A salt-resistant and calcium-resistant imbibition-displacement system suitable for low-permeability tight oil reservoirs and its preparation method

Abstract

The present invention discloses a salt-resistant and calcium-resistant imbibition-flooding system suitable for low-permeability and tight oil reservoirs and a preparation method thereof. The imbibition-flooding system is composed of the following raw materials by weight, calculated as 100%, including 0.05-1.5% of a double-hydrophilic head group double-hydrophobic chain surfactant, 0.05-1.5% of a double-hydrophilic head group single-hydrophobic chain surfactant, and the balance being water; wherein the double-hydrophilic head group double-hydrophobic chain surfactant is didecylhydroxysulfonate, didodecylhydroxysulfonate, ditetradecylhydroxysulfonate, or dihexadecylhydroxysulfonate; and the double-hydrophilic head group single-hydrophobic chain surfactant is dodecyl amino acid salt, tetradecyl amino acid salt, hexadecyl amino acid salt, or octadecyl amino acid salt. The imbibition-flooding system can be applied to low-permeability and tight oil reservoir formation water environments with high total salinity and high calcium ion content, can effectively reduce interfacial tension, and has imbibition-flooding performance.

Description

Technical Field

[0001] The invention belongs to the technical field of oilfield development and enhanced recovery, and particularly relates to a salt-resistant and calcium-resistant imbibition-displacement system suitable for low-permeability and tight oil reservoirs and a preparation method thereof. Background Art

[0002] Low-permeability, tight oil reservoirs, as a key component of unconventional oil and gas resources, occupy a crucial position in the global energy mix. However, these reservoirs are generally characterized by complex pore structures, extremely low permeability, and insufficient natural energy. Conventional waterflooding is ineffective, necessitating an urgent need for efficient development technologies. Surfactant flooding, a key chemical flooding technology, holds broad application prospects in enhanced oil recovery. Surfactants effectively improve oil washing efficiency and sweep coefficient by reducing oil-water interfacial tension, altering rock wettability, and emulsifying crude oil, thereby significantly enhancing oil recovery. Furthermore, imbibition, as a key oil recovery mechanism, exhibits unique advantages in the development of low-permeability, tight oil reservoirs. Imbibition systems, through the synergistic effects of capillary forces and interfacial tension, spontaneously displace crude oil from tiny pores, making them particularly suitable for water-wet, low-permeability, tight oil reservoirs. However, due to the high salinity (above 100,000 mg / L) and high divalent calcium and magnesium ion contents (above 10,000 mg / L) of formation water, conventional imbibition and flooding systems face numerous challenges in their application. The presence of high mineralization and divalent calcium and magnesium ions can easily lead to emulsification, precipitation and adsorption failure of imbibition and oil displacement agents, significantly reducing the efficiency of imbibition and oil displacement, and even causing formation damage and poor adaptability.

[0003] Therefore, a salt-resistant and calcium-resistant imbibition-displacement system suitable for low-permeability tight oil reservoirs is developed to overcome the limitations of complex formation conditions, improve the crude oil recovery rate of low-permeability tight oil reservoirs, and provide technical support for the efficient development of low-permeability tight oil reservoirs. Summary of the Invention

[0004] In response to the defects of the existing technology, the present invention provides a salt-resistant and calcium-resistant imbibition-displacement system suitable for low-permeability and tight oil reservoirs and a preparation method thereof. The imbibition-displacement system can be applied to low-permeability and tight oil reservoir formation water environments with a total mineralization of up to 120,000 mg / L and a divalent calcium ion content of up to 20,000 mg / L. It can effectively reduce interfacial tension and has imbibition-displacement performance.

[0005] A salt-resistant and calcium-resistant imbibition-displacement system suitable for low-permeability tight oil reservoirs, comprising the following raw materials by weight, calculated as 100%: 0.05-1.5% of a double-hydrophilic head group double-hydrophobic chain surfactant, 0.05-1.5% of a double-hydrophilic head group single-hydrophobic chain surfactant, and the balance water;

[0006] Wherein, the double hydrophilic head group double hydrophobic chain surfactant is didecyl hydroxysulfonate, didodecyl hydroxysulfonate, ditetradecyl hydroxysulfonate or dihexadecyl hydroxysulfonate;

[0007] The double hydrophilic head group single hydrophobic chain surfactant is a dodecyl amino acid salt, a tetradecyl amino acid salt, a hexadecyl amino acid salt or an octadecyl amino acid salt.

