A fracture-hydrolyzable polymer surfactant for fracturing, and its preparation method and application

Abstract

The present application discloses a fracture-hydrolyzed polymer surfactant for fracturing, its preparation method and application, and belongs to the field of oil reservoir production engineering. The polymer surfactant has a structure shown in Formula I: wherein R is selected from one of the following: R1 is selected from a C1-C3 hydrocarbon group or R2 is selected from a C1-C3 hydrocarbon group or R3 is selected from a C 12 ‑C 18 The hydrocarbon group or R4 is selected from a:b:c=4-6:1:0-2; c is not 0. This polymer surfactant avoids premature adsorption near the wellbore; upon reaching distal fissures, it rapidly dissolves (within tens of minutes) during the soaking period (days or weeks) and penetrates the oil layer to exert its oil displacement effect. After hydrolysis, the residue rate can be less than 0.1%, thus avoiding clogging of oil and water channels in the reservoir.

Description

Technical Field

[0001] The present application relates to a fracture-hydrolyzable polymer surfactant for fracturing, a preparation method thereof, and an application thereof, and belongs to the field of oil reservoir production engineering. Background Art

[0002] In the oil and gas industry, fracturing refers to the use of hydraulic pressure to create cracks in oil and gas layers during oil or gas production. Fracturing artificially creates cracks in the formation, improving the flow of oil underground and increasing well production. It plays a crucial role in improving bottomhole flow conditions, mitigating interlayer friction, and improving reservoir production.

[0003] Currently, the primary method of fracturing is hydraulic fracturing. Hydraulic fracturing relies on a surface-based high-pressure pump truck fleet to inject fluid into a well at high speed. Using the high pressure built up at the bottom of the well, the oil layer rocks are fractured and cracks are created. To prevent the cracks from closing again due to a pressure drop after the pump truck stops working, sand, which is several times denser than the formation, is mixed into the injected fluid after the formation fractures. Sand enters the cracks along with the fluid and remains permanently within them, keeping them open and improving the oil flow environment over the long term. Hydraulic fracturing technology is now highly mature, with significant results in increasing oil well production, and has long been the preferred and commonly used technique. The results are particularly pronounced for oil layers with very small oil flow channels, that is, those with low permeability.

[0004] Fracturing fluid is a crucial component of the fracturing process. Its primary function is to create fractures and transport proppant along the opened fractures, so the fluid's viscosity is crucial. Successful fracturing operations require not only high viscosity within the fractures but also rapid gel breakdown, rapid flowback after the operation, effective control of fluid loss, low friction during pumping, and economic viability.

[0005] There are about 60×10 8 t of low permeability reservoir reserves, ultra-low permeability reservoirs (Class II 1×10 -3 -10×10 -3 μm 2 , Class III 0.1×10 -3 -1×10 -3 μm 2 ) accounts for more than 58%, and there are more than 300 oil fields. The recovery rate of ultra-low and ultra-low permeability oil fields is generally between 5% and 28%, with an average level of 13.6%. Common problems include low formation pressure (low crude oil driving energy), low permeability, low recovery rate, difficulty in water injection, and many formation sensitivity issues. In addition, my country's continental shale oil resources are approximately 1500×10 8 t, with recoverable resources of approximately 30×10 8 -60×10 8Shale oil reservoirs have low porosity and extremely low permeability. Under natural conditions, they have no natural production capacity or commercial mining value, and require special mining technologies such as fracturing.

[0006] Ultra-low and ultra-low permeability oil and gas reservoirs, as well as shale oil and gas reservoirs, are the main targets for further exploitation in the future. Their development is related to the fracture systems (natural fractures and artificial fractures created by hydraulic fracturing) that exist in these reservoirs. For these ultra-low and ultra-low permeability oil and gas reservoirs containing natural fractures or after hydraulic fracturing, the main mechanism of oil recovery is to use imbibition to cause water in the fractures to be absorbed into the matrix, displacing crude oil and producing oil. Therefore, the properties of the fracturing fluid are one of the key factors affecting the recovery rate of this type of reservoir. (Note: Due to the extremely low permeability of this type of reservoir, it is often not possible to increase oil production through methods such as water injection, polymer injection, and surfactant injection as with traditional reservoirs; therefore, the rational use of tens of thousands (hundreds of thousands) of cubic meters of fracturing fluid during fracturing to improve the imbibition and oil recovery performance of the fracturing fluid is a method currently receiving attention.)

