A nitrogen foam fracturing fluid system for sandstone reservoirs and its preparation method and application

Abstract

The present invention belongs to the technical field of oil production, and in particular to a nitrogen foam fracturing fluid system for sandstone reservoirs and its preparation method and application. The preparation method is as follows: 4,6-diaminoresorcinol, ethanol, and dodecyl halide are added to the reactor, stirred evenly, heated and insulated to react, and the pH is maintained at 8-9; vacuum distillation, toluene is added, transferred to an autoclave, a catalyst is added, ethylene oxide is passed, heated and insulated to react, and the system is cooled; pH is adjusted to 2-3, aminosulfonic acid powder is added, stirred, heated and insulated to react, cooled, and pH is adjusted to 8-9; filtered, vacuum distilled to obtain a viscous solid, i.e., a foaming agent product; foaming agent, foam stabilizer, and simulated water are stirred evenly to obtain a foam fracturing fluid system. The foam fracturing fluid system of the present invention has the advantages of large foaming volume and long half-life, and the foaming volume reaches more than 800ml at room temperature, and the half-life reaches 1100s and more at room temperature.

Description

Technical Field

[0001] The invention belongs to the technical field of petroleum extraction, and in particular relates to a sandstone reservoir nitrogen foam fracturing fluid system and a preparation method and application thereof. Background Art

[0002] As an innovative fracturing fluid technology, the development and application of nitrogen foam fracturing technology has gradually occupied an important position in the field of oil and gas exploration and development. The core of this technology is to use nitrogen and foam mixture as fracturing fluid, which is pressed into the wellbore through the fracturing pipe, generating force under high pressure, cutting the formation and creating channels to support fluid flow. As the pressure is relieved, the nitrogen foam will retreat to the wellhead and enter the recovery system.

[0003] Nitrogen foam fracturing technology has many significant features and advantages. First, the fracturing fluid system has a large foam volume and a long foam half-life, which ensures stability and durability during the fracturing process. Second, the system does not contain large molecular polymers, has a fast flowback speed, uses less fluid, has little damage to the formation, has a simple formula and is low in cost.

[0004] Although nitrogen foam fracturing technology has shown many advantages, it still faces some technical challenges in its actual application. How to ensure the stability of nitrogen foam under high temperature and high pressure conditions is the key to technological breakthroughs. Therefore, the development of new, efficient, stable and environmentally friendly foaming agents is of great significance to promote the development of nitrogen foam fracturing technology.

[0005] CN102020981A discloses a temperature-resistant, salt-resistant, low-tension foam oil-displacing agent, wherein the raw materials are composed of 40-55 parts of alkanolamide, 10-50 parts of bipolar surfactant, and 100-200 parts of water; wherein the alkanolamide is coconut oil alkanolamide, fatty acid monoethanolamide or coconut oil diethanolamine; and the bipolar surfactant is alkyl dicarboxyethyl imizoline, alkyl alcohol polyoxyethylene ether sulfate, alkylphenol polyoxyethylene ether sulfate, sulfonic acid betaine, carboxylic acid betaine or dialkyl diphenyl ether sulfonate. However, the main agent of the foaming agent is alkanolamide and bipolar surfactant, and alkanolamide is easy to hydrolyze, has poor high temperature stability, is easy to fail in the formation, and its application is limited.

[0006] CN104312563B discloses a cationic micro-bubble surfactant for drilling fluid and a preparation method thereof, which is obtained by mixing a vinyl cationic monomer and a vinyl amide compound in a mass ratio of 10:1 to 10, adding a relative molecular mass regulator, and copolymerizing the mixture through free radicals. However, the foaming performance and foam stabilization performance are poor, and the effect in actual application is difficult to meet the on-site requirements. Summary of the invention

[0007] The present invention aims to provide a nitrogen foam fracturing fluid system for sandstone reservoirs and its preparation method and application in view of the above-mentioned deficiencies in the prior art. The foam fracturing fluid system of the present invention has the advantages of large foaming volume and long half-life, the foaming volume reaches more than 800 mL at room temperature, and the half-life reaches 1100 s or more at room temperature.

[0008] One of the purposes of the present invention is to disclose a nitrogen foam fracturing fluid system for sandstone oil reservoirs, wherein the composition and components of the foam fracturing fluid system are as follows:

[0009] Foaming agent 0.15-0.3 parts by mass;

[0010] Foam stabilizer 0.05-0.1 parts by mass;

[0011] 100 parts by mass of simulated water.