[0008] Preferably, the structural formula of the double hydrophilic head group and double hydrophobic chain surfactant is as follows:

[0009] , n=9, 11, 13 or 15.

[0010] Preferably, the structural formula of the double hydrophilic head group single hydrophobic chain surfactant is as follows:

[0011] , m=10, 12, 14 or 16.

[0012] Preferably, the double hydrophilic head group double hydrophobic chain surfactant is prepared by the following method:

[0013] (a1) Ethylenediamine and sodium chloroethylsulfonate were weighed, distilled water was added thereto, and the mixture was reacted at 70-90°C for 12-24 hours. The pH of the system was controlled to be 8-9 during the reaction. After the reaction, the solvent was removed by rotary evaporation, and the mixture was washed with anhydrous ethanol, filtered, and dried to obtain intermediate a as a white powder product.

[0014] (a2) Weighing the intermediate a, dissolving it in distilled water, controlling the solution pH to 7, adding epichlorohydrin dropwise thereto, and reacting at a constant temperature of 25-35°C for 3-6 hours. After the reaction, remove the solvent by rotary evaporation to obtain the intermediate b as a light brown gel product;

[0015] (a3) Weigh the intermediate b, dissolve it in distilled water, raise the temperature to 75-90°C, add the corresponding organic amine, and react at a constant temperature for 12-24 hours. During the reaction, control the pH of the system to be 8-9. After the reaction, add anhydrous ethanol, cool it, filter it, recrystallize the solid product from a chloroform-methanol mixture, and dry it. The organic amine is decylamine, dodecylamine, tetradecylamine, or hexadecylamine.

[0016] Preferably, the molar ratio of ethylenediamine to sodium chloroethylsulfonate in step (a1) is (1-1.5): (1-2.5); the molar ratio of intermediate a to epichlorohydrin in step (a2) is (1-1.5): (2-2.5); and the molar ratio of intermediate b to organic amine in step (a3) ​​is (1-1.5): (2-2.5).

[0017] Preferably, in step (a2), the formic acid or acetic acid solution is used to control the solution pH=7; in steps (a1) and (a3), an alkaline aqueous solution is used to control the pH; and the volume ratio of the chloroform-methanol mixture is 9:1.

[0018] Preferably, the drying conditions in step (a1) are drying at 60-80° C. for 2-4 hours; and the vacuum drying conditions in step (a3) ​​are vacuum drying at 40-60° C. for 1-2 hours.

[0019] Preferably, the double hydrophilic head group single hydrophobic chain surfactant is prepared by the following method:

[0020] (b1) Weigh glycine and sodium hydroxide, add distilled water thereto, and stir uniformly at 65-85° C. to obtain an amino acid salt solution;

[0021] (b2) while stirring, simultaneously adding an alkyl acyl chloride and an aqueous NaOH solution to the aqueous amino acid salt solution, controlling the reaction temperature to 10-15° C., controlling the pH of the system to 12-13 by adjusting the amount of the aqueous NaOH solution, and stirring the reaction for 2-6 hours to obtain a crude product, an alkyl glycine salt; the alkyl acyl chloride is selected from the group consisting of dodecyl acyl chloride, tetradecyl acyl chloride, hexadecyl acyl chloride, and octadecyl acyl chloride;

[0022] (b3) heating the crude alkyl glycine salt to 60-80° C. and acidifying with formic acid to a pH of 2-4 to completely acidify it into dodecyl glycine, which is insoluble in water, but allows excess glycine and the product sodium chloride to pass through. Adding deionized water, stirring, and then filtering to remove the filtrate, repeating the process until the pH of the filtrate is 5-6 and no chloride ions are present, and then recrystallizing with petroleum ether to obtain pure alkyl glycine;

[0023] (b4) After drying the pure alkylglycine, dissolve it in ethanol, slowly add NaOH ethanol solution to it at 50-70° C., stir and react for 1-2 hours, and remove the solvent by rotary evaporation.

[0024] Preferably, in step (b1), the molar ratio of glycine to sodium hydroxide is (1-1.2):(1-1.5); in step (b2), the molar ratio of the alkyl acyl chloride to the amino acid salt is (1-1.2):(1-1.5); in step (b4), the molar amount of the alkyl glycine is equal to the molar amount of NaOH in the ethanol solution of NaOH.

[0025] Preferably, the rotary evaporation conditions are a temperature of 40-60° C. and a pressure of -0.095 MPa.

[0026] Preferably, the vacuum drying in step (b4) is carried out at 40-50° C. for 1-2 h.