[0007] Currently, to further improve the recovery rate of ultra-low and ultra-low permeability reservoirs and shale reservoirs, given certain reservoir properties and fracturing processes, it is necessary to use fracturing fluids to replenish energy, improve seepage, prevent scaling, and increase water injection efficiency. Furthermore, it is necessary to explore fluid dynamics to improve oil seepage efficiency and enhance oil-water migration capacity, allowing crude oil to fully enter the main fracture channel, thereby increasing single-well productivity and achieving the goal of increasing production.

[0008] Based on the above needs, the industry has developed an integrated fracturing fluid system for reducing resistance and flooding oil. While meeting the needs of fracturing projects, it has excellent absorption-promoting effects and can effectively increase the recovery effect of fracturing fluids. The component that plays a role is the absorption-promoting surfactant added to the fracturing fluid. The surfactant has an ionic polar head or a lone pair of electrons and is easily adsorbed on the formation. During the construction process, it will be adsorbed in large quantities in the formation near the wellbore of the fracturing wellbore, resulting in a loss of effective concentration and an inability to reach the far end of the fracture in a high concentration. In addition, many of the current imbibing agents are formulated, and "chromatographic separation" will occur during the migration of the reservoir, that is, the multiple components cannot always remain evenly distributed, so the comprehensive performance achieved in indoor experimental tests cannot be achieved. Summary of the Invention

[0009] As mentioned above, existing imbibition oil displacement agents have shortcomings such as large-scale adsorption in the formation near the wellbore and "chromatographic separation" during migration. The invention has prepared a fracture-hydrolyzable polymer surfactant for fracturing. The finished surfactant can be in liquid form, making it easy to pump. Upon contact with water, the solvent dissolves in water, and the surfactant precipitates as a solid in the fracturing fluid. It enters the formation along with the fracturing fluid and migrates to the far end as the fracture extends. Because the hydrolyzable functional groups in the molecular structure require a certain amount of time to hydrolyze, the surfactant is in solid form during migration, avoiding premature adsorption near the wellbore. When it reaches the far end of the fracture, it will rapidly dissolve during the soaking process (several days or weeks) and penetrate into the oil layer to exert its oil displacement effect. Moreover, because the surfactant is a polymer surfactant and not a formula, it will not undergo "chromatographic separation" during reservoir migration like traditional formula surfactants, that is, the multiple components cannot remain uniformly distributed at all times, and the comprehensive performance achieved in indoor experimental tests cannot be achieved. Alternating copolymers derived from styrene and maleic anhydride exist in other industries, but they are not used in this industry, let alone in imbibition displacement agents. Furthermore, these copolymers cannot be completely hydrolyzed, easily producing large amounts of residues with residue rates far exceeding 1%, making them unsuitable for fracturing. In contrast, the polymer surfactants obtained by copolymerizing styrene, maleic anhydride, and cationic monomers in this application can be completely hydrolyzed with a residue rate of less than 0.1%, improving oil displacement efficiency while avoiding clogging of oil and water channels in the reservoir.

[0010] According to the first aspect of the present application, a hydrolyzable polymer surfactant for use in fracture fractures is provided. The polymer surfactant comprises a styrene polymer portion providing hydrophobicity, maleic anhydride providing two carboxyl groups after hydrolysis, and a cationic monomer providing a cationic head and partial hydrophobicity. Furthermore, after complete hydrolysis, the molar content of the cationic monomer is less than half the molar content of maleic anhydride (ensuring that the molecule as a whole is neutral or negatively charged); a single mole of ionic head (COO after hydrolysis) is sufficient to provide a hydrophobicity. - The effective carbon number corresponding to the total number of cations (the benzene ring is equivalent to about 3.5 carbons) should preferably be less than 18 carbons (the water solubility will deteriorate if it is greater than this value).

[0011] A fracture-hydrolyzable polymer surfactant for fracturing, wherein the polymer surfactant has a structure shown in Formula I:

[0012]

[0013] Wherein, R is selected from One of the following;

[0014] R1 is selected from C1-C3 hydrocarbon group or

[0015] R2 is selected from C1-C3 hydrocarbon or

[0016] R3 is selected from C 12 -C 18 Hydrocarbon or

[0017] R4 is selected from

[0018] a:b:c=4-6:1:0-2;

[0019] c is not 0.

[0020] Preferably, a:b:c=4-6:1:0.5-2.

[0021] Optionally, the values ​​of a:b are independently selected from any value among 4:1, 4.5:1, 5:1, 5.5:1, 6:1 or any range therebetween.

[0022] Optionally, the values ​​of b:c are independently selected from any value among 1:0.1, 1:0.2, 1:0.3, 1:0.4, 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:1.0, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, 1:2.0, or any range between two of them.

[0023] The m in formula I represents the degree of polymerization, which is not limited in this application.

