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

Abstract

The present invention belongs to the technical field of oil exploitation, and particularly relates to a nitrogen foam fracturing fluid system for shale reservoirs, a preparation method thereof and an application. The preparation method is as follows: Sodium lauroiminodipropionate, a solvent and 1-bromo-6-(trimethylammonium) hexyl bromide are added into a reactor, stirred evenly, heated under reflux, and the pH is adjusted and maintained at 8-9 with sodium hydroxide; The viscous liquid is obtained by reduced pressure distillation, recrystallized with ethyl acetate to obtain a solid, dried to obtain a foaming agent; The foaming agent, foam stabilizer and simulated water are stirred evenly in proportion to obtain the product foam fracturing fluid system. The foam fracturing fluid system of the present invention has the advantages of large foaming volume and long half-life period.

Description

Technical Field

[0001] The present invention belongs to the technical field of oil extraction, and particularly relates to a nitrogen foam fracturing fluid system for shale reservoirs, a preparation method thereof, and an application thereof. Background Art

[0002] In the field of shale reservoir development, fracturing technology is one of the key measures to improve the production and recovery rate of oil and gas wells. Traditional fracturing fluid systems mainly include water-based fracturing fluids, oil-based fracturing fluids, and alcohol-based fracturing fluids, etc. However, these traditional fracturing fluid systems all have certain limitations in practical applications.

[0003] With the expansion of oil and gas exploration and development into deep and unconventional oil and gas reservoir fields, the formation conditions are more complex, posing higher requirements for fracturing technology. For example, deep oil and gas reservoirs have higher temperatures and pressures, the formation rocks are dense and have low porosity, and conventional fracturing fluids are difficult to effectively fracture the formation and form a complex fracture network, thus unable to achieve efficient oil and gas production.

[0004] Foam fracturing technology emerged as a new type of fracturing technology. Foam fracturing fluid is a multiphase system composed of a gas phase (usually gases such as nitrogen, carbon dioxide, etc.), a liquid phase (water or other liquid additives), and additives such as surfactants. Its unique foam structure endows the fracturing fluid with many excellent properties. First, the foam fracturing fluid has a low filtration loss, which can reduce the loss of fracturing fluid in the formation, improve the utilization rate of fracturing fluid, and reduce the damage to the formation. Second, the presence of foam gives it good sand-carrying capacity, which can effectively transport the proppant into the formation fractures and maintain the conductivity of the fractures. In addition, the foam fracturing fluid has a high apparent viscosity and can better control the propagation of fractures under high-pressure conditions, forming a more complex fracture network, which is beneficial to improving the production and recovery rate of oil and gas wells.

[0005] However, there are still some problems in the existing foam fracturing technology that need to be further solved. For example, the stability of the foam is difficult to precisely control. Under high-temperature and high-pressure conditions, the foam is prone to rupture, resulting in a decline in the performance of the fracturing fluid; the formula of the foam fracturing fluid is relatively complex, and the synergistic mechanism between components has not been fully clarified, and its adaptability under different formation conditions needs to be improved; the preparation process and construction equipment of the foam fracturing fluid also need to be further optimized to improve the efficiency and reliability of its industrial application. In summary, developing a more stable and efficient foam fracturing system has important practical significance and broad application prospects for promoting foam fracturing technology.

[0006] CN104312563B discloses a surfactant for cationic microbubble drilling fluid and its preparation method, which is obtained by radical copolymerization of vinyl cation monomer A and vinyl amide compound B in a mass ratio of 10:1 to 10, followed by adding a relative molecular mass regulator, and its average relative molecular mass is between 1000 and 4000. However, the foaming performance and foam stability of this invention are poor, and it is difficult to meet the on-site requirements in practical applications.

[0007] CN102020981A discloses a temperature-resistant, salt-resistant and low-tension foam flooding agent and its preparation method, which is prepared by continuously stirring alkanolamide, bipolar surfactant and water at 40 - 60 °C until completely dissolved. The temperature-resistant, salt-resistant and low-tension foam agent of this invention is applicable to tertiary oil recovery under the conditions of a temperature of 50 - 120 °C and a salinity of 0 - 100,000 ppm. However, the main agents of this foam agent are alkanolamide and bipolar surfactant. Alkanolamide is easy to hydrolyze, has poor high-temperature stability, and is easy to fail in the formation, so its application is limited. Summary of the Invention

[0008] The present invention provides a nitrogen foam fracturing fluid system for shale oil reservoirs, its preparation method and application in view of the deficiencies of the above-mentioned existing technologies. The foam fracturing fluid system of the present invention has the advantages of large foaming volume and long half-life.