[0027] The method for preparing the salt-resistant and calcium-resistant imbibition-displacement system suitable for low-permeability tight oil reservoirs comprises the following steps: mixing the double-hydrophilic head group double-hydrophobic chain surfactant, the double-hydrophilic head group single-hydrophobic chain surfactant, and water, and stirring them evenly.

[0028] Advantages of the present invention:

[0029] The surfactant of the present invention improves its salt and calcium resistance by introducing a double hydrophilic head group, and adjusts the surfactant's interfacial activity and changes its wetting properties by changing the number and length of hydrophobic carbon chains contained in the surfactant's molecular structure. The prepared imbibition-displacement system is suitable for oil fields with a permeability of less than 1×10 -3 μm 2 The low permeability and dense oil reservoir with a total mineralization of up to 120,000 mg / L and a divalent calcium ion content of up to 20,000 mg / L is used to prepare a salt-resistant and calcium-resistant imbibition-displacement system with an interfacial tension as low as 10 -2 The interfacial tension is on the order of mN / m, which belongs to the low interfacial tension category and can effectively change the hydrophilic wettability of rocks. It has a higher oil displacement efficiency than water flooding and exhibits good oil washing and permeability enhancement effects. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is the infrared spectrum of the double hydrophilic head group and double hydrophobic chain surfactant in Example 1;

[0031] Figure 2 is the nuclear magnetic resonance spectrum of the double hydrophilic head group and double hydrophobic chain surfactant in Example 1;

[0032] Figure 3 This is the infrared spectrum of the double hydrophilic head group single hydrophobic chain surfactant in Example 1. DETAILED DESCRIPTION

[0033] The present invention does not limit the water in the raw materials of the imbibition-displacement system, and surface water or formation water can be prepared. In order to evaluate its salt and calcium resistance, simulated formation water with high mineralization and high calcium ion content is used in the examples of the present invention.

[0034] Example 1

[0035] 1. Preparation of double hydrophilic head group double hydrophobic chain surfactant sodium didodecyl hydroxysulfonate, the method is as follows:

[0036] (a1) Ethylenediamine and sodium chloroethylsulfonate were weighed at a molar ratio of 1:1, and distilled water was added thereto. The mixture was reacted at 80°C for 18 hours. During the reaction, the pH of the system was controlled to 8-9 using an aqueous NaOH solution. After the reaction, the solvent was removed by rotary evaporation at 60°C and -0.095 MPa. The mixture was then washed with anhydrous ethanol, filtered, and dried at 70°C for 3 hours to obtain intermediate a as a white powder.

[0037] (a2) The intermediate a was weighed and dissolved in distilled water. The pH of the system was controlled to 7 by using a formic acid solution. The corresponding epichlorohydrin was added dropwise thereto in a molar ratio of intermediate a to epichlorohydrin of 1:2. The reaction was carried out at 30°C for 4 hours. After the reaction, the solvent was removed by rotary evaporation at 60°C and -0.095 MPa to obtain intermediate b as a light brown gel product.

[0038] (a3) The intermediate b is weighed and dissolved in distilled water, the temperature is raised to 85°C, and the corresponding dodecylamine is added in a molar ratio of intermediate b to dodecylamine of 1:2. The reaction is carried out at a constant temperature for 18 hours. During the reaction, the pH of the system is controlled to 8-9 using an aqueous NaOH solution. After the reaction is completed, anhydrous ethanol is added, and the mixture is cooled and filtered. The solid product is recrystallized three times using a chloroform-methanol mixture with a volume ratio of 9:1, and vacuum dried at 50°C for 1.5 hours to obtain sodium didodecylhydroxysulfonate, referred to as main agent A, with the following structural formula:

[0039] , n=11.

[0040] Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance spectroscopy ( 1 H NMR) was used to characterize the structure of the final product obtained in this example, and its FT-IR spectrum and 1 H NMR spectra are shown in Figure 1 and Figure 2 .

[0041] Depend on Figure 1 Available, 3405.45cm -1 The stretching vibration characteristic absorption peak of -OH- is at 1470.72cm -1 The bending vibration characteristic absorption peak of CN is at 1599.36cm -1 The in-plane bending and stretching vibration characteristic absorption peak of -CH- is at 3056.12cm -1 The out-of-plane bending vibration peak of -NH- is at 1193.40cm -1 and 1051.67cm -1 The antisymmetric and symmetric stretching vibration characteristic absorption peaks of -SO3 are at 2916.14cm-1 The stretching vibration characteristic absorption peaks of methyl and methylene are at 730.99cm -1 The long methylene chain in the molecule. The presence of hydroxyl (-OH), sulfonic acid (-SO3), -NH- connecting the hydrophobic carbon chain, and CN connecting the two hydrophobic chains in the synthetic product is consistent with the target molecular structure.

