WO2021056665A1 - Gemini surfactant for oil displacement, binary combination system for oil displacement, and preparation method for and application of gemini surfactant - Google Patents

Abstract

Disclosed in the present invention are a gemini surfactant for oil displacement, and a preparation method for and an application of the gemini surfactant. The gemini surfactant is 1,3-dialkyl-1,3-dipolyoxyethylene ether urea or 1,3-dialkyl-1,3-dipolyoxypropylene ether urea. The gemini surfactant for oil displacement provided by the present invention has good chemical stability and excellent salt tolerance in a wide pH range, has good performance in reducing interfacial tension, and can enhance the oil recovery by about 18% when applied in alkali-free binary (surfactant + polymer) combination flooding.

Description

Gemini surfactant for oil displacement, binary composite system and preparation method and application thereof Technical field

The invention relates to a surfactant for oil displacement, in particular to a gemini surfactant for oil displacement, and a preparation method and application thereof.

Background technique

After most oil reservoirs are discovered, part of the natural energy of the oil reservoir can be used to recover part of it. This stage is called primary oil recovery. In order to delay or prevent the pressure drop in the reservoir, water and other fluids are injected into the reservoir within a certain period of time after the primary oil recovery, and the fluid is used to "hold pressure" to recover a part of it. This oil recovery method is usually called secondary oil recovery. When the secondary oil recovery reaches the economic limit, fluids that can cause physical and/or chemical changes or energy changes are injected into the formation to further recover oil. This oil recovery method is usually called tertiary oil recovery. Chemical flooding is a commonly used technology in tertiary oil recovery, including alkaline flooding, polymer flooding, surfactant flooding and combined flooding. Various chemical flooding technologies have significant characteristics and advantages, but they also have some limitations.

Combination flooding technology is a new tertiary oil recovery technology, which is characterized by the use of alkalis, surfactants and polymers to organically compound them, play a synergistic effect between various chemical agents, and greatly improve oil displacement efficiency. It is an innovative technology based on alkaline flooding, polymer flooding and surfactant flooding. It takes advantage of these three flooding technologies to greatly reduce costs while improving oil recovery. Therefore, combined flooding is considered to be another more potential new method of tertiary oil recovery after polymer flooding.

In the past two to thirty years, the field has extensively carried out research on alkaline-surfactant-polymer ternary combination flooding technology. The results show that ASP flooding can reduce the interfacial tension between crude oil and formation water to an ultra-low level, reaching the order of 10 ^-3 mN/m. Based on water flooding, the recovery factor can be increased by 15%-20%. An effective tertiary oil recovery method. Although the surfactants in the existing ASP flooding can achieve good oil-increasing and precipitation effects, field tests have gradually revealed the defects of ASP flooding, that is, alkali will reduce the thickening effect of polymers, corrode equipment, and interfere with Minerals in the rock or formation water react to produce insoluble substances, causing scaling of injection equipment and oil wells and clogging of capillary channels, which destroys the porous capillary structure of the oil reservoir. In severe cases, the oil well may be scrapped. In view of these side effects, especially the irreversible damage to the formation structure, the replacement of ASP flooding is an inevitable trend of technological development.

However, the cheap surfactants commonly used in ASP flooding, such as petroleum sulfonate, heavy alkylbenzene sulfonate, natural carboxylate, petroleum carboxylate, and lignosulfonate, are usually It is difficult to reduce the interfacial tension between crude oil and water to an ultra-low level. For this reason, it is necessary to develop a new type of surfactant.

Summary of the invention

The purpose of the present invention is to provide a gemini surfactant for oil displacement that can reduce the interfacial tension of crude oil and water to ultra-low under the condition of no alkali, aiming at the technical defects existing in the prior art. Alkyl-1,3-dipolyoxyethylene ether-based urea (structure formula 1) or 1,3-dialkyl-1,3-dipolyoxypropylene ether-based urea (structure formula 2),

In the structural formula, R=C _q H _2q+1 , q=10-18 (preferably q=12), and n=1-20 (preferably 5-15).