[0009] One object of the present invention discloses a nitrogen foam fracturing fluid system for shale oil reservoirs. The composition and components of the foam fracturing fluid system are as follows:

[0010] Foaming agent 0.1 - 0.3 parts by mass;

[0011] Foam stabilizer 0.05 - 0.2 parts by mass;

[0012] Simulated water 100 parts by mass.

[0013] The foam stabilizer is one or more of carboxymethyl cellulose, hydroxyethyl cellulose, polyvinyl alcohol, sodium lauryl polyoxyethylene ether sulfate.

[0014] The simulated water contains 1 wt% sodium chloride, 0.1 wt% calcium chloride, 0.05 wt% sodium bicarbonate, and the rest is water, and its pH value is 7.5.

[0015] The molecular structural formula of the foaming agent is as follows:

[0016] .

[0017] Another object of the present invention discloses a preparation method of the above foam fracturing fluid system. The specific steps of the preparation method are as follows:

[0018] (1)Sodium lauryldiiminodipropionate, a solvent, and 1-bromo-6-(trimethylammonium)hexyl bromide are added to a reactor, stirred evenly, heated under reflux, and the pH is adjusted and maintained at 8-9 with sodium hydroxide;

[0019] (2)The viscous liquid is obtained by vacuum distillation, recrystallized with ethyl acetate to obtain a solid, and dried to obtain a foaming agent;

[0020] (3)The foaming agent, foam stabilizer, and simulated water are stirred evenly in proportion to obtain a product foam fracturing fluid system.

[0021] In the present invention, preferably, based on 1 mole part of sodium lauryldiiminodipropionate, the dosage of 1-bromo-6-(trimethylammonium)hexyl bromide is 0.8-1.2 mole parts; more preferably, based on 1 mole part of sodium lauryldiiminodipropionate, the dosage of 1-bromo-6-(trimethylammonium)hexyl bromide is 0.9-1.1 mole parts.

[0022] Preferably, in step (1), the solvent is one of methanol, ethanol, propanol, isopropanol, butanol, and isobutanol, more preferably one of ethanol and isobutanol, and the weight ratio to sodium lauryldiiminodipropionate is 20-40:1.

[0023] Preferably, the heating reflux time in step (1) is 24-72 h.

[0024] Preferably, in step (3), the foam stabilizer is one or more of carboxymethyl cellulose, hydroxyethyl cellulose, polyvinyl alcohol, and sodium lauryl polyoxyethylene ether sulfate.

[0025] The synthesis reaction equation of the foaming agent of the present invention is as follows:

[0026]

[0027] The third object of the present invention discloses the application of the above foam fracturing fluid system in shale reservoir fracturing.

[0028] The nitrogen foam fracturing fluid system for shale reservoirs of the present invention is composed of a foaming agent, a foam stabilizer and water. The foaming agent is an amphoteric surfactant. The lipophilic group is a fatty alkyl group, and the hydrophilic group is a dicarboxylic acid and a bisquaternary ammonium salt. When the present invention is stirred or bubbled, air will enter the solution to form bubbles. When the bubbles contact and collide, due to the buffering effect of the foaming agent molecules and the hydration layer of their polar groups in the middle, the bubbles are difficult to merge, and small bubbles are therefore easy to preserve. In addition, the foaming agent can also make the surface of the bubbles elastic, and when the bubbles are vibrated or acted upon by an external force, they can maintain their shape and stability. The foam stabilizer can control the structural stability of the bubble liquid film, so that the surfactant molecules are orderly distributed on the liquid film of the bubbles, thereby endowing the foam with good elasticity and self-healing ability.

[0029] The present invention has the following advantages and beneficial effects compared with the prior art:

[0030] (1) The nitrogen foam fracturing fluid system for shale reservoirs of the present invention has the characteristic of a large foaming volume, reaching 800 mL or more at room temperature;

[0031] (2) The nitrogen foam fracturing fluid system for shale reservoirs of the present invention has the characteristic of a long half-life, reaching more than 1300 s at room temperature. Specific embodiments

[0032] In the ranges disclosed herein, the endpoints and any values are not limited to the exact 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, between the endpoint values of each range and individual point values, and between individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0033] Example 1

[0034] (1) Add 20 mmol of disodium lauroiminodipropionate, 149 g of methanol, and 16 mmol of 1-bromo-6-(trimethylammonium) hexyl bromide to the reactor, stir evenly, heat under reflux for 24 h, and adjust and maintain the pH at 8 - 9 with sodium hydroxide;

[0035] (2) Obtain a viscous liquid by vacuum distillation, recrystallize with ethyl acetate to obtain a solid, and dry it to obtain the foaming agent.