[0042] Depend on Figure 2 It can be obtained that δ: 1.14 (t, 3H, -CH3), 2.41 [m, 24H, -(CH2) 11 ], 2.79~2.92[t, 4H, -CH2-NH-CH2-; t, 4H, -CH2-N-CH2-], 3.78(m, 2H, -CH2-SO 3) , 1.52 (m, H, -NH-), 4.73 (m, H, CHOH), 4.65 (d, H, -OH). 1 The H NMR spectrum confirmed the assignment of hydrogen atoms of the main functional groups in the target product, which was consistent with the structure of the target product.

[0043] 2. Preparation of double hydrophilic head group single hydrophobic chain surfactant dodecyl amino acid salt, the method is as follows:

[0044] (b1) Weighing glycine and sodium hydroxide at a molar ratio of glycine to sodium hydroxide of 1:1, adding distilled water thereto, and stirring at 75° C. to obtain an amino acid salt solution;

[0045] (b2) Adding dodecyl acyl chloride and a 30 wt % NaOH aqueous solution to two constant pressure dropping funnels, respectively, and simultaneously adding dodecyl acyl chloride and a 30 wt % NaOH aqueous solution to the amino acid salt aqueous solution. The reaction temperature was controlled at 12° C., and the pH of the system was controlled at 12-13 by adjusting the amount of the NaOH aqueous solution. The reaction was stirred for 4 h to obtain a crude product, alkyl glycine salt, wherein the molar ratio of dodecyl acyl chloride to amino acid salt was 1:1.

[0046] (b3) The crude alkyl glycine salt product is heated to 70° C. and acidified with formic acid to a pH of 3 to completely acidify it into dodecyl glycine. Dodecyl glycine is insoluble in water. Excess glycine and the product sodium chloride can be dissolved and removed by filtration by adding water. Therefore, deionized water is added, stirred, and then filtered to remove the filtrate. The operation is repeated until the pH of the filtrate is 5-6 and no chloride ions are present. The product is then recrystallized from petroleum ether three times to obtain pure alkyl glycine.

[0047] (b4) The pure alkylglycine was vacuum dried at 45°C for 1.5 hours, dissolved in ethanol, and an ethanolic solution of NaOH was slowly added thereto at 60°C, wherein the molar amount of NaOH in the ethanolic solution of alkylglycine and NaOH was equal. The mixture was stirred for 1.5 hours, and the solvent was removed by rotary evaporation at 60°C and -0.095 MPa to obtain sodium dodecylamino acid, referred to as main agent B, with the following structural formula:

[0048] , m=10.

[0049] The structure of the final product was characterized by Fourier transform infrared spectroscopy (FT-IR). Figure 3 As shown, 3302.57 cm -1 、1291.52 cm -1 is the stretching vibration absorption peak of NH and CN in secondary amine, among which 3302.57cm -1 3331.31cm of the primary amine -1 The absorption peak at 2958.38 cm-1 is blue-shifted, which is significantly different from the characteristic absorption peak of primary amine. -1 、2918.88cm -1 It is the antisymmetric stretching vibration absorption peak of CH in -CH3 and -CH2; 1592.95 cm -1 、1439.07cm -1 It is the antisymmetric and symmetric stretching vibration absorption peak of C=O in the carboxyl group of carboxylate, which is consistent with the main functional group structure of the target product.

[0050] 3. Simulated formation water with varying salinity and calcium ion content was prepared. The dual-hydrophilic headgroup dual-hydrophobic chain surfactant (main agent A), the dual-hydrophilic headgroup single-hydrophobic chain surfactant (main agent B), and the simulated formation water were mixed and stirred uniformly to obtain a salt-tolerant and calcium-resistant imbibition-displacement system, which was then subjected to performance testing.

[0051] 1. Oil-water interfacial tension test

[0052] The oil-water interfacial tension of the system was measured using a TX-500C interfacial tension meter at a reservoir temperature of 50°C. The salinity, calcium ion content, system composition, and interfacial tension results of the simulated formation water are shown in Table 1.

[0053] Table 1 Oil-water interfacial tension of different salt-tolerant and calcium-resistant imbibition-displacement systems

[0054]

[0055] As shown in Table 1, the interfacial tension of the system is always maintained at 10 -2It is of the order of magnitude and is in the range of low interfacial tension. It can significantly reduce the oil-water interfacial tension and show good salt and calcium resistance.