Another object of the present invention is to provide a method for preparing the aforementioned gemini surfactant for oil displacement, wherein the gemini surfactant for oil displacement is 1,3-dialkyl-1,3-dipolyoxyethylene ether urea or 1 ,3-Dialkyl-1,3-dipolyoxypropylene ether urea, using urea and alkylene oxide (ethylene oxide or propylene oxide) as raw materials, first react to obtain N,N'-bis(2 -Hydroxyethyl)-urea or N,N'-bis(2-hydroxypropyl)-urea, and then substituted with brominated alkane to obtain the intermediate, and finally obtained by addition with ethylene oxide.

The gemini surfactant for oil displacement is 1,3-dialkyl-1,3-dipolyoxyethylene ether urea, which is firstly reacted with urea and ethylene oxide to obtain N,N'-bis(2-hydroxyl Ethyl)-urea is reacted with 1-bromoalkane to obtain 1,3-dialkyl-1,3-dihydroxyethyl urea intermediate, and finally is obtained by addition with ethylene oxide. The synthesis reaction equation is as follows As shown in formula I:

In the formula, R=C _q H _2q+1 , q=10-18; n=1-20;

The 1,3-dialkyl-1,3-dihydroxyethylurea intermediate is composed of N,N'-bis(2-hydroxyethyl)-urea at 70°C and KOH as a catalyst. The 1,3-dialkyl-1,3-dipolyoxyethylene ether-based urea is obtained from the reaction of substituted alkane, and the 1,3-dialkyl-1,3-dihydroxyethyl urea intermediate is It is obtained by reacting with ethylene oxide under KOH catalyst at 140～150℃.

The gemini surfactant for oil displacement is 1,3-dialkyl-1,3-dipolyoxypropylene ether urea, which is firstly reacted with urea and propylene oxide to obtain N,N'-bis(2-hydroxypropane) Yl)-urea, then react with 1-bromoalkane to obtain 1,3-dialkyl-1,3-dihydroxypropyl urea intermediate, and finally add with ethylene oxide to obtain, the synthesis reaction equation is as follows As shown in Ⅱ:

In the formula, R=C _q H _2q+1 , q=10-18; n=1-20;

The 1,3-dialkyl-1,3-dihydroxypropyl urea intermediate is composed of N,N'-bis(2-hydroxypropyl)-urea at 80°C and KI as a catalyst. The 1,3-dialkyl-1,3-dipolyoxypropylene ether-based urea is obtained from the reaction of substituted alkane, and the 1,3-dialkyl-1,3-dihydroxypropyl urea intermediate is It is obtained by reacting with propylene oxide under KOH catalyst at 140～150℃.

The preparation of the 1,3-dialkyl-1,3-dipolyoxyethylene ether urea specifically includes the following steps:

(1) The aqueous solution of urea reacts with ethylene oxide in the presence of acetic acid at 5-10°C to obtain N,N'-bis(2-hydroxyethyl)-urea, as shown in formula (1):

(2) The toluene solution of N,N'-bis(2-hydroxyethyl)-urea reacts with 1-bromoalkane at 70℃, KOH and trioctylmethylammonium chloride to obtain 1,3- The intermediate of dialkyl-1,3-dihydroxyethylurea, as shown in formula (2):

(3) 1,3-Dialkyl-1,3-dihydroxyethylurea intermediate reacts with ethylene oxide at 140～150℃ under KOH catalyst to obtain 1,3-dialkyl-1,3 -Dipolyoxyethylene ether urea, as shown in formula (3):

The preparation of the 1,3-dialkyl-1,3-dipolyoxypropylene ether urea specifically includes the following steps:

1,3-Dialkyl-1,3-dihydroxypropylurea intermediate reacts with propylene oxide at 140～150℃ under KOH catalyst to obtain 1,3-dialkyl-1,3-dipolyoxypropylene Ether urea