[0024] It is connected to other groups of formula I through the nitrogen on it.

[0025] According to one embodiment of the present application, R1, R2, R3, and R4 are independently selected from C1-C3 alkyl, C 12 -C 18 The alkyl group,

[0026] According to one embodiment of the present application, R1, R2, R3, and R4 are independently selected from methyl, ethyl, propyl, (CH2) 11 CH3, (CH2) 13 CH3, (CH2) 15 CH3, (CH2) 17 CH3,

[0027]

[0028] According to one embodiment of the present application, the polymer surfactant has the structure shown below:

[0029]

[0030] According to one embodiment of the present application, when R is When the anion is selected from one of chloride ion, bromide ion and fluoride ion.

[0031] According to one embodiment of the present application, the interfacial tension of the polymer surfactant is less than 1 mN / m.

[0032] According to one embodiment of the present application, the surface tension of the polymer surfactant is less than 28 mN / m.

[0033] According to one embodiment of the present application, the wetting contact angle of the hydrolyzed solution of the polymer surfactant is less than 75°.

[0034] According to a second aspect of the present application, a method for preparing a polymer surfactant is provided.

[0035] A method for preparing a polymer surfactant comprises the following steps:

[0036] A mixture containing styrene, maleic anhydride, a cationic monomer, an initiator and a solvent is reacted to obtain the polymer surfactant.

[0037] According to one embodiment of the present application, the cationic monomer is an amine / ammonium hydrophilic monomer.

[0038] According to one embodiment of the present application, the cationic monomer is selected from at least one of tetraallylammonium chloride, diallylamine, dimethyldiallylammonium chloride, dodecyldimethylallylammonium chloride, tetradecyldimethylallylammonium chloride, hexadecyldimethylallylammonium chloride, and octadecyldimethylallylammonium chloride.

[0039] According to one embodiment of the present application, the initiator is selected from at least one of azobisisobutyronitrile, benzoyl peroxide, and di-tert-butyl peroxide.

[0040] According to one embodiment of the present application, the solvent is selected from at least one of N,N-dimethylformamide, dimethyl sulfoxide, and acetone.

[0041] According to one embodiment of the present application, the molar ratio of the styrene, the maleic anhydride, and the cationic monomer is 4-6:1:0-2.

[0042] Wherein, the content of the cationic monomer is not 0.

[0043] Preferably, the molar ratio of the styrene, the maleic anhydride, and the cationic monomer is 4-6:1:0.5-2.

[0044] Optionally, the molar ratio of the styrene to the maleic anhydride is independently selected from any value among 4:1, 4.5:1, 5:1, 5.5:1, 6:1 or any range between the two.

[0045] Optionally, the molar ratio of the maleic anhydride to the cationic monomer is independently selected from any value among 1:0.1, 1:0.2, 1:0.3, 1:0.4, 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:1.0, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, 1:2.0 or any range value therebetween.

[0046] According to one embodiment of the present application, the amount of the initiator used is 0.1%-0.5% of the total mass of all monomer raw materials.

[0047] According to one embodiment of the present application, the reaction conditions are as follows:

[0048] Temperature is 75-85℃;

[0049] The time is 0.5-1.5h.

[0050] According to one embodiment of the present application, the following steps are included:

[0051] S1, obtaining a solution A containing maleic anhydride and a cationic monomer;

[0052] S2, obtaining a solution B containing an initiator;

[0053] S3, obtaining a solution C containing styrene;

[0054] S4. Add the solution A and the solution B to the solution C, control the dropwise addition time to be 90-180 min, and react at 75-85° C. for 0.5-1.5 h to obtain the polymer surfactant.

[0055] According to one embodiment of the present application, the reaction uses DMF as solvent.

[0056] The reactants are prepared by polymerizing a hydrophobic monomer styrene, a hydrophilic monomer maleic anhydride and one or more amine / ammonium hydrophilic monomers.

[0057] Use pre-mixing outside the autoclave. Pre-mixing: ① Dissolve part of the solvent (DMF), the hydrophilic monomer (maleic anhydride), and one or more amine / ammonium hydrophilic monomers at room temperature (≤30°C). ② Dissolve part of the solvent (DMF), the initiator (azobisisobutyronitrile), at room temperature (≤30°C). Be careful not to overheat the temperature to prevent unintended polymerization of the monomers due to impurities.

[0058] First add DMF and styrene into the kettle, then heat to 75-85℃ and stir at 80-200r / min;

[0059] Use a diaphragm pump to slowly add solutions ① and ② to the kettle, respectively, over a period of 90-180 minutes. During this time, the kettle temperature should not exceed 90°C. If it does, stop adding. Continue adding until the temperature drops below 85°C. Maintain the temperature at 75-85°C and continue the reaction for 0.5-1.5 hours.