[0036] (3) Stir 0.5 g of the foaming agent, 1 g of carboxymethyl cellulose, and 500 g of simulated water evenly to obtain the product foam fracturing fluid system.

[0037] Example 2

[0038] (1) Add 20 mmol of sodium N-lauroyliminodipropionate, 249 g of ethanol, and 24 mmol of 1-bromo-6-(trimethylammonium)hexyl bromide into the reactor, stir evenly, heat under reflux for 24 h, and adjust and maintain the pH at 8 - 9 with sodium hydroxide;

[0039] (2) Obtain a viscous liquid by vacuum distillation, recrystallize with ethyl acetate to obtain a solid, dry it to obtain a foaming agent.

[0040] (3) Stir 0.8 g of the foaming agent, 0.5 g of carboxymethyl cellulose, and 500 g of simulated water evenly to obtain the product foam fracturing fluid system.

[0041] Example 3

[0042] (1) Add 20 mmol of sodium N-lauroyliminodipropionate, 200 g of propanol, and 17 mmol of 1-bromo-6-(trimethylammonium)hexyl bromide into the reactor, stir evenly, heat under reflux for 24 h, and adjust and maintain the pH at 8 - 9 with sodium hydroxide;

[0043] (2) Obtain a viscous liquid by vacuum distillation, recrystallize with ethyl acetate to obtain a solid, dry it to obtain a foaming agent.

[0044] (3) Stir 1 g of the foaming agent, 0.25 g of hydroxyethyl cellulose, and 500 g of simulated water evenly to obtain the product foam fracturing fluid system.

[0045] Example 4

[0046] (1) Add 20 mmol of sodium N-lauroyliminodipropionate, 298 g of methanol, and 22 mmol of 1-bromo-6-(trimethylammonium)hexyl bromide into the reactor, stir evenly, heat under reflux for 72 h, and adjust and maintain the pH at 8 - 9 with sodium hydroxide;

[0047] (2) Obtain a viscous liquid by vacuum distillation, recrystallize with ethyl acetate to obtain a solid, dry it to obtain a foaming agent.

[0048] (3) Stir 1 g of the foaming agent, 0.5 g of hydroxyethyl cellulose, and 500 g of simulated water evenly to obtain the product foam fracturing fluid system.

[0049] Example 5

[0050] (1) Add 20 mmol of sodium N-lauroyliminodipropionate, 250 g of butanol, and 18 mmol of 1-bromo-6-(trimethylammonium)hexyl bromide into the reactor, stir evenly, heat under reflux for 72 h, and adjust and maintain the pH at 8 - 9 with sodium hydroxide;

[0051] (2) Obtain a viscous liquid by vacuum distillation, recrystallize with ethyl acetate to obtain a solid, dry it to obtain a foaming agent.

[0052] (3) Stir 1.2 g of foaming agent, 0.7 g of polyvinyl alcohol, and 500 g of simulated water evenly to obtain the product foam fracturing fluid system.

[0053] Example 6

[0054] (1) Add 20 mmol of sodium lauroiminodipropionate, 264 g of isopropanol, and 19 mmol of 1-bromo-6-(trimethylammonium) hexyl bromide to the reactor, stir evenly, heat under reflux for 48 h, and adjust and maintain the pH at 8 - 9 with sodium hydroxide.

[0055] (2) Obtain a viscous liquid by vacuum distillation, recrystallize with ethyl acetate to obtain a solid, and dry it to obtain the foaming agent.

[0056] (3) Stir 1.2 g of foaming agent, 1 g of sodium lauryl polyoxyethylene ether sulfate, and 500 g of simulated water evenly to obtain the product foam fracturing fluid system.

[0057] Example 7

[0058] (1) Add 20 mmol of sodium lauroiminodipropionate, 290 g of ethanol, and 20 mmol of 1-bromo-6-(trimethylammonium) hexyl bromide to the reactor, stir evenly, heat under reflux for 48 h, and adjust and maintain the pH at 8 - 9 with sodium hydroxide.

[0059] (2) Obtain a viscous liquid by vacuum distillation, recrystallize with ethyl acetate to obtain a solid, and dry it to obtain the foaming agent.

[0060] (3) Stir 1.3 g of foaming agent, 0.5 g of sodium lauryl polyoxyethylene ether sulfate, 0.5 g of hydroxyethyl cellulose, and 500 g of simulated water evenly to obtain the product foam fracturing fluid system.

[0061] Example 8

[0062] (1) Add 20 mmol of sodium lauroiminodipropionate, 270 g of isobutanol, and 21 mmol of 1-bromo-6-(trimethylammonium) hexyl bromide to the reactor, stir evenly, heat under reflux for 48 h, and adjust and maintain the pH at 8 - 9 with sodium hydroxide.