(1) The aqueous solution of urea reacts with propylene oxide in the presence of acetic acid at 5-10°C to obtain N,N'-bis(2-hydroxypropyl)-urea, as shown in formula (4):

(2) The toluene solution of N,N'-bis(2-hydroxypropyl)-urea reacts with 1-bromoalkane at 80℃, KOH and trioctylmethylammonium chloride to obtain 1,3- Dialkyl-1,3-dihydroxypropyl urea intermediate, as shown in formula (5):

(3) 1,3-Dialkyl-1,3-dihydroxypropylurea intermediate reacts with ethylene oxide at 140～150℃ under KOH catalyst to obtain 1,3-dialkyl-1,3 -Dipolyoxypropylene ether urea, as shown in formula (6):

Another object of the present invention is to provide a composite surfactant for oil displacement, including the aforementioned Gemini surfactant for oil displacement and other conventional surfactants for oil displacement, and the conventional surfactant is compatible with the Gemini surfactant for oil displacement. The active agents are mixed according to the mass ratio (1-9): (9-1), and the preferred mixing ratio is (4-6): (4-6); the conventional surfactants include petroleum sulfonate and heavy alkyl benzene At least one of sulfonates and the like.

Another object of the present invention is to provide a binary composite system for flooding, including 0.025-0.3wt% (preferably 0.1-0.3wt%) surfactant and 500-1500mg/L polymer, excluding alkali, so The surfactant includes the gemini surfactant for oil displacement or the composite surfactant for oil displacement; preferably, the interfacial tension between the binary composite system and crude oil and formation water reaches 0.01 mN/m after acting for 20 minutes Or less (preferably 0.01 mN/m or less when acting for 10 minutes).

Another object of the present invention is to provide an oil displacement method using the above-mentioned binary composite system. After water flooding, a binary composite system prepared by using the gemini surfactant for oil displacement according to any one of claims 1 to 6 is used. Or the binary composite system of claim 9 is injected alternately with the polymer, and then water flooded; the oil displacement injection method is (0.025-0.3) PV binary composite system + (0.05-0.3) PV polymer alternate injection (1-5 times) + (0.1-0.3) PV polymer.

The gemini surfactant for oil displacement provided by the present invention has the gemini amide and ether oxygen structure in the molecule, so that the surfactant has good chemical stability and excellent salt tolerance in a wide pH range; and Because of its linear molecular structure, the surfactant can be closely arranged at the water/air interface and the oil/water interface, and has excellent interfacial tension reduction performance, especially when combined with petroleum sulfonate surfactants. Under the condition of alkali-free, the interfacial tension of crude oil/formation water is reduced to ultra-low, and it can be used in alkali-free binary (surfactant + polymer) combination flooding, which can increase the recovery rate by about 18% on the basis of water flooding.

Description of the drawings

Figure 1 shows the infrared spectrum of the Gemini surfactant for oil displacement of the present invention;

Figure 2 shows the dynamic graph of crude oil/formation water interfacial tension (45°C) of the alkali-free oil displacement agent obtained by compounding Gemini surfactant and petroleum sulfonate surfactant;

Figure 3 shows the dynamic oil/water interfacial tension of carboxylated laureth polyoxyethylene maleate diester gemini surfactant solution.

detailed description

In recent years, researches on surfactants for alkali-free oil displacement have been widely carried out in this field. The reported surfactants for alkali-free oil displacement include anionic types such as petroleum sulfonates, α-olefin sulfonate derivatives, and sulfosuccinates. Acid esters, alkyl naphthalene sulfonates; cationic, such as gemini surfactants (which are formed by chemical bonding between the ionic heads of two amphiphilic molecules via a linking group); amphoteric surfactants and non-ionic surfactants.