[0060] After the final reaction, the reactants in the kettle turned into a light yellow, uniform, stable, slightly viscous liquid.

[0061] (3) Principle of hydrolysis within cracks

[0062] The styrene polymerization part in the polymer provides hydrophobicity, maleic anhydride provides two carboxyl groups after hydrolysis, and the cationic monomer provides a cationic head and partial hydrophobicity.

[0063]

[0064] The product itself is a liquid with DMF as the solvent, making it easy to pump. When the product is pumped into the fracturing fluid, the DMF dissolves in water. At this point, because the anhydride portion of the polymer has not yet been hydrolyzed, the entire molecule exhibits strong hydrophobicity. Under stirring, it precipitates as loose solid particles and enters the wellbore along with the fracturing fluid. It then enters the fracture system created by the fracturing and gradually migrates to the far end of the fracture network.

[0065] The fracturing operation has a large displacement (about 10-20m per minute). 3 ), the precipitated solid polymer will quickly (within a few minutes) enter the formation fracture system along with the fracturing fluid, and migrate along with the fracturing gap, avoiding premature adsorption near the wellbore, making it easier to approach the oil layer. When it reaches the distal gap, it will quickly (tens of minutes) dissolve during the soaking process (several days or weeks), and penetrate into the oil layer to play the role of oil displacement (a well will be soaked according to the specific situation after the fracturing is completed, usually for a few days or sometimes longer, at which time the wellhead is closed. After the designed soaking time is reached, the well will be opened for flowback (a part of the fracturing fluid will be discharged, and oil and gas will gradually appear). Because the dissolution time of the polymer drainage agent is short, most of it will be dissolved during fracturing, and a small amount of undissolved will also be completely dissolved in this process), thereby obtaining a hydrolyzed polymer surfactant and playing its role.

[0066] According to a third aspect of the present application, a resistance-reducing and oil-displacing integrated fracturing fluid system is provided.

[0067] An integrated fracturing fluid system for reducing resistance and flooding oil, comprising a polymer surfactant and a solvent;

[0068] The polymer surfactant is selected from the polymer surfactant described above or the polymer surfactant obtained by the preparation method described above;

[0069] The solvent is selected from at least one of N,N-dimethylformamide, dimethyl sulfoxide, and acetone.

[0070] The integrated fracturing fluid system for reducing resistance and flooding oil further comprises a resistance reducing agent, an anti-swelling agent, a drainage aid, and a gel breaker.

[0071] According to a fourth aspect of the present application, a use of a polymer surfactant is provided.

[0072] Application of the above-mentioned polymer surfactant or the polymer surfactant obtained by the above-mentioned preparation method in an integrated fracturing fluid system for reducing resistance and flooding oil.

[0073] According to one embodiment of the present application, the polymer surfactant is mixed with the solvent to form a liquid, which is then pumped into the fracturing fluid, and finally the well is soaked.

[0074] The polymer can be a liquid with DMF as the solvent for easier pumping. When the product is pumped into the fracturing fluid, the DMF dissolves in the water. At this point, because the anhydride portion of the polymer has not yet been hydrolyzed, the entire molecule exhibits strong hydrophobicity. Under stirring, it precipitates as loose solid particles and enters the wellbore along with the fracturing fluid. It then enters the fracture system created by the fracturing and gradually migrates to the far end of the fracture network.

[0075] In this application, C1-C3, C 12 -C 18 The numbers refer to the number of carbon atoms in the group.

[0076] In the present application, the term "alkyl" refers to a group formed by losing any hydrogen atom from an alkane compound molecule.

[0077] In the present application, the term "hydrocarbyl group" refers to a group formed by losing any hydrogen atom from a hydrocarbon.

[0078] The beneficial effects of this application include:

[0079] 1) This application provides a fracture-hydrolyzable polymer surfactant for fracturing. This polymer surfactant incorporates a cationic monomer copolymerized with styrene and maleic anhydride, preventing premature adsorption near the wellbore. Upon reaching the distal fracture, it rapidly dissolves (in tens of minutes) during the soaking period (days or weeks) and penetrates the oil layer to displace oil. After hydrolysis, the residue rate can be less than 0.1%, preventing clogging of the reservoir's oil-water channels. Because this surfactant is a polymer surfactant and not a formula, it will not undergo "chromatographic separation" during reservoir migration, as with conventional surfactant formulations. This means that the multiple components cannot remain uniformly distributed throughout, failing to achieve the comprehensive performance achieved in laboratory testing.