[0056] 2. Wettability and absorption efficiency test

[0057] A contact angle tester was used to measure the wetting angle of the core surface of a salt-tolerant and calcium-resistant imbibition-displacement system prepared with simulated formation water containing a total mineralization of 120,000 mg / L and a divalent calcium ion content of 20,000 mg / L. Static imbibition experiments were conducted to measure the static imbibition effect of the salt-tolerant and calcium-resistant imbibition-displacement system on low-permeability and dense cores. The results are shown in Table 2.

[0058] Table 2 Wettability and static dialysis effect

[0059]

[0060] As shown in Table 2, both water and the salt- and calcium-resistant imbibition-displacement system described herein can displace oil through imbibition, but the salt- and calcium-resistant imbibition-displacement system consistently outperforms water in its imbibition efficiency. The salt- and calcium-resistant imbibition-displacement system improves imbibition efficiency by adsorbing on the rock surface and the oil-water interface, altering rock wettability and enhancing hydrophilicity. This reduces interfacial tension, promotes oil droplet separation, strengthens capillary forces, and optimizes oil-water distribution.

[0061] 3. Core dynamic oil displacement efficiency test

[0062] Dynamic core flooding experiments were conducted to test the oil displacement effect of the salt-tolerant and calcium-resistant imbibition-displacement system under simulated reservoir temperature of 50°C and reservoir pressure of 9 MPa, in a simulated formation water environment with a high salinity of 120,000 mg / L and a divalent calcium ion content of 20,000 mg / L. The salt-tolerant and calcium-resistant imbibition-displacement system of the present invention was further used for displacement on the basis of water flooding. The results are shown in Table 3. In the table, "oil displacement efficiency of the present invention" refers to the oil displacement efficiency further improved on the basis of water flooding.

[0063] Table 3 Core dynamic oil displacement efficiency test results

[0064]

[0065] As shown in Table 3, the salt-resistant and calcium-resistant imbibition-displacement system of the present invention can further improve the crude oil recovery rate on the basis of water flooding, with the maximum increase reaching 28.64 percentage points.

[0066] Example 2

[0067] 1. Preparation of double hydrophilic head group double hydrophobic chain surfactant sodium didecyl hydroxysulfonate, the method is as follows:

[0068] (a1) Ethylenediamine and sodium chloroethylsulfonate were weighed at a molar ratio of 1.5:2.5, and distilled water was added thereto. The mixture was reacted at 70°C for 24 hours. During the reaction, the pH of the system was controlled to 8-9 using an aqueous NaOH solution. After the reaction, the solvent was removed by rotary evaporation at 40°C and -0.095 MPa. The mixture was then washed with anhydrous ethanol, filtered, and dried at 60°C for 4 hours to obtain intermediate a as a white powder.

[0069] (a2) The intermediate a was weighed and dissolved in distilled water. The pH of the system was controlled to 7 by using a formic acid solution. The corresponding epichlorohydrin was added dropwise thereto in a molar ratio of intermediate a to epichlorohydrin of 1.5:2.5. The reaction was carried out at a constant temperature of 25°C for 6 hours. After the reaction, the solvent was removed by rotary evaporation at 60°C and -0.095 MPa to obtain the intermediate b as a light brown gel product.

[0070] (a3) The intermediate b was weighed and dissolved in distilled water, and the temperature was raised to 75°C. The corresponding decylamine was added in a molar ratio of intermediate b to decylamine of 1.5:2.5, and the reaction was carried out at a constant temperature for 24 hours. During the reaction, the pH of the system was controlled to 8-9 using an aqueous NaOH solution. After the reaction, anhydrous ethanol was added, and the mixture was cooled and filtered. The solid product was recrystallized three times using a chloroform-methanol mixture with a volume ratio of 9:1, and vacuum dried at 40°C for 2 hours to obtain sodium didecylhydroxysulfonate, referred to as main agent A, with the following structural formula:

[0071] , n=9.