Among them, the Gemini surfactants in the cationic surfactants for alkali-free flooding are a kind of surfactants with a special structure, and their molecules generally contain two hydrophobic chains, two hydrophilic groups and one Bridging group. Gemini surfactants not only have extremely high surface activity, but also have a very low critical micelle concentration and good water solubility. Gemini surfactants also exhibit peculiar viscosity behavior in dilute solutions, which can effectively adjust the viscosity of the water phase. Gemini surfactants have the ability to reduce the interfacial tension of oil and water without any additives. Under different salt concentrations, Gemini surfactants have high interfacial activity, and have good synergy with salt, and can effectively reduce the oil-water interfacial tension within a wide range of surfactant concentration and salinity. In addition, the mixture of gemini surfactants and conventional surfactants exhibits a stronger tendency to synergistic effects than binary mixtures of conventional surfactants. However, most of the existing Gemini surfactants have complex structures, many reaction steps, and low yields. The alkali-free binary flooding systems generally have low oil displacement effects.

The following describes the content of the present invention in more detail with reference to the drawings and specific embodiments, and further explains the present invention, but these embodiments do not limit the present invention in any way. Any changes made by those skilled in the art to the embodiments of the present invention under the enlightenment of this specification will fall within the scope of the present invention.

Example 1. Preparation of Gemini Surfactant for Oil Displacement of the Invention

(1) Using commercially available urea (content 98%) and ethylene oxide (propylene oxide can also be used) as raw materials to prepare N,N'-bis(2-hydroxyethyl/propyl)-urea, the reaction equation See formula (1) and formula (4), add 61.22g of urea aqueous solution containing 50wt% urea into a three-necked flask, keep the temperature at 5～10℃, then pass in 88g of ethylene oxide, add 10ml of acetic acid, and then the reaction liquid Incubate and stir for 120 minutes at 5-10°C. After the water and low boilers are removed by atmospheric pressure, the crude product is separated by column chromatography to obtain 126.68g of N,N'-bis(2-hydroxyethyl/propyl)- Urea, the reaction yield was 85.6%.

(2) Substituting N,N'-bis(2-hydroxyethyl/propyl)-urea with 1-bromoalkane to obtain 1,3-dialkyl-1,3-dihydroxyethyl /Propylurea intermediate, the reaction equation is shown in formula (2) and formula (5); specifically: add 100ml of toluene to a three-necked flask to dissolve 14.8g N,N'-bis(2-hydroxyethyl/propyl)- Urea and 49.8g 1-bromododecane were added, and 11.2g potassium hydroxide was added. The reaction solution was reacted at 70°C for 12 hours. After cooling, it was acidified with dilute hydrochloric acid to make it acidic. The solvent was removed by rotary evaporation and column chromatography was used. After separation, 41.2 g of 1,3-di(dodecyl)-1,3-dihydroxyethyl/propylurea intermediate was obtained, and the reaction yield was 85.2%. The 1,3-dialkyl-1,3-dihydroxyethyl/propylurea intermediate has a small HLB value (Hydrophile-Lipophile Balance), which is used to indicate the hydrophilic group in the molecule The balance relationship with lipophilic groups, the smaller the value, the more hydrophobic, the larger the value, the more hydrophilic), and its water solubility is weaker. The inventor found that adding it to ethylene oxide under appropriate conditions can improve its water solubility and adjust the HLB value to meet the requirements of being used as a surfactant for flooding. Therefore, the next step was designed.