[0012] The foam stabilizer is one or more of hydroxyethyl cellulose, hydroxypropyl cellulose, gelatin, and sodium lauryl polyoxyethylene ether sulfate.

[0013] The simulated water is sodium chloride, 0.5wt%; calcium chloride, 0.2wt%; sodium bicarbonate, 0.05wt%, pH 7.5.

[0014] The molecular structural formula of the foaming agent is as follows:

[0015] or or two, wherein n=5-20.

[0016] Another object of the present invention is to disclose a method for preparing the above-mentioned nitrogen foam fracturing fluid system for sandstone reservoirs, wherein the specific steps of the preparation method are as follows:

[0017] (1) Add 4,6-diaminoresorcinol, ethanol and dodecyl halide into the reactor, stir evenly, heat and keep warm for reaction, and adjust and maintain the pH at 8-9 with sodium hydroxide;

[0018] (2) A viscous liquid is obtained by vacuum distillation, toluene is added, the mixture is evenly mixed and transferred to a high-pressure reactor, a catalyst is added, the reactor and pipelines are purged with nitrogen for 2-3 minutes, the reactor is closed, vacuumized, and ethylene oxide is introduced. After the introduction is completed, heating and insulation are performed for reaction. The reaction pressure gradually decreases. When the pressure no longer decreases, heating is stopped and the system is cooled to below 50°C using circulating cooling water;

[0019] (3) Adjust the pH to 2-3 with 50wt% sulfuric acid, add aminosulfonic acid powder to the above autoclave, stir, heat and keep warm for reaction, cool to below 40°C, and adjust the pH to 8-9 with sodium hydroxide;

[0020] (4) filtering and distilling under reduced pressure to obtain a viscous solid, i.e., a foaming agent product;

[0021] (5) The foaming agent, foam stabilizer and simulated water are mixed evenly in proportion to obtain a foam fracturing fluid system.

[0022] In the present invention, preferably, based on 1 mole of 4,6-diaminoresorcinol, the amounts of dodecyl halide, ethylene oxide and aminosulfonic acid are 3-5 mole parts, 10-40 mole parts and 0.8-2.5 mole parts respectively; more preferably, based on 1 mole of 4,6-diaminoresorcinol, the amounts of dodecyl halide, ethylene oxide and aminosulfonic acid are 3.5-4.5 mole parts, 16-32 mole parts and 1.5-2.2 mole parts respectively.

[0023] Preferably, the mass ratio of ethanol to 4,6-diaminoresorcinol in step (1) is 20-40:1.

[0024] Preferably, the heating and heat preservation reaction temperature in step (1) is 70-80°C and the time is 1-6h.

[0025] Preferably, the mass ratio of toluene to 4,6-diaminoresorcinol in step (2) is 4-10:1.

[0026] Preferably, the catalyst in step (2) is one of sodium hydroxide, calcium hydroxide and potassium hydroxide, and the mass ratio of the catalyst to 4,6-diaminoresorcinol is 0.3-0.6:1.

[0027] Preferably, the heating and heat preservation reaction temperature in step (2) is 150-180°C.

[0028] Preferably, the heating and heat preservation reaction temperature in step (3) is 120-140° C. and the time is 1-4 h.

[0029] The foaming agent synthesis reaction equation of the present invention is as follows:

[0030] or Wherein, X is Cl or Br.

[0031] The third object of the present invention is to disclose the application of the above-mentioned fracturing fluid system in sandstone reservoir fracturing.

[0032] The nitrogen foam fracturing fluid system for sandstone reservoirs of the present invention is composed of a foaming agent, a foam stabilizer and water. The foaming agent is a composite surfactant, the lipophilic group is four dodecyl groups, and the hydrophilic group is a nonionic polyoxyethylene ether and an anionic sulfate group. The foaming agent of the present invention is more active than conventional single-active group surfactants, can greatly reduce surface tension, increase foaming volume and capacity, and has high stability. The molecules are multilinear molecules, have strong flexibility, and cover a large area. When the foam liquid film becomes thinner, it can quickly laterally attract other parts of the liquid film to supplement and enhance the stability of the foam. The foam stabilizer can control the structural stability of the bubble liquid film, so that the surfactant molecules are orderly distributed on the bubble liquid film, thereby giving the foam good elasticity and self-repairing ability.