[0072] 2. Preparation of double hydrophilic head group single hydrophobic chain surfactant sodium octadecyl amino acid, the method is as follows:

[0073] (b1) Weighing glycine and sodium hydroxide at a molar ratio of glycine to sodium hydroxide of 1.2:1.5, adding distilled water thereto, and stirring at 65° C. to obtain an amino acid salt solution;

[0074] (b2) Adding octadecyl acyl chloride and a 30 wt % NaOH aqueous solution to two constant pressure dropping funnels, respectively, and simultaneously adding octadecyl acyl chloride and a 30 wt % NaOH aqueous solution to the amino acid salt aqueous solution, respectively, while controlling the reaction temperature to 13-15° C. and adjusting the amount of the NaOH aqueous solution to maintain the pH of the system at 12-13. The reaction was stirred for 2 h to obtain a crude alkyl glycine salt; wherein the molar ratio of octadecyl acyl chloride to amino acid salt was 1.2:1.5;

[0075] (b3) The crude alkyl glycine salt product is heated to 60° C. and acidified with formic acid to a pH of 2 to completely acidify it into octadecyl glycine. Octadecyl glycine is insoluble in water. Excess glycine and the product sodium chloride can be dissolved and removed by filtration by adding water. Therefore, deionized water is added, stirred, and then filtered to remove the filtrate. The operation is repeated until the pH of the filtrate is 5-6 and no chloride ions are present. The product is then recrystallized from petroleum ether three times to obtain pure alkyl glycine.

[0076] (b4) The pure alkylglycine is vacuum-dried at 40°C for 2 hours, dissolved in ethanol, and an ethanolic solution of NaOH is slowly added thereto at 50°C, wherein the molar amounts of NaOH in the alkylglycine and the ethanolic solution of NaOH are equal. The mixture is stirred for 1 hour, and the solvent is removed by rotary evaporation at 40°C and -0.095 MPa to obtain sodium octadecylamino acid, referred to as main agent B, having the following structural formula:

[0077] , m=16.

[0078] III. Prepare simulated formation water with a total mineralization of 120,000 mg / L and a calcium ion content of 20,000 mg / L. Mix the dual-hydrophilic headgroup dual-hydrophobic chain surfactant (main agent A), the dual-hydrophilic headgroup single-hydrophobic chain surfactant (main agent B), and the simulated formation water and stir evenly to produce a salt-tolerant and calcium-resistant imbibition-displacement system. The simulated formation water has a total mineralization of 120,000 mg / L and a calcium ion content of 20,000 mg / L. The weight of the salt-tolerant and calcium-resistant imbibition-displacement system is assumed to be 100%. The performance test results for systems with different component contents are as follows:

[0079] 1. Oil-water interfacial tension test

[0080] The test method is the same as in Example 1, and the results are shown in Table 4.

[0081] Table 4 Oil-water interfacial tension of different salt-tolerant and calcium-resistant imbibition-displacement systems

[0082]

[0083] 2. Wettability and absorption efficiency test

[0084] The test method is the same as in Example 1, and the results are shown in Table 5.

[0085] Table 5 Wettability and static dialysis effect

[0086]

[0087] 3. Core dynamic oil displacement efficiency test

[0088] The test method is the same as in Example 1, and the results are shown in Table 6.

[0089] Table 6 Core dynamic oil displacement efficiency test results

[0090] .

[0091] Example 3

[0092] 1. Preparation of double hydrophilic head group double hydrophobic chain surfactant sodium bis-hexadecyl hydroxysulfonate by the following method:

[0093] (a1) Ethylenediamine and sodium chloroethylsulfonate were weighed at a molar ratio of 1:2.5, and distilled water was added thereto. The mixture was reacted at 90°C for 12 h. During the reaction, the pH of the system was controlled to 8-9 using an aqueous NaOH solution. After the reaction, the solvent was removed by rotary evaporation at 50°C and -0.095 MPa. The mixture was then washed with anhydrous ethanol, filtered, and dried at 80°C for 2 h to obtain intermediate a as a white powder.

[0094] (a2) The intermediate a was weighed and dissolved in distilled water. The pH of the system was controlled to 7 by formic acid solution. The corresponding epichlorohydrin was added dropwise thereto in a molar ratio of intermediate a to epichlorohydrin of 1:2.5. The reaction was carried out at 35°C for 3 hours. After the reaction, the solvent was removed by rotary evaporation at 50°C and -0.095 MPa to obtain intermediate b as a light brown gel product.

[0095] (a3) The intermediate b was weighed and dissolved in distilled water, which was heated to 90°C. The corresponding hexadecylamine was added in a molar ratio of 1:2.5 between the intermediate b and hexadecylamine, and the reaction was carried out at a constant temperature for 12 hours. During the reaction, the pH of the system was controlled to 8-9 using an aqueous NaOH solution. After the reaction, anhydrous ethanol was added, and the mixture was cooled and filtered. The solid product was recrystallized three times using a chloroform-methanol mixture with a volume ratio of 9:1, and vacuum-dried at 60°C for 1 hour to obtain sodium bis(hexadecyl)hydroxysulfonate, referred to as main agent A, having the following structural formula:

[0096] , n=15.