(3) Addition reaction of 1,3-dialkyl-1,3-dihydroxyethyl/propylurea intermediate and ethylene oxide (or propylene oxide) under KOH catalyst, the amount of catalyst is The 1,3-dialkyl-1,3-dihydroxyethylurea intermediate mass is 1%, the reaction temperature is 140～150℃, and the number of additions of ethylene oxide is controlled n=1-20 (preferably 5-15 ) To obtain a white 1,3-dialkyl-1,3-dipolyoxyethylene/propylene ether urea product. The chemical reaction formula is shown in formula (3) and formula (6), specifically: adding in the autoclave 11g of 1,3-bis(dodecyl)-1,3-dihydroxyethyl/propylurea and 1.2g of potassium hydroxide were purged with nitrogen to replace the air in the kettle twice, then heated to 120°C, stirred, After nitrogen gas was introduced into the kettle, a vacuum was drawn. Heat up to 140°C, introduce ethylene oxide until the pressure of the reactor is 0.3-0.7MPa, pass cooling water to make the temperature of the reaction system react at 140°C-150°C, continuously pass ethylene oxide to the theoretical amount of addition number , Continue the reaction until the system pressure drops to 0MPa, stop heating, and the temperature drops to 100°C for discharge. After the reaction is completed, the catalyst is neutralized with glacial acetic acid, washed with water and filtered to obtain a white viscous solid product. The infrared spectrum of the prepared 1,3-bis(dodecyl)-1,3-dipolyoxyethylene/propylene ether urea is shown in Figure 1. As can be seen from Figure 1, ^{the broad peak at 3279.5-3432.4 cm -1} in the figure is the bonded -OH absorption peak; ^{the strong and sharp absorption peak at 1687.9 cm -1} is the C=O stretching in the amide bond vibration; peak at 1651.8cm ^-1 is the stretching vibration peak tertiary amide; absorption peak at 1055.7cm ^-1 is the stretching vibration of C-OH is a primary alcohol; 723.9cm ^-1 absorption peak at a long chain alkyl group Based on the bending vibration, it can be inferred that the product is 1,3-bis(dodecyl)-1,3-dipolyoxyethylene ether urea. The number of ethylene oxide added to each 1,3-dialkyl-1,3-dihydroxyethylurea intermediate molecule is controlled to be n=1-20, with 5-15 being the best. This step of addition reaction is carried out in an ordinary autoclave, using alkali (KOH) as a catalyst, and reacting at 140-150°C until the system pressure (gauge pressure) drops to zero. This reaction is also very mature in industry, and the resulting product is a homologous mixture, namely polyoxyethylene (polyoxyethylene is the reaction substrate and the chain link in the molecule after addition. The homologous mixture mentioned here refers to n rings Oxyethane molecules are a mixture of products with different values.) Has a certain chain length distribution.

Example 2: The influence of Gemini surfactant for oil displacement of the present invention on the interfacial tension of oil and water

Take the gemini surfactant for oil displacement of the present invention, namely 1,3-dialkyl-1,3-dipolyoxyethylene ether urea (n=14) as the main surfactant, and petroleum sulfonate surfactant Compound (the mole fraction of the Gemini surfactant of the present invention in the two compound surfactants is ≥0.5, and the total mole fraction is 1), the mass ratio of the Gemini surfactant of the present invention to petroleum sulfonate is 6:4, the total concentration of the two surfactants is shown in Table 1, and a binary composite system is obtained. Under the conditions of 50°C and 6000r/min, the interfacial tension was measured with a rotating drop interfacial tensiometer. The results are shown in Figure 2 and Table 1. The mass fractions in columns 2-6 in Table 1 are the total mass fractions of the Gemini surfactant + petroleum sulfonate surfactant of the present invention.

Table 1 Surfactant dynamic interfacial tension

From the results in Figure 2 and Table 1, it can be seen that the Gemini surfactant of the present invention can reduce the interfacial tension of crude oil and formation water without adding any alkali, alkaline salt, or any neutral inorganic salt when used alone. To ultra-low (interfacial tension <0.01mN/m is ultra-low). When the Gemini surfactant for oil displacement of the present invention is compounded with petroleum sulfonate, the interfacial tension decreases faster than the Gemini surfactant of the present invention is used alone. Generally, the interfacial tension can be reduced to ultra-low within 10 minutes ( The figure shows that the interfacial tension of each surfactant is already below this value at about 10 minutes, and it has reached the order of 10 ^{-4 at} 60 minutes); when it is balanced, the equilibrium interfacial tension can be reduced to 10 ^-3 ～10 ^-4 mN /m order of magnitude. In addition, the gemini surfactant for oil displacement of the present invention is compounded with petroleum sulfonate to obtain a wide concentration range of ultra-low interfacial tension, that is, 0.025 wt% to 0.3 wt%.