[0080] 2) This application provides a hydrolyzable polymer surfactant for fracturing applications. This polymer surfactant, when dissolved in N,N-dimethylformamide (DMF), forms a pale yellow liquid. Performance tests of its hydrolyzed solution show that a 0.1% aqueous solution has an interfacial tension of less than 1 mN / m and a surface tension of less than 28 mN / m. Capillary imbibition height tests show excellent imbibition performance, effectively promoting oil-phase imbibition and meeting standards for fracturing imbibants. Wettability tests also show that the hydrolyzed solution has a wetting contact angle of less than 75°, indicating that it can convert the wettability of oleophilic surfaces to hydrophilic ones. BRIEF DESCRIPTION OF THE DRAWINGS

[0081] Figure 1 This is the liquid product obtained in the examples of this application.

[0082] Figure 2 The liquid product obtained in the embodiment of the present application becomes a loose solid after contacting water.

[0083] Figure 3 This is the liquid product (1%) obtained in the examples of this application before hydrolysis.

[0084] Figure 4 This is the liquid product (1%) obtained in the examples of this application after hydrolysis. DETAILED DESCRIPTION

[0085] The present application is described in detail below with reference to embodiments, but the present application is not limited to these embodiments.

[0086] Unless otherwise specified, the raw materials in the examples of this application were purchased from commercial channels, including:

[0087] Styrene: molecular weight 104.14 boiling point 145.2°C;

[0088] Maleic anhydride: molecular weight 98.06;

[0089] Tetraallylammonium chloride: molecular weight 135.64;

[0090] Diallylamine: molecular weight 97.16;

[0091] Dimethyldiallylammonium chloride: molecular weight 161.67;

[0092] Dodecyldimethylallylammonium chloride: molecular weight 289.93;

[0093] Tetradecyldimethylallylammonium chloride: molecular weight 317.69;

[0094] Hexadecyldimethylallylammonium chloride: molecular weight 346.04;

[0095] Octadecyldimethylallylammonium chloride: molecular weight 374.09;

[0096] N,N-dimethylformamide (DMF): molecular weight 73.10 boiling point 153°C;

[0097] Azobisisobutyronitrile: molecular weight 164.21.

[0098] Unless otherwise specified, conventional test methods or test methods recommended by the instrument shall be used.

[0099] The analysis method in the examples of this application is as follows:

[0100] (1) Surface tension test

[0101] The surface tension test is carried out in accordance with standards SY / T 5370 and Q / SH 3580 0160.

[0102] (2) Capillary self-priming height test

[0103] ① Preparation of lipophilic capillaries.

[0104] A capillary with an inner diameter of 0.3 mm was ultrasonically treated with carbon tetrachloride and a mixed solvent (benzene:acetone:ethanol=7:1.5:1.5 (volume ratio)) for 20 min in sequence to remove organic matter on the surface.

[0105] Then, ultrasonically treat with dilute hydrochloric acid solution (1:10) and hydrofluoric acid solution (10%) for 20 minutes respectively to roughen and activate the capillary surface; then ultrasonically clean with distilled water to remove residual acid until the pH is greater than 6.5, and dry at 105°C.

[0106] Simulated oil was prepared according to the ratio of kerosene to 90# asphalt = 7:3 (mass ratio). The treated capillary was completely immersed in the simulated oil and allowed to stand at 60°C for 30 days.

[0107] Take out the capillary tube and wipe the outside of the tube clean to obtain the lipophilic capillary tube for use.

[0108] ② Capillary self-priming test.

[0109] Prepare a 0.3% osmolyte solution with distilled water and add a drop of red ink. Keep the solution temperature at (25(3)℃. Pour the solution to be tested into the cuvette to the top edge and place the ruler close to the back wall.

[0110] Place the three treated capillaries vertically in a cuvette, read and record the rising liquid level of the aqueous solution in the capillary, record the liquid level when the capillary is submerged in the liquid for 10 minutes, and take the arithmetic mean as the measurement result.

[0111] ③ Capillary self-imbibition test after high temperature aging.

[0112] Prepare 200 g of 0.3% sorbent solution with distilled water, put it into a high-temperature aging tank, place it in a 150℃ oven for aging for 3 days, take it out and cool it to room temperature, and determine the capillary self-imbibition height value of the 3% aqueous solution of the sorbent after high-temperature aging according to method ②.

[0113] ④ Capillary self-imbibition test of high mineralization aqueous solution.