[0033] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0034] (1) The nitrogen foam fracturing fluid system for sandstone oil reservoirs of the present invention has the characteristic of large foaming volume, which reaches more than 800 mL at room temperature;

[0035] (2) The nitrogen foam fracturing fluid system for sandstone oil reservoirs of the present invention has the characteristic of a long half-life, which can reach 1100 seconds or more at room temperature. DETAILED DESCRIPTION

[0036] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0037] Example 1

[0038] (1) Add 0.05 mol 4,6-diaminoresorcinol, 140 g ethanol, and 0.15 mol dodecyl chloride into the reactor, stir evenly, heat to 70°C, keep warm for 6 hours, and adjust and maintain the pH at 8-9 with sodium hydroxide;

[0039] (2) A viscous liquid was obtained by vacuum distillation, 28 g of toluene was added, the mixture was evenly mixed and transferred to a high-pressure reactor, 2.1 g of sodium hydroxide was added, the reactor and pipeline were purged with nitrogen for 2-3 min, the reactor was closed, vacuumed, 0.5 mol of ethylene oxide was introduced, and after the introduction was completed, it was heated to 150°C and kept warm for reaction. The reaction pressure gradually decreased. When the pressure no longer decreased, the heating was stopped and the system was cooled to below 50°C using circulating cooling water;

[0040] (3) Adjust the pH to 2-3 with 50wt% sulfuric acid, add 0.04mol aminosulfonic acid powder to the above autoclave, stir, heat to 120°C, keep warm for 1h, cool to below 40°C, and adjust the pH to 8-9 with sodium hydroxide;

[0041] (4) filtering and distilling under reduced pressure to obtain a viscous solid, i.e., a foaming agent product;

[0042] (5) 0.15 g of foaming agent, 0.05 g of hydroxyethyl cellulose, and 100 g of simulated water were mixed evenly in proportion to obtain a foam fracturing fluid system.

[0043] Example 2

[0044] (1) Add 0.05 mol 4,6-diaminoresorcinol, 280 g ethanol, and 0.25 mol dodecyl chloride into the reactor, stir evenly, heat to 80°C, keep warm for 1 hour, and adjust and maintain the pH at 8-9 with sodium hydroxide;

[0045] (2) A viscous liquid is obtained by vacuum distillation, 70 g of toluene is added, the mixture is mixed evenly and transferred to a high-pressure reactor, 4.2 g of sodium hydroxide is added, the reactor and pipelines are purged with nitrogen for 2-3 min, the reactor is closed, vacuumized, and 2 mol of ethylene oxide is introduced. After the introduction is completed, the reaction is heated to 180°C and kept warm for reaction. The reaction pressure gradually decreases. When the pressure no longer decreases, the heating is stopped and the system is cooled to below 50°C using circulating cooling water;

[0046] (3) Adjust the pH to 2-3 with 50wt% sulfuric acid, add 0.125mol aminosulfonic acid powder to the above autoclave, stir, heat to 120°C, keep warm for 4h, cool to below 40°C, and adjust the pH to 8-9 with sodium hydroxide;

[0047] (4) filtering and distilling under reduced pressure to obtain a viscous solid, i.e., a foaming agent product;

[0048] (5) 0.18 g of foaming agent, 0.06 g of hydroxypropyl cellulose, and 100 g of simulated water were mixed evenly in proportion to obtain a foam fracturing fluid system.

[0049] Example 3

[0050] (1) Add 0.05 mol 4,6-diaminoresorcinol, 180 g ethanol, and 0.16 mol dodecyl chloride into the reactor, stir evenly, heat to 75°C, keep warm for 2 hours, and adjust and maintain the pH at 8-9 with sodium hydroxide;

[0051] (2) A viscous liquid was obtained by vacuum distillation, 39 g of toluene was added, the mixture was evenly mixed and transferred to a high-pressure reactor, 2.6 g of calcium hydroxide was added, the reactor and pipeline were purged with nitrogen for 2-3 min, the reactor was closed, vacuumed, 1 mol of ethylene oxide was introduced, and after the introduction was completed, it was heated to 160°C and kept warm for reaction. The reaction pressure gradually decreased. When the pressure no longer decreased, the heating was stopped and the system was cooled to below 50°C using circulating cooling water;

[0052] (3) Adjust the pH to 2-3 with 50wt% sulfuric acid, add 0.06mol aminosulfonic acid powder to the above autoclave, stir, heat to 140°C, keep the temperature for 1h, cool to below 40°C, and adjust the pH to 8-9 with sodium hydroxide;

[0053] (4) filtering and distilling under reduced pressure to obtain a viscous solid, i.e., a foaming agent product;

[0054] (5) 0.2 g of foaming agent, 0.07 g of gelatin, and 100 g of simulated water were mixed evenly in proportion to obtain a foam fracturing fluid system.