Under the conditions of 50℃ and 6000r/min, the concentration of 10g/L and 20g/L carboxylated laureth maleic acid diester (CAPM, structural formula see formula III) was determined by rotating drop interfacial tensiometer respectively. The dynamic oil/water interfacial tension between the solution and the crude oil is shown in Figure 3. The results in Figure 3 show that with a certain surfactant concentration, the dynamic oil/water interfacial tension between the CAPM solution and the crude oil decreases with the extension of the test time, and it takes more than 50 minutes for the dynamic oil/water interfacial tension to reach an ultra-low equilibrium interface. Tension value (10 ^-3 mN/m order of magnitude), and its equilibrium interfacial tension value is 8.9×10 ^-3 mN/m, not only when it reaches the ultra-low equilibrium interfacial tension value (10 min in the present invention) but also the equilibrium interfacial tension value It is much higher than the test result of using the gemini surfactant of the present invention alone, and the combination of the gemini surfactant of the present invention and petroleum sulfonate.

Under the conditions of 50°C and 6000r/min, the dynamic oil/water interfacial tension between petroleum sulfonate solution and crude oil was measured with a rotating drop interfacial tension meter. The concentration and results are shown in Table 2.

Table 2 Dynamic interfacial tension of petroleum sulfonate alkali-free system

The results in Table 2 show that in the case of using petroleum sulfonate surfactant alone without adding any alkali and salt, under the test conditions of 50℃ and 6000r/min, the alkali-free system has both balanced interfacial tension and dynamic interfacial tension. (Table 2) failed to reach ultra-low (<0.01mN/m).

Example 3: Physical simulation flooding experiment of Gemini surfactant for flooding of the present invention

Take the 1,3-dialkyl-1,3-dipolyoxyethylene ether urea (n=14) of the present invention as the main surfactant and petroleum sulfonate surfactant to obtain a binary composite system (this The mole fraction of the gemini surfactant for oil displacement of the invention in the two compound surfactants is ≥0.5, and the total mole fraction is 1), without adding any alkali or alkaline salt, and without adding any neutral inorganic salt. Next, the physical simulation flooding test was carried out with natural cores, and the injection method was first to use 0.1PV polymer flooding (HPAM polymer, molecular weight 16-19 million, 1200mg/L) + 0.1PV to-be-tested system flooding, alternating 3 times, The system to be tested is a binary composite system, containing 0.3wt% of the tested surfactant and 1200mg/L HPAM polymer (molecular weight 16-19 million), without alkali; then 0.2PV polymer flooding (HPAM polymer, molecular weight 1600 -19 million, 1200mg/L), the results are shown in Table 3.

Table 3 Natural core flooding experiment results

It can be seen from the results in Table 3 that the binary composite system prepared by using the gemini surfactant of the present invention as the main agent and petroleum sulfonate (mass ratio = 6:4) is used as an alkali-free oil displacement agent and is applied to Crude oil, on the basis of water flooding, can further increase the recovery rate by more than 18% OOIP (the binary flooding system mentioned here refers to a solution prepared by surfactants and polymers. Therefore, the actual composition of the binary system obtained by the present invention is Gemini Surfactant, petroleum sulfonate surfactant and polymer aqueous solution. The concentration of each component is shown in Table 2) of the results of the flooding experiment. If the 1,3-dialkyl-1,3-dipolyoxyethylene ether-based urea of the present invention is used alone as a surfactant, the same injection method is adopted as the non-alkali binary flooding system formulated with polymers. On the basis of flooding, the enhanced recovery rate can only reach 8% OOIP (see 11 ^# and 12 ^# ). Use the existing commercially available carboxylated laureth polyoxyethylene ether maleate diester (CAPM) solution alone as the surfactant, and use the same injection method as the alkali-free binary flooding system formulated with polymers. On the basis, the enhanced oil recovery can only reach 7% OOIP (see 13 ^# and 14 ^# ).

