in parts by weight: 3-5 parts of high-temperature resistant gemini surfactant, 0.5-1 part of co-surfactant, 5-7 parts of excretion aid, 1-2 parts of nanoparticles, and 70-80 parts of water; the structural formula of the high-temperature resistant gemini surfactant is shown in Formula I: Among them, R1, R2, and R3 are C6-C12 alkyl chains; The nanoparticle agent is a surfactant-modified silica nanoparticle.

2. The high-temperature resistant clean fracturing fluid according to claim 1, characterized in that, The preparation method of the high-temperature resistant gemini surfactant is as follows: S1. Reaction of long-chain fatty alcohols with epichlorohydrin yields intermediate 1, with the following structure: S2. Reaction of ethylenediamine with a haloalkane yields intermediate 2, with the following structure: S3. Intermediate 1 and intermediate 2 are reacted to obtain intermediate 3, with the following structure: S4. Intermediate 3 was reacted with butyryl lactone to obtain intermediate 4, with the following structure: S5. React intermediate 4 with 4-bromoalkoxybenzene to obtain the product.

3. The high-temperature resistant clean fracturing fluid according to claim 2, characterized in that, In step S1, the molar ratio of the long-chain fatty alcohol to epichlorohydrin is 1:1.2-1.

5. The long-chain fatty alcohol is selected from at least one of acetalol, heptol, octanol, nonanol, decol, and dodecylol. A base is also added, which is NaOH or KOH. The reaction temperature is 30-50℃ and the reaction time is 5-7h. In step S2, the molar ratio of ethylenediamine to haloalkanes is 1.1-1.2:

2. The haloalkanes are selected from at least one of 1-chlorohexane, 1-bromohexane, 1-chloroheptane, 1-bromoheptane, 1-chlorooctane, 1-bromooctane, 1-chlorononane, 1-bromononane, 1-chlorodecane, 1-bromodecane, 1-chlorododecane, and 1-bromododecane. The reaction temperature is 40-50℃ and the reaction time is 3-5h.

4. The high-temperature resistant cleaning fracturing fluid according to claim 2, characterized in that, In step S3, the molar ratio of intermediate 1 to intermediate 2 is 1:1-1.1, the reaction temperature is 30-40℃, and the time is 8-12h; in step S4, the molar ratio of intermediate 3 to butyrylolactone is 1:2-2.2, the reaction temperature is 30-40℃, and the time is 10-12h; in step S5, the molar ratio of intermediate 4 to 4-bromoalkoxybenzene is 1:1-1.2, the reaction temperature is 50-60℃, and the time is 5-7h. A base is also added, the base being selected from at least one of triethylamine, NaOH, and KOH, and the 4-bromoalkoxybenzene being selected from at least one of 4-bromohexyloxybenzene, 4-bromoheptyloxybenzene, 4-bromononoxybenzene, 4-bromooctyloxybenzene, 4-bromodiphenyloxybenzene, 4-bromoundecyloxybenzene, and 4-bromododecyloxybenzene.

5. The high-temperature resistant cleaning fracturing fluid according to claim 2, characterized in that, The preparation method of the nanoparticles is as follows: T1. Preparation of silica nanospheres: Ethanol, ammonia and water were mixed evenly, tetraethyl orthosilicate was added, the mixture was heated to hydrolyze, centrifuged, washed and dried to obtain silica nanospheres; T2. Aminosilane modification: The silica nanospheres obtained in step T1 were added to ethanol, and an amino-containing silane coupling agent was added. The mixture was heated and stirred to react, centrifuged, washed, and dried to obtain aminosilane-modified silica nanospheres. T3. Surface modification: The aminosilane-modified silica nanospheres obtained in step T2 are added to acetonitrile, triethylamine and haloalkanes are added, the mixture is heated and stirred to react, centrifuged, washed and dried to obtain nanoparticles.

6. The high-temperature resistant clean fracturing fluid according to claim 5, characterized in that, In step T1, the mass ratio of ethanol, ammonia, water, and tetraethyl orthosilicate is 160-170:3-4:15-20:9-12, and the heating and hydrolysis reaction takes 10-12 hours at a temperature of 30-35°C. In step T2, the amino-containing silane coupling agent is selected from at least one of KH550, KH602, and KH792, and the mass ratio of silica nanospheres to the amino-containing silane coupling agent is 100:7-10. The heating and stirring reaction... The temperature is 40-45℃, and the time is 2-4h; in step T3, the mass ratio of aminosilane-modified silica nanospheres, triethylamine, and haloalkanes is 100:12-15:15-20, and the haloalkanes are selected from at least one of 1-chlorododecane, 1-chlorotetradecane, 1-chlorohexadecane, 1-chlorooctadecane, 1-bromododecane, 1-bromotetradecane, 1-bromohexadecane, and 1-bromooctadecane; the heating and stirring reaction is carried out at a temperature of 50-60℃ for 3-5h.

7. The high-temperature resistant clean fracturing fluid according to claim 5, characterized in that, The co-surfactant is selected from at least one of sodium dodecylbenzenesulfonate, sodium dodecyl sulfonate, sodium dodecyl sulfate, sodium tetradecyl sulfonate, sodium tetradecylbenzenesulfonate, sodium tetradecyl sulfate, sodium hexadecyl sulfate, sodium hexadecyl sulfonate, and sodium hexadecylbenzenesulfonate.

8. The high-temperature resistant clean fracturing fluid according to claim 5, characterized in that, The discharge aid is selected from at least one of methanol, ethanol, isopropanol, and cyclohexanol.

9. A method for preparing a high-temperature resistant clean fracturing fluid as described in any one of claims 1-8, characterized in that, Includes the following steps: (1) Dissolve the high-temperature resistant Gemini surfactant and co-surfactant in water, stir and mix evenly, add nanoparticles, emulsify, and obtain a mixture. (2) Add drainage aid to the mixture in step (1), stir and mix evenly to obtain high temperature resistant clean fracturing fluid.

10. The application of a high-temperature resistant clean fracturing fluid as described in any one of claims 1-8 in oil and gas field development and production enhancement.

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