[0055] Example 4

[0056] (1) Add 0.05 mol 4,6-diaminoresorcinol, 250 g ethanol, and 0.23 mol dodecyl chloride into the reactor, stir evenly, heat to 73°C, keep warm for 2 hours, and adjust and maintain the pH at 8-9 with sodium hydroxide;

[0057] (2) A viscous liquid was obtained by vacuum distillation, 48 g of toluene was added, the mixture was evenly mixed and transferred to a high-pressure reactor, 3.1 g of calcium hydroxide was added, the reactor and pipeline were purged with nitrogen for 2-3 min, the reactor was closed, vacuumed, and 1.2 mol of ethylene oxide was introduced. After the introduction was completed, the reaction was heated to 160°C and kept warm for reaction. The reaction pressure gradually decreased. When the pressure no longer decreased, the heating was stopped and the system was cooled to below 50°C using circulating cooling water;

[0058] (3) Adjust the pH to 2-3 with 50wt% sulfuric acid, add 0.08mol aminosulfonic acid powder to the above autoclave, stir, heat to 130°C, keep warm for 2h, cool to below 40°C, and adjust the pH to 8-9 with sodium hydroxide;

[0059] (4) filtering and distilling under reduced pressure to obtain a viscous solid, i.e., a foaming agent product;

[0060] (5) 0.3 g of foaming agent, 0.08 g of sodium lauryl polyoxyethylene ether sulfate, and 100 g of simulated water were mixed uniformly in proportion to obtain a foam fracturing fluid system.

[0061] Example 5

[0062] (1) Add 0.05 mol 4,6-diaminoresorcinol, 223 g ethanol, and 0.18 mol dodecyl bromide into the reactor, stir evenly, heat to 76°C, keep warm for 3 hours, and adjust and maintain the pH at 8-9 with sodium hydroxide;

[0063] (2) A viscous liquid was obtained by vacuum distillation, 50 g of toluene was added, the mixture was evenly mixed and transferred to a high-pressure reactor, 3.8 g of potassium hydroxide was added, the reactor and pipeline were purged with nitrogen for 2-3 min, the reactor was closed, vacuumed, and 1.4 mol of ethylene oxide was introduced. After the introduction was completed, the reaction was heated to 170°C and kept warm for reaction. The reaction pressure gradually decreased. When the pressure no longer decreased, the heating was stopped and the system was cooled to below 50°C using circulating cooling water;

[0064] (3) Adjust the pH to 2-3 with 50wt% sulfuric acid, add 0.095mol aminosulfonic acid powder to the above autoclave, stir, heat to 120°C, keep warm for 2h, cool to below 40°C, and adjust the pH to 8-9 with sodium hydroxide;

[0065] (4) filtering and distilling under reduced pressure to obtain a viscous solid, i.e., a foaming agent product;

[0066] (5) 0.25 g of foaming agent, 0.05 g of hydroxyethyl cellulose, 0.05 g of gelatin, and 100 g of simulated water were mixed evenly in proportion to obtain a foam fracturing fluid system.

[0067] Example 6

[0068] (1) Add 0.05 mol 4,6-diaminoresorcinol, 257 g ethanol, and 0.22 mol dodecyl bromide into the reactor, stir evenly, heat to 78°C, keep warm for 4 hours, and adjust and maintain the pH at 8-9 with sodium hydroxide;

[0069] (2) A viscous liquid was obtained by vacuum distillation, 60 g of toluene was added, the mixture was evenly mixed and transferred to a high-pressure reactor, 3.5 g of potassium hydroxide was added, the reactor and pipelines were purged with nitrogen for 2-3 min, the reactor was closed, vacuumed, and 1.5 mol of ethylene oxide was introduced. After the introduction was completed, the reaction was heated to 170°C and kept warm for reaction. The reaction pressure gradually decreased. When the pressure no longer decreased, the heating was stopped and the system was cooled to below 50°C using circulating cooling water;

[0070] (3) Adjust the pH to 2-3 with 50wt% sulfuric acid, add 0.102mol of aminosulfonic acid powder to the above autoclave, stir, heat to 120°C, keep the temperature for 3h, cool to below 40°C, and adjust the pH to 8-9 with sodium hydroxide;

[0071] (4) filtering and distilling under reduced pressure to obtain a viscous solid, i.e., a foaming agent product;

[0072] (5) 0.25 g of foaming agent, 0.05 g of hydroxyethyl cellulose, 0.05 g of sodium lauryl polyoxyethylene ether sulfate, and 100 g of simulated water were mixed uniformly in proportion to obtain a foam fracturing fluid system.