In the oil displacement method of Gemini surfactant for oil displacement + petroleum sulfonate provided by the present invention, after water flooding, oil displacement system and polymer flooding are used for alternate injection, and then water flooding; the oil displacement injection method can be It is one of the following: (1) (0.025-0.3) PV Gemini surfactant + petroleum sulfonate alkali-free flooding system + (0.05-0.3) PV polymer alternate injection (1-5 times) + (0.1- 0.3) PV polymer; (2) The mass ratio of gemini surfactant to petroleum sulfonate in the oil displacement system can be any ratio between 1:9 and 9:1, and the preferred range is 4:6-6: 4.

Industrial applicability

The gemini surfactant for oil displacement provided by the present invention has good chemical stability, excellent salt resistance and interfacial tension reduction effect in a wide pH range, and is applied to alkali-free binary (surfactant + polymerization). Compound flooding can increase the recovery rate by about 18% on the basis of water flooding, which is suitable for industrial applications.

Claims (12)

1. A gemini surfactant for oil displacement, which is characterized in that it is 1,3-dialkyl-1,3-dipolyoxyethylene ether urea (the structural formula is formula 1) or 1,3-dialkyl-1 , 3-Dipolyoxypropylene ether urea (the structural formula is formula 2),

   

   In the structural formula, R=C _q H _2q+1 , q=10-18, n=1-20 (preferably 5-15).
2. The Gemini surfactant for oil displacement according to claim 1, wherein q=12.
3. A method for preparing the gemini surfactant for oil displacement according to claim 1 or 2, characterized in that the gemini surfactant for oil displacement is 1,3-dialkyl-1,3-dipolyoxyethylene Ether-based urea or 1,3-dialkyl-1,3-dipolyoxypropylene ether-based urea, using urea and alkylene oxide (ethylene oxide or propylene oxide) as raw materials, first react to obtain N,N '-Bis(2-hydroxyethyl)-urea or N,N'-bis(2-hydroxypropyl)-urea, and then substituted with brominated alkane to obtain an intermediate, and finally obtained by addition with ethylene oxide.
4. The method according to claim 3, wherein the gemini surfactant for oil displacement is 1,3-dialkyl-1,3-dipolyoxyethylene ether-based urea, which is preceded by urea and ethylene oxide. The reaction obtains N,N'-bis(2-hydroxyethyl)-urea, and then reacts with 1-bromoalkane to obtain 1,3-dialkyl-1,3-dihydroxyethylurea intermediate, and finally Ethylene oxide is obtained by addition, and the synthesis reaction equation is shown in formula I:

   

   In the formula, R=C _q H _2q+1 , q=10-18; n=1-20;

   The 1,3-dialkyl-1,3-dihydroxyethylurea intermediate is composed of N,N'-bis(2-hydroxyethyl)-urea at 70°C and KOH as a catalyst. The 1,3-dialkyl-1,3-dipolyoxyethylene ether-based urea is obtained from the reaction of substituted alkane, and the 1,3-dialkyl-1,3-dihydroxyethyl urea intermediate is It is obtained by reacting with ethylene oxide under KOH catalyst at 140～150℃.
5. The method according to claim 3, wherein the gemini surfactant for oil displacement is 1,3-dialkyl-1,3-dipolyoxypropylene ether urea, which is firstly reacted by urea and propylene oxide N,N'-bis(2-hydroxypropyl)-urea is obtained, and then reacted with 1-bromoalkane to obtain 1,3-dialkyl-1,3-dihydroxypropylurea intermediate, and finally with the ring Oxyethane is obtained by addition, and the synthesis reaction equation is shown in formula II:

   