[0063] (2) Obtain a viscous liquid by vacuum distillation, recrystallize with ethyl acetate to obtain a solid, and dry it to obtain the foaming agent.

[0064] (3) Stir 1.5 g of foaming agent, 0.8 g of sodium lauryl polyoxyethylene ether sulfate, 0.2 g of polyvinyl alcohol, and 500 g of simulated water evenly to obtain the product foam fracturing fluid system.

[0065] Performance Test of the Foaming Agent in Example 9

[0066] Take 100 mL of the foam fracturing fluid system of the present invention and pour it into a high-speed stirring cup. Place it on a high-speed stirrer, introduce nitrogen gas at the upper end to maintain a nitrogen atmosphere, start the high-speed stirrer, and record the time with a stopwatch at the same time. Stir at a rotational speed of (11000 ± 300) r / min for 60 s. Quickly remove the high-speed stirring cup, pour all the generated foam liquid into a 1000 mL graduated cylinder, and record the time with a stopwatch. Then observe and record the foam volume in the graduated cylinder, which is the foaming volume.

[0067] Record the time used from the liquid precipitation from the foam to 50 mL, which is the half-life.

[0068] Configure the foaming agent DRKJ-13 for fracturing of Zhengzhou Derong Technology Co., Ltd. into a concentration of 0.3 wt% with simulated water for a comparative experiment.

[0069] Table 1 Test results of foaming performance

[0070]

[0071] As can be seen from Table 1:

[0072] (1) The foam fracturing fluid system of the present invention has the characteristic of large foaming volume. The foaming volume reaches 800 mL or more at room temperature, and the highest reaches 890 mL (Examples 7 and 8), while the foaming volume of the comparative example is 390 mL, which is significantly lower than that of the present invention.

[0073] (2) The foam fracturing fluid system of the present invention has the characteristic of long half-life. The half-life reaches more than 1300 s at room temperature, and the highest reaches 1580 s (Example 8), while the half-life of the comparative example is 410 s, which is significantly lower than that of the present invention.

[0074] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, and these simple modifications all belong to the protection scope of the present invention.

[0075] In addition, it should be noted that, among the various specific technical features described in the above specific embodiments, they can be combined in any appropriate manner without contradiction. To avoid unnecessary repetition, the present invention will not further describe various possible combination methods.

[0076] In addition, any combination can be made between various different embodiments of the present invention as long as it does not violate the idea of the present invention, and it should also be regarded as the content disclosed by the present invention.

Claims

1. A preparation method of a nitrogen foam fracturing fluid system for shale reservoirs, characterized in that, The specific steps of the preparation method are as follows: (1) Add disodium lauroiminodipropionate, a solvent, and 1-bromo-6-(trimethylammonium)hexyl bromide into a reactor, stir evenly, heat under reflux, and adjust and maintain the pH value at 8-9 with sodium hydroxide. The solvent is one of methanol, ethanol, propanol, isopropanol, butanol, and isobutanol, and the weight ratio to disodium lauroiminodipropionate is 20-40:1; (2) Obtain a viscous liquid by vacuum distillation, recrystallize with ethyl acetate to obtain a solid, and dry it to obtain a foaming agent; (3) Stir evenly the foaming agent, foam stabilizer, and simulated water in proportion to obtain a product foam fracturing fluid system. The foam stabilizer is one or several of carboxymethyl cellulose, hydroxyethyl cellulose, polyvinyl alcohol, and sodium lauryl polyoxyethylene ether sulfate. The simulated water contains 1 wt% sodium chloride, 0.1 wt% calcium chloride, 0.05 wt% sodium bicarbonate, and the rest is water, and its pH value is 7.

5. The mass ratio of the foaming agent, foam stabilizer, and simulated water is 0.1-0.3:0.05-0.2:100; Based on 1 mole part of disodium lauroiminodipropionate, the dosage of 1-bromo-6-(trimethylammonium)hexyl bromide is 0.8-1.2 mole parts.

2. The preparation method of a nitrogen foam fracturing fluid system for a shale oil reservoir according to claim 1, wherein Based on 1 mole part of disodium lauroiminodipropionate, the dosage of 1-bromo-6-(trimethylammonium)hexyl bromide is 0.9-1.1 mole parts.

3. The preparation method of a nitrogen foam fracturing fluid system for a shale reservoir according to claim 1, characterized in that, The heating reflux time in step (1) is 24-72 h.

4. A fracturing fluid system prepared by the preparation method of the fracturing fluid system according to claim 1.

5. The application of the fracturing fluid system according to claim 4 in shale reservoir fracturing.

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