[0073] Example 7

[0074] (1) Add 0.05 mol 4,6-diaminoresorcinol, 240 g ethanol, and 0.2 mol dodecyl bromide into the reactor, stir evenly, heat to 76°C, keep warm for 3 hours, and adjust and maintain the pH at 8-9 with sodium hydroxide;

[0075] (2) A viscous liquid was obtained by vacuum distillation, 60 g of toluene was added, the mixture was evenly mixed and transferred to a high-pressure reactor, 3.2 g of potassium hydroxide was added, the reactor and pipelines were purged with nitrogen for 2-3 min, the reactor was closed, vacuumed, and 1.6 mol of ethylene oxide was introduced. After the introduction was completed, the reaction was heated to 170°C and kept warm for reaction. The reaction pressure gradually decreased. When the pressure no longer decreased, the heating was stopped and the system was cooled to below 50°C using circulating cooling water;

[0076] (3) Adjust the pH to 2-3 with 50wt% sulfuric acid, add 0.11mol aminosulfonic acid powder to the above autoclave, stir, heat to 130°C, keep warm for 2h, cool to below 40°C, and adjust the pH to 8-9 with sodium hydroxide;

[0077] (4) filtering and distilling under reduced pressure to obtain a viscous solid, i.e., a foaming agent product;

[0078] (5) 0.28 g of foaming agent, 0.03 g of hydroxyethyl cellulose, 0.07 g of sodium lauryl polyoxyethylene ether sulfate, and 100 g of simulated water were mixed uniformly in proportion to obtain a foam fracturing fluid system.

[0079] Example 8 Foaming agent performance test

[0080] Take 100 mL of the foam fracturing fluid system of the present invention, pour it into a high-stirring cup, place it on a high-speed stirrer, introduce nitrogen into the upper end to maintain the nitrogen atmosphere, start the high-speed stirrer, and record the time with a stopwatch. Stir for 60 seconds at a speed of (11000±300) r / min, quickly remove the high-stirring cup, pour all the generated foam liquid into a 1000 mL measuring cylinder, and record the time with a stopwatch. Then observe and record the foam volume in the measuring cylinder, which is the foaming volume.

[0081] The time taken for 50 mL of liquid to separate out from the foam is recorded as the half-life.

[0082] The fracturing foaming agent DRKJ-13 produced by Zhengzhou Derong Technology Co., Ltd. was prepared with simulated water to a concentration of 0.3wt% for comparative experiments.

[0083] Table 1 Foaming performance test results

[0084]

[0085] From Table 1 we can see that:

[0086] (1) The foam fracturing fluid system of the present invention has the characteristic of large foaming volume. The foaming volume at room temperature reaches more than 800 mL, and the highest reaches 870 mL (Example 7). The foaming volume of the comparative example is 380 mL, which is significantly lower than that of the present invention.

[0087] (2) The foam fracturing fluid system of the present invention has the characteristic of a long half-life, which reaches 1100 s or more at room temperature, and the highest reaches 1800 s (Example 7), while the half-life of the comparative example is 400 s, which is significantly lower than that of the present invention.

[0088] The preferred embodiments of the present invention are described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, a variety of simple modifications can be made to the technical solution of the present invention, and these simple modifications all belong to the protection scope of the present invention.

[0089] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0090] In addition, various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A nitrogen foam fracturing fluid system for sandstone reservoirs, characterized in that: The composition and components of the fracturing fluid system are as follows: Foaming agent 0.15-0.3 parts by mass; Foam stabilizer 0.05-0.1 parts by mass; 100 parts by mass of simulated water; The foam stabilizer is one or more of hydroxyethyl cellulose, hydroxypropyl cellulose, gelatin, and sodium lauryl polyoxyethylene ether sulfate; The simulated water is sodium chloride, 0.5wt%; calcium chloride, 0.2wt%; sodium bicarbonate, 0.05wt%, pH 7.5; The specific steps of the preparation method of the fracturing fluid system are as follows: (1) Add 4,6-diaminoresorcinol, ethanol and dodecyl halide into the reactor, stir evenly, heat and keep warm for reaction, and adjust and maintain the pH at 8-9 with sodium hydroxide; (2) A viscous liquid is obtained by vacuum distillation, toluene is added, the mixture is evenly mixed and transferred to a high-pressure reactor, a catalyst is added, the reactor and pipelines are purged with nitrogen for 2-3 minutes, the reactor is closed, vacuumized, and ethylene oxide is introduced. After the introduction is completed, heating and insulation are performed for reaction. The reaction pressure gradually decreases. When the pressure no longer decreases, heating is stopped and the system is cooled to below 50°C using circulating cooling water; (3) Adjust the pH to 2-3 with 50wt% sulfuric acid, add aminosulfonic acid powder to the above autoclave, stir, heat and keep warm for reaction, cool to below 40°C, and adjust the pH to 8-9 with sodium hydroxide; (4) filtering and distilling under reduced pressure to obtain a viscous solid, i.e., a foaming agent product; (5) Mixing the foaming agent, the foam stabilizer and the simulated water in proportion to obtain a foam fracturing fluid system; Based on 1 mole of 4,6-diaminoresorcinol, the amounts of dodecyl halide, ethylene oxide and aminosulfonic acid are 3-5 mole parts, 10-40 mole parts and 0.8-2.5 mole parts respectively.