[0114] Simulated water for fracturing imbibition agent experiments: Add 750g of distilled water to a 1L volumetric flask; add the following substances in order: 5g of calcium chloride, 5g of magnesium chloride, and 240g of sodium chloride. After adding each reagent, shake until it is completely dissolved before adding the next reagent. The prepared solution has a total mineralization of 25×10 4 mg / L, homogeneous and transparent, without precipitation, valid for 7 days.

[0115] Prepare 0.3% imbibition agent solution with simulated water, measure according to method ②, and record the self-imbibition height value.

[0116] (3) Wettability evaluation

[0117] According to the classification in standard SY / T 5153, the method of judging wettability by wetting angle is shown in Table 1.

[0118] Table 1 Wettability judgment criteria using contact angle method

[0119] Contact angle θ 0°≤θ<75° 75°≤θ≤105° 105°<θ≤180° Wettability hydrophilic neutral lipophilic

[0120] The wetting contact angle of the polymer hydrolyzed solution on the quartz sheet was measured at 30°C using a quartz sheet according to the method in SY / T 5153.

[0121] (4) Residue rate evaluation

[0122] Seal 200 ml of a solution containing 1% active polymer surfactant and place it in a 90°C oven for 2 hours. Weigh the filter paper and filter the solution. Place the filter paper and filter residue in an oven at 100°C until they reach a constant weight. Calculate the difference between the two values ​​to obtain the residue mass (M grams). The residue rate is (M / 2) x 100%. If it is less than 0.1%, it is recorded as <0.1%.

[0123] Comparative Example 1

[0124] (1) Raw materials

[0125] Styrene 416g

[0126] Maleic anhydride 98g

[0127] (2) Process

[0128] The reactants used DMF as solvent, and the total amount used was the total weight of all monomers, 514 g.

[0129] Use pre-mixing outside the autoclave. Pre-mixing: ① Mix maleic anhydride with an equal mass of 98g of DMF solvent and dissolve at room temperature (≤30°C). ② Dissolve the initiator, azobisisobutyronitrile, in 50g of DMF solvent at 0.1% of the total monomer mass. Dissolve at room temperature (≤30°C). Be careful not to overheat to prevent unintended polymerization or decomposition of the monomers due to impurities.

[0130] First, 416 g of DMF and styrene were added into the kettle, and then the temperature was raised to 75°C and stirred at 80 r / min.

[0131] Use a diaphragm pump to slowly add solutions ① and ② to the kettle over a 90-minute dropwise addition period. The temperature in the kettle should not exceed 90°C. If it does, stop adding the solution. Continue adding the solution until the temperature drops below 85°C. Maintain the temperature at 75°C and continue the reaction for 0.5 hour.

[0132] After the final reaction, the reactants in the kettle turned into a light yellow, uniform, stable, slightly viscous liquid. Its structural formula is as follows:

[0133]

[0134] A 0.1% concentration polymer surfactant solution was prepared with deionized water, placed at 90°C and hydrolyzed for 2 hours, and the surface tension, capillary self-absorption height, and wettability of the hydrolyzed solution were tested.

[0135] The synthesis process of the following comparative examples is the same as that of comparative example 1-1, except that the raw material ratio is changed; the surface tension, capillary self-imbibition height, wettability, and residue rate of the hydrolyzed solution are also tested.

[0136] Comparative Example 1-2

[0137] Styrene 521g

[0138] Maleic anhydride 98g

[0139] Comparative Examples 1-3

[0140] Styrene 625g

[0141] Maleic anhydride 98g

[0142] Example 2-1

[0143] The synthesis process of this embodiment is the same as that of Comparative Example 1-1, except that 68 g of tetraallyl ammonium chloride is added to solution ①; the surface tension, capillary self-imbibition height, and wettability of the hydrolyzed solution are also tested.

[0144] Styrene 416g

[0145] Maleic anhydride 98g

[0146] Tetraallyl ammonium chloride 68g

[0147] The structural formula of the synthesized polymer is as follows:

[0148]

[0149] The synthesis process of the following examples is the same as that of Example 2-1, except that different types of cationic monomers and raw materials in different ratios are added to solution ①; the surface tension, capillary self-imbibition height, wettability, and residue rate of the hydrolyzed solution are also tested.