[0097] 2. Preparation of a double hydrophilic head group single hydrophobic chain surfactant sodium tetradecyl amino acid as follows:

[0098] (b1) Weighing glycine and sodium hydroxide at a molar ratio of glycine to sodium hydroxide of 1:1.5, adding distilled water thereto, and stirring at 85° C. to obtain an amino acid salt solution;

[0099] (b2) adding tetradecyl chloride and a 30 wt % aqueous NaOH solution to two constant pressure dropping funnels, respectively, and simultaneously adding tetradecyl chloride and a 30 wt % aqueous NaOH solution to the amino acid salt aqueous solution, controlling the reaction temperature to 12-14° C. and adjusting the amount of the NaOH solution to maintain the pH of the system at 12-13, and stirring the reaction for 6 h to obtain a crude alkyl glycine salt; wherein the molar ratio of tetradecyl chloride to amino acid salt is 1:1.5;

[0100] (b3) The crude alkyl glycine salt product is heated to 60° C. and acidified with formic acid to pH = 2 to completely acidify it into tetradecyl glycine. Tetradecyl glycine is insoluble in water. Excess glycine and the product sodium chloride can be dissolved and removed by filtration by adding water. Therefore, deionized water is added, stirred, and then filtered to remove the filtrate. The operation is repeated until the pH of the filtrate is 5-6 and no chloride ions are present. Then, the product is recrystallized from petroleum ether three times to obtain pure alkyl glycine.

[0101] (b4) The pure alkylglycine was vacuum dried at 50°C for 1 hour, dissolved in ethanol, and an ethanolic solution of NaOH was slowly added thereto at 50°C, wherein the molar amount of NaOH in the ethanolic solution of alkylglycine and NaOH was equal. The mixture was stirred for 1 hour, and the solvent was removed by rotary evaporation at 40°C and -0.095 MPa to obtain sodium tetradecylamino acid, referred to as main agent B, with the following structural formula:

[0102] , m=12.

[0103] III. Prepare simulated formation water with a total mineralization of 120,000 mg / L and a calcium ion content of 20,000 mg / L. Mix the dual-hydrophilic headgroup dual-hydrophobic chain surfactant (main agent A), the dual-hydrophilic headgroup single-hydrophobic chain surfactant (main agent B), and the simulated formation water and stir evenly to produce a salt-tolerant and calcium-resistant imbibition-displacement system. The simulated formation water has a total mineralization of 120,000 mg / L and a calcium ion content of 20,000 mg / L. The weight of the salt-tolerant and calcium-resistant imbibition-displacement system is assumed to be 100%. The performance test results for systems with different component contents are as follows:

[0104] 1. Oil-water interfacial tension test

[0105] The test method is the same as in Example 1, and the results are shown in Table 7.

[0106] Table 7 Oil-water interfacial tension of different salt-tolerant and calcium-resistant imbibition-displacement systems

[0107]

[0108] 2. Wettability and absorption efficiency test

[0109] The test method is the same as in Example 1, and the results are shown in Table 8.

[0110] Table 8 Wettability and static dialysis effect

[0111]

[0112] 3. Core dynamic oil displacement efficiency test

[0113] The test method is the same as in Example 1, and the results are shown in Table 9.

[0114] Table 9 Core dynamic oil displacement efficiency test results

[0115] .