2. A method for preparing a nitrogen foam fracturing system for sandstone reservoirs, characterized in that: The specific steps of the preparation method are as follows: (1) Add 4,6-diaminoresorcinol, ethanol and dodecyl halide into the reactor, stir evenly, heat and keep warm for reaction, and adjust and maintain the pH at 8-9 with sodium hydroxide; (2) A viscous liquid is obtained by vacuum distillation, toluene is added, the mixture is evenly mixed and transferred to a high-pressure reactor, a catalyst is added, the reactor and pipelines are purged with nitrogen for 2-3 minutes, the reactor is closed, vacuumized, and ethylene oxide is introduced. After the introduction is completed, heating and insulation are performed for reaction. The reaction pressure gradually decreases. When the pressure no longer decreases, heating is stopped and the system is cooled to below 50°C using circulating cooling water; (3) Adjust the pH to 2-3 with 50wt% sulfuric acid, add aminosulfonic acid powder to the above autoclave, stir, heat and keep warm for reaction, cool to below 40°C, and adjust the pH to 8-9 with sodium hydroxide; (4) filtering and distilling under reduced pressure to obtain a viscous solid, i.e., a foaming agent product; (5) Mixing the foaming agent, the foam stabilizer and the simulated water in proportion to obtain a foam fracturing fluid system; Based on 1 mole of 4,6-diaminoresorcinol, the amounts of dodecyl halide, ethylene oxide and aminosulfonic acid are 3-5 mole parts, 10-40 mole parts and 0.8-2.5 mole parts respectively.

3. The method for preparing a nitrogen foam fracturing fluid system for sandstone oil reservoirs according to claim 2, characterized in that: Based on 1 mole of 4,6-diaminoresorcinol, the amounts of dodecyl halide, ethylene oxide and aminosulfonic acid are 3.5-4.5 moles, 16-32 moles and 1.5-2.2 moles respectively.

4. The method for preparing a nitrogen foam fracturing fluid system for sandstone oil reservoirs according to claim 2, characterized in that: The heating and heat preservation reaction temperature in step (1) is 70-80°C and the time is 1-6h.

5. The method for preparing a nitrogen foam fracturing fluid system for sandstone oil reservoirs according to claim 2, characterized in that: The catalyst in step (2) is one of sodium hydroxide, calcium hydroxide and potassium hydroxide, and the mass ratio of the catalyst to 4,6-diaminoresorcinol is 0.3-0.6:

1.

6. The method for preparing a nitrogen foam fracturing fluid system for sandstone oil reservoirs according to claim 2, characterized in that: The heating and heat preservation reaction temperature in step (2) is 150-180°C.

7. The method for preparing a nitrogen foam fracturing fluid system for sandstone reservoirs according to claim 2, characterized in that: The heating and heat preservation reaction temperature in step (3) is 120-140°C and the time is 1-4h.

8. The method for preparing a nitrogen foam fracturing fluid system for sandstone oil reservoirs according to claim 2, characterized in that: The foam stabilizer is one or more of hydroxyethyl cellulose, hydroxypropyl cellulose, gelatin, and sodium lauryl polyoxyethylene ether sulfate.

9. The method for preparing a nitrogen foam fracturing fluid system for sandstone oil reservoirs according to claim 2, characterized in that: The mass ratio of the foaming agent, the foam stabilizer and the simulated water in step (5) is 0.15-0.3:0.05-0.1:

100.

10. Use of the fracturing fluid system according to claim 1 in fracturing of sandstone reservoirs.

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