[0150] Example 2-2

[0151] Styrene 468g

[0152] Maleic anhydride 98g Tetraallylammonium chloride 135g

[0153] Example 2-3

[0154] Styrene 520g

[0155] Maleic anhydride 98g Tetraallylammonium chloride 271g

[0156] Example 3-1

[0157] Styrene 416g

[0158] Maleic anhydride 98g Diallylamine 97g

[0159] The structural formula of the synthesized polymer is as follows:

[0160]

[0161] Example 3-2

[0162] Styrene 416g

[0163] Maleic anhydride 98g Diallylamine 45g

[0164] Example 3-3

[0165] Styrene 468g

[0166] Maleic anhydride 98g Diallylamine 25g

[0167] Example 4-1

[0168] Styrene 572g

[0169] Maleic anhydride 98g

[0170] Dimethyldiallylammonium chloride 162g

[0171] The structural formula of the synthesized polymer is as follows:

[0172]

[0173] Example 4-2

[0174] Styrene 520g

[0175] Maleic anhydride 98g

[0176] Dimethyldiallylammonium chloride 324g Example 4-3

[0177] Styrene 520g

[0178] Maleic anhydride 98g

[0179] Dimethyldiallylammonium chloride 85g Example 5-1

[0180] Styrene 416g

[0181] Maleic anhydride 98g

[0182] The polymer structure of 579g of dodecyldimethylallyl ammonium chloride is as follows:

[0183]

[0184] Example 5-2

[0185] Styrene 521g

[0186] Maleic anhydride 98g

[0187] Dodecyldimethylallyl ammonium chloride 435g Example 5-3

[0188] Styrene 625g

[0189] Maleic anhydride 98g

[0190] Dodecyldimethylallylammonium chloride 289g Example 6-1

[0191] Styrene 416g

[0192] Maleic anhydride 98g

[0193] The polymer structure of 635g of tetradecyl dimethyl allyl ammonium chloride is as follows:

[0194]

[0195] Example 6-2

[0196] Styrene 521g

[0197] Maleic anhydride 98g

[0198] Tetradecyldimethylallylammonium chloride 476g Example 6-3

[0199] Styrene 625g

[0200] Maleic anhydride 98g

[0201] Tetradecyldimethylallylammonium chloride 317g Example 7-1

[0202] Styrene 416g

[0203] Maleic anhydride 98g

[0204] The polymer structure of 692g of hexadecyldimethylallyl ammonium chloride is as follows:

[0205]

[0206] Example 7-2

[0207] Styrene 521g

[0208] Maleic anhydride 98g

[0209] Hexadecyldimethylallylammonium chloride 519g Example 7-3

[0210] Styrene 625g

[0211] Maleic anhydride 98g

[0212] Hexadecyldimethylallylammonium chloride 346g Example 8-1

[0213] Styrene 416g

[0214] Maleic anhydride 98g

[0215] The polymer structure of 748g of octadecyl dimethyl allyl ammonium chloride is as follows:

[0216]

[0217] Example 8-2

[0218] Styrene 521g

[0219] Maleic anhydride 98g

[0220] Octadecyldimethylallylammonium chloride 561g Example 8-3

[0221] Styrene 625g

[0222] Maleic anhydride 98g

[0223] Octadecyldimethylallylammonium chloride 374g

[0224] Table 2 Surface tension, capillary self-imbibition height, and wettability test of 0.1% polymer hydrolyzate

[0225]

[0226] Summary: Experiments show that 0.1% polymer hydrolyzates have low surface tension, most of which are less than 30mN / m; they have good capillary self-priming height, most of which are greater than 50mm; contact angle tests show that all test samples are less than 75°, that is, the surface becomes hydrophilic after treatment with polymer hydrolyzate.

[0227] Table 3 Residue rate test

[0228]

[0229]

[0230] In summary, the polymer in Comparative Example 1-1 produces a large amount of residue after hydrolysis, with a residue rate far exceeding 1%, which can clog oil and water channels in the reservoir. However, due to the introduction of cationic monomers, the polymers in Examples 2-1, 3-1, 4-1, and 5-1 have a residue rate of less than 0.1% after hydrolysis, improving oil displacement efficiency while avoiding clogging oil and water channels in the reservoir.

[0231] The polymer product itself is a liquid with DMF as solvent (such as Figure 1 When the product is pumped into the fracturing fluid, DMF will dissolve in the water. At this time, because the anhydride part of the polymer has not yet been hydrolyzed, the entire molecule exhibits strong hydrophobicity and will precipitate in the form of loose solid particles under stirring (as shown in the figure). Figure 2 It enters the wellbore along with the fracturing fluid, further enters the fracture system created by fracturing, and gradually migrates to the far end of the fracture network.

[0232] The fracturing operation has a large displacement (about 10-20m per minute). 3 ), the precipitated solid polymer will quickly (within a few minutes) enter the formation fracture system along with the fracturing fluid and migrate along the fracturing gap, avoiding premature adsorption near the wellbore, making it easier to approach the oil layer. When it reaches the distal gap, it will quickly (tens of minutes) dissolve (such as) during the soaking process (several days or weeks). Figure 4 and penetrate into the oil layer to play the role of oil displacement.