   In the formula, R=C _q H _2q+1 , q=10-18; n=1-20;

   The 1,3-dialkyl-1,3-dihydroxypropyl urea intermediate is composed of N,N'-bis(2-hydroxypropyl)-urea at 80°C and KI as a catalyst. The 1,3-dialkyl-1,3-dipolyoxypropylene ether-based urea is obtained from the reaction of substituted alkane, and the 1,3-dialkyl-1,3-dihydroxypropyl urea intermediate is It is obtained by reacting with propylene oxide under KOH catalyst at 140～150℃.
6. The method according to claim 5, wherein the preparation of the 1,3-dialkyl-1,3-dipolyoxyethylene ether-based urea specifically comprises the following steps:

   (1) The aqueous solution of urea reacts with ethylene oxide in the presence of acetic acid at 5-10°C to obtain N,N'-bis(2-hydroxyethyl)-urea, as shown in formula (1):

   

   (2) The toluene solution of N,N'-bis(2-hydroxyethyl)-urea reacts with 1-bromoalkane at 70℃, KOH and trioctylmethylammonium chloride to obtain 1,3- The intermediate of dialkyl-1,3-dihydroxyethylurea, as shown in formula (2):

   

   (3) 1,3-Dialkyl-1,3-dihydroxyethylurea intermediate reacts with ethylene oxide at 140～150℃ under KOH catalyst to obtain 1,3-dialkyl-1,3 -Dipolyoxyethylene ether urea, as shown in formula (3):

   
7. The method according to claim 5, wherein the preparation of the 1,3-dialkyl-1,3-dipolyoxypropylene ether-based urea specifically comprises the following steps:

   (1) The aqueous solution of urea reacts with propylene oxide in the presence of acetic acid at 5-10℃ to obtain N,N'-bis(2-

   

   (2) The toluene solution of N,N'-bis(2-hydroxypropyl)-urea reacts with 1-bromoalkane at 80℃, KOH and trioctylmethylammonium chloride to obtain 1,3- Dialkyl-1,3-dihydroxypropyl urea intermediate, as shown in formula (5):

   

   (3) 1,3-Dialkyl-1,3-dihydroxypropylurea intermediate reacts with ethylene oxide at 140～150℃ under KOH catalyst to obtain 1,3-dialkyl-1,3 -Dipolyoxypropylene ether urea, as shown in formula (6):

   
8. A composite surfactant for oil displacement, comprising the gemini surfactant for oil displacement according to claim 1 or 2 and other conventional surfactants for oil displacement, and the conventional surfactant is active with the gemini surfactant for oil displacement The agents are mixed according to the mass ratio (1-9): (9-1), and the preferred mixing ratio is (4-6): (4-6).
9. The composite surfactant for oil displacement according to claim 8, wherein the conventional surfactant is selected from at least one of petroleum sulfonate and heavy alkylbenzene sulfonate.
10. A binary composite system for oil displacement, comprising 0.025-0.3wt% (preferably 0.1-0.3wt%) surfactant and 500-1500mg/L polymer, excluding alkali, characterized in that the surface activity The agent is the gemini surfactant for oil displacement according to claim 1 or 2 or the composite surfactant for oil displacement according to claim 8 or 9.
11. The binary composite system according to claim 10, characterized in that the interfacial tension between the binary composite system and crude oil and formation water reaches 0.01 mN/m or less when acting for 20 minutes (preferably reaching 0.01 mN when acting for 10 minutes /m or less).
12. An oil displacement method of a binary composite system, characterized in that, after water flooding, a binary composite system prepared by using any of the Gemini surfactants for oil displacement according to any one of claims 1-6 or claim 10 or claim 10 is used. 11 The binary composite system and polymer are injected alternately, and then water flooded; the oil displacement injection method is (0.025-0.3) PV binary composite system + (0.05-0.3) PV polymer alternate injection (1- 5 times) + (0.1-0.3) PV polymer.

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