Claims

1. A salt-tolerant and calcium-resistant imbibition-displacement system suitable for low-permeability tight oil reservoirs, characterized by: Based on 100%, it is composed of the following raw materials by weight: 0.05-1.5% of a double hydrophilic head group double hydrophobic chain surfactant, 0.05-1.5% of a double hydrophilic head group single hydrophobic chain surfactant, and the balance water; wherein the double hydrophilic head group double hydrophobic chain surfactant is didecyl hydroxysulfonate, didodecyl hydroxysulfonate, ditetradecyl hydroxysulfonate or dihexadecyl hydroxysulfonate; The double hydrophilic head group single hydrophobic chain surfactant is a dodecyl amino acid salt, a tetradecyl amino acid salt, a hexadecyl amino acid salt or an octadecyl amino acid salt; The structural formula of the double hydrophilic head group single hydrophobic chain surfactant is as follows: , m=10, 12, 14 or 16; The double hydrophilic head group and double hydrophobic chain surfactant is prepared by the following method: (a1) Weighing ethylenediamine and sodium chloroethylsulfonate, adding distilled water, and reacting at 70-90°C for 12-24 hours, controlling the pH of the system to 8-9 during the reaction. After the reaction, remove the solvent by rotary evaporation, wash with anhydrous ethanol, filter, and dry to obtain intermediate a; (a2) weighing the intermediate a and dissolving it in distilled water to control the solution pH to 7, adding epichlorohydrin dropwise thereto, and reacting at a constant temperature of 25-35°C for 3-6 hours. After the reaction, the solvent is removed by rotary evaporation to obtain the intermediate b; (a3) Weigh the intermediate b, dissolve it in distilled water, raise the temperature to 75-90°C, add the corresponding organic amine, and react at a constant temperature for 12-24 hours. During the reaction, control the pH of the system to be 8-9. After the reaction, add anhydrous ethanol, cool it, filter it, recrystallize the solid product from a chloroform-methanol mixture, and dry it in vacuo. The organic amine is decylamine, dodecylamine, tetradecylamine, or hexadecylamine.

2. The salt-resistant and calcium-resistant imbibition-displacement system suitable for low-permeability tight oil reservoirs according to claim 1, characterized in that: The molar ratio of ethylenediamine to sodium chloroethylsulfonate in step (a1) is (1-1.5): (1-2.5); the molar ratio of intermediate a to epichlorohydrin in step (a2) is (1-1.5): (2-2.5); and the molar ratio of intermediate b to organic amine in step (a3) ​​is (1-1.5): (2-2.5).

3. The salt-resistant and calcium-resistant imbibition-displacement system suitable for low-permeability tight oil reservoirs according to claim 1, characterized in that: In step (a2), the pH value of the solution is controlled by formic acid or acetic acid solution = 7; in steps (a1) and (a3), the pH value is controlled by alkaline aqueous solution; and the volume ratio of the chloroform-methanol mixture is 9:

1.

4. The salt-resistant and calcium-resistant imbibition-displacement system suitable for low-permeability tight oil reservoirs according to claim 1, characterized in that: The double hydrophilic head group single hydrophobic chain surfactant is prepared by the following method: (b1) Weigh glycine and sodium hydroxide, add distilled water thereto, and stir uniformly at 65-85° C. to obtain an amino acid salt solution; (b2) while stirring, simultaneously adding an alkyl acyl chloride and an aqueous NaOH solution to the aqueous amino acid salt solution, controlling the reaction temperature to 10-15° C., controlling the pH of the system to 12-13 by adjusting the amount of the aqueous NaOH solution, and stirring the reaction for 2-6 hours to obtain a crude product, an alkyl glycine salt; the alkyl acyl chloride is selected from the group consisting of dodecyl acyl chloride, tetradecyl acyl chloride, hexadecyl acyl chloride, and octadecyl acyl chloride; (b3) heating the crude alkyl glycine salt to 60-80° C., acidifying with formic acid to a pH of 2-4, adding deionized water, stirring, and then filtering with suction to remove the filtrate, repeating the process until the pH of the filtrate is 5-6 and no chloride ions are present, and then recrystallizing with petroleum ether to obtain pure alkyl glycine; (b4) The pure alkylglycine is vacuum-dried and dissolved in ethanol. An ethanol solution of NaOH is slowly added thereto at 50-70° C., and the mixture is stirred for 1-2 hours. The solvent is then removed by rotary evaporation.

5. The salt-resistant and calcium-resistant imbibition-displacement system suitable for low-permeability tight oil reservoirs according to claim 4, characterized in that: In step (b1), the molar ratio of glycine to sodium hydroxide is (1-1.2):(1-1.5); in step (b2), the molar ratio of the alkyl acyl chloride to the amino acid salt is (1-1.2):(1-1.5); in step (b4), the molar amount of the alkyl glycine is equal to the molar amount of NaOH in the ethanol solution of NaOH.

6. A salt-resistant and calcium-resistant imbibition-displacement system suitable for low-permeability tight oil reservoirs according to claim 1 or 4, characterized in that: The conditions for the rotary evaporation are a temperature of 40-60° C. and a pressure of -0.095 MPa.

7. The method for preparing a salt-resistant and calcium-resistant imbibition-displacement system suitable for low-permeability tight oil reservoirs according to claim 1, characterized in that: The double hydrophilic head group double hydrophobic chain surfactant, the double hydrophilic head group single hydrophobic chain surfactant and water are mixed and stirred evenly.

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