[0233] The above descriptions are merely a few embodiments of the present application and do not constitute any form of limitation to the present application. Although the present application discloses the preferred embodiments as above, they are not intended to limit the present application. Any technical personnel familiar with the present profession, without departing from the scope of the technical solution of the present application, using the technical content disclosed above to make slight changes or modifications are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A fracture-hydrolyzable polymer surfactant for fracturing, characterized in that: The polymer surfactant has the structure shown in Formula I: Formula I; Wherein, R is selected from 、 In one of the formulas, the N atom in R is connected to the methylene group in formula I, when R is When, Formula I further comprises an anion, wherein the anion is selected from one of chloride ion, bromide ion and fluoride ion; R1 is selected from C1-C3 hydrocarbon group or ; R2 is selected from C1-C3 hydrocarbon or ; R3 is selected from C 12 -C 18 Hydrocarbon or ; R4 is selected from ; a:b:c=4-6:1:0-2; c is not 0.

2. The polymer surfactant according to claim 1, characterized in that R1, R2, independently selected from C1-C3 alkyl or ; R3 is selected from C 12 -C 18 Alkyl or .

3. The polymer surfactant according to claim 2, characterized in that R1, R2 are independently selected from methyl, ethyl, propyl or ; R3 is selected from (CH2) 11 CH3, (CH2) 13 CH3, (CH2) 15 CH3, (CH2) 17 CH3 or 。 4. The polymer surfactant according to any one of claims 1 to 3, characterized in that a:b:c=4-6:1:0.5-2.

5. The polymer surfactant according to any one of claims 1 to 3, characterized in that The interfacial tension of the polymer surfactant is less than 1 mN / m; and / or, the surface tension of the polymeric surfactant is less than 28 mN / m; And / or, the wetting contact angle of the hydrolyzed solution of the polymer surfactant is less than 75°.

6. A method for preparing a polymer surfactant, characterized in that: The following steps are involved: A mixture consisting of styrene, maleic anhydride, a cationic monomer, an initiator, and a solvent is reacted to obtain the polymer surfactant; the cationic monomer is selected from at least one of tetraallylammonium chloride, diallylamine, dimethyldiallylammonium chloride, dodecyldimethylallylammonium chloride, tetradecyldimethylallylammonium chloride, hexadecyldimethylallylammonium chloride, and octadecyldimethylallylammonium chloride; the molar ratio of the styrene, the maleic anhydride, and the cationic monomer is 4-6:1:0-2; and the molar number of the cationic monomer is not 0.

7. The preparation method according to claim 6, characterized in that The initiator is selected from at least one of azobisisobutyronitrile, benzoyl peroxide, and di-tert-butyl peroxide; And / or, the solvent is selected from at least one of N,N-dimethylformamide, dimethyl sulfoxide, and acetone.

8. The preparation method according to claim 6 or 7, characterized in that The molar ratio of the styrene, the maleic anhydride, and the cationic monomer is 4-6:1:0.5-2; and / or, the amount of the initiator used is 0.1%-0.5% of the total mass of all monomer raw materials; And / or, the reaction conditions are as follows: Temperature is 75-85 ℃; The time is 0.5-1.5 h.

9. The preparation method according to claim 6 or 7, characterized in that: The following steps are involved: S1, obtaining a solution A containing maleic anhydride and a cationic monomer; S2, obtaining a solution B containing an initiator; S3, obtaining a solution C containing styrene; S4. Add the solution A and the solution B to the solution C, control the dropwise addition time to be 90-180 min, and react at 75-85° C. for 0.5-1.5 h to obtain the polymer surfactant.

10. An integrated fracturing fluid system for reducing resistance and flooding oil, characterized in that: including polymer surfactants and solvents; The polymer surfactant is selected from the polymer surfactant according to any one of claims 1 to 5 or the polymer surfactant obtained by the preparation method according to any one of claims 6 to 9; The solvent is selected from at least one of N,N-dimethylformamide, dimethyl sulfoxide, and acetone.

11. Use of the polymer surfactant according to any one of claims 1 to 5 or the polymer surfactant obtained by the preparation method according to any one of claims 6 to 9 in an integrated fracturing fluid system for reducing resistance and flooding oil.

12. The use according to claim 11, characterized in that The polymer surfactant is mixed with a solvent to form a liquid, which is then pumped into the fracturing fluid, and finally the well is soaked; The solvent is selected from at least one of N,N-dimethylformamide, dimethyl sulfoxide, and acetone.

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